Adding upstream version 110.0.1.upstream/110.0.1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

75 files changed, 36682 insertions, 0 deletions

diff --git a/layout/painting/ActiveLayerTracker.cpp b/layout/painting/ActiveLayerTracker.cpp
new file mode 100644
index 0000000000..fd36734c3c
--- /dev/null
+++ b/layout/painting/ActiveLayerTracker.cpp
@@ -0,0 +1,414 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "ActiveLayerTracker.h"
+
+#include "mozilla/AnimationUtils.h"
+#include "mozilla/ArrayUtils.h"
+#include "mozilla/gfx/gfxVars.h"
+#include "mozilla/gfx/Matrix.h"
+#include "mozilla/EffectSet.h"
+#include "mozilla/MotionPathUtils.h"
+#include "mozilla/PodOperations.h"
+#include "mozilla/StaticPtr.h"
+#include "gfx2DGlue.h"
+#include "nsExpirationTracker.h"
+#include "nsContainerFrame.h"
+#include "nsIContent.h"
+#include "nsRefreshDriver.h"
+#include "nsPIDOMWindow.h"
+#include "mozilla/dom/Document.h"
+#include "nsAnimationManager.h"
+#include "nsStyleTransformMatrix.h"
+#include "nsTransitionManager.h"
+#include "nsDisplayList.h"
+#include "nsDOMCSSDeclaration.h"
+#include "nsLayoutUtils.h"
+
+namespace mozilla {
+
+using namespace gfx;
+
+/**
+ * This tracks the state of a frame that may need active layers due to
+ * ongoing content changes or style changes that indicate animation.
+ *
+ * When no changes of *any* kind are detected after 75-100ms we remove this
+ * object. Because we only track all kinds of activity with a single
+ * nsExpirationTracker, it's possible a frame might remain active somewhat
+ * spuriously if different kinds of changes kept happening, but that almost
+ * certainly doesn't matter.
+ */
+class LayerActivity {
+ public:
+  enum ActivityIndex {
+    ACTIVITY_OPACITY,
+    ACTIVITY_TRANSFORM,
+
+    ACTIVITY_SCALE,
+    ACTIVITY_TRIGGERED_REPAINT,
+
+    // keep as last item
+    ACTIVITY_COUNT
+  };
+
+  explicit LayerActivity(nsIFrame* aFrame) : mFrame(aFrame), mContent(nullptr) {
+    PodArrayZero(mRestyleCounts);
+  }
+  ~LayerActivity();
+  nsExpirationState* GetExpirationState() { return &mState; }
+  uint8_t& RestyleCountForProperty(nsCSSPropertyID aProperty) {
+    return mRestyleCounts[GetActivityIndexForProperty(aProperty)];
+  }
+
+  static ActivityIndex GetActivityIndexForProperty(nsCSSPropertyID aProperty) {
+    switch (aProperty) {
+      case eCSSProperty_opacity:
+        return ACTIVITY_OPACITY;
+      case eCSSProperty_transform:
+      case eCSSProperty_translate:
+      case eCSSProperty_rotate:
+      case eCSSProperty_scale:
+      case eCSSProperty_offset_path:
+      case eCSSProperty_offset_distance:
+      case eCSSProperty_offset_rotate:
+      case eCSSProperty_offset_anchor:
+        // TODO: Bug 1559232: Add offset-position.
+        return ACTIVITY_TRANSFORM;
+      default:
+        MOZ_ASSERT(false);
+        return ACTIVITY_OPACITY;
+    }
+  }
+
+  static ActivityIndex GetActivityIndexForPropertySet(
+      const nsCSSPropertyIDSet& aPropertySet) {
+    if (aPropertySet.IsSubsetOf(
+            nsCSSPropertyIDSet::TransformLikeProperties())) {
+      return ACTIVITY_TRANSFORM;
+    }
+    MOZ_ASSERT(
+        aPropertySet.IsSubsetOf(nsCSSPropertyIDSet::OpacityProperties()));
+    return ACTIVITY_OPACITY;
+  }
+
+  // While tracked, exactly one of mFrame or mContent is non-null, depending
+  // on whether this property is stored on a frame or on a content node.
+  // When this property is expired by the layer activity tracker, both mFrame
+  // and mContent are nulled-out and the property is deleted.
+  nsIFrame* mFrame;
+  nsIContent* mContent;
+
+  nsExpirationState mState;
+
+  // Previous scale due to the CSS transform property.
+  Maybe<MatrixScales> mPreviousTransformScale;
+
+  // Number of restyle operations detected
+  uint8_t mRestyleCounts[ACTIVITY_COUNT];
+};
+
+class LayerActivityTracker final
+    : public nsExpirationTracker<LayerActivity, 4> {
+ public:
+  // 75-100ms is a good timeout period. We use 4 generations of 25ms each.
+  enum { GENERATION_MS = 100 };
+
+  explicit LayerActivityTracker(nsIEventTarget* aEventTarget)
+      : nsExpirationTracker<LayerActivity, 4>(
+            GENERATION_MS, "LayerActivityTracker", aEventTarget) {}
+  ~LayerActivityTracker() override { AgeAllGenerations(); }
+
+  void NotifyExpired(LayerActivity* aObject) override;
+};
+
+static StaticAutoPtr<LayerActivityTracker> gLayerActivityTracker;
+
+LayerActivity::~LayerActivity() {
+  if (mFrame || mContent) {
+    NS_ASSERTION(gLayerActivityTracker, "Should still have a tracker");
+    gLayerActivityTracker->RemoveObject(this);
+  }
+}
+
+// Frames with this property have NS_FRAME_HAS_LAYER_ACTIVITY_PROPERTY set
+NS_DECLARE_FRAME_PROPERTY_DELETABLE(LayerActivityProperty, LayerActivity)
+
+void LayerActivityTracker::NotifyExpired(LayerActivity* aObject) {
+  RemoveObject(aObject);
+
+  nsIFrame* f = aObject->mFrame;
+  nsIContent* c = aObject->mContent;
+  aObject->mFrame = nullptr;
+  aObject->mContent = nullptr;
+
+  MOZ_ASSERT((f == nullptr) != (c == nullptr),
+             "A LayerActivity object should always have a reference to either "
+             "its frame or its content");
+
+  if (f) {
+    f->RemoveStateBits(NS_FRAME_HAS_LAYER_ACTIVITY_PROPERTY);
+    f->RemoveProperty(LayerActivityProperty());
+  } else {
+    c->RemoveProperty(nsGkAtoms::LayerActivity);
+  }
+}
+
+static LayerActivity* GetLayerActivity(nsIFrame* aFrame) {
+  if (!aFrame->HasAnyStateBits(NS_FRAME_HAS_LAYER_ACTIVITY_PROPERTY)) {
+    return nullptr;
+  }
+  return aFrame->GetProperty(LayerActivityProperty());
+}
+
+static LayerActivity* GetLayerActivityForUpdate(nsIFrame* aFrame) {
+  LayerActivity* layerActivity = GetLayerActivity(aFrame);
+  if (layerActivity) {
+    gLayerActivityTracker->MarkUsed(layerActivity);
+  } else {
+    if (!gLayerActivityTracker) {
+      gLayerActivityTracker =
+          new LayerActivityTracker(GetMainThreadSerialEventTarget());
+    }
+    layerActivity = new LayerActivity(aFrame);
+    gLayerActivityTracker->AddObject(layerActivity);
+    aFrame->AddStateBits(NS_FRAME_HAS_LAYER_ACTIVITY_PROPERTY);
+    aFrame->SetProperty(LayerActivityProperty(), layerActivity);
+  }
+  return layerActivity;
+}
+
+static void IncrementMutationCount(uint8_t* aCount) {
+  *aCount = uint8_t(std::min(0xFF, *aCount + 1));
+}
+
+/* static */
+void ActiveLayerTracker::TransferActivityToContent(nsIFrame* aFrame,
+                                                   nsIContent* aContent) {
+  if (!aFrame->HasAnyStateBits(NS_FRAME_HAS_LAYER_ACTIVITY_PROPERTY)) {
+    return;
+  }
+  LayerActivity* layerActivity = aFrame->TakeProperty(LayerActivityProperty());
+  aFrame->RemoveStateBits(NS_FRAME_HAS_LAYER_ACTIVITY_PROPERTY);
+  if (!layerActivity) {
+    return;
+  }
+  layerActivity->mFrame = nullptr;
+  layerActivity->mContent = aContent;
+  aContent->SetProperty(nsGkAtoms::LayerActivity, layerActivity,
+                        nsINode::DeleteProperty<LayerActivity>, true);
+}
+
+/* static */
+void ActiveLayerTracker::TransferActivityToFrame(nsIContent* aContent,
+                                                 nsIFrame* aFrame) {
+  auto* layerActivity = static_cast<LayerActivity*>(
+      aContent->TakeProperty(nsGkAtoms::LayerActivity));
+  if (!layerActivity) {
+    return;
+  }
+  layerActivity->mContent = nullptr;
+  layerActivity->mFrame = aFrame;
+  aFrame->AddStateBits(NS_FRAME_HAS_LAYER_ACTIVITY_PROPERTY);
+  aFrame->SetProperty(LayerActivityProperty(), layerActivity);
+}
+
+static void IncrementScaleRestyleCountIfNeeded(nsIFrame* aFrame,
+                                               LayerActivity* aActivity) {
+  const nsStyleDisplay* display = aFrame->StyleDisplay();
+  if (!display->HasTransformProperty() && !display->HasIndividualTransform() &&
+      display->mOffsetPath.IsNone()) {
+    // The transform was removed.
+    aActivity->mPreviousTransformScale = Nothing();
+    IncrementMutationCount(
+        &aActivity->mRestyleCounts[LayerActivity::ACTIVITY_SCALE]);
+    return;
+  }
+
+  // Compute the new scale due to the CSS transform property.
+  // Note: Motion path doesn't contribute to scale factor. (It only has 2d
+  // translate and 2d rotate, so we use Nothing() for it.)
+  nsStyleTransformMatrix::TransformReferenceBox refBox(aFrame);
+  Matrix4x4 transform = nsStyleTransformMatrix::ReadTransforms(
+      display->mTranslate, display->mRotate, display->mScale, Nothing(),
+      display->mTransform, refBox, AppUnitsPerCSSPixel());
+  Matrix transform2D;
+  if (!transform.Is2D(&transform2D)) {
+    // We don't attempt to handle 3D transforms; just assume the scale changed.
+    aActivity->mPreviousTransformScale = Nothing();
+    IncrementMutationCount(
+        &aActivity->mRestyleCounts[LayerActivity::ACTIVITY_SCALE]);
+    return;
+  }
+
+  MatrixScales scale = transform2D.ScaleFactors();
+  if (aActivity->mPreviousTransformScale == Some(scale)) {
+    return;  // Nothing changed.
+  }
+
+  aActivity->mPreviousTransformScale = Some(scale);
+  IncrementMutationCount(
+      &aActivity->mRestyleCounts[LayerActivity::ACTIVITY_SCALE]);
+}
+
+/* static */
+void ActiveLayerTracker::NotifyRestyle(nsIFrame* aFrame,
+                                       nsCSSPropertyID aProperty) {
+  LayerActivity* layerActivity = GetLayerActivityForUpdate(aFrame);
+  uint8_t& mutationCount = layerActivity->RestyleCountForProperty(aProperty);
+  IncrementMutationCount(&mutationCount);
+
+  if (nsCSSPropertyIDSet::TransformLikeProperties().HasProperty(aProperty)) {
+    IncrementScaleRestyleCountIfNeeded(aFrame, layerActivity);
+  }
+}
+
+static bool IsPresContextInScriptAnimationCallback(
+    nsPresContext* aPresContext) {
+  if (aPresContext->RefreshDriver()->IsInRefresh()) {
+    return true;
+  }
+  // Treat timeouts/setintervals as scripted animation callbacks for our
+  // purposes.
+  nsPIDOMWindowInner* win = aPresContext->Document()->GetInnerWindow();
+  return win && win->IsRunningTimeout();
+}
+
+/* static */
+void ActiveLayerTracker::NotifyInlineStyleRuleModified(
+    nsIFrame* aFrame, nsCSSPropertyID aProperty) {
+  if (IsPresContextInScriptAnimationCallback(aFrame->PresContext())) {
+    LayerActivity* layerActivity = GetLayerActivityForUpdate(aFrame);
+    // We know this is animated, so just hack the mutation count.
+    layerActivity->RestyleCountForProperty(aProperty) = 0xff;
+  }
+}
+
+/* static */
+void ActiveLayerTracker::NotifyNeedsRepaint(nsIFrame* aFrame) {
+  LayerActivity* layerActivity = GetLayerActivityForUpdate(aFrame);
+  if (IsPresContextInScriptAnimationCallback(aFrame->PresContext())) {
+    // This is mirroring NotifyInlineStyleRuleModified's NotifyAnimated logic.
+    // Just max out the restyle count if we're in an animation callback.
+    layerActivity->mRestyleCounts[LayerActivity::ACTIVITY_TRIGGERED_REPAINT] =
+        0xFF;
+  } else {
+    IncrementMutationCount(
+        &layerActivity
+             ->mRestyleCounts[LayerActivity::ACTIVITY_TRIGGERED_REPAINT]);
+  }
+}
+
+static bool IsMotionPathAnimated(nsDisplayListBuilder* aBuilder,
+                                 nsIFrame* aFrame) {
+  return ActiveLayerTracker::IsStyleAnimated(
+             aBuilder, aFrame, nsCSSPropertyIDSet{eCSSProperty_offset_path}) ||
+         (!aFrame->StyleDisplay()->mOffsetPath.IsNone() &&
+          ActiveLayerTracker::IsStyleAnimated(
+              aBuilder, aFrame,
+              nsCSSPropertyIDSet{eCSSProperty_offset_distance,
+                                 eCSSProperty_offset_rotate,
+                                 eCSSProperty_offset_anchor}));
+}
+
+/* static */
+bool ActiveLayerTracker::IsTransformAnimated(nsDisplayListBuilder* aBuilder,
+                                             nsIFrame* aFrame) {
+  return IsStyleAnimated(aBuilder, aFrame,
+                         nsCSSPropertyIDSet::CSSTransformProperties()) ||
+         IsMotionPathAnimated(aBuilder, aFrame);
+}
+
+/* static */
+bool ActiveLayerTracker::IsTransformMaybeAnimated(nsIFrame* aFrame) {
+  return IsStyleAnimated(nullptr, aFrame,
+                         nsCSSPropertyIDSet::CSSTransformProperties()) ||
+         IsMotionPathAnimated(nullptr, aFrame);
+}
+
+/* static */
+bool ActiveLayerTracker::IsStyleAnimated(
+    nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+    const nsCSSPropertyIDSet& aPropertySet) {
+  MOZ_ASSERT(
+      aPropertySet.IsSubsetOf(nsCSSPropertyIDSet::TransformLikeProperties()) ||
+          aPropertySet.IsSubsetOf(nsCSSPropertyIDSet::OpacityProperties()),
+      "Only subset of opacity or transform-like properties set calls this");
+
+  // For display:table content, transforms are applied to the table wrapper
+  // (primary frame) but their will-change style will be specified on the style
+  // frame and, unlike other transform properties, not inherited.
+  // As a result, for transform properties only we need to be careful to look up
+  // the will-change style on the _style_ frame.
+  const nsIFrame* styleFrame = nsLayoutUtils::GetStyleFrame(aFrame);
+  const nsCSSPropertyIDSet transformSet =
+      nsCSSPropertyIDSet::TransformLikeProperties();
+  if ((styleFrame && (styleFrame->StyleDisplay()->mWillChange.bits &
+                      StyleWillChangeBits::TRANSFORM)) &&
+      aPropertySet.Intersects(transformSet) &&
+      (!aBuilder ||
+       aBuilder->IsInWillChangeBudget(aFrame, aFrame->GetSize()))) {
+    return true;
+  }
+  if ((aFrame->StyleDisplay()->mWillChange.bits &
+       StyleWillChangeBits::OPACITY) &&
+      aPropertySet.Intersects(nsCSSPropertyIDSet::OpacityProperties()) &&
+      (!aBuilder ||
+       aBuilder->IsInWillChangeBudget(aFrame, aFrame->GetSize()))) {
+    return !StaticPrefs::gfx_will_change_ignore_opacity();
+  }
+
+  LayerActivity* layerActivity = GetLayerActivity(aFrame);
+  if (layerActivity) {
+    LayerActivity::ActivityIndex activityIndex =
+        LayerActivity::GetActivityIndexForPropertySet(aPropertySet);
+    if (layerActivity->mRestyleCounts[activityIndex] >= 2) {
+      // If the frame needs to be repainted frequently, we probably don't get
+      // much from treating the property as animated, *unless* this frame's
+      // 'scale' (which includes the bounds changes of a rotation) is changing.
+      // Marking a scaling transform as animating allows us to avoid resizing
+      // the texture, even if we have to repaint the contents of that texture.
+      if (layerActivity
+                  ->mRestyleCounts[LayerActivity::ACTIVITY_TRIGGERED_REPAINT] <
+              2 ||
+          (aPropertySet.Intersects(transformSet) &&
+           IsScaleSubjectToAnimation(aFrame))) {
+        return true;
+      }
+    }
+  }
+
+  if (nsLayoutUtils::HasEffectiveAnimation(aFrame, aPropertySet)) {
+    return true;
+  }
+
+  if (!aPropertySet.Intersects(transformSet) ||
+      !aFrame->Combines3DTransformWithAncestors()) {
+    return false;
+  }
+
+  // For preserve-3d, we check if there is any transform animation on its parent
+  // frames in the 3d rendering context. If there is one, this function will
+  // return true.
+  return IsStyleAnimated(aBuilder, aFrame->GetParent(), aPropertySet);
+}
+
+/* static */
+bool ActiveLayerTracker::IsScaleSubjectToAnimation(nsIFrame* aFrame) {
+  // Check whether JavaScript is animating this frame's scale.
+  LayerActivity* layerActivity = GetLayerActivity(aFrame);
+  if (layerActivity &&
+      layerActivity->mRestyleCounts[LayerActivity::ACTIVITY_SCALE] >= 2) {
+    return true;
+  }
+
+  return AnimationUtils::FrameHasAnimatedScale(aFrame);
+}
+
+/* static */
+void ActiveLayerTracker::Shutdown() { gLayerActivityTracker = nullptr; }
+
+}  // namespace mozilla
diff --git a/layout/painting/ActiveLayerTracker.h b/layout/painting/ActiveLayerTracker.h
new file mode 100644
index 0000000000..7a6005f284
--- /dev/null
+++ b/layout/painting/ActiveLayerTracker.h
@@ -0,0 +1,102 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef ACTIVELAYERTRACKER_H_
+#define ACTIVELAYERTRACKER_H_
+
+#include "nsCSSPropertyID.h"
+
+class nsIFrame;
+class nsIContent;
+class nsCSSPropertyIDSet;
+class nsDOMCSSDeclaration;
+
+namespace mozilla {
+
+class nsDisplayListBuilder;
+
+/**
+ * This class receives various notifications about style changes and content
+ * changes that affect layerization decisions, and implements the heuristics
+ * that drive those decisions. It manages per-frame state to support those
+ * heuristics.
+ */
+class ActiveLayerTracker {
+ public:
+  static void Shutdown();
+
+  /*
+   * We track style changes to selected styles:
+   *   eCSSProperty_transform, eCSSProperty_translate,
+   *   eCSSProperty_rotate, eCSSProperty_scale
+   *   eCSSProperty_offset_path, eCSSProperty_offset_distance,
+   *   eCSSProperty_offset_rotate, eCSSProperty_offset_anchor,
+   *   eCSSProperty_opacity
+   * and use that information to guess whether style changes are animated.
+   */
+
+  /**
+   * Notify aFrame's style property as having changed due to a restyle,
+   * and therefore possibly wanting an active layer to render that style.
+   * Any such marking will time out after a short period.
+   * @param aProperty the property that has changed
+   */
+  static void NotifyRestyle(nsIFrame* aFrame, nsCSSPropertyID aProperty);
+
+  /**
+   * Notify that a property in the inline style rule of aFrame's element
+   * has been modified.
+   */
+  static void NotifyInlineStyleRuleModified(nsIFrame* aFrame,
+                                            nsCSSPropertyID aProperty);
+  /**
+   * Notify that a frame needs to be repainted. This is important for layering
+   * decisions where, say, aFrame's transform is updated from JS, but we need
+   * to repaint aFrame anyway, so we get no benefit from giving it its own
+   * layer.
+   */
+  static void NotifyNeedsRepaint(nsIFrame* aFrame);
+  /**
+   * Return true if aFrame's property style in |aPropertySet| should be
+   * considered as being animated for constructing active layers.
+   */
+  static bool IsStyleAnimated(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                              const nsCSSPropertyIDSet& aPropertySet);
+  /**
+   * Return true if aFrame's transform-like property,
+   * i.e. transform/translate/rotate/scale, is animated.
+   */
+  static bool IsTransformAnimated(nsDisplayListBuilder* aBuilder,
+                                  nsIFrame* aFrame);
+  /**
+   * Return true if aFrame's transform style should be considered as being
+   * animated for pre-rendering.
+   */
+  static bool IsTransformMaybeAnimated(nsIFrame* aFrame);
+  /**
+   * Return true if aFrame either has an animated scale now, or is likely to
+   * have one in the future because it has a CSS animation or transition
+   * (which may not be playing right now) that affects its scale.
+   */
+  static bool IsScaleSubjectToAnimation(nsIFrame* aFrame);
+
+  /**
+   * Transfer the LayerActivity property to the frame's content node when the
+   * frame is about to be destroyed so that layer activity can be tracked
+   * throughout reframes of an element. Only call this when aFrame is the
+   * primary frame of aContent.
+   */
+  static void TransferActivityToContent(nsIFrame* aFrame, nsIContent* aContent);
+  /**
+   * Transfer the LayerActivity property back to the content node's primary
+   * frame after the frame has been created.
+   */
+  static void TransferActivityToFrame(nsIContent* aContent, nsIFrame* aFrame);
+};
+
+}  // namespace mozilla
+
+#endif /* ACTIVELAYERTRACKER_H_ */
diff --git a/layout/painting/BorderCache.h b/layout/painting/BorderCache.h
new file mode 100644
index 0000000000..bb6bf7e4ed
--- /dev/null
+++ b/layout/painting/BorderCache.h
@@ -0,0 +1,67 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_BorderCache_h_
+#define mozilla_BorderCache_h_
+
+#include "mozilla/gfx/2D.h"
+#include "mozilla/HashFunctions.h"
+#include "PLDHashTable.h"
+
+namespace mozilla {
+// Cache for best overlap and best dashLength.
+
+struct FourFloats {
+  typedef mozilla::gfx::Float Float;
+
+  Float n[4];
+
+  FourFloats() {
+    n[0] = 0.0f;
+    n[1] = 0.0f;
+    n[2] = 0.0f;
+    n[3] = 0.0f;
+  }
+
+  FourFloats(Float a, Float b, Float c, Float d) {
+    n[0] = a;
+    n[1] = b;
+    n[2] = c;
+    n[3] = d;
+  }
+
+  bool operator==(const FourFloats& aOther) const {
+    return n[0] == aOther.n[0] && n[1] == aOther.n[1] && n[2] == aOther.n[2] &&
+           n[3] == aOther.n[3];
+  }
+};
+
+class FourFloatsHashKey : public PLDHashEntryHdr {
+ public:
+  typedef const FourFloats& KeyType;
+  typedef const FourFloats* KeyTypePointer;
+
+  explicit FourFloatsHashKey(KeyTypePointer aKey) : mValue(*aKey) {}
+  FourFloatsHashKey(const FourFloatsHashKey& aToCopy)
+      : mValue(aToCopy.mValue) {}
+  ~FourFloatsHashKey() = default;
+
+  KeyType GetKey() const { return mValue; }
+  bool KeyEquals(KeyTypePointer aKey) const { return *aKey == mValue; }
+
+  static KeyTypePointer KeyToPointer(KeyType aKey) { return &aKey; }
+  static PLDHashNumber HashKey(KeyTypePointer aKey) {
+    return HashBytes(aKey->n, sizeof(mozilla::gfx::Float) * 4);
+  }
+  enum { ALLOW_MEMMOVE = true };
+
+ private:
+  const FourFloats mValue;
+};
+
+}  // namespace mozilla
+
+#endif /* mozilla_BorderCache_h_ */
diff --git a/layout/painting/BorderConsts.h b/layout/painting/BorderConsts.h
new file mode 100644
index 0000000000..e25c697101
--- /dev/null
+++ b/layout/painting/BorderConsts.h
@@ -0,0 +1,22 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_BorderConsts_h_
+#define mozilla_BorderConsts_h_
+
+// thickness of dashed line relative to dotted line
+#define DOT_LENGTH 1   // square
+#define DASH_LENGTH 3  // 3 times longer than dot
+
+#define C_TL mozilla::eCornerTopLeft
+#define C_TR mozilla::eCornerTopRight
+#define C_BR mozilla::eCornerBottomRight
+#define C_BL mozilla::eCornerBottomLeft
+
+#define BORDER_SEGMENT_COUNT_MAX 100
+#define BORDER_DOTTED_CORNER_MAX_RADIUS 100000
+
+#endif /* mozilla_BorderConsts_h_ */
diff --git a/layout/painting/DashedCornerFinder.cpp b/layout/painting/DashedCornerFinder.cpp
new file mode 100644
index 0000000000..c892179df9
--- /dev/null
+++ b/layout/painting/DashedCornerFinder.cpp
@@ -0,0 +1,416 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "DashedCornerFinder.h"
+
+#include <utility>
+
+#include "BorderCache.h"
+#include "BorderConsts.h"
+#include "nsTHashMap.h"
+
+namespace mozilla {
+
+using namespace gfx;
+
+struct BestDashLength {
+  typedef mozilla::gfx::Float Float;
+
+  Float dashLength;
+  size_t count;
+
+  BestDashLength() : dashLength(0.0f), count(0) {}
+
+  BestDashLength(Float aDashLength, size_t aCount)
+      : dashLength(aDashLength), count(aCount) {}
+};
+
+static const size_t DashedCornerCacheSize = 256;
+nsTHashMap<FourFloatsHashKey, BestDashLength> DashedCornerCache;
+
+DashedCornerFinder::DashedCornerFinder(const Bezier& aOuterBezier,
+                                       const Bezier& aInnerBezier,
+                                       Float aBorderWidthH, Float aBorderWidthV,
+                                       const Size& aCornerDim)
+    : mOuterBezier(aOuterBezier),
+      mInnerBezier(aInnerBezier),
+      mLastOuterP(aOuterBezier.mPoints[0]),
+      mLastInnerP(aInnerBezier.mPoints[0]),
+      mLastOuterT(0.0f),
+      mLastInnerT(0.0f),
+      mBestDashLength(DOT_LENGTH * DASH_LENGTH),
+      mHasZeroBorderWidth(false),
+      mHasMore(true),
+      mMaxCount(aCornerDim.width + aCornerDim.height),
+      mType(OTHER),
+      mI(0),
+      mCount(0) {
+  NS_ASSERTION(aBorderWidthH > 0.0f || aBorderWidthV > 0.0f,
+               "At least one side should have non-zero width.");
+
+  DetermineType(aBorderWidthH, aBorderWidthV);
+
+  Reset();
+}
+
+void DashedCornerFinder::DetermineType(Float aBorderWidthH,
+                                       Float aBorderWidthV) {
+  if (aBorderWidthH < aBorderWidthV) {
+    // Always draw from wider side to thinner side.
+    std::swap(mInnerBezier.mPoints[0], mInnerBezier.mPoints[3]);
+    std::swap(mInnerBezier.mPoints[1], mInnerBezier.mPoints[2]);
+    std::swap(mOuterBezier.mPoints[0], mOuterBezier.mPoints[3]);
+    std::swap(mOuterBezier.mPoints[1], mOuterBezier.mPoints[2]);
+    mLastOuterP = mOuterBezier.mPoints[0];
+    mLastInnerP = mInnerBezier.mPoints[0];
+  }
+
+  // See the comment at mType declaration for each condition.
+
+  Float borderRadiusA =
+      fabs(mOuterBezier.mPoints[0].x - mOuterBezier.mPoints[3].x);
+  Float borderRadiusB =
+      fabs(mOuterBezier.mPoints[0].y - mOuterBezier.mPoints[3].y);
+  if (aBorderWidthH == aBorderWidthV && borderRadiusA == borderRadiusB &&
+      borderRadiusA > aBorderWidthH * 2.0f) {
+    Float curveHeight = borderRadiusA - aBorderWidthH / 2.0;
+
+    mType = PERFECT;
+    Float borderLength = M_PI * curveHeight / 2.0f;
+
+    Float dashWidth = aBorderWidthH * DOT_LENGTH * DASH_LENGTH;
+    size_t count = ceil(borderLength / dashWidth);
+    if (count % 2) {
+      count++;
+    }
+    mCount = count / 2 + 1;
+    mBestDashLength = borderLength / (aBorderWidthH * count);
+  }
+
+  Float minBorderWidth = std::min(aBorderWidthH, aBorderWidthV);
+  if (minBorderWidth == 0.0f) {
+    mHasZeroBorderWidth = true;
+  }
+
+  if (mType == OTHER && !mHasZeroBorderWidth) {
+    Float minBorderRadius = std::min(borderRadiusA, borderRadiusB);
+    Float maxBorderRadius = std::max(borderRadiusA, borderRadiusB);
+    Float maxBorderWidth = std::max(aBorderWidthH, aBorderWidthV);
+
+    FindBestDashLength(minBorderWidth, maxBorderWidth, minBorderRadius,
+                       maxBorderRadius);
+  }
+}
+
+bool DashedCornerFinder::HasMore(void) const {
+  if (mHasZeroBorderWidth) {
+    return mI < mMaxCount && mHasMore;
+  }
+
+  return mI < mCount;
+}
+
+DashedCornerFinder::Result DashedCornerFinder::Next(void) {
+  Float lastOuterT, lastInnerT, outerT, innerT;
+
+  if (mI == 0) {
+    lastOuterT = 0.0f;
+    lastInnerT = 0.0f;
+  } else {
+    if (mType == PERFECT) {
+      lastOuterT = lastInnerT = (mI * 2.0f - 0.5f) / ((mCount - 1) * 2.0f);
+    } else {
+      Float last2OuterT = mLastOuterT;
+      Float last2InnerT = mLastInnerT;
+
+      (void)FindNext(mBestDashLength);
+
+      //
+      //          mLastOuterT   lastOuterT
+      //                    |   |
+      //                    v   v
+      //            +---+---+---+---+ <- last2OuterT
+      //            |   |###|###|   |
+      //            |   |###|###|   |
+      //            |   |###|###|   |
+      //            +---+---+---+---+ <- last2InnerT
+      //                    ^   ^
+      //                    |   |
+      //          mLastInnerT   lastInnerT
+      lastOuterT = (mLastOuterT + last2OuterT) / 2.0f;
+      lastInnerT = (mLastInnerT + last2InnerT) / 2.0f;
+    }
+  }
+
+  if ((!mHasZeroBorderWidth && mI == mCount - 1) ||
+      (mHasZeroBorderWidth && !mHasMore)) {
+    outerT = 1.0f;
+    innerT = 1.0f;
+  } else {
+    if (mType == PERFECT) {
+      outerT = innerT = (mI * 2.0f + 0.5f) / ((mCount - 1) * 2.0f);
+    } else {
+      Float last2OuterT = mLastOuterT;
+      Float last2InnerT = mLastInnerT;
+
+      (void)FindNext(mBestDashLength);
+
+      //
+      //               outerT   last2OuterT
+      //                    |   |
+      //                    v   v
+      // mLastOuterT -> +---+---+---+---+
+      //                |   |###|###|   |
+      //                |   |###|###|   |
+      //                |   |###|###|   |
+      // mLastInnerT -> +---+---+---+---+
+      //                    ^   ^
+      //                    |   |
+      //               innerT   last2InnerT
+      outerT = (mLastOuterT + last2OuterT) / 2.0f;
+      innerT = (mLastInnerT + last2InnerT) / 2.0f;
+    }
+  }
+
+  mI++;
+
+  Bezier outerSectionBezier;
+  Bezier innerSectionBezier;
+  GetSubBezier(&outerSectionBezier, mOuterBezier, lastOuterT, outerT);
+  GetSubBezier(&innerSectionBezier, mInnerBezier, lastInnerT, innerT);
+  return DashedCornerFinder::Result(outerSectionBezier, innerSectionBezier);
+}
+
+void DashedCornerFinder::Reset(void) {
+  mLastOuterP = mOuterBezier.mPoints[0];
+  mLastInnerP = mInnerBezier.mPoints[0];
+  mLastOuterT = 0.0f;
+  mLastInnerT = 0.0f;
+  mHasMore = true;
+}
+
+Float DashedCornerFinder::FindNext(Float dashLength) {
+  Float upper = 1.0f;
+  Float lower = mLastOuterT;
+
+  Point OuterP, InnerP;
+  // Start from upper bound to check if this is the last segment.
+  Float outerT = upper;
+  Float innerT;
+  Float W = 0.0f;
+  Float L = 0.0f;
+
+  const Float LENGTH_MARGIN = 0.1f;
+  for (size_t i = 0; i < MAX_LOOP; i++) {
+    OuterP = GetBezierPoint(mOuterBezier, outerT);
+    InnerP = FindBezierNearestPoint(mInnerBezier, OuterP, outerT, &innerT);
+
+    // Calculate approximate dash length.
+    //
+    //   W = (W1 + W2) / 2
+    //   L = (OuterL + InnerL) / 2
+    //   dashLength = L / W
+    //
+    //              ____----+----____
+    // OuterP ___---        |         ---___    mLastOuterP
+    //    +---              |               ---+
+    //    |                  |                 |
+    //    |                  |                 |
+    //     |               W |              W1 |
+    //     |                  |                |
+    //  W2 |                  |                |
+    //     |                  |    ______------+
+    //     |              ____+----             mLastInnerP
+    //      |       ___---
+    //      |  __---
+    //      +--
+    //    InnerP
+    //                     OuterL
+    //              ____---------____
+    // OuterP ___---                  ---___    mLastOuterP
+    //    +---                              ---+
+    //    |                  L                 |
+    //    |            ___----------______     |
+    //     |      __---                   -----+
+    //     |  __--                             |
+    //     +--                                 |
+    //     |                InnerL ______------+
+    //     |              ____-----             mLastInnerP
+    //      |       ___---
+    //      |  __---
+    //      +--
+    //    InnerP
+    Float W1 = (mLastOuterP - mLastInnerP).Length();
+    Float W2 = (OuterP - InnerP).Length();
+    Float OuterL = GetBezierLength(mOuterBezier, mLastOuterT, outerT);
+    Float InnerL = GetBezierLength(mInnerBezier, mLastInnerT, innerT);
+    W = (W1 + W2) / 2.0f;
+    L = (OuterL + InnerL) / 2.0f;
+    if (L > W * dashLength + LENGTH_MARGIN) {
+      if (i > 0) {
+        upper = outerT;
+      }
+    } else if (L < W * dashLength - LENGTH_MARGIN) {
+      if (i == 0) {
+        // This is the last segment with shorter dashLength.
+        mHasMore = false;
+        break;
+      }
+      lower = outerT;
+    } else {
+      break;
+    }
+
+    outerT = (upper + lower) / 2.0f;
+  }
+
+  mLastOuterP = OuterP;
+  mLastInnerP = InnerP;
+  mLastOuterT = outerT;
+  mLastInnerT = innerT;
+
+  if (W == 0.0f) {
+    return 1.0f;
+  }
+
+  return L / W;
+}
+
+void DashedCornerFinder::FindBestDashLength(Float aMinBorderWidth,
+                                            Float aMaxBorderWidth,
+                                            Float aMinBorderRadius,
+                                            Float aMaxBorderRadius) {
+  // If dashLength is not calculateable, find it with binary search,
+  // such that there exists i that OuterP_i == OuterP_n and
+  // InnerP_i == InnerP_n with given dashLength.
+
+  FourFloats key(aMinBorderWidth, aMaxBorderWidth, aMinBorderRadius,
+                 aMaxBorderRadius);
+  BestDashLength best;
+  if (DashedCornerCache.Get(key, &best)) {
+    mCount = best.count;
+    mBestDashLength = best.dashLength;
+    return;
+  }
+
+  Float lower = 1.0f;
+  Float upper = DOT_LENGTH * DASH_LENGTH;
+  Float dashLength = upper;
+  size_t targetCount = 0;
+
+  const Float LENGTH_MARGIN = 0.1f;
+  for (size_t j = 0; j < MAX_LOOP; j++) {
+    size_t count;
+    Float actualDashLength;
+    if (!GetCountAndLastDashLength(dashLength, &count, &actualDashLength)) {
+      if (j == 0) {
+        mCount = mMaxCount;
+        break;
+      }
+    }
+
+    if (j == 0) {
+      if (count == 1) {
+        // If only 1 segment fits, fill entire region
+        //
+        //   count = 1
+        //   mCount = 1
+        //   |   1   |
+        //   +---+---+
+        //   |###|###|
+        //   |###|###|
+        //   |###|###|
+        //   +---+---+
+        //       1
+        mCount = 1;
+        break;
+      }
+
+      // targetCount should be 2n.
+      //
+      //   targetCount = 2
+      //   mCount = 2
+      //   |   1   |   2   |
+      //   +---+---+---+---+
+      //   |###|   |   |###|
+      //   |###|   |   |###|
+      //   |###|   |   |###|
+      //   +---+---+---+---+
+      //     1           2
+      //
+      //   targetCount = 6
+      //   mCount = 4
+      //   |   1   |   2   |   3   |   4   |   5   |   6   |
+      //   +---+---+---+---+---+---+---+---+---+---+---+---+
+      //   |###|   |   |###|###|   |   |###|###|   |   |###|
+      //   |###|   |   |###|###|   |   |###|###|   |   |###|
+      //   |###|   |   |###|###|   |   |###|###|   |   |###|
+      //   +---+---+---+---+---+---+---+---+---+---+---+---+
+      //     1             2               3             4
+      if (count % 2) {
+        targetCount = count + 1;
+      } else {
+        targetCount = count;
+      }
+
+      mCount = targetCount / 2 + 1;
+    }
+
+    if (count == targetCount) {
+      mBestDashLength = dashLength;
+
+      // actualDashLength won't be greater than dashLength.
+      if (actualDashLength > dashLength - LENGTH_MARGIN) {
+        break;
+      }
+
+      // We started from upper bound, no need to update range when j == 0.
+      if (j > 0) {
+        upper = dashLength;
+      }
+    } else {
+      // |j == 0 && count != targetCount| means that |targetCount = count + 1|,
+      // and we started from upper bound, no need to update range when j == 0.
+      if (j > 0) {
+        if (count > targetCount) {
+          lower = dashLength;
+        } else {
+          upper = dashLength;
+        }
+      }
+    }
+
+    dashLength = (upper + lower) / 2.0f;
+  }
+
+  if (DashedCornerCache.Count() > DashedCornerCacheSize) {
+    DashedCornerCache.Clear();
+  }
+  DashedCornerCache.InsertOrUpdate(key,
+                                   BestDashLength(mBestDashLength, mCount));
+}
+
+bool DashedCornerFinder::GetCountAndLastDashLength(Float aDashLength,
+                                                   size_t* aCount,
+                                                   Float* aActualDashLength) {
+  // Return the number of segments and the last segment's dashLength for
+  // the given dashLength.
+
+  Reset();
+
+  for (size_t i = 0; i < mMaxCount; i++) {
+    Float actualDashLength = FindNext(aDashLength);
+    if (mLastOuterT >= 1.0f) {
+      *aCount = i + 1;
+      *aActualDashLength = actualDashLength;
+      return true;
+    }
+  }
+
+  return false;
+}
+
+}  // namespace mozilla
diff --git a/layout/painting/DashedCornerFinder.h b/layout/painting/DashedCornerFinder.h
new file mode 100644
index 0000000000..3a409d19f7
--- /dev/null
+++ b/layout/painting/DashedCornerFinder.h
@@ -0,0 +1,274 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_DashedCornerFinder_h_
+#define mozilla_DashedCornerFinder_h_
+
+#include "mozilla/gfx/2D.h"
+#include "mozilla/gfx/BezierUtils.h"
+
+namespace mozilla {
+
+// Calculate {OuterT_i, InnerT_i} for each 1 < i < n, that
+//   (OuterL_i + InnerL_i) / 2 == dashLength * (W_i + W_{i-1}) / 2
+// where
+//   OuterP_i: OuterCurve(OuterT_i)
+//   InnerP_i: InnerCurve(OuterT_i)
+//   OuterL_i: Elliptic arc length between OuterP_i - OuterP_{i-1}
+//   InnerL_i: Elliptic arc length between InnerP_i - InnerP_{i-1}
+//   W_i = |OuterP_i - InnerP_i|
+//   1.0 < dashLength < 3.0
+//
+//                                         OuterP_1          OuterP_0
+//                                         _+__-----------+ OuterCurve
+//                          OuterP_2 __---- |   OuterL_1  |
+//                             __+---       |             |
+//                        __---  | OuterL_2 |             |
+//            OuterP_3 _--       |           | W_1        | W_0
+//                   _+           |          |            |
+//                  /  \       W_2 |         |            |
+//                 /    \          |          | InnerL_1  |
+//                |      \          | InnerL_2|____-------+ InnerCurve
+//                |       \          |____----+          InnerP_0
+//               |     .   \    __---+       InnerP_1
+//               |          \ /     InnerP_2
+//              |     .     /+ InnerP_3
+//              |          |
+//              |    .    |
+//              |         |
+//              |        |
+//              |        |
+// OuterP_{n-1} +--------+ InnerP_{n-1}
+//              |        |
+//              |        |
+//              |        |
+//              |        |
+//              |        |
+//     OuterP_n +--------+ InnerP_n
+//
+// Returns region with [OuterCurve((OuterT_{2j} + OuterT_{2j-1}) / 2),
+//                      OuterCurve((OuterT_{2j} + OuterT_{2j-1}) / 2),
+//                      InnerCurve((OuterT_{2j} + OuterT_{2j+1}) / 2),
+//                      InnerCurve((OuterT_{2j} + OuterT_{2j+1}) / 2)],
+// to start and end with half segment.
+//
+//                                     _+__----+------+ OuterCurve
+//                               _+---- |      |######|
+//                         __+---#|     |      |######|
+//                    _+---##|####|     |      |######|
+//                 _-- |#####|#####|     |      |#####|
+//               _+     |#####|#####|    |      |#####|
+//              /  \     |#####|####|    |      |#####|
+//             /    \     |####|#####|    |     |#####|
+//            |      \     |####|####|    |____-+-----+ InnerCurve
+//            |       \     |####|____+---+
+//           |     .   \   __+---+
+//           |          \ /
+//          |     .     /+
+//          |          |
+//          |    .    |
+//          |         |
+//          |        |
+//          |        |
+//          +--------+
+//          |        |
+//          |        |
+//          +--------+
+//          |########|
+//          |########|
+//          +--------+
+
+class DashedCornerFinder {
+  typedef mozilla::gfx::Bezier Bezier;
+  typedef mozilla::gfx::Float Float;
+  typedef mozilla::gfx::Point Point;
+  typedef mozilla::gfx::Size Size;
+
+ public:
+  struct Result {
+    // Control points for the outer curve and the inner curve.
+    //
+    //   outerSectionBezier
+    //        |
+    //        v     _+ 3
+    //        ___---#|
+    //  0 +---#######|
+    //    |###########|
+    //     |###########|
+    //      |##########|
+    //       |##########|
+    //        |#########|
+    //         |#####____+ 3
+    //        0 +----
+    //              ^
+    //              |
+    //   innerSectionBezier
+    Bezier outerSectionBezier;
+    Bezier innerSectionBezier;
+
+    Result(const Bezier& aOuterSectionBezier, const Bezier& aInnerSectionBezier)
+        : outerSectionBezier(aOuterSectionBezier),
+          innerSectionBezier(aInnerSectionBezier) {}
+  };
+
+  //                       aCornerDim.width
+  //                     |<----------------->|
+  //                     |                   |
+  //                   --+-------------___---+--
+  //                   ^ |         __--      | ^
+  //                   | |       _-          | |
+  //                   | |     /             | | aBorderWidthH
+  //                   | |   /               | |
+  //                   | |  |                | v
+  //                   | | |             __--+--
+  // aCornerDim.height | ||            _-
+  //                   | ||           /
+  //                   | |           /
+  //                   | |          |
+  //                   | |          |
+  //                   | |         |
+  //                   | |         |
+  //                   v |         |
+  //                   --+---------+
+  //                     |         |
+  //                     |<------->|
+  //                     aBorderWidthV
+  DashedCornerFinder(const Bezier& aOuterBezier, const Bezier& aInnerBezier,
+                     Float aBorderWidthH, Float aBorderWidthV,
+                     const Size& aCornerDim);
+
+  bool HasMore(void) const;
+  Result Next(void);
+
+ private:
+  static const size_t MAX_LOOP = 32;
+
+  // Bezier control points for the outer curve and the inner curve.
+  //
+  //               ___---+ outer curve
+  //           __--      |
+  //         _-          |
+  //       /             |
+  //     /               |
+  //    |                |
+  //   |             __--+ inner curve
+  //  |            _-
+  //  |           /
+  // |           /
+  // |          |
+  // |          |
+  // |         |
+  // |         |
+  // |         |
+  // +---------+
+  Bezier mOuterBezier;
+  Bezier mInnerBezier;
+
+  Point mLastOuterP;
+  Point mLastInnerP;
+  Float mLastOuterT;
+  Float mLastInnerT;
+
+  // Length for each segment, ratio of the border width at that point.
+  Float mBestDashLength;
+
+  // If one of border-widths is 0, do not calculate mBestDashLength, and draw
+  // segments until it reaches the other side or exceeds mMaxCount.
+  bool mHasZeroBorderWidth;
+  bool mHasMore;
+
+  // The maximum number of segments.
+  size_t mMaxCount;
+
+  enum {
+    //                      radius.width
+    //                 |<----------------->|
+    //                 |                   |
+    //               --+-------------___---+--
+    //               ^ |         __--      | ^
+    //               | |       _-          | |
+    //               | |     /             + | top-width
+    //               | |   /               | |
+    //               | |  |                | v
+    //               | | |             __--+--
+    // radius.height | ||            _-
+    //               | ||           /
+    //               | |           /
+    //               | |          |
+    //               | |          |
+    //               | |         |
+    //               | |         |
+    //               v |         |
+    //               --+----+----+
+    //                 |         |
+    //                 |<------->|
+    //                  left-width
+
+    // * top-width == left-width
+    // * radius.width == radius.height
+    // * top-width < radius.width * 2
+    //
+    // Split the perfect circle's arc into 2n segments, each segment's length is
+    // top-width * dashLength. Then split the inner curve and the outer curve
+    // with same angles.
+    //
+    //                        radius.width
+    //                 |<---------------------->|
+    //                 |                        | v
+    //               --+------------------------+--
+    //               ^ |                        | | top-width / 2
+    //               | | perfect                | |
+    //               | | circle's         ___---+--
+    //               | | arc          __-+      | ^
+    //               | |  |         _-   |      |
+    // radius.height | |  |       +       |     +--
+    //               | |  |     /  \      |     |
+    //               | |  |    |     \     |    |
+    //               | |  |   |       \     |   |
+    //               | |  +->|          \   |   |
+    //               | |    +---__       \   |  |
+    //               | |    |     --__     \  | |
+    //               | |    |         ---__ \ | |
+    //               v |    |              --_\||
+    //               --+----+----+--------------+
+    //                 |    |    |
+    //                 |<-->|    |
+    //               left-width / 2
+    PERFECT,
+
+    // Other cases.
+    //
+    // Split the outer curve and the inner curve into 2n segments, each segment
+    // satisfies following:
+    //   (OuterL_i + InnerL_i) / 2 == dashLength * (W_i + W_{i-1}) / 2
+    OTHER
+  } mType;
+
+  size_t mI;
+  size_t mCount;
+
+  // Determine mType from parameters.
+  void DetermineType(Float aBorderWidthH, Float aBorderWidthV);
+
+  // Reset calculation.
+  void Reset(void);
+
+  // Find next segment.
+  Float FindNext(Float dashLength);
+
+  // Find mBestDashLength for parameters.
+  void FindBestDashLength(Float aMinBorderWidth, Float aMaxBorderWidth,
+                          Float aMinBorderRadius, Float aMaxBorderRadius);
+
+  // Fill corner with dashes with given dash length, and return the number of
+  // segments and last segment's dash length.
+  bool GetCountAndLastDashLength(Float aDashLength, size_t* aCount,
+                                 Float* aActualDashLength);
+};
+
+}  // namespace mozilla
+
+#endif /* mozilla_DashedCornerFinder_h_ */
diff --git a/layout/painting/DisplayItemClip.cpp b/layout/painting/DisplayItemClip.cpp
new file mode 100644
index 0000000000..78aae2e1ec
--- /dev/null
+++ b/layout/painting/DisplayItemClip.cpp
@@ -0,0 +1,486 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "DisplayItemClip.h"
+
+#include "gfxContext.h"
+#include "gfxUtils.h"
+#include "mozilla/gfx/2D.h"
+#include "mozilla/gfx/PathHelpers.h"
+#include "mozilla/layers/StackingContextHelper.h"
+#include "mozilla/StaticPtr.h"
+#include "mozilla/webrender/WebRenderTypes.h"
+#include "nsPresContext.h"
+#include "nsCSSRendering.h"
+#include "nsLayoutUtils.h"
+#include "nsRegion.h"
+
+using namespace mozilla::gfx;
+
+namespace mozilla {
+
+void DisplayItemClip::SetTo(const nsRect& aRect) { SetTo(aRect, nullptr); }
+
+void DisplayItemClip::SetTo(const nsRect& aRect, const nscoord* aRadii) {
+  mHaveClipRect = true;
+  mClipRect = aRect;
+  if (aRadii) {
+    mRoundedClipRects.SetLength(1);
+    mRoundedClipRects[0].mRect = aRect;
+    memcpy(mRoundedClipRects[0].mRadii, aRadii, sizeof(nscoord) * 8);
+  } else {
+    mRoundedClipRects.Clear();
+  }
+}
+
+void DisplayItemClip::SetTo(const nsRect& aRect, const nsRect& aRoundedRect,
+                            const nscoord* aRadii) {
+  mHaveClipRect = true;
+  mClipRect = aRect;
+  mRoundedClipRects.SetLength(1);
+  mRoundedClipRects[0].mRect = aRoundedRect;
+  memcpy(mRoundedClipRects[0].mRadii, aRadii, sizeof(nscoord) * 8);
+}
+
+bool DisplayItemClip::MayIntersect(const nsRect& aRect) const {
+  if (!mHaveClipRect) {
+    return !aRect.IsEmpty();
+  }
+  nsRect r = aRect.Intersect(mClipRect);
+  if (r.IsEmpty()) {
+    return false;
+  }
+  for (uint32_t i = 0; i < mRoundedClipRects.Length(); ++i) {
+    const RoundedRect& rr = mRoundedClipRects[i];
+    if (!nsLayoutUtils::RoundedRectIntersectsRect(rr.mRect, rr.mRadii, r)) {
+      return false;
+    }
+  }
+  return true;
+}
+
+void DisplayItemClip::IntersectWith(const DisplayItemClip& aOther) {
+  if (!aOther.mHaveClipRect) {
+    return;
+  }
+  if (!mHaveClipRect) {
+    *this = aOther;
+    return;
+  }
+  if (!mClipRect.IntersectRect(mClipRect, aOther.mClipRect)) {
+    mRoundedClipRects.Clear();
+    return;
+  }
+  mRoundedClipRects.AppendElements(aOther.mRoundedClipRects);
+}
+
+void DisplayItemClip::ApplyTo(gfxContext* aContext, int32_t A2D) const {
+  ApplyRectTo(aContext, A2D);
+  ApplyRoundedRectClipsTo(aContext, A2D, 0, mRoundedClipRects.Length());
+}
+
+void DisplayItemClip::ApplyRectTo(gfxContext* aContext, int32_t A2D) const {
+  aContext->NewPath();
+  gfxRect clip = nsLayoutUtils::RectToGfxRect(mClipRect, A2D);
+  aContext->SnappedRectangle(clip);
+  aContext->Clip();
+}
+
+void DisplayItemClip::ApplyRoundedRectClipsTo(gfxContext* aContext, int32_t A2D,
+                                              uint32_t aBegin,
+                                              uint32_t aEnd) const {
+  DrawTarget& aDrawTarget = *aContext->GetDrawTarget();
+
+  aEnd = std::min<uint32_t>(aEnd, mRoundedClipRects.Length());
+
+  for (uint32_t i = aBegin; i < aEnd; ++i) {
+    RefPtr<Path> roundedRect =
+        MakeRoundedRectPath(aDrawTarget, A2D, mRoundedClipRects[i]);
+    aContext->Clip(roundedRect);
+  }
+}
+
+void DisplayItemClip::FillIntersectionOfRoundedRectClips(
+    gfxContext* aContext, const DeviceColor& aColor,
+    int32_t aAppUnitsPerDevPixel) const {
+  DrawTarget& aDrawTarget = *aContext->GetDrawTarget();
+
+  uint32_t end = mRoundedClipRects.Length();
+  if (!end) {
+    return;
+  }
+
+  // Push clips for any rects that come BEFORE the rect at |aEnd - 1|, if any:
+  ApplyRoundedRectClipsTo(aContext, aAppUnitsPerDevPixel, 0, end - 1);
+
+  // Now fill the rect at |aEnd - 1|:
+  RefPtr<Path> roundedRect = MakeRoundedRectPath(
+      aDrawTarget, aAppUnitsPerDevPixel, mRoundedClipRects[end - 1]);
+  aDrawTarget.Fill(roundedRect, ColorPattern(aColor));
+
+  // Finally, pop any clips that we may have pushed:
+  for (uint32_t i = 0; i < end - 1; ++i) {
+    aContext->PopClip();
+  }
+}
+
+already_AddRefed<Path> DisplayItemClip::MakeRoundedRectPath(
+    DrawTarget& aDrawTarget, int32_t A2D, const RoundedRect& aRoundRect) const {
+  RectCornerRadii pixelRadii;
+  nsCSSRendering::ComputePixelRadii(aRoundRect.mRadii, A2D, &pixelRadii);
+
+  Rect rect = NSRectToSnappedRect(aRoundRect.mRect, A2D, aDrawTarget);
+
+  return MakePathForRoundedRect(aDrawTarget, rect, pixelRadii);
+}
+
+nsRect DisplayItemClip::ApproximateIntersectInward(const nsRect& aRect) const {
+  nsRect r = aRect;
+  if (mHaveClipRect) {
+    r.IntersectRect(r, mClipRect);
+  }
+  for (uint32_t i = 0, iEnd = mRoundedClipRects.Length(); i < iEnd; ++i) {
+    const RoundedRect& rr = mRoundedClipRects[i];
+    nsRegion rgn =
+        nsLayoutUtils::RoundedRectIntersectRect(rr.mRect, rr.mRadii, r);
+    r = rgn.GetLargestRectangle();
+  }
+  return r;
+}
+
+// Test if (aXPoint, aYPoint) is in the ellipse with center (aXCenter, aYCenter)
+// and radii aXRadius, aYRadius.
+static bool IsInsideEllipse(nscoord aXRadius, nscoord aXCenter, nscoord aXPoint,
+                            nscoord aYRadius, nscoord aYCenter,
+                            nscoord aYPoint) {
+  float scaledX = float(aXPoint - aXCenter) / float(aXRadius);
+  float scaledY = float(aYPoint - aYCenter) / float(aYRadius);
+  return scaledX * scaledX + scaledY * scaledY < 1.0f;
+}
+
+bool DisplayItemClip::IsRectClippedByRoundedCorner(const nsRect& aRect) const {
+  if (mRoundedClipRects.IsEmpty()) return false;
+
+  nsRect rect;
+  rect.IntersectRect(aRect, NonRoundedIntersection());
+  for (uint32_t i = 0, iEnd = mRoundedClipRects.Length(); i < iEnd; ++i) {
+    const RoundedRect& rr = mRoundedClipRects[i];
+    // top left
+    if (rect.x < rr.mRect.x + rr.mRadii[eCornerTopLeftX] &&
+        rect.y < rr.mRect.y + rr.mRadii[eCornerTopLeftY]) {
+      if (!IsInsideEllipse(rr.mRadii[eCornerTopLeftX],
+                           rr.mRect.x + rr.mRadii[eCornerTopLeftX], rect.x,
+                           rr.mRadii[eCornerTopLeftY],
+                           rr.mRect.y + rr.mRadii[eCornerTopLeftY], rect.y)) {
+        return true;
+      }
+    }
+    // top right
+    if (rect.XMost() > rr.mRect.XMost() - rr.mRadii[eCornerTopRightX] &&
+        rect.y < rr.mRect.y + rr.mRadii[eCornerTopRightY]) {
+      if (!IsInsideEllipse(rr.mRadii[eCornerTopRightX],
+                           rr.mRect.XMost() - rr.mRadii[eCornerTopRightX],
+                           rect.XMost(), rr.mRadii[eCornerTopRightY],
+                           rr.mRect.y + rr.mRadii[eCornerTopRightY], rect.y)) {
+        return true;
+      }
+    }
+    // bottom left
+    if (rect.x < rr.mRect.x + rr.mRadii[eCornerBottomLeftX] &&
+        rect.YMost() > rr.mRect.YMost() - rr.mRadii[eCornerBottomLeftY]) {
+      if (!IsInsideEllipse(rr.mRadii[eCornerBottomLeftX],
+                           rr.mRect.x + rr.mRadii[eCornerBottomLeftX], rect.x,
+                           rr.mRadii[eCornerBottomLeftY],
+                           rr.mRect.YMost() - rr.mRadii[eCornerBottomLeftY],
+                           rect.YMost())) {
+        return true;
+      }
+    }
+    // bottom right
+    if (rect.XMost() > rr.mRect.XMost() - rr.mRadii[eCornerBottomRightX] &&
+        rect.YMost() > rr.mRect.YMost() - rr.mRadii[eCornerBottomRightY]) {
+      if (!IsInsideEllipse(rr.mRadii[eCornerBottomRightX],
+                           rr.mRect.XMost() - rr.mRadii[eCornerBottomRightX],
+                           rect.XMost(), rr.mRadii[eCornerBottomRightY],
+                           rr.mRect.YMost() - rr.mRadii[eCornerBottomRightY],
+                           rect.YMost())) {
+        return true;
+      }
+    }
+  }
+  return false;
+}
+
+nsRect DisplayItemClip::NonRoundedIntersection() const {
+  NS_ASSERTION(mHaveClipRect, "Must have a clip rect!");
+  nsRect result = mClipRect;
+  for (uint32_t i = 0, iEnd = mRoundedClipRects.Length(); i < iEnd; ++i) {
+    result.IntersectRect(result, mRoundedClipRects[i].mRect);
+  }
+  return result;
+}
+
+bool DisplayItemClip::IsRectAffectedByClip(const nsRect& aRect) const {
+  if (mHaveClipRect && !mClipRect.Contains(aRect)) {
+    return true;
+  }
+  for (uint32_t i = 0, iEnd = mRoundedClipRects.Length(); i < iEnd; ++i) {
+    const RoundedRect& rr = mRoundedClipRects[i];
+    nsRegion rgn =
+        nsLayoutUtils::RoundedRectIntersectRect(rr.mRect, rr.mRadii, aRect);
+    if (!rgn.Contains(aRect)) {
+      return true;
+    }
+  }
+  return false;
+}
+
+bool DisplayItemClip::IsRectAffectedByClip(const nsIntRect& aRect,
+                                           float aXScale, float aYScale,
+                                           int32_t A2D) const {
+  if (mHaveClipRect) {
+    nsIntRect pixelClipRect =
+        mClipRect.ScaleToNearestPixels(aXScale, aYScale, A2D);
+    if (!pixelClipRect.Contains(aRect)) {
+      return true;
+    }
+  }
+
+  // Rounded rect clipping only snaps to user-space pixels, not device space.
+  nsIntRect unscaled = aRect;
+  unscaled.Scale(1 / aXScale, 1 / aYScale);
+
+  for (uint32_t i = 0, iEnd = mRoundedClipRects.Length(); i < iEnd; ++i) {
+    const RoundedRect& rr = mRoundedClipRects[i];
+
+    nsIntRect pixelRect = rr.mRect.ToNearestPixels(A2D);
+
+    RectCornerRadii pixelRadii;
+    nsCSSRendering::ComputePixelRadii(rr.mRadii, A2D, &pixelRadii);
+
+    nsIntRegion rgn = nsLayoutUtils::RoundedRectIntersectIntRect(
+        pixelRect, pixelRadii, unscaled);
+    if (!rgn.Contains(unscaled)) {
+      return true;
+    }
+  }
+  return false;
+}
+
+nsRect DisplayItemClip::ApplyNonRoundedIntersection(const nsRect& aRect) const {
+  if (!mHaveClipRect) {
+    return aRect;
+  }
+
+  nsRect result = aRect.Intersect(mClipRect);
+  for (uint32_t i = 0, iEnd = mRoundedClipRects.Length(); i < iEnd; ++i) {
+    result = result.Intersect(mRoundedClipRects[i].mRect);
+  }
+  return result;
+}
+
+void DisplayItemClip::RemoveRoundedCorners() {
+  if (mRoundedClipRects.IsEmpty()) return;
+
+  mClipRect = NonRoundedIntersection();
+  mRoundedClipRects.Clear();
+}
+
+// Computes the difference between aR1 and aR2, limited to aBounds.
+static void AccumulateRectDifference(const nsRect& aR1, const nsRect& aR2,
+                                     const nsRect& aBounds, nsRegion* aOut) {
+  if (aR1.IsEqualInterior(aR2)) return;
+  nsRegion r;
+  r.Xor(aR1, aR2);
+  r.And(r, aBounds);
+  aOut->Or(*aOut, r);
+}
+
+static void AccumulateRoundedRectDifference(
+    const DisplayItemClip::RoundedRect& aR1,
+    const DisplayItemClip::RoundedRect& aR2, const nsRect& aBounds,
+    const nsRect& aOtherBounds, nsRegion* aOut) {
+  const nsRect& rect1 = aR1.mRect;
+  const nsRect& rect2 = aR2.mRect;
+
+  // If the two rectangles are totally disjoint, just add them both - otherwise
+  // we'd end up adding one big enclosing rect
+  if (!rect1.Intersects(rect2) ||
+      memcmp(aR1.mRadii, aR2.mRadii, sizeof(aR1.mRadii))) {
+    aOut->Or(*aOut, rect1.Intersect(aBounds));
+    aOut->Or(*aOut, rect2.Intersect(aOtherBounds));
+    return;
+  }
+
+  nscoord lowestBottom = std::max(rect1.YMost(), rect2.YMost());
+  nscoord highestTop = std::min(rect1.Y(), rect2.Y());
+  nscoord maxRight = std::max(rect1.XMost(), rect2.XMost());
+  nscoord minLeft = std::min(rect1.X(), rect2.X());
+
+  // At this point, we know that the radii haven't changed, and that the bounds
+  // are different in some way. To explain how this works, consider the case
+  // where the rounded rect has just been translated along the X direction.
+  // |          ______________________ _ _ _ _ _ _            |
+  // |        /           /            \           \          |
+  // |       |                          |                     |
+  // |       |     aR1   |              |     aR2   |         |
+  // |       |                          |                     |
+  // |        \ __________\___________ / _ _ _ _ _ /          |
+  // |                                                        |
+  // The invalidation region will be as if we lopped off the left rounded part
+  // of aR2, and the right rounded part of aR1, and XOR'd them:
+  // |          ______________________ _ _ _ _ _ _            |
+  // |       -/-----------/-          -\-----------\-         |
+  // |       |--------------          --|------------         |
+  // |       |-----aR1---|--          --|-----aR2---|         |
+  // |       |--------------          --|------------         |
+  // |       -\ __________\-__________-/ _ _ _ _ _ /-          |
+  // |                                                        |
+  // The logic below just implements this idea, but generalized to both the
+  // X and Y dimensions. The "(...)Adjusted(...)" values represent the lopped
+  // off sides.
+  nscoord highestAdjustedBottom = std::min(
+      rect1.YMost() - aR1.mRadii[eCornerBottomLeftY],
+      std::min(rect1.YMost() - aR1.mRadii[eCornerBottomRightY],
+               std::min(rect2.YMost() - aR2.mRadii[eCornerBottomLeftY],
+                        rect2.YMost() - aR2.mRadii[eCornerBottomRightY])));
+  nscoord lowestAdjustedTop =
+      std::max(rect1.Y() + aR1.mRadii[eCornerTopLeftY],
+               std::max(rect1.Y() + aR1.mRadii[eCornerTopRightY],
+                        std::max(rect2.Y() + aR2.mRadii[eCornerTopLeftY],
+                                 rect2.Y() + aR2.mRadii[eCornerTopRightY])));
+
+  nscoord minAdjustedRight = std::min(
+      rect1.XMost() - aR1.mRadii[eCornerTopRightX],
+      std::min(rect1.XMost() - aR1.mRadii[eCornerBottomRightX],
+               std::min(rect2.XMost() - aR2.mRadii[eCornerTopRightX],
+                        rect2.XMost() - aR2.mRadii[eCornerBottomRightX])));
+  nscoord maxAdjustedLeft =
+      std::max(rect1.X() + aR1.mRadii[eCornerTopLeftX],
+               std::max(rect1.X() + aR1.mRadii[eCornerBottomLeftX],
+                        std::max(rect2.X() + aR2.mRadii[eCornerTopLeftX],
+                                 rect2.X() + aR2.mRadii[eCornerBottomLeftX])));
+
+  // We only want to add an invalidation rect if the bounds have changed. If we
+  // always added all of the 4 rects below, we would always be invalidating a
+  // border around the rects, even in cases where we just translated along the X
+  // or Y axis.
+  nsRegion r;
+  // First, or with the Y delta rects, wide along the X axis
+  if (rect1.Y() != rect2.Y()) {
+    r.Or(r, nsRect(minLeft, highestTop, maxRight - minLeft,
+                   lowestAdjustedTop - highestTop));
+  }
+  if (rect1.YMost() != rect2.YMost()) {
+    r.Or(r, nsRect(minLeft, highestAdjustedBottom, maxRight - minLeft,
+                   lowestBottom - highestAdjustedBottom));
+  }
+  // Then, or with the X delta rects, wide along the Y axis
+  if (rect1.X() != rect2.X()) {
+    r.Or(r, nsRect(minLeft, highestTop, maxAdjustedLeft - minLeft,
+                   lowestBottom - highestTop));
+  }
+  if (rect1.XMost() != rect2.XMost()) {
+    r.Or(r, nsRect(minAdjustedRight, highestTop, maxRight - minAdjustedRight,
+                   lowestBottom - highestTop));
+  }
+
+  r.And(r, aBounds.Union(aOtherBounds));
+  aOut->Or(*aOut, r);
+}
+
+void DisplayItemClip::AddOffsetAndComputeDifference(
+    const nsPoint& aOffset, const nsRect& aBounds,
+    const DisplayItemClip& aOther, const nsRect& aOtherBounds,
+    nsRegion* aDifference) {
+  if (mHaveClipRect != aOther.mHaveClipRect ||
+      mRoundedClipRects.Length() != aOther.mRoundedClipRects.Length()) {
+    aDifference->Or(*aDifference, aBounds);
+    aDifference->Or(*aDifference, aOtherBounds);
+    return;
+  }
+  if (mHaveClipRect) {
+    AccumulateRectDifference(mClipRect + aOffset, aOther.mClipRect,
+                             aBounds.Union(aOtherBounds), aDifference);
+  }
+  for (uint32_t i = 0; i < mRoundedClipRects.Length(); ++i) {
+    if (mRoundedClipRects[i] + aOffset != aOther.mRoundedClipRects[i]) {
+      AccumulateRoundedRectDifference(mRoundedClipRects[i] + aOffset,
+                                      aOther.mRoundedClipRects[i], aBounds,
+                                      aOtherBounds, aDifference);
+    }
+  }
+}
+
+void DisplayItemClip::AppendRoundedRects(nsTArray<RoundedRect>* aArray) const {
+  aArray->AppendElements(mRoundedClipRects.Elements(),
+                         mRoundedClipRects.Length());
+}
+
+bool DisplayItemClip::ComputeRegionInClips(const DisplayItemClip* aOldClip,
+                                           const nsPoint& aShift,
+                                           nsRegion* aCombined) const {
+  if (!mHaveClipRect || (aOldClip && !aOldClip->mHaveClipRect)) {
+    return false;
+  }
+
+  if (aOldClip) {
+    *aCombined = aOldClip->NonRoundedIntersection();
+    aCombined->MoveBy(aShift);
+    aCombined->Or(*aCombined, NonRoundedIntersection());
+  } else {
+    *aCombined = NonRoundedIntersection();
+  }
+  return true;
+}
+
+void DisplayItemClip::MoveBy(const nsPoint& aPoint) {
+  if (!mHaveClipRect) {
+    return;
+  }
+  mClipRect += aPoint;
+  for (uint32_t i = 0; i < mRoundedClipRects.Length(); ++i) {
+    mRoundedClipRects[i].mRect += aPoint;
+  }
+}
+
+static StaticAutoPtr<DisplayItemClip> gNoClip;
+
+const DisplayItemClip& DisplayItemClip::NoClip() {
+  if (!gNoClip) {
+    gNoClip = new DisplayItemClip();
+  }
+  return *gNoClip;
+}
+
+void DisplayItemClip::Shutdown() { gNoClip = nullptr; }
+
+nsCString DisplayItemClip::ToString() const {
+  nsAutoCString str;
+  if (mHaveClipRect) {
+    str.AppendPrintf("%d,%d,%d,%d", mClipRect.x, mClipRect.y, mClipRect.width,
+                     mClipRect.height);
+    for (uint32_t i = 0; i < mRoundedClipRects.Length(); ++i) {
+      const RoundedRect& r = mRoundedClipRects[i];
+      str.AppendPrintf(" [%d,%d,%d,%d corners %d,%d,%d,%d,%d,%d,%d,%d]",
+                       r.mRect.x, r.mRect.y, r.mRect.width, r.mRect.height,
+                       r.mRadii[0], r.mRadii[1], r.mRadii[2], r.mRadii[3],
+                       r.mRadii[4], r.mRadii[5], r.mRadii[6], r.mRadii[7]);
+    }
+  }
+  return std::move(str);
+}
+
+void DisplayItemClip::ToComplexClipRegions(
+    int32_t aAppUnitsPerDevPixel,
+    nsTArray<wr::ComplexClipRegion>& aOutArray) const {
+  for (const auto& clipRect : mRoundedClipRects) {
+    aOutArray.AppendElement(wr::ToComplexClipRegion(
+        clipRect.mRect, clipRect.mRadii, aAppUnitsPerDevPixel));
+  }
+}
+
+}  // namespace mozilla
diff --git a/layout/painting/DisplayItemClip.h b/layout/painting/DisplayItemClip.h
new file mode 100644
index 0000000000..ff9df26603
--- /dev/null
+++ b/layout/painting/DisplayItemClip.h
@@ -0,0 +1,193 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef DISPLAYITEMCLIP_H_
+#define DISPLAYITEMCLIP_H_
+
+#include "mozilla/RefPtr.h"
+#include "nsRect.h"
+#include "nsTArray.h"
+
+class gfxContext;
+class nsPresContext;
+class nsRegion;
+
+namespace mozilla {
+namespace gfx {
+class DrawTarget;
+class Path;
+}  // namespace gfx
+namespace layers {
+class StackingContextHelper;
+}  // namespace layers
+namespace wr {
+struct ComplexClipRegion;
+}  // namespace wr
+}  // namespace mozilla
+
+namespace mozilla {
+
+/**
+ * An DisplayItemClip represents the intersection of an optional rectangle
+ * with a list of rounded rectangles (which is often empty), all in appunits.
+ * It can represent everything CSS clipping can do to an element (except for
+ * SVG clip-path), including no clipping at all.
+ */
+class DisplayItemClip {
+  typedef mozilla::gfx::DeviceColor DeviceColor;
+  typedef mozilla::gfx::DrawTarget DrawTarget;
+  typedef mozilla::gfx::Path Path;
+
+ public:
+  struct RoundedRect {
+    nsRect mRect;
+    // Indices into mRadii are the HalfCorner values in gfx/2d/Types.h
+    nscoord mRadii[8];
+
+    RoundedRect operator+(const nsPoint& aOffset) const {
+      RoundedRect r = *this;
+      r.mRect += aOffset;
+      return r;
+    }
+    bool operator==(const RoundedRect& aOther) const {
+      if (!mRect.IsEqualInterior(aOther.mRect)) {
+        return false;
+      }
+
+      for (const auto corner : mozilla::AllPhysicalHalfCorners()) {
+        if (mRadii[corner] != aOther.mRadii[corner]) {
+          return false;
+        }
+      }
+      return true;
+    }
+    bool operator!=(const RoundedRect& aOther) const {
+      return !(*this == aOther);
+    }
+  };
+
+  // Constructs a DisplayItemClip that does no clipping at all.
+  DisplayItemClip() : mHaveClipRect(false) {}
+
+  void SetTo(const nsRect& aRect);
+  void SetTo(const nsRect& aRect, const nscoord* aRadii);
+  void SetTo(const nsRect& aRect, const nsRect& aRoundedRect,
+             const nscoord* aRadii);
+  void IntersectWith(const DisplayItemClip& aOther);
+
+  // Apply this |DisplayItemClip| to the given gfxContext.  Any saving of state
+  // or clearing of other clips must be done by the caller.
+  // See aBegin/aEnd note on ApplyRoundedRectsTo.
+  void ApplyTo(gfxContext* aContext, int32_t A2D) const;
+
+  void ApplyRectTo(gfxContext* aContext, int32_t A2D) const;
+  // Applies the rounded rects in this Clip to aContext
+  // Will only apply rounded rects from aBegin (inclusive) to aEnd
+  // (exclusive) or the number of rounded rects, whichever is smaller.
+  void ApplyRoundedRectClipsTo(gfxContext* aContext, int32_t A2DPRInt32,
+                               uint32_t aBegin, uint32_t aEnd) const;
+
+  // Draw (fill) the rounded rects in this clip to aContext
+  void FillIntersectionOfRoundedRectClips(gfxContext* aContext,
+                                          const DeviceColor& aColor,
+                                          int32_t aAppUnitsPerDevPixel) const;
+  // 'Draw' (create as a path, does not stroke or fill) aRoundRect to aContext
+  already_AddRefed<Path> MakeRoundedRectPath(
+      DrawTarget& aDrawTarget, int32_t A2D,
+      const RoundedRect& aRoundRect) const;
+
+  // Returns true if the intersection of aRect and this clip region is
+  // non-empty. This is precise for DisplayItemClips with at most one
+  // rounded rectangle. When multiple rounded rectangles are present, we just
+  // check that the rectangle intersects all of them (but possibly in different
+  // places). So it may return true when the correct answer is false.
+  bool MayIntersect(const nsRect& aRect) const;
+
+  // Return a rectangle contained in the intersection of aRect with this
+  // clip region. Tries to return the largest possible rectangle, but may
+  // not succeed.
+  nsRect ApproximateIntersectInward(const nsRect& aRect) const;
+
+  /*
+   * Computes a region which contains the clipped area of this DisplayItemClip,
+   * or if aOldClip is non-null, the union of the clipped area of this
+   * DisplayItemClip with the clipped area of aOldClip translated by aShift.
+   * The result is stored in aCombined. If the result would be infinite
+   * (because one or both of the clips does no clipping), returns false.
+   */
+  bool ComputeRegionInClips(const DisplayItemClip* aOldClip,
+                            const nsPoint& aShift, nsRegion* aCombined) const;
+
+  // Returns false if aRect is definitely not clipped by a rounded corner in
+  // this clip. Returns true if aRect is clipped by a rounded corner in this
+  // clip or it can not be quickly determined that it is not clipped by a
+  // rounded corner in this clip.
+  bool IsRectClippedByRoundedCorner(const nsRect& aRect) const;
+
+  // Returns false if aRect is definitely not clipped by anything in this clip.
+  // Fast but not necessarily accurate.
+  bool IsRectAffectedByClip(const nsRect& aRect) const;
+  bool IsRectAffectedByClip(const nsIntRect& aRect, float aXScale,
+                            float aYScale, int32_t A2D) const;
+
+  // Intersection of all rects in this clip ignoring any rounded corners.
+  nsRect NonRoundedIntersection() const;
+
+  // Intersect the given rects with all rects in this clip, ignoring any
+  // rounded corners.
+  nsRect ApplyNonRoundedIntersection(const nsRect& aRect) const;
+
+  // Gets rid of any rounded corners in this clip.
+  void RemoveRoundedCorners();
+
+  // Adds the difference between Intersect(*this + aPoint, aBounds) and
+  // Intersect(aOther, aOtherBounds) to aDifference (or a bounding-box thereof).
+  void AddOffsetAndComputeDifference(const nsPoint& aPoint,
+                                     const nsRect& aBounds,
+                                     const DisplayItemClip& aOther,
+                                     const nsRect& aOtherBounds,
+                                     nsRegion* aDifference);
+
+  bool operator==(const DisplayItemClip& aOther) const {
+    return mHaveClipRect == aOther.mHaveClipRect &&
+           (!mHaveClipRect || mClipRect.IsEqualInterior(aOther.mClipRect)) &&
+           mRoundedClipRects == aOther.mRoundedClipRects;
+  }
+  bool operator!=(const DisplayItemClip& aOther) const {
+    return !(*this == aOther);
+  }
+
+  bool HasClip() const { return mHaveClipRect; }
+  const nsRect& GetClipRect() const {
+    NS_ASSERTION(HasClip(), "No clip rect!");
+    return mClipRect;
+  }
+
+  void MoveBy(const nsPoint& aPoint);
+
+  nsCString ToString() const;
+
+  uint32_t GetRoundedRectCount() const { return mRoundedClipRects.Length(); }
+  void AppendRoundedRects(nsTArray<RoundedRect>* aArray) const;
+
+  void ToComplexClipRegions(int32_t aAppUnitsPerDevPixel,
+                            nsTArray<wr::ComplexClipRegion>& aOutArray) const;
+
+  static const DisplayItemClip& NoClip();
+
+  static void Shutdown();
+
+ private:
+  nsRect mClipRect;
+  CopyableTArray<RoundedRect> mRoundedClipRects;
+  // If mHaveClipRect is false then this object represents no clipping at all
+  // and mRoundedClipRects must be empty.
+  bool mHaveClipRect;
+};
+
+}  // namespace mozilla
+
+#endif /* DISPLAYITEMCLIP_H_ */
diff --git a/layout/painting/DisplayItemClipChain.cpp b/layout/painting/DisplayItemClipChain.cpp
new file mode 100644
index 0000000000..537c3615a1
--- /dev/null
+++ b/layout/painting/DisplayItemClipChain.cpp
@@ -0,0 +1,88 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "DisplayItemClipChain.h"
+
+#include "nsDisplayList.h"
+
+namespace mozilla {
+
+/* static */ const DisplayItemClip* DisplayItemClipChain::ClipForASR(
+    const DisplayItemClipChain* aClipChain, const ActiveScrolledRoot* aASR) {
+  while (aClipChain &&
+         !ActiveScrolledRoot::IsAncestor(aClipChain->mASR, aASR)) {
+    aClipChain = aClipChain->mParent;
+  }
+  return (aClipChain && aClipChain->mASR == aASR) ? &aClipChain->mClip
+                                                  : nullptr;
+}
+
+bool DisplayItemClipChain::Equal(const DisplayItemClipChain* aClip1,
+                                 const DisplayItemClipChain* aClip2) {
+  if (aClip1 == aClip2) {
+    return true;
+  }
+
+  if (!aClip1 || !aClip2) {
+    return false;
+  }
+
+  bool ret = aClip1->mASR == aClip2->mASR && aClip1->mClip == aClip2->mClip &&
+             Equal(aClip1->mParent, aClip2->mParent);
+  // Sanity check: if two clip chains are equal they must hash to the same
+  // thing too, or Bad Things (TM) will happen.
+  MOZ_ASSERT(!ret || (Hash(aClip1) == Hash(aClip2)));
+  return ret;
+}
+
+uint32_t DisplayItemClipChain::Hash(const DisplayItemClipChain* aClip) {
+  if (!aClip) {
+    return 0;
+  }
+
+  // We include the number of rounded rects in the hash but not their contents.
+  // This is to keep the hash fast, because most clips will not have rounded
+  // rects and including them will slow down the hash in the common case. Note
+  // that the ::Equal check still checks the rounded rect contents, so in case
+  // of hash collisions the clip chains can still be distinguished using that.
+  uint32_t hash = HashGeneric(aClip->mASR, aClip->mClip.GetRoundedRectCount());
+  if (aClip->mClip.HasClip()) {
+    const nsRect& rect = aClip->mClip.GetClipRect();
+    // empty rects are considered equal in DisplayItemClipChain::Equal, even
+    // though they may have different x and y coordinates. So make sure they
+    // hash to the same thing in those cases too.
+    if (!rect.IsEmpty()) {
+      hash = AddToHash(hash, rect.x, rect.y, rect.width, rect.height);
+    }
+  }
+
+  return hash;
+}
+
+/* static */
+nsCString DisplayItemClipChain::ToString(
+    const DisplayItemClipChain* aClipChain) {
+  nsAutoCString str;
+  for (auto* sc = aClipChain; sc; sc = sc->mParent) {
+    if (sc->mASR) {
+      str.AppendPrintf("0x%p <%s> [0x%p]", sc, sc->mClip.ToString().get(),
+                       sc->mASR->mScrollableFrame);
+    } else {
+      str.AppendPrintf("0x%p <%s> [root asr]", sc, sc->mClip.ToString().get());
+    }
+    if (sc->mParent) {
+      str.AppendLiteral(", ");
+    }
+  }
+  return std::move(str);
+}
+
+bool DisplayItemClipChain::HasRoundedCorners() const {
+  return mClip.GetRoundedRectCount() > 0 ||
+         (mParent && mParent->HasRoundedCorners());
+}
+
+}  // namespace mozilla
diff --git a/layout/painting/DisplayItemClipChain.h b/layout/painting/DisplayItemClipChain.h
new file mode 100644
index 0000000000..32779e09c0
--- /dev/null
+++ b/layout/painting/DisplayItemClipChain.h
@@ -0,0 +1,117 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef DISPLAYITEMCLIPCHAIN_H_
+#define DISPLAYITEMCLIPCHAIN_H_
+
+#include "mozilla/Assertions.h"
+#include "DisplayItemClip.h"
+#include "nsString.h"
+
+class nsIScrollableFrame;
+
+namespace mozilla {
+
+struct ActiveScrolledRoot;
+
+/**
+ * A DisplayItemClipChain is a linked list of DisplayItemClips where each clip
+ * is associated with an active scrolled root that describes what the clip
+ * moves with.
+ * We use a chain instead of just one intersected clip due to async scrolling:
+ * A clip that moves along with a display item can be fused to the item's
+ * contents when drawing the layer contents, but all other clips in the chain
+ * need to be kept separate so that they can be applied at composition time,
+ * after any async scroll offsets have been applied.
+ * The clip chain is created during display list construction by the builder's
+ * DisplayListClipState.
+ * The clip chain order is determined by the active scrolled root order.
+ * For every DisplayItemClipChain object |clipChain|, the following holds:
+ * !clipChain->mParent ||
+ * ActiveScrolledRoot::IsAncestor(clipChain->mParent->mASR, clipChain->mASR).
+ * The clip chain can skip over active scrolled roots. That just means that
+ * there is no clip that moves with the skipped ASR in this chain.
+ */
+struct DisplayItemClipChain {
+  /**
+   * Get the display item clip in this chain that moves with aASR, or nullptr
+   * if no such clip exists. aClipChain can be null.
+   */
+  static const DisplayItemClip* ClipForASR(
+      const DisplayItemClipChain* aClipChain, const ActiveScrolledRoot* aASR);
+
+  static bool Equal(const DisplayItemClipChain* aClip1,
+                    const DisplayItemClipChain* aClip2);
+  /**
+   * Hash function that returns the same value for any two clips A and B
+   * where Equal(A, B) is true.
+   */
+  static uint32_t Hash(const DisplayItemClipChain* aClip);
+
+  static nsCString ToString(const DisplayItemClipChain* aClipChain);
+
+  bool HasRoundedCorners() const;
+
+  void AddRef() { mRefCount++; }
+  void Release() {
+    MOZ_ASSERT(mRefCount > 0);
+    mRefCount--;
+  }
+
+  DisplayItemClipChain(const DisplayItemClip& aClip,
+                       const ActiveScrolledRoot* aASR,
+                       const DisplayItemClipChain* aParent,
+                       DisplayItemClipChain* aNextClipChainToDestroy)
+      : mClip(aClip),
+        mASR(aASR),
+        mParent(aParent),
+        mNextClipChainToDestroy(aNextClipChainToDestroy)
+#ifdef DEBUG
+        ,
+        mOnStack(true)
+#endif
+  {
+  }
+
+  DisplayItemClipChain()
+      : mASR(nullptr),
+        mNextClipChainToDestroy(nullptr)
+#ifdef DEBUG
+        ,
+        mOnStack(true)
+#endif
+  {
+  }
+
+  DisplayItemClip mClip;
+  const ActiveScrolledRoot* mASR;
+  RefPtr<const DisplayItemClipChain> mParent;
+  uint32_t mRefCount = 0;
+  DisplayItemClipChain* mNextClipChainToDestroy;
+#ifdef DEBUG
+  bool mOnStack;
+#endif
+};
+
+struct DisplayItemClipChainHasher {
+  typedef const DisplayItemClipChain* Key;
+
+  std::size_t operator()(const Key& aKey) const {
+    return DisplayItemClipChain::Hash(aKey);
+  }
+};
+
+struct DisplayItemClipChainEqualer {
+  typedef const DisplayItemClipChain* Key;
+
+  bool operator()(const Key& lhs, const Key& rhs) const {
+    return DisplayItemClipChain::Equal(lhs, rhs);
+  }
+};
+
+}  // namespace mozilla
+
+#endif /* DISPLAYITEMCLIPCHAIN_H_ */
diff --git a/layout/painting/DisplayListClipState.cpp b/layout/painting/DisplayListClipState.cpp
new file mode 100644
index 0000000000..8a87e2906b
--- /dev/null
+++ b/layout/painting/DisplayListClipState.cpp
@@ -0,0 +1,149 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "DisplayListClipState.h"
+
+#include "nsDisplayList.h"
+
+namespace mozilla {
+
+const DisplayItemClipChain* DisplayListClipState::GetCurrentCombinedClipChain(
+    nsDisplayListBuilder* aBuilder) {
+  if (mCurrentCombinedClipChainIsValid) {
+    return mCurrentCombinedClipChain;
+  }
+  if (!mClipChainContentDescendants && !mClipChainContainingBlockDescendants) {
+    mCurrentCombinedClipChain = nullptr;
+    mCurrentCombinedClipChainIsValid = true;
+    return nullptr;
+  }
+
+  mCurrentCombinedClipChain = aBuilder->CreateClipChainIntersection(
+      mCurrentCombinedClipChain, mClipChainContentDescendants,
+      mClipChainContainingBlockDescendants);
+  mCurrentCombinedClipChainIsValid = true;
+  return mCurrentCombinedClipChain;
+}
+
+static void ApplyClip(nsDisplayListBuilder* aBuilder,
+                      const DisplayItemClipChain*& aClipToModify,
+                      const ActiveScrolledRoot* aASR,
+                      DisplayItemClipChain& aClipChainOnStack) {
+  aClipChainOnStack.mASR = aASR;
+  if (aClipToModify && aClipToModify->mASR == aASR) {
+    // Intersect with aClipToModify and replace the clip chain item.
+    aClipChainOnStack.mClip.IntersectWith(aClipToModify->mClip);
+    aClipChainOnStack.mParent = aClipToModify->mParent;
+    aClipToModify = &aClipChainOnStack;
+  } else if (!aClipToModify ||
+             ActiveScrolledRoot::IsAncestor(aClipToModify->mASR, aASR)) {
+    // Add a new clip chain item at the bottom.
+    aClipChainOnStack.mParent = aClipToModify;
+    aClipToModify = &aClipChainOnStack;
+  } else {
+    // We need to insert / intersect a DisplayItemClipChain in the middle of the
+    // aClipToModify chain. This is a very rare case.
+    // Find the common ancestor and have the builder create the
+    // DisplayItemClipChain intersection. This will create new
+    // DisplayItemClipChain objects for all descendants of ancestorSC and we
+    // will not hold on to a pointer to aClipChainOnStack.
+    const DisplayItemClipChain* ancestorSC = aClipToModify;
+    while (ancestorSC &&
+           ActiveScrolledRoot::IsAncestor(aASR, ancestorSC->mASR)) {
+      ancestorSC = ancestorSC->mParent;
+    }
+    ancestorSC = aBuilder->CopyWholeChain(ancestorSC);
+    aClipChainOnStack.mParent = nullptr;
+    aClipToModify = aBuilder->CreateClipChainIntersection(
+        ancestorSC, aClipToModify, &aClipChainOnStack);
+  }
+}
+
+void DisplayListClipState::ClipContainingBlockDescendants(
+    nsDisplayListBuilder* aBuilder, const nsRect& aRect, const nscoord* aRadii,
+    DisplayItemClipChain& aClipChainOnStack) {
+  if (aRadii) {
+    aClipChainOnStack.mClip.SetTo(aRect, aRadii);
+  } else {
+    aClipChainOnStack.mClip.SetTo(aRect);
+  }
+  const ActiveScrolledRoot* asr = aBuilder->CurrentActiveScrolledRoot();
+  ApplyClip(aBuilder, mClipChainContainingBlockDescendants, asr,
+            aClipChainOnStack);
+  InvalidateCurrentCombinedClipChain(asr);
+}
+
+void DisplayListClipState::ClipContentDescendants(
+    nsDisplayListBuilder* aBuilder, const nsRect& aRect, const nscoord* aRadii,
+    DisplayItemClipChain& aClipChainOnStack) {
+  if (aRadii) {
+    aClipChainOnStack.mClip.SetTo(aRect, aRadii);
+  } else {
+    aClipChainOnStack.mClip.SetTo(aRect);
+  }
+  const ActiveScrolledRoot* asr = aBuilder->CurrentActiveScrolledRoot();
+  ApplyClip(aBuilder, mClipChainContentDescendants, asr, aClipChainOnStack);
+  InvalidateCurrentCombinedClipChain(asr);
+}
+
+void DisplayListClipState::ClipContentDescendants(
+    nsDisplayListBuilder* aBuilder, const nsRect& aRect,
+    const nsRect& aRoundedRect, const nscoord* aRadii,
+    DisplayItemClipChain& aClipChainOnStack) {
+  if (aRadii) {
+    aClipChainOnStack.mClip.SetTo(aRect, aRoundedRect, aRadii);
+  } else {
+    nsRect intersect = aRect.Intersect(aRoundedRect);
+    aClipChainOnStack.mClip.SetTo(intersect);
+  }
+  const ActiveScrolledRoot* asr = aBuilder->CurrentActiveScrolledRoot();
+  ApplyClip(aBuilder, mClipChainContentDescendants, asr, aClipChainOnStack);
+  InvalidateCurrentCombinedClipChain(asr);
+}
+
+void DisplayListClipState::InvalidateCurrentCombinedClipChain(
+    const ActiveScrolledRoot* aInvalidateUpTo) {
+  mClippedToDisplayPort = false;
+  mCurrentCombinedClipChainIsValid = false;
+  while (mCurrentCombinedClipChain &&
+         ActiveScrolledRoot::IsAncestor(aInvalidateUpTo,
+                                        mCurrentCombinedClipChain->mASR)) {
+    mCurrentCombinedClipChain = mCurrentCombinedClipChain->mParent;
+  }
+}
+
+void DisplayListClipState::ClipContainingBlockDescendantsToContentBox(
+    nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+    DisplayItemClipChain& aClipChainOnStack, uint32_t aFlags) {
+  nscoord radii[8];
+  bool hasBorderRadius = aFrame->GetContentBoxBorderRadii(radii);
+  if (!hasBorderRadius &&
+      (aFlags & ASSUME_DRAWING_RESTRICTED_TO_CONTENT_RECT)) {
+    return;
+  }
+
+  nsRect clipRect = aFrame->GetContentRectRelativeToSelf() +
+                    aBuilder->ToReferenceFrame(aFrame);
+  // If we have a border-radius, we have to clip our content to that
+  // radius.
+  ClipContainingBlockDescendants(
+      aBuilder, clipRect, hasBorderRadius ? radii : nullptr, aClipChainOnStack);
+}
+
+DisplayListClipState::AutoSaveRestore::AutoSaveRestore(
+    nsDisplayListBuilder* aBuilder)
+    : mBuilder(aBuilder),
+      mState(aBuilder->ClipState()),
+      mSavedState(aBuilder->ClipState())
+#ifdef DEBUG
+      ,
+      mClipUsed(false),
+      mRestored(false)
+#endif
+{
+}
+
+}  // namespace mozilla
diff --git a/layout/painting/DisplayListClipState.h b/layout/painting/DisplayListClipState.h
new file mode 100644
index 0000000000..0f1df2ca58
--- /dev/null
+++ b/layout/painting/DisplayListClipState.h
@@ -0,0 +1,301 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef DISPLAYLISTCLIPSTATE_H_
+#define DISPLAYLISTCLIPSTATE_H_
+
+#include "DisplayItemClip.h"
+#include "DisplayItemClipChain.h"
+
+#include "mozilla/DebugOnly.h"
+
+class nsIFrame;
+class nsIScrollableFrame;
+
+namespace mozilla {
+
+class nsDisplayListBuilder;
+
+/**
+ * All clip coordinates are in appunits relative to the reference frame
+ * for the display item we're building.
+ */
+class DisplayListClipState {
+ public:
+  DisplayListClipState()
+      : mClipChainContentDescendants(nullptr),
+        mClipChainContainingBlockDescendants(nullptr),
+        mCurrentCombinedClipChain(nullptr),
+        mCurrentCombinedClipChainIsValid(false),
+        mClippedToDisplayPort(false) {}
+
+  void SetClippedToDisplayPort() { mClippedToDisplayPort = true; }
+  bool IsClippedToDisplayPort() const { return mClippedToDisplayPort; }
+
+  /**
+   * Returns intersection of mClipChainContainingBlockDescendants and
+   * mClipChainContentDescendants, allocated on aBuilder's arena.
+   */
+  const DisplayItemClipChain* GetCurrentCombinedClipChain(
+      nsDisplayListBuilder* aBuilder);
+
+  const DisplayItemClipChain* GetClipChainForContainingBlockDescendants()
+      const {
+    return mClipChainContainingBlockDescendants;
+  }
+  const DisplayItemClipChain* GetClipChainForContentDescendants() const {
+    return mClipChainContentDescendants;
+  }
+
+  const ActiveScrolledRoot* GetContentClipASR() const {
+    return mClipChainContentDescendants ? mClipChainContentDescendants->mASR
+                                        : nullptr;
+  }
+
+  class AutoSaveRestore;
+
+  class AutoClipContainingBlockDescendantsToContentBox;
+
+  class AutoClipMultiple;
+
+  enum { ASSUME_DRAWING_RESTRICTED_TO_CONTENT_RECT = 0x01 };
+
+ private:
+  void Clear() {
+    mClipChainContentDescendants = nullptr;
+    mClipChainContainingBlockDescendants = nullptr;
+    mCurrentCombinedClipChain = nullptr;
+    mCurrentCombinedClipChainIsValid = false;
+    mClippedToDisplayPort = false;
+  }
+
+  void SetClipChainForContainingBlockDescendants(
+      const DisplayItemClipChain* aClipChain) {
+    mClipChainContainingBlockDescendants = aClipChain;
+    InvalidateCurrentCombinedClipChain(aClipChain ? aClipChain->mASR : nullptr);
+  }
+
+  /**
+   * Intersects the given clip rect (with optional aRadii) with the current
+   * mClipContainingBlockDescendants and sets mClipContainingBlockDescendants to
+   * the result, stored in aClipOnStack.
+   */
+  void ClipContainingBlockDescendants(nsDisplayListBuilder* aBuilder,
+                                      const nsRect& aRect,
+                                      const nscoord* aRadii,
+                                      DisplayItemClipChain& aClipChainOnStack);
+
+  void ClipContentDescendants(nsDisplayListBuilder* aBuilder,
+                              const nsRect& aRect, const nscoord* aRadii,
+                              DisplayItemClipChain& aClipChainOnStack);
+  void ClipContentDescendants(nsDisplayListBuilder* aBuilder,
+                              const nsRect& aRect, const nsRect& aRoundedRect,
+                              const nscoord* aRadii,
+                              DisplayItemClipChain& aClipChainOnStack);
+
+  void InvalidateCurrentCombinedClipChain(
+      const ActiveScrolledRoot* aInvalidateUpTo);
+
+  /**
+   * Clips containing-block descendants to the frame's content-box,
+   * taking border-radius into account.
+   * If aFlags contains ASSUME_DRAWING_RESTRICTED_TO_CONTENT_RECT then
+   * we assume display items will not draw outside the content rect, so
+   * clipping is only required if there is a border-radius. This is an
+   * optimization to reduce the amount of clipping required.
+   */
+  void ClipContainingBlockDescendantsToContentBox(
+      nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+      DisplayItemClipChain& aClipChainOnStack, uint32_t aFlags);
+
+  /**
+   * All content descendants (i.e. following placeholder frames to their
+   * out-of-flows if necessary) should be clipped by
+   * mClipChainContentDescendants. Null if no clipping applies.
+   */
+  const DisplayItemClipChain* mClipChainContentDescendants;
+  /**
+   * All containing-block descendants (i.e. frame descendants), including
+   * display items for the current frame, should be clipped by
+   * mClipChainContainingBlockDescendants.
+   * Null if no clipping applies.
+   */
+  const DisplayItemClipChain* mClipChainContainingBlockDescendants;
+  /**
+   * The intersection of mClipChainContentDescendants and
+   * mClipChainContainingBlockDescendants.
+   * Allocated in the nsDisplayListBuilder arena. Null if none has been
+   * allocated or both mClipChainContentDescendants and
+   * mClipChainContainingBlockDescendants are null.
+   */
+  const DisplayItemClipChain* mCurrentCombinedClipChain;
+  bool mCurrentCombinedClipChainIsValid;
+  /**
+   * A flag that is used by sticky positioned items to know if the clip applied
+   * to them is just the displayport clip or if there is additional clipping.
+   */
+  bool mClippedToDisplayPort;
+};
+
+/**
+ * A class to automatically save and restore the current clip state. Also
+ * offers methods for modifying the clip state. Only one modification is allowed
+ * to be in scope at a time using one of these objects; multiple modifications
+ * require nested objects. The interface is written this way to prevent
+ * dangling pointers to DisplayItemClips.
+ */
+class DisplayListClipState::AutoSaveRestore {
+ public:
+  explicit AutoSaveRestore(nsDisplayListBuilder* aBuilder);
+  void Restore() {
+    mState = mSavedState;
+#ifdef DEBUG
+    mRestored = true;
+#endif
+  }
+  ~AutoSaveRestore() { Restore(); }
+
+  void Clear() {
+    NS_ASSERTION(!mRestored, "Already restored!");
+    mState.Clear();
+#ifdef DEBUG
+    mClipUsed = false;
+#endif
+  }
+
+  void SetClipChainForContainingBlockDescendants(
+      const DisplayItemClipChain* aClipChain) {
+    mState.SetClipChainForContainingBlockDescendants(aClipChain);
+  }
+
+  /**
+   * Intersects the given clip rect (with optional aRadii) with the current
+   * mClipContainingBlockDescendants and sets mClipContainingBlockDescendants to
+   * the result, stored in aClipOnStack.
+   */
+  void ClipContainingBlockDescendants(const nsRect& aRect,
+                                      const nscoord* aRadii = nullptr) {
+    NS_ASSERTION(!mRestored, "Already restored!");
+    NS_ASSERTION(!mClipUsed, "mClip already used");
+#ifdef DEBUG
+    mClipUsed = true;
+#endif
+    mState.ClipContainingBlockDescendants(mBuilder, aRect, aRadii, mClipChain);
+  }
+
+  void ClipContentDescendants(const nsRect& aRect,
+                              const nscoord* aRadii = nullptr) {
+    NS_ASSERTION(!mRestored, "Already restored!");
+    NS_ASSERTION(!mClipUsed, "mClip already used");
+#ifdef DEBUG
+    mClipUsed = true;
+#endif
+    mState.ClipContentDescendants(mBuilder, aRect, aRadii, mClipChain);
+  }
+
+  void ClipContentDescendants(const nsRect& aRect, const nsRect& aRoundedRect,
+                              const nscoord* aRadii = nullptr) {
+    NS_ASSERTION(!mRestored, "Already restored!");
+    NS_ASSERTION(!mClipUsed, "mClip already used");
+#ifdef DEBUG
+    mClipUsed = true;
+#endif
+    mState.ClipContentDescendants(mBuilder, aRect, aRoundedRect, aRadii,
+                                  mClipChain);
+  }
+
+  /**
+   * Clips containing-block descendants to the frame's content-box,
+   * taking border-radius into account.
+   * If aFlags contains ASSUME_DRAWING_RESTRICTED_TO_CONTENT_RECT then
+   * we assume display items will not draw outside the content rect, so
+   * clipping is only required if there is a border-radius. This is an
+   * optimization to reduce the amount of clipping required.
+   */
+  void ClipContainingBlockDescendantsToContentBox(
+      nsDisplayListBuilder* aBuilder, nsIFrame* aFrame, uint32_t aFlags = 0) {
+    NS_ASSERTION(!mRestored, "Already restored!");
+    NS_ASSERTION(!mClipUsed, "mClip already used");
+#ifdef DEBUG
+    mClipUsed = true;
+#endif
+    mState.ClipContainingBlockDescendantsToContentBox(aBuilder, aFrame,
+                                                      mClipChain, aFlags);
+  }
+
+  void SetClippedToDisplayPort() { mState.SetClippedToDisplayPort(); }
+  bool IsClippedToDisplayPort() const {
+    return mState.IsClippedToDisplayPort();
+  }
+
+ protected:
+  nsDisplayListBuilder* mBuilder;
+  DisplayListClipState& mState;
+  DisplayListClipState mSavedState;
+  DisplayItemClipChain mClipChain;
+#ifdef DEBUG
+  bool mClipUsed;
+  bool mRestored;
+#endif
+};
+
+class DisplayListClipState::AutoClipContainingBlockDescendantsToContentBox
+    : public AutoSaveRestore {
+ public:
+  AutoClipContainingBlockDescendantsToContentBox(nsDisplayListBuilder* aBuilder,
+                                                 nsIFrame* aFrame,
+                                                 uint32_t aFlags = 0)
+      : AutoSaveRestore(aBuilder) {
+#ifdef DEBUG
+    mClipUsed = true;
+#endif
+    mState.ClipContainingBlockDescendantsToContentBox(aBuilder, aFrame,
+                                                      mClipChain, aFlags);
+  }
+};
+
+/**
+ * Do not use this outside of nsIFrame::BuildDisplayListForChild, use
+ * multiple AutoSaveRestores instead. We provide this class just to ensure
+ * BuildDisplayListForChild is as efficient as possible.
+ */
+class DisplayListClipState::AutoClipMultiple : public AutoSaveRestore {
+ public:
+  explicit AutoClipMultiple(nsDisplayListBuilder* aBuilder)
+      : AutoSaveRestore(aBuilder)
+#ifdef DEBUG
+        ,
+        mExtraClipUsed(false)
+#endif
+  {
+  }
+
+  /**
+   * Intersects the given clip rect (with optional aRadii) with the current
+   * mClipContainingBlockDescendants and sets mClipContainingBlockDescendants to
+   * the result, stored in aClipOnStack.
+   */
+  void ClipContainingBlockDescendantsExtra(const nsRect& aRect,
+                                           const nscoord* aRadii) {
+    NS_ASSERTION(!mRestored, "Already restored!");
+    NS_ASSERTION(!mExtraClipUsed, "mExtraClip already used");
+#ifdef DEBUG
+    mExtraClipUsed = true;
+#endif
+    mState.ClipContainingBlockDescendants(mBuilder, aRect, aRadii,
+                                          mExtraClipChain);
+  }
+
+ protected:
+  DisplayItemClipChain mExtraClipChain;
+#ifdef DEBUG
+  bool mExtraClipUsed;
+#endif
+};
+
+}  // namespace mozilla
+
+#endif /* DISPLAYLISTCLIPSTATE_H_ */
diff --git a/layout/painting/DottedCornerFinder.cpp b/layout/painting/DottedCornerFinder.cpp
new file mode 100644
index 0000000000..2e8408d80b
--- /dev/null
+++ b/layout/painting/DottedCornerFinder.cpp
@@ -0,0 +1,539 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "DottedCornerFinder.h"
+
+#include <utility>
+
+#include "BorderCache.h"
+#include "BorderConsts.h"
+#include "nsTHashMap.h"
+
+namespace mozilla {
+
+using namespace gfx;
+
+static inline Float Square(Float x) { return x * x; }
+
+static Point PointRotateCCW90(const Point& aP) { return Point(aP.y, -aP.x); }
+
+struct BestOverlap {
+  Float overlap;
+  size_t count;
+
+  BestOverlap() : overlap(0.0f), count(0) {}
+
+  BestOverlap(Float aOverlap, size_t aCount)
+      : overlap(aOverlap), count(aCount) {}
+};
+
+static const size_t DottedCornerCacheSize = 256;
+nsTHashMap<FourFloatsHashKey, BestOverlap> DottedCornerCache;
+
+DottedCornerFinder::DottedCornerFinder(const Bezier& aOuterBezier,
+                                       const Bezier& aInnerBezier,
+                                       Corner aCorner, Float aBorderRadiusX,
+                                       Float aBorderRadiusY, const Point& aC0,
+                                       Float aR0, const Point& aCn, Float aRn,
+                                       const Size& aCornerDim)
+    : mOuterBezier(aOuterBezier),
+      mInnerBezier(aInnerBezier),
+      mCorner(aCorner),
+      mNormalSign((aCorner == C_TL || aCorner == C_BR) ? -1.0f : 1.0f),
+      mC0(aC0),
+      mCn(aCn),
+      mR0(aR0),
+      mRn(aRn),
+      mMaxR(std::max(aR0, aRn)),
+      mCenterCurveOrigin(mC0.x, mCn.y),
+      mCenterCurveR(0.0),
+      mInnerCurveOrigin(mInnerBezier.mPoints[0].x, mInnerBezier.mPoints[3].y),
+      mBestOverlap(0.0f),
+      mHasZeroBorderWidth(false),
+      mHasMore(true),
+      mMaxCount(aCornerDim.width + aCornerDim.height),
+      mType(OTHER),
+      mI(0),
+      mCount(0) {
+  NS_ASSERTION(mR0 > 0.0f || mRn > 0.0f,
+               "At least one side should have non-zero radius.");
+
+  mInnerWidth = fabs(mInnerBezier.mPoints[0].x - mInnerBezier.mPoints[3].x);
+  mInnerHeight = fabs(mInnerBezier.mPoints[0].y - mInnerBezier.mPoints[3].y);
+
+  DetermineType(aBorderRadiusX, aBorderRadiusY);
+
+  Reset();
+}
+
+static bool IsSingleCurve(Float aMinR, Float aMaxR, Float aMinBorderRadius,
+                          Float aMaxBorderRadius) {
+  return aMinR > 0.0f && aMinBorderRadius > aMaxR * 4.0f &&
+         aMinBorderRadius / aMaxBorderRadius > 0.5f;
+}
+
+void DottedCornerFinder::DetermineType(Float aBorderRadiusX,
+                                       Float aBorderRadiusY) {
+  // Calculate parameters for the center curve before swap.
+  Float centerCurveWidth = fabs(mC0.x - mCn.x);
+  Float centerCurveHeight = fabs(mC0.y - mCn.y);
+  Point cornerPoint(mCn.x, mC0.y);
+
+  bool swapped = false;
+  if (mR0 < mRn) {
+    // Always draw from wider side to thinner side.
+    std::swap(mC0, mCn);
+    std::swap(mR0, mRn);
+    std::swap(mInnerBezier.mPoints[0], mInnerBezier.mPoints[3]);
+    std::swap(mInnerBezier.mPoints[1], mInnerBezier.mPoints[2]);
+    std::swap(mOuterBezier.mPoints[0], mOuterBezier.mPoints[3]);
+    std::swap(mOuterBezier.mPoints[1], mOuterBezier.mPoints[2]);
+    mNormalSign = -mNormalSign;
+    swapped = true;
+  }
+
+  // See the comment at mType declaration for each condition.
+
+  Float minR = std::min(mR0, mRn);
+  Float minBorderRadius = std::min(aBorderRadiusX, aBorderRadiusY);
+  Float maxBorderRadius = std::max(aBorderRadiusX, aBorderRadiusY);
+  if (IsSingleCurve(minR, mMaxR, minBorderRadius, maxBorderRadius)) {
+    if (mR0 == mRn) {
+      Float borderLength;
+      if (minBorderRadius == maxBorderRadius) {
+        mType = PERFECT;
+        borderLength = M_PI * centerCurveHeight / 2.0f;
+
+        mCenterCurveR = centerCurveWidth;
+      } else {
+        mType = SINGLE_CURVE_AND_RADIUS;
+        borderLength =
+            GetQuarterEllipticArcLength(centerCurveWidth, centerCurveHeight);
+      }
+
+      Float diameter = mR0 * 2.0f;
+      size_t count = round(borderLength / diameter);
+      if (count % 2) {
+        count++;
+      }
+      mCount = count / 2 - 1;
+      if (mCount > 0) {
+        mBestOverlap = 1.0f - borderLength / (diameter * count);
+      }
+    } else {
+      mType = SINGLE_CURVE;
+    }
+  }
+
+  if (mType == SINGLE_CURVE_AND_RADIUS || mType == SINGLE_CURVE) {
+    Size cornerSize(centerCurveWidth, centerCurveHeight);
+    GetBezierPointsForCorner(&mCenterBezier, mCorner, cornerPoint, cornerSize);
+    if (swapped) {
+      std::swap(mCenterBezier.mPoints[0], mCenterBezier.mPoints[3]);
+      std::swap(mCenterBezier.mPoints[1], mCenterBezier.mPoints[2]);
+    }
+  }
+
+  if (minR == 0.0f) {
+    mHasZeroBorderWidth = true;
+  }
+
+  if ((mType == SINGLE_CURVE || mType == OTHER) && !mHasZeroBorderWidth) {
+    FindBestOverlap(minR, minBorderRadius, maxBorderRadius);
+  }
+}
+
+bool DottedCornerFinder::HasMore(void) const {
+  if (mHasZeroBorderWidth) {
+    return mI < mMaxCount && mHasMore;
+  }
+
+  return mI < mCount;
+}
+
+DottedCornerFinder::Result DottedCornerFinder::Next(void) {
+  mI++;
+
+  if (mType == PERFECT) {
+    Float phi = mI * 4.0f * mR0 * (1 - mBestOverlap) / mCenterCurveR;
+    if (mCorner == C_TL) {
+      phi = -M_PI / 2.0f - phi;
+    } else if (mCorner == C_TR) {
+      phi = -M_PI / 2.0f + phi;
+    } else if (mCorner == C_BR) {
+      phi = M_PI / 2.0f - phi;
+    } else {
+      phi = M_PI / 2.0f + phi;
+    }
+
+    Point C(mCenterCurveOrigin.x + mCenterCurveR * cos(phi),
+            mCenterCurveOrigin.y + mCenterCurveR * sin(phi));
+    return DottedCornerFinder::Result(C, mR0);
+  }
+
+  // Find unfilled and filled circles.
+  (void)FindNext(mBestOverlap);
+  if (mHasMore) {
+    (void)FindNext(mBestOverlap);
+  }
+
+  return Result(mLastC, mLastR);
+}
+
+void DottedCornerFinder::Reset(void) {
+  mLastC = mC0;
+  mLastR = mR0;
+  mLastT = 0.0f;
+  mHasMore = true;
+}
+
+void DottedCornerFinder::FindPointAndRadius(Point& C, Float& r,
+                                            const Point& innerTangent,
+                                            const Point& normal, Float t) {
+  // Find radius for the given tangent point on the inner curve such that the
+  // circle is also tangent to the outer curve.
+
+  NS_ASSERTION(mType == OTHER, "Wrong mType");
+
+  Float lower = 0.0f;
+  Float upper = mMaxR;
+  const Float DIST_MARGIN = 0.1f;
+  for (size_t i = 0; i < MAX_LOOP; i++) {
+    r = (upper + lower) / 2.0f;
+    C = innerTangent + normal * r;
+
+    Point Near = FindBezierNearestPoint(mOuterBezier, C, t);
+    Float distSquare = (C - Near).LengthSquare();
+
+    if (distSquare > Square(r + DIST_MARGIN)) {
+      lower = r;
+    } else if (distSquare < Square(r - DIST_MARGIN)) {
+      upper = r;
+    } else {
+      break;
+    }
+  }
+}
+
+Float DottedCornerFinder::FindNext(Float overlap) {
+  Float lower = mLastT;
+  Float upper = 1.0f;
+  Float t;
+
+  Point C = mLastC;
+  Float r = 0.0f;
+
+  Float factor = (1.0f - overlap);
+
+  Float circlesDist = 0.0f;
+  Float expectedDist = 0.0f;
+
+  const Float DIST_MARGIN = 0.1f;
+  if (mType == SINGLE_CURVE_AND_RADIUS) {
+    r = mR0;
+
+    expectedDist = (r + mLastR) * factor;
+
+    // Find C_i on the center curve.
+    for (size_t i = 0; i < MAX_LOOP; i++) {
+      t = (upper + lower) / 2.0f;
+      C = GetBezierPoint(mCenterBezier, t);
+
+      // Check overlap along arc.
+      circlesDist = GetBezierLength(mCenterBezier, mLastT, t);
+      if (circlesDist < expectedDist - DIST_MARGIN) {
+        lower = t;
+      } else if (circlesDist > expectedDist + DIST_MARGIN) {
+        upper = t;
+      } else {
+        break;
+      }
+    }
+  } else if (mType == SINGLE_CURVE) {
+    // Find C_i on the center curve, and calculate r_i.
+    for (size_t i = 0; i < MAX_LOOP; i++) {
+      t = (upper + lower) / 2.0f;
+      C = GetBezierPoint(mCenterBezier, t);
+
+      Point Diff = GetBezierDifferential(mCenterBezier, t);
+      Float DiffLength = Diff.Length();
+      if (DiffLength == 0.0f) {
+        // Basically this shouldn't happen.
+        // If differential is 0, we cannot calculate tangent circle,
+        // skip this point.
+        t = (t + upper) / 2.0f;
+        continue;
+      }
+
+      Point normal = PointRotateCCW90(Diff / DiffLength) * (-mNormalSign);
+      r = CalculateDistanceToEllipticArc(C, normal, mInnerCurveOrigin,
+                                         mInnerWidth, mInnerHeight);
+
+      // Check overlap along arc.
+      circlesDist = GetBezierLength(mCenterBezier, mLastT, t);
+      expectedDist = (r + mLastR) * factor;
+      if (circlesDist < expectedDist - DIST_MARGIN) {
+        lower = t;
+      } else if (circlesDist > expectedDist + DIST_MARGIN) {
+        upper = t;
+      } else {
+        break;
+      }
+    }
+  } else {
+    Float distSquareMax = Square(mMaxR * 3.0f);
+    Float circlesDistSquare = 0.0f;
+
+    // Find C_i and r_i.
+    for (size_t i = 0; i < MAX_LOOP; i++) {
+      t = (upper + lower) / 2.0f;
+      Point innerTangent = GetBezierPoint(mInnerBezier, t);
+      if ((innerTangent - mLastC).LengthSquare() > distSquareMax) {
+        // It's clear that this tangent point is too far, skip it.
+        upper = t;
+        continue;
+      }
+
+      Point Diff = GetBezierDifferential(mInnerBezier, t);
+      Float DiffLength = Diff.Length();
+      if (DiffLength == 0.0f) {
+        // Basically this shouldn't happen.
+        // If differential is 0, we cannot calculate tangent circle,
+        // skip this point.
+        t = (t + upper) / 2.0f;
+        continue;
+      }
+
+      Point normal = PointRotateCCW90(Diff / DiffLength) * mNormalSign;
+      FindPointAndRadius(C, r, innerTangent, normal, t);
+
+      // Check overlap with direct distance.
+      circlesDistSquare = (C - mLastC).LengthSquare();
+      expectedDist = (r + mLastR) * factor;
+      if (circlesDistSquare < Square(expectedDist - DIST_MARGIN)) {
+        lower = t;
+      } else if (circlesDistSquare > Square(expectedDist + DIST_MARGIN)) {
+        upper = t;
+      } else {
+        break;
+      }
+    }
+
+    circlesDist = sqrt(circlesDistSquare);
+  }
+
+  if (mHasZeroBorderWidth) {
+    // When calculating circle around r=0, it may result in wrong radius that
+    // is bigger than previous circle.  Detect it and stop calculating.
+    const Float R_MARGIN = 0.1f;
+    if (mLastR < R_MARGIN && r > mLastR) {
+      mHasMore = false;
+      mLastR = 0.0f;
+      return 0.0f;
+    }
+  }
+
+  mLastT = t;
+  mLastC = C;
+  mLastR = r;
+
+  if (mHasZeroBorderWidth) {
+    const Float T_MARGIN = 0.001f;
+    if (mLastT >= 1.0f - T_MARGIN ||
+        (mLastC - mCn).LengthSquare() < Square(mLastR)) {
+      mHasMore = false;
+    }
+  }
+
+  if (expectedDist == 0.0f) {
+    return 0.0f;
+  }
+
+  return 1.0f - circlesDist * factor / expectedDist;
+}
+
+void DottedCornerFinder::FindBestOverlap(Float aMinR, Float aMinBorderRadius,
+                                         Float aMaxBorderRadius) {
+  // If overlap is not calculateable, find it with binary search,
+  // such that there exists i that C_i == C_n with the given overlap.
+
+  FourFloats key(aMinR, mMaxR, aMinBorderRadius, aMaxBorderRadius);
+  BestOverlap best;
+  if (DottedCornerCache.Get(key, &best)) {
+    mCount = best.count;
+    mBestOverlap = best.overlap;
+    return;
+  }
+
+  Float lower = 0.0f;
+  Float upper = 0.5f;
+  // Start from lower bound to find the minimum number of circles.
+  Float overlap = 0.0f;
+  mBestOverlap = overlap;
+  size_t targetCount = 0;
+
+  const Float OVERLAP_MARGIN = 0.1f;
+  for (size_t j = 0; j < MAX_LOOP; j++) {
+    Reset();
+
+    size_t count;
+    Float actualOverlap;
+    if (!GetCountAndLastOverlap(overlap, &count, &actualOverlap)) {
+      if (j == 0) {
+        mCount = mMaxCount;
+        break;
+      }
+    }
+
+    if (j == 0) {
+      if (count < 3 || (count == 3 && actualOverlap > 0.5f)) {
+        // |count == 3 && actualOverlap > 0.5f| means there could be
+        // a circle but it is too near from both ends.
+        //
+        // if actualOverlap == 0.0
+        //               1       2       3
+        //   +-------+-------+-------+-------+
+        //   | ##### | ***** | ##### | ##### |
+        //   |#######|*******|#######|#######|
+        //   |###+###|***+***|###+###|###+###|
+        //   |# C_0 #|* C_1 *|# C_2 #|# C_n #|
+        //   | ##### | ***** | ##### | ##### |
+        //   +-------+-------+-------+-------+
+        //                   |
+        //                   V
+        //   +-------+---+-------+---+-------+
+        //   | ##### |   | ##### |   | ##### |
+        //   |#######|   |#######|   |#######|
+        //   |###+###|   |###+###|   |###+###| Find the best overlap to place
+        //   |# C_0 #|   |# C_1 #|   |# C_n #| C_1 at the middle of them
+        //   | ##### |   | ##### |   | ##### |
+        //   +-------+---+-------+---|-------+
+        //
+        // if actualOverlap == 0.5
+        //               1       2     3
+        //   +-------+-------+-------+---+
+        //   | ##### | ***** | ##### |## |
+        //   |#######|*******|##### C_n #|
+        //   |###+###|***+***|###+###+###|
+        //   |# C_0 #|* C_1 *|# C_2 #|###|
+        //   | ##### | ***** | ##### |## |
+        //   +-------+-------+-------+---+
+        //                 |
+        //                 V
+        //   +-------+-+-------+-+-------+
+        //   | ##### | | ##### | | ##### |
+        //   |#######| |#######| |#######|
+        //   |###+###| |###+###| |###+###| Even if we place C_1 at the middle
+        //   |# C_0 #| |# C_1 #| |# C_n #| of them, it's too near from them
+        //   | ##### | | ##### | | ##### |
+        //   +-------+-+-------+-|-------+
+        //                 |
+        //                 V
+        //   +-------+-----------+-------+
+        //   | ##### |           | ##### |
+        //   |#######|           |#######|
+        //   |###+###|           |###+###| Do not draw any circle
+        //   |# C_0 #|           |# C_n #|
+        //   | ##### |           | ##### |
+        //   +-------+-----------+-------+
+        mCount = 0;
+        break;
+      }
+
+      // targetCount should be 2n, as we're searching C_1 to C_n.
+      //
+      //   targetCount = 4
+      //   mCount = 1
+      //               1       2       3       4
+      //   +-------+-------+-------+-------+-------+
+      //   | ##### | ***** | ##### | ***** | ##### |
+      //   |#######|*******|#######|*******|#######|
+      //   |###+###|***+***|###+###|***+***|###+###|
+      //   |# C_0 #|* C_1 *|# C_2 #|* C_3 *|# C_n #|
+      //   | ##### | ***** | ##### | ***** | ##### |
+      //   +-------+-------+-------+-------+-------+
+      //                       1
+      //
+      //   targetCount = 6
+      //   mCount = 2
+      //               1       2       3       4       5       6
+      //   +-------+-------+-------+-------+-------+-------+-------+
+      //   | ##### | ***** | ##### | ***** | ##### | ***** | ##### |
+      //   |#######|*******|#######|*******|#######|*******|#######|
+      //   |###+###|***+***|###+###|***+***|###+###|***+***|###+###|
+      //   |# C_0 #|* C_1 *|# C_2 #|* C_3 *|# C_4 #|* C_5 *|# C_n #|
+      //   | ##### | ***** | ##### | ***** | ##### | ***** | ##### |
+      //   +-------+-------+-------+-------+-------+-------+-------+
+      //                       1               2
+      if (count % 2) {
+        targetCount = count + 1;
+      } else {
+        targetCount = count;
+      }
+
+      mCount = targetCount / 2 - 1;
+    }
+
+    if (count == targetCount) {
+      mBestOverlap = overlap;
+
+      if (fabs(actualOverlap - overlap) < OVERLAP_MARGIN) {
+        break;
+      }
+
+      // We started from upper bound, no need to update range when j == 0.
+      if (j > 0) {
+        if (actualOverlap > overlap) {
+          lower = overlap;
+        } else {
+          upper = overlap;
+        }
+      }
+    } else {
+      // |j == 0 && count != targetCount| means that |targetCount = count + 1|,
+      // and we started from upper bound, no need to update range when j == 0.
+      if (j > 0) {
+        if (count > targetCount) {
+          upper = overlap;
+        } else {
+          lower = overlap;
+        }
+      }
+    }
+
+    overlap = (upper + lower) / 2.0f;
+  }
+
+  if (DottedCornerCache.Count() > DottedCornerCacheSize) {
+    DottedCornerCache.Clear();
+  }
+  DottedCornerCache.InsertOrUpdate(key, BestOverlap(mBestOverlap, mCount));
+}
+
+bool DottedCornerFinder::GetCountAndLastOverlap(Float aOverlap, size_t* aCount,
+                                                Float* aActualOverlap) {
+  // Return the number of circles and the last circles' overlap for the
+  // given overlap.
+
+  Reset();
+
+  const Float T_MARGIN = 0.001f;
+  const Float DIST_MARGIN = 0.1f;
+  const Float DIST_MARGIN_SQUARE = Square(DIST_MARGIN);
+  for (size_t i = 0; i < mMaxCount; i++) {
+    Float actualOverlap = FindNext(aOverlap);
+    if (mLastT >= 1.0f - T_MARGIN ||
+        (mLastC - mCn).LengthSquare() < DIST_MARGIN_SQUARE) {
+      *aCount = i + 1;
+      *aActualOverlap = actualOverlap;
+      return true;
+    }
+  }
+
+  return false;
+}
+
+}  // namespace mozilla
diff --git a/layout/painting/DottedCornerFinder.h b/layout/painting/DottedCornerFinder.h
new file mode 100644
index 0000000000..fd3a9e5d04
--- /dev/null
+++ b/layout/painting/DottedCornerFinder.h
@@ -0,0 +1,432 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_DottedCornerFinder_h_
+#define mozilla_DottedCornerFinder_h_
+
+#include "mozilla/gfx/2D.h"
+#include "mozilla/gfx/BezierUtils.h"
+#include "gfxRect.h"
+
+namespace mozilla {
+
+// Calculate C_i and r_i for each filled/unfilled circles in dotted corner.
+// Returns circle with C_{2j} and r_{2j} where 0 < 2j < n.
+//
+//                            ____-----------+
+//                      __----  *****     ###|
+//                __----      *********  ####|
+//           __---  #####    ***********#####|
+//        _--     #########  *****+*****#####+ C_0
+//      _-       ########### *** C_1****#####|
+//     /         #####+#####  *********  ####|
+//    /       .  ### C_2 ###    *****     ###|
+//   |            #########       ____-------+
+//   |     .        #####____-----
+//  |              __----
+//  |    .       /
+// |           /
+// |  *****   |
+// | ******* |
+// |*********|
+// |****+****|
+// | C_{n-1} |
+// | ******* |
+// |  *****  |
+// |  #####  |
+// | ####### |
+// |#########|
+// +----+----+
+//     C_n
+
+class DottedCornerFinder {
+  typedef mozilla::gfx::Bezier Bezier;
+  typedef mozilla::gfx::Float Float;
+  typedef mozilla::gfx::Point Point;
+  typedef mozilla::gfx::Size Size;
+
+ public:
+  struct Result {
+    // Center point of dot and its radius.
+    Point C;
+    Float r;
+
+    Result(const Point& aC, Float aR) : C(aC), r(aR) { MOZ_ASSERT(aR >= 0); }
+  };
+
+  //                        aBorderRadiusX
+  //                       aCornerDim.width
+  //                     |<----------------->|
+  //                     |                   | v
+  //                   --+-------------___---+--
+  //                   ^ |         __--      | |
+  //                   | |       _-          | | aR0
+  //                   | |     /         aC0 +--
+  //                   | |   /               | ^
+  //                   | |  |                |
+  //  aBorderRadiusY   | | |             __--+
+  // aCornerDim.height | ||            _-
+  //                   | ||           /
+  //                   | |           /
+  //                   | |          |
+  //                   | |          |
+  //                   | |         |
+  //                   | |         |
+  //                   v |    aCn  |
+  //                   --+----+----+
+  //                     |    |
+  //                     |<-->|
+  //                      aRn
+  //
+  // aCornerDim and (aBorderRadiusX, aBorderRadiusY) can be different when
+  // aBorderRadiusX is smaller than aRn*2 or
+  // aBorderRadiusY is smaller than aR0*2.
+  //
+  //                                        aCornerDim.width
+  //                                      |<----------------->|
+  //                                      |                   |
+  //                                      | aBorderRadiusX    |
+  //                                      |<--------->|       |
+  //                                      |           |       |
+  //                   -------------------+-------__--+-------+--
+  //                   ^                ^ |     _-            | ^
+  //                   |                | |   /               | |
+  //                   |                | |  /                | |
+  //                   | aBorderRadiusY | | |                 | | aR0
+  //                   |                | ||                  | |
+  //                   |                | |                   | |
+  // aCornerDim.height |                v |                   | v
+  //                   |                --+               aC0 +--
+  //                   |                  |                   |
+  //                   |                  |                   |
+  //                   |                  |                   |
+  //                   |                  |                   |
+  //                   |                  |                   |
+  //                   v                  |        aCn        |
+  //                   -------------------+---------+---------+
+  //                                      |         |
+  //                                      |<------->|
+  //                                          aRn
+  DottedCornerFinder(const Bezier& aOuterBezier, const Bezier& aInnerBezier,
+                     mozilla::Corner aCorner, Float aBorderRadiusX,
+                     Float aBorderRadiusY, const Point& aC0, Float aR0,
+                     const Point& aCn, Float aRn, const Size& aCornerDim);
+
+  bool HasMore(void) const;
+  Result Next(void);
+
+ private:
+  static const size_t MAX_LOOP = 32;
+
+  // Bezier control points for the outer curve, the inner curve, and a curve
+  // that center points of circles are on (center curve).
+  //
+  //               ___---+ outer curve
+  //           __--      |
+  //         _-          |
+  //       /        __---+ center curve
+  //     /      __--     |
+  //    |     /          |
+  //   |    /        __--+ inner curve
+  //  |    |       _-
+  //  |    |      /
+  // |     |     /
+  // |    |     |
+  // |    |     |
+  // |    |    |
+  // |    |    |
+  // |    |    |
+  // +----+----+
+  Bezier mOuterBezier;
+  Bezier mInnerBezier;
+  Bezier mCenterBezier;
+
+  mozilla::Corner mCorner;
+
+  // Sign of the normal vector used in radius calculation, flipped depends on
+  // corner and start and end radii.
+  Float mNormalSign;
+
+  // Center points and raii for start and end circles, mR0 >= mRn.
+  // mMaxR = max(mR0, mRn)
+  //
+  //                           v
+  //               ___---+------
+  //           __--     #|#    | mRn
+  //         _-        ##|##   |
+  //       /           ##+## ---
+  //     /              mCn    ^
+  //    |               #|#
+  //   |             __--+
+  //  |            _-
+  //  |           /
+  // |           /
+  // |          |
+  // |          |
+  // |  #####  |
+  // | ####### |
+  // |#########|
+  // +----+----+
+  // |## mC0 ##|
+  // | ####### |
+  // |  #####  |
+  // |    |
+  // |<-->|
+  //
+  //  mR0
+  //
+  Point mC0;
+  Point mCn;
+  Float mR0;
+  Float mRn;
+  Float mMaxR;
+
+  // Parameters for the center curve with perfect circle and the inner curve.
+  // The center curve doesn't necessarily share the origin with others.
+  //
+  //               ___---+
+  //           __--      |
+  //         _-          |
+  //       /        __-+ |
+  //     /      __--     |
+  //    |     /          |
+  //   |    /        __--+--
+  //  |    |       _-    | ^
+  //  |    |      /      | |
+  // |     |     /       | |
+  // |    |     |        | |
+  // |    |     |        | | mInnerHeight
+  // |    |    |         | |
+  // |    +    |         | |
+  // |         |         | v
+  // +---------+---------+
+  //           |         | mInnerCurveOrigin
+  //           |<------->|
+  //           mInnerWidth
+  //
+  //               ___---+
+  //           __--
+  //         _-
+  //       /        __-+
+  //     /      __--   |
+  //    |     /        |
+  //   |    /        __--+
+  //  |    |       _-  |
+  //  |    |      /    |
+  // |     |     /     |
+  // |    |     |      |
+  // |    |     |      |
+  // |    |    |       |
+  // |    +--- | ------+
+  // |    |    |       | mCenterCurveOrigin
+  // +    |    +       |
+  //      |            |
+  //      |            |
+  //      |            |
+  //      |            |
+  //      |<---------->|
+  //       mCenterCurveR
+  //
+  Point mCenterCurveOrigin;
+  Float mCenterCurveR;
+  Point mInnerCurveOrigin;
+  Float mInnerWidth;
+  Float mInnerHeight;
+
+  Point mLastC;
+  Float mLastR;
+  Float mLastT;
+
+  // Overlap between two circles.
+  // It uses arc length on PERFECT, SINGLE_CURVE_AND_RADIUS, and SINGLE_CURVE,
+  // and direct distance on OTHER.
+  Float mBestOverlap;
+
+  // If one of border-widths is 0, do not calculate overlap, and draw circles
+  // until it reaches the other side or exceeds mMaxCount.
+  bool mHasZeroBorderWidth;
+  bool mHasMore;
+
+  // The maximum number of filled/unfilled circles.
+  size_t mMaxCount;
+
+  enum {
+    //                      radius.width
+    //                 |<----------------->|
+    //                 |                   |
+    //               --+-------------___---+----
+    //               ^ |         __--     #|#  ^
+    //               | |       _-        ##|## |
+    //               | |     /           ##+## | top-width
+    //               | |   /             ##|## |
+    //               | |  |               #|#  v
+    //               | | |             __--+----
+    // radius.height | ||            _-
+    //               | ||           /
+    //               | |           /
+    //               | |          |
+    //               | |          |
+    //               | |  #####  |
+    //               | | ####### |
+    //               v |#########|
+    //               --+----+----+
+    //                 |#########|
+    //                 | ####### |
+    //                 |  #####  |
+    //                 |         |
+    //                 |<------->|
+    //                  left-width
+
+    // * top-width == left-width
+    // * radius.width == radius.height
+    // * top-width < radius.width * 2
+    //
+    // All circles has same radii and are on single perfect circle's arc.
+    // Overlap is known.
+    //
+    // Split the perfect circle's arc into 2n segments, each segment's length is
+    // top-width * (1 - overlap).  Place each circle's center point C_i on each
+    // end of the segment, each circle's radius r_i is top-width / 2
+    //
+    //                       #####
+    //                      #######
+    // perfect             #########
+    // circle's          ___---+####
+    // arc     ##### __--  ## C_0 ##
+    //   |    #####_-       ###|###
+    //   |   ####+####       ##|##
+    //   |   ##/C_i ##         |
+    //   |    |######          |
+    //   |   | #####           |
+    //   +->|                  |
+    //     |                   |
+    //   ##|##                 |
+    //  ###|###                |
+    // ####|####               |
+    // ####+-------------------+
+    // ## C_n ##
+    //  #######
+    //   #####
+    PERFECT,
+
+    // * top-width == left-width
+    // * 0.5 < radius.width / radius.height < 2.0
+    // * top-width < min(radius.width, radius.height) * 2
+    //
+    // All circles has same radii and are on single elliptic arc.
+    // Overlap is known.
+    //
+    // Split the elliptic arc into 2n segments, each segment's length is
+    // top-width * (1 - overlap).  Place each circle's center point C_i on each
+    // end of the segment, each circle's radius r_i is top-width / 2
+    //
+    //                            #####
+    //                           #######
+    //             #####        #########
+    //            #######   ____----+####
+    // elliptic  ######__---    ## C_0 ##
+    // arc       ##__+-###       ###|###
+    //   |      / # C_i #         ##|##
+    //   +--> /    #####            |
+    //       |                      |
+    //   ###|#                      |
+    //  ###|###                     |
+    // ####|####                    |
+    // ####+------------------------+
+    // ## C_n ##
+    //  #######
+    //   #####
+    SINGLE_CURVE_AND_RADIUS,
+
+    // * top-width != left-width
+    // * 0 < min(top-width, left-width)
+    // * 0.5 < radius.width / radius.height < 2.0
+    // * max(top-width, left-width) < min(radius.width, radius.height) * 2
+    //
+    // All circles are on single elliptic arc.
+    // Overlap is unknown.
+    //
+    // Place each circle's center point C_i on elliptic arc, each circle's
+    // radius r_i is the distance between the center point and the inner curve.
+    // The arc segment's length between C_i and C_{i-1} is
+    // (r_i + r_{i-1}) * (1 - overlap).
+    //
+    //  outer curve
+    //           /
+    //          /
+    //         /         / center curve
+    //        / ####### /
+    //       /##       /#
+    //      +#        /  #
+    //     /#        /    #
+    //    / #   C_i /     #
+    //   /  #      +      #  /
+    //  /   #     /  \    # / inner curve
+    //      #    /     \  #/
+    //       #  /   r_i  \+
+    //        #/       ##/
+    //        / ####### /
+    //                 /
+    SINGLE_CURVE,
+
+    // Other cases.
+    // Circles are not on single elliptic arc.
+    // Overlap are unknown.
+    //
+    // Place tangent point innerTangent on the inner curve and find circle's
+    // center point C_i and radius r_i where the circle is also tangent to the
+    // outer curve.
+    // Distance between C_i and C_{i-1} is (r_i + r_{i-1}) * (1 - overlap).
+    //
+    //  outer curve
+    //           /
+    //          /
+    //         /
+    //        / #######
+    //       /##       ##
+    //      +#           #
+    //     /# \           #
+    //    / #    \        #
+    //   /  #      +      #  /
+    //  /   #   C_i  \    # / inner curve
+    //      #          \  #/
+    //       #      r_i  \+
+    //        ##       ##/ innerTangent
+    //          ####### /
+    //                 /
+    OTHER
+  } mType;
+
+  size_t mI;
+  size_t mCount;
+
+  // Determine mType from parameters.
+  void DetermineType(Float aBorderRadiusX, Float aBorderRadiusY);
+
+  // Reset calculation.
+  void Reset(void);
+
+  // Find radius for the given tangent point on the inner curve such that the
+  // circle is also tangent to the outer curve.
+  void FindPointAndRadius(Point& C, Float& r, const Point& innerTangent,
+                          const Point& normal, Float t);
+
+  // Find next dot.
+  Float FindNext(Float overlap);
+
+  // Find mBestOverlap for parameters.
+  void FindBestOverlap(Float aMinR, Float aMinBorderRadius,
+                       Float aMaxBorderRadius);
+
+  // Fill corner with dots with given overlap, and return the number of dots
+  // and last two dots's overlap.
+  bool GetCountAndLastOverlap(Float aOverlap, size_t* aCount,
+                              Float* aActualOverlap);
+};
+
+}  // namespace mozilla
+
+#endif /* mozilla_DottedCornerFinder_h_ */
diff --git a/layout/painting/HitTestInfo.cpp b/layout/painting/HitTestInfo.cpp
new file mode 100644
index 0000000000..872773c32f
--- /dev/null
+++ b/layout/painting/HitTestInfo.cpp
@@ -0,0 +1,74 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "HitTestInfo.h"
+
+#include "mozilla/StaticPtr.h"
+#include "mozilla/webrender/WebRenderAPI.h"
+#include "nsDisplayList.h"
+#include "nsIFrame.h"
+#include "mozilla/layers/ScrollableLayerGuid.h"
+
+using namespace mozilla::gfx;
+
+namespace mozilla {
+
+static StaticAutoPtr<const HitTestInfo> gEmptyHitTestInfo;
+
+const HitTestInfo& HitTestInfo::Empty() {
+  if (!gEmptyHitTestInfo) {
+    gEmptyHitTestInfo = new HitTestInfo();
+  }
+
+  return *gEmptyHitTestInfo;
+}
+
+void HitTestInfo::Shutdown() { gEmptyHitTestInfo = nullptr; }
+
+using ViewID = layers::ScrollableLayerGuid::ViewID;
+
+ViewID HitTestInfo::GetViewId(wr::DisplayListBuilder& aBuilder,
+                              const ActiveScrolledRoot* aASR) const {
+  if (mScrollTarget) {
+    return *mScrollTarget;
+  }
+
+  Maybe<ViewID> fixedTarget = aBuilder.GetContainingFixedPosScrollTarget(aASR);
+
+  if (fixedTarget) {
+    return *fixedTarget;
+  }
+
+  if (aASR) {
+    return aASR->GetViewId();
+  }
+
+  return layers::ScrollableLayerGuid::NULL_SCROLL_ID;
+}
+
+void HitTestInfo::Initialize(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame) {
+  if (!aBuilder->BuildCompositorHitTestInfo()) {
+    return;
+  }
+
+  mInfo = aFrame->GetCompositorHitTestInfo(aBuilder);
+  if (mInfo != gfx::CompositorHitTestInvisibleToHit) {
+    mArea = aFrame->GetCompositorHitTestArea(aBuilder);
+    InitializeScrollTarget(aBuilder);
+  }
+}
+
+void HitTestInfo::InitializeScrollTarget(nsDisplayListBuilder* aBuilder) {
+  if (aBuilder->GetCurrentScrollbarDirection().isSome()) {
+    // In the case of scrollbar frames, we use the scrollbar's target
+    // scrollframe instead of the scrollframe with which the scrollbar actually
+    // moves.
+    MOZ_ASSERT(Info().contains(CompositorHitTestFlags::eScrollbar));
+    mScrollTarget = Some(aBuilder->GetCurrentScrollbarTarget());
+  }
+}
+
+}  // namespace mozilla
diff --git a/layout/painting/HitTestInfo.h b/layout/painting/HitTestInfo.h
new file mode 100644
index 0000000000..95438b810c
--- /dev/null
+++ b/layout/painting/HitTestInfo.h
@@ -0,0 +1,59 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef GFX_HITTESTINFO_H
+#define GFX_HITTESTINFO_H
+
+#include "mozilla/gfx/CompositorHitTestInfo.h"
+#include "mozilla/layers/ScrollableLayerGuid.h"
+#include "nsRect.h"
+
+class nsIFrame;
+
+namespace mozilla {
+
+class nsDisplayListBuilder;
+struct ActiveScrolledRoot;
+
+namespace wr {
+class DisplayListBuilder;
+}  // namespace wr
+
+/**
+ * A helper class that manages compositor hit testing information.
+ */
+class HitTestInfo {
+ public:
+  using CompositorHitTestInfo = gfx::CompositorHitTestInfo;
+  using ViewID = layers::ScrollableLayerGuid::ViewID;
+
+  ViewID GetViewId(wr::DisplayListBuilder& aBuilder,
+                   const ActiveScrolledRoot* aASR) const;
+
+  void Initialize(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame);
+  void InitializeScrollTarget(nsDisplayListBuilder* aBuilder);
+
+  void SetAreaAndInfo(const nsRect& aArea, const CompositorHitTestInfo& aInfo) {
+    mArea = aArea;
+    mInfo = aInfo;
+  }
+
+  static void Shutdown();
+
+  const nsRect& Area() const { return mArea; }
+  const CompositorHitTestInfo& Info() const { return mInfo; }
+
+  static const HitTestInfo& Empty();
+
+ private:
+  nsRect mArea;
+  CompositorHitTestInfo mInfo;
+  mozilla::Maybe<ViewID> mScrollTarget;
+};
+
+}  // namespace mozilla
+
+#endif
diff --git a/layout/painting/LayerState.h b/layout/painting/LayerState.h
new file mode 100644
index 0000000000..d570ae95b0
--- /dev/null
+++ b/layout/painting/LayerState.h
@@ -0,0 +1,29 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef LAYERSTATE_H_
+#define LAYERSTATE_H_
+
+#include <cstdint>
+
+namespace mozilla {
+
+enum class LayerState : uint8_t {
+  LAYER_NONE,
+  LAYER_INACTIVE,
+  LAYER_ACTIVE,
+  // Force an active layer even if it causes incorrect rendering, e.g.
+  // when the layer has rounded rect clips.
+  LAYER_ACTIVE_FORCE,
+  // Special layer that is metadata only.
+  LAYER_ACTIVE_EMPTY,
+  // Inactive style layer for rendering SVG effects.
+  LAYER_SVG_EFFECTS
+};
+
+}  // namespace mozilla
+
+#endif
diff --git a/layout/painting/MaskLayerImageCache.cpp b/layout/painting/MaskLayerImageCache.cpp
new file mode 100644
index 0000000000..2b3b63dc57
--- /dev/null
+++ b/layout/painting/MaskLayerImageCache.cpp
@@ -0,0 +1,64 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "MaskLayerImageCache.h"
+
+#include "ImageContainer.h"
+#include "mozilla/layers/KnowsCompositor.h"
+
+using namespace mozilla::layers;
+
+namespace mozilla {
+
+MaskLayerImageCache::MaskLayerImageCache() {
+  MOZ_COUNT_CTOR(MaskLayerImageCache);
+}
+MaskLayerImageCache::~MaskLayerImageCache() {
+  MOZ_COUNT_DTOR(MaskLayerImageCache);
+}
+
+void MaskLayerImageCache::Sweep() {
+  for (auto iter = mMaskImageContainers.Iter(); !iter.Done(); iter.Next()) {
+    const auto& key = iter.Get()->mKey;
+    if (key->HasZeroLayerCount()) {
+      iter.Remove();
+    }
+  }
+}
+
+ImageContainer* MaskLayerImageCache::FindImageFor(
+    const MaskLayerImageKey** aKey) {
+  if (MaskLayerImageEntry* entry = mMaskImageContainers.GetEntry(**aKey)) {
+    *aKey = entry->mKey.get();
+    return entry->mContainer;
+  }
+
+  return nullptr;
+}
+
+void MaskLayerImageCache::PutImage(const MaskLayerImageKey* aKey,
+                                   ImageContainer* aContainer) {
+  MaskLayerImageEntry* entry = mMaskImageContainers.PutEntry(*aKey);
+  entry->mContainer = aContainer;
+}
+
+MaskLayerImageCache::MaskLayerImageKey::MaskLayerImageKey()
+    : mRoundedClipRects(), mLayerCount(0) {
+  MOZ_COUNT_CTOR(MaskLayerImageKey);
+}
+
+MaskLayerImageCache::MaskLayerImageKey::MaskLayerImageKey(
+    const MaskLayerImageKey& aKey)
+    : mRoundedClipRects(aKey.mRoundedClipRects.Clone()),
+      mLayerCount(aKey.mLayerCount) {
+  MOZ_COUNT_CTOR(MaskLayerImageKey);
+}
+
+MaskLayerImageCache::MaskLayerImageKey::~MaskLayerImageKey() {
+  MOZ_COUNT_DTOR(MaskLayerImageKey);
+}
+
+}  // namespace mozilla
diff --git a/layout/painting/MaskLayerImageCache.h b/layout/painting/MaskLayerImageCache.h
new file mode 100644
index 0000000000..7e20f72a20
--- /dev/null
+++ b/layout/painting/MaskLayerImageCache.h
@@ -0,0 +1,257 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef MASKLAYERIMAGECACHE_H_
+#define MASKLAYERIMAGECACHE_H_
+
+#include "DisplayItemClip.h"
+#include "nsPresContext.h"
+#include "mozilla/gfx/Matrix.h"
+#include "mozilla/UniquePtr.h"
+
+namespace mozilla {
+
+namespace layers {
+class ImageContainer;
+class KnowsCompositor;
+}  // namespace layers
+
+/**
+ * Keeps a record of image containers for mask layers, containers are mapped
+ * from the rounded rects used to create them.
+ * The cache stores MaskLayerImageEntries indexed by MaskLayerImageKeys.
+ * Each MaskLayerImageEntry owns a heap-allocated MaskLayerImageKey
+ * (heap-allocated so that a mask layer's userdata can keep a pointer to the
+ * key for its image, in spite of the hashtable moving its entries around).
+ * The key consists of the rounded rects used to create the mask,
+ * an nsRefPtr to the ImageContainer containing the image, and a count
+ * of the number of layers currently using this ImageContainer.
+ * When the key's layer count is zero, the cache
+ * may remove the entry, which deletes the key object.
+ */
+class MaskLayerImageCache {
+  typedef mozilla::layers::ImageContainer ImageContainer;
+  typedef mozilla::layers::KnowsCompositor KnowsCompositor;
+
+ public:
+  MaskLayerImageCache();
+  ~MaskLayerImageCache();
+
+  /**
+   * Representation of a rounded rectangle in device pixel coordinates, in
+   * contrast to DisplayItemClip::RoundedRect, which uses app units.
+   * In particular, our internal representation uses a gfxRect, rather than
+   * an nsRect, so this class is easier to use with transforms.
+   */
+  struct PixelRoundedRect {
+    PixelRoundedRect() = delete;
+
+    PixelRoundedRect(const DisplayItemClip::RoundedRect& aRRect,
+                     nsPresContext* aPresContext)
+        : mRect(aPresContext->AppUnitsToGfxUnits(aRRect.mRect.x),
+                aPresContext->AppUnitsToGfxUnits(aRRect.mRect.y),
+                aPresContext->AppUnitsToGfxUnits(aRRect.mRect.width),
+                aPresContext->AppUnitsToGfxUnits(aRRect.mRect.height)) {
+      MOZ_COUNT_CTOR(PixelRoundedRect);
+      for (const auto corner : mozilla::AllPhysicalHalfCorners()) {
+        mRadii[corner] =
+            aPresContext->AppUnitsToGfxUnits(aRRect.mRadii[corner]);
+      }
+    }
+
+    PixelRoundedRect(const PixelRoundedRect& aPRR) : mRect(aPRR.mRect) {
+      MOZ_COUNT_CTOR(PixelRoundedRect);
+      for (const auto corner : mozilla::AllPhysicalHalfCorners()) {
+        mRadii[corner] = aPRR.mRadii[corner];
+      }
+    }
+
+    MOZ_COUNTED_DTOR(PixelRoundedRect)
+
+    // Applies the scale and translate components of aTransform.
+    // It is an error to pass a matrix which does more than just scale
+    // and translate.
+    void ScaleAndTranslate(const gfx::Matrix& aTransform) {
+      NS_ASSERTION(aTransform._12 == 0 && aTransform._21 == 0,
+                   "Transform has a component other than scale and translate");
+
+      mRect = aTransform.TransformBounds(mRect);
+
+      for (size_t i = 0; i < ArrayLength(mRadii); i += 2) {
+        mRadii[i] *= aTransform._11;
+        mRadii[i + 1] *= aTransform._22;
+      }
+    }
+
+    bool operator==(const PixelRoundedRect& aOther) const {
+      if (!mRect.IsEqualInterior(aOther.mRect)) {
+        return false;
+      }
+
+      for (const auto corner : mozilla::AllPhysicalHalfCorners()) {
+        if (mRadii[corner] != aOther.mRadii[corner]) {
+          return false;
+        }
+      }
+      return true;
+    }
+    bool operator!=(const PixelRoundedRect& aOther) const {
+      return !(*this == aOther);
+    }
+
+    // Create a hash for this object.
+    PLDHashNumber Hash() const {
+      PLDHashNumber hash = HashBytes(&mRect.x, 4 * sizeof(gfxFloat));
+      hash = AddToHash(hash, HashBytes(mRadii, 8 * sizeof(gfxFloat)));
+
+      return hash;
+    }
+
+    gfx::Rect mRect;
+    // Indices into mRadii are the enum HalfCorner constants in gfx/2d/Types.h
+    gfxFloat mRadii[8];
+  };
+
+  struct MaskLayerImageKeyRef;
+
+  /**
+   * A key to identify cached image containers.
+   * The const-ness of this class is with respect to its use as a key into a
+   * hashtable, so anything not used to create the hash is mutable.
+   * mLayerCount counts the number of mask layers which have a reference to
+   * MaskLayerImageEntry::mContainer; it is maintained by MaskLayerUserData,
+   * which keeps a reference to the key. There will usually be mLayerCount + 1
+   * pointers to a key object (the +1 being from the hashtable entry), but this
+   * invariant may be temporarily broken.
+   */
+  struct MaskLayerImageKey {
+    friend struct MaskLayerImageKeyRef;
+
+    MaskLayerImageKey();
+    MaskLayerImageKey(const MaskLayerImageKey& aKey);
+
+    ~MaskLayerImageKey();
+
+    bool HasZeroLayerCount() const { return mLayerCount == 0; }
+
+    PLDHashNumber Hash() const {
+      PLDHashNumber hash = 0;
+
+      for (uint32_t i = 0; i < mRoundedClipRects.Length(); ++i) {
+        hash = AddToHash(hash, mRoundedClipRects[i].Hash());
+      }
+      hash = AddToHash(hash, mKnowsCompositor.get());
+
+      return hash;
+    }
+
+    bool operator==(const MaskLayerImageKey& aOther) const {
+      return mKnowsCompositor == aOther.mKnowsCompositor &&
+             mRoundedClipRects == aOther.mRoundedClipRects;
+    }
+
+    nsTArray<PixelRoundedRect> mRoundedClipRects;
+    RefPtr<KnowsCompositor> mKnowsCompositor;
+
+   private:
+    void IncLayerCount() const { ++mLayerCount; }
+    void DecLayerCount() const {
+      NS_ASSERTION(mLayerCount > 0, "Inconsistent layer count");
+      --mLayerCount;
+    }
+    mutable uint32_t mLayerCount;
+  };
+
+  /**
+   * This struct maintains a reference to a MaskLayerImageKey, via a variant on
+   * refcounting. When a key is passed in via Reset(), we increment the
+   * passed-in key's mLayerCount, and we decrement its mLayerCount when we're
+   * destructed (or when the key is replaced via a second Reset() call).
+   *
+   * However, unlike standard refcounting smart-pointers, this object does
+   * *not* delete the tracked MaskLayerImageKey -- instead, deletion happens
+   * in MaskLayerImageCache::Sweep(), for any keys whose mLayerCount is 0.
+   */
+  struct MaskLayerImageKeyRef {
+    ~MaskLayerImageKeyRef() {
+      if (mRawPtr) {
+        mRawPtr->DecLayerCount();
+      }
+    }
+
+    MaskLayerImageKeyRef() : mRawPtr(nullptr) {}
+    MaskLayerImageKeyRef(const MaskLayerImageKeyRef&) = delete;
+    void operator=(const MaskLayerImageKeyRef&) = delete;
+
+    void Reset(const MaskLayerImageKey* aPtr) {
+      MOZ_ASSERT(
+          aPtr, "Cannot initialize a MaskLayerImageKeyRef with a null pointer");
+      aPtr->IncLayerCount();
+      if (mRawPtr) {
+        mRawPtr->DecLayerCount();
+      }
+      mRawPtr = aPtr;
+    }
+
+   private:
+    const MaskLayerImageKey* mRawPtr;
+  };
+
+  // Find an image container for aKey, returns nullptr if there is no suitable
+  // cached image. If there is an image, then aKey is set to point at the stored
+  // key for the image.
+  ImageContainer* FindImageFor(const MaskLayerImageKey** aKey);
+
+  // Add an image container with a key to the cache
+  // The image container used will be set as the container in aKey and aKey
+  // itself will be linked from this cache
+  void PutImage(const MaskLayerImageKey* aKey, ImageContainer* aContainer);
+
+  // Sweep the cache for old image containers that can be deleted
+  void Sweep();
+
+ protected:
+  class MaskLayerImageEntry : public PLDHashEntryHdr {
+   public:
+    typedef const MaskLayerImageKey& KeyType;
+    typedef const MaskLayerImageKey* KeyTypePointer;
+
+    explicit MaskLayerImageEntry(KeyTypePointer aKey) : mKey(aKey) {
+      MOZ_COUNT_CTOR(MaskLayerImageEntry);
+    }
+    MaskLayerImageEntry(const MaskLayerImageEntry& aOther)
+        : mKey(aOther.mKey.get()) {
+      NS_ERROR("ALLOW_MEMMOVE == true, should never be called");
+    }
+    MOZ_COUNTED_DTOR(MaskLayerImageEntry)
+
+    // KeyEquals(): does this entry match this key?
+    bool KeyEquals(KeyTypePointer aKey) const { return *mKey == *aKey; }
+
+    // KeyToPointer(): Convert KeyType to KeyTypePointer
+    static KeyTypePointer KeyToPointer(KeyType aKey) { return &aKey; }
+
+    // HashKey(): calculate the hash number
+    static PLDHashNumber HashKey(KeyTypePointer aKey) { return aKey->Hash(); }
+
+    // ALLOW_MEMMOVE can we move this class with memmove(), or do we have
+    // to use the copy constructor?
+    enum { ALLOW_MEMMOVE = true };
+
+    bool operator==(const MaskLayerImageEntry& aOther) const {
+      return KeyEquals(aOther.mKey.get());
+    }
+
+    mozilla::UniquePtr<const MaskLayerImageKey> mKey;
+    RefPtr<ImageContainer> mContainer;
+  };
+
+  nsTHashtable<MaskLayerImageEntry> mMaskImageContainers;
+};
+
+}  // namespace mozilla
+
+#endif
diff --git a/layout/painting/MatrixStack.h b/layout/painting/MatrixStack.h
new file mode 100644
index 0000000000..320d08317b
--- /dev/null
+++ b/layout/painting/MatrixStack.h
@@ -0,0 +1,61 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef MOZILLA_PAINTING_MATRIXSTACK_H
+#define MOZILLA_PAINTING_MATRIXSTACK_H
+
+#include "nsTArray.h"
+#include "mozilla/gfx/MatrixFwd.h"
+
+namespace mozilla {
+
+/**
+ * MatrixStack stores a stack of matrices and keeps track of the accumulated
+ * transform matrix.
+ */
+template <typename T>
+class MatrixStack {
+ public:
+  MatrixStack() = default;
+
+  ~MatrixStack() { MOZ_ASSERT(mMatrices.IsEmpty()); }
+
+  /**
+   * Returns the current accumulated transform matrix.
+   */
+  const T& CurrentMatrix() const { return mCurrentMatrix; }
+
+  /**
+   * Returns true if any matrices are currently pushed to the stack.
+   */
+  bool HasTransform() const { return mMatrices.Length() > 0; }
+
+  /**
+   * Pushes the given |aMatrix| to the stack.
+   */
+  void Push(const T& aMatrix) {
+    mMatrices.AppendElement(mCurrentMatrix);
+    mCurrentMatrix = aMatrix * mCurrentMatrix;
+  }
+
+  /**
+   * Pops the most recently added matrix from the stack.
+   */
+  void Pop() {
+    MOZ_ASSERT(mMatrices.Length() > 0);
+    mCurrentMatrix = mMatrices.PopLastElement();
+  }
+
+ private:
+  T mCurrentMatrix;
+  AutoTArray<T, 2> mMatrices;
+};
+
+typedef MatrixStack<gfx::Matrix4x4Flagged> MatrixStack4x4;
+
+}  // namespace mozilla
+
+#endif /* MOZILLA_PAINTING_MATRIXSTACK_H */
diff --git a/layout/painting/PaintTracker.cpp b/layout/painting/PaintTracker.cpp
new file mode 100644
index 0000000000..208f037e7a
--- /dev/null
+++ b/layout/painting/PaintTracker.cpp
@@ -0,0 +1,13 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/PaintTracker.h"
+
+namespace mozilla {
+
+int PaintTracker::gPaintTracker;
+
+}  // namespace mozilla
diff --git a/layout/painting/PaintTracker.h b/layout/painting/PaintTracker.h
new file mode 100644
index 0000000000..1f5554f983
--- /dev/null
+++ b/layout/painting/PaintTracker.h
@@ -0,0 +1,31 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_PaintTracker_h
+#define mozilla_PaintTracker_h
+
+#include "mozilla/Attributes.h"
+#include "nsDebug.h"
+
+namespace mozilla {
+
+class MOZ_STACK_CLASS PaintTracker {
+ public:
+  PaintTracker() { ++gPaintTracker; }
+  ~PaintTracker() {
+    NS_ASSERTION(gPaintTracker > 0, "Mismatched constructor/destructor");
+    --gPaintTracker;
+  }
+
+  static bool IsPainting() { return !!gPaintTracker; }
+
+ private:
+  static int gPaintTracker;
+};
+
+}  // namespace mozilla
+
+#endif  // mozilla_PaintTracker_h
diff --git a/layout/painting/RetainedDisplayListBuilder.cpp b/layout/painting/RetainedDisplayListBuilder.cpp
new file mode 100644
index 0000000000..2834213789
--- /dev/null
+++ b/layout/painting/RetainedDisplayListBuilder.cpp
@@ -0,0 +1,1702 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+#include "RetainedDisplayListBuilder.h"
+
+#include "mozilla/Attributes.h"
+#include "mozilla/StaticPrefs_layout.h"
+#include "nsIFrame.h"
+#include "nsIFrameInlines.h"
+#include "nsIScrollableFrame.h"
+#include "nsPlaceholderFrame.h"
+#include "nsSubDocumentFrame.h"
+#include "nsViewManager.h"
+#include "nsCanvasFrame.h"
+#include "mozilla/AutoRestore.h"
+#include "mozilla/DisplayPortUtils.h"
+#include "mozilla/PresShell.h"
+#include "mozilla/ProfilerLabels.h"
+
+/**
+ * Code for doing display list building for a modified subset of the window,
+ * and then merging it into the existing display list (for the full window).
+ *
+ * The approach primarily hinges on the observation that the 'true' ordering
+ * of display items is represented by a DAG (only items that intersect in 2d
+ * space have a defined ordering). Our display list is just one of a many
+ * possible linear representations of this ordering.
+ *
+ * Each time a frame changes (gets a new ComputedStyle, or has a size/position
+ * change), we schedule a paint (as we do currently), but also reord the frame
+ * that changed.
+ *
+ * When the next paint occurs we union the overflow areas (in screen space) of
+ * the changed frames, and compute a rect/region that contains all changed
+ * items. We then build a display list just for this subset of the screen and
+ * merge it into the display list from last paint.
+ *
+ * Any items that exist in one list and not the other must not have a defined
+ * ordering in the DAG, since they need to intersect to have an ordering and
+ * we would have built both in the new list if they intersected. Given that, we
+ * can align items that appear in both lists, and any items that appear between
+ * matched items can be inserted into the merged list in any order.
+ *
+ * Frames that are a stacking context, containing blocks for position:fixed
+ * descendants, and don't have any continuations (see
+ * CanStoreDisplayListBuildingRect) trigger recursion into the algorithm with
+ * separate retaining decisions made.
+ *
+ * RDL defines the concept of an AnimatedGeometryRoot (AGR), the nearest
+ * ancestor frame which can be moved asynchronously on the compositor thread.
+ * These are currently nsDisplayItems which return true from CanMoveAsync
+ * (animated nsDisplayTransform and nsDisplayStickyPosition) and
+ * ActiveScrolledRoots.
+ *
+ * For each context that we run the retaining algorithm, there can only be
+ * mutations to one AnimatedGeometryRoot. This is because we are unable to
+ * reason about intersections of items that might then move relative to each
+ * other without RDL running again. If there are mutations to multiple
+ * AnimatedGeometryRoots, then we bail out and rebuild all the items in the
+ * context.
+ *
+ * Otherwise, when mutations are restricted to a single AGR, we pre-process the
+ * old display list and mark the frames for all existing (unmodified!) items
+ * that belong to a different AGR and ensure that we rebuild those items for
+ * correct sorting with the modified ones.
+ */
+
+namespace mozilla {
+
+RetainedDisplayListData::RetainedDisplayListData()
+    : mModifiedFrameLimit(
+          StaticPrefs::layout_display_list_rebuild_frame_limit()) {}
+
+void RetainedDisplayListData::AddModifiedFrame(nsIFrame* aFrame) {
+  MOZ_ASSERT(!aFrame->IsFrameModified());
+  Flags(aFrame) += RetainedDisplayListData::FrameFlag::Modified;
+  aFrame->SetFrameIsModified(true);
+  mModifiedFrameCount++;
+}
+
+static void MarkFramesWithItemsAndImagesModified(nsDisplayList* aList) {
+  for (nsDisplayItem* i : *aList) {
+    if (!i->HasDeletedFrame() && i->CanBeReused() &&
+        !i->Frame()->IsFrameModified()) {
+      // If we have existing cached geometry for this item, then check that for
+      // whether we need to invalidate for a sync decode. If we don't, then
+      // use the item's flags.
+      // XXX: handle webrender case by looking up retained data for the item
+      // and checking InvalidateForSyncDecodeImages
+      bool invalidate = false;
+      if (!(i->GetFlags() & TYPE_RENDERS_NO_IMAGES)) {
+        invalidate = true;
+      }
+
+      if (invalidate) {
+        DL_LOGV("RDL - Invalidating item %p (%s)", i, i->Name());
+        i->FrameForInvalidation()->MarkNeedsDisplayItemRebuild();
+        if (i->GetDependentFrame()) {
+          i->GetDependentFrame()->MarkNeedsDisplayItemRebuild();
+        }
+      }
+    }
+    if (i->GetChildren()) {
+      MarkFramesWithItemsAndImagesModified(i->GetChildren());
+    }
+  }
+}
+
+static nsIFrame* SelectAGRForFrame(nsIFrame* aFrame, nsIFrame* aParentAGR) {
+  if (!aFrame->IsStackingContext() || !aFrame->IsFixedPosContainingBlock()) {
+    return aParentAGR;
+  }
+
+  if (!aFrame->HasOverrideDirtyRegion()) {
+    return nullptr;
+  }
+
+  nsDisplayListBuilder::DisplayListBuildingData* data =
+      aFrame->GetProperty(nsDisplayListBuilder::DisplayListBuildingRect());
+
+  return data && data->mModifiedAGR ? data->mModifiedAGR : nullptr;
+}
+
+void RetainedDisplayListBuilder::AddSizeOfIncludingThis(
+    nsWindowSizes& aSizes) const {
+  aSizes.mLayoutRetainedDisplayListSize += aSizes.mState.mMallocSizeOf(this);
+  mBuilder.AddSizeOfExcludingThis(aSizes);
+  mList.AddSizeOfExcludingThis(aSizes);
+}
+
+bool AnyContentAncestorModified(nsIFrame* aFrame, nsIFrame* aStopAtFrame) {
+  nsIFrame* f = aFrame;
+  while (f) {
+    if (f->IsFrameModified()) {
+      return true;
+    }
+
+    if (aStopAtFrame && f == aStopAtFrame) {
+      break;
+    }
+
+    f = nsLayoutUtils::GetDisplayListParent(f);
+  }
+
+  return false;
+}
+
+// Removes any display items that belonged to a frame that was deleted,
+// and mark frames that belong to a different AGR so that get their
+// items built again.
+// TODO: We currently descend into all children even if we don't have an AGR
+// to mark, as child stacking contexts might. It would be nice if we could
+// jump into those immediately rather than walking the entire thing.
+bool RetainedDisplayListBuilder::PreProcessDisplayList(
+    RetainedDisplayList* aList, nsIFrame* aAGR, PartialUpdateResult& aUpdated,
+    nsIFrame* aAsyncAncestor, const ActiveScrolledRoot* aAsyncAncestorASR,
+    nsIFrame* aOuterFrame, uint32_t aCallerKey, uint32_t aNestingDepth,
+    bool aKeepLinked) {
+  // The DAG merging algorithm does not have strong mechanisms in place to keep
+  // the complexity of the resulting DAG under control. In some cases we can
+  // build up edges very quickly. Detect those cases and force a full display
+  // list build if we hit them.
+  static const uint32_t kMaxEdgeRatio = 5;
+  const bool initializeDAG = !aList->mDAG.Length();
+  if (!aKeepLinked && !initializeDAG &&
+      aList->mDAG.mDirectPredecessorList.Length() >
+          (aList->mDAG.mNodesInfo.Length() * kMaxEdgeRatio)) {
+    return false;
+  }
+
+  // If we had aKeepLinked=true for this list on the previous paint, then
+  // mOldItems will already be initialized as it won't have been consumed during
+  // a merge.
+  const bool initializeOldItems = aList->mOldItems.IsEmpty();
+  if (initializeOldItems) {
+    aList->mOldItems.SetCapacity(aList->Length());
+  } else {
+    MOZ_RELEASE_ASSERT(!initializeDAG);
+  }
+
+  MOZ_RELEASE_ASSERT(
+      initializeDAG ||
+      aList->mDAG.Length() ==
+          (initializeOldItems ? aList->Length() : aList->mOldItems.Length()));
+
+  nsDisplayList out(Builder());
+
+  size_t i = 0;
+  while (nsDisplayItem* item = aList->RemoveBottom()) {
+#ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
+    item->SetMergedPreProcessed(false, true);
+#endif
+
+    // If we have a previously initialized old items list, then it can differ
+    // from the current list due to items removed for having a deleted frame.
+    // We can't easily remove these, since the DAG has entries for those indices
+    // and it's hard to rewrite in-place.
+    // Skip over entries with no current item to keep the iterations in sync.
+    if (!initializeOldItems) {
+      while (!aList->mOldItems[i].mItem) {
+        i++;
+      }
+    }
+
+    if (initializeDAG) {
+      if (i == 0) {
+        aList->mDAG.AddNode(Span<const MergedListIndex>());
+      } else {
+        MergedListIndex previous(i - 1);
+        aList->mDAG.AddNode(Span<const MergedListIndex>(&previous, 1));
+      }
+    }
+
+    if (!item->CanBeReused() || item->HasDeletedFrame() ||
+        AnyContentAncestorModified(item->FrameForInvalidation(), aOuterFrame)) {
+      if (initializeOldItems) {
+        aList->mOldItems.AppendElement(OldItemInfo(nullptr));
+      } else {
+        MOZ_RELEASE_ASSERT(aList->mOldItems[i].mItem == item);
+        aList->mOldItems[i].mItem = nullptr;
+      }
+
+      if (item->IsGlassItem() && item == mBuilder.GetGlassDisplayItem()) {
+        mBuilder.ClearGlassDisplayItem();
+      }
+
+      item->Destroy(&mBuilder);
+      Metrics()->mRemovedItems++;
+
+      i++;
+      aUpdated = PartialUpdateResult::Updated;
+      continue;
+    }
+
+    if (initializeOldItems) {
+      aList->mOldItems.AppendElement(OldItemInfo(item));
+    }
+
+    // If we're not going to keep the list linked, then this old item entry
+    // is the only pointer to the item. Let it know that it now strongly
+    // owns the item, so it can destroy it if it goes away.
+    aList->mOldItems[i].mOwnsItem = !aKeepLinked;
+
+    item->SetOldListIndex(aList, OldListIndex(i), aCallerKey, aNestingDepth);
+
+    nsIFrame* f = item->Frame();
+
+    if (item->GetChildren()) {
+      // If children inside this list were invalid, then we'd have walked the
+      // ancestors and set ForceDescendIntoVisible on the current frame. If an
+      // ancestor is modified, then we'll throw this away entirely. Either way,
+      // we won't need to run merging on this sublist, and we can keep the items
+      // linked into their display list.
+      // The caret can move without invalidating, but we always set the force
+      // descend into frame state bit on that frame, so check for that too.
+      // TODO: AGR marking below can call MarkFrameForDisplayIfVisible and make
+      // us think future siblings need to be merged, even though we don't really
+      // need to.
+      bool keepLinked = aKeepLinked;
+      nsIFrame* invalid = item->FrameForInvalidation();
+      if (!invalid->ForceDescendIntoIfVisible() &&
+          !invalid->HasAnyStateBits(NS_FRAME_FORCE_DISPLAY_LIST_DESCEND_INTO)) {
+        keepLinked = true;
+      }
+
+      // If this item's frame is an AGR (can be moved asynchronously by the
+      // compositor), then use that frame for descendants. Also pass the ASR
+      // for that item, so that descendants can compare to see if any new
+      // ASRs have been pushed since.
+      nsIFrame* asyncAncestor = aAsyncAncestor;
+      const ActiveScrolledRoot* asyncAncestorASR = aAsyncAncestorASR;
+      if (item->CanMoveAsync()) {
+        asyncAncestor = item->Frame();
+        asyncAncestorASR = item->GetActiveScrolledRoot();
+      }
+
+      if (!PreProcessDisplayList(
+              item->GetChildren(), SelectAGRForFrame(f, aAGR), aUpdated,
+              asyncAncestor, asyncAncestorASR, item->Frame(),
+              item->GetPerFrameKey(), aNestingDepth + 1, keepLinked)) {
+        MOZ_RELEASE_ASSERT(
+            !aKeepLinked,
+            "Can't early return since we need to move the out list back");
+        return false;
+      }
+    }
+
+    // TODO: We should be able to check the clipped bounds relative
+    // to the common AGR (of both the existing item and the invalidated
+    // frame) and determine if they can ever intersect.
+    // TODO: We only really need to build the ancestor container item that is a
+    // sibling of the changed thing to get correct ordering. The changed content
+    // is a frame though, and it's hard to map that to container items in this
+    // list.
+    // If an ancestor display item is an AGR, and our ASR matches the ASR
+    // of that item, then there can't have been any new ASRs pushed since that
+    // item, so that item is our AGR. Otherwise, our AGR is our ASR.
+    // TODO: If aAsyncAncestorASR is non-null, then item->GetActiveScrolledRoot
+    // should be the same or a descendant and also non-null. Unfortunately an
+    // RDL bug means this can be wrong for sticky items after a partial update,
+    // so we have to work around it. Bug 1730749 and bug 1730826 should resolve
+    // this.
+    nsIFrame* agrFrame = nullptr;
+    if (aAsyncAncestorASR == item->GetActiveScrolledRoot() ||
+        !item->GetActiveScrolledRoot()) {
+      agrFrame = aAsyncAncestor;
+    } else {
+      agrFrame =
+          item->GetActiveScrolledRoot()->mScrollableFrame->GetScrolledFrame();
+    }
+
+    if (aAGR && agrFrame != aAGR) {
+      mBuilder.MarkFrameForDisplayIfVisible(f, RootReferenceFrame());
+    }
+
+    // If we're going to keep this linked list and not merge it, then mark the
+    // item as used and put it back into the list.
+    if (aKeepLinked) {
+      item->SetReused(true);
+      if (item->GetChildren()) {
+        item->UpdateBounds(Builder());
+      }
+      if (item->GetType() == DisplayItemType::TYPE_SUBDOCUMENT) {
+        IncrementSubDocPresShellPaintCount(item);
+      }
+      out.AppendToTop(item);
+    }
+    i++;
+  }
+
+  MOZ_RELEASE_ASSERT(aList->mOldItems.Length() == aList->mDAG.Length());
+
+  if (aKeepLinked) {
+    aList->AppendToTop(&out);
+  }
+
+  return true;
+}
+
+void IncrementPresShellPaintCount(nsDisplayListBuilder* aBuilder,
+                                  nsDisplayItem* aItem) {
+  MOZ_ASSERT(aItem->GetType() == DisplayItemType::TYPE_SUBDOCUMENT);
+
+  nsSubDocumentFrame* subDocFrame =
+      static_cast<nsDisplaySubDocument*>(aItem)->SubDocumentFrame();
+  MOZ_ASSERT(subDocFrame);
+
+  PresShell* presShell = subDocFrame->GetSubdocumentPresShellForPainting(0);
+  MOZ_ASSERT(presShell);
+
+  aBuilder->IncrementPresShellPaintCount(presShell);
+}
+
+void RetainedDisplayListBuilder::IncrementSubDocPresShellPaintCount(
+    nsDisplayItem* aItem) {
+  IncrementPresShellPaintCount(&mBuilder, aItem);
+}
+
+static Maybe<const ActiveScrolledRoot*> SelectContainerASR(
+    const DisplayItemClipChain* aClipChain, const ActiveScrolledRoot* aItemASR,
+    Maybe<const ActiveScrolledRoot*>& aContainerASR) {
+  const ActiveScrolledRoot* itemClipASR =
+      aClipChain ? aClipChain->mASR : nullptr;
+
+  const ActiveScrolledRoot* finiteBoundsASR =
+      ActiveScrolledRoot::PickDescendant(itemClipASR, aItemASR);
+
+  if (!aContainerASR) {
+    return Some(finiteBoundsASR);
+  }
+
+  return Some(
+      ActiveScrolledRoot::PickAncestor(*aContainerASR, finiteBoundsASR));
+}
+
+static void UpdateASR(nsDisplayItem* aItem,
+                      Maybe<const ActiveScrolledRoot*>& aContainerASR) {
+  if (!aContainerASR) {
+    return;
+  }
+
+  nsDisplayWrapList* wrapList = aItem->AsDisplayWrapList();
+  if (!wrapList) {
+    aItem->SetActiveScrolledRoot(*aContainerASR);
+    return;
+  }
+
+  wrapList->SetActiveScrolledRoot(ActiveScrolledRoot::PickAncestor(
+      wrapList->GetFrameActiveScrolledRoot(), *aContainerASR));
+}
+
+static void CopyASR(nsDisplayItem* aOld, nsDisplayItem* aNew) {
+  aNew->SetActiveScrolledRoot(aOld->GetActiveScrolledRoot());
+}
+
+OldItemInfo::OldItemInfo(nsDisplayItem* aItem)
+    : mItem(aItem), mUsed(false), mDiscarded(false), mOwnsItem(false) {
+  if (mItem) {
+    // Clear cached modified frame state when adding an item to the old list.
+    mItem->SetModifiedFrame(false);
+  }
+}
+
+void OldItemInfo::AddedMatchToMergedList(RetainedDisplayListBuilder* aBuilder,
+                                         MergedListIndex aIndex) {
+  AddedToMergedList(aIndex);
+}
+
+void OldItemInfo::Discard(RetainedDisplayListBuilder* aBuilder,
+                          nsTArray<MergedListIndex>&& aDirectPredecessors) {
+  MOZ_ASSERT(!IsUsed());
+  mUsed = mDiscarded = true;
+  mDirectPredecessors = std::move(aDirectPredecessors);
+  if (mItem) {
+    MOZ_ASSERT(mOwnsItem);
+    mItem->Destroy(aBuilder->Builder());
+    aBuilder->Metrics()->mRemovedItems++;
+  }
+  mItem = nullptr;
+}
+
+bool OldItemInfo::IsChanged() {
+  return !mItem || !mItem->CanBeReused() || mItem->HasDeletedFrame();
+}
+
+/**
+ * A C++ implementation of Markus Stange's merge-dags algorithm.
+ * https://github.com/mstange/merge-dags
+ *
+ * MergeState handles combining a new list of display items into an existing
+ * DAG and computes the new DAG in a single pass.
+ * Each time we add a new item, we resolve all dependencies for it, so that the
+ * resulting list and DAG are built in topological ordering.
+ */
+class MergeState {
+ public:
+  MergeState(RetainedDisplayListBuilder* aBuilder,
+             RetainedDisplayList& aOldList, nsDisplayItem* aOuterItem)
+      : mBuilder(aBuilder),
+        mOldList(&aOldList),
+        mOldItems(std::move(aOldList.mOldItems)),
+        mOldDAG(
+            std::move(*reinterpret_cast<DirectedAcyclicGraph<OldListUnits>*>(
+                &aOldList.mDAG))),
+        mMergedItems(aBuilder->Builder()),
+        mOuterItem(aOuterItem),
+        mResultIsModified(false) {
+    mMergedDAG.EnsureCapacityFor(mOldDAG);
+    MOZ_RELEASE_ASSERT(mOldItems.Length() == mOldDAG.Length());
+  }
+
+  Maybe<MergedListIndex> ProcessItemFromNewList(
+      nsDisplayItem* aNewItem, const Maybe<MergedListIndex>& aPreviousItem) {
+    OldListIndex oldIndex;
+    MOZ_DIAGNOSTIC_ASSERT(aNewItem->HasModifiedFrame() ==
+                          HasModifiedFrame(aNewItem));
+    if (!aNewItem->HasModifiedFrame() &&
+        HasMatchingItemInOldList(aNewItem, &oldIndex)) {
+      mBuilder->Metrics()->mRebuiltItems++;
+      nsDisplayItem* oldItem = mOldItems[oldIndex.val].mItem;
+      MOZ_DIAGNOSTIC_ASSERT(oldItem->GetPerFrameKey() ==
+                                aNewItem->GetPerFrameKey() &&
+                            oldItem->Frame() == aNewItem->Frame());
+      if (!mOldItems[oldIndex.val].IsChanged()) {
+        MOZ_DIAGNOSTIC_ASSERT(!mOldItems[oldIndex.val].IsUsed());
+        nsDisplayItem* destItem;
+        if (ShouldUseNewItem(aNewItem)) {
+          destItem = aNewItem;
+        } else {
+          destItem = oldItem;
+          // The building rect can depend on the overflow rect (when the parent
+          // frame is position:fixed), which can change without invalidating
+          // the frame/items. If we're using the old item, copy the building
+          // rect across from the new item.
+          oldItem->SetBuildingRect(aNewItem->GetBuildingRect());
+        }
+
+        if (destItem == aNewItem) {
+          if (oldItem->IsGlassItem() &&
+              oldItem == mBuilder->Builder()->GetGlassDisplayItem()) {
+            mBuilder->Builder()->ClearGlassDisplayItem();
+          }
+        }  // aNewItem can't be the glass item on the builder yet.
+
+        if (destItem->IsGlassItem()) {
+          if (destItem != oldItem ||
+              destItem != mBuilder->Builder()->GetGlassDisplayItem()) {
+            mBuilder->Builder()->SetGlassDisplayItem(destItem);
+          }
+        }
+
+        MergeChildLists(aNewItem, oldItem, destItem);
+
+        AutoTArray<MergedListIndex, 2> directPredecessors =
+            ProcessPredecessorsOfOldNode(oldIndex);
+        MergedListIndex newIndex = AddNewNode(
+            destItem, Some(oldIndex), directPredecessors, aPreviousItem);
+        mOldItems[oldIndex.val].AddedMatchToMergedList(mBuilder, newIndex);
+        if (destItem == aNewItem) {
+          oldItem->Destroy(mBuilder->Builder());
+        } else {
+          aNewItem->Destroy(mBuilder->Builder());
+        }
+        return Some(newIndex);
+      }
+    }
+    mResultIsModified = true;
+    if (aNewItem->IsGlassItem()) {
+      mBuilder->Builder()->SetGlassDisplayItem(aNewItem);
+    }
+    return Some(AddNewNode(aNewItem, Nothing(), Span<MergedListIndex>(),
+                           aPreviousItem));
+  }
+
+  void MergeChildLists(nsDisplayItem* aNewItem, nsDisplayItem* aOldItem,
+                       nsDisplayItem* aOutItem) {
+    if (!aOutItem->GetChildren()) {
+      return;
+    }
+
+    Maybe<const ActiveScrolledRoot*> containerASRForChildren;
+    nsDisplayList empty(mBuilder->Builder());
+    const bool modified = mBuilder->MergeDisplayLists(
+        aNewItem ? aNewItem->GetChildren() : &empty, aOldItem->GetChildren(),
+        aOutItem->GetChildren(), containerASRForChildren, aOutItem);
+    if (modified) {
+      aOutItem->InvalidateCachedChildInfo(mBuilder->Builder());
+      UpdateASR(aOutItem, containerASRForChildren);
+      mResultIsModified = true;
+    } else if (aOutItem == aNewItem) {
+      // If nothing changed, but we copied the contents across to
+      // the new item, then also copy the ASR data.
+      CopyASR(aOldItem, aNewItem);
+    }
+    // Ideally we'd only UpdateBounds if something changed, but
+    // nsDisplayWrapList also uses this to update the clip chain for the
+    // current ASR, which gets reset during RestoreState(), so we always need
+    // to run it again.
+    aOutItem->UpdateBounds(mBuilder->Builder());
+  }
+
+  bool ShouldUseNewItem(nsDisplayItem* aNewItem) {
+    // Generally we want to use the old item when the frame isn't marked as
+    // modified so that any cached information on the item (or referencing the
+    // item) gets retained. Quite a few FrameLayerBuilder performance
+    // improvements benefit by this. Sometimes, however, we can end up where the
+    // new item paints something different from the old item, even though we
+    // haven't modified the frame, and it's hard to fix. In these cases we just
+    // always use the new item to be safe.
+    DisplayItemType type = aNewItem->GetType();
+    if (type == DisplayItemType::TYPE_CANVAS_BACKGROUND_COLOR ||
+        type == DisplayItemType::TYPE_SOLID_COLOR) {
+      // The canvas background color item can paint the color from another
+      // frame, and even though we schedule a paint, we don't mark the canvas
+      // frame as invalid.
+      return true;
+    }
+
+    if (type == DisplayItemType::TYPE_TABLE_BORDER_COLLAPSE) {
+      // We intentionally don't mark the root table frame as modified when a
+      // subframe changes, even though the border collapse item for the root
+      // frame is what paints the changed border. Marking the root frame as
+      // modified would rebuild display items for the whole table area, and we
+      // don't want that.
+      return true;
+    }
+
+    if (type == DisplayItemType::TYPE_TEXT_OVERFLOW) {
+      // Text overflow marker items are created with the wrapping block as their
+      // frame, and have an index value to note which line they are created for.
+      // Their rendering can change if the items on that line change, which may
+      // not mark the block as modified. We rebuild them if we build any item on
+      // the line, so we should always get new items if they might have changed
+      // rendering, and it's easier to just use the new items rather than
+      // computing if we actually need them.
+      return true;
+    }
+
+    if (type == DisplayItemType::TYPE_SUBDOCUMENT ||
+        type == DisplayItemType::TYPE_STICKY_POSITION) {
+      // nsDisplaySubDocument::mShouldFlatten can change without an invalidation
+      // (and is the reason we unconditionally build the subdocument item), so
+      // always use the new one to make sure we get the right value.
+      // Same for |nsDisplayStickyPosition::mShouldFlatten|.
+      return true;
+    }
+
+    if (type == DisplayItemType::TYPE_CARET) {
+      // The caret can change position while still being owned by the same frame
+      // and we don't invalidate in that case. Use the new version since the
+      // changed bounds are needed for DLBI.
+      return true;
+    }
+
+    if (type == DisplayItemType::TYPE_MASK ||
+        type == DisplayItemType::TYPE_FILTER ||
+        type == DisplayItemType::TYPE_SVG_WRAPPER) {
+      // SVG items have some invalidation issues, see bugs 1494110 and 1494663.
+      return true;
+    }
+
+    if (type == DisplayItemType::TYPE_TRANSFORM) {
+      // Prerendering of transforms can change without frame invalidation.
+      return true;
+    }
+
+    return false;
+  }
+
+  RetainedDisplayList Finalize() {
+    for (size_t i = 0; i < mOldDAG.Length(); i++) {
+      if (mOldItems[i].IsUsed()) {
+        continue;
+      }
+
+      AutoTArray<MergedListIndex, 2> directPredecessors =
+          ResolveNodeIndexesOldToMerged(
+              mOldDAG.GetDirectPredecessors(OldListIndex(i)));
+      ProcessOldNode(OldListIndex(i), std::move(directPredecessors));
+    }
+
+    RetainedDisplayList result(mBuilder->Builder());
+    result.AppendToTop(&mMergedItems);
+    result.mDAG = std::move(mMergedDAG);
+    MOZ_RELEASE_ASSERT(result.mDAG.Length() == result.Length());
+    return result;
+  }
+
+  bool HasMatchingItemInOldList(nsDisplayItem* aItem, OldListIndex* aOutIndex) {
+    // Look for an item that matches aItem's frame and per-frame-key, but isn't
+    // the same item.
+    uint32_t outerKey = mOuterItem ? mOuterItem->GetPerFrameKey() : 0;
+    nsIFrame* frame = aItem->Frame();
+    for (nsDisplayItem* i : frame->DisplayItems()) {
+      if (i != aItem && i->Frame() == frame &&
+          i->GetPerFrameKey() == aItem->GetPerFrameKey()) {
+        if (i->GetOldListIndex(mOldList, outerKey, aOutIndex)) {
+          return true;
+        }
+      }
+    }
+    return false;
+  }
+
+#ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
+  bool HasModifiedFrame(nsDisplayItem* aItem) {
+    nsIFrame* stopFrame = mOuterItem ? mOuterItem->Frame() : nullptr;
+    return AnyContentAncestorModified(aItem->FrameForInvalidation(), stopFrame);
+  }
+#endif
+
+  void UpdateContainerASR(nsDisplayItem* aItem) {
+    mContainerASR = SelectContainerASR(
+        aItem->GetClipChain(), aItem->GetActiveScrolledRoot(), mContainerASR);
+  }
+
+  MergedListIndex AddNewNode(
+      nsDisplayItem* aItem, const Maybe<OldListIndex>& aOldIndex,
+      Span<const MergedListIndex> aDirectPredecessors,
+      const Maybe<MergedListIndex>& aExtraDirectPredecessor) {
+    UpdateContainerASR(aItem);
+    aItem->NotifyUsed(mBuilder->Builder());
+
+#ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
+    for (nsDisplayItem* i : aItem->Frame()->DisplayItems()) {
+      if (i->Frame() == aItem->Frame() &&
+          i->GetPerFrameKey() == aItem->GetPerFrameKey()) {
+        MOZ_DIAGNOSTIC_ASSERT(!i->IsMergedItem());
+      }
+    }
+
+    aItem->SetMergedPreProcessed(true, false);
+#endif
+
+    mMergedItems.AppendToTop(aItem);
+    mBuilder->Metrics()->mTotalItems++;
+
+    MergedListIndex newIndex =
+        mMergedDAG.AddNode(aDirectPredecessors, aExtraDirectPredecessor);
+    return newIndex;
+  }
+
+  void ProcessOldNode(OldListIndex aNode,
+                      nsTArray<MergedListIndex>&& aDirectPredecessors) {
+    nsDisplayItem* item = mOldItems[aNode.val].mItem;
+    if (mOldItems[aNode.val].IsChanged()) {
+      if (item && item->IsGlassItem() &&
+          item == mBuilder->Builder()->GetGlassDisplayItem()) {
+        mBuilder->Builder()->ClearGlassDisplayItem();
+      }
+
+      mOldItems[aNode.val].Discard(mBuilder, std::move(aDirectPredecessors));
+      mResultIsModified = true;
+    } else {
+      MergeChildLists(nullptr, item, item);
+
+      if (item->GetType() == DisplayItemType::TYPE_SUBDOCUMENT) {
+        mBuilder->IncrementSubDocPresShellPaintCount(item);
+      }
+      item->SetReused(true);
+      mBuilder->Metrics()->mReusedItems++;
+      mOldItems[aNode.val].AddedToMergedList(
+          AddNewNode(item, Some(aNode), aDirectPredecessors, Nothing()));
+    }
+  }
+
+  struct PredecessorStackItem {
+    PredecessorStackItem(OldListIndex aNode, Span<OldListIndex> aPredecessors)
+        : mNode(aNode),
+          mDirectPredecessors(aPredecessors),
+          mCurrentPredecessorIndex(0) {}
+
+    bool IsFinished() {
+      return mCurrentPredecessorIndex == mDirectPredecessors.Length();
+    }
+
+    OldListIndex GetAndIncrementCurrentPredecessor() {
+      return mDirectPredecessors[mCurrentPredecessorIndex++];
+    }
+
+    OldListIndex mNode;
+    Span<OldListIndex> mDirectPredecessors;
+    size_t mCurrentPredecessorIndex;
+  };
+
+  AutoTArray<MergedListIndex, 2> ProcessPredecessorsOfOldNode(
+      OldListIndex aNode) {
+    AutoTArray<PredecessorStackItem, 256> mStack;
+    mStack.AppendElement(
+        PredecessorStackItem(aNode, mOldDAG.GetDirectPredecessors(aNode)));
+
+    while (true) {
+      if (mStack.LastElement().IsFinished()) {
+        // If we've finished processing all the entries in the current set, then
+        // pop it off the processing stack and process it.
+        PredecessorStackItem item = mStack.PopLastElement();
+        AutoTArray<MergedListIndex, 2> result =
+            ResolveNodeIndexesOldToMerged(item.mDirectPredecessors);
+
+        if (mStack.IsEmpty()) {
+          return result;
+        }
+
+        ProcessOldNode(item.mNode, std::move(result));
+      } else {
+        // Grab the current predecessor, push predecessors of that onto the
+        // processing stack (if it hasn't already been processed), and then
+        // advance to the next entry.
+        OldListIndex currentIndex =
+            mStack.LastElement().GetAndIncrementCurrentPredecessor();
+        if (!mOldItems[currentIndex.val].IsUsed()) {
+          mStack.AppendElement(PredecessorStackItem(
+              currentIndex, mOldDAG.GetDirectPredecessors(currentIndex)));
+        }
+      }
+    }
+  }
+
+  AutoTArray<MergedListIndex, 2> ResolveNodeIndexesOldToMerged(
+      Span<OldListIndex> aDirectPredecessors) {
+    AutoTArray<MergedListIndex, 2> result;
+    result.SetCapacity(aDirectPredecessors.Length());
+    for (OldListIndex index : aDirectPredecessors) {
+      OldItemInfo& oldItem = mOldItems[index.val];
+      if (oldItem.IsDiscarded()) {
+        for (MergedListIndex inner : oldItem.mDirectPredecessors) {
+          if (!result.Contains(inner)) {
+            result.AppendElement(inner);
+          }
+        }
+      } else {
+        result.AppendElement(oldItem.mIndex);
+      }
+    }
+    return result;
+  }
+
+  RetainedDisplayListBuilder* mBuilder;
+  RetainedDisplayList* mOldList;
+  Maybe<const ActiveScrolledRoot*> mContainerASR;
+  nsTArray<OldItemInfo> mOldItems;
+  DirectedAcyclicGraph<OldListUnits> mOldDAG;
+  // Unfortunately we can't use strong typing for the hashtables
+  // since they internally encode the type with the mOps pointer,
+  // and assert when we try swap the contents
+  nsDisplayList mMergedItems;
+  DirectedAcyclicGraph<MergedListUnits> mMergedDAG;
+  nsDisplayItem* mOuterItem;
+  bool mResultIsModified;
+};
+
+#ifdef DEBUG
+void VerifyNotModified(nsDisplayList* aList) {
+  for (nsDisplayItem* item : *aList) {
+    MOZ_ASSERT(!AnyContentAncestorModified(item->FrameForInvalidation()));
+
+    if (item->GetChildren()) {
+      VerifyNotModified(item->GetChildren());
+    }
+  }
+}
+#endif
+
+/**
+ * Takes two display lists and merges them into an output list.
+ *
+ * Display lists wthout an explicit DAG are interpreted as linear DAGs (with a
+ * maximum of one direct predecessor and one direct successor per node). We add
+ * the two DAGs together, and then output the topological sorted ordering as the
+ * final display list.
+ *
+ * Once we've merged a list, we then retain the DAG (as part of the
+ * RetainedDisplayList object) to use for future merges.
+ */
+bool RetainedDisplayListBuilder::MergeDisplayLists(
+    nsDisplayList* aNewList, RetainedDisplayList* aOldList,
+    RetainedDisplayList* aOutList,
+    mozilla::Maybe<const mozilla::ActiveScrolledRoot*>& aOutContainerASR,
+    nsDisplayItem* aOuterItem) {
+  AUTO_PROFILER_LABEL_CATEGORY_PAIR(GRAPHICS_DisplayListMerging);
+
+  if (!aOldList->IsEmpty()) {
+    // If we still have items in the actual list, then it is because
+    // PreProcessDisplayList decided that it was sure it can't be modified. We
+    // can just use it directly, and throw any new items away.
+
+    aNewList->DeleteAll(&mBuilder);
+#ifdef DEBUG
+    VerifyNotModified(aOldList);
+#endif
+
+    if (aOldList != aOutList) {
+      *aOutList = std::move(*aOldList);
+    }
+
+    return false;
+  }
+
+  MergeState merge(this, *aOldList, aOuterItem);
+
+  Maybe<MergedListIndex> previousItemIndex;
+  for (nsDisplayItem* item : aNewList->TakeItems()) {
+    Metrics()->mNewItems++;
+    previousItemIndex = merge.ProcessItemFromNewList(item, previousItemIndex);
+  }
+
+  *aOutList = merge.Finalize();
+  aOutContainerASR = merge.mContainerASR;
+  return merge.mResultIsModified;
+}
+
+void RetainedDisplayListBuilder::GetModifiedAndFramesWithProps(
+    nsTArray<nsIFrame*>* aOutModifiedFrames,
+    nsTArray<nsIFrame*>* aOutFramesWithProps) {
+  for (auto it = Data()->ConstIterator(); !it.Done(); it.Next()) {
+    nsIFrame* frame = it.Key();
+    const RetainedDisplayListData::FrameFlags& flags = it.Data();
+
+    if (flags.contains(RetainedDisplayListData::FrameFlag::Modified)) {
+      aOutModifiedFrames->AppendElement(frame);
+    }
+
+    if (flags.contains(RetainedDisplayListData::FrameFlag::HasProps)) {
+      aOutFramesWithProps->AppendElement(frame);
+    }
+
+    if (flags.contains(RetainedDisplayListData::FrameFlag::HadWillChange)) {
+      Builder()->RemoveFromWillChangeBudgets(frame);
+    }
+  }
+
+  Data()->Clear();
+}
+
+// ComputeRebuildRegion  debugging
+// #define CRR_DEBUG 1
+#if CRR_DEBUG
+#  define CRR_LOG(...) printf_stderr(__VA_ARGS__)
+#else
+#  define CRR_LOG(...)
+#endif
+
+static nsDisplayItem* GetFirstDisplayItemWithChildren(nsIFrame* aFrame) {
+  for (nsDisplayItem* i : aFrame->DisplayItems()) {
+    if (i->HasDeletedFrame() || i->Frame() != aFrame) {
+      // The main frame for the display item has been deleted or the display
+      // item belongs to another frame.
+      continue;
+    }
+
+    if (i->HasChildren()) {
+      return static_cast<nsDisplayItem*>(i);
+    }
+  }
+  return nullptr;
+}
+
+static bool IsInPreserve3DContext(const nsIFrame* aFrame) {
+  return aFrame->Extend3DContext() ||
+         aFrame->Combines3DTransformWithAncestors();
+}
+
+// Returns true if |aFrame| can store a display list building rect.
+// These limitations are necessary to guarantee that
+// 1) Just enough items are rebuilt to properly update display list
+// 2) Modified frames will be visited during a partial display list build.
+static bool CanStoreDisplayListBuildingRect(nsDisplayListBuilder* aBuilder,
+                                            nsIFrame* aFrame) {
+  return aFrame != aBuilder->RootReferenceFrame() &&
+         aFrame->IsStackingContext() && aFrame->IsFixedPosContainingBlock() &&
+         // Split frames might have placeholders for modified frames in their
+         // unmodified continuation frame.
+         !aFrame->GetPrevContinuation() && !aFrame->GetNextContinuation();
+}
+
+static bool ProcessFrameInternal(nsIFrame* aFrame,
+                                 nsDisplayListBuilder* aBuilder,
+                                 nsIFrame** aAGR, nsRect& aOverflow,
+                                 const nsIFrame* aStopAtFrame,
+                                 nsTArray<nsIFrame*>& aOutFramesWithProps,
+                                 const bool aStopAtStackingContext) {
+  nsIFrame* currentFrame = aFrame;
+
+  while (currentFrame != aStopAtFrame) {
+    CRR_LOG("currentFrame: %p (placeholder=%d), aOverflow: %d %d %d %d\n",
+            currentFrame, !aStopAtStackingContext, aOverflow.x, aOverflow.y,
+            aOverflow.width, aOverflow.height);
+
+    // If the current frame is an OOF frame, DisplayListBuildingData needs to be
+    // set on all the ancestor stacking contexts of the  placeholder frame, up
+    // to the containing block of the OOF frame. This is done to ensure that the
+    // content that might be behind the OOF frame is built for merging.
+    nsIFrame* placeholder = currentFrame->HasAnyStateBits(NS_FRAME_OUT_OF_FLOW)
+                                ? currentFrame->GetPlaceholderFrame()
+                                : nullptr;
+
+    if (placeholder) {
+      nsRect placeholderOverflow = aOverflow;
+      auto rv = nsLayoutUtils::TransformRect(currentFrame, placeholder,
+                                             placeholderOverflow);
+      if (rv != nsLayoutUtils::TRANSFORM_SUCCEEDED) {
+        placeholderOverflow = nsRect();
+      }
+
+      CRR_LOG("Processing placeholder %p for OOF frame %p\n", placeholder,
+              currentFrame);
+
+      CRR_LOG("OOF frame draw area: %d %d %d %d\n", placeholderOverflow.x,
+              placeholderOverflow.y, placeholderOverflow.width,
+              placeholderOverflow.height);
+
+      // Tracking AGRs for the placeholder processing is not necessary, as the
+      // goal is to only modify the DisplayListBuildingData rect.
+      nsIFrame* dummyAGR = nullptr;
+
+      // Find a common ancestor frame to handle frame continuations.
+      // TODO: It might be possible to write a more specific and efficient
+      // function for this.
+      const nsIFrame* ancestor = nsLayoutUtils::FindNearestCommonAncestorFrame(
+          currentFrame->GetParent(), placeholder->GetParent());
+
+      if (!ProcessFrameInternal(placeholder, aBuilder, &dummyAGR,
+                                placeholderOverflow, ancestor,
+                                aOutFramesWithProps, false)) {
+        return false;
+      }
+    }
+
+    // Convert 'aOverflow' into the coordinate space of the nearest stacking
+    // context or display port ancestor and update 'currentFrame' to point to
+    // that frame.
+    aOverflow = nsLayoutUtils::TransformFrameRectToAncestor(
+        currentFrame, aOverflow, aStopAtFrame, nullptr, nullptr,
+        /* aStopAtStackingContextAndDisplayPortAndOOFFrame = */ true,
+        &currentFrame);
+    if (IsInPreserve3DContext(currentFrame)) {
+      return false;
+    }
+
+    MOZ_ASSERT(currentFrame);
+
+    // Check whether the current frame is a scrollable frame with display port.
+    nsRect displayPort;
+    nsIScrollableFrame* sf = do_QueryFrame(currentFrame);
+    nsIContent* content = sf ? currentFrame->GetContent() : nullptr;
+
+    if (content && DisplayPortUtils::GetDisplayPort(content, &displayPort)) {
+      CRR_LOG("Frame belongs to displayport frame %p\n", currentFrame);
+
+      // Get overflow relative to the scrollport (from the scrollframe)
+      nsRect r = aOverflow - sf->GetScrollPortRect().TopLeft();
+      r.IntersectRect(r, displayPort);
+      if (!r.IsEmpty()) {
+        nsRect* rect = currentFrame->GetProperty(
+            nsDisplayListBuilder::DisplayListBuildingDisplayPortRect());
+        if (!rect) {
+          rect = new nsRect();
+          currentFrame->SetProperty(
+              nsDisplayListBuilder::DisplayListBuildingDisplayPortRect(), rect);
+          currentFrame->SetHasOverrideDirtyRegion(true);
+          aOutFramesWithProps.AppendElement(currentFrame);
+        }
+        rect->UnionRect(*rect, r);
+        CRR_LOG("Adding area to displayport draw area: %d %d %d %d\n", r.x, r.y,
+                r.width, r.height);
+
+        // TODO: Can we just use MarkFrameForDisplayIfVisible, plus
+        // MarkFramesForDifferentAGR to ensure that this displayport, plus any
+        // items that move relative to it get rebuilt, and then not contribute
+        // to the root dirty area?
+        aOverflow = sf->GetScrollPortRect();
+      } else {
+        // Don't contribute to the root dirty area at all.
+        aOverflow.SetEmpty();
+      }
+    } else {
+      aOverflow.IntersectRect(aOverflow,
+                              currentFrame->InkOverflowRectRelativeToSelf());
+    }
+
+    if (aOverflow.IsEmpty()) {
+      break;
+    }
+
+    if (CanStoreDisplayListBuildingRect(aBuilder, currentFrame)) {
+      CRR_LOG("Frame belongs to stacking context frame %p\n", currentFrame);
+      // If we found an intermediate stacking context with an existing display
+      // item then we can store the dirty rect there and stop. If we couldn't
+      // find one then we need to keep bubbling up to the next stacking context.
+      nsDisplayItem* wrapperItem =
+          GetFirstDisplayItemWithChildren(currentFrame);
+      if (!wrapperItem) {
+        continue;
+      }
+
+      // Store the stacking context relative dirty area such
+      // that display list building will pick it up when it
+      // gets to it.
+      nsDisplayListBuilder::DisplayListBuildingData* data =
+          currentFrame->GetProperty(
+              nsDisplayListBuilder::DisplayListBuildingRect());
+      if (!data) {
+        data = new nsDisplayListBuilder::DisplayListBuildingData();
+        currentFrame->SetProperty(
+            nsDisplayListBuilder::DisplayListBuildingRect(), data);
+        currentFrame->SetHasOverrideDirtyRegion(true);
+        aOutFramesWithProps.AppendElement(currentFrame);
+      }
+      CRR_LOG("Adding area to stacking context draw area: %d %d %d %d\n",
+              aOverflow.x, aOverflow.y, aOverflow.width, aOverflow.height);
+      data->mDirtyRect.UnionRect(data->mDirtyRect, aOverflow);
+
+      if (!aStopAtStackingContext) {
+        // Continue ascending the frame tree until we reach aStopAtFrame.
+        continue;
+      }
+
+      // Grab the visible (display list building) rect for children of this
+      // wrapper item and convert into into coordinate relative to the current
+      // frame.
+      nsRect previousVisible = wrapperItem->GetBuildingRectForChildren();
+      if (wrapperItem->ReferenceFrameForChildren() != wrapperItem->Frame()) {
+        previousVisible -= wrapperItem->ToReferenceFrame();
+      }
+
+      if (!previousVisible.Contains(aOverflow)) {
+        // If the overflow area of the changed frame isn't contained within the
+        // old item, then we might change the size of the item and need to
+        // update its sorting accordingly. Keep propagating the overflow area up
+        // so that we build intersecting items for sorting.
+        continue;
+      }
+
+      if (!data->mModifiedAGR) {
+        data->mModifiedAGR = *aAGR;
+      } else if (data->mModifiedAGR != *aAGR) {
+        data->mDirtyRect = currentFrame->InkOverflowRectRelativeToSelf();
+        CRR_LOG(
+            "Found multiple modified AGRs within this stacking context, "
+            "giving up\n");
+      }
+
+      // Don't contribute to the root dirty area at all.
+      aOverflow.SetEmpty();
+      *aAGR = nullptr;
+
+      break;
+    }
+  }
+  return true;
+}
+
+bool RetainedDisplayListBuilder::ProcessFrame(
+    nsIFrame* aFrame, nsDisplayListBuilder* aBuilder, nsIFrame* aStopAtFrame,
+    nsTArray<nsIFrame*>& aOutFramesWithProps, const bool aStopAtStackingContext,
+    nsRect* aOutDirty, nsIFrame** aOutModifiedAGR) {
+  if (aFrame->HasOverrideDirtyRegion()) {
+    aOutFramesWithProps.AppendElement(aFrame);
+  }
+
+  if (aFrame->HasAnyStateBits(NS_FRAME_IN_POPUP)) {
+    return true;
+  }
+
+  // TODO: There is almost certainly a faster way of doing this, probably can be
+  // combined with the ancestor walk for TransformFrameRectToAncestor.
+  nsIFrame* agrFrame = aBuilder->FindAnimatedGeometryRootFrameFor(aFrame);
+
+  CRR_LOG("Processing frame %p with agr %p\n", aFrame, agr->mFrame);
+
+  // Convert the frame's overflow rect into the coordinate space
+  // of the nearest stacking context that has an existing display item.
+  // We store that as a dirty rect on that stacking context so that we build
+  // all items that intersect the changed frame within the stacking context,
+  // and then we use MarkFrameForDisplayIfVisible to make sure the stacking
+  // context itself gets built. We don't need to build items that intersect
+  // outside of the stacking context, since we know the stacking context item
+  // exists in the old list, so we can trivially merge without needing other
+  // items.
+  nsRect overflow = aFrame->InkOverflowRectRelativeToSelf();
+
+  // If the modified frame is also a caret frame, include the caret area.
+  // This is needed because some frames (for example text frames without text)
+  // might have an empty overflow rect.
+  if (aFrame == aBuilder->GetCaretFrame()) {
+    overflow.UnionRect(overflow, aBuilder->GetCaretRect());
+  }
+
+  if (!ProcessFrameInternal(aFrame, aBuilder, &agrFrame, overflow, aStopAtFrame,
+                            aOutFramesWithProps, aStopAtStackingContext)) {
+    return false;
+  }
+
+  if (!overflow.IsEmpty()) {
+    aOutDirty->UnionRect(*aOutDirty, overflow);
+    CRR_LOG("Adding area to root draw area: %d %d %d %d\n", overflow.x,
+            overflow.y, overflow.width, overflow.height);
+
+    // If we get changed frames from multiple AGRS, then just give up as it gets
+    // really complex to track which items would need to be marked in
+    // MarkFramesForDifferentAGR.
+    if (!*aOutModifiedAGR) {
+      CRR_LOG("Setting %p as root stacking context AGR\n", agrFrame);
+      *aOutModifiedAGR = agrFrame;
+    } else if (agrFrame && *aOutModifiedAGR != agrFrame) {
+      CRR_LOG("Found multiple AGRs in root stacking context, giving up\n");
+      return false;
+    }
+  }
+  return true;
+}
+
+static void AddFramesForContainingBlock(nsIFrame* aBlock,
+                                        const nsFrameList& aFrames,
+                                        nsTArray<nsIFrame*>& aExtraFrames) {
+  for (nsIFrame* f : aFrames) {
+    if (!f->IsFrameModified() && AnyContentAncestorModified(f, aBlock)) {
+      CRR_LOG("Adding invalid OOF %p\n", f);
+      aExtraFrames.AppendElement(f);
+    }
+  }
+}
+
+// Placeholder descendants of aFrame don't contribute to aFrame's overflow area.
+// Find all the containing blocks that might own placeholders under us, walk
+// their OOF frames list, and manually invalidate any frames that are
+// descendants of a modified frame (us, or another frame we'll get to soon).
+// This is combined with the work required for MarkFrameForDisplayIfVisible,
+// so that we can avoid an extra ancestor walk, and we can reuse the flag
+// to detect when we've already visited an ancestor (and thus all further
+// ancestors must also be visited).
+static void FindContainingBlocks(nsIFrame* aFrame,
+                                 nsTArray<nsIFrame*>& aExtraFrames) {
+  for (nsIFrame* f = aFrame; f; f = nsLayoutUtils::GetDisplayListParent(f)) {
+    if (f->ForceDescendIntoIfVisible()) {
+      return;
+    }
+    f->SetForceDescendIntoIfVisible(true);
+    CRR_LOG("Considering OOFs for %p\n", f);
+
+    AddFramesForContainingBlock(f, f->GetChildList(FrameChildListID::Float),
+                                aExtraFrames);
+    AddFramesForContainingBlock(f, f->GetChildList(f->GetAbsoluteListID()),
+                                aExtraFrames);
+  }
+}
+
+/**
+ * Given a list of frames that has been modified, computes the region that we
+ * need to do display list building for in order to build all modified display
+ * items.
+ *
+ * When a modified frame is within a stacking context (with an existing display
+ * item), then we only contribute to the build area within the stacking context,
+ * as well as forcing display list building to descend to the stacking context.
+ * We don't need to add build area outside of the stacking context (and force
+ * items above/below the stacking context container item to be built), since
+ * just matching the position of the stacking context container item is
+ * sufficient to ensure correct ordering during merging.
+ *
+ * We need to rebuild all items that might intersect with the modified frame,
+ * both now and during async changes on the compositor. We do this by rebuilding
+ * the area covered by the changed frame, as well as rebuilding all items that
+ * have a different (async) AGR to the changed frame. If we have changes to
+ * multiple AGRs (within a stacking context), then we rebuild that stacking
+ * context entirely.
+ *
+ * @param aModifiedFrames The list of modified frames.
+ * @param aOutDirty The result region to use for display list building.
+ * @param aOutModifiedAGR The modified AGR for the root stacking context.
+ * @param aOutFramesWithProps The list of frames to which we attached partial
+ * build data so that it can be cleaned up.
+ *
+ * @return true if we succesfully computed a partial rebuild region, false if a
+ * full build is required.
+ */
+bool RetainedDisplayListBuilder::ComputeRebuildRegion(
+    nsTArray<nsIFrame*>& aModifiedFrames, nsRect* aOutDirty,
+    nsIFrame** aOutModifiedAGR, nsTArray<nsIFrame*>& aOutFramesWithProps) {
+  CRR_LOG("Computing rebuild regions for %zu frames:\n",
+          aModifiedFrames.Length());
+  nsTArray<nsIFrame*> extraFrames;
+  for (nsIFrame* f : aModifiedFrames) {
+    MOZ_ASSERT(f);
+
+    mBuilder.AddFrameMarkedForDisplayIfVisible(f);
+    FindContainingBlocks(f, extraFrames);
+
+    if (!ProcessFrame(f, &mBuilder, RootReferenceFrame(), aOutFramesWithProps,
+                      true, aOutDirty, aOutModifiedAGR)) {
+      return false;
+    }
+  }
+
+  // Since we set modified to true on the extraFrames, add them to
+  // aModifiedFrames so that it will get reverted.
+  aModifiedFrames.AppendElements(extraFrames);
+
+  for (nsIFrame* f : extraFrames) {
+    f->SetFrameIsModified(true);
+
+    if (!ProcessFrame(f, &mBuilder, RootReferenceFrame(), aOutFramesWithProps,
+                      true, aOutDirty, aOutModifiedAGR)) {
+      return false;
+    }
+  }
+
+  return true;
+}
+
+bool RetainedDisplayListBuilder::ShouldBuildPartial(
+    nsTArray<nsIFrame*>& aModifiedFrames) {
+  if (mList.IsEmpty()) {
+    // Partial builds without a previous display list do not make sense.
+    Metrics()->mPartialUpdateFailReason = PartialUpdateFailReason::EmptyList;
+    return false;
+  }
+
+  if (aModifiedFrames.Length() >
+      StaticPrefs::layout_display_list_rebuild_frame_limit()) {
+    // Computing a dirty rect with too many modified frames can be slow.
+    Metrics()->mPartialUpdateFailReason = PartialUpdateFailReason::RebuildLimit;
+    return false;
+  }
+
+  // We don't support retaining with overlay scrollbars, since they require
+  // us to look at the display list and pick the highest z-index, which
+  // we can't do during partial building.
+  if (mBuilder.DisablePartialUpdates()) {
+    mBuilder.SetDisablePartialUpdates(false);
+    Metrics()->mPartialUpdateFailReason = PartialUpdateFailReason::Disabled;
+    return false;
+  }
+
+  for (nsIFrame* f : aModifiedFrames) {
+    MOZ_ASSERT(f);
+
+    const LayoutFrameType type = f->Type();
+
+    // If we have any modified frames of the following types, it is likely that
+    // doing a partial rebuild of the display list will be slower than doing a
+    // full rebuild.
+    // This is because these frames either intersect or may intersect with most
+    // of the page content. This is either due to display port size or different
+    // async AGR.
+    if (type == LayoutFrameType::Viewport ||
+        type == LayoutFrameType::PageContent ||
+        type == LayoutFrameType::Canvas || type == LayoutFrameType::Scrollbar) {
+      Metrics()->mPartialUpdateFailReason = PartialUpdateFailReason::FrameType;
+      return false;
+    }
+
+    // Detect root scroll frame and do a full rebuild for them too for the same
+    // reasons as above, but also because top layer items should to be marked
+    // modified if the root scroll frame is modified. Putting this check here
+    // means we don't need to check everytime a frame is marked modified though.
+    if (type == LayoutFrameType::Scroll && f->GetParent() &&
+        !f->GetParent()->GetParent()) {
+      Metrics()->mPartialUpdateFailReason = PartialUpdateFailReason::FrameType;
+      return false;
+    }
+  }
+
+  return true;
+}
+
+void RetainedDisplayListBuilder::InvalidateCaretFramesIfNeeded() {
+  if (mPreviousCaret == mBuilder.GetCaretFrame()) {
+    // The current caret frame is the same as the previous one.
+    return;
+  }
+
+  if (mPreviousCaret) {
+    mPreviousCaret->MarkNeedsDisplayItemRebuild();
+  }
+
+  if (mBuilder.GetCaretFrame()) {
+    mBuilder.GetCaretFrame()->MarkNeedsDisplayItemRebuild();
+  }
+
+  mPreviousCaret = mBuilder.GetCaretFrame();
+}
+
+static void ClearFrameProps(nsTArray<nsIFrame*>& aFrames) {
+  for (nsIFrame* f : aFrames) {
+    DL_LOGV("RDL - Clearing modified flags for frame %p", f);
+    if (f->HasOverrideDirtyRegion()) {
+      f->SetHasOverrideDirtyRegion(false);
+      f->RemoveProperty(nsDisplayListBuilder::DisplayListBuildingRect());
+      f->RemoveProperty(
+          nsDisplayListBuilder::DisplayListBuildingDisplayPortRect());
+    }
+
+    f->SetFrameIsModified(false);
+    f->SetHasModifiedDescendants(false);
+  }
+}
+
+class AutoClearFramePropsArray {
+ public:
+  explicit AutoClearFramePropsArray(size_t aCapacity) : mFrames(aCapacity) {}
+  AutoClearFramePropsArray() = default;
+  ~AutoClearFramePropsArray() { ClearFrameProps(mFrames); }
+
+  nsTArray<nsIFrame*>& Frames() { return mFrames; }
+  bool IsEmpty() const { return mFrames.IsEmpty(); }
+
+ private:
+  nsTArray<nsIFrame*> mFrames;
+};
+
+void RetainedDisplayListBuilder::ClearFramesWithProps() {
+  AutoClearFramePropsArray modifiedFrames;
+  AutoClearFramePropsArray framesWithProps;
+  GetModifiedAndFramesWithProps(&modifiedFrames.Frames(),
+                                &framesWithProps.Frames());
+}
+
+void RetainedDisplayListBuilder::ClearRetainedData() {
+  DL_LOGI("(%p) RDL - Clearing retained display list builder data", this);
+  List()->DeleteAll(Builder());
+  ClearFramesWithProps();
+  ClearReuseableDisplayItems();
+}
+
+namespace RDLUtils {
+
+MOZ_NEVER_INLINE_DEBUG void AssertFrameSubtreeUnmodified(
+    const nsIFrame* aFrame) {
+  MOZ_ASSERT(!aFrame->IsFrameModified());
+  MOZ_ASSERT(!aFrame->HasModifiedDescendants());
+
+  for (const auto& childList : aFrame->ChildLists()) {
+    for (nsIFrame* child : childList.mList) {
+      AssertFrameSubtreeUnmodified(child);
+    }
+  }
+}
+
+MOZ_NEVER_INLINE_DEBUG void AssertDisplayListUnmodified(nsDisplayList* aList) {
+  for (nsDisplayItem* item : *aList) {
+    AssertDisplayItemUnmodified(item);
+  }
+}
+
+MOZ_NEVER_INLINE_DEBUG void AssertDisplayItemUnmodified(nsDisplayItem* aItem) {
+  MOZ_ASSERT(!aItem->HasDeletedFrame());
+  MOZ_ASSERT(!AnyContentAncestorModified(aItem->FrameForInvalidation()));
+
+  if (aItem->GetChildren()) {
+    AssertDisplayListUnmodified(aItem->GetChildren());
+  }
+}
+
+}  // namespace RDLUtils
+
+namespace RDL {
+
+void MarkAncestorFrames(nsIFrame* aFrame,
+                        nsTArray<nsIFrame*>& aOutFramesWithProps) {
+  nsIFrame* frame = nsLayoutUtils::GetDisplayListParent(aFrame);
+  while (frame && !frame->HasModifiedDescendants()) {
+    aOutFramesWithProps.AppendElement(frame);
+    frame->SetHasModifiedDescendants(true);
+    frame = nsLayoutUtils::GetDisplayListParent(frame);
+  }
+}
+
+/**
+ * Iterates over the modified frames array and updates the frame tree flags
+ * so that container frames know whether they have modified descendant frames.
+ * Frames that were marked modified are added to |aOutFramesWithProps|, so that
+ * the modified status can be cleared after the display list build.
+ */
+void MarkAllAncestorFrames(const nsTArray<nsIFrame*>& aModifiedFrames,
+                           nsTArray<nsIFrame*>& aOutFramesWithProps) {
+  nsAutoString frameName;
+  DL_LOGI("RDL - Modified frames: %zu", aModifiedFrames.Length());
+  for (nsIFrame* frame : aModifiedFrames) {
+#ifdef DEBUG
+    frame->GetFrameName(frameName);
+#endif
+    DL_LOGV("RDL - Processing modified frame: %p (%s)", frame,
+            NS_ConvertUTF16toUTF8(frameName).get());
+
+    MarkAncestorFrames(frame, aOutFramesWithProps);
+  }
+}
+
+/**
+ * Marks the given display item |aItem| as reuseable container, and updates the
+ * bounds in case some child items were destroyed.
+ */
+MOZ_NEVER_INLINE_DEBUG void ReuseStackingContextItem(
+    nsDisplayListBuilder* aBuilder, nsDisplayItem* aItem) {
+  aItem->SetPreProcessed();
+
+  if (aItem->HasChildren()) {
+    aItem->UpdateBounds(aBuilder);
+  }
+
+  aBuilder->AddReusableDisplayItem(aItem);
+  DL_LOGD("Reusing display item %p", aItem);
+}
+
+bool IsSupportedFrameType(const nsIFrame* aFrame) {
+  // The way table backgrounds are handled makes these frames incompatible with
+  // this retained display list approach.
+  if (aFrame->IsTableColFrame()) {
+    return false;
+  }
+
+  if (aFrame->IsTableColGroupFrame()) {
+    return false;
+  }
+
+  if (aFrame->IsTableRowFrame()) {
+    return false;
+  }
+
+  if (aFrame->IsTableRowGroupFrame()) {
+    return false;
+  }
+
+  if (aFrame->IsTableCellFrame()) {
+    return false;
+  }
+
+  // Everything else should work.
+  return true;
+}
+
+bool IsReuseableStackingContextItem(nsDisplayItem* aItem) {
+  if (!IsSupportedFrameType(aItem->Frame())) {
+    return false;
+  }
+
+  if (!aItem->IsReusable()) {
+    return false;
+  }
+
+  const nsIFrame* frame = aItem->FrameForInvalidation();
+  return !frame->HasModifiedDescendants() && !frame->GetPrevContinuation() &&
+         !frame->GetNextContinuation();
+}
+
+/**
+ * Recursively visits every display item of the display list and destroys all
+ * display items that depend on deleted or modified frames.
+ * The stacking context display items for unmodified frame subtrees are kept
+ * linked and collected in given |aOutItems| array.
+ */
+void CollectStackingContextItems(nsDisplayListBuilder* aBuilder,
+                                 nsDisplayList* aList, nsIFrame* aOuterFrame,
+                                 int aDepth = 0, bool aParentReused = false) {
+  for (nsDisplayItem* item : aList->TakeItems()) {
+    if (DL_LOG_TEST(LogLevel::Debug)) {
+      DL_LOGD(
+          "%*s Preprocessing item %p (%s) (frame: %p) "
+          "(children: %zu) (depth: %d) (parentReused: %d)",
+          aDepth, "", item, item->Name(),
+          item->HasDeletedFrame() ? nullptr : item->Frame(),
+          item->GetChildren() ? item->GetChildren()->Length() : 0, aDepth,
+          aParentReused);
+    }
+
+    if (!item->CanBeReused() || item->HasDeletedFrame() ||
+        AnyContentAncestorModified(item->FrameForInvalidation(), aOuterFrame)) {
+      DL_LOGD("%*s Deleted modified or temporary item %p", aDepth, "", item);
+      item->Destroy(aBuilder);
+      continue;
+    }
+
+    MOZ_ASSERT(!AnyContentAncestorModified(item->FrameForInvalidation()));
+    MOZ_ASSERT(!item->IsPreProcessed());
+    item->InvalidateCachedChildInfo(aBuilder);
+#ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
+    item->SetMergedPreProcessed(false, true);
+#endif
+    item->SetReused(true);
+
+    const bool isStackingContextItem = IsReuseableStackingContextItem(item);
+
+    if (item->GetChildren()) {
+      CollectStackingContextItems(aBuilder, item->GetChildren(), item->Frame(),
+                                  aDepth + 1,
+                                  aParentReused || isStackingContextItem);
+    }
+
+    if (aParentReused) {
+      // Keep the contents of the current container item linked.
+#ifdef DEBUG
+      RDLUtils::AssertDisplayItemUnmodified(item);
+#endif
+      aList->AppendToTop(item);
+    } else if (isStackingContextItem) {
+      // |item| is a stacking context item that can be reused.
+      ReuseStackingContextItem(aBuilder, item);
+    } else {
+      // |item| is inside a container item that will be destroyed later.
+      DL_LOGD("%*s Deleted unused item %p", aDepth, "", item);
+      item->Destroy(aBuilder);
+      continue;
+    }
+
+    if (item->GetType() == DisplayItemType::TYPE_SUBDOCUMENT) {
+      IncrementPresShellPaintCount(aBuilder, item);
+    }
+  }
+}
+
+}  // namespace RDL
+
+bool RetainedDisplayListBuilder::TrySimpleUpdate(
+    const nsTArray<nsIFrame*>& aModifiedFrames,
+    nsTArray<nsIFrame*>& aOutFramesWithProps) {
+  if (!mBuilder.IsReusingStackingContextItems()) {
+    return false;
+  }
+
+  RDL::MarkAllAncestorFrames(aModifiedFrames, aOutFramesWithProps);
+  RDL::CollectStackingContextItems(&mBuilder, &mList, RootReferenceFrame());
+
+  return true;
+}
+
+PartialUpdateResult RetainedDisplayListBuilder::AttemptPartialUpdate(
+    nscolor aBackstop) {
+  DL_LOGI("(%p) RDL - AttemptPartialUpdate, root frame: %p", this,
+          RootReferenceFrame());
+
+  mBuilder.RemoveModifiedWindowRegions();
+
+  if (mBuilder.ShouldSyncDecodeImages()) {
+    DL_LOGI("RDL - Sync decoding images");
+    MarkFramesWithItemsAndImagesModified(&mList);
+  }
+
+  InvalidateCaretFramesIfNeeded();
+
+  // We set the override dirty regions during ComputeRebuildRegion or in
+  // DisplayPortUtils::InvalidateForDisplayPortChange. The display port change
+  // also marks the frame modified, so those regions are cleared here as well.
+  AutoClearFramePropsArray modifiedFrames(64);
+  AutoClearFramePropsArray framesWithProps(64);
+  GetModifiedAndFramesWithProps(&modifiedFrames.Frames(),
+                                &framesWithProps.Frames());
+
+  if (!ShouldBuildPartial(modifiedFrames.Frames())) {
+    // Do not allow partial builds if the |ShouldBuildPartial()| heuristic
+    // fails.
+    mBuilder.SetPartialBuildFailed(true);
+    return PartialUpdateResult::Failed;
+  }
+
+  nsRect modifiedDirty;
+  nsDisplayList modifiedDL(&mBuilder);
+  nsIFrame* modifiedAGR = nullptr;
+  PartialUpdateResult result = PartialUpdateResult::NoChange;
+  const bool simpleUpdate =
+      TrySimpleUpdate(modifiedFrames.Frames(), framesWithProps.Frames());
+
+  mBuilder.EnterPresShell(RootReferenceFrame());
+
+  if (!simpleUpdate) {
+    if (!ComputeRebuildRegion(modifiedFrames.Frames(), &modifiedDirty,
+                              &modifiedAGR, framesWithProps.Frames()) ||
+        !PreProcessDisplayList(&mList, modifiedAGR, result,
+                               RootReferenceFrame(), nullptr)) {
+      DL_LOGI("RDL - Partial update aborted");
+      mBuilder.SetPartialBuildFailed(true);
+      mBuilder.LeavePresShell(RootReferenceFrame(), nullptr);
+      mList.DeleteAll(&mBuilder);
+      return PartialUpdateResult::Failed;
+    }
+  } else {
+    modifiedDirty = mBuilder.GetVisibleRect();
+  }
+
+  // This is normally handled by EnterPresShell, but we skipped it so that we
+  // didn't call MarkFrameForDisplayIfVisible before ComputeRebuildRegion.
+  nsIScrollableFrame* sf =
+      RootReferenceFrame()->PresShell()->GetRootScrollFrameAsScrollable();
+  if (sf) {
+    nsCanvasFrame* canvasFrame = do_QueryFrame(sf->GetScrolledFrame());
+    if (canvasFrame) {
+      mBuilder.MarkFrameForDisplayIfVisible(canvasFrame, RootReferenceFrame());
+    }
+  }
+
+  modifiedDirty.IntersectRect(
+      modifiedDirty, RootReferenceFrame()->InkOverflowRectRelativeToSelf());
+
+  mBuilder.SetDirtyRect(modifiedDirty);
+  mBuilder.SetPartialUpdate(true);
+  mBuilder.SetPartialBuildFailed(false);
+
+  DL_LOGI("RDL - Starting display list build");
+  RootReferenceFrame()->BuildDisplayListForStackingContext(&mBuilder,
+                                                           &modifiedDL);
+  DL_LOGI("RDL - Finished display list build");
+
+  if (!modifiedDL.IsEmpty()) {
+    nsLayoutUtils::AddExtraBackgroundItems(
+        &mBuilder, &modifiedDL, RootReferenceFrame(),
+        nsRect(nsPoint(0, 0), RootReferenceFrame()->GetSize()),
+        RootReferenceFrame()->InkOverflowRectRelativeToSelf(), aBackstop);
+  }
+  mBuilder.SetPartialUpdate(false);
+
+  if (mBuilder.PartialBuildFailed()) {
+    DL_LOGI("RDL - Partial update failed!");
+    mBuilder.LeavePresShell(RootReferenceFrame(), nullptr);
+    mBuilder.ClearReuseableDisplayItems();
+    mList.DeleteAll(&mBuilder);
+    modifiedDL.DeleteAll(&mBuilder);
+    Metrics()->mPartialUpdateFailReason = PartialUpdateFailReason::Content;
+    return PartialUpdateResult::Failed;
+  }
+
+  // printf_stderr("Painting --- Modified list (dirty %d,%d,%d,%d):\n",
+  //              modifiedDirty.x, modifiedDirty.y, modifiedDirty.width,
+  //              modifiedDirty.height);
+  // nsIFrame::PrintDisplayList(&mBuilder, modifiedDL);
+
+  // |modifiedDL| can sometimes be empty here. We still perform the
+  // display list merging to prune unused items (for example, items that
+  // are not visible anymore) from the old list.
+  // TODO: Optimization opportunity. In this case, MergeDisplayLists()
+  // unnecessarily creates a hashtable of the old items.
+  // TODO: Ideally we could skip this if result is NoChange, but currently when
+  // we call RestoreState on nsDisplayWrapList it resets the clip to the base
+  // clip, and we need the UpdateBounds call (within MergeDisplayLists) to
+  // move it to the correct inner clip.
+  if (!simpleUpdate) {
+    Maybe<const ActiveScrolledRoot*> dummy;
+    if (MergeDisplayLists(&modifiedDL, &mList, &mList, dummy)) {
+      result = PartialUpdateResult::Updated;
+    }
+  } else {
+    MOZ_ASSERT(mList.IsEmpty());
+    mList = std::move(modifiedDL);
+    mBuilder.ClearReuseableDisplayItems();
+    result = PartialUpdateResult::Updated;
+  }
+
+#if 0
+  if (DL_LOG_TEST(LogLevel::Verbose)) {
+    printf_stderr("Painting --- Display list:\n");
+    nsIFrame::PrintDisplayList(&mBuilder, mList);
+  }
+#endif
+
+  mBuilder.LeavePresShell(RootReferenceFrame(), List());
+  return result;
+}
+
+}  // namespace mozilla
diff --git a/layout/painting/RetainedDisplayListBuilder.h b/layout/painting/RetainedDisplayListBuilder.h
new file mode 100644
index 0000000000..da5f2d845b
--- /dev/null
+++ b/layout/painting/RetainedDisplayListBuilder.h
@@ -0,0 +1,282 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef RETAINEDDISPLAYLISTBUILDER_H_
+#define RETAINEDDISPLAYLISTBUILDER_H_
+
+#include "nsDisplayList.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/EnumSet.h"
+
+class nsWindowSizes;
+
+namespace mozilla {
+
+class nsDisplayItem;
+class nsDisplayList;
+
+/**
+ * RetainedDisplayListData contains frame invalidation information.
+ * Currently this is implemented as a map of frame pointers to flags.
+ */
+struct RetainedDisplayListData {
+  enum class FrameFlag : uint8_t { Modified, HasProps, HadWillChange };
+  using FrameFlags = mozilla::EnumSet<FrameFlag, uint8_t>;
+
+  RetainedDisplayListData();
+
+  /**
+   * Adds the frame to modified frames list.
+   */
+  void AddModifiedFrame(nsIFrame* aFrame);
+
+  /**
+   * Removes all the frames from this RetainedDisplayListData.
+   */
+  void Clear() {
+    mFrames.Clear();
+    mModifiedFrameCount = 0;
+  }
+
+  /**
+   * Returns a mutable reference to flags set for the given |aFrame|.
+   */
+  FrameFlags& Flags(nsIFrame* aFrame) { return mFrames.LookupOrInsert(aFrame); }
+
+  /**
+   * Returns flags set for the given |aFrame|, or FrameFlags::None if the frame
+   * is not in this RetainedDisplayListData.
+   */
+  FrameFlags GetFlags(nsIFrame* aFrame) const { return mFrames.Get(aFrame); }
+
+  bool IsModified(nsIFrame* aFrame) const {
+    return GetFlags(aFrame).contains(FrameFlag::Modified);
+  }
+
+  bool HasProps(nsIFrame* aFrame) const {
+    return GetFlags(aFrame).contains(FrameFlag::HasProps);
+  }
+
+  bool HadWillChange(nsIFrame* aFrame) const {
+    return GetFlags(aFrame).contains(FrameFlag::HadWillChange);
+  }
+
+  /**
+   * Returns an iterator to the underlying frame storage.
+   */
+  auto ConstIterator() { return mFrames.ConstIter(); }
+
+  /**
+   * Returns true if the modified frame limit has been reached.
+   */
+  bool AtModifiedFrameLimit() {
+    return mModifiedFrameCount >= mModifiedFrameLimit;
+  }
+
+  /**
+   * Removes the given |aFrame| from this RetainedDisplayListData.
+   */
+  bool Remove(nsIFrame* aFrame) { return mFrames.Remove(aFrame); }
+
+ private:
+  nsTHashMap<nsPtrHashKey<nsIFrame>, FrameFlags> mFrames;
+  uint32_t mModifiedFrameCount = 0;
+  uint32_t mModifiedFrameLimit;  // initialized to a pref value in constructor
+};
+
+enum class PartialUpdateResult { Failed, NoChange, Updated };
+
+enum class PartialUpdateFailReason {
+  NA,
+  EmptyList,
+  RebuildLimit,
+  FrameType,
+  Disabled,
+  Content,
+  VisibleRect,
+};
+
+struct RetainedDisplayListMetrics {
+  RetainedDisplayListMetrics() { Reset(); }
+
+  void Reset() {
+    mNewItems = 0;
+    mRebuiltItems = 0;
+    mRemovedItems = 0;
+    mReusedItems = 0;
+    mTotalItems = 0;
+    mPartialBuildDuration = 0;
+    mFullBuildDuration = 0;
+    mPartialUpdateFailReason = PartialUpdateFailReason::NA;
+    mPartialUpdateResult = PartialUpdateResult::NoChange;
+  }
+
+  void StartBuild() { mStartTime = mozilla::TimeStamp::Now(); }
+
+  void EndFullBuild() { mFullBuildDuration = Elapsed(); }
+
+  void EndPartialBuild(PartialUpdateResult aResult) {
+    mPartialBuildDuration = Elapsed();
+    mPartialUpdateResult = aResult;
+  }
+
+  double Elapsed() {
+    return (mozilla::TimeStamp::Now() - mStartTime).ToMilliseconds();
+  }
+
+  const char* FailReasonString() const {
+    switch (mPartialUpdateFailReason) {
+      case PartialUpdateFailReason::NA:
+        return "N/A";
+      case PartialUpdateFailReason::EmptyList:
+        return "Empty list";
+      case PartialUpdateFailReason::RebuildLimit:
+        return "Rebuild limit";
+      case PartialUpdateFailReason::FrameType:
+        return "Frame type";
+      case PartialUpdateFailReason::Disabled:
+        return "Disabled";
+      case PartialUpdateFailReason::Content:
+        return "Content";
+      case PartialUpdateFailReason::VisibleRect:
+        return "VisibleRect";
+      default:
+        MOZ_ASSERT_UNREACHABLE("Enum value not handled!");
+    }
+  }
+
+  unsigned int mNewItems;
+  unsigned int mRebuiltItems;
+  unsigned int mRemovedItems;
+  unsigned int mReusedItems;
+  unsigned int mTotalItems;
+
+  mozilla::TimeStamp mStartTime;
+  double mPartialBuildDuration;
+  double mFullBuildDuration;
+  PartialUpdateFailReason mPartialUpdateFailReason;
+  PartialUpdateResult mPartialUpdateResult;
+};
+
+class RetainedDisplayListBuilder {
+ public:
+  RetainedDisplayListBuilder(nsIFrame* aReferenceFrame,
+                             nsDisplayListBuilderMode aMode, bool aBuildCaret)
+      : mBuilder(aReferenceFrame, aMode, aBuildCaret, true), mList(&mBuilder) {}
+  ~RetainedDisplayListBuilder() { mList.DeleteAll(&mBuilder); }
+
+  nsDisplayListBuilder* Builder() { return &mBuilder; }
+
+  nsDisplayList* List() { return &mList; }
+
+  RetainedDisplayListMetrics* Metrics() { return &mMetrics; }
+
+  RetainedDisplayListData* Data() { return &mData; }
+
+  PartialUpdateResult AttemptPartialUpdate(nscolor aBackstop);
+
+  /**
+   * Clears the modified state for frames in the retained display list data.
+   */
+  void ClearFramesWithProps();
+
+  void ClearRetainedData();
+
+  void ClearReuseableDisplayItems() { mBuilder.ClearReuseableDisplayItems(); }
+
+  void AddSizeOfIncludingThis(nsWindowSizes&) const;
+
+  NS_DECLARE_FRAME_PROPERTY_DELETABLE(Cached, RetainedDisplayListBuilder)
+
+ private:
+  void GetModifiedAndFramesWithProps(nsTArray<nsIFrame*>* aOutModifiedFrames,
+                                     nsTArray<nsIFrame*>* aOutFramesWithProps);
+
+  void IncrementSubDocPresShellPaintCount(nsDisplayItem* aItem);
+
+  /**
+   * Invalidates the current and previous caret frame if they have changed.
+   */
+  void InvalidateCaretFramesIfNeeded();
+
+  /**
+   * A simple early exit heuristic to avoid slow partial display list rebuilds.
+   * Returns true if a partial display list build should be attempted.
+   */
+  bool ShouldBuildPartial(nsTArray<nsIFrame*>& aModifiedFrames);
+
+  /**
+   * Recursively pre-processes the old display list tree before building the
+   * new partial display lists, and serializes the old list into an array,
+   * recording indices on items for fast lookup during merging. Builds an
+   * initial linear DAG for the list if we don't have an existing one. Finds
+   * items that have a different AGR from the specified one, and marks them to
+   * also be built so that we get relative ordering correct. Passes
+   * aKeepLinked=true internally for sub-lists that can't be changed to keep the
+   * original list structure linked for fast re-use.
+   */
+  bool PreProcessDisplayList(
+      RetainedDisplayList* aList, nsIFrame* aAGR, PartialUpdateResult& aUpdated,
+      nsIFrame* aAsyncAncestor, const ActiveScrolledRoot* aAsyncAncestorASR,
+      nsIFrame* aOuterFrame = nullptr, uint32_t aCallerKey = 0,
+      uint32_t aNestingDepth = 0, bool aKeepLinked = false);
+
+  /**
+   * Merges items from aNewList into non-invalidated items from aOldList and
+   * stores the result in aOutList.
+   *
+   * aOuterItem is a pointer to an item that owns one of the lists, if
+   * available. If both lists are populated, then both outer items must not be
+   * invalidated, and identical, so either can be passed here.
+   *
+   * Returns true if changes were made, and the resulting display list (in
+   * aOutList) is different from aOldList.
+   */
+  bool MergeDisplayLists(
+      nsDisplayList* aNewList, RetainedDisplayList* aOldList,
+      RetainedDisplayList* aOutList,
+      mozilla::Maybe<const mozilla::ActiveScrolledRoot*>& aOutContainerASR,
+      nsDisplayItem* aOuterItem = nullptr);
+
+  bool ComputeRebuildRegion(nsTArray<nsIFrame*>& aModifiedFrames,
+                            nsRect* aOutDirty, nsIFrame** aOutModifiedAGR,
+                            nsTArray<nsIFrame*>& aOutFramesWithProps);
+
+  bool ProcessFrame(nsIFrame* aFrame, nsDisplayListBuilder* aBuilder,
+                    nsIFrame* aStopAtFrame,
+                    nsTArray<nsIFrame*>& aOutFramesWithProps,
+                    const bool aStopAtStackingContext, nsRect* aOutDirty,
+                    nsIFrame** aOutModifiedAGR);
+
+  nsIFrame* RootReferenceFrame() { return mBuilder.RootReferenceFrame(); }
+
+  /**
+   * Tries to perform a simple partial display list build without display list
+   * merging. In this mode, only the top-level stacking context items and their
+   * contents are reused, when the frame subtree has not been modified.
+   */
+  bool TrySimpleUpdate(const nsTArray<nsIFrame*>& aModifiedFrames,
+                       nsTArray<nsIFrame*>& aOutFramesWithProps);
+
+  friend class MergeState;
+
+  nsDisplayListBuilder mBuilder;
+  RetainedDisplayList mList;
+  WeakFrame mPreviousCaret;
+  RetainedDisplayListMetrics mMetrics;
+  RetainedDisplayListData mData;
+};
+
+namespace RDLUtils {
+
+void AssertFrameSubtreeUnmodified(const nsIFrame* aFrame);
+void AssertDisplayItemUnmodified(nsDisplayItem* aItem);
+void AssertDisplayListUnmodified(nsDisplayList* aList);
+
+}  // namespace RDLUtils
+}  // namespace mozilla
+
+#endif  // RETAINEDDISPLAYLISTBUILDER_H_
diff --git a/layout/painting/RetainedDisplayListHelpers.h b/layout/painting/RetainedDisplayListHelpers.h
new file mode 100644
index 0000000000..933ab31a7a
--- /dev/null
+++ b/layout/painting/RetainedDisplayListHelpers.h
@@ -0,0 +1,187 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef RETAINEDDISPLAYLISTHELPERS_H_
+#define RETAINEDDISPLAYLISTHELPERS_H_
+
+#include "mozilla/Span.h"
+#include "PLDHashTable.h"
+
+class nsIFrame;
+
+namespace mozilla {
+
+struct DisplayItemKey {
+  bool operator==(const DisplayItemKey& aOther) const {
+    return mFrame == aOther.mFrame && mPerFrameKey == aOther.mPerFrameKey;
+  }
+
+  nsIFrame* mFrame;
+  uint32_t mPerFrameKey;
+};
+
+class DisplayItemHashEntry : public PLDHashEntryHdr {
+ public:
+  typedef DisplayItemKey KeyType;
+  typedef const DisplayItemKey* KeyTypePointer;
+
+  explicit DisplayItemHashEntry(KeyTypePointer aKey) : mKey(*aKey) {}
+  DisplayItemHashEntry(DisplayItemHashEntry&&) = default;
+
+  ~DisplayItemHashEntry() = default;
+
+  KeyType GetKey() const { return mKey; }
+  bool KeyEquals(KeyTypePointer aKey) const { return mKey == *aKey; }
+
+  static KeyTypePointer KeyToPointer(KeyType& aKey) { return &aKey; }
+  static PLDHashNumber HashKey(KeyTypePointer aKey) {
+    if (!aKey) {
+      return 0;
+    }
+
+    return mozilla::HashGeneric(aKey->mFrame, aKey->mPerFrameKey);
+  }
+  enum { ALLOW_MEMMOVE = true };
+
+  DisplayItemKey mKey;
+};
+
+template <typename T>
+bool SpanContains(mozilla::Span<const T>& aSpan, T aItem) {
+  for (const T& i : aSpan) {
+    if (i == aItem) {
+      return true;
+    }
+  }
+  return false;
+}
+
+class OldListUnits {};
+class MergedListUnits {};
+
+template <typename Units>
+struct Index {
+  Index() : val(0) {}
+  explicit Index(size_t aVal) : val(aVal) {
+    MOZ_RELEASE_ASSERT(aVal < std::numeric_limits<uint32_t>::max(),
+                       "List index overflowed");
+  }
+
+  bool operator==(const Index<Units>& aOther) const {
+    return val == aOther.val;
+  }
+
+  uint32_t val;
+};
+typedef Index<OldListUnits> OldListIndex;
+typedef Index<MergedListUnits> MergedListIndex;
+
+template <typename T>
+class DirectedAcyclicGraph {
+ public:
+  DirectedAcyclicGraph() = default;
+  DirectedAcyclicGraph(DirectedAcyclicGraph&& aOther)
+      : mNodesInfo(std::move(aOther.mNodesInfo)),
+        mDirectPredecessorList(std::move(aOther.mDirectPredecessorList)) {}
+
+  DirectedAcyclicGraph& operator=(DirectedAcyclicGraph&& aOther) {
+    mNodesInfo = std::move(aOther.mNodesInfo);
+    mDirectPredecessorList = std::move(aOther.mDirectPredecessorList);
+    return *this;
+  }
+
+  Index<T> AddNode(
+      mozilla::Span<const Index<T>> aDirectPredecessors,
+      const mozilla::Maybe<Index<T>>& aExtraPredecessor = mozilla::Nothing()) {
+    size_t index = mNodesInfo.Length();
+    mNodesInfo.AppendElement(NodeInfo(mDirectPredecessorList.Length(),
+                                      aDirectPredecessors.Length()));
+    if (aExtraPredecessor &&
+        !SpanContains(aDirectPredecessors, aExtraPredecessor.value())) {
+      mNodesInfo.LastElement().mDirectPredecessorCount++;
+      mDirectPredecessorList.SetCapacity(mDirectPredecessorList.Length() +
+                                         aDirectPredecessors.Length() + 1);
+      mDirectPredecessorList.AppendElements(aDirectPredecessors);
+      mDirectPredecessorList.AppendElement(aExtraPredecessor.value());
+    } else {
+      mDirectPredecessorList.AppendElements(aDirectPredecessors);
+    }
+    return Index<T>(index);
+  }
+
+  size_t Length() { return mNodesInfo.Length(); }
+
+  mozilla::Span<Index<T>> GetDirectPredecessors(Index<T> aNodeIndex) {
+    NodeInfo& node = mNodesInfo[aNodeIndex.val];
+    const auto span = mozilla::Span{mDirectPredecessorList};
+    return span.Subspan(node.mIndexInDirectPredecessorList,
+                        node.mDirectPredecessorCount);
+  }
+
+  template <typename OtherUnits>
+  void EnsureCapacityFor(const DirectedAcyclicGraph<OtherUnits>& aOther) {
+    mNodesInfo.SetCapacity(aOther.mNodesInfo.Length());
+    mDirectPredecessorList.SetCapacity(aOther.mDirectPredecessorList.Length());
+  }
+
+  void Clear() {
+    mNodesInfo.Clear();
+    mDirectPredecessorList.Clear();
+  }
+
+  struct NodeInfo {
+    NodeInfo(size_t aIndexInDirectPredecessorList,
+             size_t aDirectPredecessorCount)
+        : mIndexInDirectPredecessorList(aIndexInDirectPredecessorList),
+          mDirectPredecessorCount(aDirectPredecessorCount) {}
+    size_t mIndexInDirectPredecessorList;
+    size_t mDirectPredecessorCount;
+  };
+
+  nsTArray<NodeInfo> mNodesInfo;
+  nsTArray<Index<T>> mDirectPredecessorList;
+};
+
+class RetainedDisplayListBuilder;
+class nsDisplayItem;
+
+struct OldItemInfo {
+  explicit OldItemInfo(nsDisplayItem* aItem);
+
+  void AddedToMergedList(MergedListIndex aIndex) {
+    MOZ_ASSERT(!IsUsed());
+    mUsed = true;
+    mIndex = aIndex;
+    mItem = nullptr;
+  }
+
+  void AddedMatchToMergedList(RetainedDisplayListBuilder* aBuilder,
+                              MergedListIndex aIndex);
+  void Discard(RetainedDisplayListBuilder* aBuilder,
+               nsTArray<MergedListIndex>&& aDirectPredecessors);
+  bool IsUsed() { return mUsed; }
+
+  bool IsDiscarded() {
+    MOZ_ASSERT(IsUsed());
+    return mDiscarded;
+  }
+
+  bool IsChanged();
+
+  nsDisplayItem* mItem;
+  nsTArray<MergedListIndex> mDirectPredecessors;
+  MergedListIndex mIndex;
+  bool mUsed;
+  bool mDiscarded;
+  bool mOwnsItem;
+};
+
+bool AnyContentAncestorModified(nsIFrame* aFrame,
+                                nsIFrame* aStopAtFrame = nullptr);
+
+}  // namespace mozilla
+
+#endif  // RETAINEDDISPLAYLISTHELPERS_H_
diff --git a/layout/painting/TransformClipNode.h b/layout/painting/TransformClipNode.h
new file mode 100644
index 0000000000..a28dc3dbc0
--- /dev/null
+++ b/layout/painting/TransformClipNode.h
@@ -0,0 +1,138 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef MOZILLA_PAINTING_TRANSFORMCLIPNODE_H
+#define MOZILLA_PAINTING_TRANSFORMCLIPNODE_H
+
+#include "mozilla/gfx/MatrixFwd.h"
+#include "mozilla/gfx/Rect.h"
+#include "mozilla/Maybe.h"
+#include "nsISupports.h"
+#include "nsRegionFwd.h"
+
+namespace mozilla {
+
+/**
+ * TransformClipNode stores a transformation matrix and a post-transform
+ * clip rect.
+ * They can be used to transform and clip a display item inside a flattened
+ * nsDisplayTransform to the coordinate space of that nsDisplayTransform.
+ */
+class TransformClipNode {
+  NS_INLINE_DECL_REFCOUNTING(TransformClipNode);
+
+ public:
+  TransformClipNode(const RefPtr<TransformClipNode>& aParent,
+                    const gfx::Matrix4x4Flagged& aTransform,
+                    const Maybe<gfx::IntRect>& aClip)
+      : mParent(aParent), mTransform(aTransform), mClip(aClip) {
+    MOZ_COUNT_CTOR(TransformClipNode);
+  }
+
+  /**
+   * Returns the parent node, or nullptr if this is the root node.
+   */
+  const RefPtr<TransformClipNode>& Parent() const { return mParent; }
+
+  /**
+   * Transforms and clips |aRect| up to the root transform node.
+   * |aRect| is expected to be in app units.
+   */
+  nsRect TransformRect(const nsRect& aRect, const int32_t aA2D) const {
+    if (aRect.IsEmpty()) {
+      return aRect;
+    }
+
+    gfx::Rect result(NSAppUnitsToFloatPixels(aRect.x, aA2D),
+                     NSAppUnitsToFloatPixels(aRect.y, aA2D),
+                     NSAppUnitsToFloatPixels(aRect.width, aA2D),
+                     NSAppUnitsToFloatPixels(aRect.height, aA2D));
+    TransformRect(result);
+    return nsRect(NSFloatPixelsToAppUnits(result.x, aA2D),
+                  NSFloatPixelsToAppUnits(result.y, aA2D),
+                  NSFloatPixelsToAppUnits(result.width, aA2D),
+                  NSFloatPixelsToAppUnits(result.height, aA2D));
+  }
+
+  /**
+   * Transforms and clips |aRect| up to the root transform node.
+   * |aRect| is expected to be in integer pixels.
+   */
+  gfx::IntRect TransformRect(const gfx::IntRect& aRect) const {
+    if (aRect.IsEmpty()) {
+      return aRect;
+    }
+
+    gfx::Rect result(IntRectToRect(aRect));
+    TransformRect(result);
+    return RoundedToInt(result);
+  }
+
+  /**
+   * Transforms and clips |aRegion| up to the root transform node.
+   * |aRegion| is expected be in integer pixels.
+   */
+  nsIntRegion TransformRegion(const nsIntRegion& aRegion) {
+    if (aRegion.IsEmpty()) {
+      return aRegion;
+    }
+
+    nsIntRegion result = aRegion;
+
+    const TransformClipNode* node = this;
+    while (node) {
+      const gfx::Matrix4x4Flagged& transform = node->Transform();
+      result = result.Transform(transform.GetMatrix());
+
+      if (node->Clip()) {
+        const gfx::IntRect clipRect = *node->Clip();
+        result.AndWith(clipRect);
+      }
+
+      node = node->Parent();
+    }
+
+    return result;
+  }
+
+ protected:
+  /**
+   * Returns the post-transform clip, if there is one.
+   */
+  const Maybe<gfx::IntRect>& Clip() const { return mClip; }
+
+  /**
+   * Returns the matrix that transforms the item bounds to the coordinate space
+   * of the flattened nsDisplayTransform.
+   */
+  const gfx::Matrix4x4Flagged& Transform() const { return mTransform; }
+
+  void TransformRect(gfx::Rect& aRect) const {
+    const TransformClipNode* node = this;
+    while (node) {
+      const gfx::Matrix4x4Flagged& transform = node->Transform();
+      gfx::Rect maxBounds = gfx::Rect::MaxIntRect();
+
+      if (node->Clip()) {
+        maxBounds = IntRectToRect(*node->Clip());
+      }
+
+      aRect = transform.TransformAndClipBounds(aRect, maxBounds);
+      node = node->Parent();
+    }
+  }
+
+ private:
+  MOZ_COUNTED_DTOR(TransformClipNode)
+
+  const RefPtr<TransformClipNode> mParent;
+  const gfx::Matrix4x4Flagged mTransform;
+  const Maybe<gfx::IntRect> mClip;
+};
+
+}  // namespace mozilla
+
+#endif /* MOZILLA_PAINTING_TRANSFORMCLIPNODE_H */
diff --git a/layout/painting/WindowRenderer.cpp b/layout/painting/WindowRenderer.cpp
new file mode 100644
index 0000000000..698e42f731
--- /dev/null
+++ b/layout/painting/WindowRenderer.cpp
@@ -0,0 +1,228 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "WindowRenderer.h"
+
+#include "gfxPlatform.h"
+#include "mozilla/dom/Animation.h"  // for Animation
+#include "mozilla/dom/AnimationEffect.h"
+#include "mozilla/EffectSet.h"
+#include "mozilla/layers/PersistentBufferProvider.h"  // for PersistentBufferProviderBasic, PersistentBufferProvider (ptr only)
+#include "nsDisplayList.h"
+
+using namespace mozilla::gfx;
+using namespace mozilla::layers;
+
+namespace mozilla {
+
+/**
+ * StartFrameTimeRecording, together with StopFrameTimeRecording
+ * enable recording of frame intervals.
+ *
+ * To allow concurrent consumers, a cyclic array is used which serves all
+ * consumers, practically stateless with regard to consumers.
+ *
+ * To save resources, the buffer is allocated on first call to
+ * StartFrameTimeRecording and recording is paused if no consumer which called
+ * StartFrameTimeRecording is able to get valid results (because the cyclic
+ * buffer was overwritten since that call).
+ *
+ * To determine availability of the data upon StopFrameTimeRecording:
+ * - mRecording.mNextIndex increases on each RecordFrame, and never resets.
+ * - Cyclic buffer position is realized as mNextIndex % bufferSize.
+ * - StartFrameTimeRecording returns mNextIndex. When StopFrameTimeRecording is
+ *   called, the required start index is passed as an arg, and we're able to
+ *   calculate the required length. If this length is bigger than bufferSize, it
+ *   means data was overwritten.  otherwise, we can return the entire sequence.
+ * - To determine if we need to pause, mLatestStartIndex is updated to
+ *   mNextIndex on each call to StartFrameTimeRecording. If this index gets
+ *   overwritten, it means that all earlier start indices obtained via
+ *   StartFrameTimeRecording were also overwritten, hence, no point in
+ *   recording, so pause.
+ * - mCurrentRunStartIndex indicates the oldest index of the recording after
+ *   which the recording was not paused. If StopFrameTimeRecording is invoked
+ *   with a start index older than this, it means that some frames were not
+ *   recorded, so data is invalid.
+ */
+uint32_t FrameRecorder::StartFrameTimeRecording(int32_t aBufferSize) {
+  if (mRecording.mIsPaused) {
+    mRecording.mIsPaused = false;
+
+    if (!mRecording.mIntervals.Length()) {  // Initialize recording buffers
+      mRecording.mIntervals.SetLength(aBufferSize);
+    }
+
+    // After being paused, recent values got invalid. Update them to now.
+    mRecording.mLastFrameTime = TimeStamp::Now();
+
+    // Any recording which started before this is invalid, since we were paused.
+    mRecording.mCurrentRunStartIndex = mRecording.mNextIndex;
+  }
+
+  // If we'll overwrite this index, there are no more consumers with aStartIndex
+  // for which we're able to provide the full recording, so no point in keep
+  // recording.
+  mRecording.mLatestStartIndex = mRecording.mNextIndex;
+  return mRecording.mNextIndex;
+}
+
+void FrameRecorder::RecordFrame() {
+  if (!mRecording.mIsPaused) {
+    TimeStamp now = TimeStamp::Now();
+    uint32_t i = mRecording.mNextIndex % mRecording.mIntervals.Length();
+    mRecording.mIntervals[i] =
+        static_cast<float>((now - mRecording.mLastFrameTime).ToMilliseconds());
+    mRecording.mNextIndex++;
+    mRecording.mLastFrameTime = now;
+
+    if (mRecording.mNextIndex >
+        (mRecording.mLatestStartIndex + mRecording.mIntervals.Length())) {
+      // We've just overwritten the most recent recording start -> pause.
+      mRecording.mIsPaused = true;
+    }
+  }
+}
+
+void FrameRecorder::StopFrameTimeRecording(uint32_t aStartIndex,
+                                           nsTArray<float>& aFrameIntervals) {
+  uint32_t bufferSize = mRecording.mIntervals.Length();
+  uint32_t length = mRecording.mNextIndex - aStartIndex;
+  if (mRecording.mIsPaused || length > bufferSize ||
+      aStartIndex < mRecording.mCurrentRunStartIndex) {
+    // aStartIndex is too old. Also if aStartIndex was issued before
+    // mRecordingNextIndex overflowed (uint32_t)
+    //   and stopped after the overflow (would happen once every 828 days of
+    //   constant 60fps).
+    length = 0;
+  }
+
+  if (!length) {
+    aFrameIntervals.Clear();
+    return;  // empty recording, return empty arrays.
+  }
+  // Set length in advance to avoid possibly repeated reallocations
+  aFrameIntervals.SetLength(length);
+
+  uint32_t cyclicPos = aStartIndex % bufferSize;
+  for (uint32_t i = 0; i < length; i++, cyclicPos++) {
+    if (cyclicPos == bufferSize) {
+      cyclicPos = 0;
+    }
+    aFrameIntervals[i] = mRecording.mIntervals[cyclicPos];
+  }
+}
+
+already_AddRefed<PersistentBufferProvider>
+WindowRenderer::CreatePersistentBufferProvider(
+    const mozilla::gfx::IntSize& aSize, mozilla::gfx::SurfaceFormat aFormat) {
+  RefPtr<PersistentBufferProviderBasic> bufferProvider;
+  // If we are using remote canvas we don't want to use acceleration in
+  // non-remote layer managers, so we always use the fallback software one.
+  if (!gfxPlatform::UseRemoteCanvas() ||
+      !gfxPlatform::IsBackendAccelerated(
+          gfxPlatform::GetPlatform()->GetPreferredCanvasBackend())) {
+    bufferProvider = PersistentBufferProviderBasic::Create(
+        aSize, aFormat,
+        gfxPlatform::GetPlatform()->GetPreferredCanvasBackend());
+  }
+
+  if (!bufferProvider) {
+    bufferProvider = PersistentBufferProviderBasic::Create(
+        aSize, aFormat, gfxPlatform::GetPlatform()->GetFallbackCanvasBackend());
+  }
+
+  return bufferProvider.forget();
+}
+
+void WindowRenderer::AddPartialPrerenderedAnimation(
+    uint64_t aCompositorAnimationId, dom::Animation* aAnimation) {
+  mPartialPrerenderedAnimations.InsertOrUpdate(aCompositorAnimationId,
+                                               RefPtr{aAnimation});
+  aAnimation->SetPartialPrerendered(aCompositorAnimationId);
+}
+void WindowRenderer::RemovePartialPrerenderedAnimation(
+    uint64_t aCompositorAnimationId, dom::Animation* aAnimation) {
+  MOZ_ASSERT(aAnimation);
+#ifdef DEBUG
+  RefPtr<dom::Animation> animation;
+  if (mPartialPrerenderedAnimations.Remove(aCompositorAnimationId,
+                                           getter_AddRefs(animation)) &&
+      // It may be possible that either animation's effect has already been
+      // nulled out via Animation::SetEffect() so ignore such cases.
+      aAnimation->GetEffect() && aAnimation->GetEffect()->AsKeyframeEffect() &&
+      animation->GetEffect() && animation->GetEffect()->AsKeyframeEffect()) {
+    MOZ_ASSERT(EffectSet::GetEffectSetForEffect(
+                   aAnimation->GetEffect()->AsKeyframeEffect()) ==
+               EffectSet::GetEffectSetForEffect(
+                   animation->GetEffect()->AsKeyframeEffect()));
+  }
+#else
+  mPartialPrerenderedAnimations.Remove(aCompositorAnimationId);
+#endif
+  aAnimation->ResetPartialPrerendered();
+}
+void WindowRenderer::UpdatePartialPrerenderedAnimations(
+    const nsTArray<uint64_t>& aJankedAnimations) {
+  for (uint64_t id : aJankedAnimations) {
+    RefPtr<dom::Animation> animation;
+    if (mPartialPrerenderedAnimations.Remove(id, getter_AddRefs(animation))) {
+      animation->UpdatePartialPrerendered();
+    }
+  }
+}
+
+void FallbackRenderer::SetTarget(gfxContext* aTarget,
+                                 layers::BufferMode aDoubleBuffering) {
+  mTarget = aTarget;
+  mBufferMode = aDoubleBuffering;
+}
+
+bool FallbackRenderer::BeginTransaction(const nsCString& aURL) {
+  if (!mTarget) {
+    return false;
+  }
+
+  return true;
+}
+
+void FallbackRenderer::EndTransactionWithColor(const nsIntRect& aRect,
+                                               const gfx::DeviceColor& aColor) {
+  mTarget->GetDrawTarget()->FillRect(Rect(aRect), ColorPattern(aColor));
+  mAnimationReadyTime = TimeStamp::Now();
+}
+
+void FallbackRenderer::EndTransactionWithList(nsDisplayListBuilder* aBuilder,
+                                              nsDisplayList* aList,
+                                              int32_t aAppUnitsPerDevPixel,
+                                              EndTransactionFlags aFlags) {
+  if (aFlags & EndTransactionFlags::END_NO_COMPOSITE) {
+    return;
+  }
+
+  DrawTarget* dt = mTarget->GetDrawTarget();
+
+  BackendType backend = gfxPlatform::GetPlatform()->GetContentBackendFor(
+      LayersBackend::LAYERS_NONE);
+  RefPtr<DrawTarget> dest =
+      gfxPlatform::GetPlatform()->CreateDrawTargetForBackend(
+          backend, dt->GetSize(), dt->GetFormat());
+  RefPtr<gfxContext> ctx = gfxContext::CreatePreservingTransformOrNull(dest);
+
+  nsRegion opaque = aList->GetOpaqueRegion(aBuilder);
+  if (opaque.Contains(aList->GetComponentAlphaBounds(aBuilder))) {
+    dest->SetPermitSubpixelAA(true);
+  }
+
+  aList->Paint(aBuilder, ctx, aAppUnitsPerDevPixel);
+
+  RefPtr<SourceSurface> snapshot = dest->Snapshot();
+  dt->DrawSurface(snapshot, Rect(dest->GetRect()), Rect(dest->GetRect()),
+                  DrawSurfaceOptions(),
+                  DrawOptions(1.0f, CompositionOp::OP_SOURCE));
+  mAnimationReadyTime = TimeStamp::Now();
+}
+
+}  // namespace mozilla
diff --git a/layout/painting/WindowRenderer.h b/layout/painting/WindowRenderer.h
new file mode 100644
index 0000000000..b58ffd307a
--- /dev/null
+++ b/layout/painting/WindowRenderer.h
@@ -0,0 +1,284 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef MOZILLA_PAINTING_WINDOWRENDERER_H
+#define MOZILLA_PAINTING_WINDOWRENDERER_H
+
+#include "mozilla/webrender/webrender_ffi.h"
+#include "mozilla/layers/LayersTypes.h"
+#include "mozilla/dom/Animation.h"  // for Animation
+#include "mozilla/layers/ScrollableLayerGuid.h"  // for ScrollableLayerGuid, ScrollableLayerGuid::ViewID
+#include "mozilla/ScrollPositionUpdate.h"  // for ScrollPositionUpdate
+#include "nsRefPtrHashtable.h"             // for nsRefPtrHashtable
+#include "gfxContext.h"
+
+namespace mozilla {
+namespace layers {
+class LayerManager;
+class WebRenderLayerManager;
+class KnowsCompositor;
+class CompositorBridgeChild;
+class FrameUniformityData;
+class PersistentBufferProvider;
+}  // namespace layers
+class FallbackRenderer;
+class nsDisplayListBuilder;
+class nsDisplayList;
+
+class FrameRecorder {
+ public:
+  /**
+   * Record (and return) frame-intervals and paint-times for frames which were
+   * presented between calling StartFrameTimeRecording and
+   * StopFrameTimeRecording.
+   *
+   * - Uses a cyclic buffer and serves concurrent consumers, so if Stop is
+   *   called too late
+   *     (elements were overwritten since Start), result is considered invalid
+   *      and hence empty.)
+   * - Buffer is capable of holding 10 seconds @ 60fps (or more if frames were
+   *   less frequent).
+   *     Can be changed (up to 1 hour) via pref:
+   *     toolkit.framesRecording.bufferSize.
+   * - Note: the first frame-interval may be longer than expected because last
+   *   frame
+   *     might have been presented some time before calling
+   *     StartFrameTimeRecording.
+   */
+
+  /**
+   * Returns a handle which represents current recording start position.
+   */
+  virtual uint32_t StartFrameTimeRecording(int32_t aBufferSize);
+
+  /**
+   *  Clears, then populates aFrameIntervals with the recorded frame timing
+   *  data. The array will be empty if data was overwritten since
+   *  aStartIndex was obtained.
+   */
+  virtual void StopFrameTimeRecording(uint32_t aStartIndex,
+                                      nsTArray<float>& aFrameIntervals);
+
+  void RecordFrame();
+
+ private:
+  struct FramesTimingRecording {
+    // Stores state and data for frame intervals and paint times recording.
+    // see LayerManager::StartFrameTimeRecording() at Layers.cpp for more
+    // details.
+    FramesTimingRecording()
+        : mNextIndex(0),
+          mLatestStartIndex(0),
+          mCurrentRunStartIndex(0),
+          mIsPaused(true) {}
+    nsTArray<float> mIntervals;
+    TimeStamp mLastFrameTime;
+    uint32_t mNextIndex;
+    uint32_t mLatestStartIndex;
+    uint32_t mCurrentRunStartIndex;
+    bool mIsPaused;
+  };
+  FramesTimingRecording mRecording;
+};
+
+/**
+ * WindowRenderer is the retained rendering object owned by an nsIWidget for
+ * drawing the contents of that window, the role previously handled by
+ * LayerManager.
+ *
+ * It can be WebRender, (deprecated) Layers, or an immediate-mode
+ * FallbackRenderer.
+ *
+ * The intention is for LayerManager to be removed entirely in the near future,
+ * with WebRender inheriting directly from this class. It is likely that more
+ * cleanup can be done once that happens.
+ */
+class WindowRenderer : public FrameRecorder {
+  NS_INLINE_DECL_REFCOUNTING(WindowRenderer)
+
+ public:
+  // Cast to implementation types.
+  virtual layers::WebRenderLayerManager* AsWebRender() { return nullptr; }
+  virtual FallbackRenderer* AsFallback() { return nullptr; }
+
+  // Required functionality
+
+  /**
+   * Start a new transaction. Nested transactions are not allowed so
+   * there must be no transaction currently in progress.
+   * This transaction will update the state of the window from which
+   * this LayerManager was obtained.
+   */
+  virtual bool BeginTransaction(const nsCString& aURL = nsCString()) = 0;
+
+  enum EndTransactionFlags {
+    END_DEFAULT = 0,
+    END_NO_IMMEDIATE_REDRAW = 1 << 0,  // Do not perform the drawing phase
+    END_NO_COMPOSITE =
+        1 << 1,  // Do not composite after drawing painted layer contents.
+    END_NO_REMOTE_COMPOSITE = 1 << 2  // Do not schedule a composition with a
+                                      // remote Compositor, if one exists.
+  };
+
+  /**
+   * Attempts to end an "empty transaction". There must have been no
+   * changes to the layer tree since the BeginTransaction().
+   * It's possible for this to fail; PaintedLayers may need to be updated
+   * due to VRAM data being lost, for example. In such cases this method
+   * returns false, and the caller must proceed with a normal layer tree
+   * update and EndTransaction.
+   */
+  virtual bool EndEmptyTransaction(
+      EndTransactionFlags aFlags = END_DEFAULT) = 0;
+
+  virtual void Destroy() {}
+
+  /**
+   * Type of layer manager this is. This is to be used sparsely in order to
+   * avoid a lot of Layers backend specific code. It should be used only when
+   * Layers backend specific functionality is necessary.
+   */
+  virtual layers::LayersBackend GetBackendType() = 0;
+
+  /**
+   * Type of layers backend that will be used to composite this layer tree.
+   * When compositing is done remotely, then this returns the layers type
+   * of the compositor.
+   */
+  virtual layers::LayersBackend GetCompositorBackendType() {
+    return GetBackendType();
+  }
+
+  /**
+   * Checks if we need to invalidate the OS widget to trigger
+   * painting when updating this renderer.
+   */
+  virtual bool NeedsWidgetInvalidation() { return true; }
+
+  /**
+   * Make sure that the previous transaction has been entirely
+   * completed.
+   *
+   * Note: This may sychronously wait on a remote compositor
+   * to complete rendering.
+   */
+  virtual void FlushRendering(wr::RenderReasons aReasons) {}
+
+  /**
+   * Make sure that the previous transaction has been
+   * received. This will synchronsly wait on a remote compositor.
+   */
+  virtual void WaitOnTransactionProcessed() {}
+
+  virtual bool IsCompositingCheap() { return true; }
+
+  /**
+   * returns the maximum texture size on this layer backend, or INT32_MAX
+   * if there is no maximum
+   */
+  virtual int32_t GetMaxTextureSize() const { return INT32_MAX; }
+
+  /**
+   * Return the name of the layer manager's backend.
+   */
+  virtual void GetBackendName(nsAString& aName) = 0;
+
+  virtual void GetFrameUniformity(layers::FrameUniformityData* aOutData) {}
+
+  virtual bool AddPendingScrollUpdateForNextTransaction(
+      layers::ScrollableLayerGuid::ViewID aScrollId,
+      const ScrollPositionUpdate& aUpdateInfo) {
+    return false;
+  }
+
+  /**
+   * Creates a PersistentBufferProvider for use with canvas which is optimized
+   * for inter-operating with this layermanager.
+   */
+  virtual already_AddRefed<layers::PersistentBufferProvider>
+  CreatePersistentBufferProvider(const mozilla::gfx::IntSize& aSize,
+                                 mozilla::gfx::SurfaceFormat aFormat);
+
+  // Helper wrappers around cast to impl and then cast again.
+
+  virtual layers::KnowsCompositor* AsKnowsCompositor() { return nullptr; }
+
+  virtual layers::CompositorBridgeChild* GetCompositorBridgeChild() {
+    return nullptr;
+  }
+
+  // Provided functionality
+
+  void AddPartialPrerenderedAnimation(uint64_t aCompositorAnimationId,
+                                      dom::Animation* aAnimation);
+  void RemovePartialPrerenderedAnimation(uint64_t aCompositorAnimationId,
+                                         dom::Animation* aAnimation);
+  void UpdatePartialPrerenderedAnimations(
+      const nsTArray<uint64_t>& aJankedAnimations);
+
+  const TimeStamp& GetAnimationReadyTime() const { return mAnimationReadyTime; }
+
+ protected:
+  virtual ~WindowRenderer() = default;
+
+  // Transform animations which are not fully pre-rendered because it's on a
+  // large frame.  We need to update the pre-rendered area once after we tried
+  // to composite area which is outside of the pre-rendered area on the
+  // compositor.
+  nsRefPtrHashtable<nsUint64HashKey, dom::Animation>
+      mPartialPrerenderedAnimations;
+
+  // The time when painting most recently finished. This is recorded so that
+  // we can time any play-pending animations from this point.
+  TimeStamp mAnimationReadyTime;
+};
+
+/**
+ * FallbackRenderer is non-retained renderer that acts as a direct wrapper
+ * around calling Paint on the provided DisplayList. This is used for cases
+ * where initializing WebRender is too costly, and we don't need
+ * retaining/invalidation (like small popup windows).
+ *
+ * It doesn't support any sort of EmptyTransaction, and only draws during
+ * EndTransaction if a composite is requested (no END_NO_COMPOSITE flag
+ * provided)
+ */
+class FallbackRenderer : public WindowRenderer {
+ public:
+  FallbackRenderer* AsFallback() override { return this; }
+
+  void SetTarget(gfxContext* aContext, layers::BufferMode aDoubleBuffering);
+
+  bool BeginTransaction(const nsCString& aURL = nsCString()) override;
+
+  bool EndEmptyTransaction(EndTransactionFlags aFlags = END_DEFAULT) override {
+    return false;
+  }
+
+  layers::LayersBackend GetBackendType() override {
+    return layers::LayersBackend::LAYERS_NONE;
+  }
+
+  virtual void GetBackendName(nsAString& name) override {
+    name.AssignLiteral("Fallback");
+  }
+
+  bool IsCompositingCheap() override { return false; }
+
+  void EndTransactionWithColor(const nsIntRect& aRect,
+                               const gfx::DeviceColor& aColor);
+  void EndTransactionWithList(nsDisplayListBuilder* aBuilder,
+                              nsDisplayList* aList,
+                              int32_t aAppUnitsPerDevPixel,
+                              EndTransactionFlags aFlags);
+
+  RefPtr<gfxContext> mTarget;
+  layers::BufferMode mBufferMode;
+};
+
+}  // namespace mozilla
+
+#endif /* MOZILLA_PAINTING_WINDOWRENDERER_H */
diff --git a/layout/painting/crashtests/1402183-1.html b/layout/painting/crashtests/1402183-1.html
new file mode 100644
index 0000000000..ea54512894
--- /dev/null
+++ b/layout/painting/crashtests/1402183-1.html
@@ -0,0 +1,20 @@
+<!DOCTYPE html>
+<html>
+<head>
+<title>Bug 1402183</title>
+<style type="text/css">
+:not(article) {
+	-webkit-text-stroke-width: 1px;
+	box-decoration-break: clone;
+	clip-path: polygon(69px 1px, 49px 1px, 0px 0px);
+}
+</style>
+</head>
+<body>
+<ins>
+<p>
+r6O#i/q]
+</p>
+</ins>
+</body>
+</html>
diff --git a/layout/painting/crashtests/1405881-1.html b/layout/painting/crashtests/1405881-1.html
new file mode 100644
index 0000000000..44c8ab1ac0
--- /dev/null
+++ b/layout/painting/crashtests/1405881-1.html
@@ -0,0 +1,24 @@
+<style type="text/css">

+    #container {

+        height: 300px;

+        width: 300px;

+    }

+    #box {

+        height: 100px;

+        width: 100px;

+        background: red;

+        animation: 2s anim;

+    }

+    @keyframes anim {

+        from {

+            -moz-transform: matrix3d(1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 10%, 10%, 0, 1);

+        }

+        to {

+            -moz-transform: matrix3d(1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 40%, 40%, 0, 1);

+        }

+    }

+

+</style>

+<div id=container>

+    <div id=box></div>

+</div>

diff --git a/layout/painting/crashtests/1407470-1.html b/layout/painting/crashtests/1407470-1.html
new file mode 100644
index 0000000000..0ddf957182
--- /dev/null
+++ b/layout/painting/crashtests/1407470-1.html
@@ -0,0 +1,19 @@
+<body id='test_body'>
+<script>
+let o = [];
+o[0] = document.createElement("tt");
+test_body.appendChild(o[0]);
+o[1] = document.createElement("center");
+o[2] = document.createElement("footer");
+o[0].appendChild(o[2]);
+o[1].animate([{
+    "padding": "80.40vw 0.0vmax",
+    "transform": "matrix(6287.56,268.76,237.34,222.80,186.72,287.94) rotateX(2.046rad)"
+  }], { duration:3845.75 });
+o[2].appendChild(o[1]);
+test_body.animate([{
+    "transform": "scale3d(0.0,5961462.820,250.41)",
+    "outline": "auto thick",
+    "mask": "exclude no-clip url(data:image/gif;base64,R0lGODlhAQABAAD/ACH/C05FVFNDQVBFMi4wAwEAAAAsAAAAAAEAAQAAAgAsAAAAAAEAAQAAAgA7),exclude", 
+  }], 3617.63433129);
+</script>
\ No newline at end of file
diff --git a/layout/painting/crashtests/1413073-1.html b/layout/painting/crashtests/1413073-1.html
new file mode 100644
index 0000000000..ddecfb2424
--- /dev/null
+++ b/layout/painting/crashtests/1413073-1.html
@@ -0,0 +1,15 @@
+<html class="reftest-wait">
+<body>
+<div style="position:fixed; width:200px; height:200px; background-color:blue">
+    <div style="position:fixed; width:200px; height:200px; left:400px; background-color:red" id="inner"></div>
+</div>
+</body>
+<script>
+  function doTest() {
+    var d = document.getElementById("inner");
+    d.style.backgroundColor = "green";
+    document.documentElement.className = "";
+  }
+  window.addEventListener("MozReftestInvalidate", doTest);
+</script>
+</html>
diff --git a/layout/painting/crashtests/1413073-2.html b/layout/painting/crashtests/1413073-2.html
new file mode 100644
index 0000000000..01d1718745
--- /dev/null
+++ b/layout/painting/crashtests/1413073-2.html
@@ -0,0 +1,18 @@
+<html class="reftest-wait">
+<body>
+<div style="position:absolute; width:200px; height:200px; opacity:0.5">
+    <div style="opacity:0.9">
+      <div style="position:fixed; width:200px; height:200px; left:400px; background-color:blue" id="fixed"></div>
+    </div>
+    <div style="width:200px; height:200px; background-color:red" id="inner"></div>
+</div>
+</body>
+<script>
+  function doTest() {
+    var d = document.getElementById("inner");
+    d.style.backgroundColor = "green";
+    document.documentElement.className = "";
+  }
+  window.addEventListener("MozReftestInvalidate", doTest);
+</script>
+</html>
diff --git a/layout/painting/crashtests/1418177-1.html b/layout/painting/crashtests/1418177-1.html
new file mode 100644
index 0000000000..6420814bce
--- /dev/null
+++ b/layout/painting/crashtests/1418177-1.html
@@ -0,0 +1,34 @@
+<html>
+  <head>
+    <style>
+      * {
+        background: url(16.png), url(16.png) transparent;
+        -webkit-background-clip: text, text;
+        -moz-tab-size: calc(1 + 1) !important;
+        background-blend-mode: screen;
+        align-content: baseline;
+        background-color: green;
+      }
+    </style>
+    <script>
+      function fun_0() {
+        try { o3 = document.createElement('th') } catch (e) {};
+        try { o1.appendChild(o3) } catch (e) {}
+      }
+
+      try { o1 = document.createElement('tr') } catch (e) {}
+      try { o2 = document.createElement('ol') } catch (e) {}
+      try { xhr = new XMLHttpRequest({mozAnon: false }) } catch (e) {}
+      try { document.documentElement.appendChild(o1) } catch (e) {}
+      try { document.documentElement.appendChild(o2) } catch (e) {}
+      for (let i = 0; i < 100; i++) {
+        try { xhr.open('GET', 'data:text/html,1', false); } catch (e) {};
+        try { xhr.send(); } catch (e) {};
+        try { fuzzPriv.GC(); fuzzPriv.CC(); fuzzPriv.GC(); fuzzPriv.CC(); } catch (e) {};
+        try { xhr.addEventListener('readystatechange', fun_0, true) } catch (e) {};
+        try { o2.offsetLeft } catch (e) {};
+        try { document.styleSheets[0].cssRules[0].style['background-origin'] = 'border-box, border-box' } catch (e) {}
+      }
+    </script>
+  </head>
+</html>
diff --git a/layout/painting/crashtests/1418722-1.html b/layout/painting/crashtests/1418722-1.html
new file mode 100644
index 0000000000..93415d3012
--- /dev/null
+++ b/layout/painting/crashtests/1418722-1.html
@@ -0,0 +1,17 @@
+<html class="reftest-wait">
+<body>
+  <div style="width:200px; height:200px; perspective:1000px">
+    <div style="width:200px; height:200px; transform:translateZ(2px); background-color:green" id="transformed"></div>
+  </div>
+  <div style="width: 200px; height:200px; background-color:red" id="helper"></div>
+</body>
+<script>
+  function doTest() {
+    var element = document.getElementById("transformed");
+    element.parentNode.removeChild(element);
+    document.getElementById("helper").style.backgroundColor = "blue";
+    document.documentElement.className = "";
+  }
+  window.addEventListener("MozReftestInvalidate", doTest);
+</script>
+</html>
diff --git a/layout/painting/crashtests/1419917.html b/layout/painting/crashtests/1419917.html
new file mode 100644
index 0000000000..a60dd15403
--- /dev/null
+++ b/layout/painting/crashtests/1419917.html
@@ -0,0 +1,15 @@
+<html>
+  <head>
+    <style>
+      :nth-last-child(2) { -moz-appearance:listbox }
+    </style>
+    <script>
+    try { o1 = document.createElement('tr') } catch(e) { }
+    try { o2 = document.createElement('th') } catch(e) { }
+    try { o3 = document.createElement('canvas') } catch(e) { }
+    try { document.documentElement.appendChild(o1) } catch(e) { }
+    try { o1.appendChild(o2) } catch(e) { }
+    try { o1.appendChild(o3) } catch(e) { }
+    </script>
+  </head>
+</html>
diff --git a/layout/painting/crashtests/1425271-1.html b/layout/painting/crashtests/1425271-1.html
new file mode 100644
index 0000000000..164cb0f11f
--- /dev/null
+++ b/layout/painting/crashtests/1425271-1.html
@@ -0,0 +1,54 @@
+<!DOCTYPE html>
+<html class="reftest-wait">
+
+<head>
+  <meta http-equiv="content-type" content="text/html; charset=UTF-8">
+  <meta charset="utf-8">
+</head>
+
+<body>
+<div id="container">
+  <div id="element">
+    <!--
+    The HTML code for this element has no other meaning than to create
+    display items that are merged together.
+    -->
+	<div style="column-count:2; column-count:2; width:300px; height:100px;">
+	  <div id="o" style="opacity:0.5; width:100px; height:200px; background:lime;">
+		<div id="d" style="height:50px; width:80px; background:red; padding:2px">Text</div>
+	  </div>
+	</div>
+  </div>
+</div>
+
+<script type="text/javascript">
+function redirect() {
+  document.documentElement.removeAttribute("class");
+
+  // Trigger root frame deletion.
+  window.location.replace("about:blank");
+}
+
+function removeElements(container) {
+  document.body.removeChild(container);
+
+  setTimeout(redirect, 0);
+}
+
+function createElements() {
+  var c = document.getElementById("container");
+  var e = document.getElementById("element");
+  for (var i = 0; i < 1000; ++i) {
+    // Populate the container with elements that cause display item merges.
+    c.appendChild(e.cloneNode(true));
+  }
+
+  setTimeout(() => removeElements(c), 0);
+}
+
+document.addEventListener("MozReftestInvalidate", createElements);
+// window.addEventListener("load", createElements);
+</script>
+
+</body>
+</html>
diff --git a/layout/painting/crashtests/1428906-1.html b/layout/painting/crashtests/1428906-1.html
new file mode 100644
index 0000000000..03e6d3aaf8
--- /dev/null
+++ b/layout/painting/crashtests/1428906-1.html
@@ -0,0 +1,16 @@
+<html><head>
+<meta http-equiv="content-type" content="text/html; charset=UTF-8"><style>
+*,m{background:url()repeat center top fixed}
+#a{transform:scale(1)}
+</style>
+<script>
+function eh1(){
+  try{c=a.insertRow()}catch(e){}
+  try{c.appendChild(b)}catch(e){}
+}
+</script>
+</head><body><table id="a">
+<tbody><tr><d id="b">
+<video>
+<source onerror="eh1()">
+</video></d></tr></tbody></table></body></html>
diff --git a/layout/painting/crashtests/1430589-1.html b/layout/painting/crashtests/1430589-1.html
new file mode 100644
index 0000000000..88bb0494a7
--- /dev/null
+++ b/layout/painting/crashtests/1430589-1.html
@@ -0,0 +1,55 @@
+<html class="reftest-wait"><head>
+<meta http-equiv="content-type" content="text/html; charset=UTF-8">
+  <style>
+    :root {
+      flex-wrap: wrap-reverse;
+    }
+    menuitem {
+      -webkit-mask-image: url(data:image/gif;base64,R0lGODlhEAAQAMQAAORHHOVSKudfOulrSOp3WOyDZu6QdvCchPGolfO0o/XBs/fNwfjZ0frl3/zy7////wAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAACH5BAkAABAALAAAAAAQABAAAAVVICSOZGlCQAosJ6mu7fiyZeKqNKToQGDsM8hBADgUXoGAiqhSvp5QAnQKGIgUhwFUYLCVDFCrKUE1lBavAViFIDlTImbKC5Gm2hB0SlBCBMQiB0UjIQA7);
+    }
+
+    * {
+      margin-right: -1px;
+      display: -webkit-box;
+      overflow: scroll;
+    }
+
+
+    .css1 {
+      -webkit-border-bottom-left-radius: 10px;
+    }
+
+
+  </style>
+<script>
+function BOOM(){
+  setTimeout(() => {
+    var elem = document.getElementById("vuln");
+    elem.style.width = 600;
+    elem.style.height = 600;
+    window.requestAnimationFrame(() => {
+      window.requestAnimationFrame(() => {
+        document.documentElement.removeAttribute("class");
+      });
+    });
+  }, 0);
+}
+
+document.addEventListener("MozReftestInvalidate", BOOM);
+//window.addEventListener("load", BOOM);
+</script></head>
+
+<body>
+  <footer>
+      <textarea id="vuln" style="width: 500px; height: 500px;">Ashitaka</textarea>
+  </footer>
+  <menu>
+    <menuitem>
+      <iframe></iframe>
+  </menuitem></menu>
+  <menuitem>
+  <hr>
+  <dialog class="css1"></dialog>
+
+
+</menuitem></body></html>
diff --git a/layout/painting/crashtests/1454105-1.html b/layout/painting/crashtests/1454105-1.html
new file mode 100644
index 0000000000..946d45992b
--- /dev/null
+++ b/layout/painting/crashtests/1454105-1.html
@@ -0,0 +1,22 @@
+<!DOCTYPE html>
+<html>
+<head>
+<meta charset="UTF-8">
+<style>
+#a {
+  filter: brightness(1);
+  border-style: solid;
+}
+#b {
+  opacity: 0.2;
+}
+</style>
+</head>
+<body>
+<span id="b">
+	<span id="a">
+		<div></div>
+	</span>
+</span>
+</body>
+</html>
diff --git a/layout/painting/crashtests/1455944-1.html b/layout/painting/crashtests/1455944-1.html
new file mode 100644
index 0000000000..c115f4dd8e
--- /dev/null
+++ b/layout/painting/crashtests/1455944-1.html
@@ -0,0 +1,14 @@
+<!DOCTYPE html>
+<html>
+<head>
+<meta http-equiv="content-type" content="text/html; charset=UTF-8">
+<meta charset="utf-8">
+</head>
+
+<body>
+<div style="opacity: 0.9;">
+    <iframe style="border: none;" src=""></iframe>
+</div>
+
+</body>
+</html>
diff --git a/layout/painting/crashtests/1458145.html b/layout/painting/crashtests/1458145.html
new file mode 100644
index 0000000000..dc5f07c204
--- /dev/null
+++ b/layout/painting/crashtests/1458145.html
@@ -0,0 +1,11 @@
+<style>
+* { position: fixed; }
+#a {
+perspective: 0px;
+overflow: scroll;
+}
+.cl2 { -webkit-transform-style: preserve-3d; }
+.cl1 { border-bottom-right-radius: 0px 1px; }
+</style>
+<del id="a" class="cl1">
+<dl class="cl2">#_k</dl>
diff --git a/layout/painting/crashtests/1465305-1.html b/layout/painting/crashtests/1465305-1.html
new file mode 100644
index 0000000000..084f524fba
--- /dev/null
+++ b/layout/painting/crashtests/1465305-1.html
@@ -0,0 +1,8 @@
+<style>
+:not(cursor) {
+  -webkit-background-clip: text;
+  border-top-right-radius: 0vh;
+}
+</style>
+><input>
+<dialog open="">
diff --git a/layout/painting/crashtests/1468124-1.html b/layout/painting/crashtests/1468124-1.html
new file mode 100644
index 0000000000..9acf1427db
--- /dev/null
+++ b/layout/painting/crashtests/1468124-1.html
@@ -0,0 +1,27 @@
+<html class="reftest-wait">
+<style>
+:not(feFuncB) {
+  position: fixed;
+}
+a:last-child {
+  -webkit-transform-style: preserve-3d;
+}
+* {
+  -webkit-backface-visibility: hidden;
+</style>
+<script>
+window.requestIdleCallback(function() {
+  document.documentElement.getBoundingClientRect();
+});
+function go() {
+  var c = document.createElement("a")
+  c.text = "-";
+  try { c.replaceChild(b, c.childNodes[0]); } catch(e) { }
+  try { document.body.appendChild(c); } catch(e) { }
+  document.documentElement.className = "";
+}
+</script>
+<body onload=go()>
+<d id="b">|
+<audio controls="">
+</html>
diff --git a/layout/painting/crashtests/1469472.html b/layout/painting/crashtests/1469472.html
new file mode 100644
index 0000000000..f53d027704
--- /dev/null
+++ b/layout/painting/crashtests/1469472.html
@@ -0,0 +1,7 @@
+<style>
+:not(polygon) {
+background-image: url(#x);
+background-blend-mode: hue, normal;
+</style>
+<table>
+<th>
diff --git a/layout/painting/crashtests/1477831-1.html b/layout/painting/crashtests/1477831-1.html
new file mode 100644
index 0000000000..d6483bde02
--- /dev/null
+++ b/layout/painting/crashtests/1477831-1.html
@@ -0,0 +1,11 @@
+<style>
+* {
+  margin-left: 1vw;
+  columns: 2;
+  opacity: 0.2;
+  -webkit-transform: rotate(0deg);
+}
+#a { float: left; }
+</style>
+<content id="a">
+<dd>A</dd>
diff --git a/layout/painting/crashtests/1504033.html b/layout/painting/crashtests/1504033.html
new file mode 100644
index 0000000000..9aeb7973be
--- /dev/null
+++ b/layout/painting/crashtests/1504033.html
@@ -0,0 +1,13 @@
+<style>
+* { -webkit-transform-style: preserve-3d }
+</style>
+<script>
+function go() {
+  a.append("x");
+}
+</script>
+<body onload=go()>
+<svg overflow="auto">
+<use xlink:href="#b" style="-webkit-transform-style: flat"/>
+<use id="b" xlink:href="#a">
+<text id="a">
diff --git a/layout/painting/crashtests/1514544-1.html b/layout/painting/crashtests/1514544-1.html
new file mode 100644
index 0000000000..8e9efdc3c4
--- /dev/null
+++ b/layout/painting/crashtests/1514544-1.html
@@ -0,0 +1,15 @@
+<html class="reftest-wait">
+<script>
+setTimeout(function() {
+  a.appendChild(b);
+  document.documentElement.className = "";
+}, 100)
+</script>
+<style>
+:root { opacity: 0 }
+</style>
+A
+<textarea id="a" hidden=""></textarea>
+<object id="b" >
+A
+</html>
diff --git a/layout/painting/crashtests/1547420-1.html b/layout/painting/crashtests/1547420-1.html
new file mode 100644
index 0000000000..ce54d67d09
--- /dev/null
+++ b/layout/painting/crashtests/1547420-1.html
@@ -0,0 +1,20 @@
+<script></script>
+<style>
+* {
+  text-align-last: right;
+  min-height: max-content;
+  min-width: 1vmin;
+  writing-mode: vertical-rl;
+}
+</style>
+<q style="writing-mode: lr">
+<marquee></marquee>
+<style></style>
+</q>
+<dl style="-webkit-transform: skew(0deg); mso-ignore: colspan">
+<dd>
+<table>
+<dt style="margin-left: 67%; scale: 7 46 0.006057077979">
+</dt>
+<marquee bgcolor="-moz-mac-accentdarkestshadow">
+<button autofocus="autofocus">
diff --git a/layout/painting/crashtests/1549909.html b/layout/painting/crashtests/1549909.html
new file mode 100644
index 0000000000..0542ee91a8
--- /dev/null
+++ b/layout/painting/crashtests/1549909.html
@@ -0,0 +1,9 @@
+<style>
+* {
+  -webkit-column-break-after: always;
+  float: left;
+  column-width: 0px;
+}
+</style>
+}
+<video controls="controls">
diff --git a/layout/painting/crashtests/1551389-1.html b/layout/painting/crashtests/1551389-1.html
new file mode 100644
index 0000000000..4ee12c1ce9
--- /dev/null
+++ b/layout/painting/crashtests/1551389-1.html
@@ -0,0 +1,6 @@
+<style>
+dl::first-letter { float: right }
+* { -webkit-box-shadow: -moz-cellhighlighttext 0px 34px 1px }
+</style>
+<s dir="RTL">
+<dl style="break-inside: avoid">AA</iframe>
diff --git a/layout/painting/crashtests/1555819-1.html b/layout/painting/crashtests/1555819-1.html
new file mode 100644
index 0000000000..0327e3690f
--- /dev/null
+++ b/layout/painting/crashtests/1555819-1.html
@@ -0,0 +1,12 @@
+<style>
+body {
+  width: 1px;
+  height: 5vmax;
+  -webkit-filter: brightness(1);
+}
+* {
+  grid-template-areas: '';
+  columns: 1px;
+}
+</style>
+<keygen autofocus="">aaaa
diff --git a/layout/painting/crashtests/1574392.html b/layout/painting/crashtests/1574392.html
new file mode 100644
index 0000000000..2e8c4d15aa
--- /dev/null
+++ b/layout/painting/crashtests/1574392.html
@@ -0,0 +1 @@
+<u>🏴󠁵󠁳󠁣󠁡󠁿</u>
diff --git a/layout/painting/crashtests/1589800-1.html b/layout/painting/crashtests/1589800-1.html
new file mode 100644
index 0000000000..8af28028a0
--- /dev/null
+++ b/layout/painting/crashtests/1589800-1.html
@@ -0,0 +1,47 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+    <meta http-equiv="content-type" content="text/html; charset=utf-8">
+    <style>
+        #parent {
+        transform: rotateZ(1deg);
+        position: absolute;
+        opacity: 0.5;
+        overflow-x: hidden;
+    }
+
+    #child {
+        width: 10px;
+        height: 10px;
+    }
+
+    .blend {
+        mix-blend-mode: color-burn;
+    }
+    </style>
+</head>
+
+<body>
+    <div id="parent">
+        <div id="child">a</div>
+    </div>
+    <div>
+        <div id="blend">a</div>
+    </div>
+    <script type="text/javascript">
+    function modify() {
+        var e = document.getElementById("child");
+        e.style.backgroundColor = "red";
+        setTimeout(addBlend, 0);
+    }
+
+    function addBlend() {
+        var e = document.getElementById("blend");
+        e.classList.add("blend");
+    }
+
+    // setTimeout(modify, 3000);
+    window.addEventListener("MozAfterPaint", modify);
+    </script>
+</body>
+</html>
diff --git a/layout/painting/crashtests/1667503-1.html b/layout/painting/crashtests/1667503-1.html
new file mode 100644
index 0000000000..70f99b3f37
--- /dev/null
+++ b/layout/painting/crashtests/1667503-1.html
@@ -0,0 +1,16 @@
+<script>
+function go() {
+  b.src = "x:"
+  b.requestFullscreen()
+}
+function fuzz() {
+  a.close("")
+  b.src = "x"
+  a.showModal()
+  a.appendChild(document.createElement("b"))
+}
+</script>
+<body onload=go()>
+<dialog id="a">
+<nav>x</nav>
+<video id="b" onerror="fuzz()"></video>
diff --git a/layout/painting/crashtests/1714584-1.html b/layout/painting/crashtests/1714584-1.html
new file mode 100644
index 0000000000..1ef2812a2d
--- /dev/null
+++ b/layout/painting/crashtests/1714584-1.html
@@ -0,0 +1,5 @@
+<style>
+output:only-of-type { opacity: 0 }
+</style>
+<output>
+<iframe src="x">x</iframe>
diff --git a/layout/painting/crashtests/1717655-1.html b/layout/painting/crashtests/1717655-1.html
new file mode 100644
index 0000000000..940dac6dfb
--- /dev/null
+++ b/layout/painting/crashtests/1717655-1.html
@@ -0,0 +1,19 @@
+<!DOCTYPE html>
+<html>
+<head>
+  <style>
+      * {
+          transform: perspective(2337713741.755817Q) !important;
+          height: 2637992280%;
+      }
+
+      * {
+          border-width: medium;
+          display: table;
+      }
+  </style>
+</head>
+<table border="32767" rules="all">
+  <caption></caption>
+</table>
+</html>
diff --git a/layout/painting/crashtests/1763006-1.html b/layout/painting/crashtests/1763006-1.html
new file mode 100644
index 0000000000..080c88e7d8
--- /dev/null
+++ b/layout/painting/crashtests/1763006-1.html
@@ -0,0 +1,23 @@
+<style>
+#a {
+  -webkit-filter: invert(10%);
+  background: url(data:image/gif;base64,R0lGODlhAQABAAD/ACwAAAAAAQABAAACADs=) repeat-x center top fixed
+}
+</style>
+<script>
+function go() {
+  window.find("1")
+  requestIdleCallback(() => {
+    a.insertCell().appendChild(b)
+    var x = window.getSelection()
+    x.extend(b)
+    x.deleteFromDocument()
+  })
+}
+</script>
+<body onload=go()>
+<table>
+<colgroup>Z1xNfp~Zdx</colgroup>
+<tr id="a">
+<th></th>
+<li id="b">
diff --git a/layout/painting/crashtests/crashtests.list b/layout/painting/crashtests/crashtests.list
new file mode 100644
index 0000000000..62e9f0935f
--- /dev/null
+++ b/layout/painting/crashtests/crashtests.list
@@ -0,0 +1,30 @@
+load 1402183-1.html
+load 1407470-1.html
+load 1413073-1.html
+load 1413073-2.html
+load 1405881-1.html
+load 1418177-1.html
+load 1418722-1.html
+load 1419917.html
+load 1425271-1.html
+load 1428906-1.html
+load 1430589-1.html
+load 1454105-1.html
+load 1455944-1.html
+load 1458145.html
+load 1465305-1.html
+load 1468124-1.html
+load 1469472.html
+load 1477831-1.html
+load 1504033.html
+load 1514544-1.html
+asserts(0-1) asserts-if(Android,0-2) load 1547420-1.html
+load 1549909.html
+load 1551389-1.html
+asserts(0-2) load 1555819-1.html
+load 1574392.html
+load 1589800-1.html
+load 1667503-1.html
+load 1717655-1.html
+load 1714584-1.html
+load 1763006-1.html
diff --git a/layout/painting/moz.build b/layout/painting/moz.build
new file mode 100644
index 0000000000..8df5368e1b
--- /dev/null
+++ b/layout/painting/moz.build
@@ -0,0 +1,73 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+with Files("**"):
+    BUG_COMPONENT = ("Core", "Web Painting")
+
+EXPORTS += [
+    "ActiveLayerTracker.h",
+    "DisplayItemClip.h",
+    "DisplayItemClipChain.h",
+    "DisplayListClipState.h",
+    "HitTestInfo.h",
+    "LayerState.h",
+    "MatrixStack.h",
+    "nsCSSRendering.h",
+    "nsCSSRenderingBorders.h",
+    "nsCSSRenderingGradients.h",
+    "nsDisplayItemTypes.h",
+    "nsDisplayItemTypesList.h",
+    "nsDisplayList.h",
+    "nsDisplayListArenaTypes.h",
+    "nsDisplayListInvalidation.h",
+    "nsImageRenderer.h",
+    "RetainedDisplayListBuilder.h",
+    "RetainedDisplayListHelpers.h",
+    "TransformClipNode.h",
+    "WindowRenderer.h",
+]
+
+EXPORTS.mozilla += [
+    "PaintTracker.h",
+]
+
+UNIFIED_SOURCES += [
+    "ActiveLayerTracker.cpp",
+    "DashedCornerFinder.cpp",
+    "DisplayItemClip.cpp",
+    "DisplayItemClipChain.cpp",
+    "DisplayListClipState.cpp",
+    "DottedCornerFinder.cpp",
+    "HitTestInfo.cpp",
+    "MaskLayerImageCache.cpp",
+    "nsCSSRendering.cpp",
+    "nsCSSRenderingBorders.cpp",
+    "nsCSSRenderingGradients.cpp",
+    "nsDisplayList.cpp",
+    "nsDisplayListInvalidation.cpp",
+    "nsImageRenderer.cpp",
+    "PaintTracker.cpp",
+    "RetainedDisplayListBuilder.cpp",
+    "WindowRenderer.cpp",
+]
+
+include("/ipc/chromium/chromium-config.mozbuild")
+
+LOCAL_INCLUDES += [
+    "/docshell/base",
+    "/dom/base",
+    "/gfx/2d",
+    "/gfx/cairo/cairo/src",
+    "/layout/base",
+    "/layout/generic",
+    "/layout/style",
+    "/layout/tables",
+    "/layout/xul",
+]
+
+LOCAL_INCLUDES += CONFIG["SKIA_INCLUDES"]
+
+FINAL_LIBRARY = "xul"
diff --git a/layout/painting/nsCSSRendering.cpp b/layout/painting/nsCSSRendering.cpp
new file mode 100644
index 0000000000..eacb7e75db
--- /dev/null
+++ b/layout/painting/nsCSSRendering.cpp
@@ -0,0 +1,4896 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/* utility functions for drawing borders and backgrounds */
+
+#include "nsCSSRendering.h"
+
+#include <ctime>
+
+#include "gfx2DGlue.h"
+#include "gfxContext.h"
+#include "mozilla/ArrayUtils.h"
+#include "mozilla/ComputedStyle.h"
+#include "mozilla/DebugOnly.h"
+#include "mozilla/StaticPrefs_layout.h"
+#include "mozilla/gfx/2D.h"
+#include "mozilla/gfx/Helpers.h"
+#include "mozilla/gfx/Logging.h"
+#include "mozilla/gfx/PathHelpers.h"
+#include "mozilla/HashFunctions.h"
+#include "mozilla/MathAlgorithms.h"
+#include "mozilla/PresShell.h"
+#include "mozilla/StaticPtr.h"
+#include "mozilla/SVGImageContext.h"
+#include "gfxFont.h"
+#include "ScaledFontBase.h"
+#include "skia/include/core/SkTextBlob.h"
+
+#include "BorderConsts.h"
+#include "nsStyleConsts.h"
+#include "nsPresContext.h"
+#include "nsIFrame.h"
+#include "nsIFrameInlines.h"
+#include "nsPoint.h"
+#include "nsRect.h"
+#include "nsFrameManager.h"
+#include "nsGkAtoms.h"
+#include "nsCSSAnonBoxes.h"
+#include "nsIContent.h"
+#include "mozilla/dom/DocumentInlines.h"
+#include "nsIScrollableFrame.h"
+#include "imgIContainer.h"
+#include "ImageOps.h"
+#include "nsCSSColorUtils.h"
+#include "nsITheme.h"
+#include "nsLayoutUtils.h"
+#include "nsBlockFrame.h"
+#include "nsStyleStructInlines.h"
+#include "nsCSSFrameConstructor.h"
+#include "nsCSSProps.h"
+#include "nsContentUtils.h"
+#include "gfxDrawable.h"
+#include "nsCSSRenderingBorders.h"
+#include "mozilla/css/ImageLoader.h"
+#include "ImageContainer.h"
+#include "mozilla/ProfilerLabels.h"
+#include "mozilla/StaticPrefs_layout.h"
+#include "mozilla/Telemetry.h"
+#include "gfxUtils.h"
+#include "gfxGradientCache.h"
+#include "nsInlineFrame.h"
+#include "nsRubyTextContainerFrame.h"
+#include <algorithm>
+#include "TextDrawTarget.h"
+
+using namespace mozilla;
+using namespace mozilla::css;
+using namespace mozilla::gfx;
+using namespace mozilla::image;
+using mozilla::CSSSizeOrRatio;
+using mozilla::dom::Document;
+
+static int gFrameTreeLockCount = 0;
+
+// To avoid storing this data on nsInlineFrame (bloat) and to avoid
+// recalculating this for each frame in a continuation (perf), hold
+// a cache of various coordinate information that we need in order
+// to paint inline backgrounds.
+struct InlineBackgroundData {
+  InlineBackgroundData()
+      : mFrame(nullptr),
+        mLineContainer(nullptr),
+        mContinuationPoint(0),
+        mUnbrokenMeasure(0),
+        mLineContinuationPoint(0),
+        mPIStartBorderData{},
+        mBidiEnabled(false),
+        mVertical(false) {}
+
+  ~InlineBackgroundData() = default;
+
+  void Reset() {
+    mBoundingBox.SetRect(0, 0, 0, 0);
+    mContinuationPoint = mLineContinuationPoint = mUnbrokenMeasure = 0;
+    mFrame = mLineContainer = nullptr;
+    mPIStartBorderData.Reset();
+  }
+
+  /**
+   * Return a continuous rect for (an inline) aFrame relative to the
+   * continuation that draws the left-most part of the background.
+   * This is used when painting backgrounds.
+   */
+  nsRect GetContinuousRect(nsIFrame* aFrame) {
+    MOZ_ASSERT(static_cast<nsInlineFrame*>(do_QueryFrame(aFrame)));
+
+    SetFrame(aFrame);
+
+    nscoord pos;  // an x coordinate if writing-mode is horizontal;
+                  // y coordinate if vertical
+    if (mBidiEnabled) {
+      pos = mLineContinuationPoint;
+
+      // Scan continuations on the same line as aFrame and accumulate the widths
+      // of frames that are to the left (if this is an LTR block) or right
+      // (if it's RTL) of the current one.
+      bool isRtlBlock = (mLineContainer->StyleVisibility()->mDirection ==
+                         StyleDirection::Rtl);
+      nscoord curOffset = mVertical ? aFrame->GetOffsetTo(mLineContainer).y
+                                    : aFrame->GetOffsetTo(mLineContainer).x;
+
+      // If the continuation is fluid we know inlineFrame is not on the same
+      // line. If it's not fluid, we need to test further to be sure.
+      nsIFrame* inlineFrame = aFrame->GetPrevContinuation();
+      while (inlineFrame && !inlineFrame->GetNextInFlow() &&
+             AreOnSameLine(aFrame, inlineFrame)) {
+        nscoord frameOffset = mVertical
+                                  ? inlineFrame->GetOffsetTo(mLineContainer).y
+                                  : inlineFrame->GetOffsetTo(mLineContainer).x;
+        if (isRtlBlock == (frameOffset >= curOffset)) {
+          pos += mVertical ? inlineFrame->GetSize().height
+                           : inlineFrame->GetSize().width;
+        }
+        inlineFrame = inlineFrame->GetPrevContinuation();
+      }
+
+      inlineFrame = aFrame->GetNextContinuation();
+      while (inlineFrame && !inlineFrame->GetPrevInFlow() &&
+             AreOnSameLine(aFrame, inlineFrame)) {
+        nscoord frameOffset = mVertical
+                                  ? inlineFrame->GetOffsetTo(mLineContainer).y
+                                  : inlineFrame->GetOffsetTo(mLineContainer).x;
+        if (isRtlBlock == (frameOffset >= curOffset)) {
+          pos += mVertical ? inlineFrame->GetSize().height
+                           : inlineFrame->GetSize().width;
+        }
+        inlineFrame = inlineFrame->GetNextContinuation();
+      }
+      if (isRtlBlock) {
+        // aFrame itself is also to the right of its left edge, so add its
+        // width.
+        pos += mVertical ? aFrame->GetSize().height : aFrame->GetSize().width;
+        // pos is now the distance from the left [top] edge of aFrame to the
+        // right [bottom] edge of the unbroken content. Change it to indicate
+        // the distance from the left [top] edge of the unbroken content to the
+        // left [top] edge of aFrame.
+        pos = mUnbrokenMeasure - pos;
+      }
+    } else {
+      pos = mContinuationPoint;
+    }
+
+    // Assume background-origin: border and return a rect with offsets
+    // relative to (0,0).  If we have a different background-origin,
+    // then our rect should be deflated appropriately by our caller.
+    return mVertical
+               ? nsRect(0, -pos, mFrame->GetSize().width, mUnbrokenMeasure)
+               : nsRect(-pos, 0, mUnbrokenMeasure, mFrame->GetSize().height);
+  }
+
+  /**
+   * Return a continuous rect for (an inline) aFrame relative to the
+   * continuation that should draw the left[top]-border.  This is used when
+   * painting borders and clipping backgrounds.  This may NOT be the same
+   * continuous rect as for drawing backgrounds; the continuation with the
+   * left[top]-border might be somewhere in the middle of that rect (e.g. BIDI),
+   * in those cases we need the reverse background order starting at the
+   * left[top]-border continuation.
+   */
+  nsRect GetBorderContinuousRect(nsIFrame* aFrame, nsRect aBorderArea) {
+    // Calling GetContinuousRect(aFrame) here may lead to Reset/Init which
+    // resets our mPIStartBorderData so we save it ...
+    PhysicalInlineStartBorderData saved(mPIStartBorderData);
+    nsRect joinedBorderArea = GetContinuousRect(aFrame);
+    if (!saved.mIsValid || saved.mFrame != mPIStartBorderData.mFrame) {
+      if (aFrame == mPIStartBorderData.mFrame) {
+        if (mVertical) {
+          mPIStartBorderData.SetCoord(joinedBorderArea.y);
+        } else {
+          mPIStartBorderData.SetCoord(joinedBorderArea.x);
+        }
+      } else if (mPIStartBorderData.mFrame) {
+        // Copy data to a temporary object so that computing the
+        // continous rect here doesn't clobber our normal state.
+        InlineBackgroundData temp = *this;
+        if (mVertical) {
+          mPIStartBorderData.SetCoord(
+              temp.GetContinuousRect(mPIStartBorderData.mFrame).y);
+        } else {
+          mPIStartBorderData.SetCoord(
+              temp.GetContinuousRect(mPIStartBorderData.mFrame).x);
+        }
+      }
+    } else {
+      // ... and restore it when possible.
+      mPIStartBorderData.SetCoord(saved.mCoord);
+    }
+    if (mVertical) {
+      if (joinedBorderArea.y > mPIStartBorderData.mCoord) {
+        joinedBorderArea.y =
+            -(mUnbrokenMeasure + joinedBorderArea.y - aBorderArea.height);
+      } else {
+        joinedBorderArea.y -= mPIStartBorderData.mCoord;
+      }
+    } else {
+      if (joinedBorderArea.x > mPIStartBorderData.mCoord) {
+        joinedBorderArea.x =
+            -(mUnbrokenMeasure + joinedBorderArea.x - aBorderArea.width);
+      } else {
+        joinedBorderArea.x -= mPIStartBorderData.mCoord;
+      }
+    }
+    return joinedBorderArea;
+  }
+
+  nsRect GetBoundingRect(nsIFrame* aFrame) {
+    SetFrame(aFrame);
+
+    // Move the offsets relative to (0,0) which puts the bounding box into
+    // our coordinate system rather than our parent's.  We do this by
+    // moving it the back distance from us to the bounding box.
+    // This also assumes background-origin: border, so our caller will
+    // need to deflate us if needed.
+    nsRect boundingBox(mBoundingBox);
+    nsPoint point = mFrame->GetPosition();
+    boundingBox.MoveBy(-point.x, -point.y);
+
+    return boundingBox;
+  }
+
+ protected:
+  // This is a coordinate on the inline axis, but is not a true logical inline-
+  // coord because it is always measured from left to right (if horizontal) or
+  // from top to bottom (if vertical), ignoring any bidi RTL directionality.
+  // We'll call this "physical inline start", or PIStart for short.
+  struct PhysicalInlineStartBorderData {
+    nsIFrame* mFrame;  // the continuation that may have a left-border
+    nscoord mCoord;    // cached GetContinuousRect(mFrame).x or .y
+    bool mIsValid;     // true if mCoord is valid
+    void Reset() {
+      mFrame = nullptr;
+      mIsValid = false;
+    }
+    void SetCoord(nscoord aCoord) {
+      mCoord = aCoord;
+      mIsValid = true;
+    }
+  };
+
+  nsIFrame* mFrame;
+  nsIFrame* mLineContainer;
+  nsRect mBoundingBox;
+  nscoord mContinuationPoint;
+  nscoord mUnbrokenMeasure;
+  nscoord mLineContinuationPoint;
+  PhysicalInlineStartBorderData mPIStartBorderData;
+  bool mBidiEnabled;
+  bool mVertical;
+
+  void SetFrame(nsIFrame* aFrame) {
+    MOZ_ASSERT(aFrame, "Need a frame");
+    NS_ASSERTION(gFrameTreeLockCount > 0,
+                 "Can't call this when frame tree is not locked");
+
+    if (aFrame == mFrame) {
+      return;
+    }
+
+    nsIFrame* prevContinuation = GetPrevContinuation(aFrame);
+
+    if (!prevContinuation || mFrame != prevContinuation) {
+      // Ok, we've got the wrong frame.  We have to start from scratch.
+      Reset();
+      Init(aFrame);
+      return;
+    }
+
+    // Get our last frame's size and add its width to our continuation
+    // point before we cache the new frame.
+    mContinuationPoint +=
+        mVertical ? mFrame->GetSize().height : mFrame->GetSize().width;
+
+    // If this a new line, update mLineContinuationPoint.
+    if (mBidiEnabled &&
+        (aFrame->GetPrevInFlow() || !AreOnSameLine(mFrame, aFrame))) {
+      mLineContinuationPoint = mContinuationPoint;
+    }
+
+    mFrame = aFrame;
+  }
+
+  nsIFrame* GetPrevContinuation(nsIFrame* aFrame) {
+    nsIFrame* prevCont = aFrame->GetPrevContinuation();
+    if (!prevCont && aFrame->HasAnyStateBits(NS_FRAME_PART_OF_IBSPLIT)) {
+      nsIFrame* block = aFrame->GetProperty(nsIFrame::IBSplitPrevSibling());
+      if (block) {
+        // The {ib} properties are only stored on first continuations
+        NS_ASSERTION(!block->GetPrevContinuation(),
+                     "Incorrect value for IBSplitPrevSibling");
+        prevCont = block->GetProperty(nsIFrame::IBSplitPrevSibling());
+        NS_ASSERTION(prevCont, "How did that happen?");
+      }
+    }
+    return prevCont;
+  }
+
+  nsIFrame* GetNextContinuation(nsIFrame* aFrame) {
+    nsIFrame* nextCont = aFrame->GetNextContinuation();
+    if (!nextCont && aFrame->HasAnyStateBits(NS_FRAME_PART_OF_IBSPLIT)) {
+      // The {ib} properties are only stored on first continuations
+      aFrame = aFrame->FirstContinuation();
+      nsIFrame* block = aFrame->GetProperty(nsIFrame::IBSplitSibling());
+      if (block) {
+        nextCont = block->GetProperty(nsIFrame::IBSplitSibling());
+        NS_ASSERTION(nextCont, "How did that happen?");
+      }
+    }
+    return nextCont;
+  }
+
+  void Init(nsIFrame* aFrame) {
+    mPIStartBorderData.Reset();
+    mBidiEnabled = aFrame->PresContext()->BidiEnabled();
+    if (mBidiEnabled) {
+      // Find the line container frame
+      mLineContainer = aFrame;
+      while (mLineContainer &&
+             mLineContainer->IsFrameOfType(nsIFrame::eLineParticipant)) {
+        mLineContainer = mLineContainer->GetParent();
+      }
+
+      MOZ_ASSERT(mLineContainer, "Cannot find line containing frame.");
+      MOZ_ASSERT(mLineContainer != aFrame,
+                 "line container frame "
+                 "should be an ancestor of the target frame.");
+    }
+
+    mVertical = aFrame->GetWritingMode().IsVertical();
+
+    // Start with the previous flow frame as our continuation point
+    // is the total of the widths of the previous frames.
+    nsIFrame* inlineFrame = GetPrevContinuation(aFrame);
+    bool changedLines = false;
+    while (inlineFrame) {
+      if (!mPIStartBorderData.mFrame &&
+          !(mVertical ? inlineFrame->GetSkipSides().Top()
+                      : inlineFrame->GetSkipSides().Left())) {
+        mPIStartBorderData.mFrame = inlineFrame;
+      }
+      nsRect rect = inlineFrame->GetRect();
+      mContinuationPoint += mVertical ? rect.height : rect.width;
+      if (mBidiEnabled &&
+          (changedLines || !AreOnSameLine(aFrame, inlineFrame))) {
+        mLineContinuationPoint += mVertical ? rect.height : rect.width;
+        changedLines = true;
+      }
+      mUnbrokenMeasure += mVertical ? rect.height : rect.width;
+      mBoundingBox.UnionRect(mBoundingBox, rect);
+      inlineFrame = GetPrevContinuation(inlineFrame);
+    }
+
+    // Next add this frame and subsequent frames to the bounding box and
+    // unbroken width.
+    inlineFrame = aFrame;
+    while (inlineFrame) {
+      if (!mPIStartBorderData.mFrame &&
+          !(mVertical ? inlineFrame->GetSkipSides().Top()
+                      : inlineFrame->GetSkipSides().Left())) {
+        mPIStartBorderData.mFrame = inlineFrame;
+      }
+      nsRect rect = inlineFrame->GetRect();
+      mUnbrokenMeasure += mVertical ? rect.height : rect.width;
+      mBoundingBox.UnionRect(mBoundingBox, rect);
+      inlineFrame = GetNextContinuation(inlineFrame);
+    }
+
+    mFrame = aFrame;
+  }
+
+  bool AreOnSameLine(nsIFrame* aFrame1, nsIFrame* aFrame2) {
+    if (nsBlockFrame* blockFrame = do_QueryFrame(mLineContainer)) {
+      bool isValid1, isValid2;
+      nsBlockInFlowLineIterator it1(blockFrame, aFrame1, &isValid1);
+      nsBlockInFlowLineIterator it2(blockFrame, aFrame2, &isValid2);
+      return isValid1 && isValid2 &&
+             // Make sure aFrame1 and aFrame2 are in the same continuation of
+             // blockFrame.
+             it1.GetContainer() == it2.GetContainer() &&
+             // And on the same line in it
+             it1.GetLine().get() == it2.GetLine().get();
+    }
+    if (nsRubyTextContainerFrame* rtcFrame = do_QueryFrame(mLineContainer)) {
+      nsBlockFrame* block = nsLayoutUtils::FindNearestBlockAncestor(rtcFrame);
+      // Ruby text container can only hold one line of text, so if they
+      // are in the same continuation, they are in the same line. Since
+      // ruby text containers are bidi isolate, they are never split for
+      // bidi reordering, which means being in different continuation
+      // indicates being in different lines.
+      for (nsIFrame* frame = rtcFrame->FirstContinuation(); frame;
+           frame = frame->GetNextContinuation()) {
+        bool isDescendant1 =
+            nsLayoutUtils::IsProperAncestorFrame(frame, aFrame1, block);
+        bool isDescendant2 =
+            nsLayoutUtils::IsProperAncestorFrame(frame, aFrame2, block);
+        if (isDescendant1 && isDescendant2) {
+          return true;
+        }
+        if (isDescendant1 || isDescendant2) {
+          return false;
+        }
+      }
+      MOZ_ASSERT_UNREACHABLE("None of the frames is a descendant of this rtc?");
+    }
+    MOZ_ASSERT_UNREACHABLE("Do we have any other type of line container?");
+    return false;
+  }
+};
+
+static StaticAutoPtr<InlineBackgroundData> gInlineBGData;
+
+// Initialize any static variables used by nsCSSRendering.
+void nsCSSRendering::Init() {
+  NS_ASSERTION(!gInlineBGData, "Init called twice");
+  gInlineBGData = new InlineBackgroundData();
+}
+
+// Clean up any global variables used by nsCSSRendering.
+void nsCSSRendering::Shutdown() { gInlineBGData = nullptr; }
+
+/**
+ * Make a bevel color
+ */
+static nscolor MakeBevelColor(mozilla::Side whichSide, StyleBorderStyle style,
+                              nscolor aBorderColor) {
+  nscolor colors[2];
+  nscolor theColor;
+
+  // Given a background color and a border color
+  // calculate the color used for the shading
+  NS_GetSpecial3DColors(colors, aBorderColor);
+
+  if ((style == StyleBorderStyle::Outset) ||
+      (style == StyleBorderStyle::Ridge)) {
+    // Flip colors for these two border styles
+    switch (whichSide) {
+      case eSideBottom:
+        whichSide = eSideTop;
+        break;
+      case eSideRight:
+        whichSide = eSideLeft;
+        break;
+      case eSideTop:
+        whichSide = eSideBottom;
+        break;
+      case eSideLeft:
+        whichSide = eSideRight;
+        break;
+    }
+  }
+
+  switch (whichSide) {
+    case eSideBottom:
+      theColor = colors[1];
+      break;
+    case eSideRight:
+      theColor = colors[1];
+      break;
+    case eSideTop:
+      theColor = colors[0];
+      break;
+    case eSideLeft:
+    default:
+      theColor = colors[0];
+      break;
+  }
+  return theColor;
+}
+
+static bool GetRadii(nsIFrame* aForFrame, const nsStyleBorder& aBorder,
+                     const nsRect& aOrigBorderArea, const nsRect& aBorderArea,
+                     nscoord aRadii[8]) {
+  bool haveRoundedCorners;
+  nsSize sz = aBorderArea.Size();
+  nsSize frameSize = aForFrame->GetSize();
+  if (&aBorder == aForFrame->StyleBorder() &&
+      frameSize == aOrigBorderArea.Size()) {
+    haveRoundedCorners = aForFrame->GetBorderRadii(sz, sz, Sides(), aRadii);
+  } else {
+    haveRoundedCorners = nsIFrame::ComputeBorderRadii(
+        aBorder.mBorderRadius, frameSize, sz, Sides(), aRadii);
+  }
+
+  return haveRoundedCorners;
+}
+
+static bool GetRadii(nsIFrame* aForFrame, const nsStyleBorder& aBorder,
+                     const nsRect& aOrigBorderArea, const nsRect& aBorderArea,
+                     RectCornerRadii* aBgRadii) {
+  nscoord radii[8];
+  bool haveRoundedCorners =
+      GetRadii(aForFrame, aBorder, aOrigBorderArea, aBorderArea, radii);
+
+  if (haveRoundedCorners) {
+    auto d2a = aForFrame->PresContext()->AppUnitsPerDevPixel();
+    nsCSSRendering::ComputePixelRadii(radii, d2a, aBgRadii);
+  }
+  return haveRoundedCorners;
+}
+
+static nsRect JoinBoxesForBlockAxisSlice(nsIFrame* aFrame,
+                                         const nsRect& aBorderArea) {
+  // Inflate the block-axis size as if our continuations were laid out
+  // adjacent in that axis.  Note that we don't touch the inline size.
+  const auto wm = aFrame->GetWritingMode();
+  const nsSize dummyContainerSize;
+  LogicalRect borderArea(wm, aBorderArea, dummyContainerSize);
+  nscoord bSize = 0;
+  nsIFrame* f = aFrame->GetNextContinuation();
+  for (; f; f = f->GetNextContinuation()) {
+    bSize += f->BSize(wm);
+  }
+  borderArea.BSize(wm) += bSize;
+  bSize = 0;
+  f = aFrame->GetPrevContinuation();
+  for (; f; f = f->GetPrevContinuation()) {
+    bSize += f->BSize(wm);
+  }
+  borderArea.BStart(wm) -= bSize;
+  borderArea.BSize(wm) += bSize;
+  return borderArea.GetPhysicalRect(wm, dummyContainerSize);
+}
+
+/**
+ * Inflate aBorderArea which is relative to aFrame's origin to calculate
+ * a hypothetical non-split frame area for all the continuations.
+ * See "Joining Boxes for 'slice'" in
+ * http://dev.w3.org/csswg/css-break/#break-decoration
+ */
+enum InlineBoxOrder { eForBorder, eForBackground };
+static nsRect JoinBoxesForSlice(nsIFrame* aFrame, const nsRect& aBorderArea,
+                                InlineBoxOrder aOrder) {
+  if (static_cast<nsInlineFrame*>(do_QueryFrame(aFrame))) {
+    return (aOrder == eForBorder
+                ? gInlineBGData->GetBorderContinuousRect(aFrame, aBorderArea)
+                : gInlineBGData->GetContinuousRect(aFrame)) +
+           aBorderArea.TopLeft();
+  }
+  return JoinBoxesForBlockAxisSlice(aFrame, aBorderArea);
+}
+
+/* static */
+bool nsCSSRendering::IsBoxDecorationSlice(const nsStyleBorder& aStyleBorder) {
+  return aStyleBorder.mBoxDecorationBreak == StyleBoxDecorationBreak::Slice;
+}
+
+/* static */
+nsRect nsCSSRendering::BoxDecorationRectForBorder(
+    nsIFrame* aFrame, const nsRect& aBorderArea, Sides aSkipSides,
+    const nsStyleBorder* aStyleBorder) {
+  if (!aStyleBorder) {
+    aStyleBorder = aFrame->StyleBorder();
+  }
+  // If aSkipSides.IsEmpty() then there are no continuations, or it's
+  // a ::first-letter that wants all border sides on the first continuation.
+  return IsBoxDecorationSlice(*aStyleBorder) && !aSkipSides.IsEmpty()
+             ? ::JoinBoxesForSlice(aFrame, aBorderArea, eForBorder)
+             : aBorderArea;
+}
+
+/* static */
+nsRect nsCSSRendering::BoxDecorationRectForBackground(
+    nsIFrame* aFrame, const nsRect& aBorderArea, Sides aSkipSides,
+    const nsStyleBorder* aStyleBorder) {
+  if (!aStyleBorder) {
+    aStyleBorder = aFrame->StyleBorder();
+  }
+  // If aSkipSides.IsEmpty() then there are no continuations, or it's
+  // a ::first-letter that wants all border sides on the first continuation.
+  return IsBoxDecorationSlice(*aStyleBorder) && !aSkipSides.IsEmpty()
+             ? ::JoinBoxesForSlice(aFrame, aBorderArea, eForBackground)
+             : aBorderArea;
+}
+
+//----------------------------------------------------------------------
+// Thebes Border Rendering Code Start
+
+/*
+ * Compute the float-pixel radii that should be used for drawing
+ * this border/outline, given the various input bits.
+ */
+/* static */
+void nsCSSRendering::ComputePixelRadii(const nscoord* aAppUnitsRadii,
+                                       nscoord aAppUnitsPerPixel,
+                                       RectCornerRadii* oBorderRadii) {
+  Float radii[8];
+  for (const auto corner : mozilla::AllPhysicalHalfCorners()) {
+    radii[corner] = Float(aAppUnitsRadii[corner]) / aAppUnitsPerPixel;
+  }
+
+  (*oBorderRadii)[C_TL] = Size(radii[eCornerTopLeftX], radii[eCornerTopLeftY]);
+  (*oBorderRadii)[C_TR] =
+      Size(radii[eCornerTopRightX], radii[eCornerTopRightY]);
+  (*oBorderRadii)[C_BR] =
+      Size(radii[eCornerBottomRightX], radii[eCornerBottomRightY]);
+  (*oBorderRadii)[C_BL] =
+      Size(radii[eCornerBottomLeftX], radii[eCornerBottomLeftY]);
+}
+
+static Maybe<nsStyleBorder> GetBorderIfVisited(const ComputedStyle& aStyle) {
+  Maybe<nsStyleBorder> result;
+  // Don't check RelevantLinkVisited here, since we want to take the
+  // same amount of time whether or not it's true.
+  const ComputedStyle* styleIfVisited = aStyle.GetStyleIfVisited();
+  if (MOZ_LIKELY(!styleIfVisited)) {
+    return result;
+  }
+
+  result.emplace(*aStyle.StyleBorder());
+  auto& newBorder = result.ref();
+  for (const auto side : mozilla::AllPhysicalSides()) {
+    nscolor color = aStyle.GetVisitedDependentColor(
+        nsStyleBorder::BorderColorFieldFor(side));
+    newBorder.BorderColorFor(side) = StyleColor::FromColor(color);
+  }
+
+  return result;
+}
+
+ImgDrawResult nsCSSRendering::PaintBorder(
+    nsPresContext* aPresContext, gfxContext& aRenderingContext,
+    nsIFrame* aForFrame, const nsRect& aDirtyRect, const nsRect& aBorderArea,
+    ComputedStyle* aStyle, PaintBorderFlags aFlags, Sides aSkipSides) {
+  AUTO_PROFILER_LABEL("nsCSSRendering::PaintBorder", GRAPHICS);
+
+  Maybe<nsStyleBorder> visitedBorder = GetBorderIfVisited(*aStyle);
+  return PaintBorderWithStyleBorder(
+      aPresContext, aRenderingContext, aForFrame, aDirtyRect, aBorderArea,
+      visitedBorder.refOr(*aStyle->StyleBorder()), aStyle, aFlags, aSkipSides);
+}
+
+Maybe<nsCSSBorderRenderer> nsCSSRendering::CreateBorderRenderer(
+    nsPresContext* aPresContext, DrawTarget* aDrawTarget, nsIFrame* aForFrame,
+    const nsRect& aDirtyRect, const nsRect& aBorderArea, ComputedStyle* aStyle,
+    bool* aOutBorderIsEmpty, Sides aSkipSides) {
+  Maybe<nsStyleBorder> visitedBorder = GetBorderIfVisited(*aStyle);
+  return CreateBorderRendererWithStyleBorder(
+      aPresContext, aDrawTarget, aForFrame, aDirtyRect, aBorderArea,
+      visitedBorder.refOr(*aStyle->StyleBorder()), aStyle, aOutBorderIsEmpty,
+      aSkipSides);
+}
+
+ImgDrawResult nsCSSRendering::CreateWebRenderCommandsForBorder(
+    nsDisplayItem* aItem, nsIFrame* aForFrame, const nsRect& aBorderArea,
+    mozilla::wr::DisplayListBuilder& aBuilder,
+    mozilla::wr::IpcResourceUpdateQueue& aResources,
+    const mozilla::layers::StackingContextHelper& aSc,
+    mozilla::layers::RenderRootStateManager* aManager,
+    nsDisplayListBuilder* aDisplayListBuilder) {
+  const auto* style = aForFrame->Style();
+  Maybe<nsStyleBorder> visitedBorder = GetBorderIfVisited(*style);
+  return nsCSSRendering::CreateWebRenderCommandsForBorderWithStyleBorder(
+      aItem, aForFrame, aBorderArea, aBuilder, aResources, aSc, aManager,
+      aDisplayListBuilder, visitedBorder.refOr(*style->StyleBorder()));
+}
+
+void nsCSSRendering::CreateWebRenderCommandsForNullBorder(
+    nsDisplayItem* aItem, nsIFrame* aForFrame, const nsRect& aBorderArea,
+    mozilla::wr::DisplayListBuilder& aBuilder,
+    mozilla::wr::IpcResourceUpdateQueue& aResources,
+    const mozilla::layers::StackingContextHelper& aSc,
+    const nsStyleBorder& aStyleBorder) {
+  bool borderIsEmpty = false;
+  Maybe<nsCSSBorderRenderer> br =
+      nsCSSRendering::CreateNullBorderRendererWithStyleBorder(
+          aForFrame->PresContext(), nullptr, aForFrame, nsRect(), aBorderArea,
+          aStyleBorder, aForFrame->Style(), &borderIsEmpty,
+          aForFrame->GetSkipSides());
+  if (!borderIsEmpty && br) {
+    br->CreateWebRenderCommands(aItem, aBuilder, aResources, aSc);
+  }
+}
+
+ImgDrawResult nsCSSRendering::CreateWebRenderCommandsForBorderWithStyleBorder(
+    nsDisplayItem* aItem, nsIFrame* aForFrame, const nsRect& aBorderArea,
+    mozilla::wr::DisplayListBuilder& aBuilder,
+    mozilla::wr::IpcResourceUpdateQueue& aResources,
+    const mozilla::layers::StackingContextHelper& aSc,
+    mozilla::layers::RenderRootStateManager* aManager,
+    nsDisplayListBuilder* aDisplayListBuilder,
+    const nsStyleBorder& aStyleBorder) {
+  auto& borderImage = aStyleBorder.mBorderImageSource;
+  // First try to create commands for simple borders.
+  if (borderImage.IsNone()) {
+    CreateWebRenderCommandsForNullBorder(
+        aItem, aForFrame, aBorderArea, aBuilder, aResources, aSc, aStyleBorder);
+    return ImgDrawResult::SUCCESS;
+  }
+
+  // Next we try image and gradient borders. Gradients are not supported at
+  // this very moment.
+  if (!borderImage.IsImageRequestType()) {
+    return ImgDrawResult::NOT_SUPPORTED;
+  }
+
+  if (aStyleBorder.mBorderImageRepeatH == StyleBorderImageRepeat::Space ||
+      aStyleBorder.mBorderImageRepeatV == StyleBorderImageRepeat::Space) {
+    return ImgDrawResult::NOT_SUPPORTED;
+  }
+
+  uint32_t flags = 0;
+  if (aDisplayListBuilder->IsPaintingToWindow()) {
+    flags |= nsImageRenderer::FLAG_PAINTING_TO_WINDOW;
+  }
+  if (aDisplayListBuilder->ShouldSyncDecodeImages()) {
+    flags |= nsImageRenderer::FLAG_SYNC_DECODE_IMAGES;
+  }
+
+  bool dummy;
+  image::ImgDrawResult result;
+  Maybe<nsCSSBorderImageRenderer> bir =
+      nsCSSBorderImageRenderer::CreateBorderImageRenderer(
+          aForFrame->PresContext(), aForFrame, aBorderArea, aStyleBorder,
+          aItem->GetBounds(aDisplayListBuilder, &dummy),
+          aForFrame->GetSkipSides(), flags, &result);
+
+  if (!bir) {
+    // We aren't ready. Try to fallback to the null border image if present but
+    // return the draw result for the border image renderer.
+    CreateWebRenderCommandsForNullBorder(
+        aItem, aForFrame, aBorderArea, aBuilder, aResources, aSc, aStyleBorder);
+    return result;
+  }
+
+  return bir->CreateWebRenderCommands(aItem, aForFrame, aBuilder, aResources,
+                                      aSc, aManager, aDisplayListBuilder);
+}
+
+static nsCSSBorderRenderer ConstructBorderRenderer(
+    nsPresContext* aPresContext, ComputedStyle* aStyle, DrawTarget* aDrawTarget,
+    nsIFrame* aForFrame, const nsRect& aDirtyRect, const nsRect& aBorderArea,
+    const nsStyleBorder& aStyleBorder, Sides aSkipSides, bool* aNeedsClip) {
+  nsMargin border = aStyleBorder.GetComputedBorder();
+
+  // Compute the outermost boundary of the area that might be painted.
+  // Same coordinate space as aBorderArea & aBGClipRect.
+  nsRect joinedBorderArea = nsCSSRendering::BoxDecorationRectForBorder(
+      aForFrame, aBorderArea, aSkipSides, &aStyleBorder);
+  RectCornerRadii bgRadii;
+  ::GetRadii(aForFrame, aStyleBorder, aBorderArea, joinedBorderArea, &bgRadii);
+
+  PrintAsFormatString(" joinedBorderArea: %d %d %d %d\n", joinedBorderArea.x,
+                      joinedBorderArea.y, joinedBorderArea.width,
+                      joinedBorderArea.height);
+
+  // start drawing
+  if (nsCSSRendering::IsBoxDecorationSlice(aStyleBorder)) {
+    if (joinedBorderArea.IsEqualEdges(aBorderArea)) {
+      // No need for a clip, just skip the sides we don't want.
+      border.ApplySkipSides(aSkipSides);
+    } else {
+      // We're drawing borders around the joined continuation boxes so we need
+      // to clip that to the slice that we want for this frame.
+      *aNeedsClip = true;
+    }
+  } else {
+    MOZ_ASSERT(joinedBorderArea.IsEqualEdges(aBorderArea),
+               "Should use aBorderArea for box-decoration-break:clone");
+    MOZ_ASSERT(
+        aForFrame->GetSkipSides().IsEmpty() ||
+            aForFrame->IsTrueOverflowContainer() ||
+            aForFrame->IsColumnSetFrame(),  // a little broader than column-rule
+        "Should not skip sides for box-decoration-break:clone except "
+        "::first-letter/line continuations or other frame types that "
+        "don't have borders but those shouldn't reach this point. "
+        "Overflow containers do reach this point though, as does "
+        "column-rule drawing (which always involves a columnset).");
+    border.ApplySkipSides(aSkipSides);
+  }
+
+  // Convert to dev pixels.
+  nscoord oneDevPixel = aPresContext->DevPixelsToAppUnits(1);
+  Rect joinedBorderAreaPx = NSRectToRect(joinedBorderArea, oneDevPixel);
+  Float borderWidths[4] = {
+      Float(border.top) / oneDevPixel, Float(border.right) / oneDevPixel,
+      Float(border.bottom) / oneDevPixel, Float(border.left) / oneDevPixel};
+  Rect dirtyRect = NSRectToRect(aDirtyRect, oneDevPixel);
+
+  StyleBorderStyle borderStyles[4];
+  nscolor borderColors[4];
+
+  // pull out styles, colors
+  for (const auto i : mozilla::AllPhysicalSides()) {
+    borderStyles[i] = aStyleBorder.GetBorderStyle(i);
+    borderColors[i] = aStyleBorder.BorderColorFor(i).CalcColor(*aStyle);
+  }
+
+  PrintAsFormatString(
+      " borderStyles: %d %d %d %d\n", static_cast<int>(borderStyles[0]),
+      static_cast<int>(borderStyles[1]), static_cast<int>(borderStyles[2]),
+      static_cast<int>(borderStyles[3]));
+
+  return nsCSSBorderRenderer(
+      aPresContext, aDrawTarget, dirtyRect, joinedBorderAreaPx, borderStyles,
+      borderWidths, bgRadii, borderColors, !aForFrame->BackfaceIsHidden(),
+      *aNeedsClip ? Some(NSRectToRect(aBorderArea, oneDevPixel)) : Nothing());
+}
+
+ImgDrawResult nsCSSRendering::PaintBorderWithStyleBorder(
+    nsPresContext* aPresContext, gfxContext& aRenderingContext,
+    nsIFrame* aForFrame, const nsRect& aDirtyRect, const nsRect& aBorderArea,
+    const nsStyleBorder& aStyleBorder, ComputedStyle* aStyle,
+    PaintBorderFlags aFlags, Sides aSkipSides) {
+  DrawTarget& aDrawTarget = *aRenderingContext.GetDrawTarget();
+
+  PrintAsStringNewline("++ PaintBorder");
+
+  // Check to see if we have an appearance defined.  If so, we let the theme
+  // renderer draw the border.  DO not get the data from aForFrame, since the
+  // passed in ComputedStyle may be different!  Always use |aStyle|!
+  StyleAppearance appearance = aStyle->StyleDisplay()->EffectiveAppearance();
+  if (appearance != StyleAppearance::None) {
+    nsITheme* theme = aPresContext->Theme();
+    if (theme->ThemeSupportsWidget(aPresContext, aForFrame, appearance)) {
+      return ImgDrawResult::SUCCESS;  // Let the theme handle it.
+    }
+  }
+
+  if (!aStyleBorder.mBorderImageSource.IsNone()) {
+    ImgDrawResult result = ImgDrawResult::SUCCESS;
+
+    uint32_t irFlags = 0;
+    if (aFlags & PaintBorderFlags::SyncDecodeImages) {
+      irFlags |= nsImageRenderer::FLAG_SYNC_DECODE_IMAGES;
+    }
+
+    // Creating the border image renderer will request a decode, and we rely on
+    // that happening.
+    Maybe<nsCSSBorderImageRenderer> renderer =
+        nsCSSBorderImageRenderer::CreateBorderImageRenderer(
+            aPresContext, aForFrame, aBorderArea, aStyleBorder, aDirtyRect,
+            aSkipSides, irFlags, &result);
+    // renderer was created successfully, which means border image is ready to
+    // be used.
+    if (renderer) {
+      MOZ_ASSERT(result == ImgDrawResult::SUCCESS);
+      return renderer->DrawBorderImage(aPresContext, aRenderingContext,
+                                       aForFrame, aDirtyRect);
+    }
+  }
+
+  ImgDrawResult result = ImgDrawResult::SUCCESS;
+
+  // If we had a border-image, but it wasn't loaded, then we should return
+  // ImgDrawResult::NOT_READY; we'll want to try again if we do a paint with
+  // sync decoding enabled.
+  if (!aStyleBorder.mBorderImageSource.IsNone()) {
+    result = ImgDrawResult::NOT_READY;
+  }
+
+  nsMargin border = aStyleBorder.GetComputedBorder();
+  if (0 == border.left && 0 == border.right && 0 == border.top &&
+      0 == border.bottom) {
+    // Empty border area
+    return result;
+  }
+
+  bool needsClip = false;
+  nsCSSBorderRenderer br = ConstructBorderRenderer(
+      aPresContext, aStyle, &aDrawTarget, aForFrame, aDirtyRect, aBorderArea,
+      aStyleBorder, aSkipSides, &needsClip);
+  if (needsClip) {
+    aDrawTarget.PushClipRect(NSRectToSnappedRect(
+        aBorderArea, aForFrame->PresContext()->AppUnitsPerDevPixel(),
+        aDrawTarget));
+  }
+
+  br.DrawBorders();
+
+  if (needsClip) {
+    aDrawTarget.PopClip();
+  }
+
+  PrintAsStringNewline();
+
+  return result;
+}
+
+Maybe<nsCSSBorderRenderer> nsCSSRendering::CreateBorderRendererWithStyleBorder(
+    nsPresContext* aPresContext, DrawTarget* aDrawTarget, nsIFrame* aForFrame,
+    const nsRect& aDirtyRect, const nsRect& aBorderArea,
+    const nsStyleBorder& aStyleBorder, ComputedStyle* aStyle,
+    bool* aOutBorderIsEmpty, Sides aSkipSides) {
+  if (!aStyleBorder.mBorderImageSource.IsNone()) {
+    return Nothing();
+  }
+  return CreateNullBorderRendererWithStyleBorder(
+      aPresContext, aDrawTarget, aForFrame, aDirtyRect, aBorderArea,
+      aStyleBorder, aStyle, aOutBorderIsEmpty, aSkipSides);
+}
+
+Maybe<nsCSSBorderRenderer>
+nsCSSRendering::CreateNullBorderRendererWithStyleBorder(
+    nsPresContext* aPresContext, DrawTarget* aDrawTarget, nsIFrame* aForFrame,
+    const nsRect& aDirtyRect, const nsRect& aBorderArea,
+    const nsStyleBorder& aStyleBorder, ComputedStyle* aStyle,
+    bool* aOutBorderIsEmpty, Sides aSkipSides) {
+  StyleAppearance appearance = aStyle->StyleDisplay()->EffectiveAppearance();
+  if (appearance != StyleAppearance::None) {
+    nsITheme* theme = aPresContext->Theme();
+    if (theme->ThemeSupportsWidget(aPresContext, aForFrame, appearance)) {
+      return Nothing();
+    }
+  }
+
+  nsMargin border = aStyleBorder.GetComputedBorder();
+  if (0 == border.left && 0 == border.right && 0 == border.top &&
+      0 == border.bottom) {
+    // Empty border area
+    if (aOutBorderIsEmpty) {
+      *aOutBorderIsEmpty = true;
+    }
+    return Nothing();
+  }
+
+  bool needsClip = false;
+  nsCSSBorderRenderer br = ConstructBorderRenderer(
+      aPresContext, aStyle, aDrawTarget, aForFrame, aDirtyRect, aBorderArea,
+      aStyleBorder, aSkipSides, &needsClip);
+  return Some(br);
+}
+
+Maybe<nsCSSBorderRenderer>
+nsCSSRendering::CreateBorderRendererForNonThemedOutline(
+    nsPresContext* aPresContext, DrawTarget* aDrawTarget, nsIFrame* aForFrame,
+    const nsRect& aDirtyRect, const nsRect& aInnerRect, ComputedStyle* aStyle) {
+  // Get our ComputedStyle's color struct.
+  const nsStyleOutline* ourOutline = aStyle->StyleOutline();
+  if (!ourOutline->ShouldPaintOutline()) {
+    // Empty outline
+    return Nothing();
+  }
+
+  const nscoord offset = ourOutline->mOutlineOffset.ToAppUnits();
+  nsRect innerRect = aInnerRect;
+  innerRect.Inflate(offset);
+
+  // If the dirty rect is completely inside the border area (e.g., only the
+  // content is being painted), then we can skip out now
+  // XXX this isn't exactly true for rounded borders, where the inside curves
+  // may encroach into the content area.  A safer calculation would be to
+  // shorten insideRect by the radius one each side before performing this test.
+  if (innerRect.Contains(aDirtyRect)) {
+    return Nothing();
+  }
+
+  nscoord width = ourOutline->GetOutlineWidth();
+
+  StyleBorderStyle outlineStyle;
+  // Themed outlines are handled by our callers, if supported.
+  if (ourOutline->mOutlineStyle.IsAuto()) {
+    if (width == 0) {
+      return Nothing();  // empty outline
+    }
+    // http://dev.w3.org/csswg/css-ui/#outline
+    // "User agents may treat 'auto' as 'solid'."
+    outlineStyle = StyleBorderStyle::Solid;
+  } else {
+    outlineStyle = ourOutline->mOutlineStyle.AsBorderStyle();
+  }
+
+  RectCornerRadii outlineRadii;
+  nsRect outerRect = innerRect;
+  outerRect.Inflate(width);
+
+  const nscoord oneDevPixel = aPresContext->AppUnitsPerDevPixel();
+  Rect oRect(NSRectToRect(outerRect, oneDevPixel));
+
+  const Float outlineWidths[4] = {
+      Float(width) / oneDevPixel, Float(width) / oneDevPixel,
+      Float(width) / oneDevPixel, Float(width) / oneDevPixel};
+
+  // convert the radii
+  nscoord twipsRadii[8];
+
+  // get the radius for our outline
+  if (aForFrame->GetBorderRadii(twipsRadii)) {
+    RectCornerRadii innerRadii;
+    ComputePixelRadii(twipsRadii, oneDevPixel, &innerRadii);
+
+    Float devPixelOffset = aPresContext->AppUnitsToFloatDevPixels(offset);
+    const Float widths[4] = {
+        outlineWidths[0] + devPixelOffset, outlineWidths[1] + devPixelOffset,
+        outlineWidths[2] + devPixelOffset, outlineWidths[3] + devPixelOffset};
+    nsCSSBorderRenderer::ComputeOuterRadii(innerRadii, widths, &outlineRadii);
+  }
+
+  StyleBorderStyle outlineStyles[4] = {outlineStyle, outlineStyle, outlineStyle,
+                                       outlineStyle};
+
+  // This handles treating the initial color as 'currentColor'; if we
+  // ever want 'invert' back we'll need to do a bit of work here too.
+  nscolor outlineColor =
+      aStyle->GetVisitedDependentColor(&nsStyleOutline::mOutlineColor);
+  nscolor outlineColors[4] = {outlineColor, outlineColor, outlineColor,
+                              outlineColor};
+
+  Rect dirtyRect = NSRectToRect(aDirtyRect, oneDevPixel);
+
+  return Some(nsCSSBorderRenderer(
+      aPresContext, aDrawTarget, dirtyRect, oRect, outlineStyles, outlineWidths,
+      outlineRadii, outlineColors, !aForFrame->BackfaceIsHidden(), Nothing()));
+}
+
+void nsCSSRendering::PaintNonThemedOutline(nsPresContext* aPresContext,
+                                           gfxContext& aRenderingContext,
+                                           nsIFrame* aForFrame,
+                                           const nsRect& aDirtyRect,
+                                           const nsRect& aInnerRect,
+                                           ComputedStyle* aStyle) {
+  Maybe<nsCSSBorderRenderer> br = CreateBorderRendererForNonThemedOutline(
+      aPresContext, aRenderingContext.GetDrawTarget(), aForFrame, aDirtyRect,
+      aInnerRect, aStyle);
+  if (!br) {
+    return;
+  }
+
+  // start drawing
+  br->DrawBorders();
+
+  PrintAsStringNewline();
+}
+
+void nsCSSRendering::PaintFocus(nsPresContext* aPresContext,
+                                DrawTarget* aDrawTarget,
+                                const nsRect& aFocusRect, nscolor aColor) {
+  nscoord oneCSSPixel = nsPresContext::CSSPixelsToAppUnits(1);
+  nscoord oneDevPixel = aPresContext->DevPixelsToAppUnits(1);
+
+  Rect focusRect(NSRectToRect(aFocusRect, oneDevPixel));
+
+  RectCornerRadii focusRadii;
+  {
+    nscoord twipsRadii[8] = {0, 0, 0, 0, 0, 0, 0, 0};
+    ComputePixelRadii(twipsRadii, oneDevPixel, &focusRadii);
+  }
+  Float focusWidths[4] = {
+      Float(oneCSSPixel) / oneDevPixel, Float(oneCSSPixel) / oneDevPixel,
+      Float(oneCSSPixel) / oneDevPixel, Float(oneCSSPixel) / oneDevPixel};
+
+  StyleBorderStyle focusStyles[4] = {
+      StyleBorderStyle::Dotted, StyleBorderStyle::Dotted,
+      StyleBorderStyle::Dotted, StyleBorderStyle::Dotted};
+  nscolor focusColors[4] = {aColor, aColor, aColor, aColor};
+
+  // Because this renders a dotted border, the background color
+  // should not be used.  Therefore, we provide a value that will
+  // be blatantly wrong if it ever does get used.  (If this becomes
+  // something that CSS can style, this function will then have access
+  // to a ComputedStyle and can use the same logic that PaintBorder
+  // and PaintOutline do.)
+  //
+  // WebRender layers-free mode don't use PaintFocus function. Just assign
+  // the backface-visibility to true for this case.
+  nsCSSBorderRenderer br(aPresContext, aDrawTarget, focusRect, focusRect,
+                         focusStyles, focusWidths, focusRadii, focusColors,
+                         true, Nothing());
+  br.DrawBorders();
+
+  PrintAsStringNewline();
+}
+
+// Thebes Border Rendering Code End
+//----------------------------------------------------------------------
+
+//----------------------------------------------------------------------
+
+/**
+ * Helper for ComputeObjectAnchorPoint; parameters are the same as for
+ * that function, except they're for a single coordinate / a single size
+ * dimension. (so, x/width vs. y/height)
+ */
+static void ComputeObjectAnchorCoord(const LengthPercentage& aCoord,
+                                     const nscoord aOriginBounds,
+                                     const nscoord aImageSize,
+                                     nscoord* aTopLeftCoord,
+                                     nscoord* aAnchorPointCoord) {
+  nscoord extraSpace = aOriginBounds - aImageSize;
+
+  // The anchor-point doesn't care about our image's size; just the size
+  // of the region we're rendering into.
+  *aAnchorPointCoord = aCoord.Resolve(
+      aOriginBounds, static_cast<nscoord (*)(float)>(NSToCoordRoundWithClamp));
+  // Adjust aTopLeftCoord by the specified % of the extra space.
+  *aTopLeftCoord = aCoord.Resolve(
+      extraSpace, static_cast<nscoord (*)(float)>(NSToCoordRoundWithClamp));
+}
+
+void nsImageRenderer::ComputeObjectAnchorPoint(const Position& aPos,
+                                               const nsSize& aOriginBounds,
+                                               const nsSize& aImageSize,
+                                               nsPoint* aTopLeft,
+                                               nsPoint* aAnchorPoint) {
+  ComputeObjectAnchorCoord(aPos.horizontal, aOriginBounds.width,
+                           aImageSize.width, &aTopLeft->x, &aAnchorPoint->x);
+
+  ComputeObjectAnchorCoord(aPos.vertical, aOriginBounds.height,
+                           aImageSize.height, &aTopLeft->y, &aAnchorPoint->y);
+}
+
+auto nsCSSRendering::FindEffectiveBackgroundColor(nsIFrame* aFrame,
+                                                  bool aStopAtThemed,
+                                                  bool aPreferBodyToCanvas)
+    -> EffectiveBackgroundColor {
+  MOZ_ASSERT(aFrame);
+
+  auto BgColorIfNotTransparent = [](nsIFrame* aFrame) -> Maybe<nscolor> {
+    nscolor c =
+        aFrame->GetVisitedDependentColor(&nsStyleBackground::mBackgroundColor);
+    if (NS_GET_A(c) == 255) {
+      return Some(c);
+    }
+    if (NS_GET_A(c)) {
+      // TODO(emilio): We should maybe just blend with ancestor bg colors and
+      // such, but this is probably good enough for now, matches pre-existing
+      // behavior.
+      const nscolor defaultBg = aFrame->PresContext()->DefaultBackgroundColor();
+      MOZ_ASSERT(NS_GET_A(defaultBg) == 255, "PreferenceSheet guarantees this");
+      return Some(NS_ComposeColors(defaultBg, c));
+    }
+    return Nothing();
+  };
+
+  for (nsIFrame* frame = aFrame; frame;
+       frame = nsLayoutUtils::GetParentOrPlaceholderForCrossDoc(frame)) {
+    if (auto bg = BgColorIfNotTransparent(frame)) {
+      return {*bg};
+    }
+
+    if (aStopAtThemed && frame->IsThemed()) {
+      return {NS_TRANSPARENT, true};
+    }
+
+    if (frame->IsCanvasFrame()) {
+      if (aPreferBodyToCanvas) {
+        if (auto* body = frame->PresContext()->Document()->GetBodyElement()) {
+          if (nsIFrame* f = body->GetPrimaryFrame()) {
+            if (auto bg = BgColorIfNotTransparent(f)) {
+              return {*bg};
+            }
+          }
+        }
+      }
+      if (nsIFrame* bgFrame = FindBackgroundFrame(frame)) {
+        if (auto bg = BgColorIfNotTransparent(bgFrame)) {
+          return {*bg};
+        }
+      }
+    }
+  }
+
+  return {aFrame->PresContext()->DefaultBackgroundColor()};
+}
+
+nsIFrame* nsCSSRendering::FindBackgroundStyleFrame(nsIFrame* aForFrame) {
+  const nsStyleBackground* result = aForFrame->StyleBackground();
+
+  // Check if we need to do propagation from BODY rather than HTML.
+  if (!result->IsTransparent(aForFrame)) {
+    return aForFrame;
+  }
+
+  nsIContent* content = aForFrame->GetContent();
+  // The root element content can't be null. We wouldn't know what
+  // frame to create for aFrame.
+  // Use |OwnerDoc| so it works during destruction.
+  if (!content) {
+    return aForFrame;
+  }
+
+  Document* document = content->OwnerDoc();
+
+  dom::Element* bodyContent = document->GetBodyElement();
+  // We need to null check the body node (bug 118829) since
+  // there are cases, thanks to the fix for bug 5569, where we
+  // will reflow a document with no body.  In particular, if a
+  // SCRIPT element in the head blocks the parser and then has a
+  // SCRIPT that does "document.location.href = 'foo'", then
+  // nsParser::Terminate will call |DidBuildModel| methods
+  // through to the content sink, which will call |StartLayout|
+  // and thus |Initialize| on the pres shell.  See bug 119351
+  // for the ugly details.
+  if (!bodyContent || aForFrame->StyleDisplay()->IsContainAny()) {
+    return aForFrame;
+  }
+
+  nsIFrame* bodyFrame = bodyContent->GetPrimaryFrame();
+  if (!bodyFrame || bodyFrame->StyleDisplay()->IsContainAny()) {
+    return aForFrame;
+  }
+
+  return nsLayoutUtils::GetStyleFrame(bodyFrame);
+}
+
+/**
+ * |FindBackground| finds the correct style data to use to paint the
+ * background.  It is responsible for handling the following two
+ * statements in section 14.2 of CSS2:
+ *
+ *   The background of the box generated by the root element covers the
+ *   entire canvas.
+ *
+ *   For HTML documents, however, we recommend that authors specify the
+ *   background for the BODY element rather than the HTML element. User
+ *   agents should observe the following precedence rules to fill in the
+ *   background: if the value of the 'background' property for the HTML
+ *   element is different from 'transparent' then use it, else use the
+ *   value of the 'background' property for the BODY element. If the
+ *   resulting value is 'transparent', the rendering is undefined.
+ *
+ * Thus, in our implementation, it is responsible for ensuring that:
+ *  + we paint the correct background on the |nsCanvasFrame| or |nsPageFrame|,
+ *  + we don't paint the background on the root element, and
+ *  + we don't paint the background on the BODY element in *some* cases,
+ *    and for SGML-based HTML documents only.
+ *
+ * |FindBackground| checks whether a background should be painted. If yes, it
+ * returns the resulting ComputedStyle to use for the background information;
+ * Otherwise, it returns nullptr.
+ */
+ComputedStyle* nsCSSRendering::FindRootFrameBackground(nsIFrame* aForFrame) {
+  return FindBackgroundStyleFrame(aForFrame)->Style();
+}
+
+// Helper for FindBackgroundFrame. Returns true if aForFrame has a meaningful
+// background that it should draw (i.e. that it hasn't propagated to another
+// frame).  See documentation for FindBackground.
+inline bool FrameHasMeaningfulBackground(const nsIFrame* aForFrame,
+                                         nsIFrame* aRootElementFrame) {
+  MOZ_ASSERT(!aForFrame->IsCanvasFrame(),
+             "FindBackgroundFrame handles canvas frames before calling us, "
+             "so we don't need to consider them here");
+
+  if (aForFrame == aRootElementFrame) {
+    // We must have propagated our background to the viewport or canvas. Abort.
+    return false;
+  }
+
+  // Return true unless the frame is for a BODY element whose background
+  // was propagated to the viewport.
+
+  nsIContent* content = aForFrame->GetContent();
+  if (!content || content->NodeInfo()->NameAtom() != nsGkAtoms::body) {
+    return true;  // not frame for a "body" element
+  }
+  // It could be a non-HTML "body" element but that's OK, we'd fail the
+  // bodyContent check below
+
+  if (aForFrame->Style()->GetPseudoType() != PseudoStyleType::NotPseudo ||
+      aForFrame->StyleDisplay()->IsContainAny()) {
+    return true;  // A pseudo-element frame, or contained.
+  }
+
+  // We should only look at the <html> background if we're in an HTML document
+  Document* document = content->OwnerDoc();
+
+  dom::Element* bodyContent = document->GetBodyElement();
+  if (bodyContent != content) {
+    return true;  // this wasn't the background that was propagated
+  }
+
+  // This can be called even when there's no root element yet, during frame
+  // construction, via nsLayoutUtils::FrameHasTransparency and
+  // nsContainerFrame::SyncFrameViewProperties.
+  if (!aRootElementFrame || aRootElementFrame->StyleDisplay()->IsContainAny()) {
+    return true;
+  }
+
+  const nsStyleBackground* htmlBG = aRootElementFrame->StyleBackground();
+  return !htmlBG->IsTransparent(aRootElementFrame);
+}
+
+nsIFrame* nsCSSRendering::FindBackgroundFrame(const nsIFrame* aForFrame) {
+  nsIFrame* rootElementFrame =
+      aForFrame->PresShell()->FrameConstructor()->GetRootElementStyleFrame();
+  if (aForFrame->IsCanvasFrame()) {
+    return FindCanvasBackgroundFrame(aForFrame, rootElementFrame);
+  }
+
+  if (FrameHasMeaningfulBackground(aForFrame, rootElementFrame)) {
+    return const_cast<nsIFrame*>(aForFrame);
+  }
+
+  return nullptr;
+}
+
+ComputedStyle* nsCSSRendering::FindBackground(const nsIFrame* aForFrame) {
+  if (auto* backgroundFrame = FindBackgroundFrame(aForFrame)) {
+    return backgroundFrame->Style();
+  }
+  return nullptr;
+}
+
+void nsCSSRendering::BeginFrameTreesLocked() { ++gFrameTreeLockCount; }
+
+void nsCSSRendering::EndFrameTreesLocked() {
+  NS_ASSERTION(gFrameTreeLockCount > 0, "Unbalanced EndFrameTreeLocked");
+  --gFrameTreeLockCount;
+  if (gFrameTreeLockCount == 0) {
+    gInlineBGData->Reset();
+  }
+}
+
+bool nsCSSRendering::HasBoxShadowNativeTheme(nsIFrame* aFrame,
+                                             bool& aMaybeHasBorderRadius) {
+  const nsStyleDisplay* styleDisplay = aFrame->StyleDisplay();
+  nsITheme::Transparency transparency;
+  if (aFrame->IsThemed(styleDisplay, &transparency)) {
+    aMaybeHasBorderRadius = false;
+    // For opaque (rectangular) theme widgets we can take the generic
+    // border-box path with border-radius disabled.
+    return transparency != nsITheme::eOpaque;
+  }
+
+  aMaybeHasBorderRadius = true;
+  return false;
+}
+
+gfx::sRGBColor nsCSSRendering::GetShadowColor(const StyleSimpleShadow& aShadow,
+                                              nsIFrame* aFrame,
+                                              float aOpacity) {
+  // Get the shadow color; if not specified, use the foreground color
+  nscolor shadowColor = aShadow.color.CalcColor(aFrame);
+  sRGBColor color = sRGBColor::FromABGR(shadowColor);
+  color.a *= aOpacity;
+  return color;
+}
+
+nsRect nsCSSRendering::GetShadowRect(const nsRect& aFrameArea,
+                                     bool aNativeTheme, nsIFrame* aForFrame) {
+  nsRect frameRect = aNativeTheme ? aForFrame->InkOverflowRectRelativeToSelf() +
+                                        aFrameArea.TopLeft()
+                                  : aFrameArea;
+  Sides skipSides = aForFrame->GetSkipSides();
+  frameRect = BoxDecorationRectForBorder(aForFrame, frameRect, skipSides);
+
+  // Explicitly do not need to account for the spread radius here
+  // Webrender does it for us or PaintBoxShadow will for non-WR
+  return frameRect;
+}
+
+bool nsCSSRendering::GetBorderRadii(const nsRect& aFrameRect,
+                                    const nsRect& aBorderRect, nsIFrame* aFrame,
+                                    RectCornerRadii& aOutRadii) {
+  const nscoord oneDevPixel = aFrame->PresContext()->DevPixelsToAppUnits(1);
+  nscoord twipsRadii[8];
+  NS_ASSERTION(
+      aBorderRect.Size() == aFrame->VisualBorderRectRelativeToSelf().Size(),
+      "unexpected size");
+  nsSize sz = aFrameRect.Size();
+  bool hasBorderRadius = aFrame->GetBorderRadii(sz, sz, Sides(), twipsRadii);
+  if (hasBorderRadius) {
+    ComputePixelRadii(twipsRadii, oneDevPixel, &aOutRadii);
+  }
+
+  return hasBorderRadius;
+}
+
+void nsCSSRendering::PaintBoxShadowOuter(nsPresContext* aPresContext,
+                                         gfxContext& aRenderingContext,
+                                         nsIFrame* aForFrame,
+                                         const nsRect& aFrameArea,
+                                         const nsRect& aDirtyRect,
+                                         float aOpacity) {
+  DrawTarget& aDrawTarget = *aRenderingContext.GetDrawTarget();
+  auto shadows = aForFrame->StyleEffects()->mBoxShadow.AsSpan();
+  if (shadows.IsEmpty()) {
+    return;
+  }
+
+  bool hasBorderRadius;
+  // mutually exclusive with hasBorderRadius
+  bool nativeTheme = HasBoxShadowNativeTheme(aForFrame, hasBorderRadius);
+  const nsStyleDisplay* styleDisplay = aForFrame->StyleDisplay();
+
+  nsRect frameRect = GetShadowRect(aFrameArea, nativeTheme, aForFrame);
+
+  // Get any border radius, since box-shadow must also have rounded corners if
+  // the frame does.
+  RectCornerRadii borderRadii;
+  const nscoord oneDevPixel = aPresContext->DevPixelsToAppUnits(1);
+  if (hasBorderRadius) {
+    nscoord twipsRadii[8];
+    NS_ASSERTION(
+        aFrameArea.Size() == aForFrame->VisualBorderRectRelativeToSelf().Size(),
+        "unexpected size");
+    nsSize sz = frameRect.Size();
+    hasBorderRadius = aForFrame->GetBorderRadii(sz, sz, Sides(), twipsRadii);
+    if (hasBorderRadius) {
+      ComputePixelRadii(twipsRadii, oneDevPixel, &borderRadii);
+    }
+  }
+
+  // We don't show anything that intersects with the frame we're blurring on. So
+  // tell the blurrer not to do unnecessary work there.
+  gfxRect skipGfxRect = ThebesRect(NSRectToRect(frameRect, oneDevPixel));
+  skipGfxRect.Round();
+  bool useSkipGfxRect = true;
+  if (nativeTheme) {
+    // Optimize non-leaf native-themed frames by skipping computing pixels
+    // in the padding-box. We assume the padding-box is going to be painted
+    // opaquely for non-leaf frames.
+    // XXX this may not be a safe assumption; we should make this go away
+    // by optimizing box-shadow drawing more for the cases where we don't have a
+    // skip-rect.
+    useSkipGfxRect = !aForFrame->IsLeaf();
+    nsRect paddingRect =
+        aForFrame->GetPaddingRectRelativeToSelf() + aFrameArea.TopLeft();
+    skipGfxRect = nsLayoutUtils::RectToGfxRect(paddingRect, oneDevPixel);
+  } else if (hasBorderRadius) {
+    skipGfxRect.Deflate(gfxMargin(
+        std::max(borderRadii[C_TL].height, borderRadii[C_TR].height), 0,
+        std::max(borderRadii[C_BL].height, borderRadii[C_BR].height), 0));
+  }
+
+  for (const StyleBoxShadow& shadow : Reversed(shadows)) {
+    if (shadow.inset) {
+      continue;
+    }
+
+    nsRect shadowRect = frameRect;
+    nsPoint shadowOffset(shadow.base.horizontal.ToAppUnits(),
+                         shadow.base.vertical.ToAppUnits());
+    shadowRect.MoveBy(shadowOffset);
+    nscoord shadowSpread = shadow.spread.ToAppUnits();
+    if (!nativeTheme) {
+      shadowRect.Inflate(shadowSpread);
+    }
+
+    // shadowRect won't include the blur, so make an extra rect here that
+    // includes the blur for use in the even-odd rule below.
+    nsRect shadowRectPlusBlur = shadowRect;
+    nscoord blurRadius = shadow.base.blur.ToAppUnits();
+    shadowRectPlusBlur.Inflate(
+        nsContextBoxBlur::GetBlurRadiusMargin(blurRadius, oneDevPixel));
+
+    Rect shadowGfxRectPlusBlur = NSRectToRect(shadowRectPlusBlur, oneDevPixel);
+    shadowGfxRectPlusBlur.RoundOut();
+    MaybeSnapToDevicePixels(shadowGfxRectPlusBlur, aDrawTarget, true);
+
+    sRGBColor gfxShadowColor = GetShadowColor(shadow.base, aForFrame, aOpacity);
+
+    if (nativeTheme) {
+      nsContextBoxBlur blurringArea;
+
+      // When getting the widget shape from the native theme, we're going
+      // to draw the widget into the shadow surface to create a mask.
+      // We need to ensure that there actually *is* a shadow surface
+      // and that we're not going to draw directly into aRenderingContext.
+      gfxContext* shadowContext = blurringArea.Init(
+          shadowRect, shadowSpread, blurRadius, oneDevPixel, &aRenderingContext,
+          aDirtyRect, useSkipGfxRect ? &skipGfxRect : nullptr,
+          nsContextBoxBlur::FORCE_MASK);
+      if (!shadowContext) continue;
+
+      MOZ_ASSERT(shadowContext == blurringArea.GetContext());
+
+      aRenderingContext.Save();
+      aRenderingContext.SetColor(gfxShadowColor);
+
+      // Draw the shape of the frame so it can be blurred. Recall how
+      // nsContextBoxBlur doesn't make any temporary surfaces if blur is 0 and
+      // it just returns the original surface? If we have no blur, we're
+      // painting this fill on the actual content surface (aRenderingContext ==
+      // shadowContext) which is why we set up the color and clip before doing
+      // this.
+
+      // We don't clip the border-box from the shadow, nor any other box.
+      // We assume that the native theme is going to paint over the shadow.
+
+      // Draw the widget shape
+      gfxContextMatrixAutoSaveRestore save(shadowContext);
+      gfxPoint devPixelOffset = nsLayoutUtils::PointToGfxPoint(
+          shadowOffset, aPresContext->AppUnitsPerDevPixel());
+      shadowContext->SetMatrixDouble(
+          shadowContext->CurrentMatrixDouble().PreTranslate(devPixelOffset));
+
+      nsRect nativeRect = aDirtyRect;
+      nativeRect.MoveBy(-shadowOffset);
+      nativeRect.IntersectRect(frameRect, nativeRect);
+      aPresContext->Theme()->DrawWidgetBackground(
+          shadowContext, aForFrame, styleDisplay->EffectiveAppearance(),
+          aFrameArea, nativeRect, nsITheme::DrawOverflow::No);
+
+      blurringArea.DoPaint();
+      aRenderingContext.Restore();
+    } else {
+      aRenderingContext.Save();
+
+      {
+        Rect innerClipRect = NSRectToRect(frameRect, oneDevPixel);
+        if (!MaybeSnapToDevicePixels(innerClipRect, aDrawTarget, true)) {
+          innerClipRect.Round();
+        }
+
+        // Clip out the interior of the frame's border edge so that the shadow
+        // is only painted outside that area.
+        RefPtr<PathBuilder> builder =
+            aDrawTarget.CreatePathBuilder(FillRule::FILL_EVEN_ODD);
+        AppendRectToPath(builder, shadowGfxRectPlusBlur);
+        if (hasBorderRadius) {
+          AppendRoundedRectToPath(builder, innerClipRect, borderRadii);
+        } else {
+          AppendRectToPath(builder, innerClipRect);
+        }
+        RefPtr<Path> path = builder->Finish();
+        aRenderingContext.Clip(path);
+      }
+
+      // Clip the shadow so that we only get the part that applies to aForFrame.
+      nsRect fragmentClip = shadowRectPlusBlur;
+      Sides skipSides = aForFrame->GetSkipSides();
+      if (!skipSides.IsEmpty()) {
+        if (skipSides.Left()) {
+          nscoord xmost = fragmentClip.XMost();
+          fragmentClip.x = aFrameArea.x;
+          fragmentClip.width = xmost - fragmentClip.x;
+        }
+        if (skipSides.Right()) {
+          nscoord xmost = fragmentClip.XMost();
+          nscoord overflow = xmost - aFrameArea.XMost();
+          if (overflow > 0) {
+            fragmentClip.width -= overflow;
+          }
+        }
+        if (skipSides.Top()) {
+          nscoord ymost = fragmentClip.YMost();
+          fragmentClip.y = aFrameArea.y;
+          fragmentClip.height = ymost - fragmentClip.y;
+        }
+        if (skipSides.Bottom()) {
+          nscoord ymost = fragmentClip.YMost();
+          nscoord overflow = ymost - aFrameArea.YMost();
+          if (overflow > 0) {
+            fragmentClip.height -= overflow;
+          }
+        }
+      }
+      fragmentClip = fragmentClip.Intersect(aDirtyRect);
+      aRenderingContext.Clip(NSRectToSnappedRect(
+          fragmentClip, aForFrame->PresContext()->AppUnitsPerDevPixel(),
+          aDrawTarget));
+
+      RectCornerRadii clipRectRadii;
+      if (hasBorderRadius) {
+        Float spreadDistance = Float(shadowSpread / oneDevPixel);
+
+        Float borderSizes[4];
+
+        borderSizes[eSideLeft] = spreadDistance;
+        borderSizes[eSideTop] = spreadDistance;
+        borderSizes[eSideRight] = spreadDistance;
+        borderSizes[eSideBottom] = spreadDistance;
+
+        nsCSSBorderRenderer::ComputeOuterRadii(borderRadii, borderSizes,
+                                               &clipRectRadii);
+      }
+      nsContextBoxBlur::BlurRectangle(
+          &aRenderingContext, shadowRect, oneDevPixel,
+          hasBorderRadius ? &clipRectRadii : nullptr, blurRadius,
+          gfxShadowColor, aDirtyRect, skipGfxRect);
+      aRenderingContext.Restore();
+    }
+  }
+}
+
+nsRect nsCSSRendering::GetBoxShadowInnerPaddingRect(nsIFrame* aFrame,
+                                                    const nsRect& aFrameArea) {
+  Sides skipSides = aFrame->GetSkipSides();
+  nsRect frameRect = BoxDecorationRectForBorder(aFrame, aFrameArea, skipSides);
+
+  nsRect paddingRect = frameRect;
+  nsMargin border = aFrame->GetUsedBorder();
+  paddingRect.Deflate(border);
+  return paddingRect;
+}
+
+bool nsCSSRendering::ShouldPaintBoxShadowInner(nsIFrame* aFrame) {
+  const Span<const StyleBoxShadow> shadows =
+      aFrame->StyleEffects()->mBoxShadow.AsSpan();
+  if (shadows.IsEmpty()) {
+    return false;
+  }
+
+  if (aFrame->IsThemed() && aFrame->GetContent() &&
+      !nsContentUtils::IsChromeDoc(aFrame->GetContent()->GetComposedDoc())) {
+    // There's no way of getting hold of a shape corresponding to a
+    // "padding-box" for native-themed widgets, so just don't draw
+    // inner box-shadows for them. But we allow chrome to paint inner
+    // box shadows since chrome can be aware of the platform theme.
+    return false;
+  }
+
+  return true;
+}
+
+bool nsCSSRendering::GetShadowInnerRadii(nsIFrame* aFrame,
+                                         const nsRect& aFrameArea,
+                                         RectCornerRadii& aOutInnerRadii) {
+  // Get any border radius, since box-shadow must also have rounded corners
+  // if the frame does.
+  nscoord twipsRadii[8];
+  nsRect frameRect =
+      BoxDecorationRectForBorder(aFrame, aFrameArea, aFrame->GetSkipSides());
+  nsSize sz = frameRect.Size();
+  nsMargin border = aFrame->GetUsedBorder();
+  aFrame->GetBorderRadii(sz, sz, Sides(), twipsRadii);
+  const nscoord oneDevPixel = aFrame->PresContext()->DevPixelsToAppUnits(1);
+
+  RectCornerRadii borderRadii;
+
+  const bool hasBorderRadius =
+      GetBorderRadii(frameRect, aFrameArea, aFrame, borderRadii);
+
+  if (hasBorderRadius) {
+    ComputePixelRadii(twipsRadii, oneDevPixel, &borderRadii);
+
+    Float borderSizes[4] = {
+        Float(border.top) / oneDevPixel, Float(border.right) / oneDevPixel,
+        Float(border.bottom) / oneDevPixel, Float(border.left) / oneDevPixel};
+    nsCSSBorderRenderer::ComputeInnerRadii(borderRadii, borderSizes,
+                                           &aOutInnerRadii);
+  }
+
+  return hasBorderRadius;
+}
+
+void nsCSSRendering::PaintBoxShadowInner(nsPresContext* aPresContext,
+                                         gfxContext& aRenderingContext,
+                                         nsIFrame* aForFrame,
+                                         const nsRect& aFrameArea) {
+  if (!ShouldPaintBoxShadowInner(aForFrame)) {
+    return;
+  }
+
+  const Span<const StyleBoxShadow> shadows =
+      aForFrame->StyleEffects()->mBoxShadow.AsSpan();
+  NS_ASSERTION(
+      aForFrame->IsFieldSetFrame() || aFrameArea.Size() == aForFrame->GetSize(),
+      "unexpected size");
+
+  nsRect paddingRect = GetBoxShadowInnerPaddingRect(aForFrame, aFrameArea);
+
+  RectCornerRadii innerRadii;
+  bool hasBorderRadius = GetShadowInnerRadii(aForFrame, aFrameArea, innerRadii);
+
+  const nscoord oneDevPixel = aPresContext->DevPixelsToAppUnits(1);
+
+  for (const StyleBoxShadow& shadow : Reversed(shadows)) {
+    if (!shadow.inset) {
+      continue;
+    }
+
+    // shadowPaintRect: the area to paint on the temp surface
+    // shadowClipRect: the area on the temporary surface within shadowPaintRect
+    //                 that we will NOT paint in
+    nscoord blurRadius = shadow.base.blur.ToAppUnits();
+    nsMargin blurMargin =
+        nsContextBoxBlur::GetBlurRadiusMargin(blurRadius, oneDevPixel);
+    nsRect shadowPaintRect = paddingRect;
+    shadowPaintRect.Inflate(blurMargin);
+
+    // Round the spread radius to device pixels (by truncation).
+    // This mostly matches what we do for borders, except that we don't round
+    // up values between zero and one device pixels to one device pixel.
+    // This way of rounding is symmetric around zero, which makes sense for
+    // the spread radius.
+    int32_t spreadDistance = shadow.spread.ToAppUnits() / oneDevPixel;
+    nscoord spreadDistanceAppUnits =
+        aPresContext->DevPixelsToAppUnits(spreadDistance);
+
+    nsRect shadowClipRect = paddingRect;
+    shadowClipRect.MoveBy(shadow.base.horizontal.ToAppUnits(),
+                          shadow.base.vertical.ToAppUnits());
+    shadowClipRect.Deflate(spreadDistanceAppUnits, spreadDistanceAppUnits);
+
+    Rect shadowClipGfxRect = NSRectToRect(shadowClipRect, oneDevPixel);
+    shadowClipGfxRect.Round();
+
+    RectCornerRadii clipRectRadii;
+    if (hasBorderRadius) {
+      // Calculate the radii the inner clipping rect will have
+      Float borderSizes[4] = {0, 0, 0, 0};
+
+      // See PaintBoxShadowOuter and bug 514670
+      if (innerRadii[C_TL].width > 0 || innerRadii[C_BL].width > 0) {
+        borderSizes[eSideLeft] = spreadDistance;
+      }
+
+      if (innerRadii[C_TL].height > 0 || innerRadii[C_TR].height > 0) {
+        borderSizes[eSideTop] = spreadDistance;
+      }
+
+      if (innerRadii[C_TR].width > 0 || innerRadii[C_BR].width > 0) {
+        borderSizes[eSideRight] = spreadDistance;
+      }
+
+      if (innerRadii[C_BL].height > 0 || innerRadii[C_BR].height > 0) {
+        borderSizes[eSideBottom] = spreadDistance;
+      }
+
+      nsCSSBorderRenderer::ComputeInnerRadii(innerRadii, borderSizes,
+                                             &clipRectRadii);
+    }
+
+    // Set the "skip rect" to the area within the frame that we don't paint in,
+    // including after blurring.
+    nsRect skipRect = shadowClipRect;
+    skipRect.Deflate(blurMargin);
+    gfxRect skipGfxRect = nsLayoutUtils::RectToGfxRect(skipRect, oneDevPixel);
+    if (hasBorderRadius) {
+      skipGfxRect.Deflate(gfxMargin(
+          std::max(clipRectRadii[C_TL].height, clipRectRadii[C_TR].height), 0,
+          std::max(clipRectRadii[C_BL].height, clipRectRadii[C_BR].height), 0));
+    }
+
+    // When there's a blur radius, gfxAlphaBoxBlur leaves the skiprect area
+    // unchanged. And by construction the gfxSkipRect is not touched by the
+    // rendered shadow (even after blurring), so those pixels must be completely
+    // transparent in the shadow, so drawing them changes nothing.
+    DrawTarget* drawTarget = aRenderingContext.GetDrawTarget();
+
+    // Clip the context to the area of the frame's padding rect, so no part of
+    // the shadow is painted outside. Also cut out anything beyond where the
+    // inset shadow will be.
+    Rect shadowGfxRect = NSRectToRect(paddingRect, oneDevPixel);
+    shadowGfxRect.Round();
+
+    sRGBColor shadowColor = GetShadowColor(shadow.base, aForFrame, 1.0);
+    aRenderingContext.Save();
+
+    // This clips the outside border radius.
+    // clipRectRadii is the border radius inside the inset shadow.
+    if (hasBorderRadius) {
+      RefPtr<Path> roundedRect =
+          MakePathForRoundedRect(*drawTarget, shadowGfxRect, innerRadii);
+      aRenderingContext.Clip(roundedRect);
+    } else {
+      aRenderingContext.Clip(shadowGfxRect);
+    }
+
+    nsContextBoxBlur insetBoxBlur;
+    gfxRect destRect =
+        nsLayoutUtils::RectToGfxRect(shadowPaintRect, oneDevPixel);
+    Point shadowOffset(shadow.base.horizontal.ToAppUnits() / oneDevPixel,
+                       shadow.base.vertical.ToAppUnits() / oneDevPixel);
+
+    insetBoxBlur.InsetBoxBlur(
+        &aRenderingContext, ToRect(destRect), shadowClipGfxRect, shadowColor,
+        blurRadius, spreadDistanceAppUnits, oneDevPixel, hasBorderRadius,
+        clipRectRadii, ToRect(skipGfxRect), shadowOffset);
+    aRenderingContext.Restore();
+  }
+}
+
+/* static */
+nsCSSRendering::PaintBGParams nsCSSRendering::PaintBGParams::ForAllLayers(
+    nsPresContext& aPresCtx, const nsRect& aDirtyRect,
+    const nsRect& aBorderArea, nsIFrame* aFrame, uint32_t aPaintFlags,
+    float aOpacity) {
+  MOZ_ASSERT(aFrame);
+
+  PaintBGParams result(aPresCtx, aDirtyRect, aBorderArea, aFrame, aPaintFlags,
+                       -1, CompositionOp::OP_OVER, aOpacity);
+
+  return result;
+}
+
+/* static */
+nsCSSRendering::PaintBGParams nsCSSRendering::PaintBGParams::ForSingleLayer(
+    nsPresContext& aPresCtx, const nsRect& aDirtyRect,
+    const nsRect& aBorderArea, nsIFrame* aFrame, uint32_t aPaintFlags,
+    int32_t aLayer, CompositionOp aCompositionOp, float aOpacity) {
+  MOZ_ASSERT(aFrame && (aLayer != -1));
+
+  PaintBGParams result(aPresCtx, aDirtyRect, aBorderArea, aFrame, aPaintFlags,
+                       aLayer, aCompositionOp, aOpacity);
+
+  return result;
+}
+
+ImgDrawResult nsCSSRendering::PaintStyleImageLayer(const PaintBGParams& aParams,
+                                                   gfxContext& aRenderingCtx) {
+  AUTO_PROFILER_LABEL("nsCSSRendering::PaintStyleImageLayer", GRAPHICS);
+
+  MOZ_ASSERT(aParams.frame,
+             "Frame is expected to be provided to PaintStyleImageLayer");
+
+  const ComputedStyle* sc = FindBackground(aParams.frame);
+  if (!sc) {
+    // We don't want to bail out if moz-appearance is set on a root
+    // node. If it has a parent content node, bail because it's not
+    // a root, otherwise keep going in order to let the theme stuff
+    // draw the background. The canvas really should be drawing the
+    // bg, but there's no way to hook that up via css.
+    if (!aParams.frame->StyleDisplay()->HasAppearance()) {
+      return ImgDrawResult::SUCCESS;
+    }
+
+    nsIContent* content = aParams.frame->GetContent();
+    if (!content || content->GetParent()) {
+      return ImgDrawResult::SUCCESS;
+    }
+
+    sc = aParams.frame->Style();
+  }
+
+  return PaintStyleImageLayerWithSC(aParams, aRenderingCtx, sc,
+                                    *aParams.frame->StyleBorder());
+}
+
+bool nsCSSRendering::CanBuildWebRenderDisplayItemsForStyleImageLayer(
+    WebRenderLayerManager* aManager, nsPresContext& aPresCtx, nsIFrame* aFrame,
+    const nsStyleBackground* aBackgroundStyle, int32_t aLayer,
+    uint32_t aPaintFlags) {
+  if (!aBackgroundStyle) {
+    return false;
+  }
+
+  MOZ_ASSERT(aFrame && aLayer >= 0 &&
+             (uint32_t)aLayer < aBackgroundStyle->mImage.mLayers.Length());
+
+  // We cannot draw native themed backgrounds
+  StyleAppearance appearance = aFrame->StyleDisplay()->EffectiveAppearance();
+  if (appearance != StyleAppearance::None) {
+    nsITheme* theme = aPresCtx.Theme();
+    if (theme->ThemeSupportsWidget(&aPresCtx, aFrame, appearance)) {
+      return false;
+    }
+  }
+
+  // We only support painting gradients and image for a single style image
+  // layer, and we don't support crop-rects.
+  const auto& styleImage =
+      aBackgroundStyle->mImage.mLayers[aLayer].mImage.FinalImage();
+  if (styleImage.IsImageRequestType()) {
+    if (styleImage.IsRect()) {
+      return false;
+    }
+
+    imgRequestProxy* requestProxy = styleImage.GetImageRequest();
+    if (!requestProxy) {
+      return false;
+    }
+
+    uint32_t imageFlags = imgIContainer::FLAG_NONE;
+    if (aPaintFlags & nsCSSRendering::PAINTBG_SYNC_DECODE_IMAGES) {
+      imageFlags |= imgIContainer::FLAG_SYNC_DECODE;
+    }
+
+    nsCOMPtr<imgIContainer> srcImage;
+    requestProxy->GetImage(getter_AddRefs(srcImage));
+    if (!srcImage ||
+        !srcImage->IsImageContainerAvailable(aManager, imageFlags)) {
+      return false;
+    }
+
+    return true;
+  }
+
+  if (styleImage.IsGradient()) {
+    return true;
+  }
+
+  return false;
+}
+
+ImgDrawResult nsCSSRendering::BuildWebRenderDisplayItemsForStyleImageLayer(
+    const PaintBGParams& aParams, mozilla::wr::DisplayListBuilder& aBuilder,
+    mozilla::wr::IpcResourceUpdateQueue& aResources,
+    const mozilla::layers::StackingContextHelper& aSc,
+    mozilla::layers::RenderRootStateManager* aManager, nsDisplayItem* aItem) {
+  MOZ_ASSERT(aParams.frame,
+             "Frame is expected to be provided to "
+             "BuildWebRenderDisplayItemsForStyleImageLayer");
+
+  ComputedStyle* sc = FindBackground(aParams.frame);
+  if (!sc) {
+    // We don't want to bail out if moz-appearance is set on a root
+    // node. If it has a parent content node, bail because it's not
+    // a root, otherwise keep going in order to let the theme stuff
+    // draw the background. The canvas really should be drawing the
+    // bg, but there's no way to hook that up via css.
+    if (!aParams.frame->StyleDisplay()->HasAppearance()) {
+      return ImgDrawResult::SUCCESS;
+    }
+
+    nsIContent* content = aParams.frame->GetContent();
+    if (!content || content->GetParent()) {
+      return ImgDrawResult::SUCCESS;
+    }
+
+    sc = aParams.frame->Style();
+  }
+  return BuildWebRenderDisplayItemsForStyleImageLayerWithSC(
+      aParams, aBuilder, aResources, aSc, aManager, aItem, sc,
+      *aParams.frame->StyleBorder());
+}
+
+static bool IsOpaqueBorderEdge(const nsStyleBorder& aBorder,
+                               mozilla::Side aSide) {
+  if (aBorder.GetComputedBorder().Side(aSide) == 0) return true;
+  switch (aBorder.GetBorderStyle(aSide)) {
+    case StyleBorderStyle::Solid:
+    case StyleBorderStyle::Groove:
+    case StyleBorderStyle::Ridge:
+    case StyleBorderStyle::Inset:
+    case StyleBorderStyle::Outset:
+      break;
+    default:
+      return false;
+  }
+
+  // If we're using a border image, assume it's not fully opaque,
+  // because we may not even have the image loaded at this point, and
+  // even if we did, checking whether the relevant tile is fully
+  // opaque would be too much work.
+  if (!aBorder.mBorderImageSource.IsNone()) {
+    return false;
+  }
+
+  StyleColor color = aBorder.BorderColorFor(aSide);
+  // We don't know the foreground color here, so if it's being used
+  // we must assume it might be transparent.
+  return !color.MaybeTransparent();
+}
+
+/**
+ * Returns true if all border edges are either missing or opaque.
+ */
+static bool IsOpaqueBorder(const nsStyleBorder& aBorder) {
+  for (const auto i : mozilla::AllPhysicalSides()) {
+    if (!IsOpaqueBorderEdge(aBorder, i)) {
+      return false;
+    }
+  }
+  return true;
+}
+
+static inline void SetupDirtyRects(const nsRect& aBGClipArea,
+                                   const nsRect& aCallerDirtyRect,
+                                   nscoord aAppUnitsPerPixel,
+                                   /* OUT: */
+                                   nsRect* aDirtyRect, gfxRect* aDirtyRectGfx) {
+  aDirtyRect->IntersectRect(aBGClipArea, aCallerDirtyRect);
+
+  // Compute the Thebes equivalent of the dirtyRect.
+  *aDirtyRectGfx = nsLayoutUtils::RectToGfxRect(*aDirtyRect, aAppUnitsPerPixel);
+  NS_WARNING_ASSERTION(aDirtyRect->IsEmpty() || !aDirtyRectGfx->IsEmpty(),
+                       "converted dirty rect should not be empty");
+  MOZ_ASSERT(!aDirtyRect->IsEmpty() || aDirtyRectGfx->IsEmpty(),
+             "second should be empty if first is");
+}
+
+static bool IsSVGStyleGeometryBox(StyleGeometryBox aBox) {
+  return (aBox == StyleGeometryBox::FillBox ||
+          aBox == StyleGeometryBox::StrokeBox ||
+          aBox == StyleGeometryBox::ViewBox);
+}
+
+static bool IsHTMLStyleGeometryBox(StyleGeometryBox aBox) {
+  return (aBox == StyleGeometryBox::ContentBox ||
+          aBox == StyleGeometryBox::PaddingBox ||
+          aBox == StyleGeometryBox::BorderBox ||
+          aBox == StyleGeometryBox::MarginBox);
+}
+
+static StyleGeometryBox ComputeBoxValue(nsIFrame* aForFrame,
+                                        StyleGeometryBox aBox) {
+  if (!aForFrame->HasAnyStateBits(NS_FRAME_SVG_LAYOUT)) {
+    // For elements with associated CSS layout box, the values fill-box,
+    // stroke-box and view-box compute to the initial value of mask-clip.
+    if (IsSVGStyleGeometryBox(aBox)) {
+      return StyleGeometryBox::BorderBox;
+    }
+  } else {
+    // For SVG elements without associated CSS layout box, the values
+    // content-box, padding-box, border-box and margin-box compute to fill-box.
+    if (IsHTMLStyleGeometryBox(aBox)) {
+      return StyleGeometryBox::FillBox;
+    }
+  }
+
+  return aBox;
+}
+
+bool nsCSSRendering::ImageLayerClipState::IsValid() const {
+  // mDirtyRectInDevPx comes from mDirtyRectInAppUnits. mDirtyRectInAppUnits
+  // can not be empty if mDirtyRectInDevPx is not.
+  if (!mDirtyRectInDevPx.IsEmpty() && mDirtyRectInAppUnits.IsEmpty()) {
+    return false;
+  }
+
+  if (mHasRoundedCorners == mClippedRadii.IsEmpty()) {
+    return false;
+  }
+
+  return true;
+}
+
+/* static */
+void nsCSSRendering::GetImageLayerClip(
+    const nsStyleImageLayers::Layer& aLayer, nsIFrame* aForFrame,
+    const nsStyleBorder& aBorder, const nsRect& aBorderArea,
+    const nsRect& aCallerDirtyRect, bool aWillPaintBorder,
+    nscoord aAppUnitsPerPixel,
+    /* out */ ImageLayerClipState* aClipState) {
+  StyleGeometryBox layerClip = ComputeBoxValue(aForFrame, aLayer.mClip);
+  if (IsSVGStyleGeometryBox(layerClip)) {
+    MOZ_ASSERT(aForFrame->IsFrameOfType(nsIFrame::eSVG) &&
+               !aForFrame->IsSVGOuterSVGFrame());
+
+    // The coordinate space of clipArea is svg user space.
+    nsRect clipArea = nsLayoutUtils::ComputeGeometryBox(aForFrame, layerClip);
+
+    nsRect strokeBox = (layerClip == StyleGeometryBox::StrokeBox)
+                           ? clipArea
+                           : nsLayoutUtils::ComputeGeometryBox(
+                                 aForFrame, StyleGeometryBox::StrokeBox);
+    nsRect clipAreaRelativeToStrokeBox = clipArea - strokeBox.TopLeft();
+
+    // aBorderArea is the stroke-box area in a coordinate space defined by
+    // the caller. This coordinate space can be svg user space of aForFrame,
+    // the space of aForFrame's reference-frame, or anything else.
+    //
+    // Which coordinate space chosen for aBorderArea is not matter. What
+    // matter is to ensure returning aClipState->mBGClipArea in the consistent
+    // coordiante space with aBorderArea. So we evaluate the position of clip
+    // area base on the position of aBorderArea here.
+    aClipState->mBGClipArea =
+        clipAreaRelativeToStrokeBox + aBorderArea.TopLeft();
+
+    SetupDirtyRects(aClipState->mBGClipArea, aCallerDirtyRect,
+                    aAppUnitsPerPixel, &aClipState->mDirtyRectInAppUnits,
+                    &aClipState->mDirtyRectInDevPx);
+    MOZ_ASSERT(aClipState->IsValid());
+    return;
+  }
+
+  if (layerClip == StyleGeometryBox::NoClip) {
+    aClipState->mBGClipArea = aCallerDirtyRect;
+
+    SetupDirtyRects(aClipState->mBGClipArea, aCallerDirtyRect,
+                    aAppUnitsPerPixel, &aClipState->mDirtyRectInAppUnits,
+                    &aClipState->mDirtyRectInDevPx);
+    MOZ_ASSERT(aClipState->IsValid());
+    return;
+  }
+
+  MOZ_ASSERT(!aForFrame->IsFrameOfType(nsIFrame::eSVG) ||
+             aForFrame->IsSVGOuterSVGFrame());
+
+  // Compute the outermost boundary of the area that might be painted.
+  // Same coordinate space as aBorderArea.
+  Sides skipSides = aForFrame->GetSkipSides();
+  nsRect clipBorderArea =
+      BoxDecorationRectForBorder(aForFrame, aBorderArea, skipSides, &aBorder);
+
+  bool haveRoundedCorners = false;
+  LayoutFrameType fType = aForFrame->Type();
+  if (fType != LayoutFrameType::TableColGroup &&
+      fType != LayoutFrameType::TableCol &&
+      fType != LayoutFrameType::TableRow &&
+      fType != LayoutFrameType::TableRowGroup) {
+    haveRoundedCorners = GetRadii(aForFrame, aBorder, aBorderArea,
+                                  clipBorderArea, aClipState->mRadii);
+  }
+  bool isSolidBorder = aWillPaintBorder && IsOpaqueBorder(aBorder);
+  if (isSolidBorder && layerClip == StyleGeometryBox::BorderBox) {
+    // If we have rounded corners, we need to inflate the background
+    // drawing area a bit to avoid seams between the border and
+    // background.
+    layerClip = haveRoundedCorners ? StyleGeometryBox::MozAlmostPadding
+                                   : StyleGeometryBox::PaddingBox;
+  }
+
+  aClipState->mBGClipArea = clipBorderArea;
+
+  if (aForFrame->IsScrollFrame() &&
+      StyleImageLayerAttachment::Local == aLayer.mAttachment) {
+    // As of this writing, this is still in discussion in the CSS Working Group
+    // http://lists.w3.org/Archives/Public/www-style/2013Jul/0250.html
+
+    // The rectangle for 'background-clip' scrolls with the content,
+    // but the background is also clipped at a non-scrolling 'padding-box'
+    // like the content. (See below.)
+    // Therefore, only 'content-box' makes a difference here.
+    if (layerClip == StyleGeometryBox::ContentBox) {
+      nsIScrollableFrame* scrollableFrame = do_QueryFrame(aForFrame);
+      // Clip at a rectangle attached to the scrolled content.
+      aClipState->mHasAdditionalBGClipArea = true;
+      aClipState->mAdditionalBGClipArea =
+          nsRect(aClipState->mBGClipArea.TopLeft() +
+                     scrollableFrame->GetScrolledFrame()->GetPosition()
+                     // For the dir=rtl case:
+                     + scrollableFrame->GetScrollRange().TopLeft(),
+                 scrollableFrame->GetScrolledRect().Size());
+      nsMargin padding = aForFrame->GetUsedPadding();
+      // padding-bottom is ignored on scrollable frames:
+      // https://bugzilla.mozilla.org/show_bug.cgi?id=748518
+      padding.bottom = 0;
+      padding.ApplySkipSides(skipSides);
+      aClipState->mAdditionalBGClipArea.Deflate(padding);
+    }
+
+    // Also clip at a non-scrolling, rounded-corner 'padding-box',
+    // same as the scrolled content because of the 'overflow' property.
+    layerClip = StyleGeometryBox::PaddingBox;
+  }
+
+  // See the comment of StyleGeometryBox::Margin.
+  // Hitting this assertion means we decide to turn on margin-box support for
+  // positioned mask from CSS parser and style system. In this case, you
+  // should *inflate* mBGClipArea by the margin returning from
+  // aForFrame->GetUsedMargin() in the code chunk bellow.
+  MOZ_ASSERT(layerClip != StyleGeometryBox::MarginBox,
+             "StyleGeometryBox::MarginBox rendering is not supported yet.\n");
+
+  if (layerClip != StyleGeometryBox::BorderBox &&
+      layerClip != StyleGeometryBox::Text) {
+    nsMargin border = aForFrame->GetUsedBorder();
+    if (layerClip == StyleGeometryBox::MozAlmostPadding) {
+      // Reduce |border| by 1px (device pixels) on all sides, if
+      // possible, so that we don't get antialiasing seams between the
+      // {background|mask} and border.
+      border.top = std::max(0, border.top - aAppUnitsPerPixel);
+      border.right = std::max(0, border.right - aAppUnitsPerPixel);
+      border.bottom = std::max(0, border.bottom - aAppUnitsPerPixel);
+      border.left = std::max(0, border.left - aAppUnitsPerPixel);
+    } else if (layerClip != StyleGeometryBox::PaddingBox) {
+      NS_ASSERTION(layerClip == StyleGeometryBox::ContentBox,
+                   "unexpected background-clip");
+      border += aForFrame->GetUsedPadding();
+    }
+    border.ApplySkipSides(skipSides);
+    aClipState->mBGClipArea.Deflate(border);
+
+    if (haveRoundedCorners) {
+      nsIFrame::AdjustBorderRadii(aClipState->mRadii, -border);
+    }
+  }
+
+  if (haveRoundedCorners) {
+    auto d2a = aForFrame->PresContext()->AppUnitsPerDevPixel();
+    nsCSSRendering::ComputePixelRadii(aClipState->mRadii, d2a,
+                                      &aClipState->mClippedRadii);
+    aClipState->mHasRoundedCorners = !aClipState->mClippedRadii.IsEmpty();
+  }
+
+  if (!haveRoundedCorners && aClipState->mHasAdditionalBGClipArea) {
+    // Do the intersection here to account for the fast path(?) below.
+    aClipState->mBGClipArea =
+        aClipState->mBGClipArea.Intersect(aClipState->mAdditionalBGClipArea);
+    aClipState->mHasAdditionalBGClipArea = false;
+  }
+
+  SetupDirtyRects(aClipState->mBGClipArea, aCallerDirtyRect, aAppUnitsPerPixel,
+                  &aClipState->mDirtyRectInAppUnits,
+                  &aClipState->mDirtyRectInDevPx);
+
+  MOZ_ASSERT(aClipState->IsValid());
+}
+
+static void SetupImageLayerClip(nsCSSRendering::ImageLayerClipState& aClipState,
+                                gfxContext* aCtx, nscoord aAppUnitsPerPixel,
+                                gfxContextAutoSaveRestore* aAutoSR) {
+  if (aClipState.mDirtyRectInDevPx.IsEmpty()) {
+    // Our caller won't draw anything under this condition, so no need
+    // to set more up.
+    return;
+  }
+
+  if (aClipState.mCustomClip) {
+    // We don't support custom clips and rounded corners, arguably a bug, but
+    // table painting seems to depend on it.
+    return;
+  }
+
+  // If we have rounded corners, clip all subsequent drawing to the
+  // rounded rectangle defined by bgArea and bgRadii (we don't know
+  // whether the rounded corners intrude on the dirtyRect or not).
+  // Do not do this if we have a caller-provided clip rect --
+  // as above with bgArea, arguably a bug, but table painting seems
+  // to depend on it.
+
+  if (aClipState.mHasAdditionalBGClipArea) {
+    gfxRect bgAreaGfx = nsLayoutUtils::RectToGfxRect(
+        aClipState.mAdditionalBGClipArea, aAppUnitsPerPixel);
+    bgAreaGfx.Round();
+    gfxUtils::ConditionRect(bgAreaGfx);
+
+    aAutoSR->EnsureSaved(aCtx);
+    aCtx->SnappedClip(bgAreaGfx);
+  }
+
+  if (aClipState.mHasRoundedCorners) {
+    Rect bgAreaGfx = NSRectToRect(aClipState.mBGClipArea, aAppUnitsPerPixel);
+    bgAreaGfx.Round();
+
+    if (bgAreaGfx.IsEmpty()) {
+      // I think it's become possible to hit this since
+      // https://hg.mozilla.org/mozilla-central/rev/50e934e4979b landed.
+      NS_WARNING("converted background area should not be empty");
+      // Make our caller not do anything.
+      aClipState.mDirtyRectInDevPx.SizeTo(gfxSize(0.0, 0.0));
+      return;
+    }
+
+    aAutoSR->EnsureSaved(aCtx);
+
+    RefPtr<Path> roundedRect = MakePathForRoundedRect(
+        *aCtx->GetDrawTarget(), bgAreaGfx, aClipState.mClippedRadii);
+    aCtx->Clip(roundedRect);
+  }
+}
+
+static void DrawBackgroundColor(nsCSSRendering::ImageLayerClipState& aClipState,
+                                gfxContext* aCtx, nscoord aAppUnitsPerPixel) {
+  if (aClipState.mDirtyRectInDevPx.IsEmpty()) {
+    // Our caller won't draw anything under this condition, so no need
+    // to set more up.
+    return;
+  }
+
+  DrawTarget* drawTarget = aCtx->GetDrawTarget();
+
+  // We don't support custom clips and rounded corners, arguably a bug, but
+  // table painting seems to depend on it.
+  if (!aClipState.mHasRoundedCorners || aClipState.mCustomClip) {
+    aCtx->NewPath();
+    aCtx->SnappedRectangle(aClipState.mDirtyRectInDevPx);
+    aCtx->Fill();
+    return;
+  }
+
+  Rect bgAreaGfx = NSRectToRect(aClipState.mBGClipArea, aAppUnitsPerPixel);
+  bgAreaGfx.Round();
+
+  if (bgAreaGfx.IsEmpty()) {
+    // I think it's become possible to hit this since
+    // https://hg.mozilla.org/mozilla-central/rev/50e934e4979b landed.
+    NS_WARNING("converted background area should not be empty");
+    // Make our caller not do anything.
+    aClipState.mDirtyRectInDevPx.SizeTo(gfxSize(0.0, 0.0));
+    return;
+  }
+
+  aCtx->Save();
+  gfxRect dirty = ThebesRect(bgAreaGfx).Intersect(aClipState.mDirtyRectInDevPx);
+
+  aCtx->SnappedClip(dirty);
+
+  if (aClipState.mHasAdditionalBGClipArea) {
+    gfxRect bgAdditionalAreaGfx = nsLayoutUtils::RectToGfxRect(
+        aClipState.mAdditionalBGClipArea, aAppUnitsPerPixel);
+    bgAdditionalAreaGfx.Round();
+    gfxUtils::ConditionRect(bgAdditionalAreaGfx);
+    aCtx->SnappedClip(bgAdditionalAreaGfx);
+  }
+
+  RefPtr<Path> roundedRect =
+      MakePathForRoundedRect(*drawTarget, bgAreaGfx, aClipState.mClippedRadii);
+  aCtx->SetPath(roundedRect);
+  aCtx->Fill();
+  aCtx->Restore();
+}
+
+enum class ScrollbarColorKind {
+  Thumb,
+  Track,
+};
+
+static Maybe<nscolor> CalcScrollbarColor(nsIFrame* aFrame,
+                                         ScrollbarColorKind aKind) {
+  ComputedStyle* scrollbarStyle = nsLayoutUtils::StyleForScrollbar(aFrame);
+  const auto& colors = scrollbarStyle->StyleUI()->mScrollbarColor;
+  if (colors.IsAuto()) {
+    return Nothing();
+  }
+  const auto& color = aKind == ScrollbarColorKind::Thumb
+                          ? colors.AsColors().thumb
+                          : colors.AsColors().track;
+  return Some(color.CalcColor(*scrollbarStyle));
+}
+
+static nscolor GetBackgroundColor(nsIFrame* aFrame,
+                                  const ComputedStyle* aStyle) {
+  switch (aStyle->StyleDisplay()->EffectiveAppearance()) {
+    case StyleAppearance::ScrollbarthumbVertical:
+    case StyleAppearance::ScrollbarthumbHorizontal: {
+      if (Maybe<nscolor> overrideColor =
+              CalcScrollbarColor(aFrame, ScrollbarColorKind::Thumb)) {
+        return *overrideColor;
+      }
+      break;
+    }
+    case StyleAppearance::ScrollbarVertical:
+    case StyleAppearance::ScrollbarHorizontal:
+    case StyleAppearance::Scrollcorner: {
+      if (Maybe<nscolor> overrideColor =
+              CalcScrollbarColor(aFrame, ScrollbarColorKind::Track)) {
+        return *overrideColor;
+      }
+      break;
+    }
+    default:
+      break;
+  }
+  return aStyle->GetVisitedDependentColor(&nsStyleBackground::mBackgroundColor);
+}
+
+nscolor nsCSSRendering::DetermineBackgroundColor(nsPresContext* aPresContext,
+                                                 const ComputedStyle* aStyle,
+                                                 nsIFrame* aFrame,
+                                                 bool& aDrawBackgroundImage,
+                                                 bool& aDrawBackgroundColor) {
+  auto shouldPaint = aFrame->ComputeShouldPaintBackground();
+  aDrawBackgroundImage = shouldPaint.mImage;
+  aDrawBackgroundColor = shouldPaint.mColor;
+
+  const nsStyleBackground* bg = aStyle->StyleBackground();
+  nscolor bgColor;
+  if (aDrawBackgroundColor) {
+    bgColor = GetBackgroundColor(aFrame, aStyle);
+    if (NS_GET_A(bgColor) == 0) {
+      aDrawBackgroundColor = false;
+    }
+  } else {
+    // If GetBackgroundColorDraw() is false, we are still expected to
+    // draw color in the background of any frame that's not completely
+    // transparent, but we are expected to use white instead of whatever
+    // color was specified.
+    bgColor = NS_RGB(255, 255, 255);
+    if (aDrawBackgroundImage || !bg->IsTransparent(aStyle)) {
+      aDrawBackgroundColor = true;
+    } else {
+      bgColor = NS_RGBA(0, 0, 0, 0);
+    }
+  }
+
+  // We can skip painting the background color if a background image is opaque.
+  nsStyleImageLayers::Repeat repeat = bg->BottomLayer().mRepeat;
+  bool xFullRepeat = repeat.mXRepeat == StyleImageLayerRepeat::Repeat ||
+                     repeat.mXRepeat == StyleImageLayerRepeat::Round;
+  bool yFullRepeat = repeat.mYRepeat == StyleImageLayerRepeat::Repeat ||
+                     repeat.mYRepeat == StyleImageLayerRepeat::Round;
+  if (aDrawBackgroundColor && xFullRepeat && yFullRepeat &&
+      bg->BottomLayer().mImage.IsOpaque() &&
+      bg->BottomLayer().mBlendMode == StyleBlend::Normal) {
+    aDrawBackgroundColor = false;
+  }
+
+  return bgColor;
+}
+
+static CompositionOp DetermineCompositionOp(
+    const nsCSSRendering::PaintBGParams& aParams,
+    const nsStyleImageLayers& aLayers, uint32_t aLayerIndex) {
+  if (aParams.layer >= 0) {
+    // When drawing a single layer, use the specified composition op.
+    return aParams.compositionOp;
+  }
+
+  const nsStyleImageLayers::Layer& layer = aLayers.mLayers[aLayerIndex];
+  // When drawing all layers, get the compositon op from each image layer.
+  if (aParams.paintFlags & nsCSSRendering::PAINTBG_MASK_IMAGE) {
+    // Always using OP_OVER mode while drawing the bottom mask layer.
+    if (aLayerIndex == (aLayers.mImageCount - 1)) {
+      return CompositionOp::OP_OVER;
+    }
+
+    return nsCSSRendering::GetGFXCompositeMode(layer.mComposite);
+  }
+
+  return nsCSSRendering::GetGFXBlendMode(layer.mBlendMode);
+}
+
+ImgDrawResult nsCSSRendering::PaintStyleImageLayerWithSC(
+    const PaintBGParams& aParams, gfxContext& aRenderingCtx,
+    const ComputedStyle* aBackgroundSC, const nsStyleBorder& aBorder) {
+  MOZ_ASSERT(aParams.frame,
+             "Frame is expected to be provided to PaintStyleImageLayerWithSC");
+
+  // If we're drawing all layers, aCompositonOp is ignored, so make sure that
+  // it was left at its default value.
+  MOZ_ASSERT(aParams.layer != -1 ||
+             aParams.compositionOp == CompositionOp::OP_OVER);
+
+  // Check to see if we have an appearance defined.  If so, we let the theme
+  // renderer draw the background and bail out.
+  // XXXzw this ignores aParams.bgClipRect.
+  StyleAppearance appearance =
+      aParams.frame->StyleDisplay()->EffectiveAppearance();
+  if (appearance != StyleAppearance::None) {
+    nsITheme* theme = aParams.presCtx.Theme();
+    if (theme->ThemeSupportsWidget(&aParams.presCtx, aParams.frame,
+                                   appearance)) {
+      nsRect drawing(aParams.borderArea);
+      theme->GetWidgetOverflow(aParams.presCtx.DeviceContext(), aParams.frame,
+                               appearance, &drawing);
+      drawing.IntersectRect(drawing, aParams.dirtyRect);
+      theme->DrawWidgetBackground(&aRenderingCtx, aParams.frame, appearance,
+                                  aParams.borderArea, drawing);
+      return ImgDrawResult::SUCCESS;
+    }
+  }
+
+  // For canvas frames (in the CSS sense) we draw the background color using
+  // a solid color item that gets added in nsLayoutUtils::PaintFrame,
+  // or nsSubDocumentFrame::BuildDisplayList (bug 488242). (The solid
+  // color may be moved into nsDisplayCanvasBackground by
+  // PresShell::AddCanvasBackgroundColorItem(), and painted by
+  // nsDisplayCanvasBackground directly.) Either way we don't need to
+  // paint the background color here.
+  bool isCanvasFrame = aParams.frame->IsCanvasFrame();
+  const bool paintMask = aParams.paintFlags & PAINTBG_MASK_IMAGE;
+
+  // Determine whether we are drawing background images and/or
+  // background colors.
+  bool drawBackgroundImage = true;
+  bool drawBackgroundColor = !paintMask;
+  nscolor bgColor = NS_RGBA(0, 0, 0, 0);
+  if (!paintMask) {
+    bgColor =
+        DetermineBackgroundColor(&aParams.presCtx, aBackgroundSC, aParams.frame,
+                                 drawBackgroundImage, drawBackgroundColor);
+  }
+
+  // Masks shouldn't be suppressed for print.
+  MOZ_ASSERT_IF(paintMask, drawBackgroundImage);
+
+  const nsStyleImageLayers& layers =
+      paintMask ? aBackgroundSC->StyleSVGReset()->mMask
+                : aBackgroundSC->StyleBackground()->mImage;
+  // If we're drawing a specific layer, we don't want to draw the
+  // background color.
+  if (drawBackgroundColor && aParams.layer >= 0) {
+    drawBackgroundColor = false;
+  }
+
+  // At this point, drawBackgroundImage and drawBackgroundColor are
+  // true if and only if we are actually supposed to paint an image or
+  // color into aDirtyRect, respectively.
+  if (!drawBackgroundImage && !drawBackgroundColor) {
+    return ImgDrawResult::SUCCESS;
+  }
+
+  // The 'bgClipArea' (used only by the image tiling logic, far below)
+  // is the caller-provided aParams.bgClipRect if any, or else the area
+  // determined by the value of 'background-clip' in
+  // SetupCurrentBackgroundClip.  (Arguably it should be the
+  // intersection, but that breaks the table painter -- in particular,
+  // taking the intersection breaks reftests/bugs/403249-1[ab].)
+  nscoord appUnitsPerPixel = aParams.presCtx.AppUnitsPerDevPixel();
+  ImageLayerClipState clipState;
+  if (aParams.bgClipRect) {
+    clipState.mBGClipArea = *aParams.bgClipRect;
+    clipState.mCustomClip = true;
+    clipState.mHasRoundedCorners = false;
+    SetupDirtyRects(clipState.mBGClipArea, aParams.dirtyRect, appUnitsPerPixel,
+                    &clipState.mDirtyRectInAppUnits,
+                    &clipState.mDirtyRectInDevPx);
+  } else {
+    GetImageLayerClip(layers.BottomLayer(), aParams.frame, aBorder,
+                      aParams.borderArea, aParams.dirtyRect,
+                      (aParams.paintFlags & PAINTBG_WILL_PAINT_BORDER),
+                      appUnitsPerPixel, &clipState);
+  }
+
+  // If we might be using a background color, go ahead and set it now.
+  if (drawBackgroundColor && !isCanvasFrame) {
+    aRenderingCtx.SetColor(sRGBColor::FromABGR(bgColor));
+  }
+
+  // If there is no background image, draw a color.  (If there is
+  // neither a background image nor a color, we wouldn't have gotten
+  // this far.)
+  if (!drawBackgroundImage) {
+    if (!isCanvasFrame) {
+      DrawBackgroundColor(clipState, &aRenderingCtx, appUnitsPerPixel);
+    }
+    return ImgDrawResult::SUCCESS;
+  }
+
+  if (layers.mImageCount < 1) {
+    // Return if there are no background layers, all work from this point
+    // onwards happens iteratively on these.
+    return ImgDrawResult::SUCCESS;
+  }
+
+  MOZ_ASSERT((aParams.layer < 0) ||
+             (layers.mImageCount > uint32_t(aParams.layer)));
+
+  // The background color is rendered over the entire dirty area,
+  // even if the image isn't.
+  if (drawBackgroundColor && !isCanvasFrame) {
+    DrawBackgroundColor(clipState, &aRenderingCtx, appUnitsPerPixel);
+  }
+
+  // Compute the outermost boundary of the area that might be painted.
+  // Same coordinate space as aParams.borderArea & aParams.bgClipRect.
+  Sides skipSides = aParams.frame->GetSkipSides();
+  nsRect paintBorderArea = BoxDecorationRectForBackground(
+      aParams.frame, aParams.borderArea, skipSides, &aBorder);
+  nsRect clipBorderArea = BoxDecorationRectForBorder(
+      aParams.frame, aParams.borderArea, skipSides, &aBorder);
+
+  ImgDrawResult result = ImgDrawResult::SUCCESS;
+  StyleGeometryBox currentBackgroundClip = StyleGeometryBox::BorderBox;
+  const bool drawAllLayers = (aParams.layer < 0);
+  uint32_t count = drawAllLayers
+                       ? layers.mImageCount  // iterate all image layers.
+                       : layers.mImageCount -
+                             aParams.layer;  // iterate from the bottom layer to
+                                             // the 'aParams.layer-th' layer.
+  NS_FOR_VISIBLE_IMAGE_LAYERS_BACK_TO_FRONT_WITH_RANGE(
+      i, layers, layers.mImageCount - 1, count) {
+    // NOTE: no Save() yet, we do that later by calling autoSR.EnsureSaved(ctx)
+    // in the cases we need it.
+    gfxContextAutoSaveRestore autoSR;
+    const nsStyleImageLayers::Layer& layer = layers.mLayers[i];
+
+    ImageLayerClipState currentLayerClipState = clipState;
+    if (!aParams.bgClipRect) {
+      bool isBottomLayer = (i == layers.mImageCount - 1);
+      if (currentBackgroundClip != layer.mClip || isBottomLayer) {
+        currentBackgroundClip = layer.mClip;
+        if (!isBottomLayer) {
+          currentLayerClipState = {};
+          // For the bottom layer, we already called GetImageLayerClip above
+          // and it stored its results in clipState.
+          GetImageLayerClip(layer, aParams.frame, aBorder, aParams.borderArea,
+                            aParams.dirtyRect,
+                            (aParams.paintFlags & PAINTBG_WILL_PAINT_BORDER),
+                            appUnitsPerPixel, &currentLayerClipState);
+        }
+        SetupImageLayerClip(currentLayerClipState, &aRenderingCtx,
+                            appUnitsPerPixel, &autoSR);
+        if (!clipBorderArea.IsEqualEdges(aParams.borderArea)) {
+          // We're drawing the background for the joined continuation boxes
+          // so we need to clip that to the slice that we want for this
+          // frame.
+          gfxRect clip = nsLayoutUtils::RectToGfxRect(aParams.borderArea,
+                                                      appUnitsPerPixel);
+          autoSR.EnsureSaved(&aRenderingCtx);
+          aRenderingCtx.SnappedClip(clip);
+        }
+      }
+    }
+
+    // Skip the following layer preparing and painting code if the current
+    // layer is not selected for drawing.
+    if (aParams.layer >= 0 && i != (uint32_t)aParams.layer) {
+      continue;
+    }
+    nsBackgroundLayerState state = PrepareImageLayer(
+        &aParams.presCtx, aParams.frame, aParams.paintFlags, paintBorderArea,
+        currentLayerClipState.mBGClipArea, layer, nullptr);
+    result &= state.mImageRenderer.PrepareResult();
+
+    // Skip the layer painting code if we found the dirty region is empty.
+    if (currentLayerClipState.mDirtyRectInDevPx.IsEmpty()) {
+      continue;
+    }
+
+    if (!state.mFillArea.IsEmpty()) {
+      CompositionOp co = DetermineCompositionOp(aParams, layers, i);
+      if (co != CompositionOp::OP_OVER) {
+        NS_ASSERTION(aRenderingCtx.CurrentOp() == CompositionOp::OP_OVER,
+                     "It is assumed the initial op is OP_OVER, when it is "
+                     "restored later");
+        aRenderingCtx.SetOp(co);
+      }
+
+      result &= state.mImageRenderer.DrawLayer(
+          &aParams.presCtx, aRenderingCtx, state.mDestArea, state.mFillArea,
+          state.mAnchor + paintBorderArea.TopLeft(),
+          currentLayerClipState.mDirtyRectInAppUnits, state.mRepeatSize,
+          aParams.opacity);
+
+      if (co != CompositionOp::OP_OVER) {
+        aRenderingCtx.SetOp(CompositionOp::OP_OVER);
+      }
+    }
+  }
+
+  return result;
+}
+
+ImgDrawResult
+nsCSSRendering::BuildWebRenderDisplayItemsForStyleImageLayerWithSC(
+    const PaintBGParams& aParams, mozilla::wr::DisplayListBuilder& aBuilder,
+    mozilla::wr::IpcResourceUpdateQueue& aResources,
+    const mozilla::layers::StackingContextHelper& aSc,
+    mozilla::layers::RenderRootStateManager* aManager, nsDisplayItem* aItem,
+    ComputedStyle* aBackgroundSC, const nsStyleBorder& aBorder) {
+  MOZ_ASSERT(!(aParams.paintFlags & PAINTBG_MASK_IMAGE));
+
+  nscoord appUnitsPerPixel = aParams.presCtx.AppUnitsPerDevPixel();
+  ImageLayerClipState clipState;
+
+  clipState.mBGClipArea = *aParams.bgClipRect;
+  clipState.mCustomClip = true;
+  clipState.mHasRoundedCorners = false;
+  SetupDirtyRects(clipState.mBGClipArea, aParams.dirtyRect, appUnitsPerPixel,
+                  &clipState.mDirtyRectInAppUnits,
+                  &clipState.mDirtyRectInDevPx);
+
+  // Compute the outermost boundary of the area that might be painted.
+  // Same coordinate space as aParams.borderArea & aParams.bgClipRect.
+  Sides skipSides = aParams.frame->GetSkipSides();
+  nsRect paintBorderArea = BoxDecorationRectForBackground(
+      aParams.frame, aParams.borderArea, skipSides, &aBorder);
+
+  const nsStyleImageLayers& layers = aBackgroundSC->StyleBackground()->mImage;
+  const nsStyleImageLayers::Layer& layer = layers.mLayers[aParams.layer];
+
+  // Skip the following layer painting code if we found the dirty region is
+  // empty or the current layer is not selected for drawing.
+  if (clipState.mDirtyRectInDevPx.IsEmpty()) {
+    return ImgDrawResult::SUCCESS;
+  }
+
+  ImgDrawResult result = ImgDrawResult::SUCCESS;
+  nsBackgroundLayerState state =
+      PrepareImageLayer(&aParams.presCtx, aParams.frame, aParams.paintFlags,
+                        paintBorderArea, clipState.mBGClipArea, layer, nullptr);
+  result &= state.mImageRenderer.PrepareResult();
+
+  if (!state.mFillArea.IsEmpty()) {
+    result &= state.mImageRenderer.BuildWebRenderDisplayItemsForLayer(
+        &aParams.presCtx, aBuilder, aResources, aSc, aManager, aItem,
+        state.mDestArea, state.mFillArea,
+        state.mAnchor + paintBorderArea.TopLeft(),
+        clipState.mDirtyRectInAppUnits, state.mRepeatSize, aParams.opacity);
+  }
+
+  return result;
+}
+
+nsRect nsCSSRendering::ComputeImageLayerPositioningArea(
+    nsPresContext* aPresContext, nsIFrame* aForFrame, const nsRect& aBorderArea,
+    const nsStyleImageLayers::Layer& aLayer, nsIFrame** aAttachedToFrame,
+    bool* aOutIsTransformedFixed) {
+  // Compute {background|mask} origin area relative to aBorderArea now as we
+  // may need  it to compute the effective image size for a CSS gradient.
+  nsRect positionArea;
+
+  StyleGeometryBox layerOrigin = ComputeBoxValue(aForFrame, aLayer.mOrigin);
+
+  if (IsSVGStyleGeometryBox(layerOrigin)) {
+    MOZ_ASSERT(aForFrame->IsFrameOfType(nsIFrame::eSVG) &&
+               !aForFrame->IsSVGOuterSVGFrame());
+    *aAttachedToFrame = aForFrame;
+
+    positionArea = nsLayoutUtils::ComputeGeometryBox(aForFrame, layerOrigin);
+
+    nsPoint toStrokeBoxOffset = nsPoint(0, 0);
+    if (layerOrigin != StyleGeometryBox::StrokeBox) {
+      nsRect strokeBox = nsLayoutUtils::ComputeGeometryBox(
+          aForFrame, StyleGeometryBox::StrokeBox);
+      toStrokeBoxOffset = positionArea.TopLeft() - strokeBox.TopLeft();
+    }
+
+    // For SVG frames, the return value is relative to the stroke box
+    return nsRect(toStrokeBoxOffset, positionArea.Size());
+  }
+
+  MOZ_ASSERT(!aForFrame->IsFrameOfType(nsIFrame::eSVG) ||
+             aForFrame->IsSVGOuterSVGFrame());
+
+  LayoutFrameType frameType = aForFrame->Type();
+  nsIFrame* geometryFrame = aForFrame;
+  if (MOZ_UNLIKELY(frameType == LayoutFrameType::Scroll &&
+                   StyleImageLayerAttachment::Local == aLayer.mAttachment)) {
+    nsIScrollableFrame* scrollableFrame = do_QueryFrame(aForFrame);
+    positionArea = nsRect(scrollableFrame->GetScrolledFrame()->GetPosition()
+                              // For the dir=rtl case:
+                              + scrollableFrame->GetScrollRange().TopLeft(),
+                          scrollableFrame->GetScrolledRect().Size());
+    // The ScrolledRect’s size does not include the borders or scrollbars,
+    // reverse the handling of background-origin
+    // compared to the common case below.
+    if (layerOrigin == StyleGeometryBox::BorderBox) {
+      nsMargin border = geometryFrame->GetUsedBorder();
+      border.ApplySkipSides(geometryFrame->GetSkipSides());
+      positionArea.Inflate(border);
+      positionArea.Inflate(scrollableFrame->GetActualScrollbarSizes());
+    } else if (layerOrigin != StyleGeometryBox::PaddingBox) {
+      nsMargin padding = geometryFrame->GetUsedPadding();
+      padding.ApplySkipSides(geometryFrame->GetSkipSides());
+      positionArea.Deflate(padding);
+      NS_ASSERTION(layerOrigin == StyleGeometryBox::ContentBox,
+                   "unknown background-origin value");
+    }
+    *aAttachedToFrame = aForFrame;
+    return positionArea;
+  }
+
+  if (MOZ_UNLIKELY(frameType == LayoutFrameType::Canvas)) {
+    geometryFrame = aForFrame->PrincipalChildList().FirstChild();
+    // geometryFrame might be null if this canvas is a page created
+    // as an overflow container (e.g. the in-flow content has already
+    // finished and this page only displays the continuations of
+    // absolutely positioned content).
+    if (geometryFrame) {
+      positionArea =
+          nsPlaceholderFrame::GetRealFrameFor(geometryFrame)->GetRect();
+    }
+  } else {
+    positionArea = nsRect(nsPoint(0, 0), aBorderArea.Size());
+  }
+
+  // See the comment of StyleGeometryBox::MarginBox.
+  // Hitting this assertion means we decide to turn on margin-box support for
+  // positioned mask from CSS parser and style system. In this case, you
+  // should *inflate* positionArea by the margin returning from
+  // geometryFrame->GetUsedMargin() in the code chunk bellow.
+  MOZ_ASSERT(aLayer.mOrigin != StyleGeometryBox::MarginBox,
+             "StyleGeometryBox::MarginBox rendering is not supported yet.\n");
+
+  // {background|mask} images are tiled over the '{background|mask}-clip' area
+  // but the origin of the tiling is based on the '{background|mask}-origin'
+  // area.
+  if (layerOrigin != StyleGeometryBox::BorderBox && geometryFrame) {
+    nsMargin border = geometryFrame->GetUsedBorder();
+    if (layerOrigin != StyleGeometryBox::PaddingBox) {
+      border += geometryFrame->GetUsedPadding();
+      NS_ASSERTION(layerOrigin == StyleGeometryBox::ContentBox,
+                   "unknown background-origin value");
+    }
+    positionArea.Deflate(border);
+  }
+
+  nsIFrame* attachedToFrame = aForFrame;
+  if (StyleImageLayerAttachment::Fixed == aLayer.mAttachment) {
+    // If it's a fixed background attachment, then the image is placed
+    // relative to the viewport, which is the area of the root frame
+    // in a screen context or the page content frame in a print context.
+    attachedToFrame = aPresContext->PresShell()->GetRootFrame();
+    NS_ASSERTION(attachedToFrame, "no root frame");
+    nsIFrame* pageContentFrame = nullptr;
+    if (aPresContext->IsPaginated()) {
+      pageContentFrame = nsLayoutUtils::GetClosestFrameOfType(
+          aForFrame, LayoutFrameType::PageContent);
+      if (pageContentFrame) {
+        attachedToFrame = pageContentFrame;
+      }
+      // else this is an embedded shell and its root frame is what we want
+    }
+
+    // If the background is affected by a transform, treat is as if it
+    // wasn't fixed.
+    if (nsLayoutUtils::IsTransformed(aForFrame, attachedToFrame)) {
+      attachedToFrame = aForFrame;
+      *aOutIsTransformedFixed = true;
+    } else {
+      // Set the background positioning area to the viewport's area
+      // (relative to aForFrame)
+      positionArea = nsRect(-aForFrame->GetOffsetTo(attachedToFrame),
+                            attachedToFrame->GetSize());
+
+      if (!pageContentFrame) {
+        // Subtract the size of scrollbars.
+        nsIScrollableFrame* scrollableFrame =
+            aPresContext->PresShell()->GetRootScrollFrameAsScrollable();
+        if (scrollableFrame) {
+          nsMargin scrollbars = scrollableFrame->GetActualScrollbarSizes();
+          positionArea.Deflate(scrollbars);
+        }
+      }
+    }
+  }
+  *aAttachedToFrame = attachedToFrame;
+
+  return positionArea;
+}
+
+/* static */
+nscoord nsCSSRendering::ComputeRoundedSize(nscoord aCurrentSize,
+                                           nscoord aPositioningSize) {
+  float repeatCount = NS_roundf(float(aPositioningSize) / float(aCurrentSize));
+  if (repeatCount < 1.0f) {
+    return aPositioningSize;
+  }
+  return nscoord(NS_lround(float(aPositioningSize) / repeatCount));
+}
+
+// Apply the CSS image sizing algorithm as it applies to background images.
+// See http://www.w3.org/TR/css3-background/#the-background-size .
+// aIntrinsicSize is the size that the background image 'would like to be'.
+// It can be found by calling nsImageRenderer::ComputeIntrinsicSize.
+static nsSize ComputeDrawnSizeForBackground(
+    const CSSSizeOrRatio& aIntrinsicSize, const nsSize& aBgPositioningArea,
+    const StyleBackgroundSize& aLayerSize, StyleImageLayerRepeat aXRepeat,
+    StyleImageLayerRepeat aYRepeat) {
+  nsSize imageSize;
+
+  // Size is dictated by cover or contain rules.
+  if (aLayerSize.IsContain() || aLayerSize.IsCover()) {
+    nsImageRenderer::FitType fitType = aLayerSize.IsCover()
+                                           ? nsImageRenderer::COVER
+                                           : nsImageRenderer::CONTAIN;
+    imageSize = nsImageRenderer::ComputeConstrainedSize(
+        aBgPositioningArea, aIntrinsicSize.mRatio, fitType);
+  } else {
+    MOZ_ASSERT(aLayerSize.IsExplicitSize());
+    const auto& width = aLayerSize.explicit_size.width;
+    const auto& height = aLayerSize.explicit_size.height;
+    // No cover/contain constraint, use default algorithm.
+    CSSSizeOrRatio specifiedSize;
+    if (width.IsLengthPercentage()) {
+      specifiedSize.SetWidth(
+          width.AsLengthPercentage().Resolve(aBgPositioningArea.width));
+    }
+    if (height.IsLengthPercentage()) {
+      specifiedSize.SetHeight(
+          height.AsLengthPercentage().Resolve(aBgPositioningArea.height));
+    }
+
+    imageSize = nsImageRenderer::ComputeConcreteSize(
+        specifiedSize, aIntrinsicSize, aBgPositioningArea);
+  }
+
+  // See https://www.w3.org/TR/css3-background/#background-size .
+  // "If 'background-repeat' is 'round' for one (or both) dimensions, there is a
+  // second
+  //  step. The UA must scale the image in that dimension (or both dimensions)
+  //  so that it fits a whole number of times in the background positioning
+  //  area."
+  // "If 'background-repeat' is 'round' for one dimension only and if
+  // 'background-size'
+  //  is 'auto' for the other dimension, then there is a third step: that other
+  //  dimension is scaled so that the original aspect ratio is restored."
+  bool isRepeatRoundInBothDimensions =
+      aXRepeat == StyleImageLayerRepeat::Round &&
+      aYRepeat == StyleImageLayerRepeat::Round;
+
+  // Calculate the rounded size only if the background-size computation
+  // returned a correct size for the image.
+  if (imageSize.width && aXRepeat == StyleImageLayerRepeat::Round) {
+    imageSize.width = nsCSSRendering::ComputeRoundedSize(
+        imageSize.width, aBgPositioningArea.width);
+    if (!isRepeatRoundInBothDimensions && aLayerSize.IsExplicitSize() &&
+        aLayerSize.explicit_size.height.IsAuto()) {
+      // Restore intrinsic ratio
+      if (aIntrinsicSize.mRatio) {
+        imageSize.height =
+            aIntrinsicSize.mRatio.Inverted().ApplyTo(imageSize.width);
+      }
+    }
+  }
+
+  // Calculate the rounded size only if the background-size computation
+  // returned a correct size for the image.
+  if (imageSize.height && aYRepeat == StyleImageLayerRepeat::Round) {
+    imageSize.height = nsCSSRendering::ComputeRoundedSize(
+        imageSize.height, aBgPositioningArea.height);
+    if (!isRepeatRoundInBothDimensions && aLayerSize.IsExplicitSize() &&
+        aLayerSize.explicit_size.width.IsAuto()) {
+      // Restore intrinsic ratio
+      if (aIntrinsicSize.mRatio) {
+        imageSize.width = aIntrinsicSize.mRatio.ApplyTo(imageSize.height);
+      }
+    }
+  }
+
+  return imageSize;
+}
+
+/* ComputeSpacedRepeatSize
+ * aImageDimension: the image width/height
+ * aAvailableSpace: the background positioning area width/height
+ * aRepeat: determine whether the image is repeated
+ * Returns the image size plus gap size of app units for use as spacing
+ */
+static nscoord ComputeSpacedRepeatSize(nscoord aImageDimension,
+                                       nscoord aAvailableSpace, bool& aRepeat) {
+  float ratio = static_cast<float>(aAvailableSpace) / aImageDimension;
+
+  if (ratio < 2.0f) {  // If you can't repeat at least twice, then don't repeat.
+    aRepeat = false;
+    return aImageDimension;
+  }
+
+  aRepeat = true;
+  return (aAvailableSpace - aImageDimension) / (NSToIntFloor(ratio) - 1);
+}
+
+/* static */
+nscoord nsCSSRendering::ComputeBorderSpacedRepeatSize(nscoord aImageDimension,
+                                                      nscoord aAvailableSpace,
+                                                      nscoord& aSpace) {
+  int32_t count = aImageDimension ? (aAvailableSpace / aImageDimension) : 0;
+  aSpace = (aAvailableSpace - aImageDimension * count) / (count + 1);
+  return aSpace + aImageDimension;
+}
+
+nsBackgroundLayerState nsCSSRendering::PrepareImageLayer(
+    nsPresContext* aPresContext, nsIFrame* aForFrame, uint32_t aFlags,
+    const nsRect& aBorderArea, const nsRect& aBGClipRect,
+    const nsStyleImageLayers::Layer& aLayer, bool* aOutIsTransformedFixed) {
+  /*
+   * The properties we need to keep in mind when drawing style image
+   * layers are:
+   *
+   *   background-image/ mask-image
+   *   background-repeat/ mask-repeat
+   *   background-attachment
+   *   background-position/ mask-position
+   *   background-clip/ mask-clip
+   *   background-origin/ mask-origin
+   *   background-size/ mask-size
+   *   background-blend-mode
+   *   box-decoration-break
+   *   mask-mode
+   *   mask-composite
+   *
+   * (background-color applies to the entire element and not to individual
+   * layers, so it is irrelevant to this method.)
+   *
+   * These properties have the following dependencies upon each other when
+   * determining rendering:
+   *
+   *   background-image/ mask-image
+   *     no dependencies
+   *   background-repeat/ mask-repeat
+   *     no dependencies
+   *   background-attachment
+   *     no dependencies
+   *   background-position/ mask-position
+   *     depends upon background-size/mask-size (for the image's scaled size)
+   *     and background-break (for the background positioning area)
+   *   background-clip/ mask-clip
+   *     no dependencies
+   *   background-origin/ mask-origin
+   *     depends upon background-attachment (only in the case where that value
+   *     is 'fixed')
+   *   background-size/ mask-size
+   *     depends upon box-decoration-break (for the background positioning area
+   *     for resolving percentages), background-image (for the image's intrinsic
+   *     size), background-repeat (if that value is 'round'), and
+   *     background-origin (for the background painting area, when
+   *     background-repeat is 'round')
+   *   background-blend-mode
+   *     no dependencies
+   *   mask-mode
+   *     no dependencies
+   *   mask-composite
+   *     no dependencies
+   *   box-decoration-break
+   *     no dependencies
+   *
+   * As a result of only-if dependencies we don't strictly do a topological
+   * sort of the above properties when processing, but it's pretty close to one:
+   *
+   *   background-clip/mask-clip (by caller)
+   *   background-image/ mask-image
+   *   box-decoration-break, background-origin/ mask origin
+   *   background-attachment (postfix for background-origin if 'fixed')
+   *   background-size/ mask-size
+   *   background-position/ mask-position
+   *   background-repeat/ mask-repeat
+   */
+
+  uint32_t irFlags = 0;
+  if (aFlags & nsCSSRendering::PAINTBG_SYNC_DECODE_IMAGES) {
+    irFlags |= nsImageRenderer::FLAG_SYNC_DECODE_IMAGES;
+  }
+  if (aFlags & nsCSSRendering::PAINTBG_TO_WINDOW) {
+    irFlags |= nsImageRenderer::FLAG_PAINTING_TO_WINDOW;
+  }
+  if (aFlags & nsCSSRendering::PAINTBG_HIGH_QUALITY_SCALING) {
+    irFlags |= nsImageRenderer::FLAG_HIGH_QUALITY_SCALING;
+  }
+  // Only do partial bg image drawing in content documents: non-content
+  // documents are viewed as UI of the browser and a partial draw of a bg image
+  // might look weird in that context.
+  if (StaticPrefs::layout_display_partial_background_images() &&
+      XRE_IsContentProcess() && !aPresContext->IsChrome()) {
+    irFlags |= nsImageRenderer::FLAG_DRAW_PARTIAL_FRAMES;
+  }
+
+  nsBackgroundLayerState state(aForFrame, &aLayer.mImage, irFlags);
+  if (!state.mImageRenderer.PrepareImage()) {
+    // There's no image or it's not ready to be painted.
+    if (aOutIsTransformedFixed &&
+        StyleImageLayerAttachment::Fixed == aLayer.mAttachment) {
+      nsIFrame* attachedToFrame = aPresContext->PresShell()->GetRootFrame();
+      NS_ASSERTION(attachedToFrame, "no root frame");
+      nsIFrame* pageContentFrame = nullptr;
+      if (aPresContext->IsPaginated()) {
+        pageContentFrame = nsLayoutUtils::GetClosestFrameOfType(
+            aForFrame, LayoutFrameType::PageContent);
+        if (pageContentFrame) {
+          attachedToFrame = pageContentFrame;
+        }
+        // else this is an embedded shell and its root frame is what we want
+      }
+
+      *aOutIsTransformedFixed =
+          nsLayoutUtils::IsTransformed(aForFrame, attachedToFrame);
+    }
+    return state;
+  }
+
+  // The frame to which the background is attached
+  nsIFrame* attachedToFrame = aForFrame;
+  // Is the background marked 'fixed', but affected by a transform?
+  bool transformedFixed = false;
+  // Compute background origin area relative to aBorderArea now as we may need
+  // it to compute the effective image size for a CSS gradient.
+  nsRect positionArea = ComputeImageLayerPositioningArea(
+      aPresContext, aForFrame, aBorderArea, aLayer, &attachedToFrame,
+      &transformedFixed);
+  if (aOutIsTransformedFixed) {
+    *aOutIsTransformedFixed = transformedFixed;
+  }
+
+  // For background-attachment:fixed backgrounds, we'll override the area
+  // where the background can be drawn to the viewport.
+  nsRect bgClipRect = aBGClipRect;
+
+  if (StyleImageLayerAttachment::Fixed == aLayer.mAttachment &&
+      !transformedFixed && (aFlags & nsCSSRendering::PAINTBG_TO_WINDOW)) {
+    bgClipRect = positionArea + aBorderArea.TopLeft();
+  }
+
+  StyleImageLayerRepeat repeatX = aLayer.mRepeat.mXRepeat;
+  StyleImageLayerRepeat repeatY = aLayer.mRepeat.mYRepeat;
+
+  // Scale the image as specified for background-size and background-repeat.
+  // Also as required for proper background positioning when background-position
+  // is defined with percentages.
+  CSSSizeOrRatio intrinsicSize = state.mImageRenderer.ComputeIntrinsicSize();
+  nsSize bgPositionSize = positionArea.Size();
+  nsSize imageSize = ComputeDrawnSizeForBackground(
+      intrinsicSize, bgPositionSize, aLayer.mSize, repeatX, repeatY);
+
+  if (imageSize.width <= 0 || imageSize.height <= 0) return state;
+
+  state.mImageRenderer.SetPreferredSize(intrinsicSize, imageSize);
+
+  // Compute the anchor point.
+  //
+  // relative to aBorderArea.TopLeft() (which is where the top-left
+  // of aForFrame's border-box will be rendered)
+  nsPoint imageTopLeft;
+
+  // Compute the position of the background now that the background's size is
+  // determined.
+  nsImageRenderer::ComputeObjectAnchorPoint(aLayer.mPosition, bgPositionSize,
+                                            imageSize, &imageTopLeft,
+                                            &state.mAnchor);
+  state.mRepeatSize = imageSize;
+  if (repeatX == StyleImageLayerRepeat::Space) {
+    bool isRepeat;
+    state.mRepeatSize.width = ComputeSpacedRepeatSize(
+        imageSize.width, bgPositionSize.width, isRepeat);
+    if (isRepeat) {
+      imageTopLeft.x = 0;
+      state.mAnchor.x = 0;
+    } else {
+      repeatX = StyleImageLayerRepeat::NoRepeat;
+    }
+  }
+
+  if (repeatY == StyleImageLayerRepeat::Space) {
+    bool isRepeat;
+    state.mRepeatSize.height = ComputeSpacedRepeatSize(
+        imageSize.height, bgPositionSize.height, isRepeat);
+    if (isRepeat) {
+      imageTopLeft.y = 0;
+      state.mAnchor.y = 0;
+    } else {
+      repeatY = StyleImageLayerRepeat::NoRepeat;
+    }
+  }
+
+  imageTopLeft += positionArea.TopLeft();
+  state.mAnchor += positionArea.TopLeft();
+  state.mDestArea = nsRect(imageTopLeft + aBorderArea.TopLeft(), imageSize);
+  state.mFillArea = state.mDestArea;
+
+  ExtendMode repeatMode = ExtendMode::CLAMP;
+  if (repeatX == StyleImageLayerRepeat::Repeat ||
+      repeatX == StyleImageLayerRepeat::Round ||
+      repeatX == StyleImageLayerRepeat::Space) {
+    state.mFillArea.x = bgClipRect.x;
+    state.mFillArea.width = bgClipRect.width;
+    repeatMode = ExtendMode::REPEAT_X;
+  }
+  if (repeatY == StyleImageLayerRepeat::Repeat ||
+      repeatY == StyleImageLayerRepeat::Round ||
+      repeatY == StyleImageLayerRepeat::Space) {
+    state.mFillArea.y = bgClipRect.y;
+    state.mFillArea.height = bgClipRect.height;
+
+    /***
+     * We're repeating on the X axis already,
+     * so if we have to repeat in the Y axis,
+     * we really need to repeat in both directions.
+     */
+    if (repeatMode == ExtendMode::REPEAT_X) {
+      repeatMode = ExtendMode::REPEAT;
+    } else {
+      repeatMode = ExtendMode::REPEAT_Y;
+    }
+  }
+  state.mImageRenderer.SetExtendMode(repeatMode);
+  state.mImageRenderer.SetMaskOp(aLayer.mMaskMode);
+
+  state.mFillArea.IntersectRect(state.mFillArea, bgClipRect);
+
+  return state;
+}
+
+nsRect nsCSSRendering::GetBackgroundLayerRect(
+    nsPresContext* aPresContext, nsIFrame* aForFrame, const nsRect& aBorderArea,
+    const nsRect& aClipRect, const nsStyleImageLayers::Layer& aLayer,
+    uint32_t aFlags) {
+  Sides skipSides = aForFrame->GetSkipSides();
+  nsRect borderArea =
+      BoxDecorationRectForBackground(aForFrame, aBorderArea, skipSides);
+  nsBackgroundLayerState state = PrepareImageLayer(
+      aPresContext, aForFrame, aFlags, borderArea, aClipRect, aLayer);
+  return state.mFillArea;
+}
+
+// Begin table border-collapsing section
+// These functions were written to not disrupt the normal ones and yet satisfy
+// some additional requirements At some point, all functions should be unified
+// to include the additional functionality that these provide
+
+static nscoord RoundIntToPixel(nscoord aValue, nscoord aOneDevPixel,
+                               bool aRoundDown = false) {
+  if (aOneDevPixel <= 0) {
+    // We must be rendering to a device that has a resolution greater than
+    // one device pixel!
+    // In that case, aValue is as accurate as it's going to get.
+    return aValue;
+  }
+
+  nscoord halfPixel = NSToCoordRound(aOneDevPixel / 2.0f);
+  nscoord extra = aValue % aOneDevPixel;
+  nscoord finalValue = (!aRoundDown && (extra >= halfPixel))
+                           ? aValue + (aOneDevPixel - extra)
+                           : aValue - extra;
+  return finalValue;
+}
+
+static nscoord RoundFloatToPixel(float aValue, nscoord aOneDevPixel,
+                                 bool aRoundDown = false) {
+  return RoundIntToPixel(NSToCoordRound(aValue), aOneDevPixel, aRoundDown);
+}
+
+static void SetPoly(const Rect& aRect, Point* poly) {
+  poly[0].x = aRect.x;
+  poly[0].y = aRect.y;
+  poly[1].x = aRect.x + aRect.width;
+  poly[1].y = aRect.y;
+  poly[2].x = aRect.x + aRect.width;
+  poly[2].y = aRect.y + aRect.height;
+  poly[3].x = aRect.x;
+  poly[3].y = aRect.y + aRect.height;
+}
+
+static void DrawDashedSegment(DrawTarget& aDrawTarget, nsRect aRect,
+                              nscoord aDashLength, nscolor aColor,
+                              int32_t aAppUnitsPerDevPixel, bool aHorizontal) {
+  ColorPattern color(ToDeviceColor(aColor));
+  DrawOptions drawOptions(1.f, CompositionOp::OP_OVER, AntialiasMode::NONE);
+  StrokeOptions strokeOptions;
+
+  Float dash[2];
+  dash[0] = Float(aDashLength) / aAppUnitsPerDevPixel;
+  dash[1] = dash[0];
+
+  strokeOptions.mDashPattern = dash;
+  strokeOptions.mDashLength = MOZ_ARRAY_LENGTH(dash);
+
+  if (aHorizontal) {
+    nsPoint left = (aRect.TopLeft() + aRect.BottomLeft()) / 2;
+    nsPoint right = (aRect.TopRight() + aRect.BottomRight()) / 2;
+    strokeOptions.mLineWidth = Float(aRect.height) / aAppUnitsPerDevPixel;
+    StrokeLineWithSnapping(left, right, aAppUnitsPerDevPixel, aDrawTarget,
+                           color, strokeOptions, drawOptions);
+  } else {
+    nsPoint top = (aRect.TopLeft() + aRect.TopRight()) / 2;
+    nsPoint bottom = (aRect.BottomLeft() + aRect.BottomRight()) / 2;
+    strokeOptions.mLineWidth = Float(aRect.width) / aAppUnitsPerDevPixel;
+    StrokeLineWithSnapping(top, bottom, aAppUnitsPerDevPixel, aDrawTarget,
+                           color, strokeOptions, drawOptions);
+  }
+}
+
+static void DrawSolidBorderSegment(
+    DrawTarget& aDrawTarget, nsRect aRect, nscolor aColor,
+    int32_t aAppUnitsPerDevPixel,
+    mozilla::Side aStartBevelSide = mozilla::eSideTop,
+    nscoord aStartBevelOffset = 0,
+    mozilla::Side aEndBevelSide = mozilla::eSideTop,
+    nscoord aEndBevelOffset = 0) {
+  ColorPattern color(ToDeviceColor(aColor));
+  DrawOptions drawOptions(1.f, CompositionOp::OP_OVER, AntialiasMode::NONE);
+
+  nscoord oneDevPixel = NSIntPixelsToAppUnits(1, aAppUnitsPerDevPixel);
+  // We don't need to bevel single pixel borders
+  if ((aRect.width == oneDevPixel) || (aRect.height == oneDevPixel) ||
+      ((0 == aStartBevelOffset) && (0 == aEndBevelOffset))) {
+    // simple rectangle
+    aDrawTarget.FillRect(
+        NSRectToSnappedRect(aRect, aAppUnitsPerDevPixel, aDrawTarget), color,
+        drawOptions);
+  } else {
+    // polygon with beveling
+    Point poly[4];
+    SetPoly(NSRectToSnappedRect(aRect, aAppUnitsPerDevPixel, aDrawTarget),
+            poly);
+
+    Float startBevelOffset =
+        NSAppUnitsToFloatPixels(aStartBevelOffset, aAppUnitsPerDevPixel);
+    switch (aStartBevelSide) {
+      case eSideTop:
+        poly[0].x += startBevelOffset;
+        break;
+      case eSideBottom:
+        poly[3].x += startBevelOffset;
+        break;
+      case eSideRight:
+        poly[1].y += startBevelOffset;
+        break;
+      case eSideLeft:
+        poly[0].y += startBevelOffset;
+    }
+
+    Float endBevelOffset =
+        NSAppUnitsToFloatPixels(aEndBevelOffset, aAppUnitsPerDevPixel);
+    switch (aEndBevelSide) {
+      case eSideTop:
+        poly[1].x -= endBevelOffset;
+        break;
+      case eSideBottom:
+        poly[2].x -= endBevelOffset;
+        break;
+      case eSideRight:
+        poly[2].y -= endBevelOffset;
+        break;
+      case eSideLeft:
+        poly[3].y -= endBevelOffset;
+    }
+
+    RefPtr<PathBuilder> builder = aDrawTarget.CreatePathBuilder();
+    builder->MoveTo(poly[0]);
+    builder->LineTo(poly[1]);
+    builder->LineTo(poly[2]);
+    builder->LineTo(poly[3]);
+    builder->Close();
+    RefPtr<Path> path = builder->Finish();
+    aDrawTarget.Fill(path, color, drawOptions);
+  }
+}
+
+static void GetDashInfo(nscoord aBorderLength, nscoord aDashLength,
+                        nscoord aOneDevPixel, int32_t& aNumDashSpaces,
+                        nscoord& aStartDashLength, nscoord& aEndDashLength) {
+  aNumDashSpaces = 0;
+  if (aStartDashLength + aDashLength + aEndDashLength >= aBorderLength) {
+    aStartDashLength = aBorderLength;
+    aEndDashLength = 0;
+  } else {
+    aNumDashSpaces =
+        (aBorderLength - aDashLength) / (2 * aDashLength);  // round down
+    nscoord extra = aBorderLength - aStartDashLength - aEndDashLength -
+                    (((2 * aNumDashSpaces) - 1) * aDashLength);
+    if (extra > 0) {
+      nscoord half = RoundIntToPixel(extra / 2, aOneDevPixel);
+      aStartDashLength += half;
+      aEndDashLength += (extra - half);
+    }
+  }
+}
+
+void nsCSSRendering::DrawTableBorderSegment(
+    DrawTarget& aDrawTarget, StyleBorderStyle aBorderStyle,
+    nscolor aBorderColor, const nsRect& aBorder, int32_t aAppUnitsPerDevPixel,
+    mozilla::Side aStartBevelSide, nscoord aStartBevelOffset,
+    mozilla::Side aEndBevelSide, nscoord aEndBevelOffset) {
+  bool horizontal =
+      ((eSideTop == aStartBevelSide) || (eSideBottom == aStartBevelSide));
+  nscoord oneDevPixel = NSIntPixelsToAppUnits(1, aAppUnitsPerDevPixel);
+
+  if ((oneDevPixel >= aBorder.width) || (oneDevPixel >= aBorder.height) ||
+      (StyleBorderStyle::Dashed == aBorderStyle) ||
+      (StyleBorderStyle::Dotted == aBorderStyle)) {
+    // no beveling for 1 pixel border, dash or dot
+    aStartBevelOffset = 0;
+    aEndBevelOffset = 0;
+  }
+
+  switch (aBorderStyle) {
+    case StyleBorderStyle::None:
+    case StyleBorderStyle::Hidden:
+      // NS_ASSERTION(false, "style of none or hidden");
+      break;
+    case StyleBorderStyle::Dotted:
+    case StyleBorderStyle::Dashed: {
+      nscoord dashLength =
+          (StyleBorderStyle::Dashed == aBorderStyle) ? DASH_LENGTH : DOT_LENGTH;
+      // make the dash length proportional to the border thickness
+      dashLength *= (horizontal) ? aBorder.height : aBorder.width;
+      // make the min dash length for the ends 1/2 the dash length
+      nscoord minDashLength =
+          (StyleBorderStyle::Dashed == aBorderStyle)
+              ? RoundFloatToPixel(((float)dashLength) / 2.0f,
+                                  aAppUnitsPerDevPixel)
+              : dashLength;
+      minDashLength = std::max(minDashLength, oneDevPixel);
+      nscoord numDashSpaces = 0;
+      nscoord startDashLength = minDashLength;
+      nscoord endDashLength = minDashLength;
+      if (horizontal) {
+        GetDashInfo(aBorder.width, dashLength, aAppUnitsPerDevPixel,
+                    numDashSpaces, startDashLength, endDashLength);
+        nsRect rect(aBorder.x, aBorder.y, startDashLength, aBorder.height);
+        DrawSolidBorderSegment(aDrawTarget, rect, aBorderColor,
+                               aAppUnitsPerDevPixel);
+
+        rect.x += startDashLength + dashLength;
+        rect.width =
+            aBorder.width - (startDashLength + endDashLength + dashLength);
+        DrawDashedSegment(aDrawTarget, rect, dashLength, aBorderColor,
+                          aAppUnitsPerDevPixel, horizontal);
+
+        rect.x += rect.width;
+        rect.width = endDashLength;
+        DrawSolidBorderSegment(aDrawTarget, rect, aBorderColor,
+                               aAppUnitsPerDevPixel);
+      } else {
+        GetDashInfo(aBorder.height, dashLength, aAppUnitsPerDevPixel,
+                    numDashSpaces, startDashLength, endDashLength);
+        nsRect rect(aBorder.x, aBorder.y, aBorder.width, startDashLength);
+        DrawSolidBorderSegment(aDrawTarget, rect, aBorderColor,
+                               aAppUnitsPerDevPixel);
+
+        rect.y += rect.height + dashLength;
+        rect.height =
+            aBorder.height - (startDashLength + endDashLength + dashLength);
+        DrawDashedSegment(aDrawTarget, rect, dashLength, aBorderColor,
+                          aAppUnitsPerDevPixel, horizontal);
+
+        rect.y += rect.height;
+        rect.height = endDashLength;
+        DrawSolidBorderSegment(aDrawTarget, rect, aBorderColor,
+                               aAppUnitsPerDevPixel);
+      }
+    } break;
+    default:
+      AutoTArray<SolidBeveledBorderSegment, 3> segments;
+      GetTableBorderSolidSegments(
+          segments, aBorderStyle, aBorderColor, aBorder, aAppUnitsPerDevPixel,
+          aStartBevelSide, aStartBevelOffset, aEndBevelSide, aEndBevelOffset);
+      for (const auto& segment : segments) {
+        DrawSolidBorderSegment(
+            aDrawTarget, segment.mRect, segment.mColor, aAppUnitsPerDevPixel,
+            segment.mStartBevel.mSide, segment.mStartBevel.mOffset,
+            segment.mEndBevel.mSide, segment.mEndBevel.mOffset);
+      }
+      break;
+  }
+}
+
+void nsCSSRendering::GetTableBorderSolidSegments(
+    nsTArray<SolidBeveledBorderSegment>& aSegments,
+    StyleBorderStyle aBorderStyle, nscolor aBorderColor, const nsRect& aBorder,
+    int32_t aAppUnitsPerDevPixel, mozilla::Side aStartBevelSide,
+    nscoord aStartBevelOffset, mozilla::Side aEndBevelSide,
+    nscoord aEndBevelOffset) {
+  const bool horizontal =
+      eSideTop == aStartBevelSide || eSideBottom == aStartBevelSide;
+  const nscoord oneDevPixel = NSIntPixelsToAppUnits(1, aAppUnitsPerDevPixel);
+
+  switch (aBorderStyle) {
+    case StyleBorderStyle::None:
+    case StyleBorderStyle::Hidden:
+      return;
+    case StyleBorderStyle::Dotted:
+    case StyleBorderStyle::Dashed:
+      MOZ_ASSERT_UNREACHABLE("Caller should have checked");
+      return;
+    case StyleBorderStyle::Groove:
+    case StyleBorderStyle::Ridge:
+      if ((horizontal && (oneDevPixel >= aBorder.height)) ||
+          (!horizontal && (oneDevPixel >= aBorder.width))) {
+        aSegments.AppendElement(
+            SolidBeveledBorderSegment{aBorder,
+                                      aBorderColor,
+                                      {aStartBevelSide, aStartBevelOffset},
+                                      {aEndBevelSide, aEndBevelOffset}});
+      } else {
+        nscoord startBevel =
+            (aStartBevelOffset > 0)
+                ? RoundFloatToPixel(0.5f * (float)aStartBevelOffset,
+                                    aAppUnitsPerDevPixel, true)
+                : 0;
+        nscoord endBevel =
+            (aEndBevelOffset > 0)
+                ? RoundFloatToPixel(0.5f * (float)aEndBevelOffset,
+                                    aAppUnitsPerDevPixel, true)
+                : 0;
+        mozilla::Side ridgeGrooveSide = (horizontal) ? eSideTop : eSideLeft;
+        // FIXME: In theory, this should use the visited-dependent
+        // background color, but I don't care.
+        nscolor bevelColor =
+            MakeBevelColor(ridgeGrooveSide, aBorderStyle, aBorderColor);
+        nsRect rect(aBorder);
+        nscoord half;
+        if (horizontal) {  // top, bottom
+          half = RoundFloatToPixel(0.5f * (float)aBorder.height,
+                                   aAppUnitsPerDevPixel);
+          rect.height = half;
+          if (eSideTop == aStartBevelSide) {
+            rect.x += startBevel;
+            rect.width -= startBevel;
+          }
+          if (eSideTop == aEndBevelSide) {
+            rect.width -= endBevel;
+          }
+          aSegments.AppendElement(
+              SolidBeveledBorderSegment{rect,
+                                        bevelColor,
+                                        {aStartBevelSide, startBevel},
+                                        {aEndBevelSide, endBevel}});
+        } else {  // left, right
+          half = RoundFloatToPixel(0.5f * (float)aBorder.width,
+                                   aAppUnitsPerDevPixel);
+          rect.width = half;
+          if (eSideLeft == aStartBevelSide) {
+            rect.y += startBevel;
+            rect.height -= startBevel;
+          }
+          if (eSideLeft == aEndBevelSide) {
+            rect.height -= endBevel;
+          }
+          aSegments.AppendElement(
+              SolidBeveledBorderSegment{rect,
+                                        bevelColor,
+                                        {aStartBevelSide, startBevel},
+                                        {aEndBevelSide, endBevel}});
+        }
+
+        rect = aBorder;
+        ridgeGrooveSide =
+            (eSideTop == ridgeGrooveSide) ? eSideBottom : eSideRight;
+        // FIXME: In theory, this should use the visited-dependent
+        // background color, but I don't care.
+        bevelColor =
+            MakeBevelColor(ridgeGrooveSide, aBorderStyle, aBorderColor);
+        if (horizontal) {
+          rect.y = rect.y + half;
+          rect.height = aBorder.height - half;
+          if (eSideBottom == aStartBevelSide) {
+            rect.x += startBevel;
+            rect.width -= startBevel;
+          }
+          if (eSideBottom == aEndBevelSide) {
+            rect.width -= endBevel;
+          }
+          aSegments.AppendElement(
+              SolidBeveledBorderSegment{rect,
+                                        bevelColor,
+                                        {aStartBevelSide, startBevel},
+                                        {aEndBevelSide, endBevel}});
+        } else {
+          rect.x = rect.x + half;
+          rect.width = aBorder.width - half;
+          if (eSideRight == aStartBevelSide) {
+            rect.y += aStartBevelOffset - startBevel;
+            rect.height -= startBevel;
+          }
+          if (eSideRight == aEndBevelSide) {
+            rect.height -= endBevel;
+          }
+          aSegments.AppendElement(
+              SolidBeveledBorderSegment{rect,
+                                        bevelColor,
+                                        {aStartBevelSide, startBevel},
+                                        {aEndBevelSide, endBevel}});
+        }
+      }
+      break;
+    case StyleBorderStyle::Double:
+      // We can only do "double" borders if the thickness of the border
+      // is more than 2px.  Otherwise, we fall through to painting a
+      // solid border.
+      if ((aBorder.width > 2 * oneDevPixel || horizontal) &&
+          (aBorder.height > 2 * oneDevPixel || !horizontal)) {
+        nscoord startBevel =
+            (aStartBevelOffset > 0)
+                ? RoundFloatToPixel(0.333333f * (float)aStartBevelOffset,
+                                    aAppUnitsPerDevPixel)
+                : 0;
+        nscoord endBevel =
+            (aEndBevelOffset > 0)
+                ? RoundFloatToPixel(0.333333f * (float)aEndBevelOffset,
+                                    aAppUnitsPerDevPixel)
+                : 0;
+        if (horizontal) {  // top, bottom
+          nscoord thirdHeight = RoundFloatToPixel(
+              0.333333f * (float)aBorder.height, aAppUnitsPerDevPixel);
+
+          // draw the top line or rect
+          nsRect topRect(aBorder.x, aBorder.y, aBorder.width, thirdHeight);
+          if (eSideTop == aStartBevelSide) {
+            topRect.x += aStartBevelOffset - startBevel;
+            topRect.width -= aStartBevelOffset - startBevel;
+          }
+          if (eSideTop == aEndBevelSide) {
+            topRect.width -= aEndBevelOffset - endBevel;
+          }
+
+          aSegments.AppendElement(
+              SolidBeveledBorderSegment{topRect,
+                                        aBorderColor,
+                                        {aStartBevelSide, startBevel},
+                                        {aEndBevelSide, endBevel}});
+
+          // draw the botom line or rect
+          nscoord heightOffset = aBorder.height - thirdHeight;
+          nsRect bottomRect(aBorder.x, aBorder.y + heightOffset, aBorder.width,
+                            aBorder.height - heightOffset);
+          if (eSideBottom == aStartBevelSide) {
+            bottomRect.x += aStartBevelOffset - startBevel;
+            bottomRect.width -= aStartBevelOffset - startBevel;
+          }
+          if (eSideBottom == aEndBevelSide) {
+            bottomRect.width -= aEndBevelOffset - endBevel;
+          }
+          aSegments.AppendElement(
+              SolidBeveledBorderSegment{bottomRect,
+                                        aBorderColor,
+                                        {aStartBevelSide, startBevel},
+                                        {aEndBevelSide, endBevel}});
+        } else {  // left, right
+          nscoord thirdWidth = RoundFloatToPixel(
+              0.333333f * (float)aBorder.width, aAppUnitsPerDevPixel);
+
+          nsRect leftRect(aBorder.x, aBorder.y, thirdWidth, aBorder.height);
+          if (eSideLeft == aStartBevelSide) {
+            leftRect.y += aStartBevelOffset - startBevel;
+            leftRect.height -= aStartBevelOffset - startBevel;
+          }
+          if (eSideLeft == aEndBevelSide) {
+            leftRect.height -= aEndBevelOffset - endBevel;
+          }
+
+          aSegments.AppendElement(
+              SolidBeveledBorderSegment{leftRect,
+                                        aBorderColor,
+                                        {aStartBevelSide, startBevel},
+                                        {aEndBevelSide, endBevel}});
+
+          nscoord widthOffset = aBorder.width - thirdWidth;
+          nsRect rightRect(aBorder.x + widthOffset, aBorder.y,
+                           aBorder.width - widthOffset, aBorder.height);
+          if (eSideRight == aStartBevelSide) {
+            rightRect.y += aStartBevelOffset - startBevel;
+            rightRect.height -= aStartBevelOffset - startBevel;
+          }
+          if (eSideRight == aEndBevelSide) {
+            rightRect.height -= aEndBevelOffset - endBevel;
+          }
+          aSegments.AppendElement(
+              SolidBeveledBorderSegment{rightRect,
+                                        aBorderColor,
+                                        {aStartBevelSide, startBevel},
+                                        {aEndBevelSide, endBevel}});
+        }
+        break;
+      }
+      // else fall through to solid
+      [[fallthrough]];
+    case StyleBorderStyle::Solid:
+      aSegments.AppendElement(
+          SolidBeveledBorderSegment{aBorder,
+                                    aBorderColor,
+                                    {aStartBevelSide, aStartBevelOffset},
+                                    {aEndBevelSide, aEndBevelOffset}});
+      break;
+    case StyleBorderStyle::Outset:
+    case StyleBorderStyle::Inset:
+      MOZ_ASSERT_UNREACHABLE(
+          "inset, outset should have been converted to groove, ridge");
+      break;
+  }
+}
+
+// End table border-collapsing section
+
+Rect nsCSSRendering::ExpandPaintingRectForDecorationLine(
+    nsIFrame* aFrame, const StyleTextDecorationStyle aStyle,
+    const Rect& aClippedRect, const Float aICoordInFrame,
+    const Float aCycleLength, bool aVertical) {
+  switch (aStyle) {
+    case StyleTextDecorationStyle::Dotted:
+    case StyleTextDecorationStyle::Dashed:
+    case StyleTextDecorationStyle::Wavy:
+      break;
+    default:
+      NS_ERROR("Invalid style was specified");
+      return aClippedRect;
+  }
+
+  nsBlockFrame* block = nullptr;
+  // Note that when we paint the decoration lines in relative positioned
+  // box, we should paint them like all of the boxes are positioned as static.
+  nscoord framePosInBlockAppUnits = 0;
+  for (nsIFrame* f = aFrame; f; f = f->GetParent()) {
+    block = do_QueryFrame(f);
+    if (block) {
+      break;
+    }
+    framePosInBlockAppUnits +=
+        aVertical ? f->GetNormalPosition().y : f->GetNormalPosition().x;
+  }
+
+  NS_ENSURE_TRUE(block, aClippedRect);
+
+  nsPresContext* pc = aFrame->PresContext();
+  Float framePosInBlock =
+      Float(pc->AppUnitsToGfxUnits(framePosInBlockAppUnits));
+  int32_t rectPosInBlock = int32_t(NS_round(framePosInBlock + aICoordInFrame));
+  int32_t extraStartEdge =
+      rectPosInBlock - (rectPosInBlock / int32_t(aCycleLength) * aCycleLength);
+  Rect rect(aClippedRect);
+  if (aVertical) {
+    rect.y -= extraStartEdge;
+    rect.height += extraStartEdge;
+  } else {
+    rect.x -= extraStartEdge;
+    rect.width += extraStartEdge;
+  }
+  return rect;
+}
+
+// Converts a GfxFont to an SkFont
+// Either returns true if it was successful, or false if something went wrong
+static bool GetSkFontFromGfxFont(DrawTarget& aDrawTarget, gfxFont* aFont,
+                                 SkFont& aSkFont) {
+  RefPtr<ScaledFont> scaledFont = aFont->GetScaledFont(&aDrawTarget);
+  if (!scaledFont) {
+    return false;
+  }
+
+  ScaledFontBase* fontBase = static_cast<ScaledFontBase*>(scaledFont.get());
+
+  SkTypeface* typeface = fontBase->GetSkTypeface();
+  if (!typeface) {
+    return false;
+  }
+
+  aSkFont = SkFont(sk_ref_sp(typeface), SkFloatToScalar(fontBase->GetSize()));
+  return true;
+}
+
+// Computes data used to position the decoration line within a
+// SkTextBlob, data is returned through aBounds
+static void GetPositioning(
+    const nsCSSRendering::PaintDecorationLineParams& aParams, const Rect& aRect,
+    Float aOneCSSPixel, Float aCenterBaselineOffset, SkScalar aBounds[]) {
+  /**
+   * How Positioning in Skia Works
+   *  Take the letter "n" for example
+   *  We set textPos as 0, 0
+   *  This is represented in Skia like so (not to scale)
+   *        ^
+   *  -10px |  _ __
+   *        | | '_ \
+   *   -5px | | | | |
+   * y-axis | |_| |_|
+   *  (0,0) ----------------------->
+   *        |     5px        10px
+   *    5px |
+   *        |
+   *   10px |
+   *        v
+   *  0 on the x axis is a line that touches the bottom of the n
+   *  (0,0) is the bottom left-hand corner of the n character
+   *  Moving "up" from the n is going in a negative y direction
+   *  Moving "down" from the n is going in a positive y direction
+   *
+   *  The intercepts that are returned in this arrangement will be
+   *  offset by the original point it starts at. (This happens in
+   *  the SkipInk function below).
+   *
+   *  In Skia, text MUST be laid out such that the next character
+   *  in the RunBuffer is further along the x-axis than the previous
+   *  character, otherwise there is undefined/strange behavior.
+   */
+
+  Float rectThickness = aParams.vertical ? aRect.Width() : aRect.Height();
+
+  // the upper and lower lines/edges of the under or over line
+  SkScalar upperLine, lowerLine;
+  if (aParams.decoration == mozilla::StyleTextDecorationLine::OVERLINE) {
+    lowerLine =
+        -aParams.offset + aParams.defaultLineThickness - aCenterBaselineOffset;
+    upperLine = lowerLine - rectThickness;
+  } else {
+    // underlines in vertical text are offset from the center of
+    // the text, and not the baseline
+    // Skia sets the text at it's baseline so we have to offset it
+    // for text in vertical-* writing modes
+    upperLine = -aParams.offset - aCenterBaselineOffset;
+    lowerLine = upperLine + rectThickness;
+  }
+
+  // set up the bounds, add in a little padding to the thickness of the line
+  // (unless the line is <= 1 CSS pixel thick)
+  Float lineThicknessPadding = aParams.lineSize.height > aOneCSSPixel
+                                   ? 0.25f * aParams.lineSize.height
+                                   : 0;
+  // don't allow padding greater than 0.75 CSS pixel
+  lineThicknessPadding = std::min(lineThicknessPadding, 0.75f * aOneCSSPixel);
+  aBounds[0] = upperLine - lineThicknessPadding;
+  aBounds[1] = lowerLine + lineThicknessPadding;
+}
+
+// positions an individual glyph according to the given offset
+static SkPoint GlyphPosition(const gfxTextRun::DetailedGlyph& aGlyph,
+                             const SkPoint& aTextPos,
+                             int32_t aAppUnitsPerDevPixel) {
+  SkPoint point = {aGlyph.mOffset.x, aGlyph.mOffset.y};
+
+  // convert to device pixels
+  point.fX /= (float)aAppUnitsPerDevPixel;
+  point.fY /= (float)aAppUnitsPerDevPixel;
+
+  // add offsets
+  point.fX += aTextPos.fX;
+  point.fY += aTextPos.fY;
+  return point;
+}
+
+// returns a count of all the glyphs that will be rendered
+// excludes ligature continuations, includes the number of individual
+// glyph records. This includes the number of DetailedGlyphs that a single
+// CompressedGlyph record points to. This function is necessary because Skia
+// needs the total length of glyphs to add to it's run buffer before it creates
+// the RunBuffer object, and this cannot be resized later.
+static uint32_t CountAllGlyphs(
+    const gfxTextRun* aTextRun,
+    const gfxTextRun::CompressedGlyph* aCompressedGlyph, uint32_t aStringStart,
+    uint32_t aStringEnd) {
+  uint32_t totalGlyphCount = 0;
+
+  for (const gfxTextRun::CompressedGlyph* cg = aCompressedGlyph + aStringStart;
+       cg < aCompressedGlyph + aStringEnd; ++cg) {
+    totalGlyphCount += cg->IsSimpleGlyph() ? 1 : cg->GetGlyphCount();
+  }
+
+  return totalGlyphCount;
+}
+
+static void AddDetailedGlyph(const SkTextBlobBuilder::RunBuffer& aRunBuffer,
+                             const gfxTextRun::DetailedGlyph& aGlyph,
+                             int aIndex, float aAppUnitsPerDevPixel,
+                             SkPoint& aTextPos) {
+  // add glyph ID to the run buffer at i
+  aRunBuffer.glyphs[aIndex] = aGlyph.mGlyphID;
+
+  // position the glyph correctly using the detailed offsets
+  SkPoint position = GlyphPosition(aGlyph, aTextPos, aAppUnitsPerDevPixel);
+  aRunBuffer.pos[2 * aIndex] = position.fX;
+  aRunBuffer.pos[(2 * aIndex) + 1] = position.fY;
+
+  // increase aTextPos.fx by the advance
+  aTextPos.fX += ((float)aGlyph.mAdvance / aAppUnitsPerDevPixel);
+}
+
+static void AddSimpleGlyph(const SkTextBlobBuilder::RunBuffer& aRunBuffer,
+                           const gfxTextRun::CompressedGlyph& aGlyph,
+                           int aIndex, float aAppUnitsPerDevPixel,
+                           SkPoint& aTextPos) {
+  aRunBuffer.glyphs[aIndex] = aGlyph.GetSimpleGlyph();
+
+  // simple glyphs are offset from 0, so we'll just use textPos
+  aRunBuffer.pos[2 * aIndex] = aTextPos.fX;
+  aRunBuffer.pos[(2 * aIndex) + 1] = aTextPos.fY;
+
+  // increase aTextPos.fX by the advance
+  aTextPos.fX += ((float)aGlyph.GetSimpleAdvance() / aAppUnitsPerDevPixel);
+}
+
+// Sets up a Skia TextBlob of the specified font, text position, and made up of
+// the glyphs between aStringStart and aStringEnd. Handles RTL and LTR text
+// and positions each glyph within the text blob
+static sk_sp<const SkTextBlob> CreateTextBlob(
+    const gfxTextRun* aTextRun,
+    const gfxTextRun::CompressedGlyph* aCompressedGlyph, const SkFont& aFont,
+    const gfxTextRun::PropertyProvider::Spacing* aSpacing,
+    uint32_t aStringStart, uint32_t aStringEnd, float aAppUnitsPerDevPixel,
+    SkPoint& aTextPos, int32_t& aSpacingOffset) {
+  // allocate space for the run buffer, then fill it with the glyphs
+  uint32_t len =
+      CountAllGlyphs(aTextRun, aCompressedGlyph, aStringStart, aStringEnd);
+  if (len <= 0) {
+    return nullptr;
+  }
+
+  SkTextBlobBuilder builder;
+  const SkTextBlobBuilder::RunBuffer& run = builder.allocRunPos(aFont, len);
+
+  // RTL text should be read in by glyph starting at aStringEnd - 1 down until
+  // aStringStart.
+  bool isRTL = aTextRun->IsRightToLeft();
+  uint32_t currIndex = isRTL ? aStringEnd - 1 : aStringStart;  // textRun index
+  // currIndex will be advanced by |step| until it reaches |limit|, which is the
+  // final index to be handled (NOT one beyond the final index)
+  int step = isRTL ? -1 : 1;
+  uint32_t limit = isRTL ? aStringStart : aStringEnd - 1;
+
+  uint32_t i = 0;  // index into the SkTextBlob we're building
+  while (true) {
+    // Loop exit test is below, just before we update currIndex.
+    aTextPos.fX +=
+        isRTL ? aSpacing[aSpacingOffset].mAfter / aAppUnitsPerDevPixel
+              : aSpacing[aSpacingOffset].mBefore / aAppUnitsPerDevPixel;
+
+    if (aCompressedGlyph[currIndex].IsSimpleGlyph()) {
+      MOZ_ASSERT(i < len, "glyph count error!");
+      AddSimpleGlyph(run, aCompressedGlyph[currIndex], i, aAppUnitsPerDevPixel,
+                     aTextPos);
+      i++;
+    } else {
+      // if it's detailed, potentially add multiple into run.glyphs
+      uint32_t count = aCompressedGlyph[currIndex].GetGlyphCount();
+      if (count > 0) {
+        gfxTextRun::DetailedGlyph* detailGlyph =
+            aTextRun->GetDetailedGlyphs(currIndex);
+        for (uint32_t d = isRTL ? count - 1 : 0; count; count--, d += step) {
+          MOZ_ASSERT(i < len, "glyph count error!");
+          AddDetailedGlyph(run, detailGlyph[d], i, aAppUnitsPerDevPixel,
+                           aTextPos);
+          i++;
+        }
+      }
+    }
+    aTextPos.fX += isRTL
+                       ? aSpacing[aSpacingOffset].mBefore / aAppUnitsPerDevPixel
+                       : aSpacing[aSpacingOffset].mAfter / aAppUnitsPerDevPixel;
+    aSpacingOffset += step;
+
+    if (currIndex == limit) {
+      break;
+    }
+    currIndex += step;
+  }
+
+  MOZ_ASSERT(i == len, "glyph count error!");
+
+  return builder.make();
+}
+
+// Given a TextBlob, the bounding lines, and the set of current intercepts this
+// function adds the intercepts for the current TextBlob into the given set of
+// previoulsy calculated intercepts. This set is either of length 0, or a
+// multiple of 2 (since every intersection with a piece of text results in two
+// intercepts: entering/exiting)
+static void GetTextIntercepts(const sk_sp<const SkTextBlob>& aBlob,
+                              const SkScalar aBounds[],
+                              nsTArray<SkScalar>& aIntercepts) {
+  // It's possible that we'll encounter a Windows exception deep inside
+  // Skia's DirectWrite code while trying to get the intercepts. To avoid
+  // crashing in this case, catch any such exception here and discard the
+  // newly-added (and incompletely filled in) elements.
+  int count = 0;
+  MOZ_SEH_TRY {
+    // https://skia.org/user/api/SkTextBlob_Reference#Text_Blob_Text_Intercepts
+    count = aBlob->getIntercepts(aBounds, nullptr);
+    if (count < 2) {
+      return;
+    }
+    aBlob->getIntercepts(aBounds, aIntercepts.AppendElements(count));
+  }
+  MOZ_SEH_EXCEPT(EXCEPTION_EXECUTE_HANDLER) {
+    gfxCriticalNote << "Exception occurred getting text intercepts";
+    aIntercepts.TruncateLength(aIntercepts.Length() - count);
+  }
+}
+
+// This function, given a set of intercepts that represent each intersection
+// between an under/overline and text, makes a series of calls to
+// PaintDecorationLineInternal that paints a series of clip rects which
+// implement the text-decoration-skip-ink property
+// Logic for where to place each clipped rect, and the length of each rect is
+// included here
+static void SkipInk(nsIFrame* aFrame, DrawTarget& aDrawTarget,
+                    const nsCSSRendering::PaintDecorationLineParams& aParams,
+                    const nsTArray<SkScalar>& aIntercepts, Float aPadding,
+                    Rect& aRect) {
+  nsCSSRendering::PaintDecorationLineParams clipParams = aParams;
+  int length = aIntercepts.Length();
+
+  SkScalar startIntercept = 0;
+  SkScalar endIntercept = 0;
+
+  // keep track of the direction we are drawing the clipped rects in
+  // for sideways text, our intercepts from the first glyph are actually
+  // decreasing (towards the top edge of the page), so we use a negative
+  // direction
+  Float dir = 1.0f;
+  Float lineStart = aParams.vertical ? aParams.pt.y : aParams.pt.x;
+  Float lineEnd = lineStart + aParams.lineSize.width;
+  if (aParams.sidewaysLeft) {
+    dir = -1.0f;
+    std::swap(lineStart, lineEnd);
+  }
+
+  for (int i = 0; i <= length; i += 2) {
+    // handle start/end edge cases and set up general case
+    startIntercept = (i > 0) ? (dir * aIntercepts[i - 1]) + lineStart
+                             : lineStart - (dir * aPadding);
+    endIntercept = (i < length) ? (dir * aIntercepts[i]) + lineStart
+                                : lineEnd + (dir * aPadding);
+
+    // remove padding at both ends for width
+    // the start of the line is calculated so the padding removes just
+    // enough so that the line starts at its normal position
+    clipParams.lineSize.width =
+        (dir * (endIntercept - startIntercept)) - (2.0 * aPadding);
+
+    // Don't draw decoration lines that have a smaller width than 1, or half
+    // the line-end padding dimension.
+    if (clipParams.lineSize.width < std::max(aPadding * 0.5, 1.0)) {
+      continue;
+    }
+
+    // Start the line right after the intercept's location plus room for
+    // padding; snap the rect edges to device pixels for consistent rendering
+    // of dots across separate fragments of a dotted line.
+    if (aParams.vertical) {
+      clipParams.pt.y = aParams.sidewaysLeft ? endIntercept + aPadding
+                                             : startIntercept + aPadding;
+      aRect.y = std::floor(clipParams.pt.y + 0.5);
+      aRect.SetBottomEdge(
+          std::floor(clipParams.pt.y + clipParams.lineSize.width + 0.5));
+    } else {
+      clipParams.pt.x = startIntercept + aPadding;
+      aRect.x = std::floor(clipParams.pt.x + 0.5);
+      aRect.SetRightEdge(
+          std::floor(clipParams.pt.x + clipParams.lineSize.width + 0.5));
+    }
+
+    nsCSSRendering::PaintDecorationLineInternal(aFrame, aDrawTarget, clipParams,
+                                                aRect);
+  }
+}
+
+void nsCSSRendering::PaintDecorationLine(
+    nsIFrame* aFrame, DrawTarget& aDrawTarget,
+    const PaintDecorationLineParams& aParams) {
+  NS_ASSERTION(aParams.style != StyleTextDecorationStyle::None,
+               "aStyle is none");
+
+  Rect rect = ToRect(GetTextDecorationRectInternal(aParams.pt, aParams));
+  if (rect.IsEmpty() || !rect.Intersects(aParams.dirtyRect)) {
+    return;
+  }
+
+  if (aParams.decoration != StyleTextDecorationLine::UNDERLINE &&
+      aParams.decoration != StyleTextDecorationLine::OVERLINE &&
+      aParams.decoration != StyleTextDecorationLine::LINE_THROUGH) {
+    MOZ_ASSERT_UNREACHABLE("Invalid text decoration value");
+    return;
+  }
+
+  // Check if decoration line will skip past ascenders/descenders
+  // text-decoration-skip-ink only applies to overlines/underlines
+  mozilla::StyleTextDecorationSkipInk skipInk =
+      aFrame->StyleText()->mTextDecorationSkipInk;
+  bool skipInkEnabled =
+      skipInk != mozilla::StyleTextDecorationSkipInk::None &&
+      aParams.decoration != StyleTextDecorationLine::LINE_THROUGH;
+
+  if (!skipInkEnabled || aParams.glyphRange.Length() == 0) {
+    PaintDecorationLineInternal(aFrame, aDrawTarget, aParams, rect);
+    return;
+  }
+
+  // check if the frame is a text frame or not
+  nsTextFrame* textFrame = nullptr;
+  if (aFrame->IsTextFrame()) {
+    textFrame = static_cast<nsTextFrame*>(aFrame);
+  } else {
+    PaintDecorationLineInternal(aFrame, aDrawTarget, aParams, rect);
+    return;
+  }
+
+  // get text run and current text offset (for line wrapping)
+  gfxTextRun* textRun =
+      textFrame->GetTextRun(nsTextFrame::TextRunType::eInflated);
+
+  // used for conversions from app units to device pixels
+  int32_t appUnitsPerDevPixel = aFrame->PresContext()->AppUnitsPerDevPixel();
+
+  // pointer to the array of glyphs for this TextRun
+  gfxTextRun::CompressedGlyph* characterGlyphs = textRun->GetCharacterGlyphs();
+
+  // get positioning info
+  SkPoint textPos = {0, aParams.baselineOffset};
+  SkScalar bounds[] = {0, 0};
+  Float oneCSSPixel = aFrame->PresContext()->CSSPixelsToDevPixels(1.0f);
+  if (!textRun->UseCenterBaseline()) {
+    GetPositioning(aParams, rect, oneCSSPixel, 0, bounds);
+  }
+
+  // array for the text intercepts
+  AutoTArray<SkScalar, 256> intercepts;
+
+  // array for spacing data
+  AutoTArray<gfxTextRun::PropertyProvider::Spacing, 64> spacing;
+  spacing.SetLength(aParams.glyphRange.Length());
+  if (aParams.provider != nullptr) {
+    aParams.provider->GetSpacing(aParams.glyphRange, spacing.Elements());
+  }
+
+  // loop through each glyph run
+  // in most cases there will only be one
+  bool isRTL = textRun->IsRightToLeft();
+  int32_t spacingOffset = isRTL ? aParams.glyphRange.Length() - 1 : 0;
+  gfxTextRun::GlyphRunIterator iter(textRun, aParams.glyphRange, isRTL);
+
+  // For any glyph run where we don't actually do skipping, we'll need to
+  // advance the current position by its width.
+  // (For runs we do process, CreateTextBlob will update the position.)
+  auto currentGlyphRunAdvance = [&]() {
+    return textRun->GetAdvanceWidth(
+               gfxTextRun::Range(iter.GetStringStart(), iter.GetStringEnd()),
+               aParams.provider) /
+           appUnitsPerDevPixel;
+  };
+
+  while (iter.NextRun()) {
+    if (iter.GetGlyphRun()->mOrientation ==
+            mozilla::gfx::ShapedTextFlags::TEXT_ORIENT_VERTICAL_UPRIGHT ||
+        (iter.GetGlyphRun()->mIsCJK &&
+         skipInk == mozilla::StyleTextDecorationSkipInk::Auto)) {
+      // We don't support upright text in vertical modes currently
+      // (see https://bugzilla.mozilla.org/show_bug.cgi?id=1572294),
+      // but we do need to update textPos so that following runs will be
+      // correctly positioned.
+      // We also don't apply skip-ink to CJK text runs because many fonts
+      // have an underline that looks really bad if this is done
+      // (see https://bugzilla.mozilla.org/show_bug.cgi?id=1573249),
+      // when skip-ink is set to 'auto'.
+      textPos.fX += currentGlyphRunAdvance();
+      continue;
+    }
+
+    gfxFont* font = iter.GetGlyphRun()->mFont;
+    // Don't try to apply skip-ink to 'sbix' fonts like Apple Color Emoji,
+    // because old macOS (10.9) may crash trying to retrieve glyph paths
+    // that don't exist.
+    if (font->GetFontEntry()->HasFontTable(TRUETYPE_TAG('s', 'b', 'i', 'x'))) {
+      textPos.fX += currentGlyphRunAdvance();
+      continue;
+    }
+
+    // get a Skia version of the glyph run's font
+    SkFont skiafont;
+    if (!GetSkFontFromGfxFont(aDrawTarget, font, skiafont)) {
+      PaintDecorationLineInternal(aFrame, aDrawTarget, aParams, rect);
+      return;
+    }
+
+    // Create a text blob with correctly positioned glyphs. This also updates
+    // textPos.fX with the advance of the glyphs.
+    sk_sp<const SkTextBlob> textBlob =
+        CreateTextBlob(textRun, characterGlyphs, skiafont, spacing.Elements(),
+                       iter.GetStringStart(), iter.GetStringEnd(),
+                       (float)appUnitsPerDevPixel, textPos, spacingOffset);
+
+    if (!textBlob) {
+      textPos.fX += currentGlyphRunAdvance();
+      continue;
+    }
+
+    if (textRun->UseCenterBaseline()) {
+      // writing modes that use a center baseline need to be adjusted on a
+      // font-by-font basis since Skia lines up the text on a alphabetic
+      // baseline, but for some vertical-* writing modes the offset is from the
+      // center.
+      gfxFont::Metrics metrics = font->GetMetrics(nsFontMetrics::eHorizontal);
+      Float centerToBaseline = (metrics.emAscent - metrics.emDescent) / 2.0f;
+      GetPositioning(aParams, rect, oneCSSPixel, centerToBaseline, bounds);
+    }
+
+    // compute the text intercepts that need to be skipped
+    GetTextIntercepts(textBlob, bounds, intercepts);
+  }
+  bool needsSkipInk = intercepts.Length() > 0;
+
+  if (needsSkipInk) {
+    // Padding between glyph intercepts and the decoration line: we use the
+    // decoration line thickness, clamped to a minimum of 1px and a maximum
+    // of 0.2em.
+    Float padding =
+        std::min(std::max(aParams.lineSize.height, oneCSSPixel),
+                 Float(textRun->GetFontGroup()->GetStyle()->size / 5.0));
+    SkipInk(aFrame, aDrawTarget, aParams, intercepts, padding, rect);
+  } else {
+    PaintDecorationLineInternal(aFrame, aDrawTarget, aParams, rect);
+  }
+}
+
+void nsCSSRendering::PaintDecorationLineInternal(
+    nsIFrame* aFrame, DrawTarget& aDrawTarget,
+    const PaintDecorationLineParams& aParams, Rect aRect) {
+  Float lineThickness = std::max(NS_round(aParams.lineSize.height), 1.0);
+
+  DeviceColor color = ToDeviceColor(aParams.color);
+  ColorPattern colorPat(color);
+  StrokeOptions strokeOptions(lineThickness);
+  DrawOptions drawOptions;
+
+  Float dash[2];
+
+  AutoPopClips autoPopClips(&aDrawTarget);
+
+  mozilla::layout::TextDrawTarget* textDrawer = nullptr;
+  if (aDrawTarget.GetBackendType() == BackendType::WEBRENDER_TEXT) {
+    textDrawer = static_cast<mozilla::layout::TextDrawTarget*>(&aDrawTarget);
+  }
+
+  switch (aParams.style) {
+    case StyleTextDecorationStyle::Solid:
+    case StyleTextDecorationStyle::Double:
+      break;
+    case StyleTextDecorationStyle::Dashed: {
+      autoPopClips.PushClipRect(aRect);
+      Float dashWidth = lineThickness * DOT_LENGTH * DASH_LENGTH;
+      dash[0] = dashWidth;
+      dash[1] = dashWidth;
+      strokeOptions.mDashPattern = dash;
+      strokeOptions.mDashLength = MOZ_ARRAY_LENGTH(dash);
+      strokeOptions.mLineCap = CapStyle::BUTT;
+      aRect = ExpandPaintingRectForDecorationLine(
+          aFrame, aParams.style, aRect, aParams.icoordInFrame, dashWidth * 2,
+          aParams.vertical);
+      // We should continue to draw the last dash even if it is not in the rect.
+      aRect.width += dashWidth;
+      break;
+    }
+    case StyleTextDecorationStyle::Dotted: {
+      autoPopClips.PushClipRect(aRect);
+      Float dashWidth = lineThickness * DOT_LENGTH;
+      if (lineThickness > 2.0) {
+        dash[0] = 0.f;
+        dash[1] = dashWidth * 2.f;
+        strokeOptions.mLineCap = CapStyle::ROUND;
+      } else {
+        dash[0] = dashWidth;
+        dash[1] = dashWidth;
+      }
+      strokeOptions.mDashPattern = dash;
+      strokeOptions.mDashLength = MOZ_ARRAY_LENGTH(dash);
+      aRect = ExpandPaintingRectForDecorationLine(
+          aFrame, aParams.style, aRect, aParams.icoordInFrame, dashWidth * 2,
+          aParams.vertical);
+      // We should continue to draw the last dot even if it is not in the rect.
+      aRect.width += dashWidth;
+      break;
+    }
+    case StyleTextDecorationStyle::Wavy:
+      autoPopClips.PushClipRect(aRect);
+      if (lineThickness > 2.0) {
+        drawOptions.mAntialiasMode = AntialiasMode::SUBPIXEL;
+      } else {
+        // Don't use anti-aliasing here.  Because looks like lighter color wavy
+        // line at this case.  And probably, users don't think the
+        // non-anti-aliased wavy line is not pretty.
+        drawOptions.mAntialiasMode = AntialiasMode::NONE;
+      }
+      break;
+    default:
+      NS_ERROR("Invalid style value!");
+      return;
+  }
+
+  // The block-direction position should be set to the middle of the line.
+  if (aParams.vertical) {
+    aRect.x += lineThickness / 2;
+  } else {
+    aRect.y += lineThickness / 2;
+  }
+
+  switch (aParams.style) {
+    case StyleTextDecorationStyle::Solid:
+    case StyleTextDecorationStyle::Dotted:
+    case StyleTextDecorationStyle::Dashed: {
+      Point p1 = aRect.TopLeft();
+      Point p2 = aParams.vertical ? aRect.BottomLeft() : aRect.TopRight();
+      if (textDrawer) {
+        textDrawer->AppendDecoration(p1, p2, lineThickness, aParams.vertical,
+                                     color, aParams.style);
+      } else {
+        aDrawTarget.StrokeLine(p1, p2, colorPat, strokeOptions, drawOptions);
+      }
+      return;
+    }
+    case StyleTextDecorationStyle::Double: {
+      /**
+       *  We are drawing double line as:
+       *
+       * +-------------------------------------------+
+       * |XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX| ^
+       * |XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX| | lineThickness
+       * |XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX| v
+       * |                                           |
+       * |                                           |
+       * |XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX| ^
+       * |XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX| | lineThickness
+       * |XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX| v
+       * +-------------------------------------------+
+       */
+      Point p1a = aRect.TopLeft();
+      Point p2a = aParams.vertical ? aRect.BottomLeft() : aRect.TopRight();
+
+      if (aParams.vertical) {
+        aRect.width -= lineThickness;
+      } else {
+        aRect.height -= lineThickness;
+      }
+
+      Point p1b = aParams.vertical ? aRect.TopRight() : aRect.BottomLeft();
+      Point p2b = aRect.BottomRight();
+
+      if (textDrawer) {
+        textDrawer->AppendDecoration(p1a, p2a, lineThickness, aParams.vertical,
+                                     color, StyleTextDecorationStyle::Solid);
+        textDrawer->AppendDecoration(p1b, p2b, lineThickness, aParams.vertical,
+                                     color, StyleTextDecorationStyle::Solid);
+      } else {
+        aDrawTarget.StrokeLine(p1a, p2a, colorPat, strokeOptions, drawOptions);
+        aDrawTarget.StrokeLine(p1b, p2b, colorPat, strokeOptions, drawOptions);
+      }
+      return;
+    }
+    case StyleTextDecorationStyle::Wavy: {
+      /**
+       *  We are drawing wavy line as:
+       *
+       *  P: Path, X: Painted pixel
+       *
+       *     +---------------------------------------+
+       *   XX|X            XXXXXX            XXXXXX  |
+       *   PP|PX          XPPPPPPX          XPPPPPPX |    ^
+       *   XX|XPX        XPXXXXXXPX        XPXXXXXXPX|    |
+       *     | XPX      XPX      XPX      XPX      XP|X   |adv
+       *     |  XPXXXXXXPX        XPXXXXXXPX        X|PX  |
+       *     |   XPPPPPPX          XPPPPPPX          |XPX v
+       *     |    XXXXXX            XXXXXX           | XX
+       *     +---------------------------------------+
+       *      <---><--->                                ^
+       *      adv  flatLengthAtVertex                   rightMost
+       *
+       *  1. Always starts from top-left of the drawing area, however, we need
+       *     to draw  the line from outside of the rect.  Because the start
+       *     point of the line is not good style if we draw from inside it.
+       *  2. First, draw horizontal line from outside the rect to top-left of
+       *     the rect;
+       *  3. Goes down to bottom of the area at 45 degrees.
+       *  4. Slides to right horizontaly, see |flatLengthAtVertex|.
+       *  5. Goes up to top of the area at 45 degrees.
+       *  6. Slides to right horizontaly.
+       *  7. Repeat from 2 until reached to right-most edge of the area.
+       *
+       * In the vertical case, swap horizontal and vertical coordinates and
+       * directions in the above description.
+       */
+
+      Float& rectICoord = aParams.vertical ? aRect.y : aRect.x;
+      Float& rectISize = aParams.vertical ? aRect.height : aRect.width;
+      const Float rectBSize = aParams.vertical ? aRect.width : aRect.height;
+
+      const Float adv = rectBSize - lineThickness;
+      const Float flatLengthAtVertex =
+          std::max((lineThickness - 1.0) * 2.0, 1.0);
+
+      // Align the start of wavy lines to the nearest ancestor block.
+      const Float cycleLength = 2 * (adv + flatLengthAtVertex);
+      aRect = ExpandPaintingRectForDecorationLine(
+          aFrame, aParams.style, aRect, aParams.icoordInFrame, cycleLength,
+          aParams.vertical);
+
+      if (textDrawer) {
+        // Undo attempted centering
+        Float& rectBCoord = aParams.vertical ? aRect.x : aRect.y;
+        rectBCoord -= lineThickness / 2;
+
+        textDrawer->AppendWavyDecoration(aRect, lineThickness, aParams.vertical,
+                                         color);
+        return;
+      }
+
+      // figure out if we can trim whole cycles from the left and right edges
+      // of the line, to try and avoid creating an unnecessarily long and
+      // complex path (but don't do this for webrender, )
+      const Float dirtyRectICoord =
+          aParams.vertical ? aParams.dirtyRect.y : aParams.dirtyRect.x;
+      int32_t skipCycles = floor((dirtyRectICoord - rectICoord) / cycleLength);
+      if (skipCycles > 0) {
+        rectICoord += skipCycles * cycleLength;
+        rectISize -= skipCycles * cycleLength;
+      }
+
+      rectICoord += lineThickness / 2.0;
+
+      Point pt(aRect.TopLeft());
+      Float& ptICoord = aParams.vertical ? pt.y.value : pt.x.value;
+      Float& ptBCoord = aParams.vertical ? pt.x.value : pt.y.value;
+      if (aParams.vertical) {
+        ptBCoord += adv;
+      }
+      Float iCoordLimit = ptICoord + rectISize + lineThickness;
+
+      const Float dirtyRectIMost = aParams.vertical ? aParams.dirtyRect.YMost()
+                                                    : aParams.dirtyRect.XMost();
+      skipCycles = floor((iCoordLimit - dirtyRectIMost) / cycleLength);
+      if (skipCycles > 0) {
+        iCoordLimit -= skipCycles * cycleLength;
+      }
+
+      RefPtr<PathBuilder> builder = aDrawTarget.CreatePathBuilder();
+      RefPtr<Path> path;
+
+      ptICoord -= lineThickness;
+      builder->MoveTo(pt);  // 1
+
+      ptICoord = rectICoord;
+      builder->LineTo(pt);  // 2
+
+      // In vertical mode, to go "down" relative to the text we need to
+      // decrease the block coordinate, whereas in horizontal we increase
+      // it. So the sense of this flag is effectively inverted.
+      bool goDown = !aParams.vertical;
+      uint32_t iter = 0;
+      while (ptICoord < iCoordLimit) {
+        if (++iter > 1000) {
+          // stroke the current path and start again, to avoid pathological
+          // behavior in cairo with huge numbers of path segments
+          path = builder->Finish();
+          aDrawTarget.Stroke(path, colorPat, strokeOptions, drawOptions);
+          builder = aDrawTarget.CreatePathBuilder();
+          builder->MoveTo(pt);
+          iter = 0;
+        }
+        ptICoord += adv;
+        ptBCoord += goDown ? adv : -adv;
+
+        builder->LineTo(pt);  // 3 and 5
+
+        ptICoord += flatLengthAtVertex;
+        builder->LineTo(pt);  // 4 and 6
+
+        goDown = !goDown;
+      }
+      path = builder->Finish();
+      aDrawTarget.Stroke(path, colorPat, strokeOptions, drawOptions);
+      return;
+    }
+    default:
+      NS_ERROR("Invalid style value!");
+  }
+}
+
+Rect nsCSSRendering::DecorationLineToPath(
+    const PaintDecorationLineParams& aParams) {
+  NS_ASSERTION(aParams.style != StyleTextDecorationStyle::None,
+               "aStyle is none");
+
+  Rect path;  // To benefit from RVO, we return this from all return points
+
+  Rect rect = ToRect(GetTextDecorationRectInternal(aParams.pt, aParams));
+  if (rect.IsEmpty() || !rect.Intersects(aParams.dirtyRect)) {
+    return path;
+  }
+
+  if (aParams.decoration != StyleTextDecorationLine::UNDERLINE &&
+      aParams.decoration != StyleTextDecorationLine::OVERLINE &&
+      aParams.decoration != StyleTextDecorationLine::LINE_THROUGH) {
+    MOZ_ASSERT_UNREACHABLE("Invalid text decoration value");
+    return path;
+  }
+
+  if (aParams.style != StyleTextDecorationStyle::Solid) {
+    // For the moment, we support only solid text decorations.
+    return path;
+  }
+
+  Float lineThickness = std::max(NS_round(aParams.lineSize.height), 1.0);
+
+  // The block-direction position should be set to the middle of the line.
+  if (aParams.vertical) {
+    rect.x += lineThickness / 2;
+    path = Rect(rect.TopLeft() - Point(lineThickness / 2, 0.0),
+                Size(lineThickness, rect.Height()));
+  } else {
+    rect.y += lineThickness / 2;
+    path = Rect(rect.TopLeft() - Point(0.0, lineThickness / 2),
+                Size(rect.Width(), lineThickness));
+  }
+
+  return path;
+}
+
+nsRect nsCSSRendering::GetTextDecorationRect(
+    nsPresContext* aPresContext, const DecorationRectParams& aParams) {
+  NS_ASSERTION(aPresContext, "aPresContext is null");
+  NS_ASSERTION(aParams.style != StyleTextDecorationStyle::None,
+               "aStyle is none");
+
+  gfxRect rect = GetTextDecorationRectInternal(Point(0, 0), aParams);
+  // The rect values are already rounded to nearest device pixels.
+  nsRect r;
+  r.x = aPresContext->GfxUnitsToAppUnits(rect.X());
+  r.y = aPresContext->GfxUnitsToAppUnits(rect.Y());
+  r.width = aPresContext->GfxUnitsToAppUnits(rect.Width());
+  r.height = aPresContext->GfxUnitsToAppUnits(rect.Height());
+  return r;
+}
+
+gfxRect nsCSSRendering::GetTextDecorationRectInternal(
+    const Point& aPt, const DecorationRectParams& aParams) {
+  NS_ASSERTION(aParams.style <= StyleTextDecorationStyle::Wavy,
+               "Invalid aStyle value");
+
+  if (aParams.style == StyleTextDecorationStyle::None) {
+    return gfxRect(0, 0, 0, 0);
+  }
+
+  bool canLiftUnderline = aParams.descentLimit >= 0.0;
+
+  gfxFloat iCoord = aParams.vertical ? aPt.y : aPt.x;
+  gfxFloat bCoord = aParams.vertical ? aPt.x : aPt.y;
+
+  // 'left' and 'right' are relative to the line, so for vertical writing modes
+  // they will actually become top and bottom of the rendered line.
+  // Similarly, aLineSize.width and .height are actually length and thickness
+  // of the line, which runs horizontally or vertically according to aVertical.
+  const gfxFloat left = floor(iCoord + 0.5),
+                 right = floor(iCoord + aParams.lineSize.width + 0.5);
+
+  // We compute |r| as if for a horizontal text run, and then swap vertical
+  // and horizontal coordinates at the end if vertical was requested.
+  gfxRect r(left, 0, right - left, 0);
+
+  gfxFloat lineThickness = NS_round(aParams.lineSize.height);
+  lineThickness = std::max(lineThickness, 1.0);
+  gfxFloat defaultLineThickness = NS_round(aParams.defaultLineThickness);
+  defaultLineThickness = std::max(defaultLineThickness, 1.0);
+
+  gfxFloat ascent = NS_round(aParams.ascent);
+  gfxFloat descentLimit = floor(aParams.descentLimit);
+
+  gfxFloat suggestedMaxRectHeight =
+      std::max(std::min(ascent, descentLimit), 1.0);
+  r.height = lineThickness;
+  if (aParams.style == StyleTextDecorationStyle::Double) {
+    /**
+     *  We will draw double line as:
+     *
+     * +-------------------------------------------+
+     * |XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX| ^
+     * |XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX| | lineThickness
+     * |XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX| v
+     * |                                           | ^
+     * |                                           | | gap
+     * |                                           | v
+     * |XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX| ^
+     * |XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX| | lineThickness
+     * |XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX| v
+     * +-------------------------------------------+
+     */
+    gfxFloat gap = NS_round(lineThickness / 2.0);
+    gap = std::max(gap, 1.0);
+    r.height = lineThickness * 2.0 + gap;
+    if (canLiftUnderline) {
+      if (r.Height() > suggestedMaxRectHeight) {
+        // Don't shrink the line height, because the thickness has some meaning.
+        // We can just shrink the gap at this time.
+        r.height = std::max(suggestedMaxRectHeight, lineThickness * 2.0 + 1.0);
+      }
+    }
+  } else if (aParams.style == StyleTextDecorationStyle::Wavy) {
+    /**
+     *  We will draw wavy line as:
+     *
+     * +-------------------------------------------+
+     * |XXXXX            XXXXXX            XXXXXX  | ^
+     * |XXXXXX          XXXXXXXX          XXXXXXXX | | lineThickness
+     * |XXXXXXX        XXXXXXXXXX        XXXXXXXXXX| v
+     * |     XXX      XXX      XXX      XXX      XX|
+     * |      XXXXXXXXXX        XXXXXXXXXX        X|
+     * |       XXXXXXXX          XXXXXXXX          |
+     * |        XXXXXX            XXXXXX           |
+     * +-------------------------------------------+
+     */
+    r.height = lineThickness > 2.0 ? lineThickness * 4.0 : lineThickness * 3.0;
+    if (canLiftUnderline) {
+      if (r.Height() > suggestedMaxRectHeight) {
+        // Don't shrink the line height even if there is not enough space,
+        // because the thickness has some meaning.  E.g., the 1px wavy line and
+        // 2px wavy line can be used for different meaning in IME selections
+        // at same time.
+        r.height = std::max(suggestedMaxRectHeight, lineThickness * 2.0);
+      }
+    }
+  }
+
+  gfxFloat baseline = floor(bCoord + aParams.ascent + 0.5);
+
+  // Calculate adjusted offset based on writing-mode/orientation and thickness
+  // of decoration line. The input value aParams.offset is the nominal position
+  // (offset from baseline) where we would draw a single, infinitely-thin line;
+  // but for a wavy or double line, we'll need to move the bounding rect of the
+  // decoration outwards from the baseline so that an underline remains below
+  // the glyphs, and an overline above them, despite the increased block-dir
+  // extent of the decoration.
+  //
+  // So adjustments by r.Height() are used to make the wider line styles (wavy
+  // and double) "grow" in the appropriate direction compared to the basic
+  // single line.
+  //
+  // Note that at this point, the decoration rect is being calculated in line-
+  // relative coordinates, where 'x' is line-rightwards, and 'y' is line-
+  // upwards. We'll swap them to be physical coords at the end.
+  gfxFloat offset = 0.0;
+
+  if (aParams.decoration == StyleTextDecorationLine::UNDERLINE) {
+    offset = aParams.offset;
+    if (canLiftUnderline) {
+      if (descentLimit < -offset + r.Height()) {
+        // If we can ignore the offset and the decoration line is overflowing,
+        // we should align the bottom edge of the decoration line rect if it's
+        // possible.  Otherwise, we should lift up the top edge of the rect as
+        // far as possible.
+        gfxFloat offsetBottomAligned = -descentLimit + r.Height();
+        gfxFloat offsetTopAligned = 0.0;
+        offset = std::min(offsetBottomAligned, offsetTopAligned);
+      }
+    }
+  } else if (aParams.decoration == StyleTextDecorationLine::OVERLINE) {
+    // For overline, we adjust the offset by defaultlineThickness (the default
+    // thickness of a single decoration line) because empirically it looks
+    // better to draw the overline just inside rather than outside the font's
+    // ascent, which is what nsTextFrame passes as aParams.offset (as fonts
+    // don't provide an explicit overline-offset).
+    offset = aParams.offset - defaultLineThickness + r.Height();
+  } else if (aParams.decoration == StyleTextDecorationLine::LINE_THROUGH) {
+    // To maintain a consistent mid-point for line-through decorations,
+    // we adjust the offset by half of the decoration rect's height.
+    gfxFloat extra = floor(r.Height() / 2.0 + 0.5);
+    extra = std::max(extra, lineThickness);
+    // computes offset for when user specifies a decoration width since
+    // aParams.offset is derived from the font metric's line height
+    gfxFloat decorationThicknessOffset =
+        (lineThickness - defaultLineThickness) / 2.0;
+    offset = aParams.offset - lineThickness + extra + decorationThicknessOffset;
+  } else {
+    MOZ_ASSERT_UNREACHABLE("Invalid text decoration value");
+  }
+
+  // Convert line-relative coordinate system (x = line-right, y = line-up)
+  // to physical coords, and move the decoration rect to the calculated
+  // offset from baseline.
+  if (aParams.vertical) {
+    std::swap(r.x, r.y);
+    std::swap(r.width, r.height);
+    // line-upwards in vertical mode = physical-right, so we /add/ offset
+    // to baseline. Except in sideways-lr mode, where line-upwards will be
+    // physical leftwards.
+    if (aParams.sidewaysLeft) {
+      r.x = baseline - floor(offset + 0.5);
+    } else {
+      r.x = baseline + floor(offset - r.Width() + 0.5);
+    }
+  } else {
+    // line-upwards in horizontal mode = physical-up, but our physical coord
+    // system works downwards, so we /subtract/ offset from baseline.
+    r.y = baseline - floor(offset + 0.5);
+  }
+
+  return r;
+}
+
+#define MAX_BLUR_RADIUS 300
+#define MAX_SPREAD_RADIUS 50
+
+static inline gfxPoint ComputeBlurStdDev(nscoord aBlurRadius,
+                                         int32_t aAppUnitsPerDevPixel,
+                                         gfxFloat aScaleX, gfxFloat aScaleY) {
+  // http://dev.w3.org/csswg/css3-background/#box-shadow says that the
+  // standard deviation of the blur should be half the given blur value.
+  gfxFloat blurStdDev = gfxFloat(aBlurRadius) / gfxFloat(aAppUnitsPerDevPixel);
+
+  return gfxPoint(
+      std::min((blurStdDev * aScaleX), gfxFloat(MAX_BLUR_RADIUS)) / 2.0,
+      std::min((blurStdDev * aScaleY), gfxFloat(MAX_BLUR_RADIUS)) / 2.0);
+}
+
+static inline IntSize ComputeBlurRadius(nscoord aBlurRadius,
+                                        int32_t aAppUnitsPerDevPixel,
+                                        gfxFloat aScaleX = 1.0,
+                                        gfxFloat aScaleY = 1.0) {
+  gfxPoint scaledBlurStdDev =
+      ComputeBlurStdDev(aBlurRadius, aAppUnitsPerDevPixel, aScaleX, aScaleY);
+  return gfxAlphaBoxBlur::CalculateBlurRadius(scaledBlurStdDev);
+}
+
+// -----
+// nsContextBoxBlur
+// -----
+gfxContext* nsContextBoxBlur::Init(const nsRect& aRect, nscoord aSpreadRadius,
+                                   nscoord aBlurRadius,
+                                   int32_t aAppUnitsPerDevPixel,
+                                   gfxContext* aDestinationCtx,
+                                   const nsRect& aDirtyRect,
+                                   const gfxRect* aSkipRect, uint32_t aFlags) {
+  if (aRect.IsEmpty()) {
+    mContext = nullptr;
+    return nullptr;
+  }
+
+  IntSize blurRadius;
+  IntSize spreadRadius;
+  GetBlurAndSpreadRadius(aDestinationCtx->GetDrawTarget(), aAppUnitsPerDevPixel,
+                         aBlurRadius, aSpreadRadius, blurRadius, spreadRadius);
+
+  mDestinationCtx = aDestinationCtx;
+
+  // If not blurring, draw directly onto the destination device
+  if (blurRadius.width <= 0 && blurRadius.height <= 0 &&
+      spreadRadius.width <= 0 && spreadRadius.height <= 0 &&
+      !(aFlags & FORCE_MASK)) {
+    mContext = aDestinationCtx;
+    return mContext;
+  }
+
+  // Convert from app units to device pixels
+  gfxRect rect = nsLayoutUtils::RectToGfxRect(aRect, aAppUnitsPerDevPixel);
+
+  gfxRect dirtyRect =
+      nsLayoutUtils::RectToGfxRect(aDirtyRect, aAppUnitsPerDevPixel);
+  dirtyRect.RoundOut();
+
+  gfxMatrix transform = aDestinationCtx->CurrentMatrixDouble();
+  rect = transform.TransformBounds(rect);
+
+  mPreTransformed = !transform.IsIdentity();
+
+  // Create the temporary surface for blurring
+  dirtyRect = transform.TransformBounds(dirtyRect);
+  bool useHardwareAccel = !(aFlags & DISABLE_HARDWARE_ACCELERATION_BLUR);
+  if (aSkipRect) {
+    gfxRect skipRect = transform.TransformBounds(*aSkipRect);
+    mContext =
+        mAlphaBoxBlur.Init(aDestinationCtx, rect, spreadRadius, blurRadius,
+                           &dirtyRect, &skipRect, useHardwareAccel);
+  } else {
+    mContext =
+        mAlphaBoxBlur.Init(aDestinationCtx, rect, spreadRadius, blurRadius,
+                           &dirtyRect, nullptr, useHardwareAccel);
+  }
+
+  if (mContext) {
+    // we don't need to blur if skipRect is equal to rect
+    // and mContext will be nullptr
+    mContext->Multiply(transform);
+  }
+  return mContext;
+}
+
+void nsContextBoxBlur::DoPaint() {
+  if (mContext == mDestinationCtx) {
+    return;
+  }
+
+  gfxContextMatrixAutoSaveRestore saveMatrix(mDestinationCtx);
+
+  if (mPreTransformed) {
+    mDestinationCtx->SetMatrix(Matrix());
+  }
+
+  mAlphaBoxBlur.Paint(mDestinationCtx);
+}
+
+gfxContext* nsContextBoxBlur::GetContext() { return mContext; }
+
+/* static */
+nsMargin nsContextBoxBlur::GetBlurRadiusMargin(nscoord aBlurRadius,
+                                               int32_t aAppUnitsPerDevPixel) {
+  IntSize blurRadius = ComputeBlurRadius(aBlurRadius, aAppUnitsPerDevPixel);
+
+  nsMargin result;
+  result.top = result.bottom = blurRadius.height * aAppUnitsPerDevPixel;
+  result.left = result.right = blurRadius.width * aAppUnitsPerDevPixel;
+  return result;
+}
+
+/* static */
+void nsContextBoxBlur::BlurRectangle(
+    gfxContext* aDestinationCtx, const nsRect& aRect,
+    int32_t aAppUnitsPerDevPixel, RectCornerRadii* aCornerRadii,
+    nscoord aBlurRadius, const sRGBColor& aShadowColor,
+    const nsRect& aDirtyRect, const gfxRect& aSkipRect) {
+  DrawTarget& aDestDrawTarget = *aDestinationCtx->GetDrawTarget();
+
+  if (aRect.IsEmpty()) {
+    return;
+  }
+
+  Rect shadowGfxRect = NSRectToRect(aRect, aAppUnitsPerDevPixel);
+
+  if (aBlurRadius <= 0) {
+    ColorPattern color(ToDeviceColor(aShadowColor));
+    if (aCornerRadii) {
+      RefPtr<Path> roundedRect =
+          MakePathForRoundedRect(aDestDrawTarget, shadowGfxRect, *aCornerRadii);
+      aDestDrawTarget.Fill(roundedRect, color);
+    } else {
+      aDestDrawTarget.FillRect(shadowGfxRect, color);
+    }
+    return;
+  }
+
+  gfxFloat scaleX = 1;
+  gfxFloat scaleY = 1;
+
+  // Do blurs in device space when possible.
+  // Chrome/Skia always does the blurs in device space
+  // and will sometimes get incorrect results (e.g. rotated blurs)
+  gfxMatrix transform = aDestinationCtx->CurrentMatrixDouble();
+  // XXX: we could probably handle negative scales but for now it's easier just
+  // to fallback
+  if (!transform.HasNonAxisAlignedTransform() && transform._11 > 0.0 &&
+      transform._22 > 0.0) {
+    scaleX = transform._11;
+    scaleY = transform._22;
+    aDestinationCtx->SetMatrix(Matrix());
+  } else {
+    transform = gfxMatrix();
+  }
+
+  gfxPoint blurStdDev =
+      ComputeBlurStdDev(aBlurRadius, aAppUnitsPerDevPixel, scaleX, scaleY);
+
+  gfxRect dirtyRect =
+      nsLayoutUtils::RectToGfxRect(aDirtyRect, aAppUnitsPerDevPixel);
+  dirtyRect.RoundOut();
+
+  gfxRect shadowThebesRect =
+      transform.TransformBounds(ThebesRect(shadowGfxRect));
+  dirtyRect = transform.TransformBounds(dirtyRect);
+  gfxRect skipRect = transform.TransformBounds(aSkipRect);
+
+  if (aCornerRadii) {
+    aCornerRadii->Scale(scaleX, scaleY);
+  }
+
+  gfxAlphaBoxBlur::BlurRectangle(aDestinationCtx, shadowThebesRect,
+                                 aCornerRadii, blurStdDev, aShadowColor,
+                                 dirtyRect, skipRect);
+}
+
+/* static */
+void nsContextBoxBlur::GetBlurAndSpreadRadius(
+    DrawTarget* aDestDrawTarget, int32_t aAppUnitsPerDevPixel,
+    nscoord aBlurRadius, nscoord aSpreadRadius, IntSize& aOutBlurRadius,
+    IntSize& aOutSpreadRadius, bool aConstrainSpreadRadius) {
+  // Do blurs in device space when possible.
+  // Chrome/Skia always does the blurs in device space
+  // and will sometimes get incorrect results (e.g. rotated blurs)
+  Matrix transform = aDestDrawTarget->GetTransform();
+  // XXX: we could probably handle negative scales but for now it's easier just
+  // to fallback
+  gfxFloat scaleX, scaleY;
+  if (transform.HasNonAxisAlignedTransform() || transform._11 <= 0.0 ||
+      transform._22 <= 0.0) {
+    scaleX = 1;
+    scaleY = 1;
+  } else {
+    scaleX = transform._11;
+    scaleY = transform._22;
+  }
+
+  // compute a large or smaller blur radius
+  aOutBlurRadius =
+      ComputeBlurRadius(aBlurRadius, aAppUnitsPerDevPixel, scaleX, scaleY);
+  aOutSpreadRadius =
+      IntSize(int32_t(aSpreadRadius * scaleX / aAppUnitsPerDevPixel),
+              int32_t(aSpreadRadius * scaleY / aAppUnitsPerDevPixel));
+
+  if (aConstrainSpreadRadius) {
+    aOutSpreadRadius.width =
+        std::min(aOutSpreadRadius.width, int32_t(MAX_SPREAD_RADIUS));
+    aOutSpreadRadius.height =
+        std::min(aOutSpreadRadius.height, int32_t(MAX_SPREAD_RADIUS));
+  }
+}
+
+/* static */
+bool nsContextBoxBlur::InsetBoxBlur(
+    gfxContext* aDestinationCtx, Rect aDestinationRect, Rect aShadowClipRect,
+    sRGBColor& aShadowColor, nscoord aBlurRadiusAppUnits,
+    nscoord aSpreadDistanceAppUnits, int32_t aAppUnitsPerDevPixel,
+    bool aHasBorderRadius, RectCornerRadii& aInnerClipRectRadii, Rect aSkipRect,
+    Point aShadowOffset) {
+  if (aDestinationRect.IsEmpty()) {
+    mContext = nullptr;
+    return false;
+  }
+
+  gfxContextAutoSaveRestore autoRestore(aDestinationCtx);
+
+  IntSize blurRadius;
+  IntSize spreadRadius;
+  // Convert the blur and spread radius to device pixels
+  bool constrainSpreadRadius = false;
+  GetBlurAndSpreadRadius(aDestinationCtx->GetDrawTarget(), aAppUnitsPerDevPixel,
+                         aBlurRadiusAppUnits, aSpreadDistanceAppUnits,
+                         blurRadius, spreadRadius, constrainSpreadRadius);
+
+  // The blur and spread radius are scaled already, so scale all
+  // input data to the blur. This way, we don't have to scale the min
+  // inset blur to the invert of the dest context, then rescale it back
+  // when we draw to the destination surface.
+  auto scale = aDestinationCtx->CurrentMatrix().ScaleFactors();
+  Matrix transform = aDestinationCtx->CurrentMatrix();
+
+  // XXX: we could probably handle negative scales but for now it's easier just
+  // to fallback
+  if (!transform.HasNonAxisAlignedTransform() && transform._11 > 0.0 &&
+      transform._22 > 0.0) {
+    // If we don't have a rotation, we're pre-transforming all the rects.
+    aDestinationCtx->SetMatrix(Matrix());
+  } else {
+    // Don't touch anything, we have a rotation.
+    transform = Matrix();
+  }
+
+  Rect transformedDestRect = transform.TransformBounds(aDestinationRect);
+  Rect transformedShadowClipRect = transform.TransformBounds(aShadowClipRect);
+  Rect transformedSkipRect = transform.TransformBounds(aSkipRect);
+
+  transformedDestRect.Round();
+  transformedShadowClipRect.Round();
+  transformedSkipRect.RoundIn();
+
+  for (size_t i = 0; i < 4; i++) {
+    aInnerClipRectRadii[i].width =
+        std::floor(scale.xScale * aInnerClipRectRadii[i].width);
+    aInnerClipRectRadii[i].height =
+        std::floor(scale.yScale * aInnerClipRectRadii[i].height);
+  }
+
+  mAlphaBoxBlur.BlurInsetBox(aDestinationCtx, transformedDestRect,
+                             transformedShadowClipRect, blurRadius,
+                             aShadowColor,
+                             aHasBorderRadius ? &aInnerClipRectRadii : nullptr,
+                             transformedSkipRect, aShadowOffset);
+  return true;
+}
diff --git a/layout/painting/nsCSSRendering.h b/layout/painting/nsCSSRendering.h
new file mode 100644
index 0000000000..74cf224455
--- /dev/null
+++ b/layout/painting/nsCSSRendering.h
@@ -0,0 +1,953 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/* utility functions for drawing borders and backgrounds */
+
+#ifndef nsCSSRendering_h___
+#define nsCSSRendering_h___
+
+#include "gfxBlur.h"
+#include "gfxContext.h"
+#include "mozilla/gfx/PathHelpers.h"
+#include "mozilla/gfx/Rect.h"
+#include "mozilla/TypedEnumBits.h"
+#include "nsStyleStruct.h"
+#include "nsIFrame.h"
+#include "nsImageRenderer.h"
+#include "nsCSSRenderingBorders.h"
+#include "gfxTextRun.h"
+
+class gfxContext;
+class nsPresContext;
+
+namespace mozilla {
+
+class ComputedStyle;
+
+namespace gfx {
+struct sRGBColor;
+class DrawTarget;
+}  // namespace gfx
+
+namespace layers {
+class ImageContainer;
+class StackingContextHelper;
+class WebRenderParentCommand;
+class WebRenderLayerManager;
+class RenderRootStateManager;
+}  // namespace layers
+
+namespace wr {
+class DisplayListBuilder;
+}  // namespace wr
+
+enum class PaintBorderFlags : uint8_t { SyncDecodeImages = 1 << 0 };
+MOZ_MAKE_ENUM_CLASS_BITWISE_OPERATORS(PaintBorderFlags)
+
+}  // namespace mozilla
+
+/**
+ * A struct representing all the information needed to paint a background
+ * image to some target, taking into account all CSS background-* properties.
+ * See PrepareImageLayer.
+ */
+struct nsBackgroundLayerState {
+  typedef mozilla::gfx::CompositionOp CompositionOp;
+  typedef mozilla::nsImageRenderer nsImageRenderer;
+
+  /**
+   * @param aFlags some combination of nsCSSRendering::PAINTBG_* flags
+   */
+  nsBackgroundLayerState(nsIFrame* aForFrame, const mozilla::StyleImage* aImage,
+                         uint32_t aFlags)
+      : mImageRenderer(aForFrame, aImage, aFlags) {}
+
+  /**
+   * The nsImageRenderer that will be used to draw the background.
+   */
+  nsImageRenderer mImageRenderer;
+  /**
+   * A rectangle that one copy of the image tile is mapped onto. Same
+   * coordinate system as aBorderArea/aBGClipRect passed into
+   * PrepareImageLayer.
+   */
+  nsRect mDestArea;
+  /**
+   * The actual rectangle that should be filled with (complete or partial)
+   * image tiles. Same coordinate system as aBorderArea/aBGClipRect passed into
+   * PrepareImageLayer.
+   */
+  nsRect mFillArea;
+  /**
+   * The anchor point that should be snapped to a pixel corner. Same
+   * coordinate system as aBorderArea/aBGClipRect passed into
+   * PrepareImageLayer.
+   */
+  nsPoint mAnchor;
+  /**
+   * The background-repeat property space keyword computes the
+   * repeat size which is image size plus spacing.
+   */
+  nsSize mRepeatSize;
+};
+
+struct nsCSSRendering {
+  typedef mozilla::gfx::sRGBColor sRGBColor;
+  typedef mozilla::gfx::CompositionOp CompositionOp;
+  typedef mozilla::gfx::DrawTarget DrawTarget;
+  typedef mozilla::gfx::Float Float;
+  typedef mozilla::gfx::Point Point;
+  typedef mozilla::gfx::Rect Rect;
+  typedef mozilla::gfx::Size Size;
+  typedef mozilla::gfx::RectCornerRadii RectCornerRadii;
+  typedef mozilla::layers::WebRenderLayerManager WebRenderLayerManager;
+  typedef mozilla::image::ImgDrawResult ImgDrawResult;
+  typedef nsIFrame::Sides Sides;
+
+  /**
+   * Initialize any static variables used by nsCSSRendering.
+   */
+  static void Init();
+
+  /**
+   * Clean up any static variables used by nsCSSRendering.
+   */
+  static void Shutdown();
+
+  static bool IsBoxDecorationSlice(const nsStyleBorder& aStyleBorder);
+  static nsRect BoxDecorationRectForBorder(
+      nsIFrame* aFrame, const nsRect& aBorderArea, Sides aSkipSides,
+      const nsStyleBorder* aStyleBorder = nullptr);
+  static nsRect BoxDecorationRectForBackground(
+      nsIFrame* aFrame, const nsRect& aBorderArea, Sides aSkipSides,
+      const nsStyleBorder* aStyleBorder = nullptr);
+
+  static bool GetShadowInnerRadii(nsIFrame* aFrame, const nsRect& aFrameArea,
+                                  RectCornerRadii& aOutInnerRadii);
+  static nsRect GetBoxShadowInnerPaddingRect(nsIFrame* aFrame,
+                                             const nsRect& aFrameArea);
+  static bool ShouldPaintBoxShadowInner(nsIFrame* aFrame);
+  static void PaintBoxShadowInner(nsPresContext* aPresContext,
+                                  gfxContext& aRenderingContext,
+                                  nsIFrame* aForFrame,
+                                  const nsRect& aFrameArea);
+
+  static bool GetBorderRadii(const nsRect& aFrameRect,
+                             const nsRect& aBorderRect, nsIFrame* aFrame,
+                             RectCornerRadii& aOutRadii);
+  static nsRect GetShadowRect(const nsRect& aFrameArea, bool aNativeTheme,
+                              nsIFrame* aForFrame);
+  static mozilla::gfx::sRGBColor GetShadowColor(
+      const mozilla::StyleSimpleShadow&, nsIFrame* aFrame, float aOpacity);
+  // Returns if the frame has a themed frame.
+  // aMaybeHasBorderRadius will return false if we can early detect
+  // that we don't have a border radius.
+  static bool HasBoxShadowNativeTheme(nsIFrame* aFrame,
+                                      bool& aMaybeHasBorderRadius);
+  static void PaintBoxShadowOuter(nsPresContext* aPresContext,
+                                  gfxContext& aRenderingContext,
+                                  nsIFrame* aForFrame, const nsRect& aFrameArea,
+                                  const nsRect& aDirtyRect,
+                                  float aOpacity = 1.0);
+
+  static void ComputePixelRadii(const nscoord* aAppUnitsRadii,
+                                nscoord aAppUnitsPerPixel,
+                                RectCornerRadii* oBorderRadii);
+
+  /**
+   * Render the border for an element using css rendering rules
+   * for borders. aSkipSides says which sides to skip
+   * when rendering, the default is to skip none.
+   */
+  static ImgDrawResult PaintBorder(
+      nsPresContext* aPresContext, gfxContext& aRenderingContext,
+      nsIFrame* aForFrame, const nsRect& aDirtyRect, const nsRect& aBorderArea,
+      mozilla::ComputedStyle* aStyle, mozilla::PaintBorderFlags aFlags,
+      Sides aSkipSides = Sides());
+
+  /**
+   * Like PaintBorder, but taking an nsStyleBorder argument instead of
+   * getting it from aStyle. aSkipSides says which sides to skip
+   * when rendering, the default is to skip none.
+   */
+  static ImgDrawResult PaintBorderWithStyleBorder(
+      nsPresContext* aPresContext, gfxContext& aRenderingContext,
+      nsIFrame* aForFrame, const nsRect& aDirtyRect, const nsRect& aBorderArea,
+      const nsStyleBorder& aBorderStyle, mozilla::ComputedStyle* aStyle,
+      mozilla::PaintBorderFlags aFlags, Sides aSkipSides = Sides());
+
+  static mozilla::Maybe<nsCSSBorderRenderer> CreateBorderRenderer(
+      nsPresContext* aPresContext, DrawTarget* aDrawTarget, nsIFrame* aForFrame,
+      const nsRect& aDirtyRect, const nsRect& aBorderArea,
+      mozilla::ComputedStyle* aStyle, bool* aOutBorderIsEmpty,
+      Sides aSkipSides = Sides());
+
+  static mozilla::Maybe<nsCSSBorderRenderer>
+  CreateBorderRendererWithStyleBorder(
+      nsPresContext* aPresContext, DrawTarget* aDrawTarget, nsIFrame* aForFrame,
+      const nsRect& aDirtyRect, const nsRect& aBorderArea,
+      const nsStyleBorder& aBorderStyle, mozilla::ComputedStyle* aStyle,
+      bool* aOutBorderIsEmpty, Sides aSkipSides = Sides());
+
+  static mozilla::Maybe<nsCSSBorderRenderer>
+  CreateNullBorderRendererWithStyleBorder(
+      nsPresContext* aPresContext, DrawTarget* aDrawTarget, nsIFrame* aForFrame,
+      const nsRect& aDirtyRect, const nsRect& aBorderArea,
+      const nsStyleBorder& aBorderStyle, mozilla::ComputedStyle* aStyle,
+      bool* aOutBorderIsEmpty, Sides aSkipSides = Sides());
+
+  static mozilla::Maybe<nsCSSBorderRenderer>
+  CreateBorderRendererForNonThemedOutline(nsPresContext* aPresContext,
+                                          DrawTarget* aDrawTarget,
+                                          nsIFrame* aForFrame,
+                                          const nsRect& aDirtyRect,
+                                          const nsRect& aInnerRect,
+                                          mozilla::ComputedStyle* aStyle);
+
+  static ImgDrawResult CreateWebRenderCommandsForBorder(
+      mozilla::nsDisplayItem* aItem, nsIFrame* aForFrame,
+      const nsRect& aBorderArea, mozilla::wr::DisplayListBuilder& aBuilder,
+      mozilla::wr::IpcResourceUpdateQueue& aResources,
+      const mozilla::layers::StackingContextHelper& aSc,
+      mozilla::layers::RenderRootStateManager* aManager,
+      mozilla::nsDisplayListBuilder* aDisplayListBuilder);
+
+  static void CreateWebRenderCommandsForNullBorder(
+      mozilla::nsDisplayItem* aItem, nsIFrame* aForFrame,
+      const nsRect& aBorderArea, mozilla::wr::DisplayListBuilder& aBuilder,
+      mozilla::wr::IpcResourceUpdateQueue& aResources,
+      const mozilla::layers::StackingContextHelper& aSc,
+      const nsStyleBorder& aStyleBorder);
+
+  static ImgDrawResult CreateWebRenderCommandsForBorderWithStyleBorder(
+      mozilla::nsDisplayItem* aItem, nsIFrame* aForFrame,
+      const nsRect& aBorderArea, mozilla::wr::DisplayListBuilder& aBuilder,
+      mozilla::wr::IpcResourceUpdateQueue& aResources,
+      const mozilla::layers::StackingContextHelper& aSc,
+      mozilla::layers::RenderRootStateManager* aManager,
+      mozilla::nsDisplayListBuilder* aDisplayListBuilder,
+      const nsStyleBorder& aStyleBorder);
+
+  /**
+   * Render the outline for an element using css rendering rules for borders.
+   */
+  static void PaintNonThemedOutline(nsPresContext* aPresContext,
+                                    gfxContext& aRenderingContext,
+                                    nsIFrame* aForFrame,
+                                    const nsRect& aDirtyRect,
+                                    const nsRect& aInnerRect,
+                                    mozilla::ComputedStyle* aStyle);
+
+  /**
+   * Render keyboard focus on an element.
+   * |aFocusRect| is the outer rectangle of the focused element.
+   * Uses a fixed style equivalent to "1px dotted |aColor|".
+   * Not used for controls, because the native theme may differ.
+   */
+  static void PaintFocus(nsPresContext* aPresContext, DrawTarget* aDrawTarget,
+                         const nsRect& aFocusRect, nscolor aColor);
+
+  /**
+   * Render a gradient for an element.
+   * aDest is the rect for a single tile of the gradient on the destination.
+   * aFill is the rect on the destination to be covered by repeated tiling of
+   * the gradient.
+   * aSrc is the part of the gradient to be rendered into a tile (aDest), if
+   * aSrc and aDest are different sizes, the image will be scaled to map aSrc
+   * onto aDest.
+   * aIntrinsicSize is the size of the source gradient.
+   */
+  static void PaintGradient(nsPresContext* aPresContext, gfxContext& aContext,
+                            const mozilla::StyleGradient& aGradient,
+                            const nsRect& aDirtyRect, const nsRect& aDest,
+                            const nsRect& aFill, const nsSize& aRepeatSize,
+                            const mozilla::CSSIntRect& aSrc,
+                            const nsSize& aIntrinsiceSize,
+                            float aOpacity = 1.0);
+
+  /**
+   * Find the frame whose background style should be used to draw the
+   * canvas background. aForFrame must be the frame for the root element
+   * whose background style should be used. This function will return
+   * aForFrame unless the <body> background should be propagated, in
+   * which case we return the frame associated with the <body>'s background.
+   */
+  static nsIFrame* FindBackgroundStyleFrame(nsIFrame* aForFrame);
+
+  /**
+   * Returns the ComputedStyle to be used to paint the background for the given
+   * frame, if its element has a meaningful background.  This applies the rules
+   * for propagating backgrounds between BODY, the root element, and the
+   * canvas.
+   *
+   * @return the ComputedStyle (if any) to be used for painting aForFrame's
+   *         background.
+   */
+  static mozilla::ComputedStyle* FindBackground(const nsIFrame* aForFrame);
+  static nsIFrame* FindBackgroundFrame(const nsIFrame* aForFrame);
+
+  /**
+   * As FindBackground, but the passed-in frame is known to be a root frame
+   * (returned from nsCSSFrameConstructor::GetRootElementStyleFrame())
+   * and there is always some meaningful background returned.
+   */
+  static mozilla::ComputedStyle* FindRootFrameBackground(nsIFrame* aForFrame);
+
+  /**
+   * Returns background style information for the canvas.
+   *
+   * @param aForFrame
+   *   the frame used to represent the canvas, in the CSS sense (i.e.
+   *   aForFrame->IsCanvasFrame() must be true)
+   * @param aRootElementFrame
+   *   the frame representing the root element of the document
+   * @param aBackground
+   *   contains background style information for the canvas on return
+   */
+
+  static nsIFrame* FindCanvasBackgroundFrame(const nsIFrame* aForFrame,
+                                             nsIFrame* aRootElementFrame) {
+    MOZ_ASSERT(aForFrame->IsCanvasFrame(), "not a canvas frame");
+    if (aRootElementFrame) {
+      return FindBackgroundStyleFrame(aRootElementFrame);
+    }
+
+    // This should always give transparent, so we'll fill it in with the
+    // default color if needed.  This seems to happen a bit while a page is
+    // being loaded.
+    return const_cast<nsIFrame*>(aForFrame);
+  }
+
+  static mozilla::ComputedStyle* FindCanvasBackground(
+      nsIFrame* aForFrame, nsIFrame* aRootElementFrame) {
+    return FindCanvasBackgroundFrame(aForFrame, aRootElementFrame)->Style();
+  }
+
+  /**
+   * Find a non-transparent background color on an ancestor, for various
+   * contrast checks. Note that this only accounts for background-color and
+   * might stop at themed frames (depending on the argument), so it might not be
+   * what you want. Note that if we stop at themed frames we might, in fact, end
+   * up returning a transparent color (but then mIsThemed will be set to true).
+   *
+   * For semi-transparent colors, right now we blend with the default
+   * background-color rather than with all ancestor backgrounds.
+   *
+   * If aPreferBodyToCanvas is true, we prefer the background color of the
+   * <body> frame, even though we found a canvas background, because the body
+   * background color is most likely what will be visible as the background
+   * color of the page, even if the html element has a different background
+   * color which prevents that of the body frame to propagate to the viewport.
+   */
+  struct EffectiveBackgroundColor {
+    nscolor mColor = 0;
+    bool mIsThemed = false;
+  };
+  static EffectiveBackgroundColor FindEffectiveBackgroundColor(
+      nsIFrame* aFrame, bool aStopAtThemed = true,
+      bool aPreferBodyToCanvas = false);
+
+  /**
+   * Determine the background color to draw taking into account print settings.
+   */
+  static nscolor DetermineBackgroundColor(nsPresContext* aPresContext,
+                                          const mozilla::ComputedStyle* aStyle,
+                                          nsIFrame* aFrame,
+                                          bool& aDrawBackgroundImage,
+                                          bool& aDrawBackgroundColor);
+
+  static nsRect ComputeImageLayerPositioningArea(
+      nsPresContext* aPresContext, nsIFrame* aForFrame,
+      const nsRect& aBorderArea, const nsStyleImageLayers::Layer& aLayer,
+      nsIFrame** aAttachedToFrame, bool* aOutTransformedFixed);
+
+  // Implementation of the formula for computation of background-repeat round
+  // See http://dev.w3.org/csswg/css3-background/#the-background-size
+  // This function returns the adjusted size of the background image.
+  static nscoord ComputeRoundedSize(nscoord aCurrentSize,
+                                    nscoord aPositioningSize);
+
+  /* ComputeBorderSpacedRepeatSize
+   * aImageDimension: the image width/height
+   * aAvailableSpace: the background positioning area width/height
+   * aSpace: the space between each image
+   * Returns the image size plus gap size of app units for use as spacing
+   */
+  static nscoord ComputeBorderSpacedRepeatSize(nscoord aImageDimension,
+                                               nscoord aAvailableSpace,
+                                               nscoord& aSpace);
+
+  static nsBackgroundLayerState PrepareImageLayer(
+      nsPresContext* aPresContext, nsIFrame* aForFrame, uint32_t aFlags,
+      const nsRect& aBorderArea, const nsRect& aBGClipRect,
+      const nsStyleImageLayers::Layer& aLayer,
+      bool* aOutIsTransformedFixed = nullptr);
+
+  struct ImageLayerClipState {
+    nsRect mBGClipArea;            // Affected by mClippedRadii
+    nsRect mAdditionalBGClipArea;  // Not affected by mClippedRadii
+    nsRect mDirtyRectInAppUnits;
+    gfxRect mDirtyRectInDevPx;
+
+    nscoord mRadii[8];
+    RectCornerRadii mClippedRadii;
+    bool mHasRoundedCorners;
+    bool mHasAdditionalBGClipArea;
+
+    // Whether we are being asked to draw with a caller provided background
+    // clipping area. If this is true we also disable rounded corners.
+    bool mCustomClip;
+
+    ImageLayerClipState()
+        : mHasRoundedCorners(false),
+          mHasAdditionalBGClipArea(false),
+          mCustomClip(false) {
+      memset(mRadii, 0, sizeof(nscoord) * 8);
+    }
+
+    bool IsValid() const;
+  };
+
+  static void GetImageLayerClip(const nsStyleImageLayers::Layer& aLayer,
+                                nsIFrame* aForFrame,
+                                const nsStyleBorder& aBorder,
+                                const nsRect& aBorderArea,
+                                const nsRect& aCallerDirtyRect,
+                                bool aWillPaintBorder,
+                                nscoord aAppUnitsPerPixel,
+                                /* out */ ImageLayerClipState* aClipState);
+
+  /**
+   * Render the background for an element using css rendering rules
+   * for backgrounds or mask.
+   */
+  enum {
+    /**
+     * When this flag is passed, the element's nsDisplayBorder will be
+     * painted immediately on top of this background.
+     */
+    PAINTBG_WILL_PAINT_BORDER = 0x01,
+    /**
+     * When this flag is passed, images are synchronously decoded.
+     */
+    PAINTBG_SYNC_DECODE_IMAGES = 0x02,
+    /**
+     * When this flag is passed, painting will go to the screen so we can
+     * take advantage of the fact that it will be clipped to the viewport.
+     */
+    PAINTBG_TO_WINDOW = 0x04,
+    /**
+     * When this flag is passed, painting will read properties of mask-image
+     * style, instead of background-image.
+     */
+    PAINTBG_MASK_IMAGE = 0x08,
+    /**
+     * When this flag is passed, images are downscaled during decode. This
+     * is also implied by PAINTBG_TO_WINDOW.
+     */
+    PAINTBG_HIGH_QUALITY_SCALING = 0x10,
+  };
+
+  struct PaintBGParams {
+    nsPresContext& presCtx;
+    nsRect dirtyRect;
+    nsRect borderArea;
+    nsIFrame* frame;
+    uint32_t paintFlags;
+    nsRect* bgClipRect = nullptr;
+    int32_t layer;  // -1 means painting all layers; other
+                    // value means painting one specific
+                    // layer only.
+    CompositionOp compositionOp;
+    float opacity;
+
+    static PaintBGParams ForAllLayers(nsPresContext& aPresCtx,
+                                      const nsRect& aDirtyRect,
+                                      const nsRect& aBorderArea,
+                                      nsIFrame* aFrame, uint32_t aPaintFlags,
+                                      float aOpacity = 1.0);
+    static PaintBGParams ForSingleLayer(
+        nsPresContext& aPresCtx, const nsRect& aDirtyRect,
+        const nsRect& aBorderArea, nsIFrame* aFrame, uint32_t aPaintFlags,
+        int32_t aLayer, CompositionOp aCompositionOp = CompositionOp::OP_OVER,
+        float aOpacity = 1.0);
+
+   private:
+    PaintBGParams(nsPresContext& aPresCtx, const nsRect& aDirtyRect,
+                  const nsRect& aBorderArea, nsIFrame* aFrame,
+                  uint32_t aPaintFlags, int32_t aLayer,
+                  CompositionOp aCompositionOp, float aOpacity)
+        : presCtx(aPresCtx),
+          dirtyRect(aDirtyRect),
+          borderArea(aBorderArea),
+          frame(aFrame),
+          paintFlags(aPaintFlags),
+          layer(aLayer),
+          compositionOp(aCompositionOp),
+          opacity(aOpacity) {}
+  };
+
+  static ImgDrawResult PaintStyleImageLayer(const PaintBGParams& aParams,
+                                            gfxContext& aRenderingCtx);
+
+  /**
+   * Same as |PaintStyleImageLayer|, except using the provided style structs.
+   * This short-circuits the code that ensures that the root element's
+   * {background|mask} is drawn on the canvas.
+   * The aLayer parameter allows you to paint a single layer of the
+   * {background|mask}.
+   * The default value for aLayer, -1, means that all layers will be painted.
+   * The background color will only be painted if the back-most layer is also
+   * being painted and (aParams.paintFlags & PAINTBG_MASK_IMAGE) is false.
+   * aCompositionOp is only respected if a single layer is specified (aLayer !=
+   * -1). If all layers are painted, the image layer's blend mode (or the mask
+   * layer's composition mode) will be used.
+   */
+  static ImgDrawResult PaintStyleImageLayerWithSC(
+      const PaintBGParams& aParams, gfxContext& aRenderingCtx,
+      const mozilla::ComputedStyle* aBackgroundSC,
+      const nsStyleBorder& aBorder);
+
+  static bool CanBuildWebRenderDisplayItemsForStyleImageLayer(
+      WebRenderLayerManager* aManager, nsPresContext& aPresCtx,
+      nsIFrame* aFrame, const nsStyleBackground* aBackgroundStyle,
+      int32_t aLayer, uint32_t aPaintFlags);
+  static ImgDrawResult BuildWebRenderDisplayItemsForStyleImageLayer(
+      const PaintBGParams& aParams, mozilla::wr::DisplayListBuilder& aBuilder,
+      mozilla::wr::IpcResourceUpdateQueue& aResources,
+      const mozilla::layers::StackingContextHelper& aSc,
+      mozilla::layers::RenderRootStateManager* aManager,
+      mozilla::nsDisplayItem* aItem);
+
+  static ImgDrawResult BuildWebRenderDisplayItemsForStyleImageLayerWithSC(
+      const PaintBGParams& aParams, mozilla::wr::DisplayListBuilder& aBuilder,
+      mozilla::wr::IpcResourceUpdateQueue& aResources,
+      const mozilla::layers::StackingContextHelper& aSc,
+      mozilla::layers::RenderRootStateManager* aManager,
+      mozilla::nsDisplayItem* aItem, mozilla::ComputedStyle* mBackgroundSC,
+      const nsStyleBorder& aBorder);
+
+  /**
+   * Returns the rectangle covered by the given background layer image, taking
+   * into account background positioning, sizing, and repetition, but not
+   * clipping.
+   */
+  static nsRect GetBackgroundLayerRect(nsPresContext* aPresContext,
+                                       nsIFrame* aForFrame,
+                                       const nsRect& aBorderArea,
+                                       const nsRect& aClipRect,
+                                       const nsStyleImageLayers::Layer& aLayer,
+                                       uint32_t aFlags);
+
+  /**
+   * Called when we start creating a display list. The frame tree will not
+   * change until a matching EndFrameTreeLocked is called.
+   */
+  static void BeginFrameTreesLocked();
+  /**
+   * Called when we've finished using a display list. When all
+   * BeginFrameTreeLocked calls have been balanced by an EndFrameTreeLocked,
+   * the frame tree may start changing again.
+   */
+  static void EndFrameTreesLocked();
+
+  // Draw a border segment in the table collapsing border model with beveling
+  // corners.
+  static void DrawTableBorderSegment(
+      DrawTarget& aDrawTarget, mozilla::StyleBorderStyle aBorderStyle,
+      nscolor aBorderColor, const nsRect& aBorderRect,
+      int32_t aAppUnitsPerDevPixel, mozilla::Side aStartBevelSide,
+      nscoord aStartBevelOffset, mozilla::Side aEndBevelSide,
+      nscoord aEndBevelOffset);
+
+  // A single border bevel.
+  struct Bevel {
+    mozilla::Side mSide;
+    nscoord mOffset;
+  };
+
+  // A single solid beveled border segment.
+  struct SolidBeveledBorderSegment {
+    nsRect mRect;
+    nscolor mColor;
+    Bevel mStartBevel;
+    Bevel mEndBevel;
+  };
+
+  // Collect the table border segments with beveling. Can't be called with
+  // dashed / dotted borders, since we don't support beveling those.
+  static void GetTableBorderSolidSegments(
+      nsTArray<SolidBeveledBorderSegment>& aSegments,
+      mozilla::StyleBorderStyle aBorderStyle, nscolor aBorderColor,
+      const nsRect& aBorderRect, int32_t aAppUnitsPerDevPixel,
+      mozilla::Side aStartBevelSide, nscoord aStartBevelOffset,
+      mozilla::Side aEndBevelSide, nscoord aEndBevelOffset);
+
+  // NOTE: pt, dirtyRect, lineSize, ascent, offset in the following
+  //       structs are non-rounded device pixels, not app units.
+  struct DecorationRectParams {
+    // The width [length] and the height [thickness] of the decoration
+    // line. This is a "logical" size in textRun orientation, so that
+    // for a vertical textrun, width will actually be a physical height;
+    // and conversely, height will be a physical width.
+    Size lineSize;
+    // The default height [thickness] of the line given by the font metrics.
+    // This is used for obtaining the correct offset for the decoration line
+    // when CSS specifies a unique thickness for a text-decoration,
+    // since the offset given by the font is derived from the font metric's
+    // assumed line height
+    Float defaultLineThickness = 0.0f;
+    // The ascent of the text.
+    Float ascent = 0.0f;
+    // The offset of the decoration line from the baseline of the text
+    // (if the value is positive, the line is lifted up).
+    Float offset = 0.0f;
+    // If descentLimit is zero or larger and the underline overflows
+    // from the descent space, the underline should be lifted up as far
+    // as possible.  Note that this does not mean the underline never
+    // overflows from this limitation, because if the underline is
+    // positioned to the baseline or upper, it causes unreadability.
+    // Note that if this is zero or larger, the underline rect may be
+    // shrunken if it's possible.  Therefore, this value is used for
+    // strikeout line and overline too.
+    Float descentLimit = -1.0f;
+    // Which line will be painted. The value can be
+    // UNDERLINE or OVERLINE or LINE_THROUGH.
+    mozilla::StyleTextDecorationLine decoration =
+        mozilla::StyleTextDecorationLine::UNDERLINE;
+    // The style of the decoration line
+    mozilla::StyleTextDecorationStyle style =
+        mozilla::StyleTextDecorationStyle::None;
+    bool vertical = false;
+    bool sidewaysLeft = false;
+    gfxTextRun::Range glyphRange;
+    gfxTextRun::PropertyProvider* provider;
+  };
+
+  struct PaintDecorationLineParams : DecorationRectParams {
+    // No need to paint outside this rect.
+    Rect dirtyRect;
+    // The top/left edge of the text.
+    Point pt;
+    // The color of the decoration line.
+    nscolor color = NS_RGBA(0, 0, 0, 0);
+    // The distance between the left edge of the given frame and the
+    // position of the text as positioned without offset of the shadow.
+    Float icoordInFrame = 0.0f;
+    // Baseline offset being applied to this text (block-direction adjustment
+    // applied to glyph positions when computing skip-ink intercepts).
+    Float baselineOffset = 0.0f;
+  };
+
+  /**
+   * Function for painting the clipped decoration lines for the text.
+   * Takes into account the rect clipping that occurs when
+   * text-decoration-skip-ink is being used for underlines or overlines
+   *
+   *  input:
+   *    @param aFrame            the frame which needs the decoration line
+   *    @param aDrawTarget       the target/backend being drawn to
+   *    @param aParams           the parameters for the decoration line
+   *                             being drawn
+   *    @param aRect             the rect representing the decoration line
+   */
+  static void PaintDecorationLineInternal(
+      nsIFrame* aFrame, DrawTarget& aDrawTarget,
+      const PaintDecorationLineParams& aParams, Rect aRect);
+
+  /**
+   * Function for painting the decoration lines for the text.
+   *
+   *   input:
+   *     @param aFrame            the frame which needs the decoration line
+   *     @param aDrawTarget       the target/backend being drawn to
+   *     @param aParams           the parameters for the decoration line
+   *                              being drawn
+   */
+  static void PaintDecorationLine(nsIFrame* aFrame, DrawTarget& aDrawTarget,
+                                  const PaintDecorationLineParams& aParams);
+
+  /**
+   * Returns a Rect corresponding to the outline of the decoration line for the
+   * given text metrics.  Arguments have the same meaning as for
+   * PaintDecorationLine.  Currently this only works for solid
+   * decorations; for other decoration styles the returned Rect will be empty.
+   */
+  static Rect DecorationLineToPath(const PaintDecorationLineParams& aParams);
+
+  /**
+   * Function for getting the decoration line rect for the text.
+   * NOTE: aLineSize, aAscent and aOffset are non-rounded device pixels,
+   *       not app units.
+   *   input:
+   *     @param aPresContext
+   *   output:
+   *     @return                  the decoration line rect for the input,
+   *                              the each values are app units.
+   */
+  static nsRect GetTextDecorationRect(nsPresContext* aPresContext,
+                                      const DecorationRectParams& aParams);
+
+  static CompositionOp GetGFXBlendMode(mozilla::StyleBlend aBlendMode) {
+    switch (aBlendMode) {
+      case mozilla::StyleBlend::Normal:
+        return CompositionOp::OP_OVER;
+      case mozilla::StyleBlend::Multiply:
+        return CompositionOp::OP_MULTIPLY;
+      case mozilla::StyleBlend::Screen:
+        return CompositionOp::OP_SCREEN;
+      case mozilla::StyleBlend::Overlay:
+        return CompositionOp::OP_OVERLAY;
+      case mozilla::StyleBlend::Darken:
+        return CompositionOp::OP_DARKEN;
+      case mozilla::StyleBlend::Lighten:
+        return CompositionOp::OP_LIGHTEN;
+      case mozilla::StyleBlend::ColorDodge:
+        return CompositionOp::OP_COLOR_DODGE;
+      case mozilla::StyleBlend::ColorBurn:
+        return CompositionOp::OP_COLOR_BURN;
+      case mozilla::StyleBlend::HardLight:
+        return CompositionOp::OP_HARD_LIGHT;
+      case mozilla::StyleBlend::SoftLight:
+        return CompositionOp::OP_SOFT_LIGHT;
+      case mozilla::StyleBlend::Difference:
+        return CompositionOp::OP_DIFFERENCE;
+      case mozilla::StyleBlend::Exclusion:
+        return CompositionOp::OP_EXCLUSION;
+      case mozilla::StyleBlend::Hue:
+        return CompositionOp::OP_HUE;
+      case mozilla::StyleBlend::Saturation:
+        return CompositionOp::OP_SATURATION;
+      case mozilla::StyleBlend::Color:
+        return CompositionOp::OP_COLOR;
+      case mozilla::StyleBlend::Luminosity:
+        return CompositionOp::OP_LUMINOSITY;
+      case mozilla::StyleBlend::PlusLighter:
+        return CompositionOp::OP_ADD;
+      default:
+        MOZ_ASSERT(false);
+        return CompositionOp::OP_OVER;
+    }
+  }
+
+  static CompositionOp GetGFXCompositeMode(
+      mozilla::StyleMaskComposite aCompositeMode) {
+    switch (aCompositeMode) {
+      case mozilla::StyleMaskComposite::Add:
+        return CompositionOp::OP_OVER;
+      case mozilla::StyleMaskComposite::Subtract:
+        return CompositionOp::OP_OUT;
+      case mozilla::StyleMaskComposite::Intersect:
+        return CompositionOp::OP_IN;
+      case mozilla::StyleMaskComposite::Exclude:
+        return CompositionOp::OP_XOR;
+      default:
+        MOZ_ASSERT(false);
+        return CompositionOp::OP_OVER;
+    }
+  }
+
+ protected:
+  static gfxRect GetTextDecorationRectInternal(
+      const Point& aPt, const DecorationRectParams& aParams);
+
+  /**
+   * Returns inflated rect for painting a decoration line.
+   * Complex style decoration lines should be painted from leftmost of nearest
+   * ancestor block box because that makes better look of connection of lines
+   * for different nodes.  ExpandPaintingRectForDecorationLine() returns
+   * a rect for actual painting rect for the clipped rect.
+   *
+   * input:
+   *     @param aFrame            the frame which needs the decoration line.
+   *     @param aStyle            the style of the complex decoration line
+   *     @param aClippedRect      the clipped rect for the decoration line.
+   *                              in other words, visible area of the line.
+   *     @param aICoordInFrame  the distance between inline-start edge of aFrame
+   *                              and aClippedRect.pos.
+   *     @param aCycleLength      the width of one cycle of the line style.
+   */
+  static Rect ExpandPaintingRectForDecorationLine(
+      nsIFrame* aFrame, const mozilla::StyleTextDecorationStyle aStyle,
+      const Rect& aClippedRect, const Float aICoordInFrame,
+      const Float aCycleLength, bool aVertical);
+};
+
+/*
+ * nsContextBoxBlur
+ * Creates an 8-bit alpha channel context for callers to draw in, blurs the
+ * contents of that context and applies it as a 1-color mask on a
+ * different existing context. Uses gfxAlphaBoxBlur as its back end.
+ *
+ * You must call Init() first to create a suitable temporary surface to draw
+ * on.  You must then draw any desired content onto the given context, then
+ * call DoPaint() to apply the blurred content as a single-color mask. You
+ * can only call Init() once, so objects cannot be reused.
+ *
+ * This is very useful for creating drop shadows or silhouettes.
+ */
+class nsContextBoxBlur {
+  typedef mozilla::gfx::sRGBColor sRGBColor;
+  typedef mozilla::gfx::DrawTarget DrawTarget;
+  typedef mozilla::gfx::RectCornerRadii RectCornerRadii;
+
+ public:
+  enum { FORCE_MASK = 0x01, DISABLE_HARDWARE_ACCELERATION_BLUR = 0x02 };
+  /**
+   * Prepares a gfxContext to draw on. Do not call this twice; if you want
+   * to get the gfxContext again use GetContext().
+   *
+   * @param aRect                The coordinates of the surface to create.
+   *                             All coordinates must be in app units.
+   *                             This must not include the blur radius, pass
+   *                             it as the second parameter and everything
+   *                             is taken care of.
+   *
+   * @param aBlurRadius          The blur radius in app units.
+   *
+   * @param aAppUnitsPerDevPixel The number of app units in a device pixel,
+   *                             for conversion.  Most of the time you'll
+   *                             pass this from the current PresContext if
+   *                             available.
+   *
+   * @param aDestinationCtx      The graphics context to apply the blurred
+   *                             mask to when you call DoPaint(). Make sure
+   *                             it is not destroyed before you call
+   *                             DoPaint(). To set the color of the
+   *                             resulting blurred graphic mask, you must
+   *                             set the color on this context before
+   *                             calling Init().
+   *
+   * @param aDirtyRect           The absolute dirty rect in app units. Used to
+   *                             optimize the temporary surface size and speed
+   * up blur.
+   *
+   * @param aSkipRect            An area in device pixels (NOT app units!) to
+   * avoid blurring over, to prevent unnecessary work.
+   *
+   * @param aFlags               FORCE_MASK to ensure that the content drawn to
+   * the returned gfxContext is used as a mask, and not drawn directly to
+   * aDestinationCtx.
+   *
+   * @return            A blank 8-bit alpha-channel-only graphics context to
+   *                    draw on, or null on error. Must not be freed. The
+   *                    context has a device offset applied to it given by
+   *                    aRect. This means you can use coordinates as if it
+   *                    were at the desired position at aRect and you don't
+   *                    need to worry about translating any coordinates to
+   *                    draw on this temporary surface.
+   *
+   * If aBlurRadius is 0, the returned context is aDestinationCtx and
+   * DoPaint() does nothing, because no blurring is required. Therefore, you
+   * should prepare the destination context as if you were going to draw
+   * directly on it instead of any temporary surface created in this class.
+   */
+  gfxContext* Init(const nsRect& aRect, nscoord aSpreadRadius,
+                   nscoord aBlurRadius, int32_t aAppUnitsPerDevPixel,
+                   gfxContext* aDestinationCtx, const nsRect& aDirtyRect,
+                   const gfxRect* aSkipRect, uint32_t aFlags = 0);
+
+  /**
+   * Does the actual blurring and mask applying. Users of this object *must*
+   * have called Init() first, then have drawn whatever they want to be
+   * blurred onto the internal gfxContext before calling this.
+   */
+  void DoPaint();
+
+  /**
+   * Gets the internal gfxContext at any time. Must not be freed. Avoid
+   * calling this before calling Init() since the context would not be
+   * constructed at that point.
+   */
+  gfxContext* GetContext();
+
+  /**
+   * Get the margin associated with the given blur radius, i.e., the
+   * additional area that might be painted as a result of it.  (The
+   * margin for a spread radius is itself, on all sides.)
+   */
+  static nsMargin GetBlurRadiusMargin(nscoord aBlurRadius,
+                                      int32_t aAppUnitsPerDevPixel);
+
+  /**
+   * Blurs a coloured rectangle onto aDestinationCtx. This is equivalent
+   * to calling Init(), drawing a rectangle onto the returned surface
+   * and then calling DoPaint, but may let us optimize better in the
+   * backend.
+   *
+   * @param aDestinationCtx      The destination to blur to.
+   * @param aRect                The rectangle to blur in app units.
+   * @param aAppUnitsPerDevPixel The number of app units in a device pixel,
+   *                             for conversion.  Most of the time you'll
+   *                             pass this from the current PresContext if
+   *                             available.
+   * @param aCornerRadii         Corner radii for aRect, if it is a rounded
+   *                             rectangle.
+   * @param aBlurRadius          The blur radius in app units.
+   * @param aShadowColor         The color to draw the blurred shadow.
+   * @param aDirtyRect           The absolute dirty rect in app units. Used to
+   *                             optimize the temporary surface size and speed
+   * up blur.
+   * @param aSkipRect            An area in device pixels (NOT app units!) to
+   * avoid blurring over, to prevent unnecessary work.
+   */
+  static void BlurRectangle(gfxContext* aDestinationCtx, const nsRect& aRect,
+                            int32_t aAppUnitsPerDevPixel,
+                            RectCornerRadii* aCornerRadii, nscoord aBlurRadius,
+                            const sRGBColor& aShadowColor,
+                            const nsRect& aDirtyRect, const gfxRect& aSkipRect);
+
+  /**
+   * Draws a blurred inset box shadow shape onto the destination surface.
+   * Like BlurRectangle, this is equivalent to calling Init(),
+   * drawing a rectangle onto the returned surface
+   * and then calling DoPaint, but may let us optimize better in the
+   * backend.
+   *
+   * @param aDestinationCtx      The destination to blur to.
+   * @param aDestinationRect     The rectangle to blur in app units.
+   * @param aShadowClipRect      The inside clip rect that creates the path.
+   * @param aShadowColor         The color of the blur
+   * @param aBlurRadiusAppUnits  The blur radius in app units
+   * @param aSpreadRadiusAppUnits The spread radius in app units.
+   * @param aAppUnitsPerDevPixel The number of app units in a device pixel,
+   *                             for conversion.  Most of the time you'll
+   *                             pass this from the current PresContext if
+   *                             available.
+   * @param aHasBorderRadius     If this inset box blur has a border radius
+   * @param aInnerClipRectRadii  The clip rect radii used for the inside rect's
+   * path.
+   * @param aSkipRect            An area in device pixels (NOT app units!) to
+   * avoid blurring over, to prevent unnecessary work.
+   */
+  bool InsetBoxBlur(gfxContext* aDestinationCtx,
+                    mozilla::gfx::Rect aDestinationRect,
+                    mozilla::gfx::Rect aShadowClipRect,
+                    mozilla::gfx::sRGBColor& aShadowColor,
+                    nscoord aBlurRadiusAppUnits, nscoord aSpreadRadiusAppUnits,
+                    int32_t aAppUnitsPerDevPixel, bool aHasBorderRadius,
+                    RectCornerRadii& aInnerClipRectRadii,
+                    mozilla::gfx::Rect aSkipRect,
+                    mozilla::gfx::Point aShadowOffset);
+
+ protected:
+  static void GetBlurAndSpreadRadius(DrawTarget* aDestDrawTarget,
+                                     int32_t aAppUnitsPerDevPixel,
+                                     nscoord aBlurRadius, nscoord aSpreadRadius,
+                                     mozilla::gfx::IntSize& aOutBlurRadius,
+                                     mozilla::gfx::IntSize& aOutSpreadRadius,
+                                     bool aConstrainSpreadRadius = true);
+
+  gfxAlphaBoxBlur mAlphaBoxBlur;
+  RefPtr<gfxContext> mContext;
+  gfxContext* mDestinationCtx;
+
+  /* This is true if the blur already has it's content transformed
+   * by mDestinationCtx's transform */
+  bool mPreTransformed;
+};
+
+#endif /* nsCSSRendering_h___ */
diff --git a/layout/painting/nsCSSRenderingBorders.cpp b/layout/painting/nsCSSRenderingBorders.cpp
new file mode 100644
index 0000000000..eb234e7d9f
--- /dev/null
+++ b/layout/painting/nsCSSRenderingBorders.cpp
@@ -0,0 +1,3906 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsCSSRenderingBorders.h"
+
+#include "gfxUtils.h"
+#include "mozilla/ArrayUtils.h"
+#include "mozilla/gfx/2D.h"
+#include "mozilla/gfx/Helpers.h"
+#include "mozilla/gfx/PathHelpers.h"
+#include "BorderConsts.h"
+#include "DashedCornerFinder.h"
+#include "DottedCornerFinder.h"
+#include "ImageRegion.h"
+#include "nsLayoutUtils.h"
+#include "nsStyleConsts.h"
+#include "nsContentUtils.h"
+#include "nsCSSColorUtils.h"
+#include "nsCSSRendering.h"
+#include "nsCSSRenderingGradients.h"
+#include "nsDisplayList.h"
+#include "nsExpirationTracker.h"
+#include "nsIScriptError.h"
+#include "nsClassHashtable.h"
+#include "nsPresContext.h"
+#include "nsStyleStruct.h"
+#include "gfx2DGlue.h"
+#include "gfxGradientCache.h"
+#include "mozilla/image/WebRenderImageProvider.h"
+#include "mozilla/layers/StackingContextHelper.h"
+#include "mozilla/layers/RenderRootStateManager.h"
+#include "mozilla/layers/WebRenderLayerManager.h"
+#include "mozilla/ProfilerLabels.h"
+#include "mozilla/Range.h"
+#include <algorithm>
+
+using namespace mozilla;
+using namespace mozilla::gfx;
+using namespace mozilla::image;
+
+#define MAX_COMPOSITE_BORDER_WIDTH LayoutDeviceIntCoord(10000)
+
+/**
+ * nsCSSRendering::PaintBorder
+ * nsCSSRendering::PaintOutline
+ *   -> DrawBorders
+ *
+ * DrawBorders
+ *   -> Ability to use specialized approach?
+ *      |- Draw using specialized function
+ *   |- separate corners?
+ *   |- dashed side mask
+ *   |
+ *   -> can border be drawn in 1 pass? (e.g., solid border same color all
+ * around)
+ *      |- DrawBorderSides with all 4 sides
+ *   -> more than 1 pass?
+ *      |- for each corner
+ *         |- clip to DoCornerClipSubPath
+ *         |- for each side adjacent to corner
+ *            |- clip to GetSideClipSubPath
+ *            |- DrawBorderSides with one side
+ *      |- for each side
+ *         |- GetSideClipWithoutCornersRect
+ *         |- DrawDashedOrDottedSide || DrawBorderSides with one side
+ */
+
+static void ComputeBorderCornerDimensions(const Float* aBorderWidths,
+                                          const RectCornerRadii& aRadii,
+                                          RectCornerRadii* aDimsResult);
+
+// given a side index, get the previous and next side index
+#define NEXT_SIDE(_s) mozilla::Side(((_s) + 1) & 3)
+#define PREV_SIDE(_s) mozilla::Side(((_s) + 3) & 3)
+
+// given a corner index, get the previous and next corner index
+#define NEXT_CORNER(_s) Corner(((_s) + 1) & 3)
+#define PREV_CORNER(_s) Corner(((_s) + 3) & 3)
+
+// from the given base color and the background color, turn
+// color into a color for the given border pattern style
+static sRGBColor MakeBorderColor(nscolor aColor,
+                                 BorderColorStyle aBorderColorStyle);
+
+// Given a line index (an index starting from the outside of the
+// border going inwards) and an array of line styles, calculate the
+// color that that stripe of the border should be rendered in.
+static sRGBColor ComputeColorForLine(uint32_t aLineIndex,
+                                     const BorderColorStyle* aBorderColorStyle,
+                                     uint32_t aBorderColorStyleCount,
+                                     nscolor aBorderColor);
+
+// little helper function to check if the array of 4 floats given are
+// equal to the given value
+static bool CheckFourFloatsEqual(const Float* vals, Float k) {
+  return (vals[0] == k && vals[1] == k && vals[2] == k && vals[3] == k);
+}
+
+static bool IsZeroSize(const Size& sz) {
+  return sz.width == 0.0 || sz.height == 0.0;
+}
+
+/* static */
+bool nsCSSBorderRenderer::AllCornersZeroSize(const RectCornerRadii& corners) {
+  return IsZeroSize(corners[eCornerTopLeft]) &&
+         IsZeroSize(corners[eCornerTopRight]) &&
+         IsZeroSize(corners[eCornerBottomRight]) &&
+         IsZeroSize(corners[eCornerBottomLeft]);
+}
+
+static mozilla::Side GetHorizontalSide(Corner aCorner) {
+  return (aCorner == C_TL || aCorner == C_TR) ? eSideTop : eSideBottom;
+}
+
+static mozilla::Side GetVerticalSide(Corner aCorner) {
+  return (aCorner == C_TL || aCorner == C_BL) ? eSideLeft : eSideRight;
+}
+
+static Corner GetCWCorner(mozilla::Side aSide) {
+  return Corner(NEXT_SIDE(aSide));
+}
+
+static Corner GetCCWCorner(mozilla::Side aSide) { return Corner(aSide); }
+
+static bool IsSingleSide(mozilla::SideBits aSides) {
+  return aSides == SideBits::eTop || aSides == SideBits::eRight ||
+         aSides == SideBits::eBottom || aSides == SideBits::eLeft;
+}
+
+static bool IsHorizontalSide(mozilla::Side aSide) {
+  return aSide == eSideTop || aSide == eSideBottom;
+}
+
+typedef enum {
+  // Normal solid square corner.  Will be rectangular, the size of the
+  // adjacent sides.  If the corner has a border radius, the corner
+  // will always be solid, since we don't do dotted/dashed etc.
+  CORNER_NORMAL,
+
+  // Paint the corner in whatever style is not dotted/dashed of the
+  // adjacent corners.
+  CORNER_SOLID,
+
+  // Paint the corner as a dot, the size of the bigger of the adjacent
+  // sides.
+  CORNER_DOT
+} CornerStyle;
+
+nsCSSBorderRenderer::nsCSSBorderRenderer(
+    nsPresContext* aPresContext, DrawTarget* aDrawTarget,
+    const Rect& aDirtyRect, Rect& aOuterRect,
+    const StyleBorderStyle* aBorderStyles, const Float* aBorderWidths,
+    RectCornerRadii& aBorderRadii, const nscolor* aBorderColors,
+    bool aBackfaceIsVisible, const Maybe<Rect>& aClipRect)
+    : mPresContext(aPresContext),
+      mDrawTarget(aDrawTarget),
+      mDirtyRect(aDirtyRect),
+      mOuterRect(aOuterRect),
+      mBorderRadii(aBorderRadii),
+      mBackfaceIsVisible(aBackfaceIsVisible),
+      mLocalClip(aClipRect) {
+  PodCopy(mBorderStyles, aBorderStyles, 4);
+  PodCopy(mBorderWidths, aBorderWidths, 4);
+  PodCopy(mBorderColors, aBorderColors, 4);
+  mInnerRect = mOuterRect;
+  mInnerRect.Deflate(Margin(
+      mBorderStyles[0] != StyleBorderStyle::None ? mBorderWidths[0] : 0,
+      mBorderStyles[1] != StyleBorderStyle::None ? mBorderWidths[1] : 0,
+      mBorderStyles[2] != StyleBorderStyle::None ? mBorderWidths[2] : 0,
+      mBorderStyles[3] != StyleBorderStyle::None ? mBorderWidths[3] : 0));
+
+  ComputeBorderCornerDimensions(mBorderWidths, mBorderRadii,
+                                &mBorderCornerDimensions);
+
+  mOneUnitBorder = CheckFourFloatsEqual(mBorderWidths, 1.0);
+  mNoBorderRadius = AllCornersZeroSize(mBorderRadii);
+  mAllBordersSameStyle = AreBorderSideFinalStylesSame(SideBits::eAll);
+  mAllBordersSameWidth = AllBordersSameWidth();
+  mAvoidStroke = false;
+}
+
+/* static */
+void nsCSSBorderRenderer::ComputeInnerRadii(const RectCornerRadii& aRadii,
+                                            const Float* aBorderSizes,
+                                            RectCornerRadii* aInnerRadiiRet) {
+  RectCornerRadii& iRadii = *aInnerRadiiRet;
+
+  iRadii[C_TL].width =
+      std::max(0.f, aRadii[C_TL].width - aBorderSizes[eSideLeft]);
+  iRadii[C_TL].height =
+      std::max(0.f, aRadii[C_TL].height - aBorderSizes[eSideTop]);
+
+  iRadii[C_TR].width =
+      std::max(0.f, aRadii[C_TR].width - aBorderSizes[eSideRight]);
+  iRadii[C_TR].height =
+      std::max(0.f, aRadii[C_TR].height - aBorderSizes[eSideTop]);
+
+  iRadii[C_BR].width =
+      std::max(0.f, aRadii[C_BR].width - aBorderSizes[eSideRight]);
+  iRadii[C_BR].height =
+      std::max(0.f, aRadii[C_BR].height - aBorderSizes[eSideBottom]);
+
+  iRadii[C_BL].width =
+      std::max(0.f, aRadii[C_BL].width - aBorderSizes[eSideLeft]);
+  iRadii[C_BL].height =
+      std::max(0.f, aRadii[C_BL].height - aBorderSizes[eSideBottom]);
+}
+
+/* static */
+void nsCSSBorderRenderer::ComputeOuterRadii(const RectCornerRadii& aRadii,
+                                            const Float* aBorderSizes,
+                                            RectCornerRadii* aOuterRadiiRet) {
+  RectCornerRadii& oRadii = *aOuterRadiiRet;
+
+  // default all corners to sharp corners
+  oRadii = RectCornerRadii(0.f);
+
+  // round the edges that have radii > 0.0 to start with
+  if (aRadii[C_TL].width > 0.f && aRadii[C_TL].height > 0.f) {
+    oRadii[C_TL].width =
+        std::max(0.f, aRadii[C_TL].width + aBorderSizes[eSideLeft]);
+    oRadii[C_TL].height =
+        std::max(0.f, aRadii[C_TL].height + aBorderSizes[eSideTop]);
+  }
+
+  if (aRadii[C_TR].width > 0.f && aRadii[C_TR].height > 0.f) {
+    oRadii[C_TR].width =
+        std::max(0.f, aRadii[C_TR].width + aBorderSizes[eSideRight]);
+    oRadii[C_TR].height =
+        std::max(0.f, aRadii[C_TR].height + aBorderSizes[eSideTop]);
+  }
+
+  if (aRadii[C_BR].width > 0.f && aRadii[C_BR].height > 0.f) {
+    oRadii[C_BR].width =
+        std::max(0.f, aRadii[C_BR].width + aBorderSizes[eSideRight]);
+    oRadii[C_BR].height =
+        std::max(0.f, aRadii[C_BR].height + aBorderSizes[eSideBottom]);
+  }
+
+  if (aRadii[C_BL].width > 0.f && aRadii[C_BL].height > 0.f) {
+    oRadii[C_BL].width =
+        std::max(0.f, aRadii[C_BL].width + aBorderSizes[eSideLeft]);
+    oRadii[C_BL].height =
+        std::max(0.f, aRadii[C_BL].height + aBorderSizes[eSideBottom]);
+  }
+}
+
+/*static*/ void ComputeBorderCornerDimensions(const Float* aBorderWidths,
+                                              const RectCornerRadii& aRadii,
+                                              RectCornerRadii* aDimsRet) {
+  Float leftWidth = aBorderWidths[eSideLeft];
+  Float topWidth = aBorderWidths[eSideTop];
+  Float rightWidth = aBorderWidths[eSideRight];
+  Float bottomWidth = aBorderWidths[eSideBottom];
+
+  if (nsCSSBorderRenderer::AllCornersZeroSize(aRadii)) {
+    // These will always be in pixel units from CSS
+    (*aDimsRet)[C_TL] = Size(leftWidth, topWidth);
+    (*aDimsRet)[C_TR] = Size(rightWidth, topWidth);
+    (*aDimsRet)[C_BR] = Size(rightWidth, bottomWidth);
+    (*aDimsRet)[C_BL] = Size(leftWidth, bottomWidth);
+  } else {
+    // Always round up to whole pixels for the corners; it's safe to
+    // make the corners bigger than necessary, and this way we ensure
+    // that we avoid seams.
+    (*aDimsRet)[C_TL] = Size(ceil(std::max(leftWidth, aRadii[C_TL].width)),
+                             ceil(std::max(topWidth, aRadii[C_TL].height)));
+    (*aDimsRet)[C_TR] = Size(ceil(std::max(rightWidth, aRadii[C_TR].width)),
+                             ceil(std::max(topWidth, aRadii[C_TR].height)));
+    (*aDimsRet)[C_BR] = Size(ceil(std::max(rightWidth, aRadii[C_BR].width)),
+                             ceil(std::max(bottomWidth, aRadii[C_BR].height)));
+    (*aDimsRet)[C_BL] = Size(ceil(std::max(leftWidth, aRadii[C_BL].width)),
+                             ceil(std::max(bottomWidth, aRadii[C_BL].height)));
+  }
+}
+
+bool nsCSSBorderRenderer::AreBorderSideFinalStylesSame(
+    mozilla::SideBits aSides) {
+  NS_ASSERTION(aSides != SideBits::eNone &&
+                   (aSides & ~SideBits::eAll) == SideBits::eNone,
+               "AreBorderSidesSame: invalid whichSides!");
+
+  /* First check if the specified styles and colors are the same for all sides
+   */
+  int firstStyle = 0;
+  for (const auto i : mozilla::AllPhysicalSides()) {
+    if (firstStyle == i) {
+      if ((static_cast<mozilla::SideBits>(1 << i) & aSides) ==
+          SideBits::eNone) {
+        firstStyle++;
+      }
+      continue;
+    }
+
+    if ((static_cast<mozilla::SideBits>(1 << i) & aSides) == SideBits::eNone) {
+      continue;
+    }
+
+    if (mBorderStyles[firstStyle] != mBorderStyles[i] ||
+        mBorderColors[firstStyle] != mBorderColors[i]) {
+      return false;
+    }
+  }
+
+  /* Then if it's one of the two-tone styles and we're not
+   * just comparing the TL or BR sides */
+  switch (mBorderStyles[firstStyle]) {
+    case StyleBorderStyle::Groove:
+    case StyleBorderStyle::Ridge:
+    case StyleBorderStyle::Inset:
+    case StyleBorderStyle::Outset:
+      return ((aSides & ~(SideBits::eTop | SideBits::eLeft)) ==
+                  SideBits::eNone ||
+              (aSides & ~(SideBits::eBottom | SideBits::eRight)) ==
+                  SideBits::eNone);
+    default:
+      return true;
+  }
+}
+
+bool nsCSSBorderRenderer::IsSolidCornerStyle(StyleBorderStyle aStyle,
+                                             Corner aCorner) {
+  switch (aStyle) {
+    case StyleBorderStyle::Solid:
+      return true;
+
+    case StyleBorderStyle::Inset:
+    case StyleBorderStyle::Outset:
+      return (aCorner == eCornerTopLeft || aCorner == eCornerBottomRight);
+
+    case StyleBorderStyle::Groove:
+    case StyleBorderStyle::Ridge:
+      return mOneUnitBorder &&
+             (aCorner == eCornerTopLeft || aCorner == eCornerBottomRight);
+
+    case StyleBorderStyle::Double:
+      return mOneUnitBorder;
+
+    default:
+      return false;
+  }
+}
+
+bool nsCSSBorderRenderer::IsCornerMergeable(Corner aCorner) {
+  // Corner between dotted borders with same width and small radii is
+  // merged into single dot.
+  //
+  //  widthH / 2.0
+  // |<---------->|
+  // |            |
+  // |radius.width|
+  // |<--->|      |
+  // |     |      |
+  // |    _+------+------------+-----
+  // |  /      ###|###         |
+  // |/    #######|#######     |
+  // +   #########|#########   |
+  // |  ##########|##########  |
+  // | ###########|########### |
+  // | ###########|########### |
+  // |############|############|
+  // +------------+############|
+  // |#########################|
+  // | ####################### |
+  // | ####################### |
+  // |  #####################  |
+  // |   ###################   |
+  // |     ###############     |
+  // |         #######         |
+  // +-------------------------+----
+  // |                         |
+  // |                         |
+  mozilla::Side sideH(GetHorizontalSide(aCorner));
+  mozilla::Side sideV(GetVerticalSide(aCorner));
+  StyleBorderStyle styleH = mBorderStyles[sideH];
+  StyleBorderStyle styleV = mBorderStyles[sideV];
+  if (styleH != styleV || styleH != StyleBorderStyle::Dotted) {
+    return false;
+  }
+
+  Float widthH = mBorderWidths[sideH];
+  Float widthV = mBorderWidths[sideV];
+  if (widthH != widthV) {
+    return false;
+  }
+
+  Size radius = mBorderRadii[aCorner];
+  return IsZeroSize(radius) ||
+         (radius.width < widthH / 2.0f && radius.height < widthH / 2.0f);
+}
+
+BorderColorStyle nsCSSBorderRenderer::BorderColorStyleForSolidCorner(
+    StyleBorderStyle aStyle, Corner aCorner) {
+  // note that this function assumes that the corner is already solid,
+  // as per the earlier function
+  switch (aStyle) {
+    case StyleBorderStyle::Solid:
+    case StyleBorderStyle::Double:
+      return BorderColorStyleSolid;
+
+    case StyleBorderStyle::Inset:
+    case StyleBorderStyle::Groove:
+      if (aCorner == eCornerTopLeft) {
+        return BorderColorStyleDark;
+      } else if (aCorner == eCornerBottomRight) {
+        return BorderColorStyleLight;
+      }
+      break;
+
+    case StyleBorderStyle::Outset:
+    case StyleBorderStyle::Ridge:
+      if (aCorner == eCornerTopLeft) {
+        return BorderColorStyleLight;
+      } else if (aCorner == eCornerBottomRight) {
+        return BorderColorStyleDark;
+      }
+      break;
+    default:
+      return BorderColorStyleNone;
+  }
+
+  return BorderColorStyleNone;
+}
+
+Rect nsCSSBorderRenderer::GetCornerRect(Corner aCorner) {
+  Point offset(0.f, 0.f);
+
+  if (aCorner == C_TR || aCorner == C_BR)
+    offset.x = mOuterRect.Width() - mBorderCornerDimensions[aCorner].width;
+  if (aCorner == C_BR || aCorner == C_BL)
+    offset.y = mOuterRect.Height() - mBorderCornerDimensions[aCorner].height;
+
+  return Rect(mOuterRect.TopLeft() + offset, mBorderCornerDimensions[aCorner]);
+}
+
+Rect nsCSSBorderRenderer::GetSideClipWithoutCornersRect(mozilla::Side aSide) {
+  Point offset(0.f, 0.f);
+
+  // The offset from the outside rect to the start of this side's
+  // box.  For the top and bottom sides, the height of the box
+  // must be the border height; the x start must take into account
+  // the corner size (which may be bigger than the right or left
+  // side's width).  The same applies to the right and left sides.
+  if (aSide == eSideTop) {
+    offset.x = mBorderCornerDimensions[C_TL].width;
+  } else if (aSide == eSideRight) {
+    offset.x = mOuterRect.Width() - mBorderWidths[eSideRight];
+    offset.y = mBorderCornerDimensions[C_TR].height;
+  } else if (aSide == eSideBottom) {
+    offset.x = mBorderCornerDimensions[C_BL].width;
+    offset.y = mOuterRect.Height() - mBorderWidths[eSideBottom];
+  } else if (aSide == eSideLeft) {
+    offset.y = mBorderCornerDimensions[C_TL].height;
+  }
+
+  // The sum of the width & height of the corners adjacent to the
+  // side.  This relies on the relationship between side indexing and
+  // corner indexing; that is, 0 == SIDE_TOP and 0 == CORNER_TOP_LEFT,
+  // with both proceeding clockwise.
+  Size sideCornerSum = mBorderCornerDimensions[GetCCWCorner(aSide)] +
+                       mBorderCornerDimensions[GetCWCorner(aSide)];
+  Rect rect(mOuterRect.TopLeft() + offset, mOuterRect.Size() - sideCornerSum);
+
+  if (IsHorizontalSide(aSide))
+    rect.height = mBorderWidths[aSide];
+  else
+    rect.width = mBorderWidths[aSide];
+
+  return rect;
+}
+
+// The side border type and the adjacent border types are
+// examined and one of the different types of clipping (listed
+// below) is selected.
+
+typedef enum {
+  // clip to the trapezoid formed by the corners of the
+  // inner and outer rectangles for the given side
+  //
+  // +---------------
+  // |\%%%%%%%%%%%%%%
+  // |  \%%%%%%%%%%%%
+  // |   \%%%%%%%%%%%
+  // |     \%%%%%%%%%
+  // |      +--------
+  // |      |
+  // |      |
+  SIDE_CLIP_TRAPEZOID,
+
+  // clip to the trapezoid formed by the outer rectangle
+  // corners and the center of the region, making sure
+  // that diagonal lines all go directly from the outside
+  // corner to the inside corner, but that they then continue on
+  // to the middle.
+  //
+  // This is needed for correctly clipping rounded borders,
+  // which might extend past the SIDE_CLIP_TRAPEZOID trap.
+  //
+  // +-------__--+---
+  //  \%%%%_-%%%%%%%%
+  //    \+-%%%%%%%%%%
+  //    / \%%%%%%%%%%
+  //   /   \%%%%%%%%%
+  //  |     +%%_-+---
+  // |        +%%%%%%
+  // |       / \%%%%%
+  // +      +    \%%%
+  // |      |      +-
+  SIDE_CLIP_TRAPEZOID_FULL,
+
+  // clip to the rectangle formed by the given side including corner.
+  // This is used by the non-dotted side next to dotted side.
+  //
+  // +---------------
+  // |%%%%%%%%%%%%%%%
+  // |%%%%%%%%%%%%%%%
+  // |%%%%%%%%%%%%%%%
+  // |%%%%%%%%%%%%%%%
+  // +------+--------
+  // |      |
+  // |      |
+  SIDE_CLIP_RECTANGLE_CORNER,
+
+  // clip to the rectangle formed by the given side excluding corner.
+  // This is used by the dotted side next to non-dotted side.
+  //
+  // +------+--------
+  // |      |%%%%%%%%
+  // |      |%%%%%%%%
+  // |      |%%%%%%%%
+  // |      |%%%%%%%%
+  // |      +--------
+  // |      |
+  // |      |
+  SIDE_CLIP_RECTANGLE_NO_CORNER,
+} SideClipType;
+
+// Given three points, p0, p1, and midPoint, move p1 further in to the
+// rectangle (of which aMidPoint is the center) so that it reaches the
+// closer of the horizontal or vertical lines intersecting the midpoint,
+// while maintaing the slope of the line.  If p0 and p1 are the same,
+// just move p1 to midPoint (since there's no slope to maintain).
+// FIXME: Extending only to the midpoint isn't actually sufficient for
+// boxes with asymmetric radii.
+static void MaybeMoveToMidPoint(Point& aP0, Point& aP1,
+                                const Point& aMidPoint) {
+  Point ps = aP1 - aP0;
+
+  if (ps.x == 0.0) {
+    if (ps.y == 0.0) {
+      aP1 = aMidPoint;
+    } else {
+      aP1.y = aMidPoint.y;
+    }
+  } else {
+    if (ps.y == 0.0) {
+      aP1.x = aMidPoint.x;
+    } else {
+      Float k =
+          std::min((aMidPoint.x - aP0.x) / ps.x, (aMidPoint.y - aP0.y) / ps.y);
+      aP1 = aP0 + ps * k;
+    }
+  }
+}
+
+already_AddRefed<Path> nsCSSBorderRenderer::GetSideClipSubPath(
+    mozilla::Side aSide) {
+  // the clip proceeds clockwise from the top left corner;
+  // so "start" in each case is the start of the region from that side.
+  //
+  // the final path will be formed like:
+  // s0 ------- e0
+  // |         /
+  // s1 ----- e1
+  //
+  // that is, the second point will always be on the inside
+
+  Point start[2];
+  Point end[2];
+
+#define IS_DOTTED(_s) ((_s) == StyleBorderStyle::Dotted)
+  bool isDotted = IS_DOTTED(mBorderStyles[aSide]);
+  bool startIsDotted = IS_DOTTED(mBorderStyles[PREV_SIDE(aSide)]);
+  bool endIsDotted = IS_DOTTED(mBorderStyles[NEXT_SIDE(aSide)]);
+#undef IS_DOTTED
+
+  SideClipType startType = SIDE_CLIP_TRAPEZOID;
+  SideClipType endType = SIDE_CLIP_TRAPEZOID;
+
+  if (!IsZeroSize(mBorderRadii[GetCCWCorner(aSide)])) {
+    startType = SIDE_CLIP_TRAPEZOID_FULL;
+  } else if (startIsDotted && !isDotted) {
+    startType = SIDE_CLIP_RECTANGLE_CORNER;
+  } else if (!startIsDotted && isDotted) {
+    startType = SIDE_CLIP_RECTANGLE_NO_CORNER;
+  }
+
+  if (!IsZeroSize(mBorderRadii[GetCWCorner(aSide)])) {
+    endType = SIDE_CLIP_TRAPEZOID_FULL;
+  } else if (endIsDotted && !isDotted) {
+    endType = SIDE_CLIP_RECTANGLE_CORNER;
+  } else if (!endIsDotted && isDotted) {
+    endType = SIDE_CLIP_RECTANGLE_NO_CORNER;
+  }
+
+  Point midPoint = mInnerRect.Center();
+
+  start[0] = mOuterRect.CCWCorner(aSide);
+  start[1] = mInnerRect.CCWCorner(aSide);
+
+  end[0] = mOuterRect.CWCorner(aSide);
+  end[1] = mInnerRect.CWCorner(aSide);
+
+  if (startType == SIDE_CLIP_TRAPEZOID_FULL) {
+    MaybeMoveToMidPoint(start[0], start[1], midPoint);
+  } else if (startType == SIDE_CLIP_RECTANGLE_CORNER) {
+    if (IsHorizontalSide(aSide)) {
+      start[1] =
+          Point(mOuterRect.CCWCorner(aSide).x, mInnerRect.CCWCorner(aSide).y);
+    } else {
+      start[1] =
+          Point(mInnerRect.CCWCorner(aSide).x, mOuterRect.CCWCorner(aSide).y);
+    }
+  } else if (startType == SIDE_CLIP_RECTANGLE_NO_CORNER) {
+    if (IsHorizontalSide(aSide)) {
+      start[0] =
+          Point(mInnerRect.CCWCorner(aSide).x, mOuterRect.CCWCorner(aSide).y);
+    } else {
+      start[0] =
+          Point(mOuterRect.CCWCorner(aSide).x, mInnerRect.CCWCorner(aSide).y);
+    }
+  }
+
+  if (endType == SIDE_CLIP_TRAPEZOID_FULL) {
+    MaybeMoveToMidPoint(end[0], end[1], midPoint);
+  } else if (endType == SIDE_CLIP_RECTANGLE_CORNER) {
+    if (IsHorizontalSide(aSide)) {
+      end[1] =
+          Point(mOuterRect.CWCorner(aSide).x, mInnerRect.CWCorner(aSide).y);
+    } else {
+      end[1] =
+          Point(mInnerRect.CWCorner(aSide).x, mOuterRect.CWCorner(aSide).y);
+    }
+  } else if (endType == SIDE_CLIP_RECTANGLE_NO_CORNER) {
+    if (IsHorizontalSide(aSide)) {
+      end[0] =
+          Point(mInnerRect.CWCorner(aSide).x, mOuterRect.CWCorner(aSide).y);
+    } else {
+      end[0] =
+          Point(mOuterRect.CWCorner(aSide).x, mInnerRect.CWCorner(aSide).y);
+    }
+  }
+
+  RefPtr<PathBuilder> builder = mDrawTarget->CreatePathBuilder();
+  builder->MoveTo(start[0]);
+  builder->LineTo(end[0]);
+  builder->LineTo(end[1]);
+  builder->LineTo(start[1]);
+  builder->Close();
+  return builder->Finish();
+}
+
+Point nsCSSBorderRenderer::GetStraightBorderPoint(mozilla::Side aSide,
+                                                  Corner aCorner,
+                                                  bool* aIsUnfilled,
+                                                  Float aDotOffset) {
+  // Calculate the end point of the side for dashed/dotted border, that is also
+  // the end point of the corner curve.  The point is specified by aSide and
+  // aCorner. (e.g. eSideTop and C_TL means the left end of border-top)
+  //
+  //
+  //  aCorner        aSide
+  //         +--------------------
+  //         |
+  //         |
+  //         |         +----------
+  //         |    the end point
+  //         |
+  //         |         +----------
+  //         |         |
+  //         |         |
+  //         |         |
+  //
+  // The position of the point depends on the border-style, border-width, and
+  // border-radius of the side, corner, and the adjacent side beyond the corner,
+  // to make those sides (and corner) interact well.
+  //
+  // If the style of aSide is dotted and the dot at the point should be
+  // unfilled, true is stored to *aIsUnfilled, otherwise false is stored.
+
+  const Float signsList[4][2] = {
+      {+1.0f, +1.0f}, {-1.0f, +1.0f}, {-1.0f, -1.0f}, {+1.0f, -1.0f}};
+  const Float(&signs)[2] = signsList[aCorner];
+
+  *aIsUnfilled = false;
+
+  Point P = mOuterRect.AtCorner(aCorner);
+  StyleBorderStyle style = mBorderStyles[aSide];
+  Float borderWidth = mBorderWidths[aSide];
+  Size dim = mBorderCornerDimensions[aCorner];
+  bool isHorizontal = IsHorizontalSide(aSide);
+  //
+  //    aCorner      aSide
+  //           +--------------
+  //           |
+  //           |   +----------
+  //           |   |
+  // otherSide |   |
+  //           |   |
+  mozilla::Side otherSide = ((uint8_t)aSide == (uint8_t)aCorner)
+                                ? PREV_SIDE(aSide)
+                                : NEXT_SIDE(aSide);
+  StyleBorderStyle otherStyle = mBorderStyles[otherSide];
+  Float otherBorderWidth = mBorderWidths[otherSide];
+  Size radius = mBorderRadii[aCorner];
+  if (IsZeroSize(radius)) {
+    radius.width = 0.0f;
+    radius.height = 0.0f;
+  }
+  if (style == StyleBorderStyle::Dotted) {
+    // Offset the dot's location along the side toward the corner by a
+    // multiple of its width.
+    if (isHorizontal) {
+      P.x -= signs[0] * aDotOffset * borderWidth;
+    } else {
+      P.y -= signs[1] * aDotOffset * borderWidth;
+    }
+  }
+  if (style == StyleBorderStyle::Dotted &&
+      otherStyle == StyleBorderStyle::Dotted) {
+    if (borderWidth == otherBorderWidth) {
+      if (radius.width < borderWidth / 2.0f &&
+          radius.height < borderWidth / 2.0f) {
+        // Two dots are merged into one and placed at the corner.
+        //
+        //  borderWidth / 2.0
+        // |<---------->|
+        // |            |
+        // |radius.width|
+        // |<--->|      |
+        // |     |      |
+        // |    _+------+------------+-----
+        // |  /      ###|###         |
+        // |/    #######|#######     |
+        // +   #########|#########   |
+        // |  ##########|##########  |
+        // | ###########|########### |
+        // | ###########|########### |
+        // |############|############|
+        // +------------+############|
+        // |########### P ###########|
+        // | ####################### |
+        // | ####################### |
+        // |  #####################  |
+        // |   ###################   |
+        // |     ###############     |
+        // |         #######         |
+        // +-------------------------+----
+        // |                         |
+        // |                         |
+        P.x += signs[0] * borderWidth / 2.0f;
+        P.y += signs[1] * borderWidth / 2.0f;
+      } else {
+        // Two dots are drawn separately.
+        //
+        //    borderWidth * 1.5
+        //   |<------------>|
+        //   |              |
+        //   |radius.width  |
+        //   |<----->|      |
+        //   |       |      |
+        //   |    _--+-+----+---
+        //   |  _-     |  ##|##
+        //   | /       | ###|###
+        //   |/        |####|####
+        //   |         |####+####
+        //   |         |### P ###
+        //   +         | ###|###
+        //   |         |  ##|##
+        //   +---------+----+---
+        //   |  #####  |
+        //   | ####### |
+        //   |#########|
+        //   +----+----+
+        //   |#########|
+        //   | ####### |
+        //   |  #####  |
+        //   |         |
+        //
+        // There should be enough gap between 2 dots even if radius.width is
+        // small but larger than borderWidth / 2.0.  borderWidth * 1.5 is the
+        // value that there's imaginally unfilled dot at the corner.  The
+        // unfilled dot may overflow from the outer curve, but filled dots
+        // doesn't, so this could be acceptable solution at least for now.
+        // We may have to find better model/value.
+        //
+        //    imaginally unfilled dot at the corner
+        //        |
+        //        v    +----+---
+        //      *****  |  ##|##
+        //     ******* | ###|###
+        //    *********|####|####
+        //    *********|####+####
+        //    *********|### P ###
+        //     ******* | ###|###
+        //      *****  |  ##|##
+        //   +---------+----+---
+        //   |  #####  |
+        //   | ####### |
+        //   |#########|
+        //   +----+----+
+        //   |#########|
+        //   | ####### |
+        //   |  #####  |
+        //   |         |
+        Float minimum = borderWidth * 1.5f;
+        if (isHorizontal) {
+          P.x += signs[0] * std::max(radius.width, minimum);
+          P.y += signs[1] * borderWidth / 2.0f;
+        } else {
+          P.x += signs[0] * borderWidth / 2.0f;
+          P.y += signs[1] * std::max(radius.height, minimum);
+        }
+      }
+
+      return P;
+    }
+
+    if (borderWidth < otherBorderWidth) {
+      // This side is smaller than other side, other side draws the corner.
+      //
+      //  otherBorderWidth + borderWidth / 2.0
+      // |<---------->|
+      // |            |
+      // +---------+--+--------
+      // |  #####  | *|*  ###
+      // | ####### |**|**#####
+      // |#########|**+**##+##
+      // |####+####|* P *#####
+      // |#########| ***  ###
+      // | ####### +-----------
+      // |  #####  |  ^
+      // |         |  |
+      // |         | first dot is not filled
+      // |         |
+      //
+      //      radius.width
+      // |<----------------->|
+      // |                   |
+      // |             ___---+-------------
+      // |         __--     #|#       ###
+      // |       _-        ##|##     #####
+      // |     /           ##+##     ##+##
+      // |   /             # P #     #####
+      // |  |               #|#       ###
+      // | |             __--+-------------
+      // ||            _-    ^
+      // ||           /      |
+      // |           /      first dot is filled
+      // |          |
+      // |          |
+      // |  #####  |
+      // | ####### |
+      // |#########|
+      // +----+----+
+      // |#########|
+      // | ####### |
+      // |  #####  |
+      Float minimum = otherBorderWidth + borderWidth / 2.0f;
+      if (isHorizontal) {
+        if (radius.width < minimum) {
+          *aIsUnfilled = true;
+          P.x += signs[0] * minimum;
+        } else {
+          P.x += signs[0] * radius.width;
+        }
+        P.y += signs[1] * borderWidth / 2.0f;
+      } else {
+        P.x += signs[0] * borderWidth / 2.0f;
+        if (radius.height < minimum) {
+          *aIsUnfilled = true;
+          P.y += signs[1] * minimum;
+        } else {
+          P.y += signs[1] * radius.height;
+        }
+      }
+
+      return P;
+    }
+
+    // This side is larger than other side, this side draws the corner.
+    //
+    //  borderWidth / 2.0
+    // |<-->|
+    // |    |
+    // +----+---------------------
+    // |  ##|##           #####
+    // | ###|###         #######
+    // |####|####       #########
+    // |####+####       ####+####
+    // |### P ###       #########
+    // | #######         #######
+    // |  #####           #####
+    // +-----+---------------------
+    // | *** |
+    // |*****|
+    // |**+**| <-- first dot in other side is not filled
+    // |*****|
+    // | *** |
+    // | ### |
+    // |#####|
+    // |##+##|
+    // |#####|
+    // | ### |
+    // |     |
+    if (isHorizontal) {
+      P.x += signs[0] * std::max(radius.width, borderWidth / 2.0f);
+      P.y += signs[1] * borderWidth / 2.0f;
+    } else {
+      P.x += signs[0] * borderWidth / 2.0f;
+      P.y += signs[1] * std::max(radius.height, borderWidth / 2.0f);
+    }
+    return P;
+  }
+
+  if (style == StyleBorderStyle::Dotted) {
+    // If only this side is dotted, other side draws the corner.
+    //
+    //  otherBorderWidth + borderWidth / 2.0
+    // |<------->|
+    // |         |
+    // +------+--+--------
+    // |##  ##| *|*  ###
+    // |##  ##|**|**#####
+    // |##  ##|**+**##+##
+    // |##  ##|* P *#####
+    // |##  ##| ***  ###
+    // |##  ##+-----------
+    // |##  ##|  ^
+    // |##  ##|  |
+    // |##  ##| first dot is not filled
+    // |##  ##|
+    //
+    //      radius.width
+    // |<----------------->|
+    // |                   |
+    // |             ___---+-------------
+    // |         __--     #|#       ###
+    // |       _-        ##|##     #####
+    // |     /           ##+##     ##+##
+    // |   /             # P #     #####
+    // |  |               #|#       ###
+    // | |             __--+-------------
+    // ||            _-    ^
+    // ||          /       |
+    // |         /        first dot is filled
+    // |        |
+    // |       |
+    // |      |
+    // |      |
+    // |      |
+    // +------+
+    // |##  ##|
+    // |##  ##|
+    // |##  ##|
+    Float minimum = otherBorderWidth + borderWidth / 2.0f;
+    if (isHorizontal) {
+      if (radius.width < minimum) {
+        *aIsUnfilled = true;
+        P.x += signs[0] * minimum;
+      } else {
+        P.x += signs[0] * radius.width;
+      }
+      P.y += signs[1] * borderWidth / 2.0f;
+    } else {
+      P.x += signs[0] * borderWidth / 2.0f;
+      if (radius.height < minimum) {
+        *aIsUnfilled = true;
+        P.y += signs[1] * minimum;
+      } else {
+        P.y += signs[1] * radius.height;
+      }
+    }
+    return P;
+  }
+
+  if (otherStyle == StyleBorderStyle::Dotted && IsZeroSize(radius)) {
+    // If other side is dotted and radius=0, draw side to the end of corner.
+    //
+    //   +-------------------------------
+    //   |##########          ##########
+    // P +##########          ##########
+    //   |##########          ##########
+    //   +-----+-------------------------
+    //   | *** |
+    //   |*****|
+    //   |**+**| <-- first dot in other side is not filled
+    //   |*****|
+    //   | *** |
+    //   | ### |
+    //   |#####|
+    //   |##+##|
+    //   |#####|
+    //   | ### |
+    //   |     |
+    if (isHorizontal) {
+      P.y += signs[1] * borderWidth / 2.0f;
+    } else {
+      P.x += signs[0] * borderWidth / 2.0f;
+    }
+    return P;
+  }
+
+  // Other cases.
+  //
+  //  dim.width
+  // |<----------------->|
+  // |                   |
+  // |             ___---+------------------
+  // |         __--      |#######        ###
+  // |       _-        P +#######        ###
+  // |     /             |#######        ###
+  // |   /          __---+------------------
+  // |  |       __--
+  // | |       /
+  // ||      /
+  // ||     |
+  // |     |
+  // |    |
+  // |   |
+  // |   |
+  // +-+-+
+  // |###|
+  // |###|
+  // |###|
+  // |###|
+  // |###|
+  // |   |
+  // |   |
+  if (isHorizontal) {
+    P.x += signs[0] * dim.width;
+    P.y += signs[1] * borderWidth / 2.0f;
+  } else {
+    P.x += signs[0] * borderWidth / 2.0f;
+    P.y += signs[1] * dim.height;
+  }
+
+  return P;
+}
+
+void nsCSSBorderRenderer::GetOuterAndInnerBezier(Bezier* aOuterBezier,
+                                                 Bezier* aInnerBezier,
+                                                 Corner aCorner) {
+  // Return bezier control points for outer and inner curve for given corner.
+  //
+  //               ___---+ outer curve
+  //           __--      |
+  //         _-          |
+  //       /             |
+  //     /               |
+  //    |                |
+  //   |             __--+ inner curve
+  //  |            _-
+  //  |           /
+  // |           /
+  // |          |
+  // |          |
+  // |         |
+  // |         |
+  // |         |
+  // +---------+
+
+  mozilla::Side sideH(GetHorizontalSide(aCorner));
+  mozilla::Side sideV(GetVerticalSide(aCorner));
+
+  Size outerCornerSize(ceil(mBorderRadii[aCorner].width),
+                       ceil(mBorderRadii[aCorner].height));
+  Size innerCornerSize(
+      ceil(std::max(0.0f, mBorderRadii[aCorner].width - mBorderWidths[sideV])),
+      ceil(
+          std::max(0.0f, mBorderRadii[aCorner].height - mBorderWidths[sideH])));
+
+  GetBezierPointsForCorner(aOuterBezier, aCorner, mOuterRect.AtCorner(aCorner),
+                           outerCornerSize);
+
+  GetBezierPointsForCorner(aInnerBezier, aCorner, mInnerRect.AtCorner(aCorner),
+                           innerCornerSize);
+}
+
+void nsCSSBorderRenderer::FillSolidBorder(const Rect& aOuterRect,
+                                          const Rect& aInnerRect,
+                                          const RectCornerRadii& aBorderRadii,
+                                          const Float* aBorderSizes,
+                                          SideBits aSides,
+                                          const ColorPattern& aColor) {
+  // Note that this function is allowed to draw more than just the
+  // requested sides.
+
+  // If we have a border radius, do full rounded rectangles
+  // and fill, regardless of what sides we're asked to draw.
+  if (!AllCornersZeroSize(aBorderRadii)) {
+    RefPtr<PathBuilder> builder = mDrawTarget->CreatePathBuilder();
+
+    RectCornerRadii innerRadii;
+    ComputeInnerRadii(aBorderRadii, aBorderSizes, &innerRadii);
+
+    // do the outer border
+    AppendRoundedRectToPath(builder, aOuterRect, aBorderRadii, true);
+
+    // then do the inner border CCW
+    AppendRoundedRectToPath(builder, aInnerRect, innerRadii, false);
+
+    RefPtr<Path> path = builder->Finish();
+
+    mDrawTarget->Fill(path, aColor);
+    return;
+  }
+
+  // If we're asked to draw all sides of an equal-sized border,
+  // stroking is fastest.  This is a fairly common path, but partial
+  // sides is probably second in the list -- there are a bunch of
+  // common border styles, such as inset and outset, that are
+  // top-left/bottom-right split.
+  if (aSides == SideBits::eAll &&
+      CheckFourFloatsEqual(aBorderSizes, aBorderSizes[0]) && !mAvoidStroke) {
+    Float strokeWidth = aBorderSizes[0];
+    Rect r(aOuterRect);
+    r.Deflate(strokeWidth / 2.f);
+    mDrawTarget->StrokeRect(r, aColor, StrokeOptions(strokeWidth));
+    return;
+  }
+
+  // Otherwise, we have unequal sized borders or we're only
+  // drawing some sides; create rectangles for each side
+  // and fill them.
+
+  Rect r[4];
+
+  // compute base rects for each side
+  if (aSides & SideBits::eTop) {
+    r[eSideTop] = Rect(aOuterRect.X(), aOuterRect.Y(), aOuterRect.Width(),
+                       aBorderSizes[eSideTop]);
+  }
+
+  if (aSides & SideBits::eBottom) {
+    r[eSideBottom] =
+        Rect(aOuterRect.X(), aOuterRect.YMost() - aBorderSizes[eSideBottom],
+             aOuterRect.Width(), aBorderSizes[eSideBottom]);
+  }
+
+  if (aSides & SideBits::eLeft) {
+    r[eSideLeft] = Rect(aOuterRect.X(), aOuterRect.Y(), aBorderSizes[eSideLeft],
+                        aOuterRect.Height());
+  }
+
+  if (aSides & SideBits::eRight) {
+    r[eSideRight] =
+        Rect(aOuterRect.XMost() - aBorderSizes[eSideRight], aOuterRect.Y(),
+             aBorderSizes[eSideRight], aOuterRect.Height());
+  }
+
+  // If two sides meet at a corner that we're rendering, then
+  // make sure that we adjust one of the sides to avoid overlap.
+  // This is especially important in the case of colors with
+  // an alpha channel.
+
+  if ((aSides & (SideBits::eTop | SideBits::eLeft)) ==
+      (SideBits::eTop | SideBits::eLeft)) {
+    // adjust the left's top down a bit
+    r[eSideLeft].y += aBorderSizes[eSideTop];
+    r[eSideLeft].height -= aBorderSizes[eSideTop];
+  }
+
+  if ((aSides & (SideBits::eTop | SideBits::eRight)) ==
+      (SideBits::eTop | SideBits::eRight)) {
+    // adjust the top's left a bit
+    r[eSideTop].width -= aBorderSizes[eSideRight];
+  }
+
+  if ((aSides & (SideBits::eBottom | SideBits::eRight)) ==
+      (SideBits::eBottom | SideBits::eRight)) {
+    // adjust the right's bottom a bit
+    r[eSideRight].height -= aBorderSizes[eSideBottom];
+  }
+
+  if ((aSides & (SideBits::eBottom | SideBits::eLeft)) ==
+      (SideBits::eBottom | SideBits::eLeft)) {
+    // adjust the bottom's left a bit
+    r[eSideBottom].x += aBorderSizes[eSideLeft];
+    r[eSideBottom].width -= aBorderSizes[eSideLeft];
+  }
+
+  // Filling these one by one is faster than filling them all at once.
+  for (uint32_t i = 0; i < 4; i++) {
+    if (aSides & static_cast<mozilla::SideBits>(1 << i)) {
+      MaybeSnapToDevicePixels(r[i], *mDrawTarget, true);
+      mDrawTarget->FillRect(r[i], aColor);
+    }
+  }
+}
+
+sRGBColor MakeBorderColor(nscolor aColor, BorderColorStyle aBorderColorStyle) {
+  nscolor colors[2];
+  int k = 0;
+
+  switch (aBorderColorStyle) {
+    case BorderColorStyleNone:
+      return sRGBColor(0.f, 0.f, 0.f, 0.f);  // transparent black
+
+    case BorderColorStyleLight:
+      k = 1;
+      [[fallthrough]];
+    case BorderColorStyleDark:
+      NS_GetSpecial3DColors(colors, aColor);
+      return sRGBColor::FromABGR(colors[k]);
+
+    case BorderColorStyleSolid:
+    default:
+      return sRGBColor::FromABGR(aColor);
+  }
+}
+
+sRGBColor ComputeColorForLine(uint32_t aLineIndex,
+                              const BorderColorStyle* aBorderColorStyle,
+                              uint32_t aBorderColorStyleCount,
+                              nscolor aBorderColor) {
+  NS_ASSERTION(aLineIndex < aBorderColorStyleCount, "Invalid lineIndex given");
+
+  return MakeBorderColor(aBorderColor, aBorderColorStyle[aLineIndex]);
+}
+
+void nsCSSBorderRenderer::DrawBorderSides(mozilla::SideBits aSides) {
+  if (aSides == SideBits::eNone ||
+      (aSides & ~SideBits::eAll) != SideBits::eNone) {
+    NS_WARNING("DrawBorderSides: invalid sides!");
+    return;
+  }
+
+  StyleBorderStyle borderRenderStyle = StyleBorderStyle::None;
+  nscolor borderRenderColor;
+
+  uint32_t borderColorStyleCount = 0;
+  BorderColorStyle borderColorStyleTopLeft[3], borderColorStyleBottomRight[3];
+  BorderColorStyle* borderColorStyle = nullptr;
+
+  for (const auto i : mozilla::AllPhysicalSides()) {
+    if ((aSides & static_cast<mozilla::SideBits>(1 << i)) == SideBits::eNone) {
+      continue;
+    }
+    borderRenderStyle = mBorderStyles[i];
+    borderRenderColor = mBorderColors[i];
+    break;
+  }
+
+  if (borderRenderStyle == StyleBorderStyle::None ||
+      borderRenderStyle == StyleBorderStyle::Hidden) {
+    return;
+  }
+
+  if (borderRenderStyle == StyleBorderStyle::Dashed ||
+      borderRenderStyle == StyleBorderStyle::Dotted) {
+    // Draw each corner separately, with the given side's color.
+    if (aSides & SideBits::eTop) {
+      DrawDashedOrDottedCorner(eSideTop, C_TL);
+    } else if (aSides & SideBits::eLeft) {
+      DrawDashedOrDottedCorner(eSideLeft, C_TL);
+    }
+
+    if (aSides & SideBits::eTop) {
+      DrawDashedOrDottedCorner(eSideTop, C_TR);
+    } else if (aSides & SideBits::eRight) {
+      DrawDashedOrDottedCorner(eSideRight, C_TR);
+    }
+
+    if (aSides & SideBits::eBottom) {
+      DrawDashedOrDottedCorner(eSideBottom, C_BL);
+    } else if (aSides & SideBits::eLeft) {
+      DrawDashedOrDottedCorner(eSideLeft, C_BL);
+    }
+
+    if (aSides & SideBits::eBottom) {
+      DrawDashedOrDottedCorner(eSideBottom, C_BR);
+    } else if (aSides & SideBits::eRight) {
+      DrawDashedOrDottedCorner(eSideRight, C_BR);
+    }
+    return;
+  }
+
+  // The borderColorStyle array goes from the outer to the inner style.
+  //
+  // If the border width is 1, we need to change the borderRenderStyle
+  // a bit to make sure that we get the right colors -- e.g. 'ridge'
+  // with a 1px border needs to look like solid, not like 'outset'.
+  if (mOneUnitBorder && (borderRenderStyle == StyleBorderStyle::Ridge ||
+                         borderRenderStyle == StyleBorderStyle::Groove ||
+                         borderRenderStyle == StyleBorderStyle::Double)) {
+    borderRenderStyle = StyleBorderStyle::Solid;
+  }
+
+  switch (borderRenderStyle) {
+    case StyleBorderStyle::Solid:
+      borderColorStyleTopLeft[0] = BorderColorStyleSolid;
+
+      borderColorStyleBottomRight[0] = BorderColorStyleSolid;
+
+      borderColorStyleCount = 1;
+      break;
+
+    case StyleBorderStyle::Groove:
+      borderColorStyleTopLeft[0] = BorderColorStyleDark;
+      borderColorStyleTopLeft[1] = BorderColorStyleLight;
+
+      borderColorStyleBottomRight[0] = BorderColorStyleLight;
+      borderColorStyleBottomRight[1] = BorderColorStyleDark;
+
+      borderColorStyleCount = 2;
+      break;
+
+    case StyleBorderStyle::Ridge:
+      borderColorStyleTopLeft[0] = BorderColorStyleLight;
+      borderColorStyleTopLeft[1] = BorderColorStyleDark;
+
+      borderColorStyleBottomRight[0] = BorderColorStyleDark;
+      borderColorStyleBottomRight[1] = BorderColorStyleLight;
+
+      borderColorStyleCount = 2;
+      break;
+
+    case StyleBorderStyle::Double:
+      borderColorStyleTopLeft[0] = BorderColorStyleSolid;
+      borderColorStyleTopLeft[1] = BorderColorStyleNone;
+      borderColorStyleTopLeft[2] = BorderColorStyleSolid;
+
+      borderColorStyleBottomRight[0] = BorderColorStyleSolid;
+      borderColorStyleBottomRight[1] = BorderColorStyleNone;
+      borderColorStyleBottomRight[2] = BorderColorStyleSolid;
+
+      borderColorStyleCount = 3;
+      break;
+
+    case StyleBorderStyle::Inset:
+      borderColorStyleTopLeft[0] = BorderColorStyleDark;
+      borderColorStyleBottomRight[0] = BorderColorStyleLight;
+
+      borderColorStyleCount = 1;
+      break;
+
+    case StyleBorderStyle::Outset:
+      borderColorStyleTopLeft[0] = BorderColorStyleLight;
+      borderColorStyleBottomRight[0] = BorderColorStyleDark;
+
+      borderColorStyleCount = 1;
+      break;
+
+    default:
+      MOZ_ASSERT_UNREACHABLE("Unhandled border style!!");
+      break;
+  }
+
+  // The only way to get to here is by having a
+  // borderColorStyleCount < 1 or > 3; this should never happen,
+  // since -moz-border-colors doesn't get handled here.
+  NS_ASSERTION(borderColorStyleCount > 0 && borderColorStyleCount < 4,
+               "Non-border-colors case with borderColorStyleCount < 1 or > 3; "
+               "what happened?");
+
+  // The caller should never give us anything with a mix
+  // of TL/BR if the border style would require a
+  // TL/BR split.
+  if (aSides & (SideBits::eBottom | SideBits::eRight)) {
+    borderColorStyle = borderColorStyleBottomRight;
+  } else {
+    borderColorStyle = borderColorStyleTopLeft;
+  }
+
+  // Distribute the border across the available space.
+  Float borderWidths[3][4];
+
+  if (borderColorStyleCount == 1) {
+    for (const auto i : mozilla::AllPhysicalSides()) {
+      borderWidths[0][i] = mBorderWidths[i];
+    }
+  } else if (borderColorStyleCount == 2) {
+    // with 2 color styles, any extra pixel goes to the outside
+    for (const auto i : mozilla::AllPhysicalSides()) {
+      borderWidths[0][i] =
+          int32_t(mBorderWidths[i]) / 2 + int32_t(mBorderWidths[i]) % 2;
+      borderWidths[1][i] = int32_t(mBorderWidths[i]) / 2;
+    }
+  } else if (borderColorStyleCount == 3) {
+    // with 3 color styles, any extra pixel (or lack of extra pixel)
+    // goes to the middle
+    for (const auto i : mozilla::AllPhysicalSides()) {
+      if (mBorderWidths[i] == 1.0) {
+        borderWidths[0][i] = 1.f;
+        borderWidths[1][i] = borderWidths[2][i] = 0.f;
+      } else {
+        int32_t rest = int32_t(mBorderWidths[i]) % 3;
+        borderWidths[0][i] = borderWidths[2][i] = borderWidths[1][i] =
+            (int32_t(mBorderWidths[i]) - rest) / 3;
+
+        if (rest == 1) {
+          borderWidths[1][i] += 1.f;
+        } else if (rest == 2) {
+          borderWidths[0][i] += 1.f;
+          borderWidths[2][i] += 1.f;
+        }
+      }
+    }
+  }
+
+  // make a copy that we can modify
+  RectCornerRadii radii = mBorderRadii;
+
+  Rect soRect(mOuterRect);
+  Rect siRect(mOuterRect);
+
+  // If adjacent side is dotted and radius=0, draw side to the end of corner.
+  //
+  // +--------------------------------
+  // |################################
+  // |
+  // |################################
+  // +-----+--------------------------
+  // |     |
+  // |     |
+  // |     |
+  // |     |
+  // |     |
+  // | ### |
+  // |#####|
+  // |#####|
+  // |#####|
+  // | ### |
+  // |     |
+  bool noMarginTop = false;
+  bool noMarginRight = false;
+  bool noMarginBottom = false;
+  bool noMarginLeft = false;
+
+  // If there is at least one dotted side, every side is rendered separately.
+  if (IsSingleSide(aSides)) {
+    if (aSides == SideBits::eTop) {
+      if (mBorderStyles[eSideRight] == StyleBorderStyle::Dotted &&
+          IsZeroSize(mBorderRadii[C_TR])) {
+        noMarginRight = true;
+      }
+      if (mBorderStyles[eSideLeft] == StyleBorderStyle::Dotted &&
+          IsZeroSize(mBorderRadii[C_TL])) {
+        noMarginLeft = true;
+      }
+    } else if (aSides == SideBits::eRight) {
+      if (mBorderStyles[eSideTop] == StyleBorderStyle::Dotted &&
+          IsZeroSize(mBorderRadii[C_TR])) {
+        noMarginTop = true;
+      }
+      if (mBorderStyles[eSideBottom] == StyleBorderStyle::Dotted &&
+          IsZeroSize(mBorderRadii[C_BR])) {
+        noMarginBottom = true;
+      }
+    } else if (aSides == SideBits::eBottom) {
+      if (mBorderStyles[eSideRight] == StyleBorderStyle::Dotted &&
+          IsZeroSize(mBorderRadii[C_BR])) {
+        noMarginRight = true;
+      }
+      if (mBorderStyles[eSideLeft] == StyleBorderStyle::Dotted &&
+          IsZeroSize(mBorderRadii[C_BL])) {
+        noMarginLeft = true;
+      }
+    } else {
+      if (mBorderStyles[eSideTop] == StyleBorderStyle::Dotted &&
+          IsZeroSize(mBorderRadii[C_TL])) {
+        noMarginTop = true;
+      }
+      if (mBorderStyles[eSideBottom] == StyleBorderStyle::Dotted &&
+          IsZeroSize(mBorderRadii[C_BL])) {
+        noMarginBottom = true;
+      }
+    }
+  }
+
+  for (unsigned int i = 0; i < borderColorStyleCount; i++) {
+    // walk siRect inwards at the start of the loop to get the
+    // correct inner rect.
+    //
+    // If noMarginTop is false:
+    //   --------------------+
+    //                      /|
+    //                     / |
+    //                    L  |
+    //   ----------------+   |
+    //                   |   |
+    //                   |   |
+    //
+    // If noMarginTop is true:
+    //   ----------------+<--+
+    //                   |   |
+    //                   |   |
+    //                   |   |
+    //                   |   |
+    //                   |   |
+    //                   |   |
+    siRect.Deflate(Margin(noMarginTop ? 0 : borderWidths[i][0],
+                          noMarginRight ? 0 : borderWidths[i][1],
+                          noMarginBottom ? 0 : borderWidths[i][2],
+                          noMarginLeft ? 0 : borderWidths[i][3]));
+
+    if (borderColorStyle[i] != BorderColorStyleNone) {
+      sRGBColor c = ComputeColorForLine(
+          i, borderColorStyle, borderColorStyleCount, borderRenderColor);
+      ColorPattern color(ToDeviceColor(c));
+
+      FillSolidBorder(soRect, siRect, radii, borderWidths[i], aSides, color);
+    }
+
+    ComputeInnerRadii(radii, borderWidths[i], &radii);
+
+    // And now soRect is the same as siRect, for the next line in.
+    soRect = siRect;
+  }
+}
+
+void nsCSSBorderRenderer::SetupDashedOptions(StrokeOptions* aStrokeOptions,
+                                             Float aDash[2],
+                                             mozilla::Side aSide,
+                                             Float aBorderLength,
+                                             bool isCorner) {
+  MOZ_ASSERT(mBorderStyles[aSide] == StyleBorderStyle::Dashed ||
+                 mBorderStyles[aSide] == StyleBorderStyle::Dotted,
+             "Style should be dashed or dotted.");
+
+  StyleBorderStyle style = mBorderStyles[aSide];
+  Float borderWidth = mBorderWidths[aSide];
+
+  // Dashed line starts and ends with half segment in most case.
+  //
+  // __--+---+---+---+---+---+---+---+---+--__
+  //     |###|   |   |###|###|   |   |###|
+  //     |###|   |   |###|###|   |   |###|
+  //     |###|   |   |###|###|   |   |###|
+  // __--+---+---+---+---+---+---+---+---+--__
+  //
+  // If radius=0 and other side is either dotted or 0-width, it starts or ends
+  // with full segment.
+  //
+  // +---+---+---+---+---+---+---+---+---+---+
+  // |###|###|   |   |###|###|   |   |###|###|
+  // |###|###|   |   |###|###|   |   |###|###|
+  // |###|###|   |   |###|###|   |   |###|###|
+  // +---++--+---+---+---+---+---+---+--++---+
+  // |    |                             |    |
+  // |    |                             |    |
+  // |    |                             |    |
+  // |    |                             |    |
+  // | ## |                             | ## |
+  // |####|                             |####|
+  // |####|                             |####|
+  // | ## |                             | ## |
+  // |    |                             |    |
+  bool fullStart = false, fullEnd = false;
+  Float halfDash;
+  if (style == StyleBorderStyle::Dashed) {
+    // If either end of the side is not connecting onto a corner then we want a
+    // full dash at that end.
+    //
+    // Note that in the case that a corner is empty, either the adjacent side
+    // has zero width, or else DrawBorders() set the corner to be empty
+    // (it does that if the adjacent side has zero length and the border widths
+    // of this and the adjacent sides are thin enough that the corner will be
+    // insignificantly small).
+
+    if (mBorderRadii[GetCCWCorner(aSide)].IsEmpty() &&
+        (mBorderCornerDimensions[GetCCWCorner(aSide)].IsEmpty() ||
+         mBorderStyles[PREV_SIDE(aSide)] == StyleBorderStyle::Dotted ||
+         // XXX why this <=1 check?
+         borderWidth <= 1.0f)) {
+      fullStart = true;
+    }
+
+    if (mBorderRadii[GetCWCorner(aSide)].IsEmpty() &&
+        (mBorderCornerDimensions[GetCWCorner(aSide)].IsEmpty() ||
+         mBorderStyles[NEXT_SIDE(aSide)] == StyleBorderStyle::Dotted)) {
+      fullEnd = true;
+    }
+
+    halfDash = borderWidth * DOT_LENGTH * DASH_LENGTH / 2.0f;
+  } else {
+    halfDash = borderWidth * DOT_LENGTH / 2.0f;
+  }
+
+  if (style == StyleBorderStyle::Dashed && aBorderLength > 0.0f) {
+    // The number of half segments, with maximum dash length.
+    int32_t count = floor(aBorderLength / halfDash);
+    Float minHalfDash = borderWidth * DOT_LENGTH / 2.0f;
+
+    if (fullStart && fullEnd) {
+      // count should be 4n + 2
+      //
+      //   1 +       4       +        4      + 1
+      //
+      // |   |               |               |   |
+      // +---+---+---+---+---+---+---+---+---+---+
+      // |###|###|   |   |###|###|   |   |###|###|
+      // |###|###|   |   |###|###|   |   |###|###|
+      // |###|###|   |   |###|###|   |   |###|###|
+      // +---+---+---+---+---+---+---+---+---+---+
+
+      // If border is too short, draw solid line.
+      if (aBorderLength < 6.0f * minHalfDash) {
+        return;
+      }
+
+      if (count % 4 == 0) {
+        count += 2;
+      } else if (count % 4 == 1) {
+        count += 1;
+      } else if (count % 4 == 3) {
+        count += 3;
+      }
+    } else if (fullStart || fullEnd) {
+      // count should be 4n + 1
+      //
+      //   1 +       4       +        4
+      //
+      // |   |               |               |
+      // +---+---+---+---+---+---+---+---+---+
+      // |###|###|   |   |###|###|   |   |###|
+      // |###|###|   |   |###|###|   |   |###|
+      // |###|###|   |   |###|###|   |   |###|
+      // +---+---+---+---+---+---+---+---+---+
+      //
+      //         4       +        4      + 1
+      //
+      // |               |               |   |
+      // +---+---+---+---+---+---+---+---+---+
+      // |###|   |   |###|###|   |   |###|###|
+      // |###|   |   |###|###|   |   |###|###|
+      // |###|   |   |###|###|   |   |###|###|
+      // +---+---+---+---+---+---+---+---+---+
+
+      // If border is too short, draw solid line.
+      if (aBorderLength < 5.0f * minHalfDash) {
+        return;
+      }
+
+      if (count % 4 == 0) {
+        count += 1;
+      } else if (count % 4 == 2) {
+        count += 3;
+      } else if (count % 4 == 3) {
+        count += 2;
+      }
+    } else {
+      // count should be 4n
+      //
+      //         4       +        4
+      //
+      // |               |               |
+      // +---+---+---+---+---+---+---+---+
+      // |###|   |   |###|###|   |   |###|
+      // |###|   |   |###|###|   |   |###|
+      // |###|   |   |###|###|   |   |###|
+      // +---+---+---+---+---+---+---+---+
+
+      // If border is too short, draw solid line.
+      if (aBorderLength < 4.0f * minHalfDash) {
+        return;
+      }
+
+      if (count % 4 == 1) {
+        count += 3;
+      } else if (count % 4 == 2) {
+        count += 2;
+      } else if (count % 4 == 3) {
+        count += 1;
+      }
+    }
+    halfDash = aBorderLength / count;
+  }
+
+  Float fullDash = halfDash * 2.0f;
+
+  aDash[0] = fullDash;
+  aDash[1] = fullDash;
+
+  if (style == StyleBorderStyle::Dashed && fullDash > 1.0f) {
+    if (!fullStart) {
+      // Draw half segments on both ends.
+      aStrokeOptions->mDashOffset = halfDash;
+    }
+  } else if (style != StyleBorderStyle::Dotted && isCorner) {
+    // If side ends with filled full segment, corner should start with unfilled
+    // full segment. Not needed for dotted corners, as they overlap one dot with
+    // the side's end.
+    //
+    //     corner            side
+    //   ------------>|<---------------------------
+    //                |
+    //          __+---+---+---+---+---+---+---+---+
+    //       _+-  |   |###|###|   |   |###|###|   |
+    //     /##|   |   |###|###|   |   |###|###|   |
+    //    +####|   |  |###|###|   |   |###|###|   |
+    //   /#\####| _+--+---+---+---+---+---+---+---+
+    //  |####\##+-
+    //  |#####+-
+    //  +--###/
+    //  |  --+
+    aStrokeOptions->mDashOffset = fullDash;
+  }
+
+  aStrokeOptions->mDashPattern = aDash;
+  aStrokeOptions->mDashLength = 2;
+
+  PrintAsFormatString("dash: %f %f\n", aDash[0], aDash[1]);
+}
+
+static Float GetBorderLength(mozilla::Side aSide, const Point& aStart,
+                             const Point& aEnd) {
+  if (aSide == eSideTop) {
+    return aEnd.x - aStart.x;
+  }
+  if (aSide == eSideRight) {
+    return aEnd.y - aStart.y;
+  }
+  if (aSide == eSideBottom) {
+    return aStart.x - aEnd.x;
+  }
+  return aStart.y - aEnd.y;
+}
+
+void nsCSSBorderRenderer::DrawDashedOrDottedSide(mozilla::Side aSide) {
+  // Draw dashed/dotted side with following approach.
+  //
+  // dashed side
+  //   Draw dashed line along the side, with appropriate dash length and gap
+  //   to make the side symmetric as far as possible.  Dash length equals to
+  //   the gap, and the ratio of the dash length to border-width is the maximum
+  //   value in in [1, 3] range.
+  //   In most case, line ends with half segment, to joint with corner easily.
+  //   If adjacent side is dotted or 0px and border-radius for the corner
+  //   between them is 0, the line ends with full segment.
+  //   (see comment for GetStraightBorderPoint for more detail)
+  //
+  // dotted side
+  //   If border-width <= 2.0, draw 1:1 dashed line.
+  //   Otherwise, draw circles along the side, with appropriate gap that makes
+  //   the side symmetric as far as possible.  The ratio of the gap to
+  //   border-width is the maximum value in [0.5, 1] range in most case.
+  //   if the side is too short and there's only 2 dots, it can be more smaller.
+  //   If there's no space to place 2 dots at the side, draw single dot at the
+  //   middle of the side.
+  //   In most case, line ends with filled dot, to joint with corner easily,
+  //   If adjacent side is dotted with larger border-width, or other style,
+  //   the line ends with unfilled dot.
+  //   (see comment for GetStraightBorderPoint for more detail)
+
+  NS_ASSERTION(mBorderStyles[aSide] == StyleBorderStyle::Dashed ||
+                   mBorderStyles[aSide] == StyleBorderStyle::Dotted,
+               "Style should be dashed or dotted.");
+
+  Float borderWidth = mBorderWidths[aSide];
+  if (borderWidth == 0.0f) {
+    return;
+  }
+
+  if (mBorderStyles[aSide] == StyleBorderStyle::Dotted && borderWidth > 2.0f) {
+    DrawDottedSideSlow(aSide);
+    return;
+  }
+
+  nscolor borderColor = mBorderColors[aSide];
+  bool ignored;
+  // Get the start and end points of the side, ensuring that any dot origins get
+  // pushed outward to account for stroking.
+  Point start =
+      GetStraightBorderPoint(aSide, GetCCWCorner(aSide), &ignored, 0.5f);
+  Point end = GetStraightBorderPoint(aSide, GetCWCorner(aSide), &ignored, 0.5f);
+  if (borderWidth < 2.0f) {
+    // Round start to draw dot on each pixel.
+    if (IsHorizontalSide(aSide)) {
+      start.x = round(start.x);
+    } else {
+      start.y = round(start.y);
+    }
+  }
+
+  Float borderLength = GetBorderLength(aSide, start, end);
+  if (borderLength < 0.0f) {
+    return;
+  }
+
+  StrokeOptions strokeOptions(borderWidth);
+  Float dash[2];
+  SetupDashedOptions(&strokeOptions, dash, aSide, borderLength, false);
+
+  // For dotted sides that can merge with their prior dotted sides, advance the
+  // dash offset to measure the distance around the combined path. This prevents
+  // two dots from bunching together at a corner.
+  mozilla::Side mergeSide = aSide;
+  while (IsCornerMergeable(GetCCWCorner(mergeSide))) {
+    mergeSide = PREV_SIDE(mergeSide);
+    // If we looped all the way around, measure starting at the top side, since
+    // we need to pick a fixed location to start measuring distance from still.
+    if (mergeSide == aSide) {
+      mergeSide = eSideTop;
+      break;
+    }
+  }
+  while (mergeSide != aSide) {
+    // Measure the length of the merged side starting from a possibly
+    // unmergeable corner up to the merged corner. A merged corner effectively
+    // has no border radius, so we can just use the cheaper AtCorner to find the
+    // end point.
+    Float mergeLength =
+        GetBorderLength(mergeSide,
+                        GetStraightBorderPoint(
+                            mergeSide, GetCCWCorner(mergeSide), &ignored, 0.5f),
+                        mOuterRect.AtCorner(GetCWCorner(mergeSide)));
+    // Add in the merged side length. Also offset the dash progress by an extra
+    // dot's width to avoid drawing a dot that would overdraw where the merged
+    // side would have ended in a gap, i.e. O_O_
+    //                                    O
+    strokeOptions.mDashOffset += mergeLength + borderWidth;
+    mergeSide = NEXT_SIDE(mergeSide);
+  }
+
+  DrawOptions drawOptions;
+  if (mBorderStyles[aSide] == StyleBorderStyle::Dotted) {
+    drawOptions.mAntialiasMode = AntialiasMode::NONE;
+  }
+
+  mDrawTarget->StrokeLine(start, end, ColorPattern(ToDeviceColor(borderColor)),
+                          strokeOptions, drawOptions);
+}
+
+void nsCSSBorderRenderer::DrawDottedSideSlow(mozilla::Side aSide) {
+  // Draw each circles separately for dotted with borderWidth > 2.0.
+  // Dashed line with CapStyle::ROUND doesn't render perfect circles.
+
+  NS_ASSERTION(mBorderStyles[aSide] == StyleBorderStyle::Dotted,
+               "Style should be dotted.");
+
+  Float borderWidth = mBorderWidths[aSide];
+  if (borderWidth == 0.0f) {
+    return;
+  }
+
+  nscolor borderColor = mBorderColors[aSide];
+  bool isStartUnfilled, isEndUnfilled;
+  Point start =
+      GetStraightBorderPoint(aSide, GetCCWCorner(aSide), &isStartUnfilled);
+  Point end = GetStraightBorderPoint(aSide, GetCWCorner(aSide), &isEndUnfilled);
+  enum {
+    // Corner is not mergeable.
+    NO_MERGE,
+
+    // Corner between different colors.
+    // Two dots are merged into one, and both side draw half dot.
+    MERGE_HALF,
+
+    // Corner between same colors, CCW corner of the side.
+    // Two dots are merged into one, and this side draw entire dot.
+    //
+    // MERGE_ALL               MERGE_NONE
+    //   |                       |
+    //   v                       v
+    // +-----------------------+----+
+    // | ##      ##      ##    | ## |
+    // |####    ####    ####   |####|
+    // |####    ####    ####   |####|
+    // | ##      ##      ##    | ## |
+    // +----+------------------+    |
+    // |    |                  |    |
+    // |    |                  |    |
+    // |    |                  |    |
+    // | ## |                  | ## |
+    // |####|                  |####|
+    MERGE_ALL,
+
+    // Corner between same colors, CW corner of the side.
+    // Two dots are merged into one, and this side doesn't draw dot.
+    MERGE_NONE
+  } mergeStart = NO_MERGE,
+    mergeEnd = NO_MERGE;
+
+  if (IsCornerMergeable(GetCCWCorner(aSide))) {
+    if (borderColor == mBorderColors[PREV_SIDE(aSide)]) {
+      mergeStart = MERGE_ALL;
+    } else {
+      mergeStart = MERGE_HALF;
+    }
+  }
+
+  if (IsCornerMergeable(GetCWCorner(aSide))) {
+    if (borderColor == mBorderColors[NEXT_SIDE(aSide)]) {
+      mergeEnd = MERGE_NONE;
+    } else {
+      mergeEnd = MERGE_HALF;
+    }
+  }
+
+  Float borderLength = GetBorderLength(aSide, start, end);
+  if (borderLength < 0.0f) {
+    if (isStartUnfilled || isEndUnfilled) {
+      return;
+    }
+    borderLength = 0.0f;
+    start = end = (start + end) / 2.0f;
+  }
+
+  Float dotWidth = borderWidth * DOT_LENGTH;
+  Float radius = borderWidth / 2.0f;
+  if (borderLength < dotWidth) {
+    // If dots on start and end may overlap, draw a dot at the middle of them.
+    //
+    //     ___---+-------+---___
+    // __--      | ##### |      --__
+    //          #|#######|#
+    //         ##|#######|##
+    //        ###|#######|###
+    //        ###+###+###+###
+    //         start ## end #
+    //         ##|#######|##
+    //          #|#######|#
+    //           | ##### |
+    //       __--+-------+--__
+    //     _-                 -_
+    //
+    // If that circle overflows from outer rect, do not draw it.
+    //
+    //           +-------+
+    //           | ##### |
+    //          #|#######|#
+    //         ##|#######|##
+    //        ###|#######|###
+    //        ###|###+###|###
+    //        ###|#######|###
+    //         ##|#######|##
+    //          #|#######|#
+    //           | ##### |
+    //           +--+-+--+
+    //           |  | |  |
+    //           |  | |  |
+    if (!mOuterRect.Contains(Rect(start.x - radius, start.y - radius,
+                                  borderWidth, borderWidth))) {
+      return;
+    }
+
+    if (isStartUnfilled || isEndUnfilled) {
+      return;
+    }
+
+    Point P = (start + end) / 2;
+    RefPtr<PathBuilder> builder = mDrawTarget->CreatePathBuilder();
+    builder->MoveTo(Point(P.x + radius, P.y));
+    builder->Arc(P, radius, 0.0f, Float(2.0 * M_PI));
+    RefPtr<Path> path = builder->Finish();
+    mDrawTarget->Fill(path, ColorPattern(ToDeviceColor(borderColor)));
+    return;
+  }
+
+  if (mergeStart == MERGE_HALF || mergeEnd == MERGE_HALF) {
+    // MERGE_HALF
+    //               Eo
+    //   -------+----+
+    //        ##### /
+    //       ######/
+    //      ######/
+    //      ####+
+    //      ##/ end
+    //       /
+    //      /
+    //   --+
+    //     Ei
+    //
+    // other (NO_MERGE, MERGE_ALL, MERGE_NONE)
+    //               Eo
+    //   ------------+
+    //        #####  |
+    //       ####### |
+    //      #########|
+    //      ####+####|
+    //      ## end ##|
+    //       ####### |
+    //        #####  |
+    //   ------------+
+    //               Ei
+
+    Point I(0.0f, 0.0f), J(0.0f, 0.0f);
+    if (aSide == eSideTop) {
+      I.x = 1.0f;
+      J.y = 1.0f;
+    } else if (aSide == eSideRight) {
+      I.y = 1.0f;
+      J.x = -1.0f;
+    } else if (aSide == eSideBottom) {
+      I.x = -1.0f;
+      J.y = -1.0f;
+    } else if (aSide == eSideLeft) {
+      I.y = -1.0f;
+      J.x = 1.0f;
+    }
+
+    Point So, Si, Eo, Ei;
+
+    So = (start + (-I + -J) * borderWidth / 2.0f);
+    Si = (mergeStart == MERGE_HALF) ? (start + (I + J) * borderWidth / 2.0f)
+                                    : (start + (-I + J) * borderWidth / 2.0f);
+    Eo = (end + (I - J) * borderWidth / 2.0f);
+    Ei = (mergeEnd == MERGE_HALF) ? (end + (-I + J) * borderWidth / 2.0f)
+                                  : (end + (I + J) * borderWidth / 2.0f);
+
+    RefPtr<PathBuilder> builder = mDrawTarget->CreatePathBuilder();
+    builder->MoveTo(So);
+    builder->LineTo(Eo);
+    builder->LineTo(Ei);
+    builder->LineTo(Si);
+    builder->Close();
+    RefPtr<Path> path = builder->Finish();
+
+    mDrawTarget->PushClip(path);
+  }
+
+  size_t count = round(borderLength / dotWidth);
+  if (isStartUnfilled == isEndUnfilled) {
+    // Split into 2n segments.
+    if (count % 2) {
+      count++;
+    }
+  } else {
+    // Split into 2n+1 segments.
+    if (count % 2 == 0) {
+      count++;
+    }
+  }
+
+  // A: radius == borderWidth / 2.0
+  // B: borderLength / count == borderWidth * (1 - overlap)
+  //
+  //   A      B         B        B        B     A
+  // |<-->|<------>|<------>|<------>|<------>|<-->|
+  // |    |        |        |        |        |    |
+  // +----+--------+--------+--------+--------+----+
+  // |  ##|##    **|**    ##|##    **|**    ##|##  |
+  // | ###|###  ***|***  ###|###  ***|***  ###|### |
+  // |####|####****|****####|####****|****####|####|
+  // |####+####****+****####+####****+****####+####|
+  // |# start #****|****####|####****|****## end ##|
+  // | ###|###  ***|***  ###|###  ***|***  ###|### |
+  // |  ##|##    **|**    ##|##    **|**    ##|##  |
+  // +----+----+---+--------+--------+---+----+----+
+  // |         |                         |         |
+  // |         |                         |         |
+
+  // If isStartUnfilled is true, draw dots on 2j+1 points, if not, draw dots on
+  // 2j points.
+  size_t from = isStartUnfilled ? 1 : 0;
+
+  // If mergeEnd == MERGE_NONE, last dot is drawn by next side.
+  size_t to = count;
+  if (mergeEnd == MERGE_NONE) {
+    if (to > 2) {
+      to -= 2;
+    } else {
+      to = 0;
+    }
+  }
+
+  Point fromP = (start * (count - from) + end * from) / count;
+  Point toP = (start * (count - to) + end * to) / count;
+  // Extend dirty rect to avoid clipping pixel for anti-aliasing.
+  const Float AA_MARGIN = 2.0f;
+
+  // The following algorithm assumes the border's rect and the dirty rect
+  // intersect.
+  MOZ_ASSERT(mDirtyRect.Intersects(mOuterRect));
+
+  if (aSide == eSideTop) {
+    // Tweak |from| and |to| to fit into |mDirtyRect + radius margin|,
+    // to render only paths that may overlap mDirtyRect.
+    //
+    //                mDirtyRect + radius margin
+    //              +--+---------------------+--+
+    //              |                           |
+    //              |         mDirtyRect        |
+    //              +  +---------------------+  +
+    // from   ===>  |from                    to |   <===  to
+    //    +-----+-----+-----+-----+-----+-----+-----+-----+
+    //   ###        |###         ###         ###|        ###
+    //  #####       #####       #####       #####       #####
+    //  #####       #####       #####       #####       #####
+    //  #####       #####       #####       #####       #####
+    //   ###        |###         ###         ###|        ###
+    //              |  |                     |  |
+    //              +  +---------------------+  +
+    //              |                           |
+    //              |                           |
+    //              +--+---------------------+--+
+
+    Float left = mDirtyRect.x - radius - AA_MARGIN;
+    if (fromP.x < left) {
+      size_t tmp = ceil(count * (left - start.x) / (end.x - start.x));
+      if (tmp > from) {
+        // We increment by 2, so odd/even should match between before/after.
+        if ((tmp & 1) != (from & 1)) {
+          from = tmp - 1;
+        } else {
+          from = tmp;
+        }
+      }
+    }
+    Float right = mDirtyRect.x + mDirtyRect.width + radius + AA_MARGIN;
+    if (toP.x > right) {
+      size_t tmp = floor(count * (right - start.x) / (end.x - start.x));
+      if (tmp < to) {
+        if ((tmp & 1) != (to & 1)) {
+          to = tmp + 1;
+        } else {
+          to = tmp;
+        }
+      }
+    }
+  } else if (aSide == eSideRight) {
+    Float top = mDirtyRect.y - radius - AA_MARGIN;
+    if (fromP.y < top) {
+      size_t tmp = ceil(count * (top - start.y) / (end.y - start.y));
+      if (tmp > from) {
+        if ((tmp & 1) != (from & 1)) {
+          from = tmp - 1;
+        } else {
+          from = tmp;
+        }
+      }
+    }
+    Float bottom = mDirtyRect.y + mDirtyRect.height + radius + AA_MARGIN;
+    if (toP.y > bottom) {
+      size_t tmp = floor(count * (bottom - start.y) / (end.y - start.y));
+      if (tmp < to) {
+        if ((tmp & 1) != (to & 1)) {
+          to = tmp + 1;
+        } else {
+          to = tmp;
+        }
+      }
+    }
+  } else if (aSide == eSideBottom) {
+    Float right = mDirtyRect.x + mDirtyRect.width + radius + AA_MARGIN;
+    if (fromP.x > right) {
+      size_t tmp = ceil(count * (right - start.x) / (end.x - start.x));
+      if (tmp > from) {
+        if ((tmp & 1) != (from & 1)) {
+          from = tmp - 1;
+        } else {
+          from = tmp;
+        }
+      }
+    }
+    Float left = mDirtyRect.x - radius - AA_MARGIN;
+    if (toP.x < left) {
+      size_t tmp = floor(count * (left - start.x) / (end.x - start.x));
+      if (tmp < to) {
+        if ((tmp & 1) != (to & 1)) {
+          to = tmp + 1;
+        } else {
+          to = tmp;
+        }
+      }
+    }
+  } else if (aSide == eSideLeft) {
+    Float bottom = mDirtyRect.y + mDirtyRect.height + radius + AA_MARGIN;
+    if (fromP.y > bottom) {
+      size_t tmp = ceil(count * (bottom - start.y) / (end.y - start.y));
+      if (tmp > from) {
+        if ((tmp & 1) != (from & 1)) {
+          from = tmp - 1;
+        } else {
+          from = tmp;
+        }
+      }
+    }
+    Float top = mDirtyRect.y - radius - AA_MARGIN;
+    if (toP.y < top) {
+      size_t tmp = floor(count * (top - start.y) / (end.y - start.y));
+      if (tmp < to) {
+        if ((tmp & 1) != (to & 1)) {
+          to = tmp + 1;
+        } else {
+          to = tmp;
+        }
+      }
+    }
+  }
+
+  RefPtr<PathBuilder> builder = mDrawTarget->CreatePathBuilder();
+  size_t segmentCount = 0;
+  for (size_t i = from; i <= to; i += 2) {
+    if (segmentCount > BORDER_SEGMENT_COUNT_MAX) {
+      RefPtr<Path> path = builder->Finish();
+      mDrawTarget->Fill(path, ColorPattern(ToDeviceColor(borderColor)));
+      builder = mDrawTarget->CreatePathBuilder();
+      segmentCount = 0;
+    }
+
+    Point P = (start * (count - i) + end * i) / count;
+    builder->MoveTo(Point(P.x + radius, P.y));
+    builder->Arc(P, radius, 0.0f, Float(2.0 * M_PI));
+    segmentCount++;
+  }
+  RefPtr<Path> path = builder->Finish();
+  mDrawTarget->Fill(path, ColorPattern(ToDeviceColor(borderColor)));
+
+  if (mergeStart == MERGE_HALF || mergeEnd == MERGE_HALF) {
+    mDrawTarget->PopClip();
+  }
+}
+
+void nsCSSBorderRenderer::DrawDashedOrDottedCorner(mozilla::Side aSide,
+                                                   Corner aCorner) {
+  // Draw dashed/dotted corner with following approach.
+  //
+  // dashed corner
+  //   If both side has same border-width and border-width <= 2.0, draw dashed
+  //   line along the corner, with appropriate dash length and gap to make the
+  //   corner symmetric as far as possible.  Dash length equals to the gap, and
+  //   the ratio of the dash length to border-width is the maximum value in in
+  //   [1, 3] range.
+  //   Otherwise, draw dashed segments along the corner, keeping same dash
+  //   length ratio to border-width at that point.
+  //   (see DashedCornerFinder.h for more detail)
+  //   Line ends with half segments, to joint with both side easily.
+  //
+  // dotted corner
+  //   If both side has same border-width and border-width <= 2.0, draw 1:1
+  //   dashed line along the corner.
+  //   Otherwise Draw circles along the corner, with appropriate gap that makes
+  //   the corner symmetric as far as possible.  The size of the circle may
+  //   change along the corner, that is tangent to the outer curver and the
+  //   inner curve.  The ratio of the gap to circle diameter is the maximum
+  //   value in [0.5, 1] range.
+  //   (see DottedCornerFinder.h for more detail)
+  //   Corner ends with filled dots but those dots are drawn by
+  //   DrawDashedOrDottedSide.  So this may draw no circles if there's no space
+  //   between 2 dots at both ends.
+
+  NS_ASSERTION(mBorderStyles[aSide] == StyleBorderStyle::Dashed ||
+                   mBorderStyles[aSide] == StyleBorderStyle::Dotted,
+               "Style should be dashed or dotted.");
+
+  if (IsCornerMergeable(aCorner)) {
+    // DrawDashedOrDottedSide will draw corner.
+    return;
+  }
+
+  mozilla::Side sideH(GetHorizontalSide(aCorner));
+  mozilla::Side sideV(GetVerticalSide(aCorner));
+  Float borderWidthH = mBorderWidths[sideH];
+  Float borderWidthV = mBorderWidths[sideV];
+  if (borderWidthH == 0.0f && borderWidthV == 0.0f) {
+    return;
+  }
+
+  StyleBorderStyle styleH = mBorderStyles[sideH];
+  StyleBorderStyle styleV = mBorderStyles[sideV];
+
+  // Corner between dotted and others with radius=0 is drawn by side.
+  if (IsZeroSize(mBorderRadii[aCorner]) &&
+      (styleV == StyleBorderStyle::Dotted ||
+       styleH == StyleBorderStyle::Dotted)) {
+    return;
+  }
+
+  Float maxRadius =
+      std::max(mBorderRadii[aCorner].width, mBorderRadii[aCorner].height);
+  if (maxRadius > BORDER_DOTTED_CORNER_MAX_RADIUS) {
+    DrawFallbackSolidCorner(aSide, aCorner);
+    return;
+  }
+
+  if (borderWidthH != borderWidthV || borderWidthH > 2.0f) {
+    StyleBorderStyle style = mBorderStyles[aSide];
+    if (style == StyleBorderStyle::Dotted) {
+      DrawDottedCornerSlow(aSide, aCorner);
+    } else {
+      DrawDashedCornerSlow(aSide, aCorner);
+    }
+    return;
+  }
+
+  nscolor borderColor = mBorderColors[aSide];
+  Point points[4];
+  bool ignored;
+  // Get the start and end points of the corner arc, ensuring that any dot
+  // origins get pushed backwards towards the edges of the corner rect to
+  // account for stroking.
+  points[0] = GetStraightBorderPoint(sideH, aCorner, &ignored, -0.5f);
+  points[3] = GetStraightBorderPoint(sideV, aCorner, &ignored, -0.5f);
+  // Round points to draw dot on each pixel.
+  if (borderWidthH < 2.0f) {
+    points[0].x = round(points[0].x);
+  }
+  if (borderWidthV < 2.0f) {
+    points[3].y = round(points[3].y);
+  }
+  points[1] = points[0];
+  points[1].x += kKappaFactor * (points[3].x - points[0].x);
+  points[2] = points[3];
+  points[2].y += kKappaFactor * (points[0].y - points[3].y);
+
+  Float len = GetQuarterEllipticArcLength(fabs(points[0].x - points[3].x),
+                                          fabs(points[0].y - points[3].y));
+
+  Float dash[2];
+  StrokeOptions strokeOptions(borderWidthH);
+  SetupDashedOptions(&strokeOptions, dash, aSide, len, true);
+
+  RefPtr<PathBuilder> builder = mDrawTarget->CreatePathBuilder();
+  builder->MoveTo(points[0]);
+  builder->BezierTo(points[1], points[2], points[3]);
+  RefPtr<Path> path = builder->Finish();
+  mDrawTarget->Stroke(path, ColorPattern(ToDeviceColor(borderColor)),
+                      strokeOptions);
+}
+
+void nsCSSBorderRenderer::DrawDottedCornerSlow(mozilla::Side aSide,
+                                               Corner aCorner) {
+  NS_ASSERTION(mBorderStyles[aSide] == StyleBorderStyle::Dotted,
+               "Style should be dotted.");
+
+  mozilla::Side sideH(GetHorizontalSide(aCorner));
+  mozilla::Side sideV(GetVerticalSide(aCorner));
+  Float R0 = mBorderWidths[sideH] / 2.0f;
+  Float Rn = mBorderWidths[sideV] / 2.0f;
+  if (R0 == 0.0f && Rn == 0.0f) {
+    return;
+  }
+
+  nscolor borderColor = mBorderColors[aSide];
+  Bezier outerBezier;
+  Bezier innerBezier;
+  GetOuterAndInnerBezier(&outerBezier, &innerBezier, aCorner);
+
+  bool ignored;
+  Point C0 = GetStraightBorderPoint(sideH, aCorner, &ignored);
+  Point Cn = GetStraightBorderPoint(sideV, aCorner, &ignored);
+  DottedCornerFinder finder(outerBezier, innerBezier, aCorner,
+                            mBorderRadii[aCorner].width,
+                            mBorderRadii[aCorner].height, C0, R0, Cn, Rn,
+                            mBorderCornerDimensions[aCorner]);
+
+  RefPtr<PathBuilder> builder = mDrawTarget->CreatePathBuilder();
+  size_t segmentCount = 0;
+  const Float AA_MARGIN = 2.0f;
+  Rect marginedDirtyRect = mDirtyRect;
+  marginedDirtyRect.Inflate(std::max(R0, Rn) + AA_MARGIN);
+  bool entered = false;
+  while (finder.HasMore()) {
+    if (segmentCount > BORDER_SEGMENT_COUNT_MAX) {
+      RefPtr<Path> path = builder->Finish();
+      mDrawTarget->Fill(path, ColorPattern(ToDeviceColor(borderColor)));
+      builder = mDrawTarget->CreatePathBuilder();
+      segmentCount = 0;
+    }
+
+    DottedCornerFinder::Result result = finder.Next();
+
+    if (marginedDirtyRect.Contains(result.C) && result.r > 0) {
+      entered = true;
+      builder->MoveTo(Point(result.C.x + result.r, result.C.y));
+      builder->Arc(result.C, result.r, 0, Float(2.0 * M_PI));
+      segmentCount++;
+    } else if (entered) {
+      break;
+    }
+  }
+  RefPtr<Path> path = builder->Finish();
+  mDrawTarget->Fill(path, ColorPattern(ToDeviceColor(borderColor)));
+}
+
+static inline bool DashedPathOverlapsRect(Rect& pathRect,
+                                          const Rect& marginedDirtyRect,
+                                          DashedCornerFinder::Result& result) {
+  // Calculate a rect that contains all control points of the |result| path,
+  // and check if it intersects with |marginedDirtyRect|.
+  pathRect.SetRect(result.outerSectionBezier.mPoints[0].x,
+                   result.outerSectionBezier.mPoints[0].y, 0, 0);
+  pathRect.ExpandToEnclose(result.outerSectionBezier.mPoints[1]);
+  pathRect.ExpandToEnclose(result.outerSectionBezier.mPoints[2]);
+  pathRect.ExpandToEnclose(result.outerSectionBezier.mPoints[3]);
+  pathRect.ExpandToEnclose(result.innerSectionBezier.mPoints[0]);
+  pathRect.ExpandToEnclose(result.innerSectionBezier.mPoints[1]);
+  pathRect.ExpandToEnclose(result.innerSectionBezier.mPoints[2]);
+  pathRect.ExpandToEnclose(result.innerSectionBezier.mPoints[3]);
+
+  return pathRect.Intersects(marginedDirtyRect);
+}
+
+void nsCSSBorderRenderer::DrawDashedCornerSlow(mozilla::Side aSide,
+                                               Corner aCorner) {
+  NS_ASSERTION(mBorderStyles[aSide] == StyleBorderStyle::Dashed,
+               "Style should be dashed.");
+
+  mozilla::Side sideH(GetHorizontalSide(aCorner));
+  mozilla::Side sideV(GetVerticalSide(aCorner));
+  Float borderWidthH = mBorderWidths[sideH];
+  Float borderWidthV = mBorderWidths[sideV];
+  if (borderWidthH == 0.0f && borderWidthV == 0.0f) {
+    return;
+  }
+
+  nscolor borderColor = mBorderColors[aSide];
+  Bezier outerBezier;
+  Bezier innerBezier;
+  GetOuterAndInnerBezier(&outerBezier, &innerBezier, aCorner);
+
+  DashedCornerFinder finder(outerBezier, innerBezier, borderWidthH,
+                            borderWidthV, mBorderCornerDimensions[aCorner]);
+
+  RefPtr<PathBuilder> builder = mDrawTarget->CreatePathBuilder();
+  size_t segmentCount = 0;
+  const Float AA_MARGIN = 2.0f;
+  Rect marginedDirtyRect = mDirtyRect;
+  marginedDirtyRect.Inflate(AA_MARGIN);
+  Rect pathRect;
+  bool entered = false;
+  while (finder.HasMore()) {
+    if (segmentCount > BORDER_SEGMENT_COUNT_MAX) {
+      RefPtr<Path> path = builder->Finish();
+      mDrawTarget->Fill(path, ColorPattern(ToDeviceColor(borderColor)));
+      builder = mDrawTarget->CreatePathBuilder();
+      segmentCount = 0;
+    }
+
+    DashedCornerFinder::Result result = finder.Next();
+
+    if (DashedPathOverlapsRect(pathRect, marginedDirtyRect, result)) {
+      entered = true;
+      builder->MoveTo(result.outerSectionBezier.mPoints[0]);
+      builder->BezierTo(result.outerSectionBezier.mPoints[1],
+                        result.outerSectionBezier.mPoints[2],
+                        result.outerSectionBezier.mPoints[3]);
+      builder->LineTo(result.innerSectionBezier.mPoints[3]);
+      builder->BezierTo(result.innerSectionBezier.mPoints[2],
+                        result.innerSectionBezier.mPoints[1],
+                        result.innerSectionBezier.mPoints[0]);
+      builder->LineTo(result.outerSectionBezier.mPoints[0]);
+      segmentCount++;
+    } else if (entered) {
+      break;
+    }
+  }
+
+  if (outerBezier.mPoints[0].x != innerBezier.mPoints[0].x) {
+    // Fill gap before the first section.
+    //
+    //     outnerPoint[0]
+    //         |
+    //         v
+    //        _+-----------+--
+    //      /   \##########|
+    //    /      \#########|
+    //   +        \########|
+    //   |\         \######|
+    //   |  \        \#####|
+    //   |    \       \####|
+    //   |      \       \##|
+    //   |        \      \#|
+    //   |          \     \|
+    //   |            \  _-+--
+    //   +--------------+  ^
+    //   |              |  |
+    //   |              |  innerPoint[0]
+    //   |              |
+    builder->MoveTo(outerBezier.mPoints[0]);
+    builder->LineTo(innerBezier.mPoints[0]);
+    builder->LineTo(Point(innerBezier.mPoints[0].x, outerBezier.mPoints[0].y));
+    builder->LineTo(outerBezier.mPoints[0]);
+  }
+
+  if (outerBezier.mPoints[3].y != innerBezier.mPoints[3].y) {
+    // Fill gap after the last section.
+    //
+    // outnerPoint[3]
+    //   |
+    //   |
+    //   |    _+-----------+--
+    //   |  /   \          |
+    //   v/      \         |
+    //   +        \        |
+    //   |\         \      |
+    //   |##\        \     |
+    //   |####\       \    |
+    //   |######\       \  |
+    //   |########\      \ |
+    //   |##########\     \|
+    //   |############\  _-+--
+    //   +--------------+<-- innerPoint[3]
+    //   |              |
+    //   |              |
+    //   |              |
+    builder->MoveTo(outerBezier.mPoints[3]);
+    builder->LineTo(innerBezier.mPoints[3]);
+    builder->LineTo(Point(outerBezier.mPoints[3].x, innerBezier.mPoints[3].y));
+    builder->LineTo(outerBezier.mPoints[3]);
+  }
+
+  RefPtr<Path> path = builder->Finish();
+  mDrawTarget->Fill(path, ColorPattern(ToDeviceColor(borderColor)));
+}
+
+void nsCSSBorderRenderer::DrawFallbackSolidCorner(mozilla::Side aSide,
+                                                  Corner aCorner) {
+  // Render too large dashed or dotted corner with solid style, to avoid hangup
+  // inside DashedCornerFinder and DottedCornerFinder.
+
+  NS_ASSERTION(mBorderStyles[aSide] == StyleBorderStyle::Dashed ||
+                   mBorderStyles[aSide] == StyleBorderStyle::Dotted,
+               "Style should be dashed or dotted.");
+
+  nscolor borderColor = mBorderColors[aSide];
+  Bezier outerBezier;
+  Bezier innerBezier;
+  GetOuterAndInnerBezier(&outerBezier, &innerBezier, aCorner);
+
+  RefPtr<PathBuilder> builder = mDrawTarget->CreatePathBuilder();
+
+  builder->MoveTo(outerBezier.mPoints[0]);
+  builder->BezierTo(outerBezier.mPoints[1], outerBezier.mPoints[2],
+                    outerBezier.mPoints[3]);
+  builder->LineTo(innerBezier.mPoints[3]);
+  builder->BezierTo(innerBezier.mPoints[2], innerBezier.mPoints[1],
+                    innerBezier.mPoints[0]);
+  builder->LineTo(outerBezier.mPoints[0]);
+
+  RefPtr<Path> path = builder->Finish();
+  mDrawTarget->Fill(path, ColorPattern(ToDeviceColor(borderColor)));
+
+  if (!mPresContext->HasWarnedAboutTooLargeDashedOrDottedRadius()) {
+    mPresContext->SetHasWarnedAboutTooLargeDashedOrDottedRadius();
+    nsContentUtils::ReportToConsole(
+        nsIScriptError::warningFlag, "CSS"_ns, mPresContext->Document(),
+        nsContentUtils::eCSS_PROPERTIES,
+        mBorderStyles[aSide] == StyleBorderStyle::Dashed
+            ? "TooLargeDashedRadius"
+            : "TooLargeDottedRadius");
+  }
+}
+
+bool nsCSSBorderRenderer::AllBordersSameWidth() {
+  if (mBorderWidths[0] == mBorderWidths[1] &&
+      mBorderWidths[0] == mBorderWidths[2] &&
+      mBorderWidths[0] == mBorderWidths[3]) {
+    return true;
+  }
+
+  return false;
+}
+
+bool nsCSSBorderRenderer::AllBordersSolid() {
+  for (const auto i : mozilla::AllPhysicalSides()) {
+    if (mBorderStyles[i] == StyleBorderStyle::Solid ||
+        mBorderStyles[i] == StyleBorderStyle::None ||
+        mBorderStyles[i] == StyleBorderStyle::Hidden) {
+      continue;
+    }
+    return false;
+  }
+
+  return true;
+}
+
+static bool IsVisible(StyleBorderStyle aStyle) {
+  if (aStyle != StyleBorderStyle::None && aStyle != StyleBorderStyle::Hidden) {
+    return true;
+  }
+  return false;
+}
+
+struct twoFloats {
+  Float a, b;
+
+  twoFloats operator*(const Size& aSize) const {
+    return {a * aSize.width, b * aSize.height};
+  }
+
+  twoFloats operator*(Float aScale) const { return {a * aScale, b * aScale}; }
+
+  twoFloats operator+(const Point& aPoint) const {
+    return {a + aPoint.x, b + aPoint.y};
+  }
+
+  operator Point() const { return Point(a, b); }
+};
+
+void nsCSSBorderRenderer::DrawSingleWidthSolidBorder() {
+  // Easy enough to deal with.
+  Rect rect = mOuterRect;
+  rect.Deflate(0.5);
+
+  const twoFloats cornerAdjusts[4] = {
+      {+0.5, 0}, {0, +0.5}, {-0.5, 0}, {0, -0.5}};
+  for (const auto side : mozilla::AllPhysicalSides()) {
+    Point firstCorner = rect.CCWCorner(side) + cornerAdjusts[side];
+    Point secondCorner = rect.CWCorner(side) + cornerAdjusts[side];
+
+    ColorPattern color(ToDeviceColor(mBorderColors[side]));
+
+    mDrawTarget->StrokeLine(firstCorner, secondCorner, color);
+  }
+}
+
+// Intersect a ray from the inner corner to the outer corner
+// with the border radius, yielding the intersection point.
+static Point IntersectBorderRadius(const Point& aCenter, const Size& aRadius,
+                                   const Point& aInnerCorner,
+                                   const Point& aCornerDirection) {
+  Point toCorner = aCornerDirection;
+  // transform to-corner ray to unit-circle space
+  toCorner.x /= aRadius.width;
+  toCorner.y /= aRadius.height;
+  // normalize to-corner ray
+  Float cornerDist = toCorner.Length();
+  if (cornerDist < 1.0e-6f) {
+    return aInnerCorner;
+  }
+  toCorner = toCorner / cornerDist;
+  // ray from inner corner to border radius center
+  Point toCenter = aCenter - aInnerCorner;
+  // transform to-center ray to unit-circle space
+  toCenter.x /= aRadius.width;
+  toCenter.y /= aRadius.height;
+  // compute offset of intersection with border radius unit circle
+  Float offset = toCenter.DotProduct(toCorner);
+  // compute discriminant to check for intersections
+  Float discrim = 1.0f - toCenter.DotProduct(toCenter) + offset * offset;
+  // choose farthest intersection
+  offset += sqrtf(std::max(discrim, 0.0f));
+  // transform to-corner ray back out of unit-circle space
+  toCorner.x *= aRadius.width;
+  toCorner.y *= aRadius.height;
+  return aInnerCorner + toCorner * offset;
+}
+
+// Calculate the split point and split angle for a border radius with
+// differing sides.
+static inline void SplitBorderRadius(const Point& aCenter, const Size& aRadius,
+                                     const Point& aOuterCorner,
+                                     const Point& aInnerCorner,
+                                     const twoFloats& aCornerMults,
+                                     Float aStartAngle, Point& aSplit,
+                                     Float& aSplitAngle) {
+  Point cornerDir = aOuterCorner - aInnerCorner;
+  if (cornerDir.x == cornerDir.y && aRadius.IsSquare()) {
+    // optimize 45-degree intersection with circle since we can assume
+    // the circle center lies along the intersection edge
+    aSplit = aCenter - aCornerMults * (aRadius * Float(1.0f / M_SQRT2));
+    aSplitAngle = aStartAngle + 0.5f * M_PI / 2.0f;
+  } else {
+    aSplit = IntersectBorderRadius(aCenter, aRadius, aInnerCorner, cornerDir);
+    aSplitAngle = atan2f((aSplit.y - aCenter.y) / aRadius.height,
+                         (aSplit.x - aCenter.x) / aRadius.width);
+  }
+}
+
+// Compute the size of the skirt needed, given the color alphas
+// of each corner side and the slope between them.
+static void ComputeCornerSkirtSize(Float aAlpha1, Float aAlpha2, Float aSlopeY,
+                                   Float aSlopeX, Float& aSizeResult,
+                                   Float& aSlopeResult) {
+  // If either side is (almost) invisible or there is no diagonal edge,
+  // then don't try to render a skirt.
+  if (aAlpha1 < 0.01f || aAlpha2 < 0.01f) {
+    return;
+  }
+  aSlopeX = fabs(aSlopeX);
+  aSlopeY = fabs(aSlopeY);
+  if (aSlopeX < 1.0e-6f || aSlopeY < 1.0e-6f) {
+    return;
+  }
+
+  // If first and second color don't match, we need to split the corner in
+  // half. The diagonal edges created may not have full pixel coverage given
+  // anti-aliasing, so we need to compute a small subpixel skirt edge. This
+  // assumes each half has half coverage to start with, and that coverage
+  // increases as the skirt is pushed over, with the end result that we want
+  // to roughly preserve the alpha value along this edge.
+  // Given slope m, alphas a and A, use quadratic formula to solve for S in:
+  //   a*(1 - 0.5*(1-S)*(1-mS))*(1 - 0.5*A) + 0.5*A = A
+  // yielding:
+  //   S = ((1+m) - sqrt((1+m)*(1+m) + 4*m*(1 - A/(a*(1-0.5*A))))) / (2*m)
+  // and substitute k = (1+m)/(2*m):
+  //   S = k - sqrt(k*k + (1 - A/(a*(1-0.5*A)))/m)
+  Float slope = aSlopeY / aSlopeX;
+  Float slopeScale = (1.0f + slope) / (2.0f * slope);
+  Float discrim = slopeScale * slopeScale +
+                  (1 - aAlpha2 / (aAlpha1 * (1.0f - 0.49f * aAlpha2))) / slope;
+  if (discrim >= 0) {
+    aSizeResult = slopeScale - sqrtf(discrim);
+    aSlopeResult = slope;
+  }
+}
+
+// Draws a border radius with possibly different sides.
+// A skirt is drawn underneath the corner intersection to hide possible
+// seams when anti-aliased drawing is used.
+static void DrawBorderRadius(
+    DrawTarget* aDrawTarget, Corner c, const Point& aOuterCorner,
+    const Point& aInnerCorner, const twoFloats& aCornerMultPrev,
+    const twoFloats& aCornerMultNext, const Size& aCornerDims,
+    const Size& aOuterRadius, const Size& aInnerRadius,
+    const DeviceColor& aFirstColor, const DeviceColor& aSecondColor,
+    Float aSkirtSize, Float aSkirtSlope) {
+  // Connect edge to outer arc start point
+  Point outerCornerStart = aOuterCorner + aCornerMultPrev * aCornerDims;
+  // Connect edge to outer arc end point
+  Point outerCornerEnd = aOuterCorner + aCornerMultNext * aCornerDims;
+  // Connect edge to inner arc start point
+  Point innerCornerStart =
+      outerCornerStart + aCornerMultNext * (aCornerDims - aInnerRadius);
+  // Connect edge to inner arc end point
+  Point innerCornerEnd =
+      outerCornerEnd + aCornerMultPrev * (aCornerDims - aInnerRadius);
+
+  // Outer arc start point
+  Point outerArcStart = aOuterCorner + aCornerMultPrev * aOuterRadius;
+  // Outer arc end point
+  Point outerArcEnd = aOuterCorner + aCornerMultNext * aOuterRadius;
+  // Inner arc start point
+  Point innerArcStart = aInnerCorner + aCornerMultPrev * aInnerRadius;
+  // Inner arc end point
+  Point innerArcEnd = aInnerCorner + aCornerMultNext * aInnerRadius;
+
+  // Outer radius center
+  Point outerCenter =
+      aOuterCorner + (aCornerMultPrev + aCornerMultNext) * aOuterRadius;
+  // Inner radius center
+  Point innerCenter =
+      aInnerCorner + (aCornerMultPrev + aCornerMultNext) * aInnerRadius;
+
+  RefPtr<PathBuilder> builder;
+  RefPtr<Path> path;
+
+  if (aFirstColor.a > 0) {
+    builder = aDrawTarget->CreatePathBuilder();
+    builder->MoveTo(outerCornerStart);
+  }
+
+  if (aFirstColor != aSecondColor) {
+    // Start and end angles of corner quadrant
+    constexpr float PIf = M_PI;
+    Float startAngle = (static_cast<float>(c) * PIf) / 2.0f - PIf;
+    Float endAngle = startAngle + PIf / 2.0f;
+    Float outerSplitAngle, innerSplitAngle;
+    Point outerSplit, innerSplit;
+
+    // Outer half-way point
+    SplitBorderRadius(outerCenter, aOuterRadius, aOuterCorner, aInnerCorner,
+                      aCornerMultPrev + aCornerMultNext, startAngle, outerSplit,
+                      outerSplitAngle);
+    // Inner half-way point
+    if (aInnerRadius.IsEmpty()) {
+      innerSplit = aInnerCorner;
+      innerSplitAngle = endAngle;
+    } else {
+      SplitBorderRadius(innerCenter, aInnerRadius, aOuterCorner, aInnerCorner,
+                        aCornerMultPrev + aCornerMultNext, startAngle,
+                        innerSplit, innerSplitAngle);
+    }
+
+    // Draw first half with first color
+    if (aFirstColor.a > 0) {
+      AcuteArcToBezier(builder.get(), outerCenter, aOuterRadius, outerArcStart,
+                       outerSplit, startAngle, outerSplitAngle);
+      // Draw skirt as part of first half
+      if (aSkirtSize > 0) {
+        builder->LineTo(outerSplit + aCornerMultNext * aSkirtSize);
+        builder->LineTo(innerSplit -
+                        aCornerMultPrev * (aSkirtSize * aSkirtSlope));
+      }
+      AcuteArcToBezier(builder.get(), innerCenter, aInnerRadius, innerSplit,
+                       innerArcStart, innerSplitAngle, startAngle);
+      if ((innerCornerStart - innerArcStart).DotProduct(aCornerMultPrev) > 0) {
+        builder->LineTo(innerCornerStart);
+      }
+      builder->Close();
+      path = builder->Finish();
+      aDrawTarget->Fill(path, ColorPattern(aFirstColor));
+    }
+
+    // Draw second half with second color
+    if (aSecondColor.a > 0) {
+      builder = aDrawTarget->CreatePathBuilder();
+      builder->MoveTo(outerCornerEnd);
+      if ((innerArcEnd - innerCornerEnd).DotProduct(aCornerMultNext) < 0) {
+        builder->LineTo(innerCornerEnd);
+      }
+      AcuteArcToBezier(builder.get(), innerCenter, aInnerRadius, innerArcEnd,
+                       innerSplit, endAngle, innerSplitAngle);
+      AcuteArcToBezier(builder.get(), outerCenter, aOuterRadius, outerSplit,
+                       outerArcEnd, outerSplitAngle, endAngle);
+      builder->Close();
+      path = builder->Finish();
+      aDrawTarget->Fill(path, ColorPattern(aSecondColor));
+    }
+  } else if (aFirstColor.a > 0) {
+    // Draw corner with single color
+    AcuteArcToBezier(builder.get(), outerCenter, aOuterRadius, outerArcStart,
+                     outerArcEnd);
+    builder->LineTo(outerCornerEnd);
+    if ((innerArcEnd - innerCornerEnd).DotProduct(aCornerMultNext) < 0) {
+      builder->LineTo(innerCornerEnd);
+    }
+    AcuteArcToBezier(builder.get(), innerCenter, aInnerRadius, innerArcEnd,
+                     innerArcStart, -kKappaFactor);
+    if ((innerCornerStart - innerArcStart).DotProduct(aCornerMultPrev) > 0) {
+      builder->LineTo(innerCornerStart);
+    }
+    builder->Close();
+    path = builder->Finish();
+    aDrawTarget->Fill(path, ColorPattern(aFirstColor));
+  }
+}
+
+// Draw a corner with possibly different sides.
+// A skirt is drawn underneath the corner intersection to hide possible
+// seams when anti-aliased drawing is used.
+static void DrawCorner(DrawTarget* aDrawTarget, const Point& aOuterCorner,
+                       const Point& aInnerCorner,
+                       const twoFloats& aCornerMultPrev,
+                       const twoFloats& aCornerMultNext,
+                       const Size& aCornerDims, const DeviceColor& aFirstColor,
+                       const DeviceColor& aSecondColor, Float aSkirtSize,
+                       Float aSkirtSlope) {
+  // Corner box start point
+  Point cornerStart = aOuterCorner + aCornerMultPrev * aCornerDims;
+  // Corner box end point
+  Point cornerEnd = aOuterCorner + aCornerMultNext * aCornerDims;
+
+  RefPtr<PathBuilder> builder;
+  RefPtr<Path> path;
+
+  if (aFirstColor.a > 0) {
+    builder = aDrawTarget->CreatePathBuilder();
+    builder->MoveTo(cornerStart);
+  }
+
+  if (aFirstColor != aSecondColor) {
+    // Draw first half with first color
+    if (aFirstColor.a > 0) {
+      builder->LineTo(aOuterCorner);
+      // Draw skirt as part of first half
+      if (aSkirtSize > 0) {
+        builder->LineTo(aOuterCorner + aCornerMultNext * aSkirtSize);
+        builder->LineTo(aInnerCorner -
+                        aCornerMultPrev * (aSkirtSize * aSkirtSlope));
+      }
+      builder->LineTo(aInnerCorner);
+      builder->Close();
+      path = builder->Finish();
+      aDrawTarget->Fill(path, ColorPattern(aFirstColor));
+    }
+
+    // Draw second half with second color
+    if (aSecondColor.a > 0) {
+      builder = aDrawTarget->CreatePathBuilder();
+      builder->MoveTo(cornerEnd);
+      builder->LineTo(aInnerCorner);
+      builder->LineTo(aOuterCorner);
+      builder->Close();
+      path = builder->Finish();
+      aDrawTarget->Fill(path, ColorPattern(aSecondColor));
+    }
+  } else if (aFirstColor.a > 0) {
+    // Draw corner with single color
+    builder->LineTo(aOuterCorner);
+    builder->LineTo(cornerEnd);
+    builder->LineTo(aInnerCorner);
+    builder->Close();
+    path = builder->Finish();
+    aDrawTarget->Fill(path, ColorPattern(aFirstColor));
+  }
+}
+
+void nsCSSBorderRenderer::DrawSolidBorder() {
+  const twoFloats cornerMults[4] = {{-1, 0}, {0, -1}, {+1, 0}, {0, +1}};
+
+  const twoFloats centerAdjusts[4] = {
+      {0, +0.5}, {-0.5, 0}, {0, -0.5}, {+0.5, 0}};
+
+  RectCornerRadii innerRadii;
+  ComputeInnerRadii(mBorderRadii, mBorderWidths, &innerRadii);
+
+  Rect strokeRect = mOuterRect;
+  strokeRect.Deflate(Margin(mBorderWidths[0] / 2.0, mBorderWidths[1] / 2.0,
+                            mBorderWidths[2] / 2.0, mBorderWidths[3] / 2.0));
+
+  for (const auto i : mozilla::AllPhysicalSides()) {
+    // We now draw the current side and the CW corner following it.
+    // The CCW corner of this side was already drawn in the previous iteration.
+    // The side will be drawn as an explicit stroke, and the CW corner will be
+    // filled separately.
+    // If the next side does not have a matching color, then we split the
+    // corner into two halves, one of each side's color and draw both.
+    // Thus, the CCW corner of the next side will end up drawn here.
+
+    // the corner index -- either 1 2 3 0 (cw) or 0 3 2 1 (ccw)
+    Corner c = Corner((i + 1) % 4);
+    Corner prevCorner = Corner(i);
+
+    // i+2 and i+3 respectively.  These are used to index into the corner
+    // multiplier table, and were deduced by calculating out the long form
+    // of each corner and finding a pattern in the signs and values.
+    int i1 = (i + 1) % 4;
+    int i2 = (i + 2) % 4;
+    int i3 = (i + 3) % 4;
+
+    Float sideWidth = 0.0f;
+    DeviceColor firstColor, secondColor;
+    if (IsVisible(mBorderStyles[i]) && mBorderWidths[i]) {
+      // draw the side since it is visible
+      sideWidth = mBorderWidths[i];
+      firstColor = ToDeviceColor(mBorderColors[i]);
+      // if the next side is visible, use its color for corner
+      secondColor = IsVisible(mBorderStyles[i1]) && mBorderWidths[i1]
+                        ? ToDeviceColor(mBorderColors[i1])
+                        : firstColor;
+    } else if (IsVisible(mBorderStyles[i1]) && mBorderWidths[i1]) {
+      // assign next side's color to both corner sides
+      firstColor = ToDeviceColor(mBorderColors[i1]);
+      secondColor = firstColor;
+    } else {
+      // neither side is visible, so nothing to do
+      continue;
+    }
+
+    Point outerCorner = mOuterRect.AtCorner(c);
+    Point innerCorner = mInnerRect.AtCorner(c);
+
+    // start and end points of border side stroke between corners
+    Point sideStart = mOuterRect.AtCorner(prevCorner) +
+                      cornerMults[i2] * mBorderCornerDimensions[prevCorner];
+    Point sideEnd = outerCorner + cornerMults[i] * mBorderCornerDimensions[c];
+    // check if the side is visible and not inverted
+    if (sideWidth > 0 && firstColor.a > 0 &&
+        -(sideEnd - sideStart).DotProduct(cornerMults[i]) > 0) {
+      mDrawTarget->StrokeLine(sideStart + centerAdjusts[i] * sideWidth,
+                              sideEnd + centerAdjusts[i] * sideWidth,
+                              ColorPattern(firstColor),
+                              StrokeOptions(sideWidth));
+    }
+
+    Float skirtSize = 0.0f, skirtSlope = 0.0f;
+    // the sides don't match, so compute a skirt
+    if (firstColor != secondColor &&
+        mPresContext->Type() != nsPresContext::eContext_Print) {
+      Point cornerDir = outerCorner - innerCorner;
+      ComputeCornerSkirtSize(
+          firstColor.a, secondColor.a, cornerDir.DotProduct(cornerMults[i]),
+          cornerDir.DotProduct(cornerMults[i3]), skirtSize, skirtSlope);
+    }
+
+    if (!mBorderRadii[c].IsEmpty()) {
+      // the corner has a border radius
+      DrawBorderRadius(mDrawTarget, c, outerCorner, innerCorner, cornerMults[i],
+                       cornerMults[i3], mBorderCornerDimensions[c],
+                       mBorderRadii[c], innerRadii[c], firstColor, secondColor,
+                       skirtSize, skirtSlope);
+    } else if (!mBorderCornerDimensions[c].IsEmpty()) {
+      // a corner with no border radius
+      DrawCorner(mDrawTarget, outerCorner, innerCorner, cornerMults[i],
+                 cornerMults[i3], mBorderCornerDimensions[c], firstColor,
+                 secondColor, skirtSize, skirtSlope);
+    }
+  }
+}
+
+void nsCSSBorderRenderer::DrawBorders() {
+  if (MOZ_UNLIKELY(!mDirtyRect.Intersects(mOuterRect))) {
+    return;
+  }
+
+  if (mAllBordersSameStyle && (mBorderStyles[0] == StyleBorderStyle::None ||
+                               mBorderStyles[0] == StyleBorderStyle::Hidden ||
+                               mBorderColors[0] == NS_RGBA(0, 0, 0, 0))) {
+    // All borders are the same style, and the style is either none or hidden,
+    // or the color is transparent.
+    return;
+  }
+
+  if (mAllBordersSameWidth && mBorderWidths[0] == 0.0) {
+    // Some of the mAllBordersSameWidth codepaths depend on the border
+    // width being greater than zero.
+    return;
+  }
+
+  AutoRestoreTransform autoRestoreTransform;
+  Matrix mat = mDrawTarget->GetTransform();
+
+  // Clamp the CTM to be pixel-aligned; we do this only
+  // for translation-only matrices now, but we could do it
+  // if the matrix has just a scale as well.  We should not
+  // do it if there's a rotation.
+  if (mat.HasNonTranslation()) {
+    if (!mat.HasNonAxisAlignedTransform()) {
+      // Scale + transform. Avoid stroke fast-paths so that we have a chance
+      // of snapping to pixel boundaries.
+      mAvoidStroke = true;
+    }
+  } else {
+    mat._31 = floor(mat._31 + 0.5);
+    mat._32 = floor(mat._32 + 0.5);
+    autoRestoreTransform.Init(mDrawTarget);
+    mDrawTarget->SetTransform(mat);
+
+    // round mOuterRect and mInnerRect; they're already an integer
+    // number of pixels apart and should stay that way after
+    // rounding. We don't do this if there's a scale in the current transform
+    // since this loses information that might be relevant when we're scaling.
+    mOuterRect.Round();
+    mInnerRect.Round();
+  }
+
+  // Initial values only used when the border colors/widths are all the same:
+  ColorPattern color(ToDeviceColor(mBorderColors[eSideTop]));
+  StrokeOptions strokeOptions(mBorderWidths[eSideTop]);  // stroke width
+
+  // First there's a couple of 'special cases' that have specifically optimized
+  // drawing paths, when none of these can be used we move on to the generalized
+  // border drawing code.
+  if (mAllBordersSameStyle && mAllBordersSameWidth &&
+      mBorderStyles[0] == StyleBorderStyle::Solid && mNoBorderRadius &&
+      !mAvoidStroke) {
+    // Very simple case.
+    Rect rect = mOuterRect;
+    rect.Deflate(mBorderWidths[0] / 2.0);
+    mDrawTarget->StrokeRect(rect, color, strokeOptions);
+    return;
+  }
+
+  if (mAllBordersSameStyle && mBorderStyles[0] == StyleBorderStyle::Solid &&
+      !mAvoidStroke && !mNoBorderRadius) {
+    // Relatively simple case.
+    RoundedRect borderInnerRect(mOuterRect, mBorderRadii);
+    borderInnerRect.Deflate(mBorderWidths[eSideTop], mBorderWidths[eSideBottom],
+                            mBorderWidths[eSideLeft],
+                            mBorderWidths[eSideRight]);
+
+    // Instead of stroking we just use two paths: an inner and an outer.
+    // This allows us to draw borders that we couldn't when stroking. For
+    // example, borders with a border width >= the border radius. (i.e. when
+    // there are square corners on the inside)
+    //
+    // Further, this approach can be more efficient because the backend
+    // doesn't need to compute an offset curve to stroke the path. We know that
+    // the rounded parts are elipses we can offset exactly and can just compute
+    // a new cubic approximation.
+    RefPtr<PathBuilder> builder = mDrawTarget->CreatePathBuilder();
+    AppendRoundedRectToPath(builder, mOuterRect, mBorderRadii, true);
+    AppendRoundedRectToPath(builder, borderInnerRect.rect,
+                            borderInnerRect.corners, false);
+    RefPtr<Path> path = builder->Finish();
+    mDrawTarget->Fill(path, color);
+    return;
+  }
+
+  const bool allBordersSolid = AllBordersSolid();
+
+  // This leaves the border corners non-interpolated for single width borders.
+  // Doing this is slightly faster and shouldn't be a problem visually.
+  if (allBordersSolid && mAllBordersSameWidth && mBorderWidths[0] == 1 &&
+      mNoBorderRadius && !mAvoidStroke) {
+    DrawSingleWidthSolidBorder();
+    return;
+  }
+
+  if (allBordersSolid && !mAvoidStroke) {
+    DrawSolidBorder();
+    return;
+  }
+
+  PrintAsString(" mOuterRect: ");
+  PrintAsString(mOuterRect);
+  PrintAsStringNewline();
+  PrintAsString(" mInnerRect: ");
+  PrintAsString(mInnerRect);
+  PrintAsStringNewline();
+  PrintAsFormatString(" mBorderColors: 0x%08x 0x%08x 0x%08x 0x%08x\n",
+                      mBorderColors[0], mBorderColors[1], mBorderColors[2],
+                      mBorderColors[3]);
+
+  // if conditioning the outside rect failed, then bail -- the outside
+  // rect is supposed to enclose the entire border
+  {
+    gfxRect outerRect = ThebesRect(mOuterRect);
+    gfxUtils::ConditionRect(outerRect);
+    if (outerRect.IsEmpty()) {
+      return;
+    }
+    mOuterRect = ToRect(outerRect);
+
+    if (MOZ_UNLIKELY(!mDirtyRect.Intersects(mOuterRect))) {
+      return;
+    }
+
+    gfxRect innerRect = ThebesRect(mInnerRect);
+    gfxUtils::ConditionRect(innerRect);
+    mInnerRect = ToRect(innerRect);
+  }
+
+  SideBits dashedSides = SideBits::eNone;
+  bool forceSeparateCorners = false;
+
+  for (const auto i : mozilla::AllPhysicalSides()) {
+    StyleBorderStyle style = mBorderStyles[i];
+    if (style == StyleBorderStyle::Dashed ||
+        style == StyleBorderStyle::Dotted) {
+      // we need to draw things separately for dashed/dotting
+      forceSeparateCorners = true;
+      dashedSides |= static_cast<mozilla::SideBits>(1 << i);
+    }
+  }
+
+  PrintAsFormatString(" mAllBordersSameStyle: %d dashedSides: 0x%02x\n",
+                      mAllBordersSameStyle,
+                      static_cast<unsigned int>(dashedSides));
+
+  if (mAllBordersSameStyle && !forceSeparateCorners) {
+    /* Draw everything in one go */
+    DrawBorderSides(SideBits::eAll);
+    PrintAsStringNewline("---------------- (1)");
+  } else {
+    AUTO_PROFILER_LABEL("nsCSSBorderRenderer::DrawBorders:multipass", GRAPHICS);
+
+    /* We have more than one pass to go.  Draw the corners separately from the
+     * sides. */
+
+    // The corner is going to have negligible size if its two adjacent border
+    // sides are only 1px wide and there is no border radius.  In that case we
+    // skip the overhead of painting the corner by setting the width or height
+    // of the corner to zero, which effectively extends one of the corner's
+    // adjacent border sides.  We extend the longer adjacent side so that
+    // opposite sides will be the same length, which is necessary for opposite
+    // dashed/dotted sides to be symmetrical.
+    //
+    //   if width > height
+    //     +--+--------------+--+    +--------------------+
+    //     |  |              |  |    |                    |
+    //     +--+--------------+--+    +--+--------------+--+
+    //     |  |              |  |    |  |              |  |
+    //     |  |              |  | => |  |              |  |
+    //     |  |              |  |    |  |              |  |
+    //     +--+--------------+--+    +--+--------------+--+
+    //     |  |              |  |    |                    |
+    //     +--+--------------+--+    +--------------------+
+    //
+    //   if width <= height
+    //     +--+--------+--+    +--+--------+--+
+    //     |  |        |  |    |  |        |  |
+    //     +--+--------+--+    |  +--------+  |
+    //     |  |        |  |    |  |        |  |
+    //     |  |        |  |    |  |        |  |
+    //     |  |        |  |    |  |        |  |
+    //     |  |        |  | => |  |        |  |
+    //     |  |        |  |    |  |        |  |
+    //     |  |        |  |    |  |        |  |
+    //     |  |        |  |    |  |        |  |
+    //     +--+--------+--+    |  +--------+  |
+    //     |  |        |  |    |  |        |  |
+    //     +--+--------+--+    +--+--------+--+
+    //
+    // Note that if we have different border widths we could end up with
+    // opposite sides of different length.  For example, if the left and
+    // bottom borders are 2px wide instead of 1px, we will end up doing
+    // something like:
+    //
+    //     +----+------------+--+    +----+---------------+
+    //     |    |            |  |    |    |               |
+    //     +----+------------+--+    +----+------------+--+
+    //     |    |            |  |    |    |            |  |
+    //     |    |            |  | => |    |            |  |
+    //     |    |            |  |    |    |            |  |
+    //     +----+------------+--+    +----+------------+--+
+    //     |    |            |  |    |    |            |  |
+    //     |    |            |  |    |    |            |  |
+    //     +----+------------+--+    +----+------------+--+
+    //
+    // XXX Should we only do this optimization if |mAllBordersSameWidth| is
+    // true?
+    //
+    // XXX In fact is this optimization even worth the complexity it adds to
+    // the code?  1px wide dashed borders are not overly common, and drawing
+    // corners for them is not that expensive.
+    for (const auto corner : mozilla::AllPhysicalCorners()) {
+      const mozilla::Side sides[2] = {mozilla::Side(corner), PREV_SIDE(corner)};
+
+      if (!IsZeroSize(mBorderRadii[corner])) {
+        continue;
+      }
+
+      if (mBorderWidths[sides[0]] == 1.0 && mBorderWidths[sides[1]] == 1.0) {
+        if (mOuterRect.Width() > mOuterRect.Height()) {
+          mBorderCornerDimensions[corner].width = 0.0;
+        } else {
+          mBorderCornerDimensions[corner].height = 0.0;
+        }
+      }
+    }
+
+    // First, the corners
+    for (const auto corner : mozilla::AllPhysicalCorners()) {
+      // if there's no corner, don't do all this work for it
+      if (IsZeroSize(mBorderCornerDimensions[corner])) {
+        continue;
+      }
+
+      const int sides[2] = {corner, PREV_SIDE(corner)};
+      SideBits sideBits =
+          static_cast<SideBits>((1 << sides[0]) | (1 << sides[1]));
+
+      bool simpleCornerStyle = AreBorderSideFinalStylesSame(sideBits);
+
+      // If we don't have anything complex going on in this corner,
+      // then we can just fill the corner with a solid color, and avoid
+      // the potentially expensive clip.
+      if (simpleCornerStyle && IsZeroSize(mBorderRadii[corner]) &&
+          IsSolidCornerStyle(mBorderStyles[sides[0]], corner)) {
+        sRGBColor color = MakeBorderColor(
+            mBorderColors[sides[0]],
+            BorderColorStyleForSolidCorner(mBorderStyles[sides[0]], corner));
+        mDrawTarget->FillRect(GetCornerRect(corner),
+                              ColorPattern(ToDeviceColor(color)));
+        continue;
+      }
+
+      // clip to the corner
+      mDrawTarget->PushClipRect(GetCornerRect(corner));
+
+      if (simpleCornerStyle) {
+        // we don't need a group for this corner, the sides are the same,
+        // but we weren't able to render just a solid block for the corner.
+        DrawBorderSides(sideBits);
+      } else {
+        // Sides are different.  We could draw using OP_ADD to
+        // get correct color blending behaviour at the seam.  We'd need
+        // to do it in an offscreen surface to ensure that we're
+        // always compositing on transparent black.  If the colors
+        // don't have transparency and the current destination surface
+        // has an alpha channel, we could just clear the region and
+        // avoid the temporary, but that situation doesn't happen all
+        // that often in practice (we double buffer to no-alpha
+        // surfaces). We choose just to seam though, as the performance
+        // advantages outway the modest easthetic improvement.
+
+        for (int cornerSide = 0; cornerSide < 2; cornerSide++) {
+          mozilla::Side side = mozilla::Side(sides[cornerSide]);
+          StyleBorderStyle style = mBorderStyles[side];
+
+          PrintAsFormatString("corner: %d cornerSide: %d side: %d style: %d\n",
+                              corner, cornerSide, side,
+                              static_cast<int>(style));
+
+          RefPtr<Path> path = GetSideClipSubPath(side);
+          mDrawTarget->PushClip(path);
+
+          DrawBorderSides(static_cast<mozilla::SideBits>(1 << side));
+
+          mDrawTarget->PopClip();
+        }
+      }
+
+      mDrawTarget->PopClip();
+
+      PrintAsStringNewline();
+    }
+
+    // in the case of a single-unit border, we already munged the
+    // corners up above; so we can just draw the top left and bottom
+    // right sides separately, if they're the same.
+    //
+    // We need to check for mNoBorderRadius, because when there is
+    // one, FillSolidBorder always draws the full rounded rectangle
+    // and expects there to be a clip in place.
+    SideBits alreadyDrawnSides = SideBits::eNone;
+    if (mOneUnitBorder && mNoBorderRadius &&
+        (dashedSides & (SideBits::eTop | SideBits::eLeft)) == SideBits::eNone) {
+      bool tlBordersSameStyle =
+          AreBorderSideFinalStylesSame(SideBits::eTop | SideBits::eLeft);
+      bool brBordersSameStyle =
+          AreBorderSideFinalStylesSame(SideBits::eBottom | SideBits::eRight);
+
+      if (tlBordersSameStyle) {
+        DrawBorderSides(SideBits::eTop | SideBits::eLeft);
+        alreadyDrawnSides |= (SideBits::eTop | SideBits::eLeft);
+      }
+
+      if (brBordersSameStyle &&
+          (dashedSides & (SideBits::eBottom | SideBits::eRight)) ==
+              SideBits::eNone) {
+        DrawBorderSides(SideBits::eBottom | SideBits::eRight);
+        alreadyDrawnSides |= (SideBits::eBottom | SideBits::eRight);
+      }
+    }
+
+    // We're done with the corners, now draw the sides.
+    for (const auto side : mozilla::AllPhysicalSides()) {
+      // if we drew it above, skip it
+      if (alreadyDrawnSides & static_cast<mozilla::SideBits>(1 << side)) {
+        continue;
+      }
+
+      // If there's no border on this side, skip it
+      if (mBorderWidths[side] == 0.0 ||
+          mBorderStyles[side] == StyleBorderStyle::Hidden ||
+          mBorderStyles[side] == StyleBorderStyle::None) {
+        continue;
+      }
+
+      if (dashedSides & static_cast<mozilla::SideBits>(1 << side)) {
+        // Dashed sides will always draw just the part ignoring the
+        // corners for the side, so no need to clip.
+        DrawDashedOrDottedSide(side);
+
+        PrintAsStringNewline("---------------- (d)");
+        continue;
+      }
+
+      // Undashed sides will currently draw the entire side,
+      // including parts that would normally be covered by a corner,
+      // so we need to clip.
+      //
+      // XXX Optimization -- it would be good to make this work like
+      // DrawDashedOrDottedSide, and have a DrawOneSide function that just
+      // draws one side and not the corners, because then we can
+      // avoid the potentially expensive clip.
+      mDrawTarget->PushClipRect(GetSideClipWithoutCornersRect(side));
+
+      DrawBorderSides(static_cast<mozilla::SideBits>(1 << side));
+
+      mDrawTarget->PopClip();
+
+      PrintAsStringNewline("---------------- (*)");
+    }
+  }
+}
+
+void nsCSSBorderRenderer::CreateWebRenderCommands(
+    nsDisplayItem* aItem, wr::DisplayListBuilder& aBuilder,
+    wr::IpcResourceUpdateQueue& aResources,
+    const layers::StackingContextHelper& aSc) {
+  LayoutDeviceRect outerRect = LayoutDeviceRect::FromUnknownRect(mOuterRect);
+  wr::LayoutRect roundedRect = wr::ToLayoutRect(outerRect);
+  wr::LayoutRect clipRect = roundedRect;
+  wr::BorderSide side[4];
+  for (const auto i : mozilla::AllPhysicalSides()) {
+    side[i] =
+        wr::ToBorderSide(ToDeviceColor(mBorderColors[i]), mBorderStyles[i]);
+  }
+
+  wr::BorderRadius borderRadius = wr::ToBorderRadius(mBorderRadii);
+
+  if (mLocalClip) {
+    LayoutDeviceRect localClip =
+        LayoutDeviceRect::FromUnknownRect(mLocalClip.value());
+    clipRect = wr::ToLayoutRect(localClip.Intersect(outerRect));
+  }
+
+  Range<const wr::BorderSide> wrsides(side, 4);
+  aBuilder.PushBorder(roundedRect, clipRect, mBackfaceIsVisible,
+                      wr::ToBorderWidths(mBorderWidths[0], mBorderWidths[1],
+                                         mBorderWidths[2], mBorderWidths[3]),
+                      wrsides, borderRadius);
+}
+
+/* static */
+Maybe<nsCSSBorderImageRenderer>
+nsCSSBorderImageRenderer::CreateBorderImageRenderer(
+    nsPresContext* aPresContext, nsIFrame* aForFrame, const nsRect& aBorderArea,
+    const nsStyleBorder& aStyleBorder, const nsRect& aDirtyRect,
+    Sides aSkipSides, uint32_t aFlags, ImgDrawResult* aDrawResult) {
+  MOZ_ASSERT(aDrawResult);
+
+  if (aDirtyRect.IsEmpty()) {
+    *aDrawResult = ImgDrawResult::SUCCESS;
+    return Nothing();
+  }
+
+  nsImageRenderer imgRenderer(aForFrame, &aStyleBorder.mBorderImageSource,
+                              aFlags);
+  if (!imgRenderer.PrepareImage()) {
+    *aDrawResult = imgRenderer.PrepareResult();
+    return Nothing();
+  }
+
+  // We should always get here with the frame's border, but we may construct an
+  // nsStyleBorder om the stack to deal with :visited and other shenaningans.
+  //
+  // We always copy the border image and such from the non-visited one, so
+  // there's no need to do anything with it.
+  MOZ_ASSERT(aStyleBorder.GetBorderImageRequest() ==
+             aForFrame->StyleBorder()->GetBorderImageRequest());
+
+  nsCSSBorderImageRenderer renderer(aForFrame, aBorderArea, aStyleBorder,
+                                    aSkipSides, imgRenderer);
+  *aDrawResult = ImgDrawResult::SUCCESS;
+  return Some(renderer);
+}
+
+ImgDrawResult nsCSSBorderImageRenderer::DrawBorderImage(
+    nsPresContext* aPresContext, gfxContext& aRenderingContext,
+    nsIFrame* aForFrame, const nsRect& aDirtyRect) {
+  // NOTE: no Save() yet, we do that later by calling autoSR.EnsureSaved()
+  // in case we need it.
+  gfxContextAutoSaveRestore autoSR;
+
+  if (!mClip.IsEmpty()) {
+    autoSR.EnsureSaved(&aRenderingContext);
+    aRenderingContext.Clip(NSRectToSnappedRect(
+        mClip, aForFrame->PresContext()->AppUnitsPerDevPixel(),
+        *aRenderingContext.GetDrawTarget()));
+  }
+
+  // intrinsicSize.CanComputeConcreteSize() return false means we can not
+  // read intrinsic size from aStyleBorder.mBorderImageSource.
+  // In this condition, we pass imageSize(a resolved size comes from
+  // default sizing algorithm) to renderer as the viewport size.
+  CSSSizeOrRatio intrinsicSize = mImageRenderer.ComputeIntrinsicSize();
+  Maybe<nsSize> svgViewportSize =
+      intrinsicSize.CanComputeConcreteSize() ? Nothing() : Some(mImageSize);
+  bool hasIntrinsicRatio = intrinsicSize.HasRatio();
+  mImageRenderer.PurgeCacheForViewportChange(svgViewportSize,
+                                             hasIntrinsicRatio);
+
+  // These helper tables recharacterize the 'slice' and 'width' margins
+  // in a more convenient form: they are the x/y/width/height coords
+  // required for various bands of the border, and they have been transformed
+  // to be relative to the innerRect (for 'slice') or the page (for 'border').
+  enum { LEFT, MIDDLE, RIGHT, TOP = LEFT, BOTTOM = RIGHT };
+  const nscoord borderX[3] = {
+      mArea.x + 0,
+      mArea.x + mWidths.left,
+      mArea.x + mArea.width - mWidths.right,
+  };
+  const nscoord borderY[3] = {
+      mArea.y + 0,
+      mArea.y + mWidths.top,
+      mArea.y + mArea.height - mWidths.bottom,
+  };
+  const nscoord borderWidth[3] = {
+      mWidths.left,
+      mArea.width - mWidths.left - mWidths.right,
+      mWidths.right,
+  };
+  const nscoord borderHeight[3] = {
+      mWidths.top,
+      mArea.height - mWidths.top - mWidths.bottom,
+      mWidths.bottom,
+  };
+  const int32_t sliceX[3] = {
+      0,
+      mSlice.left,
+      mImageSize.width - mSlice.right,
+  };
+  const int32_t sliceY[3] = {
+      0,
+      mSlice.top,
+      mImageSize.height - mSlice.bottom,
+  };
+  const int32_t sliceWidth[3] = {
+      mSlice.left,
+      std::max(mImageSize.width - mSlice.left - mSlice.right, 0),
+      mSlice.right,
+  };
+  const int32_t sliceHeight[3] = {
+      mSlice.top,
+      std::max(mImageSize.height - mSlice.top - mSlice.bottom, 0),
+      mSlice.bottom,
+  };
+
+  ImgDrawResult result = ImgDrawResult::SUCCESS;
+
+  for (int i = LEFT; i <= RIGHT; i++) {
+    for (int j = TOP; j <= BOTTOM; j++) {
+      StyleBorderImageRepeat fillStyleH, fillStyleV;
+      nsSize unitSize;
+
+      if (i == MIDDLE && j == MIDDLE) {
+        // Discard the middle portion unless set to fill.
+        if (!mFill) {
+          continue;
+        }
+
+        // css-background:
+        //     The middle image's width is scaled by the same factor as the
+        //     top image unless that factor is zero or infinity, in which
+        //     case the scaling factor of the bottom is substituted, and
+        //     failing that, the width is not scaled. The height of the
+        //     middle image is scaled by the same factor as the left image
+        //     unless that factor is zero or infinity, in which case the
+        //     scaling factor of the right image is substituted, and failing
+        //     that, the height is not scaled.
+        gfxFloat hFactor, vFactor;
+
+        if (0 < mWidths.left && 0 < mSlice.left) {
+          vFactor = gfxFloat(mWidths.left) / mSlice.left;
+        } else if (0 < mWidths.right && 0 < mSlice.right) {
+          vFactor = gfxFloat(mWidths.right) / mSlice.right;
+        } else {
+          vFactor = 1;
+        }
+
+        if (0 < mWidths.top && 0 < mSlice.top) {
+          hFactor = gfxFloat(mWidths.top) / mSlice.top;
+        } else if (0 < mWidths.bottom && 0 < mSlice.bottom) {
+          hFactor = gfxFloat(mWidths.bottom) / mSlice.bottom;
+        } else {
+          hFactor = 1;
+        }
+
+        unitSize.width = sliceWidth[i] * hFactor;
+        unitSize.height = sliceHeight[j] * vFactor;
+        fillStyleH = mRepeatModeHorizontal;
+        fillStyleV = mRepeatModeVertical;
+
+      } else if (i == MIDDLE) {  // top, bottom
+        // Sides are always stretched to the thickness of their border,
+        // and stretched proportionately on the other axis.
+        gfxFloat factor;
+        if (0 < borderHeight[j] && 0 < sliceHeight[j]) {
+          factor = gfxFloat(borderHeight[j]) / sliceHeight[j];
+        } else {
+          factor = 1;
+        }
+
+        unitSize.width = sliceWidth[i] * factor;
+        unitSize.height = borderHeight[j];
+        fillStyleH = mRepeatModeHorizontal;
+        fillStyleV = StyleBorderImageRepeat::Stretch;
+
+      } else if (j == MIDDLE) {  // left, right
+        gfxFloat factor;
+        if (0 < borderWidth[i] && 0 < sliceWidth[i]) {
+          factor = gfxFloat(borderWidth[i]) / sliceWidth[i];
+        } else {
+          factor = 1;
+        }
+
+        unitSize.width = borderWidth[i];
+        unitSize.height = sliceHeight[j] * factor;
+        fillStyleH = StyleBorderImageRepeat::Stretch;
+        fillStyleV = mRepeatModeVertical;
+
+      } else {
+        // Corners are always stretched to fit the corner.
+        unitSize.width = borderWidth[i];
+        unitSize.height = borderHeight[j];
+        fillStyleH = StyleBorderImageRepeat::Stretch;
+        fillStyleV = StyleBorderImageRepeat::Stretch;
+      }
+
+      nsRect destArea(borderX[i], borderY[j], borderWidth[i], borderHeight[j]);
+      nsRect subArea(sliceX[i], sliceY[j], sliceWidth[i], sliceHeight[j]);
+      if (subArea.IsEmpty()) continue;
+
+      nsIntRect intSubArea = subArea.ToOutsidePixels(AppUnitsPerCSSPixel());
+      result &= mImageRenderer.DrawBorderImageComponent(
+          aPresContext, aRenderingContext, aDirtyRect, destArea,
+          CSSIntRect(intSubArea.x, intSubArea.y, intSubArea.width,
+                     intSubArea.height),
+          fillStyleH, fillStyleV, unitSize, j * (RIGHT + 1) + i,
+          svgViewportSize, hasIntrinsicRatio);
+    }
+  }
+
+  return result;
+}
+
+ImgDrawResult nsCSSBorderImageRenderer::CreateWebRenderCommands(
+    nsDisplayItem* aItem, nsIFrame* aForFrame,
+    mozilla::wr::DisplayListBuilder& aBuilder,
+    mozilla::wr::IpcResourceUpdateQueue& aResources,
+    const mozilla::layers::StackingContextHelper& aSc,
+    mozilla::layers::RenderRootStateManager* aManager,
+    nsDisplayListBuilder* aDisplayListBuilder) {
+  if (!mImageRenderer.IsReady()) {
+    return ImgDrawResult::NOT_READY;
+  }
+
+  float widths[4];
+  float slice[4];
+  float outset[4];
+  const int32_t appUnitsPerDevPixel =
+      aForFrame->PresContext()->AppUnitsPerDevPixel();
+  for (const auto i : mozilla::AllPhysicalSides()) {
+    slice[i] = (float)(mSlice.Side(i)) / appUnitsPerDevPixel;
+    widths[i] = (float)(mWidths.Side(i)) / appUnitsPerDevPixel;
+
+    // The outset is already taken into account by the adjustments to mArea
+    // in our constructor. We use mArea as our dest rect so we can just supply
+    // zero outsets to WebRender.
+    outset[i] = 0.0f;
+  }
+
+  LayoutDeviceRect destRect =
+      LayoutDeviceRect::FromAppUnits(mArea, appUnitsPerDevPixel);
+  destRect.Round();
+  wr::LayoutRect dest = wr::ToLayoutRect(destRect);
+
+  wr::LayoutRect clip = dest;
+  if (!mClip.IsEmpty()) {
+    LayoutDeviceRect clipRect =
+        LayoutDeviceRect::FromAppUnits(mClip, appUnitsPerDevPixel);
+    clip = wr::ToLayoutRect(clipRect);
+  }
+
+  ImgDrawResult drawResult = ImgDrawResult::SUCCESS;
+  switch (mImageRenderer.GetType()) {
+    case StyleImage::Tag::Rect:
+    case StyleImage::Tag::Url: {
+      RefPtr<imgIContainer> img = mImageRenderer.GetImage();
+      if (!img || img->GetType() == imgIContainer::TYPE_VECTOR) {
+        // Vector images will redraw each segment of the border up to 8 times.
+        // We draw using a restricted region derived from the segment's clip and
+        // scale the image accordingly (see ClippedImage::Draw). If we follow
+        // this convention as is for WebRender, we will need to rasterize the
+        // entire vector image scaled up without the restriction region, which
+        // means our main thread CPU and memory footprints will be much higher.
+        // Ideally we would be able to provide a raster image for each segment
+        // of the border. For now we use fallback.
+        return ImgDrawResult::NOT_SUPPORTED;
+      }
+
+      uint32_t flags = aDisplayListBuilder->GetImageDecodeFlags();
+
+      LayoutDeviceRect imageRect = LayoutDeviceRect::FromAppUnits(
+          nsRect(nsPoint(), mImageRenderer.GetSize()), appUnitsPerDevPixel);
+
+      SVGImageContext svgContext;
+      Maybe<ImageIntRegion> region;
+      gfx::IntSize decodeSize =
+          nsLayoutUtils::ComputeImageContainerDrawingParameters(
+              img, aForFrame, imageRect, imageRect, aSc, flags, svgContext,
+              region);
+
+      RefPtr<WebRenderImageProvider> provider;
+      drawResult = img->GetImageProvider(aManager->LayerManager(), decodeSize,
+                                         svgContext, region, flags,
+                                         getter_AddRefs(provider));
+
+      Maybe<wr::ImageKey> key =
+          aManager->CommandBuilder().CreateImageProviderKey(
+              aItem, provider, drawResult, aResources);
+      if (key.isNothing()) {
+        break;
+      }
+
+      auto rendering =
+          wr::ToImageRendering(aItem->Frame()->UsedImageRendering());
+      if (mFill) {
+        float epsilon = 0.0001;
+        bool noVerticalBorders = widths[0] <= epsilon && widths[2] < epsilon;
+        bool noHorizontalBorders = widths[1] <= epsilon && widths[3] < epsilon;
+
+        // Border image with no border. It's a little silly but WebRender
+        // currently does not handle this. We could fall back to a blob image
+        // but there are reftests that are sensible to the test going through a
+        // blob while the reference doesn't.
+        if (noVerticalBorders && noHorizontalBorders) {
+          aBuilder.PushImage(dest, clip, !aItem->BackfaceIsHidden(), false,
+                             rendering, key.value());
+          break;
+        }
+
+        // Fall-back if we want to fill the middle area and opposite edges are
+        // both empty.
+        // TODO(bug 1609893): moving some of the repetition handling code out
+        // of the image shader will make it easier to handle these cases
+        // properly.
+        if (noHorizontalBorders || noVerticalBorders) {
+          return ImgDrawResult::NOT_SUPPORTED;
+        }
+      }
+
+      wr::WrBorderImage params{
+          wr::ToBorderWidths(widths[0], widths[1], widths[2], widths[3]),
+          key.value(),
+          rendering,
+          mImageSize.width / appUnitsPerDevPixel,
+          mImageSize.height / appUnitsPerDevPixel,
+          mFill,
+          wr::ToDeviceIntSideOffsets(slice[0], slice[1], slice[2], slice[3]),
+          wr::ToLayoutSideOffsets(outset[0], outset[1], outset[2], outset[3]),
+          wr::ToRepeatMode(mRepeatModeHorizontal),
+          wr::ToRepeatMode(mRepeatModeVertical)};
+
+      aBuilder.PushBorderImage(dest, clip, !aItem->BackfaceIsHidden(), params);
+      break;
+    }
+    case StyleImage::Tag::Gradient: {
+      const StyleGradient& gradient = *mImageRenderer.GetGradientData();
+      nsCSSGradientRenderer renderer = nsCSSGradientRenderer::Create(
+          aForFrame->PresContext(), aForFrame->Style(), gradient, mImageSize);
+
+      wr::ExtendMode extendMode;
+      nsTArray<wr::GradientStop> stops;
+      LayoutDevicePoint lineStart;
+      LayoutDevicePoint lineEnd;
+      LayoutDeviceSize gradientRadius;
+      LayoutDevicePoint gradientCenter;
+      float gradientAngle;
+      renderer.BuildWebRenderParameters(1.0, extendMode, stops, lineStart,
+                                        lineEnd, gradientRadius, gradientCenter,
+                                        gradientAngle);
+
+      if (gradient.IsLinear()) {
+        LayoutDevicePoint startPoint =
+            LayoutDevicePoint(dest.min.x, dest.min.y) + lineStart;
+        LayoutDevicePoint endPoint =
+            LayoutDevicePoint(dest.min.x, dest.min.y) + lineEnd;
+
+        aBuilder.PushBorderGradient(
+            dest, clip, !aItem->BackfaceIsHidden(),
+            wr::ToBorderWidths(widths[0], widths[1], widths[2], widths[3]),
+            (float)(mImageSize.width) / appUnitsPerDevPixel,
+            (float)(mImageSize.height) / appUnitsPerDevPixel, mFill,
+            wr::ToDeviceIntSideOffsets(slice[0], slice[1], slice[2], slice[3]),
+            wr::ToLayoutPoint(startPoint), wr::ToLayoutPoint(endPoint), stops,
+            extendMode,
+            wr::ToLayoutSideOffsets(outset[0], outset[1], outset[2],
+                                    outset[3]));
+      } else if (gradient.IsRadial()) {
+        aBuilder.PushBorderRadialGradient(
+            dest, clip, !aItem->BackfaceIsHidden(),
+            wr::ToBorderWidths(widths[0], widths[1], widths[2], widths[3]),
+            mFill, wr::ToLayoutPoint(lineStart),
+            wr::ToLayoutSize(gradientRadius), stops, extendMode,
+            wr::ToLayoutSideOffsets(outset[0], outset[1], outset[2],
+                                    outset[3]));
+      } else {
+        MOZ_ASSERT(gradient.IsConic());
+        aBuilder.PushBorderConicGradient(
+            dest, clip, !aItem->BackfaceIsHidden(),
+            wr::ToBorderWidths(widths[0], widths[1], widths[2], widths[3]),
+            mFill, wr::ToLayoutPoint(gradientCenter), gradientAngle, stops,
+            extendMode,
+            wr::ToLayoutSideOffsets(outset[0], outset[1], outset[2],
+                                    outset[3]));
+      }
+      break;
+    }
+    default:
+      MOZ_ASSERT_UNREACHABLE("Unsupport border image type");
+      drawResult = ImgDrawResult::NOT_SUPPORTED;
+  }
+
+  return drawResult;
+}
+
+nsCSSBorderImageRenderer::nsCSSBorderImageRenderer(
+    const nsCSSBorderImageRenderer& aRhs)
+    : mImageRenderer(aRhs.mImageRenderer),
+      mImageSize(aRhs.mImageSize),
+      mSlice(aRhs.mSlice),
+      mWidths(aRhs.mWidths),
+      mImageOutset(aRhs.mImageOutset),
+      mArea(aRhs.mArea),
+      mClip(aRhs.mClip),
+      mRepeatModeHorizontal(aRhs.mRepeatModeHorizontal),
+      mRepeatModeVertical(aRhs.mRepeatModeVertical),
+      mFill(aRhs.mFill) {
+  Unused << mImageRenderer.PrepareResult();
+}
+
+nsCSSBorderImageRenderer& nsCSSBorderImageRenderer::operator=(
+    const nsCSSBorderImageRenderer& aRhs) {
+  mImageRenderer = aRhs.mImageRenderer;
+  mImageSize = aRhs.mImageSize;
+  mSlice = aRhs.mSlice;
+  mWidths = aRhs.mWidths;
+  mImageOutset = aRhs.mImageOutset;
+  mArea = aRhs.mArea;
+  mClip = aRhs.mClip;
+  mRepeatModeHorizontal = aRhs.mRepeatModeHorizontal;
+  mRepeatModeVertical = aRhs.mRepeatModeVertical;
+  mFill = aRhs.mFill;
+  Unused << mImageRenderer.PrepareResult();
+
+  return *this;
+}
+
+nsCSSBorderImageRenderer::nsCSSBorderImageRenderer(
+    nsIFrame* aForFrame, const nsRect& aBorderArea,
+    const nsStyleBorder& aStyleBorder, Sides aSkipSides,
+    const nsImageRenderer& aImageRenderer)
+    : mImageRenderer(aImageRenderer) {
+  // Determine the border image area, which by default corresponds to the
+  // border box but can be modified by 'border-image-outset'.
+  // Note that 'border-radius' do not apply to 'border-image' borders per
+  // <http://dev.w3.org/csswg/css-backgrounds/#corner-clipping>.
+  nsMargin borderWidths(aStyleBorder.GetComputedBorder());
+  mImageOutset = aStyleBorder.GetImageOutset();
+  if (nsCSSRendering::IsBoxDecorationSlice(aStyleBorder) &&
+      !aSkipSides.IsEmpty()) {
+    mArea = nsCSSRendering::BoxDecorationRectForBorder(
+        aForFrame, aBorderArea, aSkipSides, &aStyleBorder);
+    if (mArea.IsEqualEdges(aBorderArea)) {
+      // No need for a clip, just skip the sides we don't want.
+      borderWidths.ApplySkipSides(aSkipSides);
+      mImageOutset.ApplySkipSides(aSkipSides);
+      mArea.Inflate(mImageOutset);
+    } else {
+      // We're drawing borders around the joined continuation boxes so we need
+      // to clip that to the slice that we want for this frame.
+      mArea.Inflate(mImageOutset);
+      mImageOutset.ApplySkipSides(aSkipSides);
+      mClip = aBorderArea;
+      mClip.Inflate(mImageOutset);
+    }
+  } else {
+    mArea = aBorderArea;
+    mArea.Inflate(mImageOutset);
+  }
+
+  // Calculate the image size used to compute slice points.
+  CSSSizeOrRatio intrinsicSize = mImageRenderer.ComputeIntrinsicSize();
+  mImageSize = nsImageRenderer::ComputeConcreteSize(
+      CSSSizeOrRatio(), intrinsicSize, mArea.Size());
+  mImageRenderer.SetPreferredSize(intrinsicSize, mImageSize);
+
+  // Compute the used values of 'border-image-slice' and 'border-image-width';
+  // we do them together because the latter can depend on the former.
+  nsMargin slice;
+  nsMargin border;
+  for (const auto s : mozilla::AllPhysicalSides()) {
+    const auto& slice = aStyleBorder.mBorderImageSlice.offsets.Get(s);
+    int32_t imgDimension =
+        SideIsVertical(s) ? mImageSize.width : mImageSize.height;
+    nscoord borderDimension = SideIsVertical(s) ? mArea.width : mArea.height;
+    double value;
+    if (slice.IsNumber()) {
+      value = nsPresContext::CSSPixelsToAppUnits(NS_lround(slice.AsNumber()));
+    } else {
+      MOZ_ASSERT(slice.IsPercentage());
+      value = slice.AsPercentage()._0 * imgDimension;
+    }
+    if (value < 0) {
+      value = 0;
+    }
+    if (value > imgDimension && imgDimension > 0) {
+      value = imgDimension;
+    }
+    mSlice.Side(s) = value;
+
+    const auto& width = aStyleBorder.mBorderImageWidth.Get(s);
+    switch (width.tag) {
+      case StyleBorderImageSideWidth::Tag::LengthPercentage:
+        value =
+            std::max(0, width.AsLengthPercentage().Resolve(borderDimension));
+        break;
+      case StyleBorderImageSideWidth::Tag::Number:
+        value = width.AsNumber() * borderWidths.Side(s);
+        break;
+      case StyleBorderImageSideWidth::Tag::Auto:
+        value = mSlice.Side(s);
+        break;
+      default:
+        MOZ_ASSERT_UNREACHABLE("unexpected CSS unit for border image area");
+        value = 0;
+        break;
+    }
+    // NSToCoordRoundWithClamp rounds towards infinity, but that's OK
+    // because we expect value to be non-negative.
+    MOZ_ASSERT(value >= 0);
+    mWidths.Side(s) = NSToCoordRoundWithClamp(value);
+    MOZ_ASSERT(mWidths.Side(s) >= 0);
+  }
+
+  // "If two opposite border-image-width offsets are large enough that they
+  // overlap, their used values are proportionately reduced until they no
+  // longer overlap."
+  uint32_t combinedBorderWidth =
+      uint32_t(mWidths.left) + uint32_t(mWidths.right);
+  double scaleX = combinedBorderWidth > uint32_t(mArea.width)
+                      ? mArea.width / double(combinedBorderWidth)
+                      : 1.0;
+  uint32_t combinedBorderHeight =
+      uint32_t(mWidths.top) + uint32_t(mWidths.bottom);
+  double scaleY = combinedBorderHeight > uint32_t(mArea.height)
+                      ? mArea.height / double(combinedBorderHeight)
+                      : 1.0;
+  double scale = std::min(scaleX, scaleY);
+  if (scale < 1.0) {
+    mWidths.left *= scale;
+    mWidths.right *= scale;
+    mWidths.top *= scale;
+    mWidths.bottom *= scale;
+    NS_ASSERTION(mWidths.left + mWidths.right <= mArea.width &&
+                     mWidths.top + mWidths.bottom <= mArea.height,
+                 "rounding error in width reduction???");
+  }
+
+  mRepeatModeHorizontal = aStyleBorder.mBorderImageRepeatH;
+  mRepeatModeVertical = aStyleBorder.mBorderImageRepeatV;
+  mFill = aStyleBorder.mBorderImageSlice.fill;
+}
diff --git a/layout/painting/nsCSSRenderingBorders.h b/layout/painting/nsCSSRenderingBorders.h
new file mode 100644
index 0000000000..8817083208
--- /dev/null
+++ b/layout/painting/nsCSSRenderingBorders.h
@@ -0,0 +1,357 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef NS_CSS_RENDERING_BORDERS_H
+#define NS_CSS_RENDERING_BORDERS_H
+
+#include "gfxRect.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/gfx/2D.h"
+#include "mozilla/gfx/BezierUtils.h"
+#include "mozilla/gfx/PathHelpers.h"
+#include "mozilla/RefPtr.h"
+#include "nsColor.h"
+#include "nsCOMPtr.h"
+#include "nsIFrame.h"
+#include "nsImageRenderer.h"
+#include "gfxUtils.h"
+
+struct nsBorderColors;
+
+namespace mozilla {
+class nsDisplayItem;
+class nsDisplayList;
+class nsDisplayListBuilder;
+
+class nsDisplayBorder;
+class nsDisplayButtonBorder;
+class nsDisplayButtonForeground;
+class nsDisplayOutline;
+
+enum class StyleBorderStyle : uint8_t;
+enum class StyleBorderImageRepeat : uint8_t;
+
+namespace gfx {
+class GradientStops;
+}  // namespace gfx
+namespace layers {
+class StackingContextHelper;
+}  // namespace layers
+}  // namespace mozilla
+
+// define this to enable a bunch of debug dump info
+#undef DEBUG_NEW_BORDERS
+
+/*
+ * Helper class that handles border rendering.
+ *
+ * aDrawTarget -- the DrawTarget to which the border should be rendered
+ * outsideRect -- the rectangle on the outer edge of the border
+ *
+ * For any parameter where an array of side values is passed in,
+ * they are in top, right, bottom, left order.
+ *
+ * borderStyles -- one border style enum per side
+ * borderWidths -- one border width per side
+ * borderRadii -- a RectCornerRadii struct describing the w/h for each rounded
+ * corner. If the corner doesn't have a border radius, 0,0 should be given for
+ * it. borderColors -- one nscolor per side
+ *
+ * skipSides -- a bit mask specifying which sides, if any, to skip
+ * backgroundColor -- the background color of the element.
+ *    Used in calculating colors for 2-tone borders, such as inset and outset
+ * gapRect - a rectangle that should be clipped out to leave a gap in a border,
+ *    or nullptr if none.
+ */
+
+typedef enum {
+  BorderColorStyleNone,
+  BorderColorStyleSolid,
+  BorderColorStyleLight,
+  BorderColorStyleDark
+} BorderColorStyle;
+
+class nsPresContext;
+
+class nsCSSBorderRenderer final {
+  typedef mozilla::gfx::Bezier Bezier;
+  typedef mozilla::gfx::ColorPattern ColorPattern;
+  typedef mozilla::gfx::DrawTarget DrawTarget;
+  typedef mozilla::gfx::Float Float;
+  typedef mozilla::gfx::Path Path;
+  typedef mozilla::gfx::Point Point;
+  typedef mozilla::gfx::Rect Rect;
+  typedef mozilla::gfx::RectCornerRadii RectCornerRadii;
+  typedef mozilla::gfx::StrokeOptions StrokeOptions;
+
+  friend class mozilla::nsDisplayOutline;
+  friend class mozilla::nsDisplayButtonBorder;
+  friend class mozilla::nsDisplayButtonForeground;
+
+ public:
+  nsCSSBorderRenderer(nsPresContext* aPresContext, DrawTarget* aDrawTarget,
+                      const Rect& aDirtyRect, Rect& aOuterRect,
+                      const mozilla::StyleBorderStyle* aBorderStyles,
+                      const Float* aBorderWidths, RectCornerRadii& aBorderRadii,
+                      const nscolor* aBorderColors, bool aBackfaceIsVisible,
+                      const mozilla::Maybe<Rect>& aClipRect);
+
+  // draw the entire border
+  void DrawBorders();
+
+  void CreateWebRenderCommands(
+      mozilla::nsDisplayItem* aItem, mozilla::wr::DisplayListBuilder& aBuilder,
+      mozilla::wr::IpcResourceUpdateQueue& aResources,
+      const mozilla::layers::StackingContextHelper& aSc);
+
+  // utility function used for background painting as well as borders
+  static void ComputeInnerRadii(const RectCornerRadii& aRadii,
+                                const Float* aBorderSizes,
+                                RectCornerRadii* aInnerRadiiRet);
+
+  // Given aRadii as the border radii for a rectangle, compute the
+  // appropriate radii for another rectangle *outside* that rectangle
+  // by increasing the radii, except keeping sharp corners sharp.
+  // Used for spread box-shadows
+  static void ComputeOuterRadii(const RectCornerRadii& aRadii,
+                                const Float* aBorderSizes,
+                                RectCornerRadii* aOuterRadiiRet);
+
+  static bool AllCornersZeroSize(const RectCornerRadii& corners);
+
+ private:
+  RectCornerRadii mBorderCornerDimensions;
+
+  nsPresContext* mPresContext;
+
+  // destination DrawTarget and dirty rect
+  DrawTarget* mDrawTarget;
+  Rect mDirtyRect;
+
+  // the rectangle of the outside and the inside of the border
+  Rect mOuterRect;
+  Rect mInnerRect;
+
+  // the style and size of the border
+  mozilla::StyleBorderStyle mBorderStyles[4];
+  Float mBorderWidths[4];
+  RectCornerRadii mBorderRadii;
+
+  // the colors for 'border-top-color' et. al.
+  nscolor mBorderColors[4];
+
+  // calculated values
+  bool mAllBordersSameStyle;
+  bool mAllBordersSameWidth;
+  bool mOneUnitBorder;
+  bool mNoBorderRadius;
+  bool mAvoidStroke;
+  bool mBackfaceIsVisible;
+  mozilla::Maybe<Rect> mLocalClip;
+
+  // For all the sides in the bitmask, would they be rendered
+  // in an identical color and style?
+  bool AreBorderSideFinalStylesSame(mozilla::SideBits aSides);
+
+  // For the given style, is the given corner a solid color?
+  bool IsSolidCornerStyle(mozilla::StyleBorderStyle aStyle,
+                          mozilla::Corner aCorner);
+
+  // For the given corner, is the given corner mergeable into one dot?
+  bool IsCornerMergeable(mozilla::Corner aCorner);
+
+  // For the given solid corner, what color style should be used?
+  BorderColorStyle BorderColorStyleForSolidCorner(
+      mozilla::StyleBorderStyle aStyle, mozilla::Corner aCorner);
+
+  //
+  // Path generation functions
+  //
+
+  // Get the Rect for drawing the given corner
+  Rect GetCornerRect(mozilla::Corner aCorner);
+  // add the path for drawing the given side without any adjacent corners to the
+  // context
+  Rect GetSideClipWithoutCornersRect(mozilla::Side aSide);
+
+  // Create a clip path for the wedge that this side of
+  // the border should take up.  This is only called
+  // when we're drawing separate border sides, so we know
+  // that ADD compositing is taking place.
+  //
+  // This code needs to make sure that the individual pieces
+  // don't ever (mathematically) overlap; the pixel overlap
+  // is taken care of by the ADD compositing.
+  already_AddRefed<Path> GetSideClipSubPath(mozilla::Side aSide);
+
+  // Return start or end point for dashed/dotted side
+  Point GetStraightBorderPoint(mozilla::Side aSide, mozilla::Corner aCorner,
+                               bool* aIsUnfilled, Float aDotOffset = 0.0f);
+
+  // Return bezier control points for the outer and the inner curve for given
+  // corner
+  void GetOuterAndInnerBezier(Bezier* aOuterBezier, Bezier* aInnerBezier,
+                              mozilla::Corner aCorner);
+
+  // Given a set of sides to fill and a color, do so in the fastest way.
+  //
+  // Stroke tends to be faster for smaller borders because it doesn't go
+  // through the tessellator, which has initialization overhead.  If
+  // we're rendering all sides, we can use stroke at any thickness; we
+  // also do TL/BR pairs at 1px thickness using stroke.
+  //
+  // If we can't stroke, then if it's a TL/BR pair, we use the specific
+  // TL/BR paths.  Otherwise, we do the full path and fill.
+  //
+  // Calling code is expected to only set up a clip as necessary; no
+  // clip is needed if we can render the entire border in 1 or 2 passes.
+  void FillSolidBorder(const Rect& aOuterRect, const Rect& aInnerRect,
+                       const RectCornerRadii& aBorderRadii,
+                       const Float* aBorderSizes, mozilla::SideBits aSides,
+                       const ColorPattern& aColor);
+
+  //
+  // core rendering
+  //
+
+  // draw the border for the given sides, using the style of the first side
+  // present in the bitmask
+  void DrawBorderSides(mozilla::SideBits aSides);
+
+  // Setup the stroke options for the given dashed/dotted side
+  void SetupDashedOptions(StrokeOptions* aStrokeOptions, Float aDash[2],
+                          mozilla::Side aSide, Float aBorderLength,
+                          bool isCorner);
+
+  // Draw the given dashed/dotte side
+  void DrawDashedOrDottedSide(mozilla::Side aSide);
+
+  // Draw the given dotted side, each dot separately
+  void DrawDottedSideSlow(mozilla::Side aSide);
+
+  // Draw the given dashed/dotted corner
+  void DrawDashedOrDottedCorner(mozilla::Side aSide, mozilla::Corner aCorner);
+
+  // Draw the given dotted corner, each segment separately
+  void DrawDottedCornerSlow(mozilla::Side aSide, mozilla::Corner aCorner);
+
+  // Draw the given dashed corner, each dot separately
+  void DrawDashedCornerSlow(mozilla::Side aSide, mozilla::Corner aCorner);
+
+  // Draw the given dashed/dotted corner with solid style
+  void DrawFallbackSolidCorner(mozilla::Side aSide, mozilla::Corner aCorner);
+
+  // Analyze if all border sides have the same width.
+  bool AllBordersSameWidth();
+
+  // Analyze if all borders are 'solid' this also considers hidden or 'none'
+  // borders because they can be considered 'solid' borders of 0 width and
+  // with no color effect.
+  bool AllBordersSolid();
+
+  // Draw a solid color border that is uniformly the same width.
+  void DrawSingleWidthSolidBorder();
+
+  // Draw any border which is solid on all sides.
+  void DrawSolidBorder();
+};
+
+class nsCSSBorderImageRenderer final {
+  typedef mozilla::nsImageRenderer nsImageRenderer;
+
+ public:
+  static mozilla::Maybe<nsCSSBorderImageRenderer> CreateBorderImageRenderer(
+      nsPresContext* aPresContext, nsIFrame* aForFrame,
+      const nsRect& aBorderArea, const nsStyleBorder& aStyleBorder,
+      const nsRect& aDirtyRect, nsIFrame::Sides aSkipSides, uint32_t aFlags,
+      mozilla::image::ImgDrawResult* aDrawResult);
+
+  mozilla::image::ImgDrawResult DrawBorderImage(nsPresContext* aPresContext,
+                                                gfxContext& aRenderingContext,
+                                                nsIFrame* aForFrame,
+                                                const nsRect& aDirtyRect);
+  mozilla::image::ImgDrawResult CreateWebRenderCommands(
+      mozilla::nsDisplayItem* aItem, nsIFrame* aForFrame,
+      mozilla::wr::DisplayListBuilder& aBuilder,
+      mozilla::wr::IpcResourceUpdateQueue& aResources,
+      const mozilla::layers::StackingContextHelper& aSc,
+      mozilla::layers::RenderRootStateManager* aManager,
+      mozilla::nsDisplayListBuilder* aDisplayListBuilder);
+
+  nsCSSBorderImageRenderer(const nsCSSBorderImageRenderer& aRhs);
+  nsCSSBorderImageRenderer& operator=(const nsCSSBorderImageRenderer& aRhs);
+
+ private:
+  nsCSSBorderImageRenderer(nsIFrame* aForFrame, const nsRect& aBorderArea,
+                           const nsStyleBorder& aStyleBorder,
+                           nsIFrame::Sides aSkipSides,
+                           const nsImageRenderer& aImageRenderer);
+
+  nsImageRenderer mImageRenderer;
+  nsSize mImageSize;
+  nsMargin mSlice;
+  nsMargin mWidths;
+  nsMargin mImageOutset;
+  nsRect mArea;
+  nsRect mClip;
+  mozilla::StyleBorderImageRepeat mRepeatModeHorizontal;
+  mozilla::StyleBorderImageRepeat mRepeatModeVertical;
+  bool mFill;
+
+  friend class mozilla::nsDisplayBorder;
+  friend struct nsCSSRendering;
+};
+
+namespace mozilla {
+#ifdef DEBUG_NEW_BORDERS
+#  include <stdarg.h>
+
+static inline void PrintAsString(const mozilla::gfx::Point& p) {
+  fprintf(stderr, "[%f,%f]", p.x, p.y);
+}
+
+static inline void PrintAsString(const mozilla::gfx::Size& s) {
+  fprintf(stderr, "[%f %f]", s.width, s.height);
+}
+
+static inline void PrintAsString(const mozilla::gfx::Rect& r) {
+  fprintf(stderr, "[%f %f %f %f]", r.X(), r.Y(), r.Width(), r.Height());
+}
+
+static inline void PrintAsString(const mozilla::gfx::Float f) {
+  fprintf(stderr, "%f", f);
+}
+
+static inline void PrintAsString(const char* s) { fprintf(stderr, "%s", s); }
+
+static inline void PrintAsStringNewline(const char* s = nullptr) {
+  if (s) fprintf(stderr, "%s", s);
+  fprintf(stderr, "\n");
+  fflush(stderr);
+}
+
+static inline MOZ_FORMAT_PRINTF(1, 2) void PrintAsFormatString(const char* fmt,
+                                                               ...) {
+  va_list vl;
+  va_start(vl, fmt);
+  vfprintf(stderr, fmt, vl);
+  va_end(vl);
+}
+
+#else
+static inline void PrintAsString(const mozilla::gfx::Point& p) {}
+static inline void PrintAsString(const mozilla::gfx::Size& s) {}
+static inline void PrintAsString(const mozilla::gfx::Rect& r) {}
+static inline void PrintAsString(const mozilla::gfx::Float f) {}
+static inline void PrintAsString(const char* s) {}
+static inline void PrintAsStringNewline(const char* s = nullptr) {}
+static inline MOZ_FORMAT_PRINTF(1, 2) void PrintAsFormatString(const char* fmt,
+                                                               ...) {}
+#endif
+
+}  // namespace mozilla
+
+#endif /* NS_CSS_RENDERING_BORDERS_H */
diff --git a/layout/painting/nsCSSRenderingGradients.cpp b/layout/painting/nsCSSRenderingGradients.cpp
new file mode 100644
index 0000000000..2b8a8e84b0
--- /dev/null
+++ b/layout/painting/nsCSSRenderingGradients.cpp
@@ -0,0 +1,1291 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/* utility functions for drawing borders and backgrounds */
+
+#include "nsCSSRenderingGradients.h"
+
+#include <tuple>
+
+#include "gfx2DGlue.h"
+#include "mozilla/ArrayUtils.h"
+#include "mozilla/ComputedStyle.h"
+#include "mozilla/DebugOnly.h"
+#include "mozilla/gfx/2D.h"
+#include "mozilla/gfx/Helpers.h"
+#include "mozilla/MathAlgorithms.h"
+#include "mozilla/ProfilerLabels.h"
+
+#include "nsLayoutUtils.h"
+#include "nsStyleConsts.h"
+#include "nsPresContext.h"
+#include "nsPoint.h"
+#include "nsRect.h"
+#include "nsCSSColorUtils.h"
+#include "gfxContext.h"
+#include "nsStyleStructInlines.h"
+#include "nsCSSProps.h"
+#include "gfxUtils.h"
+#include "gfxGradientCache.h"
+
+#include "mozilla/layers/StackingContextHelper.h"
+#include "mozilla/layers/WebRenderLayerManager.h"
+#include "mozilla/webrender/WebRenderTypes.h"
+#include "mozilla/webrender/WebRenderAPI.h"
+#include "Units.h"
+
+using namespace mozilla;
+using namespace mozilla::gfx;
+
+static CSSPoint ResolvePosition(const Position& aPos, const CSSSize& aSize) {
+  CSSCoord h = aPos.horizontal.ResolveToCSSPixels(aSize.width);
+  CSSCoord v = aPos.vertical.ResolveToCSSPixels(aSize.height);
+  return CSSPoint(h, v);
+}
+
+// Given a box with size aBoxSize and origin (0,0), and an angle aAngle,
+// and a starting point for the gradient line aStart, find the endpoint of
+// the gradient line --- the intersection of the gradient line with a line
+// perpendicular to aAngle that passes through the farthest corner in the
+// direction aAngle.
+static CSSPoint ComputeGradientLineEndFromAngle(const CSSPoint& aStart,
+                                                double aAngle,
+                                                const CSSSize& aBoxSize) {
+  double dx = cos(-aAngle);
+  double dy = sin(-aAngle);
+  CSSPoint farthestCorner(dx > 0 ? aBoxSize.width : 0,
+                          dy > 0 ? aBoxSize.height : 0);
+  CSSPoint delta = farthestCorner - aStart;
+  double u = delta.x * dy - delta.y * dx;
+  return farthestCorner + CSSPoint(-u * dy, u * dx);
+}
+
+// Compute the start and end points of the gradient line for a linear gradient.
+static std::tuple<CSSPoint, CSSPoint> ComputeLinearGradientLine(
+    nsPresContext* aPresContext, const StyleGradient& aGradient,
+    const CSSSize& aBoxSize) {
+  using X = StyleHorizontalPositionKeyword;
+  using Y = StyleVerticalPositionKeyword;
+
+  const StyleLineDirection& direction = aGradient.AsLinear().direction;
+  const bool isModern =
+      aGradient.AsLinear().compat_mode == StyleGradientCompatMode::Modern;
+
+  CSSPoint center(aBoxSize.width / 2, aBoxSize.height / 2);
+  switch (direction.tag) {
+    case StyleLineDirection::Tag::Angle: {
+      double angle = direction.AsAngle().ToRadians();
+      if (isModern) {
+        angle = M_PI_2 - angle;
+      }
+      CSSPoint end = ComputeGradientLineEndFromAngle(center, angle, aBoxSize);
+      CSSPoint start = CSSPoint(aBoxSize.width, aBoxSize.height) - end;
+      return {start, end};
+    }
+    case StyleLineDirection::Tag::Vertical: {
+      CSSPoint start(center.x, 0);
+      CSSPoint end(center.x, aBoxSize.height);
+      if (isModern == (direction.AsVertical() == Y::Top)) {
+        std::swap(start.y, end.y);
+      }
+      return {start, end};
+    }
+    case StyleLineDirection::Tag::Horizontal: {
+      CSSPoint start(0, center.y);
+      CSSPoint end(aBoxSize.width, center.y);
+      if (isModern == (direction.AsHorizontal() == X::Left)) {
+        std::swap(start.x, end.x);
+      }
+      return {start, end};
+    }
+    case StyleLineDirection::Tag::Corner: {
+      const auto& corner = direction.AsCorner();
+      const X& h = corner._0;
+      const Y& v = corner._1;
+
+      if (isModern) {
+        float xSign = h == X::Right ? 1.0 : -1.0;
+        float ySign = v == Y::Top ? 1.0 : -1.0;
+        double angle = atan2(ySign * aBoxSize.width, xSign * aBoxSize.height);
+        CSSPoint end = ComputeGradientLineEndFromAngle(center, angle, aBoxSize);
+        CSSPoint start = CSSPoint(aBoxSize.width, aBoxSize.height) - end;
+        return {start, end};
+      }
+
+      CSSCoord startX = h == X::Left ? 0.0 : aBoxSize.width;
+      CSSCoord startY = v == Y::Top ? 0.0 : aBoxSize.height;
+
+      CSSPoint start(startX, startY);
+      CSSPoint end = CSSPoint(aBoxSize.width, aBoxSize.height) - start;
+      return {start, end};
+    }
+    default:
+      break;
+  }
+  MOZ_ASSERT_UNREACHABLE("Unknown line direction");
+  return {CSSPoint(), CSSPoint()};
+}
+
+using EndingShape = StyleGenericEndingShape<Length, LengthPercentage>;
+using RadialGradientRadii =
+    Variant<StyleShapeExtent, std::pair<CSSCoord, CSSCoord>>;
+
+static RadialGradientRadii ComputeRadialGradientRadii(const EndingShape& aShape,
+                                                      const CSSSize& aSize) {
+  if (aShape.IsCircle()) {
+    auto& circle = aShape.AsCircle();
+    if (circle.IsExtent()) {
+      return RadialGradientRadii(circle.AsExtent());
+    }
+    CSSCoord radius = circle.AsRadius().ToCSSPixels();
+    return RadialGradientRadii(std::make_pair(radius, radius));
+  }
+  auto& ellipse = aShape.AsEllipse();
+  if (ellipse.IsExtent()) {
+    return RadialGradientRadii(ellipse.AsExtent());
+  }
+
+  auto& radii = ellipse.AsRadii();
+  return RadialGradientRadii(
+      std::make_pair(radii._0.ResolveToCSSPixels(aSize.width),
+                     radii._1.ResolveToCSSPixels(aSize.height)));
+}
+
+// Compute the start and end points of the gradient line for a radial gradient.
+// Also returns the horizontal and vertical radii defining the circle or
+// ellipse to use.
+static std::tuple<CSSPoint, CSSPoint, CSSCoord, CSSCoord>
+ComputeRadialGradientLine(const StyleGradient& aGradient,
+                          const CSSSize& aBoxSize) {
+  const auto& radial = aGradient.AsRadial();
+  const EndingShape& endingShape = radial.shape;
+  const Position& position = radial.position;
+  CSSPoint start = ResolvePosition(position, aBoxSize);
+
+  // Compute gradient shape: the x and y radii of an ellipse.
+  CSSCoord radiusX, radiusY;
+  CSSCoord leftDistance = Abs(start.x);
+  CSSCoord rightDistance = Abs(aBoxSize.width - start.x);
+  CSSCoord topDistance = Abs(start.y);
+  CSSCoord bottomDistance = Abs(aBoxSize.height - start.y);
+
+  auto radii = ComputeRadialGradientRadii(endingShape, aBoxSize);
+  if (radii.is<StyleShapeExtent>()) {
+    switch (radii.as<StyleShapeExtent>()) {
+      case StyleShapeExtent::ClosestSide:
+        radiusX = std::min(leftDistance, rightDistance);
+        radiusY = std::min(topDistance, bottomDistance);
+        if (endingShape.IsCircle()) {
+          radiusX = radiusY = std::min(radiusX, radiusY);
+        }
+        break;
+      case StyleShapeExtent::ClosestCorner: {
+        // Compute x and y distances to nearest corner
+        CSSCoord offsetX = std::min(leftDistance, rightDistance);
+        CSSCoord offsetY = std::min(topDistance, bottomDistance);
+        if (endingShape.IsCircle()) {
+          radiusX = radiusY = NS_hypot(offsetX, offsetY);
+        } else {
+          // maintain aspect ratio
+          radiusX = offsetX * M_SQRT2;
+          radiusY = offsetY * M_SQRT2;
+        }
+        break;
+      }
+      case StyleShapeExtent::FarthestSide:
+        radiusX = std::max(leftDistance, rightDistance);
+        radiusY = std::max(topDistance, bottomDistance);
+        if (endingShape.IsCircle()) {
+          radiusX = radiusY = std::max(radiusX, radiusY);
+        }
+        break;
+      case StyleShapeExtent::FarthestCorner: {
+        // Compute x and y distances to nearest corner
+        CSSCoord offsetX = std::max(leftDistance, rightDistance);
+        CSSCoord offsetY = std::max(topDistance, bottomDistance);
+        if (endingShape.IsCircle()) {
+          radiusX = radiusY = NS_hypot(offsetX, offsetY);
+        } else {
+          // maintain aspect ratio
+          radiusX = offsetX * M_SQRT2;
+          radiusY = offsetY * M_SQRT2;
+        }
+        break;
+      }
+      default:
+        MOZ_ASSERT_UNREACHABLE("Unknown shape extent keyword?");
+        radiusX = radiusY = 0;
+    }
+  } else {
+    auto pair = radii.as<std::pair<CSSCoord, CSSCoord>>();
+    radiusX = pair.first;
+    radiusY = pair.second;
+  }
+
+  // The gradient line end point is where the gradient line intersects
+  // the ellipse.
+  CSSPoint end = start + CSSPoint(radiusX, 0);
+  return {start, end, radiusX, radiusY};
+}
+
+// Compute the center and the start angle of the conic gradient.
+static std::tuple<CSSPoint, float> ComputeConicGradientProperties(
+    const StyleGradient& aGradient, const CSSSize& aBoxSize) {
+  const auto& conic = aGradient.AsConic();
+  const Position& position = conic.position;
+  float angle = static_cast<float>(conic.angle.ToRadians());
+  CSSPoint center = ResolvePosition(position, aBoxSize);
+
+  return {center, angle};
+}
+
+static float Interpolate(float aF1, float aF2, float aFrac) {
+  return aF1 + aFrac * (aF2 - aF1);
+}
+
+static StyleAnimatedRGBA Interpolate(const StyleAnimatedRGBA& aLeft,
+                                     const StyleAnimatedRGBA& aRight,
+                                     float aFrac) {
+  // NOTE: This has to match the interpolation method that WebRender uses which
+  // right now is sRGB. In the future we should implement interpolation in more
+  // gradient color-spaces.
+  static constexpr auto kMethod = StyleColorInterpolationMethod{
+      StyleColorSpace::Srgb,
+      StyleHueInterpolationMethod::Shorter,
+  };
+  return Servo_InterpolateColor(&kMethod, &aRight, &aLeft, aFrac);
+}
+
+static nscoord FindTileStart(nscoord aDirtyCoord, nscoord aTilePos,
+                             nscoord aTileDim) {
+  NS_ASSERTION(aTileDim > 0, "Non-positive tile dimension");
+  double multiples = floor(double(aDirtyCoord - aTilePos) / aTileDim);
+  return NSToCoordRound(multiples * aTileDim + aTilePos);
+}
+
+static gfxFloat LinearGradientStopPositionForPoint(
+    const gfxPoint& aGradientStart, const gfxPoint& aGradientEnd,
+    const gfxPoint& aPoint) {
+  gfxPoint d = aGradientEnd - aGradientStart;
+  gfxPoint p = aPoint - aGradientStart;
+  /**
+   * Compute a parameter t such that a line perpendicular to the
+   * d vector, passing through aGradientStart + d*t, also
+   * passes through aPoint.
+   *
+   * t is given by
+   *   (p.x - d.x*t)*d.x + (p.y - d.y*t)*d.y = 0
+   *
+   * Solving for t we get
+   *   numerator = d.x*p.x + d.y*p.y
+   *   denominator = d.x^2 + d.y^2
+   *   t = numerator/denominator
+   *
+   * In nsCSSRendering::PaintGradient we know the length of d
+   * is not zero.
+   */
+  double numerator = d.x.value * p.x.value + d.y.value * p.y.value;
+  double denominator = d.x.value * d.x.value + d.y.value * d.y.value;
+  return numerator / denominator;
+}
+
+static bool RectIsBeyondLinearGradientEdge(const gfxRect& aRect,
+                                           const gfxMatrix& aPatternMatrix,
+                                           const nsTArray<ColorStop>& aStops,
+                                           const gfxPoint& aGradientStart,
+                                           const gfxPoint& aGradientEnd,
+                                           StyleAnimatedRGBA* aOutEdgeColor) {
+  gfxFloat topLeft = LinearGradientStopPositionForPoint(
+      aGradientStart, aGradientEnd,
+      aPatternMatrix.TransformPoint(aRect.TopLeft()));
+  gfxFloat topRight = LinearGradientStopPositionForPoint(
+      aGradientStart, aGradientEnd,
+      aPatternMatrix.TransformPoint(aRect.TopRight()));
+  gfxFloat bottomLeft = LinearGradientStopPositionForPoint(
+      aGradientStart, aGradientEnd,
+      aPatternMatrix.TransformPoint(aRect.BottomLeft()));
+  gfxFloat bottomRight = LinearGradientStopPositionForPoint(
+      aGradientStart, aGradientEnd,
+      aPatternMatrix.TransformPoint(aRect.BottomRight()));
+
+  const ColorStop& firstStop = aStops[0];
+  if (topLeft < firstStop.mPosition && topRight < firstStop.mPosition &&
+      bottomLeft < firstStop.mPosition && bottomRight < firstStop.mPosition) {
+    *aOutEdgeColor = firstStop.mColor;
+    return true;
+  }
+
+  const ColorStop& lastStop = aStops.LastElement();
+  if (topLeft >= lastStop.mPosition && topRight >= lastStop.mPosition &&
+      bottomLeft >= lastStop.mPosition && bottomRight >= lastStop.mPosition) {
+    *aOutEdgeColor = lastStop.mColor;
+    return true;
+  }
+
+  return false;
+}
+
+static void ResolveMidpoints(nsTArray<ColorStop>& stops) {
+  for (size_t x = 1; x < stops.Length() - 1;) {
+    if (!stops[x].mIsMidpoint) {
+      x++;
+      continue;
+    }
+
+    const auto& color1 = stops[x - 1].mColor;
+    const auto& color2 = stops[x + 1].mColor;
+    float offset1 = stops[x - 1].mPosition;
+    float offset2 = stops[x + 1].mPosition;
+    float offset = stops[x].mPosition;
+    // check if everything coincides. If so, ignore the midpoint.
+    if (offset - offset1 == offset2 - offset) {
+      stops.RemoveElementAt(x);
+      continue;
+    }
+
+    // Check if we coincide with the left colorstop.
+    if (offset1 == offset) {
+      // Morph the midpoint to a regular stop with the color of the next
+      // color stop.
+      stops[x].mColor = color2;
+      stops[x].mIsMidpoint = false;
+      continue;
+    }
+
+    // Check if we coincide with the right colorstop.
+    if (offset2 == offset) {
+      // Morph the midpoint to a regular stop with the color of the previous
+      // color stop.
+      stops[x].mColor = color1;
+      stops[x].mIsMidpoint = false;
+      continue;
+    }
+
+    float midpoint = (offset - offset1) / (offset2 - offset1);
+    ColorStop newStops[9];
+    if (midpoint > .5f) {
+      for (size_t y = 0; y < 7; y++) {
+        newStops[y].mPosition = offset1 + (offset - offset1) * (7 + y) / 13;
+      }
+
+      newStops[7].mPosition = offset + (offset2 - offset) / 3;
+      newStops[8].mPosition = offset + (offset2 - offset) * 2 / 3;
+    } else {
+      newStops[0].mPosition = offset1 + (offset - offset1) / 3;
+      newStops[1].mPosition = offset1 + (offset - offset1) * 2 / 3;
+
+      for (size_t y = 0; y < 7; y++) {
+        newStops[y + 2].mPosition = offset + (offset2 - offset) * y / 13;
+      }
+    }
+    // calculate colors
+
+    for (auto& newStop : newStops) {
+      // Calculate the intermediate color stops per the formula of the CSS
+      // images spec. http://dev.w3.org/csswg/css-images/#color-stop-syntax 9
+      // points were chosen since it is the minimum number of stops that always
+      // give the smoothest appearace regardless of midpoint position and
+      // difference in luminance of the end points.
+      const float relativeOffset =
+          (newStop.mPosition - offset1) / (offset2 - offset1);
+      const float multiplier = powf(relativeOffset, logf(.5f) / logf(midpoint));
+
+      const float red = color1.red + multiplier * (color2.red - color1.red);
+      const float green =
+          color1.green + multiplier * (color2.green - color1.green);
+      const float blue = color1.blue + multiplier * (color2.blue - color1.blue);
+      const float alpha =
+          color1.alpha + multiplier * (color2.alpha - color1.alpha);
+
+      newStop.mColor = {red, green, blue, alpha};
+    }
+
+    stops.ReplaceElementsAt(x, 1, newStops, 9);
+    x += 9;
+  }
+}
+
+static StyleAnimatedRGBA TransparentColor(const StyleAnimatedRGBA& aColor) {
+  auto color = aColor;
+  color.alpha = 0.0f;
+  return color;
+}
+
+// Adjusts and adds color stops in such a way that drawing the gradient with
+// unpremultiplied interpolation looks nearly the same as if it were drawn with
+// premultiplied interpolation.
+static const float kAlphaIncrementPerGradientStep = 0.1f;
+static void ResolvePremultipliedAlpha(nsTArray<ColorStop>& aStops) {
+  for (size_t x = 1; x < aStops.Length(); x++) {
+    const ColorStop leftStop = aStops[x - 1];
+    const ColorStop rightStop = aStops[x];
+
+    // if the left and right stop have the same alpha value, we don't need
+    // to do anything. Hardstops should be instant, and also should never
+    // require dealing with interpolation.
+    if (leftStop.mColor.alpha == rightStop.mColor.alpha ||
+        leftStop.mPosition == rightStop.mPosition) {
+      continue;
+    }
+
+    // Is the stop on the left 100% transparent? If so, have it adopt the color
+    // of the right stop
+    if (leftStop.mColor.alpha == 0) {
+      aStops[x - 1].mColor = TransparentColor(rightStop.mColor);
+      continue;
+    }
+
+    // Is the stop on the right completely transparent?
+    // If so, duplicate it and assign it the color on the left.
+    if (rightStop.mColor.alpha == 0) {
+      ColorStop newStop = rightStop;
+      newStop.mColor = TransparentColor(leftStop.mColor);
+      aStops.InsertElementAt(x, newStop);
+      x++;
+      continue;
+    }
+
+    // Now handle cases where one or both of the stops are partially
+    // transparent.
+    if (leftStop.mColor.alpha != 1.0f || rightStop.mColor.alpha != 1.0f) {
+      // Calculate how many extra steps. We do a step per 10% transparency.
+      size_t stepCount =
+          NSToIntFloor(fabsf(leftStop.mColor.alpha - rightStop.mColor.alpha) /
+                       kAlphaIncrementPerGradientStep);
+      for (size_t y = 1; y < stepCount; y++) {
+        float frac = static_cast<float>(y) / stepCount;
+        ColorStop newStop(
+            Interpolate(leftStop.mPosition, rightStop.mPosition, frac), false,
+            Interpolate(leftStop.mColor, rightStop.mColor, frac));
+        aStops.InsertElementAt(x, newStop);
+        x++;
+      }
+    }
+  }
+}
+
+static ColorStop InterpolateColorStop(const ColorStop& aFirst,
+                                      const ColorStop& aSecond,
+                                      double aPosition,
+                                      const StyleAnimatedRGBA& aDefault) {
+  MOZ_ASSERT(aFirst.mPosition <= aPosition);
+  MOZ_ASSERT(aPosition <= aSecond.mPosition);
+
+  double delta = aSecond.mPosition - aFirst.mPosition;
+  if (delta < 1e-6) {
+    return ColorStop(aPosition, false, aDefault);
+  }
+
+  return ColorStop(aPosition, false,
+                   Interpolate(aFirst.mColor, aSecond.mColor,
+                               (aPosition - aFirst.mPosition) / delta));
+}
+
+// Clamp and extend the given ColorStop array in-place to fit exactly into the
+// range [0, 1].
+static void ClampColorStops(nsTArray<ColorStop>& aStops) {
+  MOZ_ASSERT(aStops.Length() > 0);
+
+  // If all stops are outside the range, then get rid of everything and replace
+  // with a single colour.
+  if (aStops.Length() < 2 || aStops[0].mPosition > 1 ||
+      aStops.LastElement().mPosition < 0) {
+    const auto c = aStops[0].mPosition > 1 ? aStops[0].mColor
+                                           : aStops.LastElement().mColor;
+    aStops.Clear();
+    aStops.AppendElement(ColorStop(0, false, c));
+    return;
+  }
+
+  // Create the 0 and 1 points if they fall in the range of |aStops|, and
+  // discard all stops outside the range [0, 1].
+  // XXX: If we have stops positioned at 0 or 1, we only keep the innermost of
+  // those stops. This should be fine for the current user(s) of this function.
+  for (size_t i = aStops.Length() - 1; i > 0; i--) {
+    if (aStops[i - 1].mPosition < 1 && aStops[i].mPosition >= 1) {
+      // Add a point to position 1.
+      aStops[i] =
+          InterpolateColorStop(aStops[i - 1], aStops[i],
+                               /* aPosition = */ 1, aStops[i - 1].mColor);
+      // Remove all the elements whose position is greater than 1.
+      aStops.RemoveLastElements(aStops.Length() - (i + 1));
+    }
+    if (aStops[i - 1].mPosition <= 0 && aStops[i].mPosition > 0) {
+      // Add a point to position 0.
+      aStops[i - 1] =
+          InterpolateColorStop(aStops[i - 1], aStops[i],
+                               /* aPosition = */ 0, aStops[i].mColor);
+      // Remove all of the preceding stops -- they are all negative.
+      aStops.RemoveElementsAt(0, i - 1);
+      break;
+    }
+  }
+
+  MOZ_ASSERT(aStops[0].mPosition >= -1e6);
+  MOZ_ASSERT(aStops.LastElement().mPosition - 1 <= 1e6);
+
+  // The end points won't exist yet if they don't fall in the original range of
+  // |aStops|. Create them if needed.
+  if (aStops[0].mPosition > 0) {
+    aStops.InsertElementAt(0, ColorStop(0, false, aStops[0].mColor));
+  }
+  if (aStops.LastElement().mPosition < 1) {
+    aStops.AppendElement(ColorStop(1, false, aStops.LastElement().mColor));
+  }
+}
+
+namespace mozilla {
+
+template <typename T>
+static StyleAnimatedRGBA GetSpecifiedColor(
+    const StyleGenericGradientItem<StyleColor, T>& aItem,
+    const ComputedStyle& aStyle) {
+  if (aItem.IsInterpolationHint()) {
+    return {0.0f, 0.0f, 0.0f, 0.0f};
+  }
+  const StyleColor& c = aItem.IsSimpleColorStop()
+                            ? aItem.AsSimpleColorStop()
+                            : aItem.AsComplexColorStop().color;
+  nscolor color = c.CalcColor(aStyle);
+  return {NS_GET_R(color) / 255.0f, NS_GET_G(color) / 255.0f,
+          NS_GET_B(color) / 255.0f, NS_GET_A(color) / 255.0f};
+}
+
+static Maybe<double> GetSpecifiedGradientPosition(
+    const StyleGenericGradientItem<StyleColor, StyleLengthPercentage>& aItem,
+    CSSCoord aLineLength) {
+  if (aItem.IsSimpleColorStop()) {
+    return Nothing();
+  }
+
+  const LengthPercentage& pos = aItem.IsComplexColorStop()
+                                    ? aItem.AsComplexColorStop().position
+                                    : aItem.AsInterpolationHint();
+
+  if (pos.ConvertsToPercentage()) {
+    return Some(pos.ToPercentage());
+  }
+
+  if (aLineLength < 1e-6) {
+    return Some(0.0);
+  }
+  return Some(pos.ResolveToCSSPixels(aLineLength) / aLineLength);
+}
+
+// aLineLength argument is unused for conic-gradients.
+static Maybe<double> GetSpecifiedGradientPosition(
+    const StyleGenericGradientItem<StyleColor, StyleAngleOrPercentage>& aItem,
+    CSSCoord aLineLength) {
+  if (aItem.IsSimpleColorStop()) {
+    return Nothing();
+  }
+
+  const StyleAngleOrPercentage& pos = aItem.IsComplexColorStop()
+                                          ? aItem.AsComplexColorStop().position
+                                          : aItem.AsInterpolationHint();
+
+  if (pos.IsPercentage()) {
+    return Some(pos.AsPercentage()._0);
+  }
+
+  return Some(pos.AsAngle().ToRadians() / (2 * M_PI));
+}
+
+template <typename T>
+static nsTArray<ColorStop> ComputeColorStopsForItems(
+    ComputedStyle* aComputedStyle,
+    Span<const StyleGenericGradientItem<StyleColor, T>> aItems,
+    CSSCoord aLineLength) {
+  MOZ_ASSERT(aItems.Length() >= 2,
+             "The parser should reject gradients with less than two stops");
+
+  nsTArray<ColorStop> stops(aItems.Length());
+
+  // If there is a run of stops before stop i that did not have specified
+  // positions, then this is the index of the first stop in that run.
+  Maybe<size_t> firstUnsetPosition;
+  for (size_t i = 0; i < aItems.Length(); ++i) {
+    const auto& stop = aItems[i];
+    double position;
+
+    Maybe<double> specifiedPosition =
+        GetSpecifiedGradientPosition(stop, aLineLength);
+
+    if (specifiedPosition) {
+      position = *specifiedPosition;
+    } else if (i == 0) {
+      // First stop defaults to position 0.0
+      position = 0.0;
+    } else if (i == aItems.Length() - 1) {
+      // Last stop defaults to position 1.0
+      position = 1.0;
+    } else {
+      // Other stops with no specified position get their position assigned
+      // later by interpolation, see below.
+      // Remember where the run of stops with no specified position starts,
+      // if it starts here.
+      if (firstUnsetPosition.isNothing()) {
+        firstUnsetPosition.emplace(i);
+      }
+      MOZ_ASSERT(!stop.IsInterpolationHint(),
+                 "Interpolation hints always specify position");
+      auto color = GetSpecifiedColor(stop, *aComputedStyle);
+      stops.AppendElement(ColorStop(0, false, color));
+      continue;
+    }
+
+    if (i > 0) {
+      // Prevent decreasing stop positions by advancing this position
+      // to the previous stop position, if necessary
+      double previousPosition = firstUnsetPosition
+                                    ? stops[*firstUnsetPosition - 1].mPosition
+                                    : stops[i - 1].mPosition;
+      position = std::max(position, previousPosition);
+    }
+    auto stopColor = GetSpecifiedColor(stop, *aComputedStyle);
+    stops.AppendElement(
+        ColorStop(position, stop.IsInterpolationHint(), stopColor));
+    if (firstUnsetPosition) {
+      // Interpolate positions for all stops that didn't have a specified
+      // position
+      double p = stops[*firstUnsetPosition - 1].mPosition;
+      double d = (stops[i].mPosition - p) / (i - *firstUnsetPosition + 1);
+      for (size_t j = *firstUnsetPosition; j < i; ++j) {
+        p += d;
+        stops[j].mPosition = p;
+      }
+      firstUnsetPosition.reset();
+    }
+  }
+
+  return stops;
+}
+
+static nsTArray<ColorStop> ComputeColorStops(ComputedStyle* aComputedStyle,
+                                             const StyleGradient& aGradient,
+                                             CSSCoord aLineLength) {
+  if (aGradient.IsLinear()) {
+    return ComputeColorStopsForItems(
+        aComputedStyle, aGradient.AsLinear().items.AsSpan(), aLineLength);
+  }
+  if (aGradient.IsRadial()) {
+    return ComputeColorStopsForItems(
+        aComputedStyle, aGradient.AsRadial().items.AsSpan(), aLineLength);
+  }
+  return ComputeColorStopsForItems(
+      aComputedStyle, aGradient.AsConic().items.AsSpan(), aLineLength);
+}
+
+nsCSSGradientRenderer nsCSSGradientRenderer::Create(
+    nsPresContext* aPresContext, ComputedStyle* aComputedStyle,
+    const StyleGradient& aGradient, const nsSize& aIntrinsicSize) {
+  auto srcSize = CSSSize::FromAppUnits(aIntrinsicSize);
+
+  // Compute "gradient line" start and end relative to the intrinsic size of
+  // the gradient.
+  CSSPoint lineStart, lineEnd, center;  // center is for conic gradients only
+  CSSCoord radiusX = 0, radiusY = 0;    // for radial gradients only
+  float angle = 0.0;                    // for conic gradients only
+  if (aGradient.IsLinear()) {
+    std::tie(lineStart, lineEnd) =
+        ComputeLinearGradientLine(aPresContext, aGradient, srcSize);
+  } else if (aGradient.IsRadial()) {
+    std::tie(lineStart, lineEnd, radiusX, radiusY) =
+        ComputeRadialGradientLine(aGradient, srcSize);
+  } else {
+    MOZ_ASSERT(aGradient.IsConic());
+    std::tie(center, angle) =
+        ComputeConicGradientProperties(aGradient, srcSize);
+  }
+  // Avoid sending Infs or Nans to downwind draw targets.
+  if (!lineStart.IsFinite() || !lineEnd.IsFinite()) {
+    lineStart = lineEnd = CSSPoint(0, 0);
+  }
+  if (!center.IsFinite()) {
+    center = CSSPoint(0, 0);
+  }
+  CSSCoord lineLength =
+      NS_hypot(lineEnd.x - lineStart.x, lineEnd.y - lineStart.y);
+
+  // Build color stop array and compute stop positions
+  nsTArray<ColorStop> stops =
+      ComputeColorStops(aComputedStyle, aGradient, lineLength);
+
+  ResolveMidpoints(stops);
+
+  nsCSSGradientRenderer renderer;
+  renderer.mPresContext = aPresContext;
+  renderer.mGradient = &aGradient;
+  renderer.mStops = std::move(stops);
+  renderer.mLineStart = {
+      aPresContext->CSSPixelsToDevPixels(lineStart.x),
+      aPresContext->CSSPixelsToDevPixels(lineStart.y),
+  };
+  renderer.mLineEnd = {
+      aPresContext->CSSPixelsToDevPixels(lineEnd.x),
+      aPresContext->CSSPixelsToDevPixels(lineEnd.y),
+  };
+  renderer.mRadiusX = aPresContext->CSSPixelsToDevPixels(radiusX);
+  renderer.mRadiusY = aPresContext->CSSPixelsToDevPixels(radiusY);
+  renderer.mCenter = {
+      aPresContext->CSSPixelsToDevPixels(center.x),
+      aPresContext->CSSPixelsToDevPixels(center.y),
+  };
+  renderer.mAngle = angle;
+  return renderer;
+}
+
+void nsCSSGradientRenderer::Paint(gfxContext& aContext, const nsRect& aDest,
+                                  const nsRect& aFillArea,
+                                  const nsSize& aRepeatSize,
+                                  const CSSIntRect& aSrc,
+                                  const nsRect& aDirtyRect, float aOpacity) {
+  AUTO_PROFILER_LABEL("nsCSSGradientRenderer::Paint", GRAPHICS);
+
+  if (aDest.IsEmpty() || aFillArea.IsEmpty()) {
+    return;
+  }
+
+  nscoord appUnitsPerDevPixel = mPresContext->AppUnitsPerDevPixel();
+
+  gfxFloat lineLength =
+      NS_hypot(mLineEnd.x - mLineStart.x, mLineEnd.y - mLineStart.y);
+  bool cellContainsFill = aDest.Contains(aFillArea);
+
+  // If a non-repeating linear gradient is axis-aligned and there are no gaps
+  // between tiles, we can optimise away most of the work by converting to a
+  // repeating linear gradient and filling the whole destination rect at once.
+  bool forceRepeatToCoverTiles =
+      mGradient->IsLinear() &&
+      (mLineStart.x == mLineEnd.x) != (mLineStart.y == mLineEnd.y) &&
+      aRepeatSize.width == aDest.width && aRepeatSize.height == aDest.height &&
+      !mGradient->AsLinear().repeating && !aSrc.IsEmpty() && !cellContainsFill;
+
+  gfxMatrix matrix;
+  if (forceRepeatToCoverTiles) {
+    // Length of the source rectangle along the gradient axis.
+    double rectLen;
+    // The position of the start of the rectangle along the gradient.
+    double offset;
+
+    // The gradient line is "backwards". Flip the line upside down to make
+    // things easier, and then rotate the matrix to turn everything back the
+    // right way up.
+    if (mLineStart.x > mLineEnd.x || mLineStart.y > mLineEnd.y) {
+      std::swap(mLineStart, mLineEnd);
+      matrix.PreScale(-1, -1);
+    }
+
+    // Fit the gradient line exactly into the source rect.
+    // aSrc is relative to aIntrinsincSize.
+    // srcRectDev will be relative to srcSize, so in the same coordinate space
+    // as lineStart / lineEnd.
+    gfxRect srcRectDev = nsLayoutUtils::RectToGfxRect(
+        CSSPixel::ToAppUnits(aSrc), appUnitsPerDevPixel);
+    if (mLineStart.x != mLineEnd.x) {
+      rectLen = srcRectDev.width;
+      offset = (srcRectDev.x - mLineStart.x) / lineLength;
+      mLineStart.x = srcRectDev.x;
+      mLineEnd.x = srcRectDev.XMost();
+    } else {
+      rectLen = srcRectDev.height;
+      offset = (srcRectDev.y - mLineStart.y) / lineLength;
+      mLineStart.y = srcRectDev.y;
+      mLineEnd.y = srcRectDev.YMost();
+    }
+
+    // Adjust gradient stop positions for the new gradient line.
+    double scale = lineLength / rectLen;
+    for (size_t i = 0; i < mStops.Length(); i++) {
+      mStops[i].mPosition = (mStops[i].mPosition - offset) * fabs(scale);
+    }
+
+    // Clamp or extrapolate gradient stops to exactly [0, 1].
+    ClampColorStops(mStops);
+
+    lineLength = rectLen;
+  }
+
+  // Eliminate negative-position stops if the gradient is radial.
+  double firstStop = mStops[0].mPosition;
+  if (mGradient->IsRadial() && firstStop < 0.0) {
+    if (mGradient->AsRadial().repeating) {
+      // Choose an instance of the repeated pattern that gives us all positive
+      // stop-offsets.
+      double lastStop = mStops[mStops.Length() - 1].mPosition;
+      double stopDelta = lastStop - firstStop;
+      // If all the stops are in approximately the same place then logic below
+      // will kick in that makes us draw just the last stop color, so don't
+      // try to do anything in that case. We certainly need to avoid
+      // dividing by zero.
+      if (stopDelta >= 1e-6) {
+        double instanceCount = ceil(-firstStop / stopDelta);
+        // Advance stops by instanceCount multiples of the period of the
+        // repeating gradient.
+        double offset = instanceCount * stopDelta;
+        for (uint32_t i = 0; i < mStops.Length(); i++) {
+          mStops[i].mPosition += offset;
+        }
+      }
+    } else {
+      // Move negative-position stops to position 0.0. We may also need
+      // to set the color of the stop to the color the gradient should have
+      // at the center of the ellipse.
+      for (uint32_t i = 0; i < mStops.Length(); i++) {
+        double pos = mStops[i].mPosition;
+        if (pos < 0.0) {
+          mStops[i].mPosition = 0.0;
+          // If this is the last stop, we don't need to adjust the color,
+          // it will fill the entire area.
+          if (i < mStops.Length() - 1) {
+            double nextPos = mStops[i + 1].mPosition;
+            // If nextPos is approximately equal to pos, then we don't
+            // need to adjust the color of this stop because it's
+            // not going to be displayed.
+            // If nextPos is negative, we don't need to adjust the color of
+            // this stop since it's not going to be displayed because
+            // nextPos will also be moved to 0.0.
+            if (nextPos >= 0.0 && nextPos - pos >= 1e-6) {
+              // Compute how far the new position 0.0 is along the interval
+              // between pos and nextPos.
+              // XXX Color interpolation (in cairo, too) should use the
+              // CSS 'color-interpolation' property!
+              float frac = float((0.0 - pos) / (nextPos - pos));
+              mStops[i].mColor =
+                  Interpolate(mStops[i].mColor, mStops[i + 1].mColor, frac);
+            }
+          }
+        }
+      }
+    }
+    firstStop = mStops[0].mPosition;
+    MOZ_ASSERT(firstStop >= 0.0, "Failed to fix stop offsets");
+  }
+
+  if (mGradient->IsRadial() && !mGradient->AsRadial().repeating) {
+    // Direct2D can only handle a particular class of radial gradients because
+    // of the way the it specifies gradients. Setting firstStop to 0, when we
+    // can, will help us stay on the fast path. Currently we don't do this
+    // for repeating gradients but we could by adjusting the stop collection
+    // to start at 0
+    firstStop = 0;
+  }
+
+  double lastStop = mStops[mStops.Length() - 1].mPosition;
+  // Cairo gradients must have stop positions in the range [0, 1]. So,
+  // stop positions will be normalized below by subtracting firstStop and then
+  // multiplying by stopScale.
+  double stopScale;
+  double stopOrigin = firstStop;
+  double stopEnd = lastStop;
+  double stopDelta = lastStop - firstStop;
+  bool zeroRadius =
+      mGradient->IsRadial() && (mRadiusX < 1e-6 || mRadiusY < 1e-6);
+  if (stopDelta < 1e-6 || (!mGradient->IsConic() && lineLength < 1e-6) ||
+      zeroRadius) {
+    // Stops are all at the same place. Map all stops to 0.0.
+    // For repeating radial gradients, or for any radial gradients with
+    // a zero radius, we need to fill with the last stop color, so just set
+    // both radii to 0.
+    if (mGradient->Repeating() || zeroRadius) {
+      mRadiusX = mRadiusY = 0.0;
+    }
+    stopDelta = 0.0;
+  }
+
+  // Don't normalize non-repeating or degenerate gradients below 0..1
+  // This keeps the gradient line as large as the box and doesn't
+  // lets us avoiding having to get padding correct for stops
+  // at 0 and 1
+  if (!mGradient->Repeating() || stopDelta == 0.0) {
+    stopOrigin = std::min(stopOrigin, 0.0);
+    stopEnd = std::max(stopEnd, 1.0);
+  }
+  stopScale = 1.0 / (stopEnd - stopOrigin);
+
+  // Create the gradient pattern.
+  RefPtr<gfxPattern> gradientPattern;
+  gfxPoint gradientStart;
+  gfxPoint gradientEnd;
+  if (mGradient->IsLinear()) {
+    // Compute the actual gradient line ends we need to pass to cairo after
+    // stops have been normalized.
+    gradientStart = mLineStart + (mLineEnd - mLineStart) * stopOrigin;
+    gradientEnd = mLineStart + (mLineEnd - mLineStart) * stopEnd;
+
+    if (stopDelta == 0.0) {
+      // Stops are all at the same place. For repeating gradients, this will
+      // just paint the last stop color. We don't need to do anything.
+      // For non-repeating gradients, this should render as two colors, one
+      // on each "side" of the gradient line segment, which is a point. All
+      // our stops will be at 0.0; we just need to set the direction vector
+      // correctly.
+      gradientEnd = gradientStart + (mLineEnd - mLineStart);
+    }
+
+    gradientPattern = new gfxPattern(gradientStart.x, gradientStart.y,
+                                     gradientEnd.x, gradientEnd.y);
+  } else if (mGradient->IsRadial()) {
+    NS_ASSERTION(firstStop >= 0.0,
+                 "Negative stops not allowed for radial gradients");
+
+    // To form an ellipse, we'll stretch a circle vertically, if necessary.
+    // So our radii are based on radiusX.
+    double innerRadius = mRadiusX * stopOrigin;
+    double outerRadius = mRadiusX * stopEnd;
+    if (stopDelta == 0.0) {
+      // Stops are all at the same place.  See above (except we now have
+      // the inside vs. outside of an ellipse).
+      outerRadius = innerRadius + 1;
+    }
+    gradientPattern = new gfxPattern(mLineStart.x, mLineStart.y, innerRadius,
+                                     mLineStart.x, mLineStart.y, outerRadius);
+    if (mRadiusX != mRadiusY) {
+      // Stretch the circles into ellipses vertically by setting a transform
+      // in the pattern.
+      // Recall that this is the transform from user space to pattern space.
+      // So to stretch the ellipse by factor of P vertically, we scale
+      // user coordinates by 1/P.
+      matrix.PreTranslate(mLineStart);
+      matrix.PreScale(1.0, mRadiusX / mRadiusY);
+      matrix.PreTranslate(-mLineStart);
+    }
+  } else {
+    gradientPattern =
+        new gfxPattern(mCenter.x, mCenter.y, mAngle, stopOrigin, stopEnd);
+  }
+  // Use a pattern transform to take account of source and dest rects
+  matrix.PreTranslate(gfxPoint(mPresContext->CSSPixelsToDevPixels(aSrc.x),
+                               mPresContext->CSSPixelsToDevPixels(aSrc.y)));
+  matrix.PreScale(
+      gfxFloat(nsPresContext::CSSPixelsToAppUnits(aSrc.width)) / aDest.width,
+      gfxFloat(nsPresContext::CSSPixelsToAppUnits(aSrc.height)) / aDest.height);
+  gradientPattern->SetMatrix(matrix);
+
+  if (stopDelta == 0.0) {
+    // Non-repeating gradient with all stops in same place -> just add
+    // first stop and last stop, both at position 0.
+    // Repeating gradient with all stops in the same place, or radial
+    // gradient with radius of 0 -> just paint the last stop color.
+    // We use firstStop offset to keep |stops| with same units (will later
+    // normalize to 0).
+    auto firstColor(mStops[0].mColor);
+    auto lastColor(mStops.LastElement().mColor);
+    mStops.Clear();
+
+    if (!mGradient->Repeating() && !zeroRadius) {
+      mStops.AppendElement(ColorStop(firstStop, false, firstColor));
+    }
+    mStops.AppendElement(ColorStop(firstStop, false, lastColor));
+  }
+
+  ResolvePremultipliedAlpha(mStops);
+
+  bool isRepeat = mGradient->Repeating() || forceRepeatToCoverTiles;
+
+  // Now set normalized color stops in pattern.
+  // Offscreen gradient surface cache (not a tile):
+  // On some backends (e.g. D2D), the GradientStops object holds an offscreen
+  // surface which is a lookup table used to evaluate the gradient. This surface
+  // can use much memory (ram and/or GPU ram) and can be expensive to create. So
+  // we cache it. The cache key correlates 1:1 with the arguments for
+  // CreateGradientStops (also the implied backend type) Note that GradientStop
+  // is a simple struct with a stop value (while GradientStops has the surface).
+  nsTArray<gfx::GradientStop> rawStops(mStops.Length());
+  rawStops.SetLength(mStops.Length());
+  for (uint32_t i = 0; i < mStops.Length(); i++) {
+    rawStops[i].color = ToDeviceColor(mStops[i].mColor);
+    rawStops[i].color.a *= aOpacity;
+    rawStops[i].offset = stopScale * (mStops[i].mPosition - stopOrigin);
+  }
+  RefPtr<mozilla::gfx::GradientStops> gs =
+      gfxGradientCache::GetOrCreateGradientStops(
+          aContext.GetDrawTarget(), rawStops,
+          isRepeat ? gfx::ExtendMode::REPEAT : gfx::ExtendMode::CLAMP);
+  gradientPattern->SetColorStops(gs);
+
+  // Paint gradient tiles. This isn't terribly efficient, but doing it this
+  // way is simple and sure to get pixel-snapping right. We could speed things
+  // up by drawing tiles into temporary surfaces and copying those to the
+  // destination, but after pixel-snapping tiles may not all be the same size.
+  nsRect dirty;
+  if (!dirty.IntersectRect(aDirtyRect, aFillArea)) return;
+
+  gfxRect areaToFill =
+      nsLayoutUtils::RectToGfxRect(aFillArea, appUnitsPerDevPixel);
+  gfxRect dirtyAreaToFill =
+      nsLayoutUtils::RectToGfxRect(dirty, appUnitsPerDevPixel);
+  dirtyAreaToFill.RoundOut();
+
+  Matrix ctm = aContext.CurrentMatrix();
+  bool isCTMPreservingAxisAlignedRectangles =
+      ctm.PreservesAxisAlignedRectangles();
+
+  // xStart/yStart are the top-left corner of the top-left tile.
+  nscoord xStart = FindTileStart(dirty.x, aDest.x, aRepeatSize.width);
+  nscoord yStart = FindTileStart(dirty.y, aDest.y, aRepeatSize.height);
+  nscoord xEnd = forceRepeatToCoverTiles ? xStart + aDest.width : dirty.XMost();
+  nscoord yEnd =
+      forceRepeatToCoverTiles ? yStart + aDest.height : dirty.YMost();
+
+  if (TryPaintTilesWithExtendMode(aContext, gradientPattern, xStart, yStart,
+                                  dirtyAreaToFill, aDest, aRepeatSize,
+                                  forceRepeatToCoverTiles)) {
+    return;
+  }
+
+  // x and y are the top-left corner of the tile to draw
+  for (nscoord y = yStart; y < yEnd; y += aRepeatSize.height) {
+    for (nscoord x = xStart; x < xEnd; x += aRepeatSize.width) {
+      // The coordinates of the tile
+      gfxRect tileRect = nsLayoutUtils::RectToGfxRect(
+          nsRect(x, y, aDest.width, aDest.height), appUnitsPerDevPixel);
+      // The actual area to fill with this tile is the intersection of this
+      // tile with the overall area we're supposed to be filling
+      gfxRect fillRect =
+          forceRepeatToCoverTiles ? areaToFill : tileRect.Intersect(areaToFill);
+      // Try snapping the fill rect. Snap its top-left and bottom-right
+      // independently to preserve the orientation.
+      gfxPoint snappedFillRectTopLeft = fillRect.TopLeft();
+      gfxPoint snappedFillRectTopRight = fillRect.TopRight();
+      gfxPoint snappedFillRectBottomRight = fillRect.BottomRight();
+      // Snap three points instead of just two to ensure we choose the
+      // correct orientation if there's a reflection.
+      if (isCTMPreservingAxisAlignedRectangles &&
+          aContext.UserToDevicePixelSnapped(snappedFillRectTopLeft, true) &&
+          aContext.UserToDevicePixelSnapped(snappedFillRectBottomRight, true) &&
+          aContext.UserToDevicePixelSnapped(snappedFillRectTopRight, true)) {
+        if (snappedFillRectTopLeft.x == snappedFillRectBottomRight.x ||
+            snappedFillRectTopLeft.y == snappedFillRectBottomRight.y) {
+          // Nothing to draw; avoid scaling by zero and other weirdness that
+          // could put the context in an error state.
+          continue;
+        }
+        // Set the context's transform to the transform that maps fillRect to
+        // snappedFillRect. The part of the gradient that was going to
+        // exactly fill fillRect will fill snappedFillRect instead.
+        gfxMatrix transform = gfxUtils::TransformRectToRect(
+            fillRect, snappedFillRectTopLeft, snappedFillRectTopRight,
+            snappedFillRectBottomRight);
+        aContext.SetMatrixDouble(transform);
+      }
+      aContext.NewPath();
+      aContext.Rectangle(fillRect);
+
+      gfxRect dirtyFillRect = fillRect.Intersect(dirtyAreaToFill);
+      gfxRect fillRectRelativeToTile = dirtyFillRect - tileRect.TopLeft();
+      StyleAnimatedRGBA edgeColor{0.0f};
+      if (mGradient->IsLinear() && !isRepeat &&
+          RectIsBeyondLinearGradientEdge(fillRectRelativeToTile, matrix, mStops,
+                                         gradientStart, gradientEnd,
+                                         &edgeColor)) {
+        edgeColor.alpha *= aOpacity;
+        aContext.SetColor(ToSRGBColor(edgeColor));
+      } else {
+        aContext.SetMatrixDouble(
+            aContext.CurrentMatrixDouble().Copy().PreTranslate(
+                tileRect.TopLeft()));
+        aContext.SetPattern(gradientPattern);
+      }
+      aContext.Fill();
+      aContext.SetMatrix(ctm);
+    }
+  }
+}
+
+bool nsCSSGradientRenderer::TryPaintTilesWithExtendMode(
+    gfxContext& aContext, gfxPattern* aGradientPattern, nscoord aXStart,
+    nscoord aYStart, const gfxRect& aDirtyAreaToFill, const nsRect& aDest,
+    const nsSize& aRepeatSize, bool aForceRepeatToCoverTiles) {
+  // If we have forced a non-repeating gradient to repeat to cover tiles,
+  // then it will be faster to just paint it once using that optimization
+  if (aForceRepeatToCoverTiles) {
+    return false;
+  }
+
+  nscoord appUnitsPerDevPixel = mPresContext->AppUnitsPerDevPixel();
+
+  // We can only use this fast path if we don't have to worry about pixel
+  // snapping, and there is no spacing between tiles. We could handle spacing
+  // by increasing the size of tileSurface and leaving it transparent, but I'm
+  // not sure it's worth it
+  bool canUseExtendModeForTiling = (aXStart % appUnitsPerDevPixel == 0) &&
+                                   (aYStart % appUnitsPerDevPixel == 0) &&
+                                   (aDest.width % appUnitsPerDevPixel == 0) &&
+                                   (aDest.height % appUnitsPerDevPixel == 0) &&
+                                   (aRepeatSize.width == aDest.width) &&
+                                   (aRepeatSize.height == aDest.height);
+
+  if (!canUseExtendModeForTiling) {
+    return false;
+  }
+
+  IntSize tileSize{
+      NSAppUnitsToIntPixels(aDest.width, appUnitsPerDevPixel),
+      NSAppUnitsToIntPixels(aDest.height, appUnitsPerDevPixel),
+  };
+
+  // Check whether this is a reasonable surface size and doesn't overflow
+  // before doing calculations with the tile size
+  if (!Factory::ReasonableSurfaceSize(tileSize)) {
+    return false;
+  }
+
+  // We only want to do this when there are enough tiles to justify the
+  // overhead of painting to an offscreen surface. The heuristic here
+  // is when we will be painting at least 16 tiles or more, this is kind
+  // of arbitrary
+  bool shouldUseExtendModeForTiling =
+      aDirtyAreaToFill.Area() > (tileSize.width * tileSize.height) * 16.0;
+
+  if (!shouldUseExtendModeForTiling) {
+    return false;
+  }
+
+  // Draw the gradient pattern into a surface for our single tile
+  RefPtr<gfx::SourceSurface> tileSurface;
+  {
+    RefPtr<gfx::DrawTarget> tileTarget =
+        aContext.GetDrawTarget()->CreateSimilarDrawTarget(
+            tileSize, gfx::SurfaceFormat::B8G8R8A8);
+    if (!tileTarget || !tileTarget->IsValid()) {
+      return false;
+    }
+
+    RefPtr<gfxContext> tileContext = gfxContext::CreateOrNull(tileTarget);
+
+    tileContext->SetPattern(aGradientPattern);
+    tileContext->Paint();
+
+    tileContext = nullptr;
+    tileSurface = tileTarget->Snapshot();
+    tileTarget = nullptr;
+  }
+
+  // Draw the gradient using tileSurface as a repeating pattern masked by
+  // the dirtyRect
+  Matrix tileTransform = Matrix::Translation(
+      NSAppUnitsToFloatPixels(aXStart, appUnitsPerDevPixel),
+      NSAppUnitsToFloatPixels(aYStart, appUnitsPerDevPixel));
+
+  aContext.NewPath();
+  aContext.Rectangle(aDirtyAreaToFill);
+  aContext.Fill(SurfacePattern(tileSurface, ExtendMode::REPEAT, tileTransform));
+
+  return true;
+}
+
+void nsCSSGradientRenderer::BuildWebRenderParameters(
+    float aOpacity, wr::ExtendMode& aMode, nsTArray<wr::GradientStop>& aStops,
+    LayoutDevicePoint& aLineStart, LayoutDevicePoint& aLineEnd,
+    LayoutDeviceSize& aGradientRadius, LayoutDevicePoint& aGradientCenter,
+    float& aGradientAngle) {
+  aMode =
+      mGradient->Repeating() ? wr::ExtendMode::Repeat : wr::ExtendMode::Clamp;
+
+  aStops.SetLength(mStops.Length());
+  for (uint32_t i = 0; i < mStops.Length(); i++) {
+    aStops[i].color = wr::ToColorF(ToDeviceColor(mStops[i].mColor));
+    aStops[i].color.a *= aOpacity;
+    aStops[i].offset = mStops[i].mPosition;
+  }
+
+  aLineStart = LayoutDevicePoint(mLineStart.x, mLineStart.y);
+  aLineEnd = LayoutDevicePoint(mLineEnd.x, mLineEnd.y);
+  aGradientRadius = LayoutDeviceSize(mRadiusX, mRadiusY);
+  aGradientCenter = LayoutDevicePoint(mCenter.x, mCenter.y);
+  aGradientAngle = mAngle;
+}
+
+void nsCSSGradientRenderer::BuildWebRenderDisplayItems(
+    wr::DisplayListBuilder& aBuilder, const layers::StackingContextHelper& aSc,
+    const nsRect& aDest, const nsRect& aFillArea, const nsSize& aRepeatSize,
+    const CSSIntRect& aSrc, bool aIsBackfaceVisible, float aOpacity) {
+  if (aDest.IsEmpty() || aFillArea.IsEmpty()) {
+    return;
+  }
+
+  wr::ExtendMode extendMode;
+  nsTArray<wr::GradientStop> stops;
+  LayoutDevicePoint lineStart;
+  LayoutDevicePoint lineEnd;
+  LayoutDeviceSize gradientRadius;
+  LayoutDevicePoint gradientCenter;
+  float gradientAngle;
+  BuildWebRenderParameters(aOpacity, extendMode, stops, lineStart, lineEnd,
+                           gradientRadius, gradientCenter, gradientAngle);
+
+  nscoord appUnitsPerDevPixel = mPresContext->AppUnitsPerDevPixel();
+
+  nsPoint firstTile =
+      nsPoint(FindTileStart(aFillArea.x, aDest.x, aRepeatSize.width),
+              FindTileStart(aFillArea.y, aDest.y, aRepeatSize.height));
+
+  // Translate the parameters into device coordinates
+  LayoutDeviceRect clipBounds =
+      LayoutDevicePixel::FromAppUnits(aFillArea, appUnitsPerDevPixel);
+  LayoutDeviceRect firstTileBounds = LayoutDevicePixel::FromAppUnits(
+      nsRect(firstTile, aDest.Size()), appUnitsPerDevPixel);
+  LayoutDeviceSize tileRepeat =
+      LayoutDevicePixel::FromAppUnits(aRepeatSize, appUnitsPerDevPixel);
+
+  // Calculate the bounds of the gradient display item, which starts at the
+  // first tile and extends to the end of clip bounds
+  LayoutDevicePoint tileToClip =
+      clipBounds.BottomRight() - firstTileBounds.TopLeft();
+  LayoutDeviceRect gradientBounds = LayoutDeviceRect(
+      firstTileBounds.TopLeft(), LayoutDeviceSize(tileToClip.x, tileToClip.y));
+
+  // Calculate the tile spacing, which is the repeat size minus the tile size
+  LayoutDeviceSize tileSpacing = tileRepeat - firstTileBounds.Size();
+
+  // srcTransform is used for scaling the gradient to match aSrc
+  LayoutDeviceRect srcTransform = LayoutDeviceRect(
+      nsPresContext::CSSPixelsToAppUnits(aSrc.x),
+      nsPresContext::CSSPixelsToAppUnits(aSrc.y),
+      aDest.width / ((float)nsPresContext::CSSPixelsToAppUnits(aSrc.width)),
+      aDest.height / ((float)nsPresContext::CSSPixelsToAppUnits(aSrc.height)));
+
+  lineStart.x = (lineStart.x - srcTransform.x) * srcTransform.width;
+  lineStart.y = (lineStart.y - srcTransform.y) * srcTransform.height;
+
+  gradientCenter.x = (gradientCenter.x - srcTransform.x) * srcTransform.width;
+  gradientCenter.y = (gradientCenter.y - srcTransform.y) * srcTransform.height;
+
+  if (mGradient->IsLinear()) {
+    lineEnd.x = (lineEnd.x - srcTransform.x) * srcTransform.width;
+    lineEnd.y = (lineEnd.y - srcTransform.y) * srcTransform.height;
+
+    aBuilder.PushLinearGradient(
+        mozilla::wr::ToLayoutRect(gradientBounds),
+        mozilla::wr::ToLayoutRect(clipBounds), aIsBackfaceVisible,
+        mozilla::wr::ToLayoutPoint(lineStart),
+        mozilla::wr::ToLayoutPoint(lineEnd), stops, extendMode,
+        mozilla::wr::ToLayoutSize(firstTileBounds.Size()),
+        mozilla::wr::ToLayoutSize(tileSpacing));
+  } else if (mGradient->IsRadial()) {
+    gradientRadius.width *= srcTransform.width;
+    gradientRadius.height *= srcTransform.height;
+
+    aBuilder.PushRadialGradient(
+        mozilla::wr::ToLayoutRect(gradientBounds),
+        mozilla::wr::ToLayoutRect(clipBounds), aIsBackfaceVisible,
+        mozilla::wr::ToLayoutPoint(lineStart),
+        mozilla::wr::ToLayoutSize(gradientRadius), stops, extendMode,
+        mozilla::wr::ToLayoutSize(firstTileBounds.Size()),
+        mozilla::wr::ToLayoutSize(tileSpacing));
+  } else {
+    MOZ_ASSERT(mGradient->IsConic());
+    aBuilder.PushConicGradient(
+        mozilla::wr::ToLayoutRect(gradientBounds),
+        mozilla::wr::ToLayoutRect(clipBounds), aIsBackfaceVisible,
+        mozilla::wr::ToLayoutPoint(gradientCenter), gradientAngle, stops,
+        extendMode, mozilla::wr::ToLayoutSize(firstTileBounds.Size()),
+        mozilla::wr::ToLayoutSize(tileSpacing));
+  }
+}
+
+}  // namespace mozilla
diff --git a/layout/painting/nsCSSRenderingGradients.h b/layout/painting/nsCSSRenderingGradients.h
new file mode 100644
index 0000000000..fdc4abf7f6
--- /dev/null
+++ b/layout/painting/nsCSSRenderingGradients.h
@@ -0,0 +1,124 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef nsCSSRenderingGradients_h__
+#define nsCSSRenderingGradients_h__
+
+#include "gfxRect.h"
+#include "nsStyleStruct.h"
+#include "Units.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/gfx/2D.h"
+#include "mozilla/webrender/webrender_ffi.h"
+
+class gfxPattern;
+
+namespace mozilla {
+
+namespace layers {
+class StackingContextHelper;
+}  // namespace layers
+
+namespace wr {
+class DisplayListBuilder;
+}  // namespace wr
+
+// A resolved color stop, with a specific position along the gradient line and
+// a color.
+struct ColorStop {
+  ColorStop() : mPosition(0), mIsMidpoint(false) {}
+  ColorStop(double aPosition, bool aIsMidPoint, const StyleAnimatedRGBA& aColor)
+      : mPosition(aPosition), mIsMidpoint(aIsMidPoint), mColor(aColor) {}
+  double mPosition;  // along the gradient line; 0=start, 1=end
+  bool mIsMidpoint;
+  StyleAnimatedRGBA mColor;
+};
+
+class nsCSSGradientRenderer final {
+ public:
+  /**
+   * Prepare a nsCSSGradientRenderer for a gradient for an element.
+   * aIntrinsicSize - the size of the source gradient.
+   */
+  static nsCSSGradientRenderer Create(nsPresContext* aPresContext,
+                                      ComputedStyle* aComputedStyle,
+                                      const StyleGradient& aGradient,
+                                      const nsSize& aIntrinsiceSize);
+
+  /**
+   * Draw the gradient to aContext
+   * aDest - where the first tile of gradient is
+   * aFill - the area to be filled with tiles of aDest
+   * aSrc - the area of the gradient that will fill aDest
+   * aRepeatSize - the distance from the origin of a tile
+   *               to the next origin of a tile
+   * aDirtyRect - pixels outside of this area may be skipped
+   */
+  void Paint(gfxContext& aContext, const nsRect& aDest, const nsRect& aFill,
+             const nsSize& aRepeatSize, const mozilla::CSSIntRect& aSrc,
+             const nsRect& aDirtyRect, float aOpacity = 1.0);
+
+  /**
+   * Collect the gradient parameters
+   */
+  void BuildWebRenderParameters(float aOpacity, wr::ExtendMode& aMode,
+                                nsTArray<wr::GradientStop>& aStops,
+                                LayoutDevicePoint& aLineStart,
+                                LayoutDevicePoint& aLineEnd,
+                                LayoutDeviceSize& aGradientRadius,
+                                LayoutDevicePoint& aGradientCenter,
+                                float& aGradientAngle);
+
+  /**
+   * Build display items for the gradient
+   * aLayer - the layer to make this display item relative to
+   * aDest - where the first tile of gradient is
+   * aFill - the area to be filled with tiles of aDest
+   * aRepeatSize - the distance from the origin of a tile
+   *               to the next origin of a tile
+   * aSrc - the area of the gradient that will fill aDest
+   */
+  void BuildWebRenderDisplayItems(wr::DisplayListBuilder& aBuilder,
+                                  const layers::StackingContextHelper& aSc,
+                                  const nsRect& aDest, const nsRect& aFill,
+                                  const nsSize& aRepeatSize,
+                                  const mozilla::CSSIntRect& aSrc,
+                                  bool aIsBackfaceVisible,
+                                  float aOpacity = 1.0);
+
+ private:
+  nsCSSGradientRenderer()
+      : mPresContext(nullptr),
+        mGradient(nullptr),
+        mRadiusX(0.0),
+        mRadiusY(0.0),
+        mAngle(0.0) {}
+
+  /**
+   * Attempts to paint the tiles for a gradient by painting it once to an
+   * offscreen surface and then painting that offscreen surface with
+   * ExtendMode::Repeat to cover all tiles.
+   *
+   * Returns false if the optimization wasn't able to be used, in which case
+   * a fallback should be used.
+   */
+  bool TryPaintTilesWithExtendMode(
+      gfxContext& aContext, gfxPattern* aGradientPattern, nscoord aXStart,
+      nscoord aYStart, const gfxRect& aDirtyAreaToFill, const nsRect& aDest,
+      const nsSize& aRepeatSize, bool aForceRepeatToCoverTiles);
+
+  nsPresContext* mPresContext;
+  const StyleGradient* mGradient;
+  nsTArray<ColorStop> mStops;
+  gfxPoint mLineStart, mLineEnd;  // only for linear/radial gradients
+  double mRadiusX, mRadiusY;      // only for radial gradients
+  gfxPoint mCenter;               // only for conic gradients
+  float mAngle;                   // only for conic gradients
+};
+
+}  // namespace mozilla
+
+#endif /* nsCSSRenderingGradients_h__ */
diff --git a/layout/painting/nsDisplayItemTypes.h b/layout/painting/nsDisplayItemTypes.h
new file mode 100644
index 0000000000..f0c7c333e0
--- /dev/null
+++ b/layout/painting/nsDisplayItemTypes.h
@@ -0,0 +1,73 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+// IWYU pragma: private, include "nsDisplayList.h"
+
+/**
+ * It's useful to be able to dynamically check the type of certain items.
+ * Every subclass of nsDisplayItem must have a new type added here for the
+ * purposes of easy comparison and matching of items in different display lists.
+ */
+
+#ifndef NSDISPLAYITEMTYPES_H_
+#define NSDISPLAYITEMTYPES_H_
+
+enum class DisplayItemType : uint8_t {
+  TYPE_ZERO = 0, /** Spacer so that the first item starts at 1 */
+
+#define DECLARE_DISPLAY_ITEM_TYPE(name, flags) TYPE_##name,
+#include "nsDisplayItemTypesList.h"
+#undef DECLARE_DISPLAY_ITEM_TYPE
+
+  TYPE_MAX
+};
+
+enum {
+  // Number of bits needed to represent all types
+  TYPE_BITS = 8
+};
+
+enum DisplayItemFlags {
+  TYPE_RENDERS_NO_IMAGES = 1 << 0,
+  TYPE_IS_CONTENTFUL = 1 << 1,
+  TYPE_IS_CONTAINER = 1 << 2
+};
+
+inline const char* DisplayItemTypeName(DisplayItemType aType) {
+  switch (aType) {
+#define DECLARE_DISPLAY_ITEM_TYPE(name, flags) \
+  case DisplayItemType::TYPE_##name:           \
+    return #name;
+#include "nsDisplayItemTypesList.h"
+#undef DECLARE_DISPLAY_ITEM_TYPE
+
+    default:
+      return "TYPE_UNKNOWN";
+  }
+}
+
+inline uint8_t GetDisplayItemFlagsForType(DisplayItemType aType) {
+  static const uint8_t flags[static_cast<uint32_t>(DisplayItemType::TYPE_MAX)] =
+      {0
+#define DECLARE_DISPLAY_ITEM_TYPE(name, flags) , flags
+#include "nsDisplayItemTypesList.h"
+#undef DECLARE_DISPLAY_ITEM_TYPE
+      };
+
+  return flags[static_cast<uint32_t>(aType)];
+}
+
+inline DisplayItemType GetDisplayItemTypeFromKey(uint32_t aDisplayItemKey) {
+  static const uint32_t typeMask = (1 << TYPE_BITS) - 1;
+  DisplayItemType type =
+      static_cast<DisplayItemType>(aDisplayItemKey & typeMask);
+  NS_ASSERTION(
+      type >= DisplayItemType::TYPE_ZERO && type < DisplayItemType::TYPE_MAX,
+      "Invalid display item type!");
+  return type;
+}
+
+#endif /*NSDISPLAYITEMTYPES_H_*/
diff --git a/layout/painting/nsDisplayItemTypesList.h b/layout/painting/nsDisplayItemTypesList.h
new file mode 100644
index 0000000000..82343e7d47
--- /dev/null
+++ b/layout/painting/nsDisplayItemTypesList.h
@@ -0,0 +1,123 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+// IWYU pragma: private, include "nsDisplayList.h"
+DECLARE_DISPLAY_ITEM_TYPE(ALT_FEEDBACK, 0)
+DECLARE_DISPLAY_ITEM_TYPE(ASYNC_ZOOM,
+                          TYPE_RENDERS_NO_IMAGES | TYPE_IS_CONTAINER)
+DECLARE_DISPLAY_ITEM_TYPE(BACKDROP_FILTER, TYPE_IS_CONTAINER)
+DECLARE_DISPLAY_ITEM_TYPE(BACKDROP_ROOT_CONTAINER, TYPE_IS_CONTAINER)
+DECLARE_DISPLAY_ITEM_TYPE(BACKGROUND, TYPE_IS_CONTENTFUL)
+DECLARE_DISPLAY_ITEM_TYPE(BACKGROUND_COLOR, TYPE_RENDERS_NO_IMAGES)
+DECLARE_DISPLAY_ITEM_TYPE(BLEND_CONTAINER,
+                          TYPE_RENDERS_NO_IMAGES | TYPE_IS_CONTAINER)
+DECLARE_DISPLAY_ITEM_TYPE(BLEND_MODE,
+                          TYPE_RENDERS_NO_IMAGES | TYPE_IS_CONTAINER)
+DECLARE_DISPLAY_ITEM_TYPE(BORDER, 0)
+DECLARE_DISPLAY_ITEM_TYPE(BOX_SHADOW_INNER, TYPE_RENDERS_NO_IMAGES)
+DECLARE_DISPLAY_ITEM_TYPE(BOX_SHADOW_OUTER, TYPE_RENDERS_NO_IMAGES)
+DECLARE_DISPLAY_ITEM_TYPE(BUTTON_BORDER_BACKGROUND, TYPE_IS_CONTENTFUL)
+DECLARE_DISPLAY_ITEM_TYPE(BUTTON_BOX_SHADOW_OUTER,
+                          TYPE_RENDERS_NO_IMAGES | TYPE_IS_CONTENTFUL)
+DECLARE_DISPLAY_ITEM_TYPE(BUTTON_FOREGROUND, TYPE_IS_CONTENTFUL)
+DECLARE_DISPLAY_ITEM_TYPE(CANVAS, TYPE_RENDERS_NO_IMAGES)
+DECLARE_DISPLAY_ITEM_TYPE(CANVAS_BACKGROUND_COLOR, TYPE_RENDERS_NO_IMAGES)
+DECLARE_DISPLAY_ITEM_TYPE(CANVAS_BACKGROUND_IMAGE, TYPE_IS_CONTENTFUL)
+DECLARE_DISPLAY_ITEM_TYPE(CANVAS_FOCUS, TYPE_RENDERS_NO_IMAGES)
+DECLARE_DISPLAY_ITEM_TYPE(CANVAS_THEMED_BACKGROUND,
+                          TYPE_RENDERS_NO_IMAGES | TYPE_IS_CONTENTFUL)
+DECLARE_DISPLAY_ITEM_TYPE(CARET, TYPE_RENDERS_NO_IMAGES | TYPE_IS_CONTENTFUL)
+DECLARE_DISPLAY_ITEM_TYPE(CHECKED_CHECKBOX,
+                          TYPE_RENDERS_NO_IMAGES | TYPE_IS_CONTENTFUL)
+DECLARE_DISPLAY_ITEM_TYPE(CHECKED_RADIOBUTTON,
+                          TYPE_RENDERS_NO_IMAGES | TYPE_IS_CONTENTFUL)
+DECLARE_DISPLAY_ITEM_TYPE(COLUMN_RULE, TYPE_RENDERS_NO_IMAGES)
+DECLARE_DISPLAY_ITEM_TYPE(COMBOBOX_FOCUS, TYPE_RENDERS_NO_IMAGES)
+DECLARE_DISPLAY_ITEM_TYPE(COMPOSITOR_HITTEST_INFO, TYPE_RENDERS_NO_IMAGES)
+DECLARE_DISPLAY_ITEM_TYPE(CONTAINER, TYPE_RENDERS_NO_IMAGES | TYPE_IS_CONTAINER)
+DECLARE_DISPLAY_ITEM_TYPE(DESTINATION, TYPE_RENDERS_NO_IMAGES)
+DECLARE_DISPLAY_ITEM_TYPE(EVENT_RECEIVER, TYPE_RENDERS_NO_IMAGES)
+DECLARE_DISPLAY_ITEM_TYPE(FIELDSET_BORDER_BACKGROUND, 0)
+DECLARE_DISPLAY_ITEM_TYPE(FILTER, TYPE_RENDERS_NO_IMAGES | TYPE_IS_CONTAINER)
+DECLARE_DISPLAY_ITEM_TYPE(FIXED_POSITION,
+                          TYPE_RENDERS_NO_IMAGES | TYPE_IS_CONTAINER)
+DECLARE_DISPLAY_ITEM_TYPE(FOREIGN_OBJECT,
+                          TYPE_IS_CONTENTFUL | TYPE_IS_CONTAINER)
+DECLARE_DISPLAY_ITEM_TYPE(FRAMESET_BLANK, TYPE_RENDERS_NO_IMAGES)
+DECLARE_DISPLAY_ITEM_TYPE(FRAMESET_BORDER, TYPE_RENDERS_NO_IMAGES)
+DECLARE_DISPLAY_ITEM_TYPE(GENERIC, TYPE_RENDERS_NO_IMAGES)
+DECLARE_DISPLAY_ITEM_TYPE(GRADIENT, TYPE_IS_CONTENTFUL)
+DECLARE_DISPLAY_ITEM_TYPE(HEADER_FOOTER, TYPE_RENDERS_NO_IMAGES)
+DECLARE_DISPLAY_ITEM_TYPE(IMAGE, TYPE_IS_CONTENTFUL)
+DECLARE_DISPLAY_ITEM_TYPE(LINK, TYPE_RENDERS_NO_IMAGES)
+DECLARE_DISPLAY_ITEM_TYPE(LIST_FOCUS, TYPE_RENDERS_NO_IMAGES)
+DECLARE_DISPLAY_ITEM_TYPE(MARGIN_GUIDES, TYPE_RENDERS_NO_IMAGES)
+DECLARE_DISPLAY_ITEM_TYPE(MASK, TYPE_IS_CONTAINER)
+DECLARE_DISPLAY_ITEM_TYPE(OPACITY, TYPE_RENDERS_NO_IMAGES | TYPE_IS_CONTAINER)
+DECLARE_DISPLAY_ITEM_TYPE(OPTION_EVENT_GRABBER,
+                          TYPE_RENDERS_NO_IMAGES | TYPE_IS_CONTAINER)
+DECLARE_DISPLAY_ITEM_TYPE(OUTLINE, TYPE_RENDERS_NO_IMAGES)
+DECLARE_DISPLAY_ITEM_TYPE(OWN_LAYER, TYPE_RENDERS_NO_IMAGES | TYPE_IS_CONTAINER)
+DECLARE_DISPLAY_ITEM_TYPE(PERSPECTIVE,
+                          TYPE_RENDERS_NO_IMAGES | TYPE_IS_CONTAINER)
+DECLARE_DISPLAY_ITEM_TYPE(RANGE_FOCUS_RING, 0)
+DECLARE_DISPLAY_ITEM_TYPE(REMOTE, TYPE_RENDERS_NO_IMAGES)
+DECLARE_DISPLAY_ITEM_TYPE(SCROLL_INFO_LAYER,
+                          TYPE_RENDERS_NO_IMAGES | TYPE_IS_CONTAINER)
+DECLARE_DISPLAY_ITEM_TYPE(SLIDER_MARKS, TYPE_RENDERS_NO_IMAGES)
+DECLARE_DISPLAY_ITEM_TYPE(SELECTION_OVERLAY, TYPE_RENDERS_NO_IMAGES)
+DECLARE_DISPLAY_ITEM_TYPE(SOLID_COLOR, TYPE_RENDERS_NO_IMAGES)
+DECLARE_DISPLAY_ITEM_TYPE(SOLID_COLOR_REGION, TYPE_RENDERS_NO_IMAGES)
+DECLARE_DISPLAY_ITEM_TYPE(SUBDOCUMENT,
+                          TYPE_RENDERS_NO_IMAGES | TYPE_IS_CONTAINER)
+DECLARE_DISPLAY_ITEM_TYPE(STICKY_POSITION,
+                          TYPE_RENDERS_NO_IMAGES | TYPE_IS_CONTAINER)
+DECLARE_DISPLAY_ITEM_TYPE(SVG_OUTER_SVG, TYPE_RENDERS_NO_IMAGES)
+DECLARE_DISPLAY_ITEM_TYPE(SVG_GEOMETRY, TYPE_IS_CONTENTFUL)
+DECLARE_DISPLAY_ITEM_TYPE(SVG_TEXT, TYPE_IS_CONTENTFUL)
+DECLARE_DISPLAY_ITEM_TYPE(SVG_WRAPPER, TYPE_IS_CONTAINER)
+DECLARE_DISPLAY_ITEM_TYPE(TABLE_BACKGROUND_COLOR, TYPE_RENDERS_NO_IMAGES)
+DECLARE_DISPLAY_ITEM_TYPE(TABLE_BACKGROUND_IMAGE, TYPE_IS_CONTENTFUL)
+DECLARE_DISPLAY_ITEM_TYPE(TABLE_BLEND_CONTAINER,
+                          TYPE_RENDERS_NO_IMAGES | TYPE_IS_CONTAINER)
+DECLARE_DISPLAY_ITEM_TYPE(TABLE_BLEND_MODE,
+                          TYPE_RENDERS_NO_IMAGES | TYPE_IS_CONTAINER)
+DECLARE_DISPLAY_ITEM_TYPE(TABLE_BORDER_COLLAPSE, 0)
+DECLARE_DISPLAY_ITEM_TYPE(TABLE_CELL_BACKGROUND, 0)
+DECLARE_DISPLAY_ITEM_TYPE(TABLE_CELL_SELECTION, TYPE_RENDERS_NO_IMAGES)
+DECLARE_DISPLAY_ITEM_TYPE(TABLE_THEMED_BACKGROUND_IMAGE, TYPE_IS_CONTENTFUL)
+DECLARE_DISPLAY_ITEM_TYPE(TABLE_FIXED_POSITION,
+                          TYPE_RENDERS_NO_IMAGES | TYPE_IS_CONTAINER)
+DECLARE_DISPLAY_ITEM_TYPE(TEXT, TYPE_RENDERS_NO_IMAGES | TYPE_IS_CONTENTFUL)
+DECLARE_DISPLAY_ITEM_TYPE(TEXT_OVERFLOW,
+                          TYPE_RENDERS_NO_IMAGES | TYPE_IS_CONTENTFUL)
+DECLARE_DISPLAY_ITEM_TYPE(THEMED_BACKGROUND, TYPE_RENDERS_NO_IMAGES)
+DECLARE_DISPLAY_ITEM_TYPE(TRANSFORM, TYPE_RENDERS_NO_IMAGES | TYPE_IS_CONTAINER)
+DECLARE_DISPLAY_ITEM_TYPE(VIDEO, TYPE_RENDERS_NO_IMAGES | TYPE_IS_CONTENTFUL)
+DECLARE_DISPLAY_ITEM_TYPE(WRAP_LIST, TYPE_RENDERS_NO_IMAGES | TYPE_IS_CONTAINER)
+DECLARE_DISPLAY_ITEM_TYPE(ZOOM, TYPE_RENDERS_NO_IMAGES | TYPE_IS_CONTAINER)
+
+#if defined(MOZ_REFLOW_PERF_DSP) && defined(MOZ_REFLOW_PERF)
+DECLARE_DISPLAY_ITEM_TYPE(REFLOW_COUNT, TYPE_RENDERS_NO_IMAGES)
+#endif
+
+DECLARE_DISPLAY_ITEM_TYPE(XUL_EVENT_REDIRECTOR,
+                          TYPE_RENDERS_NO_IMAGES | TYPE_IS_CONTAINER)
+DECLARE_DISPLAY_ITEM_TYPE(XUL_GROUP_BACKGROUND, 0)
+DECLARE_DISPLAY_ITEM_TYPE(XUL_IMAGE, 0)
+DECLARE_DISPLAY_ITEM_TYPE(XUL_TEXT_BOX, TYPE_RENDERS_NO_IMAGES)
+DECLARE_DISPLAY_ITEM_TYPE(XUL_TREE_BODY, 0)
+DECLARE_DISPLAY_ITEM_TYPE(XUL_TREE_COL_SPLITTER_TARGET, TYPE_RENDERS_NO_IMAGES)
+
+DECLARE_DISPLAY_ITEM_TYPE(MATHML_BAR, TYPE_RENDERS_NO_IMAGES)
+DECLARE_DISPLAY_ITEM_TYPE(MATHML_CHAR_FOREGROUND, TYPE_RENDERS_NO_IMAGES)
+DECLARE_DISPLAY_ITEM_TYPE(MATHML_ERROR, TYPE_RENDERS_NO_IMAGES)
+DECLARE_DISPLAY_ITEM_TYPE(MATHML_MENCLOSE_NOTATION, TYPE_RENDERS_NO_IMAGES)
+DECLARE_DISPLAY_ITEM_TYPE(MATHML_SELECTION_RECT, TYPE_RENDERS_NO_IMAGES)
+DECLARE_DISPLAY_ITEM_TYPE(MATHML_SLASH, TYPE_RENDERS_NO_IMAGES)
+#ifdef DEBUG
+DECLARE_DISPLAY_ITEM_TYPE(MATHML_BOUNDING_METRICS, TYPE_RENDERS_NO_IMAGES)
+DECLARE_DISPLAY_ITEM_TYPE(MATHML_CHAR_DEBUG, TYPE_RENDERS_NO_IMAGES)
+#endif
diff --git a/layout/painting/nsDisplayList.cpp b/layout/painting/nsDisplayList.cpp
new file mode 100644
index 0000000000..2d83a9514f
--- /dev/null
+++ b/layout/painting/nsDisplayList.cpp
@@ -0,0 +1,8668 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+/*
+ * structures that represent things to be painted (ordered in z-order),
+ * used during painting and hit testing
+ */
+
+#include "nsDisplayList.h"
+
+#include <stdint.h>
+#include <algorithm>
+#include <limits>
+
+#include "gfxContext.h"
+#include "gfxUtils.h"
+#include "mozilla/DisplayPortUtils.h"
+#include "mozilla/Likely.h"
+#include "mozilla/dom/BrowserChild.h"
+#include "mozilla/dom/HTMLCanvasElement.h"
+#include "mozilla/dom/RemoteBrowser.h"
+#include "mozilla/dom/Selection.h"
+#include "mozilla/dom/ServiceWorkerRegistrar.h"
+#include "mozilla/dom/ServiceWorkerRegistration.h"
+#include "mozilla/dom/SVGElement.h"
+#include "mozilla/dom/TouchEvent.h"
+#include "mozilla/gfx/2D.h"
+#include "mozilla/PresShell.h"
+#include "mozilla/ShapeUtils.h"
+#include "mozilla/StaticPrefs_apz.h"
+#include "mozilla/StaticPrefs_gfx.h"
+#include "mozilla/StaticPrefs_layers.h"
+#include "mozilla/StaticPrefs_layout.h"
+#include "mozilla/StaticPrefs_print.h"
+#include "mozilla/SVGIntegrationUtils.h"
+#include "mozilla/SVGUtils.h"
+#include "mozilla/ViewportUtils.h"
+#include "nsCSSRendering.h"
+#include "nsCSSRenderingGradients.h"
+#include "nsRefreshDriver.h"
+#include "nsRegion.h"
+#include "nsStyleStructInlines.h"
+#include "nsStyleTransformMatrix.h"
+#include "nsTransitionManager.h"
+#include "gfxMatrix.h"
+#include "nsLayoutUtils.h"
+#include "nsIScrollableFrame.h"
+#include "nsIFrameInlines.h"
+#include "nsStyleConsts.h"
+#include "BorderConsts.h"
+#include "mozilla/MathAlgorithms.h"
+
+#include "imgIContainer.h"
+#include "nsBoxFrame.h"
+#include "nsImageFrame.h"
+#include "nsSubDocumentFrame.h"
+#include "nsViewManager.h"
+#include "ImageContainer.h"
+#include "nsCanvasFrame.h"
+#include "nsSubDocumentFrame.h"
+#include "StickyScrollContainer.h"
+#include "mozilla/AnimationPerformanceWarning.h"
+#include "mozilla/AnimationUtils.h"
+#include "mozilla/AutoRestore.h"
+#include "mozilla/EffectCompositor.h"
+#include "mozilla/EffectSet.h"
+#include "mozilla/HashTable.h"
+#include "mozilla/LookAndFeel.h"
+#include "mozilla/OperatorNewExtensions.h"
+#include "mozilla/PendingAnimationTracker.h"
+#include "mozilla/Preferences.h"
+#include "mozilla/ProfilerLabels.h"
+#include "mozilla/ProfilerMarkers.h"
+#include "mozilla/StyleAnimationValue.h"
+#include "mozilla/ServoBindings.h"
+#include "mozilla/SVGClipPathFrame.h"
+#include "mozilla/SVGMaskFrame.h"
+#include "mozilla/SVGObserverUtils.h"
+#include "mozilla/Telemetry.h"
+#include "mozilla/UniquePtr.h"
+#include "mozilla/Unused.h"
+#include "mozilla/ViewportFrame.h"
+#include "mozilla/gfx/gfxVars.h"
+#include "ActiveLayerTracker.h"
+#include "nsEscape.h"
+#include "nsPrintfCString.h"
+#include "UnitTransforms.h"
+#include "LayerAnimationInfo.h"
+#include "mozilla/EventStateManager.h"
+#include "nsCaret.h"
+#include "nsDOMTokenList.h"
+#include "nsCSSProps.h"
+#include "nsTableCellFrame.h"
+#include "nsTableColFrame.h"
+#include "nsTextFrame.h"
+#include "nsSliderFrame.h"
+#include "nsFocusManager.h"
+#include "TextDrawTarget.h"
+#include "mozilla/layers/AnimationHelper.h"
+#include "mozilla/layers/CompositorThread.h"
+#include "mozilla/layers/InputAPZContext.h"
+#include "mozilla/layers/RenderRootStateManager.h"
+#include "mozilla/layers/StackingContextHelper.h"
+#include "mozilla/layers/TreeTraversal.h"
+#include "mozilla/layers/WebRenderBridgeChild.h"
+#include "mozilla/layers/WebRenderLayerManager.h"
+#include "mozilla/layers/WebRenderMessages.h"
+#include "mozilla/layers/WebRenderScrollData.h"
+
+namespace mozilla {
+
+using namespace dom;
+using namespace gfx;
+using namespace layout;
+using namespace layers;
+using namespace image;
+
+LazyLogModule sContentDisplayListLog("dl.content");
+LazyLogModule sParentDisplayListLog("dl.parent");
+
+LazyLogModule& GetLoggerByProcess() {
+  return XRE_IsContentProcess() ? sContentDisplayListLog
+                                : sParentDisplayListLog;
+}
+
+#ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
+void AssertUniqueItem(nsDisplayItem* aItem) {
+  for (nsDisplayItem* i : aItem->Frame()->DisplayItems()) {
+    if (i != aItem && !i->HasDeletedFrame() && i->Frame() == aItem->Frame() &&
+        i->GetPerFrameKey() == aItem->GetPerFrameKey()) {
+      if (i->IsPreProcessedItem() || i->IsPreProcessed()) {
+        continue;
+      }
+      MOZ_DIAGNOSTIC_ASSERT(false, "Duplicate display item!");
+    }
+  }
+}
+#endif
+
+bool ShouldBuildItemForEvents(const DisplayItemType aType) {
+  return aType == DisplayItemType::TYPE_COMPOSITOR_HITTEST_INFO ||
+         (GetDisplayItemFlagsForType(aType) & TYPE_IS_CONTAINER);
+}
+
+static bool ItemTypeSupportsHitTesting(const DisplayItemType aType) {
+  switch (aType) {
+    case DisplayItemType::TYPE_BACKGROUND:
+    case DisplayItemType::TYPE_BACKGROUND_COLOR:
+    case DisplayItemType::TYPE_THEMED_BACKGROUND:
+      return true;
+    default:
+      return false;
+  }
+}
+
+void InitializeHitTestInfo(nsDisplayListBuilder* aBuilder,
+                           nsPaintedDisplayItem* aItem,
+                           const DisplayItemType aType) {
+  if (ItemTypeSupportsHitTesting(aType)) {
+    aItem->InitializeHitTestInfo(aBuilder);
+  }
+}
+
+/* static */
+already_AddRefed<ActiveScrolledRoot> ActiveScrolledRoot::CreateASRForFrame(
+    const ActiveScrolledRoot* aParent, nsIScrollableFrame* aScrollableFrame,
+    bool aIsRetained) {
+  nsIFrame* f = do_QueryFrame(aScrollableFrame);
+
+  RefPtr<ActiveScrolledRoot> asr;
+  if (aIsRetained) {
+    asr = f->GetProperty(ActiveScrolledRootCache());
+  }
+
+  if (!asr) {
+    asr = new ActiveScrolledRoot();
+
+    if (aIsRetained) {
+      RefPtr<ActiveScrolledRoot> ref = asr;
+      f->SetProperty(ActiveScrolledRootCache(), ref.forget().take());
+    }
+  }
+  asr->mParent = aParent;
+  asr->mScrollableFrame = aScrollableFrame;
+  asr->mViewId = Nothing();
+  asr->mDepth = aParent ? aParent->mDepth + 1 : 1;
+  asr->mRetained = aIsRetained;
+
+  return asr.forget();
+}
+
+/* static */
+bool ActiveScrolledRoot::IsAncestor(const ActiveScrolledRoot* aAncestor,
+                                    const ActiveScrolledRoot* aDescendant) {
+  if (!aAncestor) {
+    // nullptr is the root
+    return true;
+  }
+  if (Depth(aAncestor) > Depth(aDescendant)) {
+    return false;
+  }
+  const ActiveScrolledRoot* asr = aDescendant;
+  while (asr) {
+    if (asr == aAncestor) {
+      return true;
+    }
+    asr = asr->mParent;
+  }
+  return false;
+}
+
+/* static */
+bool ActiveScrolledRoot::IsProperAncestor(
+    const ActiveScrolledRoot* aAncestor,
+    const ActiveScrolledRoot* aDescendant) {
+  return aAncestor != aDescendant && IsAncestor(aAncestor, aDescendant);
+}
+
+/* static */
+nsCString ActiveScrolledRoot::ToString(
+    const ActiveScrolledRoot* aActiveScrolledRoot) {
+  nsAutoCString str;
+  for (const auto* asr = aActiveScrolledRoot; asr; asr = asr->mParent) {
+    str.AppendPrintf("<0x%p>", asr->mScrollableFrame);
+    if (asr->mParent) {
+      str.AppendLiteral(", ");
+    }
+  }
+  return std::move(str);
+}
+
+ScrollableLayerGuid::ViewID ActiveScrolledRoot::ComputeViewId() const {
+  nsIContent* content = mScrollableFrame->GetScrolledFrame()->GetContent();
+  return nsLayoutUtils::FindOrCreateIDFor(content);
+}
+
+ActiveScrolledRoot::~ActiveScrolledRoot() {
+  if (mScrollableFrame && mRetained) {
+    nsIFrame* f = do_QueryFrame(mScrollableFrame);
+    f->RemoveProperty(ActiveScrolledRootCache());
+  }
+}
+
+static uint64_t AddAnimationsForWebRender(
+    nsDisplayItem* aItem, RenderRootStateManager* aManager,
+    nsDisplayListBuilder* aDisplayListBuilder,
+    const Maybe<LayoutDevicePoint>& aPosition = Nothing()) {
+  EffectSet* effects =
+      EffectSet::GetEffectSetForFrame(aItem->Frame(), aItem->GetType());
+  if (!effects || effects->IsEmpty()) {
+    // If there is no animation on the nsIFrame, that means
+    //  1) we've never created any animations on this frame or
+    //  2) the frame was reconstruced or
+    //  3) all animations on the frame have finished
+    // in such cases we don't need do anything here.
+    //
+    // Even if there is a WebRenderAnimationData for the display item type on
+    // this frame, it's going to be discarded since it's not marked as being
+    // used.
+    return 0;
+  }
+
+  RefPtr<WebRenderAnimationData> animationData =
+      aManager->CommandBuilder()
+          .CreateOrRecycleWebRenderUserData<WebRenderAnimationData>(aItem);
+  AnimationInfo& animationInfo = animationData->GetAnimationInfo();
+  animationInfo.AddAnimationsForDisplayItem(
+      aItem->Frame(), aDisplayListBuilder, aItem, aItem->GetType(),
+      aManager->LayerManager(), aPosition);
+  animationInfo.StartPendingAnimations(
+      aManager->LayerManager()->GetAnimationReadyTime());
+
+  // Note that animationsId can be 0 (uninitialized in AnimationInfo) if there
+  // are no active animations.
+  uint64_t animationsId = animationInfo.GetCompositorAnimationsId();
+  if (!animationInfo.GetAnimations().IsEmpty()) {
+    OpAddCompositorAnimations anim(
+        CompositorAnimations(animationInfo.GetAnimations(), animationsId));
+    aManager->WrBridge()->AddWebRenderParentCommand(anim);
+    aManager->AddActiveCompositorAnimationId(animationsId);
+  } else if (animationsId) {
+    aManager->AddCompositorAnimationsIdForDiscard(animationsId);
+    animationsId = 0;
+  }
+
+  return animationsId;
+}
+
+static bool GenerateAndPushTextMask(nsIFrame* aFrame, gfxContext* aContext,
+                                    const nsRect& aFillRect,
+                                    nsDisplayListBuilder* aBuilder) {
+  if (aBuilder->IsForGenerateGlyphMask()) {
+    return false;
+  }
+
+  SVGObserverUtils::GetAndObserveBackgroundClip(aFrame);
+
+  // The main function of enabling background-clip:text property value.
+  // When a nsDisplayBackgroundImage detects "text" bg-clip style, it will call
+  // this function to
+  // 1. Generate a mask by all descendant text frames
+  // 2. Push the generated mask into aContext.
+
+  gfxContext* sourceCtx = aContext;
+  LayoutDeviceRect bounds = LayoutDeviceRect::FromAppUnits(
+      aFillRect, aFrame->PresContext()->AppUnitsPerDevPixel());
+
+  // Create a mask surface.
+  RefPtr<DrawTarget> sourceTarget = sourceCtx->GetDrawTarget();
+  RefPtr<DrawTarget> maskDT = sourceTarget->CreateClippedDrawTarget(
+      bounds.ToUnknownRect(), SurfaceFormat::A8);
+  if (!maskDT || !maskDT->IsValid()) {
+    return false;
+  }
+  RefPtr<gfxContext> maskCtx =
+      gfxContext::CreatePreservingTransformOrNull(maskDT);
+  MOZ_ASSERT(maskCtx);
+  maskCtx->Multiply(Matrix::Translation(bounds.TopLeft().ToUnknownPoint()));
+
+  // Shade text shape into mask A8 surface.
+  nsLayoutUtils::PaintFrame(
+      maskCtx, aFrame, nsRect(nsPoint(0, 0), aFrame->GetSize()),
+      NS_RGB(255, 255, 255), nsDisplayListBuilderMode::GenerateGlyph);
+
+  // Push the generated mask into aContext, so that the caller can pop and
+  // blend with it.
+
+  Matrix currentMatrix = sourceCtx->CurrentMatrix();
+  Matrix invCurrentMatrix = currentMatrix;
+  invCurrentMatrix.Invert();
+
+  RefPtr<SourceSurface> maskSurface = maskDT->Snapshot();
+  sourceCtx->PushGroupForBlendBack(gfxContentType::COLOR_ALPHA, 1.0,
+                                   maskSurface, invCurrentMatrix);
+
+  return true;
+}
+
+nsDisplayWrapper* nsDisplayWrapList::CreateShallowCopy(
+    nsDisplayListBuilder* aBuilder) {
+  const nsDisplayWrapList* wrappedItem = AsDisplayWrapList();
+  MOZ_ASSERT(wrappedItem);
+
+  // Create a new nsDisplayWrapList using a copy-constructor. This is done
+  // to preserve the information about bounds.
+  nsDisplayWrapper* wrapper =
+      new (aBuilder) nsDisplayWrapper(aBuilder, *wrappedItem);
+  wrapper->SetType(nsDisplayWrapper::ItemType());
+  MOZ_ASSERT(wrapper);
+
+  // Set the display list pointer of the new wrapper item to the display list
+  // of the wrapped item.
+  wrapper->mListPtr = wrappedItem->mListPtr;
+  return wrapper;
+}
+
+nsDisplayWrapList* nsDisplayListBuilder::MergeItems(
+    nsTArray<nsDisplayItem*>& aItems) {
+  // For merging, we create a temporary item by cloning the last item of the
+  // mergeable items list. This ensures that the temporary item will have the
+  // correct frame and bounds.
+  nsDisplayWrapList* last = aItems.PopLastElement()->AsDisplayWrapList();
+  MOZ_ASSERT(last);
+  nsDisplayWrapList* merged = last->Clone(this);
+  MOZ_ASSERT(merged);
+  AddTemporaryItem(merged);
+
+  // Create nsDisplayWrappers that point to the internal display lists of the
+  // items we are merging. These nsDisplayWrappers are added to the display list
+  // of the temporary item.
+  for (nsDisplayItem* item : aItems) {
+    MOZ_ASSERT(item);
+    MOZ_ASSERT(merged->CanMerge(item));
+    merged->Merge(item);
+    MOZ_ASSERT(item->AsDisplayWrapList());
+    merged->GetChildren()->AppendToTop(
+        static_cast<nsDisplayWrapList*>(item)->CreateShallowCopy(this));
+  }
+
+  merged->GetChildren()->AppendToTop(last->CreateShallowCopy(this));
+
+  return merged;
+}
+
+void nsDisplayListBuilder::AutoCurrentActiveScrolledRootSetter::
+    SetCurrentActiveScrolledRoot(
+        const ActiveScrolledRoot* aActiveScrolledRoot) {
+  MOZ_ASSERT(!mUsed);
+
+  // Set the builder's mCurrentActiveScrolledRoot.
+  mBuilder->mCurrentActiveScrolledRoot = aActiveScrolledRoot;
+
+  // We also need to adjust the builder's mCurrentContainerASR.
+  // mCurrentContainerASR needs to be an ASR that all the container's
+  // contents have finite bounds with respect to. If aActiveScrolledRoot
+  // is an ancestor ASR of mCurrentContainerASR, that means we need to
+  // set mCurrentContainerASR to aActiveScrolledRoot, because otherwise
+  // the items that will be created with aActiveScrolledRoot wouldn't
+  // have finite bounds with respect to mCurrentContainerASR. There's one
+  // exception, in the case where there's a content clip on the builder
+  // that is scrolled by a descendant ASR of aActiveScrolledRoot. This
+  // content clip will clip all items that are created while this
+  // AutoCurrentActiveScrolledRootSetter exists. This means that the items
+  // created during our lifetime will have finite bounds with respect to
+  // the content clip's ASR, even if the items' actual ASR is an ancestor
+  // of that. And it also means that mCurrentContainerASR only needs to be
+  // set to the content clip's ASR and not all the way to aActiveScrolledRoot.
+  // This case is tested by fixed-pos-scrolled-clip-opacity-layerize.html
+  // and fixed-pos-scrolled-clip-opacity-inside-layerize.html.
+
+  // finiteBoundsASR is the leafmost ASR that all items created during
+  // object's lifetime have finite bounds with respect to.
+  const ActiveScrolledRoot* finiteBoundsASR =
+      ActiveScrolledRoot::PickDescendant(mContentClipASR, aActiveScrolledRoot);
+
+  // mCurrentContainerASR is adjusted so that it's still an ancestor of
+  // finiteBoundsASR.
+  mBuilder->mCurrentContainerASR = ActiveScrolledRoot::PickAncestor(
+      mBuilder->mCurrentContainerASR, finiteBoundsASR);
+
+  // If we are entering out-of-flow content inside a CSS filter, mark
+  // scroll frames wrt. which the content is fixed as containing such content.
+  if (mBuilder->mFilterASR && ActiveScrolledRoot::IsAncestor(
+                                  aActiveScrolledRoot, mBuilder->mFilterASR)) {
+    for (const ActiveScrolledRoot* asr = mBuilder->mFilterASR;
+         asr && asr != aActiveScrolledRoot; asr = asr->mParent) {
+      asr->mScrollableFrame->SetHasOutOfFlowContentInsideFilter();
+    }
+  }
+
+  mUsed = true;
+}
+
+void nsDisplayListBuilder::AutoCurrentActiveScrolledRootSetter::
+    InsertScrollFrame(nsIScrollableFrame* aScrollableFrame) {
+  MOZ_ASSERT(!mUsed);
+  size_t descendantsEndIndex = mBuilder->mActiveScrolledRoots.Length();
+  const ActiveScrolledRoot* parentASR = mBuilder->mCurrentActiveScrolledRoot;
+  const ActiveScrolledRoot* asr =
+      mBuilder->AllocateActiveScrolledRoot(parentASR, aScrollableFrame);
+  mBuilder->mCurrentActiveScrolledRoot = asr;
+
+  // All child ASRs of parentASR that were created while this
+  // AutoCurrentActiveScrolledRootSetter object was on the stack belong to us
+  // now. Reparent them to asr.
+  for (size_t i = mDescendantsStartIndex; i < descendantsEndIndex; i++) {
+    ActiveScrolledRoot* descendantASR = mBuilder->mActiveScrolledRoots[i];
+    if (ActiveScrolledRoot::IsAncestor(parentASR, descendantASR)) {
+      descendantASR->IncrementDepth();
+      if (descendantASR->mParent == parentASR) {
+        descendantASR->mParent = asr;
+      }
+    }
+  }
+
+  mUsed = true;
+}
+
+nsDisplayListBuilder::AutoContainerASRTracker::AutoContainerASRTracker(
+    nsDisplayListBuilder* aBuilder)
+    : mBuilder(aBuilder), mSavedContainerASR(aBuilder->mCurrentContainerASR) {
+  mBuilder->mCurrentContainerASR = mBuilder->mCurrentActiveScrolledRoot;
+}
+
+nsPresContext* nsDisplayListBuilder::CurrentPresContext() {
+  return CurrentPresShellState()->mPresShell->GetPresContext();
+}
+
+/* static */
+nsRect nsDisplayListBuilder::OutOfFlowDisplayData::ComputeVisibleRectForFrame(
+    nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+    const nsRect& aVisibleRect, const nsRect& aDirtyRect,
+    nsRect* aOutDirtyRect) {
+  nsRect visible = aVisibleRect;
+  nsRect dirtyRectRelativeToDirtyFrame = aDirtyRect;
+
+  bool inPartialUpdate =
+      aBuilder->IsRetainingDisplayList() && aBuilder->IsPartialUpdate();
+  if (StaticPrefs::apz_allow_zooming() &&
+      DisplayPortUtils::IsFixedPosFrameInDisplayPort(aFrame) &&
+      aBuilder->IsPaintingToWindow() && !inPartialUpdate) {
+    dirtyRectRelativeToDirtyFrame =
+        nsRect(nsPoint(0, 0), aFrame->GetParent()->GetSize());
+
+    // If there's a visual viewport size set, restrict the amount of the
+    // fixed-position element we paint to the visual viewport. (In general
+    // the fixed-position element can be as large as the layout viewport,
+    // which at a high zoom level can cause us to paint too large of an
+    // area.)
+    PresShell* presShell = aFrame->PresShell();
+    if (presShell->IsVisualViewportSizeSet()) {
+      dirtyRectRelativeToDirtyFrame =
+          nsRect(presShell->GetVisualViewportOffsetRelativeToLayoutViewport(),
+                 presShell->GetVisualViewportSize());
+      // But if we have a displayport, expand it to the displayport, so
+      // that async-scrolling the visual viewport within the layout viewport
+      // will not checkerboard.
+      if (nsIFrame* rootScrollFrame = presShell->GetRootScrollFrame()) {
+        nsRect displayport;
+        // Note that the displayport here is already in the right coordinate
+        // space: it's relative to the scroll port (= layout viewport), but
+        // covers the visual viewport with some margins around it, which is
+        // exactly what we want.
+        if (DisplayPortUtils::GetDisplayPort(
+                rootScrollFrame->GetContent(), &displayport,
+                DisplayPortOptions().With(ContentGeometryType::Fixed))) {
+          dirtyRectRelativeToDirtyFrame = displayport;
+        }
+      }
+    }
+    visible = dirtyRectRelativeToDirtyFrame;
+    if (StaticPrefs::apz_test_logging_enabled() &&
+        presShell->GetDocument()->IsContentDocument()) {
+      nsLayoutUtils::LogAdditionalTestData(
+          aBuilder, "fixedPosDisplayport",
+          ToString(CSSSize::FromAppUnits(visible)));
+    }
+  }
+
+  *aOutDirtyRect = dirtyRectRelativeToDirtyFrame - aFrame->GetPosition();
+  visible -= aFrame->GetPosition();
+
+  nsRect overflowRect = aFrame->InkOverflowRect();
+
+  if (aFrame->IsTransformed() && EffectCompositor::HasAnimationsForCompositor(
+                                     aFrame, DisplayItemType::TYPE_TRANSFORM)) {
+    /**
+     * Add a fuzz factor to the overflow rectangle so that elements only
+     * just out of view are pulled into the display list, so they can be
+     * prerendered if necessary.
+     */
+    overflowRect.Inflate(nsPresContext::CSSPixelsToAppUnits(32));
+  }
+
+  visible.IntersectRect(visible, overflowRect);
+  aOutDirtyRect->IntersectRect(*aOutDirtyRect, overflowRect);
+
+  return visible;
+}
+
+nsDisplayListBuilder::Linkifier::Linkifier(nsDisplayListBuilder* aBuilder,
+                                           nsIFrame* aFrame,
+                                           nsDisplayList* aList)
+    : mList(aList) {
+  // Find the element that we need to check for link-ness, bailing out if
+  // we can't find one.
+  Element* elem = Element::FromNodeOrNull(aFrame->GetContent());
+  if (!elem) {
+    return;
+  }
+
+  // If the element has an id and/or name attribute, generate a destination
+  // for possible internal linking.
+  auto maybeGenerateDest = [&](const nsAtom* aAttr) {
+    nsAutoString attrValue;
+    elem->GetAttr(aAttr, attrValue);
+    if (!attrValue.IsEmpty()) {
+      NS_ConvertUTF16toUTF8 dest(attrValue);
+      // Ensure that we only emit a given destination once, although there may
+      // be multiple frames associated with a given element; we'll simply use
+      // the first of them as the target of any links to it.
+      // XXX(jfkthame) This prevents emitting duplicate destinations *on the
+      // same page*, but does not prevent duplicates on subsequent pages, as
+      // each new page is handled by a new temporary DisplayListBuilder. This
+      // seems to be harmless in practice, though a bit wasteful of space. To
+      // fix, we need to maintain the set of already-seen destinations globally
+      // for the print job, rather than attached to the (per-page) builder.
+      if (aBuilder->mDestinations.EnsureInserted(dest)) {
+        auto* destination = MakeDisplayItem<nsDisplayDestination>(
+            aBuilder, aFrame, dest.get(), aFrame->GetRect().TopLeft());
+        mList->AppendToTop(destination);
+      }
+    }
+  };
+
+  if (StaticPrefs::print_save_as_pdf_internal_destinations_enabled()) {
+    if (elem->HasID()) {
+      maybeGenerateDest(nsGkAtoms::id);
+    }
+    if (elem->HasName()) {
+      maybeGenerateDest(nsGkAtoms::name);
+    }
+  }
+
+  // Links don't nest, so if the builder already has a destination, no need to
+  // check for a link element here.
+  if (!aBuilder->mLinkSpec.IsEmpty()) {
+    return;
+  }
+
+  // Check if we have actually found a link.
+  if (!elem->IsLink()) {
+    return;
+  }
+
+  nsCOMPtr<nsIURI> uri = elem->GetHrefURI();
+  if (!uri) {
+    return;
+  }
+
+  // Is it a local (in-page) destination?
+  bool hasRef, eqExRef;
+  nsIURI* docURI;
+  if (StaticPrefs::print_save_as_pdf_internal_destinations_enabled() &&
+      NS_SUCCEEDED(uri->GetHasRef(&hasRef)) && hasRef &&
+      (docURI = aFrame->PresContext()->Document()->GetDocumentURI()) &&
+      NS_SUCCEEDED(uri->EqualsExceptRef(docURI, &eqExRef)) && eqExRef) {
+    if (NS_FAILED(uri->GetRef(aBuilder->mLinkSpec)) ||
+        aBuilder->mLinkSpec.IsEmpty()) {
+      return;
+    }
+    // The destination name is simply a string; we don't want URL-escaping
+    // applied to it.
+    NS_UnescapeURL(aBuilder->mLinkSpec);
+    // Mark the link spec as being an internal destination
+    aBuilder->mLinkSpec.Insert('#', 0);
+  } else {
+    if (NS_FAILED(uri->GetSpec(aBuilder->mLinkSpec)) ||
+        aBuilder->mLinkSpec.IsEmpty()) {
+      return;
+    }
+  }
+
+  // Record that we need to reset the builder's state on destruction.
+  mBuilderToReset = aBuilder;
+}
+
+void nsDisplayListBuilder::Linkifier::MaybeAppendLink(
+    nsDisplayListBuilder* aBuilder, nsIFrame* aFrame) {
+  // Note that we may generate a link here even if the constructor bailed out
+  // without updating aBuilder->LinkSpec(), because it may have been set by
+  // an ancestor that was associated with a link element.
+  if (!aBuilder->mLinkSpec.IsEmpty()) {
+    auto* link = MakeDisplayItem<nsDisplayLink>(
+        aBuilder, aFrame, aBuilder->mLinkSpec.get(), aFrame->GetRect());
+    mList->AppendToTop(link);
+  }
+}
+
+nsDisplayListBuilder::nsDisplayListBuilder(nsIFrame* aReferenceFrame,
+                                           nsDisplayListBuilderMode aMode,
+                                           bool aBuildCaret,
+                                           bool aRetainingDisplayList)
+    : mReferenceFrame(aReferenceFrame),
+      mIgnoreScrollFrame(nullptr),
+      mCurrentActiveScrolledRoot(nullptr),
+      mCurrentContainerASR(nullptr),
+      mCurrentFrame(aReferenceFrame),
+      mCurrentReferenceFrame(aReferenceFrame),
+      mBuildingExtraPagesForPageNum(0),
+      mDirtyRect(-1, -1, -1, -1),
+      mGlassDisplayItem(nullptr),
+      mHasGlassItemDuringPartial(false),
+      mCaretFrame(nullptr),
+      mScrollInfoItemsForHoisting(nullptr),
+      mFirstClipChainToDestroy(nullptr),
+      mMode(aMode),
+      mTableBackgroundSet(nullptr),
+      mCurrentScrollParentId(ScrollableLayerGuid::NULL_SCROLL_ID),
+      mCurrentScrollbarTarget(ScrollableLayerGuid::NULL_SCROLL_ID),
+      mFilterASR(nullptr),
+      mContainsBlendMode(false),
+      mIsBuildingScrollbar(false),
+      mCurrentScrollbarWillHaveLayer(false),
+      mBuildCaret(aBuildCaret),
+      mRetainingDisplayList(aRetainingDisplayList),
+      mPartialUpdate(false),
+      mIgnoreSuppression(false),
+      mIncludeAllOutOfFlows(false),
+      mDescendIntoSubdocuments(true),
+      mSelectedFramesOnly(false),
+      mAllowMergingAndFlattening(true),
+      mInTransform(false),
+      mInEventsOnly(false),
+      mInFilter(false),
+      mInPageSequence(false),
+      mIsInChromePresContext(false),
+      mSyncDecodeImages(false),
+      mIsPaintingToWindow(false),
+      mUseHighQualityScaling(false),
+      mIsPaintingForWebRender(false),
+      mIsCompositingCheap(false),
+      mAncestorHasApzAwareEventHandler(false),
+      mHaveScrollableDisplayPort(false),
+      mWindowDraggingAllowed(false),
+      mIsBuildingForPopup(nsLayoutUtils::IsPopup(aReferenceFrame)),
+      mForceLayerForScrollParent(false),
+      mContainsNonMinimalDisplayPort(false),
+      mAsyncPanZoomEnabled(nsLayoutUtils::AsyncPanZoomEnabled(aReferenceFrame)),
+      mBuildingInvisibleItems(false),
+      mIsBuilding(false),
+      mInInvalidSubtree(false),
+      mDisablePartialUpdates(false),
+      mPartialBuildFailed(false),
+      mIsInActiveDocShell(false),
+      mBuildAsyncZoomContainer(false),
+      mIsRelativeToLayoutViewport(false),
+      mUseOverlayScrollbars(false),
+      mAlwaysLayerizeScrollbars(false) {
+  MOZ_COUNT_CTOR(nsDisplayListBuilder);
+
+  mBuildCompositorHitTestInfo = mAsyncPanZoomEnabled && IsForPainting();
+
+  ShouldRebuildDisplayListDueToPrefChange();
+
+  mUseOverlayScrollbars =
+      !!LookAndFeel::GetInt(LookAndFeel::IntID::UseOverlayScrollbars);
+
+  mAlwaysLayerizeScrollbars =
+      StaticPrefs::layout_scrollbars_always_layerize_track();
+
+  static_assert(
+      static_cast<uint32_t>(DisplayItemType::TYPE_MAX) < (1 << TYPE_BITS),
+      "Check TYPE_MAX should not overflow");
+
+  mIsReusingStackingContextItems =
+      mRetainingDisplayList && StaticPrefs::layout_display_list_retain_sc();
+}
+
+static PresShell* GetFocusedPresShell() {
+  nsPIDOMWindowOuter* focusedWnd =
+      nsFocusManager::GetFocusManager()->GetFocusedWindow();
+  if (!focusedWnd) {
+    return nullptr;
+  }
+
+  nsCOMPtr<nsIDocShell> focusedDocShell = focusedWnd->GetDocShell();
+  if (!focusedDocShell) {
+    return nullptr;
+  }
+
+  return focusedDocShell->GetPresShell();
+}
+
+void nsDisplayListBuilder::BeginFrame() {
+  nsCSSRendering::BeginFrameTreesLocked();
+
+  mIsPaintingToWindow = false;
+  mUseHighQualityScaling = false;
+  mIgnoreSuppression = false;
+  mInTransform = false;
+  mInFilter = false;
+  mSyncDecodeImages = false;
+
+  if (!mBuildCaret) {
+    return;
+  }
+
+  RefPtr<PresShell> presShell = GetFocusedPresShell();
+  if (presShell) {
+    RefPtr<nsCaret> caret = presShell->GetCaret();
+    mCaretFrame = caret->GetPaintGeometry(&mCaretRect);
+
+    // The focused pres shell may not be in the document that we're
+    // painting, or be in a popup. Check if the display root for
+    // the caret matches the display root that we're painting, and
+    // only use it if it matches.
+    if (mCaretFrame &&
+        nsLayoutUtils::GetDisplayRootFrame(mCaretFrame) !=
+            nsLayoutUtils::GetDisplayRootFrame(mReferenceFrame)) {
+      mCaretFrame = nullptr;
+    }
+  }
+}
+
+void nsDisplayListBuilder::AddEffectUpdate(dom::RemoteBrowser* aBrowser,
+                                           const dom::EffectsInfo& aUpdate) {
+  dom::EffectsInfo update = aUpdate;
+  // For printing we create one display item for each page that an iframe
+  // appears on, the proper visible rect is the union of all the visible rects
+  // we get from each display item.
+  nsPresContext* pc =
+      mReferenceFrame ? mReferenceFrame->PresContext() : nullptr;
+  if (pc && (pc->Type() != nsPresContext::eContext_Galley)) {
+    Maybe<dom::EffectsInfo> existing = mEffectsUpdates.MaybeGet(aBrowser);
+    if (existing.isSome()) {
+      // Only the visible rect should differ, the scales should match.
+      MOZ_ASSERT(existing->mRasterScale == aUpdate.mRasterScale &&
+                 existing->mTransformToAncestorScale ==
+                     aUpdate.mTransformToAncestorScale);
+      update.mVisibleRect = update.mVisibleRect.Union(existing->mVisibleRect);
+    }
+  }
+  mEffectsUpdates.InsertOrUpdate(aBrowser, update);
+}
+
+void nsDisplayListBuilder::EndFrame() {
+  NS_ASSERTION(!mInInvalidSubtree,
+               "Someone forgot to cleanup mInInvalidSubtree!");
+  mActiveScrolledRoots.Clear();
+  mEffectsUpdates.Clear();
+  FreeClipChains();
+  FreeTemporaryItems();
+  nsCSSRendering::EndFrameTreesLocked();
+  mCaretFrame = nullptr;
+}
+
+void nsDisplayListBuilder::MarkFrameForDisplay(nsIFrame* aFrame,
+                                               const nsIFrame* aStopAtFrame) {
+  mFramesMarkedForDisplay.AppendElement(aFrame);
+  for (nsIFrame* f = aFrame; f;
+       f = nsLayoutUtils::GetParentOrPlaceholderForCrossDoc(f)) {
+    if (f->HasAnyStateBits(NS_FRAME_FORCE_DISPLAY_LIST_DESCEND_INTO)) {
+      return;
+    }
+    f->AddStateBits(NS_FRAME_FORCE_DISPLAY_LIST_DESCEND_INTO);
+    if (f == aStopAtFrame) {
+      // we've reached a frame that we know will be painted, so we can stop.
+      break;
+    }
+  }
+}
+
+void nsDisplayListBuilder::AddFrameMarkedForDisplayIfVisible(nsIFrame* aFrame) {
+  mFramesMarkedForDisplayIfVisible.AppendElement(aFrame);
+}
+
+void nsDisplayListBuilder::MarkFrameForDisplayIfVisible(
+    nsIFrame* aFrame, const nsIFrame* aStopAtFrame) {
+  AddFrameMarkedForDisplayIfVisible(aFrame);
+  for (nsIFrame* f = aFrame; f; f = nsLayoutUtils::GetDisplayListParent(f)) {
+    if (f->ForceDescendIntoIfVisible()) {
+      return;
+    }
+    f->SetForceDescendIntoIfVisible(true);
+    if (f == aStopAtFrame) {
+      // we've reached a frame that we know will be painted, so we can stop.
+      break;
+    }
+  }
+}
+
+void nsDisplayListBuilder::SetGlassDisplayItem(nsDisplayItem* aItem) {
+  // Web pages or extensions could trigger the "Multiple glass backgrounds
+  // found?" warning by using -moz-appearance:win-borderless-glass etc on their
+  // own elements (as long as they are root frames, which is rare as each doc
+  // only gets one near the root). We only care about the first one, since that
+  // will be the background of the root window.
+
+  if (IsPartialUpdate()) {
+    if (aItem->Frame()->Style()->IsRootElementStyle()) {
+#ifdef DEBUG
+      if (mHasGlassItemDuringPartial) {
+        NS_WARNING("Multiple glass backgrounds found?");
+      } else
+#endif
+          if (!mHasGlassItemDuringPartial) {
+        mHasGlassItemDuringPartial = true;
+        aItem->SetIsGlassItem();
+      }
+    }
+    return;
+  }
+
+  if (aItem->Frame()->Style()->IsRootElementStyle()) {
+#ifdef DEBUG
+    if (mGlassDisplayItem) {
+      NS_WARNING("Multiple glass backgrounds found?");
+    } else
+#endif
+        if (!mGlassDisplayItem) {
+      mGlassDisplayItem = aItem;
+      mGlassDisplayItem->SetIsGlassItem();
+    }
+  }
+}
+
+bool nsDisplayListBuilder::NeedToForceTransparentSurfaceForItem(
+    nsDisplayItem* aItem) {
+  return aItem == mGlassDisplayItem;
+}
+
+void nsDisplayListBuilder::SetIsRelativeToLayoutViewport() {
+  mIsRelativeToLayoutViewport = true;
+  UpdateShouldBuildAsyncZoomContainer();
+}
+
+void nsDisplayListBuilder::UpdateShouldBuildAsyncZoomContainer() {
+  const Document* document = mReferenceFrame->PresContext()->Document();
+  mBuildAsyncZoomContainer = !mIsRelativeToLayoutViewport &&
+                             !document->Fullscreen() &&
+                             nsLayoutUtils::AllowZoomingForDocument(document);
+}
+
+// Certain prefs may cause display list items to be added or removed when they
+// are toggled. In those cases, we need to fully rebuild the display list.
+bool nsDisplayListBuilder::ShouldRebuildDisplayListDueToPrefChange() {
+  // If we transition between wrapping the RCD-RSF contents into an async
+  // zoom container vs. not, we need to rebuild the display list. This only
+  // happens when the zooming or container scrolling prefs are toggled
+  // (manually by the user, or during test setup).
+  bool didBuildAsyncZoomContainer = mBuildAsyncZoomContainer;
+  UpdateShouldBuildAsyncZoomContainer();
+
+  bool hadOverlayScrollbarsLastTime = mUseOverlayScrollbars;
+  mUseOverlayScrollbars =
+      !!LookAndFeel::GetInt(LookAndFeel::IntID::UseOverlayScrollbars);
+
+  bool alwaysLayerizedScrollbarsLastTime = mAlwaysLayerizeScrollbars;
+  mAlwaysLayerizeScrollbars =
+      StaticPrefs::layout_scrollbars_always_layerize_track();
+
+  if (didBuildAsyncZoomContainer != mBuildAsyncZoomContainer) {
+    return true;
+  }
+
+  if (hadOverlayScrollbarsLastTime != mUseOverlayScrollbars) {
+    return true;
+  }
+
+  if (alwaysLayerizedScrollbarsLastTime != mAlwaysLayerizeScrollbars) {
+    return true;
+  }
+
+  return false;
+}
+
+void nsDisplayListBuilder::AddScrollFrameToNotify(
+    nsIScrollableFrame* aScrollFrame) {
+  mScrollFramesToNotify.insert(aScrollFrame);
+}
+
+void nsDisplayListBuilder::NotifyAndClearScrollFrames() {
+  for (const auto& it : mScrollFramesToNotify) {
+    it->NotifyApzTransaction();
+  }
+  mScrollFramesToNotify.clear();
+}
+
+bool nsDisplayListBuilder::MarkOutOfFlowFrameForDisplay(
+    nsIFrame* aDirtyFrame, nsIFrame* aFrame, const nsRect& aVisibleRect,
+    const nsRect& aDirtyRect) {
+  MOZ_ASSERT(aFrame->GetParent() == aDirtyFrame);
+  nsRect dirty;
+  nsRect visible = OutOfFlowDisplayData::ComputeVisibleRectForFrame(
+      this, aFrame, aVisibleRect, aDirtyRect, &dirty);
+  if (!aFrame->HasAnyStateBits(NS_FRAME_FORCE_DISPLAY_LIST_DESCEND_INTO) &&
+      visible.IsEmpty()) {
+    return false;
+  }
+
+  // Only MarkFrameForDisplay if we're dirty. If this is a nested out-of-flow
+  // frame, then it will also mark any outer frames to ensure that building
+  // reaches the dirty feame.
+  if (!dirty.IsEmpty() || aFrame->ForceDescendIntoIfVisible()) {
+    MarkFrameForDisplay(aFrame, aDirtyFrame);
+  }
+
+  return true;
+}
+
+static void UnmarkFrameForDisplay(nsIFrame* aFrame,
+                                  const nsIFrame* aStopAtFrame) {
+  for (nsIFrame* f = aFrame; f;
+       f = nsLayoutUtils::GetParentOrPlaceholderForCrossDoc(f)) {
+    if (!f->HasAnyStateBits(NS_FRAME_FORCE_DISPLAY_LIST_DESCEND_INTO)) {
+      return;
+    }
+    f->RemoveStateBits(NS_FRAME_FORCE_DISPLAY_LIST_DESCEND_INTO);
+    if (f == aStopAtFrame) {
+      // we've reached a frame that we know will be painted, so we can stop.
+      break;
+    }
+  }
+}
+
+static void UnmarkFrameForDisplayIfVisible(nsIFrame* aFrame) {
+  for (nsIFrame* f = aFrame; f; f = nsLayoutUtils::GetDisplayListParent(f)) {
+    if (!f->ForceDescendIntoIfVisible()) {
+      return;
+    }
+    f->SetForceDescendIntoIfVisible(false);
+  }
+}
+
+nsDisplayListBuilder::~nsDisplayListBuilder() {
+  NS_ASSERTION(mFramesMarkedForDisplay.Length() == 0,
+               "All frames should have been unmarked");
+  NS_ASSERTION(mFramesWithOOFData.Length() == 0,
+               "All OOF data should have been removed");
+  NS_ASSERTION(mPresShellStates.Length() == 0,
+               "All presshells should have been exited");
+
+  DisplayItemClipChain* c = mFirstClipChainToDestroy;
+  while (c) {
+    DisplayItemClipChain* next = c->mNextClipChainToDestroy;
+    c->DisplayItemClipChain::~DisplayItemClipChain();
+    c = next;
+  }
+
+  MOZ_COUNT_DTOR(nsDisplayListBuilder);
+}
+
+uint32_t nsDisplayListBuilder::GetBackgroundPaintFlags() {
+  uint32_t flags = 0;
+  if (mSyncDecodeImages) {
+    flags |= nsCSSRendering::PAINTBG_SYNC_DECODE_IMAGES;
+  }
+  if (mIsPaintingToWindow) {
+    flags |= nsCSSRendering::PAINTBG_TO_WINDOW;
+  }
+  if (mUseHighQualityScaling) {
+    flags |= nsCSSRendering::PAINTBG_HIGH_QUALITY_SCALING;
+  }
+  return flags;
+}
+
+// TODO(emilio): Maybe unify BackgroundPaintFlags and IamgeRendererFlags.
+uint32_t nsDisplayListBuilder::GetImageRendererFlags() const {
+  uint32_t flags = 0;
+  if (mSyncDecodeImages) {
+    flags |= nsImageRenderer::FLAG_SYNC_DECODE_IMAGES;
+  }
+  if (mIsPaintingToWindow) {
+    flags |= nsImageRenderer::FLAG_PAINTING_TO_WINDOW;
+  }
+  if (mUseHighQualityScaling) {
+    flags |= nsImageRenderer::FLAG_HIGH_QUALITY_SCALING;
+  }
+  return flags;
+}
+
+uint32_t nsDisplayListBuilder::GetImageDecodeFlags() const {
+  uint32_t flags = imgIContainer::FLAG_ASYNC_NOTIFY;
+  if (mSyncDecodeImages) {
+    flags |= imgIContainer::FLAG_SYNC_DECODE;
+  } else {
+    flags |= imgIContainer::FLAG_SYNC_DECODE_IF_FAST;
+  }
+  if (mIsPaintingToWindow || mUseHighQualityScaling) {
+    flags |= imgIContainer::FLAG_HIGH_QUALITY_SCALING;
+  }
+  return flags;
+}
+
+void nsDisplayListBuilder::SubtractFromVisibleRegion(nsRegion* aVisibleRegion,
+                                                     const nsRegion& aRegion) {
+  if (aRegion.IsEmpty()) {
+    return;
+  }
+
+  nsRegion tmp;
+  tmp.Sub(*aVisibleRegion, aRegion);
+  // Don't let *aVisibleRegion get too complex, but don't let it fluff out
+  // to its bounds either, which can be very bad (see bug 516740).
+  // Do let aVisibleRegion get more complex if by doing so we reduce its
+  // area by at least half.
+  if (tmp.GetNumRects() <= 15 || tmp.Area() <= aVisibleRegion->Area() / 2) {
+    *aVisibleRegion = tmp;
+  }
+}
+
+nsCaret* nsDisplayListBuilder::GetCaret() {
+  RefPtr<nsCaret> caret = CurrentPresShellState()->mPresShell->GetCaret();
+  return caret;
+}
+
+void nsDisplayListBuilder::IncrementPresShellPaintCount(PresShell* aPresShell) {
+  if (mIsPaintingToWindow) {
+    aPresShell->IncrementPaintCount();
+  }
+}
+
+void nsDisplayListBuilder::EnterPresShell(const nsIFrame* aReferenceFrame,
+                                          bool aPointerEventsNoneDoc) {
+  PresShellState* state = mPresShellStates.AppendElement();
+  state->mPresShell = aReferenceFrame->PresShell();
+  state->mFirstFrameMarkedForDisplay = mFramesMarkedForDisplay.Length();
+  state->mFirstFrameWithOOFData = mFramesWithOOFData.Length();
+
+  nsIScrollableFrame* sf = state->mPresShell->GetRootScrollFrameAsScrollable();
+  if (sf && IsInSubdocument()) {
+    // We are forcing a rebuild of nsDisplayCanvasBackgroundColor to make sure
+    // that the canvas background color will be set correctly, and that only one
+    // unscrollable item will be created.
+    // This is done to avoid, for example, a case where only scrollbar frames
+    // are invalidated - we would skip creating nsDisplayCanvasBackgroundColor
+    // and possibly end up with an extra nsDisplaySolidColor item.
+    // We skip this for the root document, since we don't want to use
+    // MarkFrameForDisplayIfVisible before ComputeRebuildRegion. We'll
+    // do it manually there.
+    nsCanvasFrame* canvasFrame = do_QueryFrame(sf->GetScrolledFrame());
+    if (canvasFrame) {
+      MarkFrameForDisplayIfVisible(canvasFrame, aReferenceFrame);
+    }
+  }
+
+#ifdef DEBUG
+  state->mAutoLayoutPhase.emplace(aReferenceFrame->PresContext(),
+                                  nsLayoutPhase::DisplayListBuilding);
+#endif
+
+  state->mPresShell->UpdateCanvasBackground();
+
+  bool buildCaret = mBuildCaret;
+  if (mIgnoreSuppression || !state->mPresShell->IsPaintingSuppressed()) {
+    state->mIsBackgroundOnly = false;
+  } else {
+    state->mIsBackgroundOnly = true;
+    buildCaret = false;
+  }
+
+  bool pointerEventsNone = aPointerEventsNoneDoc;
+  if (IsInSubdocument()) {
+    pointerEventsNone |= mPresShellStates[mPresShellStates.Length() - 2]
+                             .mInsidePointerEventsNoneDoc;
+  }
+  state->mInsidePointerEventsNoneDoc = pointerEventsNone;
+
+  state->mPresShellIgnoreScrollFrame =
+      state->mPresShell->IgnoringViewportScrolling()
+          ? state->mPresShell->GetRootScrollFrame()
+          : nullptr;
+
+  nsPresContext* pc = aReferenceFrame->PresContext();
+  mIsInChromePresContext = pc->IsChrome();
+  nsIDocShell* docShell = pc->GetDocShell();
+
+  if (docShell) {
+    docShell->GetWindowDraggingAllowed(&mWindowDraggingAllowed);
+  }
+
+  state->mTouchEventPrefEnabledDoc = dom::TouchEvent::PrefEnabled(docShell);
+
+  if (!buildCaret) {
+    return;
+  }
+
+  // Caret frames add visual area to their frame, but we don't update the
+  // overflow area. Use flags to make sure we build display items for that frame
+  // instead.
+  if (mCaretFrame && mCaretFrame->PresShell() == state->mPresShell) {
+    MarkFrameForDisplay(mCaretFrame, aReferenceFrame);
+  }
+}
+
+// A non-blank paint is a paint that does not just contain the canvas
+// background.
+static bool DisplayListIsNonBlank(nsDisplayList* aList) {
+  for (nsDisplayItem* i : *aList) {
+    switch (i->GetType()) {
+      case DisplayItemType::TYPE_COMPOSITOR_HITTEST_INFO:
+      case DisplayItemType::TYPE_CANVAS_BACKGROUND_COLOR:
+      case DisplayItemType::TYPE_CANVAS_BACKGROUND_IMAGE:
+        continue;
+      case DisplayItemType::TYPE_SOLID_COLOR:
+      case DisplayItemType::TYPE_BACKGROUND:
+      case DisplayItemType::TYPE_BACKGROUND_COLOR:
+        if (i->Frame()->IsCanvasFrame()) {
+          continue;
+        }
+        return true;
+      default:
+        return true;
+    }
+  }
+  return false;
+}
+
+// A contentful paint is a paint that does contains DOM content (text,
+// images, non-blank canvases, SVG): "First Contentful Paint entry
+// contains a DOMHighResTimeStamp reporting the time when the browser
+// first rendered any text, image (including background images),
+// non-white canvas or SVG. This excludes any content of iframes, but
+// includes text with pending webfonts. This is the first time users
+// could start consuming page content."
+static bool DisplayListIsContentful(nsDisplayListBuilder* aBuilder,
+                                    nsDisplayList* aList) {
+  for (nsDisplayItem* i : *aList) {
+    DisplayItemType type = i->GetType();
+    nsDisplayList* children = i->GetChildren();
+
+    switch (type) {
+      case DisplayItemType::TYPE_SUBDOCUMENT:  // iframes are ignored
+        break;
+      // CANVASes check if they may have been modified (as a stand-in
+      // actually tracking all modifications)
+      default:
+        if (i->IsContentful()) {
+          bool dummy;
+          nsRect bound = i->GetBounds(aBuilder, &dummy);
+          if (!bound.IsEmpty()) {
+            return true;
+          }
+        }
+        if (children) {
+          if (DisplayListIsContentful(aBuilder, children)) {
+            return true;
+          }
+        }
+        break;
+    }
+  }
+  return false;
+}
+
+void nsDisplayListBuilder::LeavePresShell(const nsIFrame* aReferenceFrame,
+                                          nsDisplayList* aPaintedContents) {
+  NS_ASSERTION(
+      CurrentPresShellState()->mPresShell == aReferenceFrame->PresShell(),
+      "Presshell mismatch");
+
+  if (mIsPaintingToWindow && aPaintedContents) {
+    nsPresContext* pc = aReferenceFrame->PresContext();
+    if (!pc->HadNonBlankPaint()) {
+      if (!CurrentPresShellState()->mIsBackgroundOnly &&
+          DisplayListIsNonBlank(aPaintedContents)) {
+        pc->NotifyNonBlankPaint();
+      }
+    }
+    nsRootPresContext* rootPresContext = pc->GetRootPresContext();
+    if (!pc->HadContentfulPaint() && rootPresContext) {
+      if (!CurrentPresShellState()->mIsBackgroundOnly) {
+        if (pc->HasEverBuiltInvisibleText() ||
+            DisplayListIsContentful(this, aPaintedContents)) {
+          pc->NotifyContentfulPaint();
+        }
+      }
+    }
+  }
+
+  ResetMarkedFramesForDisplayList(aReferenceFrame);
+  mPresShellStates.RemoveLastElement();
+
+  if (!mPresShellStates.IsEmpty()) {
+    nsPresContext* pc = CurrentPresContext();
+    nsIDocShell* docShell = pc->GetDocShell();
+    if (docShell) {
+      docShell->GetWindowDraggingAllowed(&mWindowDraggingAllowed);
+    }
+    mIsInChromePresContext = pc->IsChrome();
+  } else {
+    for (uint32_t i = 0; i < mFramesMarkedForDisplayIfVisible.Length(); ++i) {
+      UnmarkFrameForDisplayIfVisible(mFramesMarkedForDisplayIfVisible[i]);
+    }
+    mFramesMarkedForDisplayIfVisible.SetLength(0);
+  }
+}
+
+void nsDisplayListBuilder::FreeClipChains() {
+  // Iterate the clip chains from newest to oldest (forward
+  // iteration), so that we destroy descendants first which
+  // will drop the ref count on their ancestors.
+  DisplayItemClipChain** indirect = &mFirstClipChainToDestroy;
+
+  while (*indirect) {
+    if (!(*indirect)->mRefCount) {
+      DisplayItemClipChain* next = (*indirect)->mNextClipChainToDestroy;
+
+      mClipDeduplicator.erase(*indirect);
+      (*indirect)->DisplayItemClipChain::~DisplayItemClipChain();
+      Destroy(DisplayListArenaObjectId::CLIPCHAIN, *indirect);
+
+      *indirect = next;
+    } else {
+      indirect = &(*indirect)->mNextClipChainToDestroy;
+    }
+  }
+}
+
+void nsDisplayListBuilder::FreeTemporaryItems() {
+  for (nsDisplayItem* i : mTemporaryItems) {
+    // Temporary display items are not added to the frames.
+    MOZ_ASSERT(i->Frame());
+    i->RemoveFrame(i->Frame());
+    i->Destroy(this);
+  }
+
+  mTemporaryItems.Clear();
+}
+
+void nsDisplayListBuilder::ResetMarkedFramesForDisplayList(
+    const nsIFrame* aReferenceFrame) {
+  // Unmark and pop off the frames marked for display in this pres shell.
+  uint32_t firstFrameForShell =
+      CurrentPresShellState()->mFirstFrameMarkedForDisplay;
+  for (uint32_t i = firstFrameForShell; i < mFramesMarkedForDisplay.Length();
+       ++i) {
+    UnmarkFrameForDisplay(mFramesMarkedForDisplay[i], aReferenceFrame);
+  }
+  mFramesMarkedForDisplay.SetLength(firstFrameForShell);
+
+  firstFrameForShell = CurrentPresShellState()->mFirstFrameWithOOFData;
+  for (uint32_t i = firstFrameForShell; i < mFramesWithOOFData.Length(); ++i) {
+    mFramesWithOOFData[i]->RemoveProperty(OutOfFlowDisplayDataProperty());
+  }
+  mFramesWithOOFData.SetLength(firstFrameForShell);
+}
+
+void nsDisplayListBuilder::ClearFixedBackgroundDisplayData() {
+  CurrentPresShellState()->mFixedBackgroundDisplayData = Nothing();
+}
+
+void nsDisplayListBuilder::MarkFramesForDisplayList(
+    nsIFrame* aDirtyFrame, const nsFrameList& aFrames) {
+  nsRect visibleRect = GetVisibleRect();
+  nsRect dirtyRect = GetDirtyRect();
+
+  // If we are entering content that is fixed to the RCD-RSF, we are
+  // crossing the async zoom container boundary, and need to convert from
+  // visual to layout coordinates.
+  if (ViewportFrame* viewportFrame = do_QueryFrame(aDirtyFrame)) {
+    if (IsForEventDelivery() && ShouldBuildAsyncZoomContainer() &&
+        viewportFrame->PresContext()->IsRootContentDocumentCrossProcess()) {
+      if (viewportFrame->PresShell()->GetRootScrollFrame()) {
+#ifdef DEBUG
+        for (nsIFrame* f : aFrames) {
+          MOZ_ASSERT(ViewportUtils::IsZoomedContentRoot(f));
+        }
+#endif
+        visibleRect = ViewportUtils::VisualToLayout(visibleRect,
+                                                    viewportFrame->PresShell());
+        dirtyRect = ViewportUtils::VisualToLayout(dirtyRect,
+                                                  viewportFrame->PresShell());
+      }
+#ifdef DEBUG
+      else {
+        // This is an edge case that should only happen if we are in a
+        // document with a XUL root element so that it does not have a root
+        // scroll frame but it has fixed pos content and all of the frames in
+        // aFrames are that fixed pos content.
+        for (nsIFrame* f : aFrames) {
+          MOZ_ASSERT(!ViewportUtils::IsZoomedContentRoot(f) &&
+                     f->GetParent() == aDirtyFrame &&
+                     f->StyleDisplay()->mPosition ==
+                         StylePositionProperty::Fixed);
+        }
+        // There's no root scroll frame so there can't be any zooming or async
+        // panning so we don't need to adjust the visible and dirty rects.
+      }
+#endif
+    }
+  }
+
+  bool markedFrames = false;
+  for (nsIFrame* e : aFrames) {
+    // Skip the AccessibleCaret frame when building no caret.
+    if (!IsBuildingCaret()) {
+      nsIContent* content = e->GetContent();
+      if (content && content->IsInNativeAnonymousSubtree() &&
+          content->IsElement()) {
+        auto* classList = content->AsElement()->ClassList();
+        if (classList->Contains(u"moz-accessiblecaret"_ns)) {
+          continue;
+        }
+      }
+    }
+    if (MarkOutOfFlowFrameForDisplay(aDirtyFrame, e, visibleRect, dirtyRect)) {
+      markedFrames = true;
+    }
+  }
+
+  if (markedFrames) {
+    // mClipState.GetClipChainForContainingBlockDescendants can return pointers
+    // to objects on the stack, so we need to clone the chain.
+    const DisplayItemClipChain* clipChain =
+        CopyWholeChain(mClipState.GetClipChainForContainingBlockDescendants());
+    const DisplayItemClipChain* combinedClipChain =
+        mClipState.GetCurrentCombinedClipChain(this);
+    const ActiveScrolledRoot* asr = mCurrentActiveScrolledRoot;
+
+    OutOfFlowDisplayData* data = new OutOfFlowDisplayData(
+        clipChain, combinedClipChain, asr, this->mCurrentScrollParentId,
+        visibleRect, dirtyRect);
+    aDirtyFrame->SetProperty(
+        nsDisplayListBuilder::OutOfFlowDisplayDataProperty(), data);
+    mFramesWithOOFData.AppendElement(aDirtyFrame);
+  }
+
+  if (!aDirtyFrame->GetParent()) {
+    // This is the viewport frame of aDirtyFrame's presshell.
+    // Store the current display data so that it can be used for fixed
+    // background images.
+    NS_ASSERTION(
+        CurrentPresShellState()->mPresShell == aDirtyFrame->PresShell(),
+        "Presshell mismatch");
+    MOZ_ASSERT(!CurrentPresShellState()->mFixedBackgroundDisplayData,
+               "already traversed this presshell's root frame?");
+
+    const DisplayItemClipChain* clipChain =
+        CopyWholeChain(mClipState.GetClipChainForContainingBlockDescendants());
+    const DisplayItemClipChain* combinedClipChain =
+        mClipState.GetCurrentCombinedClipChain(this);
+    const ActiveScrolledRoot* asr = mCurrentActiveScrolledRoot;
+    CurrentPresShellState()->mFixedBackgroundDisplayData.emplace(
+        clipChain, combinedClipChain, asr, this->mCurrentScrollParentId,
+        GetVisibleRect(), GetDirtyRect());
+  }
+}
+
+/**
+ * Mark all preserve-3d children with
+ * NS_FRAME_FORCE_DISPLAY_LIST_DESCEND_INTO to make sure
+ * nsIFrame::BuildDisplayListForChild() would visit them.  Also compute
+ * dirty rect for preserve-3d children.
+ *
+ * @param aDirtyFrame is the frame to mark children extending context.
+ */
+void nsDisplayListBuilder::MarkPreserve3DFramesForDisplayList(
+    nsIFrame* aDirtyFrame) {
+  for (const auto& childList : aDirtyFrame->ChildLists()) {
+    for (nsIFrame* child : childList.mList) {
+      if (child->Combines3DTransformWithAncestors()) {
+        MarkFrameForDisplay(child, aDirtyFrame);
+      }
+
+      if (child->IsBlockWrapper()) {
+        // Mark preserve-3d frames inside the block wrapper.
+        MarkPreserve3DFramesForDisplayList(child);
+      }
+    }
+  }
+}
+
+ActiveScrolledRoot* nsDisplayListBuilder::AllocateActiveScrolledRoot(
+    const ActiveScrolledRoot* aParent, nsIScrollableFrame* aScrollableFrame) {
+  RefPtr<ActiveScrolledRoot> asr = ActiveScrolledRoot::CreateASRForFrame(
+      aParent, aScrollableFrame, IsRetainingDisplayList());
+  mActiveScrolledRoots.AppendElement(asr);
+  return asr;
+}
+
+const DisplayItemClipChain* nsDisplayListBuilder::AllocateDisplayItemClipChain(
+    const DisplayItemClip& aClip, const ActiveScrolledRoot* aASR,
+    const DisplayItemClipChain* aParent) {
+  MOZ_ASSERT(!(aParent && aParent->mOnStack));
+  void* p = Allocate(sizeof(DisplayItemClipChain),
+                     DisplayListArenaObjectId::CLIPCHAIN);
+  DisplayItemClipChain* c = new (KnownNotNull, p)
+      DisplayItemClipChain(aClip, aASR, aParent, mFirstClipChainToDestroy);
+#ifdef DEBUG
+  c->mOnStack = false;
+#endif
+  auto result = mClipDeduplicator.insert(c);
+  if (!result.second) {
+    // An equivalent clip chain item was already created, so let's return that
+    // instead. Destroy the one we just created.
+    // Note that this can cause clip chains from different coordinate systems to
+    // collapse into the same clip chain object, because clip chains do not keep
+    // track of the reference frame that they were created in.
+    c->DisplayItemClipChain::~DisplayItemClipChain();
+    Destroy(DisplayListArenaObjectId::CLIPCHAIN, c);
+    return *(result.first);
+  }
+  mFirstClipChainToDestroy = c;
+  return c;
+}
+
+struct ClipChainItem {
+  DisplayItemClip clip;
+  const ActiveScrolledRoot* asr;
+};
+
+static const DisplayItemClipChain* FindCommonAncestorClipForIntersection(
+    const DisplayItemClipChain* aOne, const DisplayItemClipChain* aTwo) {
+  for (const ActiveScrolledRoot* asr =
+           ActiveScrolledRoot::PickDescendant(aOne->mASR, aTwo->mASR);
+       asr; asr = asr->mParent) {
+    if (aOne == aTwo) {
+      return aOne;
+    }
+    if (aOne->mASR == asr) {
+      aOne = aOne->mParent;
+    }
+    if (aTwo->mASR == asr) {
+      aTwo = aTwo->mParent;
+    }
+    if (!aOne) {
+      return aTwo;
+    }
+    if (!aTwo) {
+      return aOne;
+    }
+  }
+  return nullptr;
+}
+
+const DisplayItemClipChain* nsDisplayListBuilder::CreateClipChainIntersection(
+    const DisplayItemClipChain* aAncestor,
+    const DisplayItemClipChain* aLeafClip1,
+    const DisplayItemClipChain* aLeafClip2) {
+  AutoTArray<ClipChainItem, 8> intersectedClips;
+
+  const DisplayItemClipChain* clip1 = aLeafClip1;
+  const DisplayItemClipChain* clip2 = aLeafClip2;
+
+  const ActiveScrolledRoot* asr = ActiveScrolledRoot::PickDescendant(
+      clip1 ? clip1->mASR : nullptr, clip2 ? clip2->mASR : nullptr);
+
+  // Build up the intersection from the leaf to the root and put it into
+  // intersectedClips. The loop below will convert intersectedClips into an
+  // actual DisplayItemClipChain.
+  // (We need to do this in two passes because we need the parent clip in order
+  // to create the DisplayItemClipChain object, but the parent clip has not
+  // been created at that point.)
+  while (!aAncestor || asr != aAncestor->mASR) {
+    if (clip1 && clip1->mASR == asr) {
+      if (clip2 && clip2->mASR == asr) {
+        DisplayItemClip intersection = clip1->mClip;
+        intersection.IntersectWith(clip2->mClip);
+        intersectedClips.AppendElement(ClipChainItem{intersection, asr});
+        clip2 = clip2->mParent;
+      } else {
+        intersectedClips.AppendElement(ClipChainItem{clip1->mClip, asr});
+      }
+      clip1 = clip1->mParent;
+    } else if (clip2 && clip2->mASR == asr) {
+      intersectedClips.AppendElement(ClipChainItem{clip2->mClip, asr});
+      clip2 = clip2->mParent;
+    }
+    if (!asr) {
+      MOZ_ASSERT(!aAncestor, "We should have exited this loop earlier");
+      break;
+    }
+    asr = asr->mParent;
+  }
+
+  // Convert intersectedClips into a DisplayItemClipChain.
+  const DisplayItemClipChain* parentSC = aAncestor;
+  for (auto& sc : Reversed(intersectedClips)) {
+    parentSC = AllocateDisplayItemClipChain(sc.clip, sc.asr, parentSC);
+  }
+  return parentSC;
+}
+
+const DisplayItemClipChain* nsDisplayListBuilder::CreateClipChainIntersection(
+    const DisplayItemClipChain* aLeafClip1,
+    const DisplayItemClipChain* aLeafClip2) {
+  // aLeafClip2 might be a reference to a clip on the stack. We need to make
+  // sure that CreateClipChainIntersection will allocate the actual intersected
+  // clip in the builder's arena, so for the aLeafClip1 == nullptr case,
+  // we supply nullptr as the common ancestor so that
+  // CreateClipChainIntersection clones the whole chain.
+  const DisplayItemClipChain* ancestorClip =
+      aLeafClip1 ? FindCommonAncestorClipForIntersection(aLeafClip1, aLeafClip2)
+                 : nullptr;
+
+  return CreateClipChainIntersection(ancestorClip, aLeafClip1, aLeafClip2);
+}
+
+const DisplayItemClipChain* nsDisplayListBuilder::CopyWholeChain(
+    const DisplayItemClipChain* aClipChain) {
+  return CreateClipChainIntersection(nullptr, aClipChain, nullptr);
+}
+
+const nsIFrame* nsDisplayListBuilder::FindReferenceFrameFor(
+    const nsIFrame* aFrame, nsPoint* aOffset) const {
+  auto MaybeApplyAdditionalOffset = [&]() {
+    if (auto offset = AdditionalOffset()) {
+      *aOffset += *offset;
+    }
+  };
+
+  if (aFrame == mCurrentFrame) {
+    if (aOffset) {
+      *aOffset = mCurrentOffsetToReferenceFrame;
+    }
+    return mCurrentReferenceFrame;
+  }
+
+  for (const nsIFrame* f = aFrame; f;
+       f = nsLayoutUtils::GetCrossDocParentFrameInProcess(f)) {
+    if (f == mReferenceFrame || f->IsTransformed()) {
+      if (aOffset) {
+        *aOffset = aFrame->GetOffsetToCrossDoc(f);
+        MaybeApplyAdditionalOffset();
+      }
+      return f;
+    }
+  }
+
+  if (aOffset) {
+    *aOffset = aFrame->GetOffsetToCrossDoc(mReferenceFrame);
+    MaybeApplyAdditionalOffset();
+  }
+
+  return mReferenceFrame;
+}
+
+// Sticky frames are active if their nearest scrollable frame is also active.
+static bool IsStickyFrameActive(nsDisplayListBuilder* aBuilder,
+                                nsIFrame* aFrame) {
+  MOZ_ASSERT(aFrame->StyleDisplay()->mPosition ==
+             StylePositionProperty::Sticky);
+
+  StickyScrollContainer* stickyScrollContainer =
+      StickyScrollContainer::GetStickyScrollContainerForFrame(aFrame);
+  return stickyScrollContainer &&
+         stickyScrollContainer->ScrollFrame()->IsMaybeAsynchronouslyScrolled();
+}
+
+bool nsDisplayListBuilder::IsAnimatedGeometryRoot(nsIFrame* aFrame,
+                                                  nsIFrame** aParent) {
+  if (aFrame == mReferenceFrame) {
+    return true;
+  }
+
+  if (!IsPaintingToWindow()) {
+    if (aParent) {
+      *aParent = nsLayoutUtils::GetCrossDocParentFrameInProcess(aFrame);
+    }
+    return false;
+  }
+
+  nsIFrame* parent = nsLayoutUtils::GetCrossDocParentFrameInProcess(aFrame);
+  if (!parent) {
+    return true;
+  }
+  *aParent = parent;
+
+  if (aFrame->StyleDisplay()->mPosition == StylePositionProperty::Sticky &&
+      IsStickyFrameActive(this, aFrame)) {
+    return true;
+  }
+
+  if (aFrame->IsTransformed()) {
+    if (EffectCompositor::HasAnimationsForCompositor(
+            aFrame, DisplayItemType::TYPE_TRANSFORM)) {
+      return true;
+    }
+  }
+
+  LayoutFrameType parentType = parent->Type();
+  if (parentType == LayoutFrameType::Scroll ||
+      parentType == LayoutFrameType::ListControl) {
+    nsIScrollableFrame* sf = do_QueryFrame(parent);
+    if (sf->GetScrolledFrame() == aFrame) {
+      MOZ_ASSERT(!aFrame->IsTransformed());
+      return sf->IsMaybeAsynchronouslyScrolled();
+    }
+  }
+
+  return false;
+}
+
+nsIFrame* nsDisplayListBuilder::FindAnimatedGeometryRootFrameFor(
+    nsIFrame* aFrame) {
+  MOZ_ASSERT(nsLayoutUtils::IsAncestorFrameCrossDocInProcess(
+      RootReferenceFrame(), aFrame));
+  nsIFrame* cursor = aFrame;
+  while (cursor != RootReferenceFrame()) {
+    nsIFrame* next;
+    if (IsAnimatedGeometryRoot(cursor, &next)) {
+      return cursor;
+    }
+    cursor = next;
+  }
+  return cursor;
+}
+
+static nsRect ApplyAllClipNonRoundedIntersection(
+    const DisplayItemClipChain* aClipChain, const nsRect& aRect) {
+  nsRect result = aRect;
+  while (aClipChain) {
+    result = aClipChain->mClip.ApplyNonRoundedIntersection(result);
+    aClipChain = aClipChain->mParent;
+  }
+  return result;
+}
+
+void nsDisplayListBuilder::AdjustWindowDraggingRegion(nsIFrame* aFrame) {
+  if (!mWindowDraggingAllowed || !IsForPainting()) {
+    return;
+  }
+
+  const nsStyleUIReset* styleUI = aFrame->StyleUIReset();
+  if (styleUI->mWindowDragging == StyleWindowDragging::Default) {
+    // This frame has the default value and doesn't influence the window
+    // dragging region.
+    return;
+  }
+
+  LayoutDeviceToLayoutDeviceMatrix4x4 referenceFrameToRootReferenceFrame;
+
+  // The const_cast is for nsLayoutUtils::GetTransformToAncestor.
+  nsIFrame* referenceFrame =
+      const_cast<nsIFrame*>(FindReferenceFrameFor(aFrame));
+
+  if (IsInTransform()) {
+    // Only support 2d rectilinear transforms. Transform support is needed for
+    // the horizontal flip transform that's applied to the urlbar textbox in
+    // RTL mode - it should be able to exclude itself from the draggable region.
+    referenceFrameToRootReferenceFrame =
+        ViewAs<LayoutDeviceToLayoutDeviceMatrix4x4>(
+            nsLayoutUtils::GetTransformToAncestor(RelativeTo{referenceFrame},
+                                                  RelativeTo{mReferenceFrame})
+                .GetMatrix());
+    Matrix referenceFrameToRootReferenceFrame2d;
+    if (!referenceFrameToRootReferenceFrame.Is2D(
+            &referenceFrameToRootReferenceFrame2d) ||
+        !referenceFrameToRootReferenceFrame2d.IsRectilinear()) {
+      return;
+    }
+  } else {
+    MOZ_ASSERT(referenceFrame == mReferenceFrame,
+               "referenceFrameToRootReferenceFrame needs to be adjusted");
+  }
+
+  // We do some basic visibility checking on the frame's border box here.
+  // We intersect it both with the current dirty rect and with the current
+  // clip. Either one is just a conservative approximation on its own, but
+  // their intersection luckily works well enough for our purposes, so that
+  // we don't have to do full-blown visibility computations.
+  // The most important case we need to handle is the scrolled-off tab:
+  // If the tab bar overflows, tab parts that are clipped by the scrollbox
+  // should not be allowed to interfere with the window dragging region. Using
+  // just the current DisplayItemClip is not enough to cover this case
+  // completely because clips are reset while building stacking context
+  // contents, so for example we'd fail to clip frames that have a clip path
+  // applied to them. But the current dirty rect doesn't get reset in that
+  // case, so we use it to make this case work.
+  nsRect borderBox = aFrame->GetRectRelativeToSelf().Intersect(mVisibleRect);
+  borderBox += ToReferenceFrame(aFrame);
+  const DisplayItemClipChain* clip =
+      ClipState().GetCurrentCombinedClipChain(this);
+  borderBox = ApplyAllClipNonRoundedIntersection(clip, borderBox);
+  if (borderBox.IsEmpty()) {
+    return;
+  }
+
+  LayoutDeviceRect devPixelBorderBox = LayoutDevicePixel::FromAppUnits(
+      borderBox, aFrame->PresContext()->AppUnitsPerDevPixel());
+
+  LayoutDeviceRect transformedDevPixelBorderBox =
+      TransformBy(referenceFrameToRootReferenceFrame, devPixelBorderBox);
+  transformedDevPixelBorderBox.Round();
+  LayoutDeviceIntRect transformedDevPixelBorderBoxInt;
+
+  if (!transformedDevPixelBorderBox.ToIntRect(
+          &transformedDevPixelBorderBoxInt)) {
+    return;
+  }
+
+  LayoutDeviceIntRegion& region =
+      styleUI->mWindowDragging == StyleWindowDragging::Drag
+          ? mWindowDraggingRegion
+          : mWindowNoDraggingRegion;
+
+  if (!IsRetainingDisplayList()) {
+    region.OrWith(transformedDevPixelBorderBoxInt);
+    return;
+  }
+
+  gfx::IntRect rect(transformedDevPixelBorderBoxInt.ToUnknownRect());
+  if (styleUI->mWindowDragging == StyleWindowDragging::Drag) {
+    mRetainedWindowDraggingRegion.Add(aFrame, rect);
+  } else {
+    mRetainedWindowNoDraggingRegion.Add(aFrame, rect);
+  }
+}
+
+LayoutDeviceIntRegion nsDisplayListBuilder::GetWindowDraggingRegion() const {
+  LayoutDeviceIntRegion result;
+  if (!IsRetainingDisplayList()) {
+    result.Sub(mWindowDraggingRegion, mWindowNoDraggingRegion);
+    return result;
+  }
+
+  LayoutDeviceIntRegion dragRegion =
+      mRetainedWindowDraggingRegion.ToLayoutDeviceIntRegion();
+
+  LayoutDeviceIntRegion noDragRegion =
+      mRetainedWindowNoDraggingRegion.ToLayoutDeviceIntRegion();
+
+  result.Sub(dragRegion, noDragRegion);
+  return result;
+}
+
+void nsDisplayTransform::AddSizeOfExcludingThis(nsWindowSizes& aSizes) const {
+  nsPaintedDisplayItem::AddSizeOfExcludingThis(aSizes);
+  aSizes.mLayoutRetainedDisplayListSize +=
+      aSizes.mState.mMallocSizeOf(mTransformPreserves3D.get());
+}
+
+void nsDisplayListBuilder::AddSizeOfExcludingThis(nsWindowSizes& aSizes) const {
+  mPool.AddSizeOfExcludingThis(aSizes, Arena::ArenaKind::DisplayList);
+
+  size_t n = 0;
+  MallocSizeOf mallocSizeOf = aSizes.mState.mMallocSizeOf;
+  n += mDocumentWillChangeBudgets.ShallowSizeOfExcludingThis(mallocSizeOf);
+  n += mFrameWillChangeBudgets.ShallowSizeOfExcludingThis(mallocSizeOf);
+  n += mEffectsUpdates.ShallowSizeOfExcludingThis(mallocSizeOf);
+  n += mWindowExcludeGlassRegion.SizeOfExcludingThis(mallocSizeOf);
+  n += mRetainedWindowDraggingRegion.SizeOfExcludingThis(mallocSizeOf);
+  n += mRetainedWindowNoDraggingRegion.SizeOfExcludingThis(mallocSizeOf);
+  n += mRetainedWindowOpaqueRegion.SizeOfExcludingThis(mallocSizeOf);
+  // XXX can't measure mClipDeduplicator since it uses std::unordered_set.
+
+  aSizes.mLayoutRetainedDisplayListSize += n;
+}
+
+void RetainedDisplayList::AddSizeOfExcludingThis(nsWindowSizes& aSizes) const {
+  for (nsDisplayItem* item : *this) {
+    item->AddSizeOfExcludingThis(aSizes);
+    if (RetainedDisplayList* children = item->GetChildren()) {
+      children->AddSizeOfExcludingThis(aSizes);
+    }
+  }
+
+  size_t n = 0;
+
+  n += mDAG.mDirectPredecessorList.ShallowSizeOfExcludingThis(
+      aSizes.mState.mMallocSizeOf);
+  n += mDAG.mNodesInfo.ShallowSizeOfExcludingThis(aSizes.mState.mMallocSizeOf);
+  n += mOldItems.ShallowSizeOfExcludingThis(aSizes.mState.mMallocSizeOf);
+
+  aSizes.mLayoutRetainedDisplayListSize += n;
+}
+
+size_t nsDisplayListBuilder::WeakFrameRegion::SizeOfExcludingThis(
+    MallocSizeOf aMallocSizeOf) const {
+  size_t n = 0;
+  n += mFrames.ShallowSizeOfExcludingThis(aMallocSizeOf);
+  for (const auto& frame : mFrames) {
+    const UniquePtr<WeakFrame>& weakFrame = frame.mWeakFrame;
+    n += aMallocSizeOf(weakFrame.get());
+  }
+  n += mRects.ShallowSizeOfExcludingThis(aMallocSizeOf);
+  return n;
+}
+
+/**
+ * Removes modified frames and rects from this WeakFrameRegion.
+ */
+void nsDisplayListBuilder::WeakFrameRegion::RemoveModifiedFramesAndRects() {
+  MOZ_ASSERT(mFrames.Length() == mRects.Length());
+
+  uint32_t i = 0;
+  uint32_t length = mFrames.Length();
+
+  while (i < length) {
+    auto& wrapper = mFrames[i];
+
+    if (!wrapper.mWeakFrame->IsAlive() ||
+        AnyContentAncestorModified(wrapper.mWeakFrame->GetFrame())) {
+      // To avoid multiple O(n) shifts in the array, move the last element of
+      // the array to the current position and decrease the array length.
+      mFrameSet.Remove(wrapper.mFrame);
+      mFrames[i] = std::move(mFrames[length - 1]);
+      mRects[i] = std::move(mRects[length - 1]);
+      length--;
+    } else {
+      i++;
+    }
+  }
+
+  mFrames.TruncateLength(length);
+  mRects.TruncateLength(length);
+}
+
+void nsDisplayListBuilder::RemoveModifiedWindowRegions() {
+  mRetainedWindowDraggingRegion.RemoveModifiedFramesAndRects();
+  mRetainedWindowNoDraggingRegion.RemoveModifiedFramesAndRects();
+  mWindowExcludeGlassRegion.RemoveModifiedFramesAndRects();
+  mRetainedWindowOpaqueRegion.RemoveModifiedFramesAndRects();
+
+  mHasGlassItemDuringPartial = false;
+}
+
+void nsDisplayListBuilder::ClearRetainedWindowRegions() {
+  mRetainedWindowDraggingRegion.Clear();
+  mRetainedWindowNoDraggingRegion.Clear();
+  mWindowExcludeGlassRegion.Clear();
+  mRetainedWindowOpaqueRegion.Clear();
+
+  mGlassDisplayItem = nullptr;
+}
+
+const uint32_t gWillChangeAreaMultiplier = 3;
+static uint32_t GetLayerizationCost(const nsSize& aSize) {
+  // There's significant overhead for each layer created from Gecko
+  // (IPC+Shared Objects) and from the backend (like an OpenGL texture).
+  // Therefore we set a minimum cost threshold of a 64x64 area.
+  const int minBudgetCost = 64 * 64;
+
+  const uint32_t budgetCost = std::max(
+      minBudgetCost, nsPresContext::AppUnitsToIntCSSPixels(aSize.width) *
+                         nsPresContext::AppUnitsToIntCSSPixels(aSize.height));
+
+  return budgetCost;
+}
+
+bool nsDisplayListBuilder::AddToWillChangeBudget(nsIFrame* aFrame,
+                                                 const nsSize& aSize) {
+  MOZ_ASSERT(IsForPainting());
+
+  if (aFrame->MayHaveWillChangeBudget()) {
+    // The frame is already in the will-change budget.
+    return true;
+  }
+
+  const nsPresContext* presContext = aFrame->PresContext();
+  const nsRect area = presContext->GetVisibleArea();
+  const uint32_t budgetLimit =
+      nsPresContext::AppUnitsToIntCSSPixels(area.width) *
+      nsPresContext::AppUnitsToIntCSSPixels(area.height);
+  const uint32_t cost = GetLayerizationCost(aSize);
+
+  DocumentWillChangeBudget& documentBudget =
+      mDocumentWillChangeBudgets.LookupOrInsert(presContext);
+
+  const bool onBudget =
+      (documentBudget + cost) / gWillChangeAreaMultiplier < budgetLimit;
+
+  if (onBudget) {
+    documentBudget += cost;
+    mFrameWillChangeBudgets.InsertOrUpdate(
+        aFrame, FrameWillChangeBudget(presContext, cost));
+    aFrame->SetMayHaveWillChangeBudget(true);
+  }
+
+  return onBudget;
+}
+
+bool nsDisplayListBuilder::IsInWillChangeBudget(nsIFrame* aFrame,
+                                                const nsSize& aSize) {
+  if (!IsForPainting()) {
+    // If this nsDisplayListBuilder is not for painting, the layerization should
+    // not matter. Do the simple thing and return false.
+    return false;
+  }
+
+  const bool onBudget = AddToWillChangeBudget(aFrame, aSize);
+  if (onBudget) {
+    return true;
+  }
+
+  auto* pc = aFrame->PresContext();
+  auto* doc = pc->Document();
+  if (!doc->HasWarnedAbout(Document::eIgnoringWillChangeOverBudget)) {
+    AutoTArray<nsString, 2> params;
+    params.AppendElement()->AppendInt(gWillChangeAreaMultiplier);
+
+    nsRect area = pc->GetVisibleArea();
+    uint32_t budgetLimit = nsPresContext::AppUnitsToIntCSSPixels(area.width) *
+                           nsPresContext::AppUnitsToIntCSSPixels(area.height);
+    params.AppendElement()->AppendInt(budgetLimit);
+
+    doc->WarnOnceAbout(Document::eIgnoringWillChangeOverBudget, false, params);
+  }
+
+  return false;
+}
+
+void nsDisplayListBuilder::ClearWillChangeBudgetStatus(nsIFrame* aFrame) {
+  MOZ_ASSERT(IsForPainting());
+
+  if (!aFrame->MayHaveWillChangeBudget()) {
+    return;
+  }
+
+  aFrame->SetMayHaveWillChangeBudget(false);
+  RemoveFromWillChangeBudgets(aFrame);
+}
+
+void nsDisplayListBuilder::RemoveFromWillChangeBudgets(const nsIFrame* aFrame) {
+  if (auto entry = mFrameWillChangeBudgets.Lookup(aFrame)) {
+    const FrameWillChangeBudget& frameBudget = entry.Data();
+
+    auto documentBudget =
+        mDocumentWillChangeBudgets.Lookup(frameBudget.mPresContext);
+
+    if (documentBudget) {
+      *documentBudget -= frameBudget.mUsage;
+    }
+
+    entry.Remove();
+  }
+}
+
+void nsDisplayListBuilder::ClearWillChangeBudgets() {
+  mFrameWillChangeBudgets.Clear();
+  mDocumentWillChangeBudgets.Clear();
+}
+
+void nsDisplayListBuilder::EnterSVGEffectsContents(
+    nsIFrame* aEffectsFrame, nsDisplayList* aHoistedItemsStorage) {
+  MOZ_ASSERT(aHoistedItemsStorage);
+  if (mSVGEffectsFrames.IsEmpty()) {
+    MOZ_ASSERT(!mScrollInfoItemsForHoisting);
+    mScrollInfoItemsForHoisting = aHoistedItemsStorage;
+  }
+  mSVGEffectsFrames.AppendElement(aEffectsFrame);
+}
+
+void nsDisplayListBuilder::ExitSVGEffectsContents() {
+  MOZ_ASSERT(!mSVGEffectsFrames.IsEmpty());
+  mSVGEffectsFrames.RemoveLastElement();
+  MOZ_ASSERT(mScrollInfoItemsForHoisting);
+  if (mSVGEffectsFrames.IsEmpty()) {
+    mScrollInfoItemsForHoisting = nullptr;
+  }
+}
+
+bool nsDisplayListBuilder::ShouldBuildScrollInfoItemsForHoisting() const {
+  /*
+   * Note: if changing the conditions under which scroll info layers
+   * are created, make a corresponding change to
+   * ScrollFrameWillBuildScrollInfoLayer() in nsSliderFrame.cpp.
+   */
+  for (nsIFrame* frame : mSVGEffectsFrames) {
+    if (SVGIntegrationUtils::UsesSVGEffectsNotSupportedInCompositor(frame)) {
+      return true;
+    }
+  }
+  return false;
+}
+
+void nsDisplayListBuilder::AppendNewScrollInfoItemForHoisting(
+    nsDisplayScrollInfoLayer* aScrollInfoItem) {
+  MOZ_ASSERT(ShouldBuildScrollInfoItemsForHoisting());
+  MOZ_ASSERT(mScrollInfoItemsForHoisting);
+  mScrollInfoItemsForHoisting->AppendToTop(aScrollInfoItem);
+}
+
+void nsDisplayListBuilder::BuildCompositorHitTestInfoIfNeeded(
+    nsIFrame* aFrame, nsDisplayList* aList) {
+  MOZ_ASSERT(aFrame);
+  MOZ_ASSERT(aList);
+
+  if (!BuildCompositorHitTestInfo()) {
+    return;
+  }
+
+  const CompositorHitTestInfo info = aFrame->GetCompositorHitTestInfo(this);
+  if (info != CompositorHitTestInvisibleToHit) {
+    aList->AppendNewToTop<nsDisplayCompositorHitTestInfo>(this, aFrame);
+  }
+}
+
+void nsDisplayListBuilder::AddReusableDisplayItem(nsDisplayItem* aItem) {
+  mReuseableItems.Insert(aItem);
+}
+
+void nsDisplayListBuilder::RemoveReusedDisplayItem(nsDisplayItem* aItem) {
+  MOZ_ASSERT(aItem->IsReusedItem());
+  mReuseableItems.Remove(aItem);
+}
+
+void nsDisplayListBuilder::ClearReuseableDisplayItems() {
+  const size_t total = mReuseableItems.Count();
+
+  size_t reused = 0;
+  for (auto* item : mReuseableItems) {
+    if (item->IsReusedItem()) {
+      reused++;
+      item->SetReusable();
+    } else {
+      item->Destroy(this);
+    }
+  }
+
+  DL_LOGI("RDL - Reused %zu of %zu SC display items", reused, total);
+  mReuseableItems.Clear();
+}
+
+void nsDisplayListBuilder::ReuseDisplayItem(nsDisplayItem* aItem) {
+  const auto* previous = mCurrentContainerASR;
+  const auto* asr = aItem->GetActiveScrolledRoot();
+  mCurrentContainerASR =
+      ActiveScrolledRoot::PickAncestor(asr, mCurrentContainerASR);
+
+  if (previous != mCurrentContainerASR) {
+    DL_LOGV("RDL - Changed mCurrentContainerASR from %p to %p", previous,
+            mCurrentContainerASR);
+  }
+
+  aItem->SetReusedItem();
+}
+
+void nsDisplayListSet::CopyTo(const nsDisplayListSet& aDestination) const {
+  for (size_t i = 0; i < mLists.size(); ++i) {
+    auto* from = mLists[i];
+    auto* to = aDestination.mLists[i];
+
+    from->CopyTo(to);
+  }
+}
+
+void nsDisplayListSet::MoveTo(const nsDisplayListSet& aDestination) const {
+  aDestination.BorderBackground()->AppendToTop(BorderBackground());
+  aDestination.BlockBorderBackgrounds()->AppendToTop(BlockBorderBackgrounds());
+  aDestination.Floats()->AppendToTop(Floats());
+  aDestination.Content()->AppendToTop(Content());
+  aDestination.PositionedDescendants()->AppendToTop(PositionedDescendants());
+  aDestination.Outlines()->AppendToTop(Outlines());
+}
+
+nsRect nsDisplayList::GetClippedBounds(nsDisplayListBuilder* aBuilder) const {
+  nsRect bounds;
+  for (nsDisplayItem* i : *this) {
+    bounds.UnionRect(bounds, i->GetClippedBounds(aBuilder));
+  }
+  return bounds;
+}
+
+nsRect nsDisplayList::GetClippedBoundsWithRespectToASR(
+    nsDisplayListBuilder* aBuilder, const ActiveScrolledRoot* aASR,
+    nsRect* aBuildingRect) const {
+  nsRect bounds;
+  for (nsDisplayItem* i : *this) {
+    nsRect r = i->GetClippedBounds(aBuilder);
+    if (aASR != i->GetActiveScrolledRoot() && !r.IsEmpty()) {
+      if (Maybe<nsRect> clip = i->GetClipWithRespectToASR(aBuilder, aASR)) {
+        r = clip.ref();
+      }
+    }
+    if (aBuildingRect) {
+      aBuildingRect->UnionRect(*aBuildingRect, i->GetBuildingRect());
+    }
+    bounds.UnionRect(bounds, r);
+  }
+  return bounds;
+}
+
+nsRect nsDisplayList::GetBuildingRect() const {
+  nsRect result;
+  for (nsDisplayItem* i : *this) {
+    result.UnionRect(result, i->GetBuildingRect());
+  }
+  return result;
+}
+
+static void TriggerPendingAnimations(Document& aDoc,
+                                     const TimeStamp& aReadyTime) {
+  MOZ_ASSERT(!aReadyTime.IsNull(),
+             "Animation ready time is not set. Perhaps we're using a layer"
+             " manager that doesn't update it");
+  if (PendingAnimationTracker* tracker = aDoc.GetPendingAnimationTracker()) {
+    PresShell* presShell = aDoc.GetPresShell();
+    // If paint-suppression is in effect then we haven't finished painting
+    // this document yet so we shouldn't start animations
+    if (!presShell || !presShell->IsPaintingSuppressed()) {
+      tracker->TriggerPendingAnimationsOnNextTick(aReadyTime);
+    }
+  }
+  auto recurse = [&aReadyTime](Document& aDoc) {
+    TriggerPendingAnimations(aDoc, aReadyTime);
+    return CallState::Continue;
+  };
+  aDoc.EnumerateSubDocuments(recurse);
+}
+
+WindowRenderer* nsDisplayListBuilder::GetWidgetWindowRenderer(nsView** aView) {
+  if (aView) {
+    *aView = RootReferenceFrame()->GetView();
+  }
+  if (RootReferenceFrame() !=
+      nsLayoutUtils::GetDisplayRootFrame(RootReferenceFrame())) {
+    return nullptr;
+  }
+  nsIWidget* window = RootReferenceFrame()->GetNearestWidget();
+  if (window) {
+    return window->GetWindowRenderer();
+  }
+  return nullptr;
+}
+
+WebRenderLayerManager* nsDisplayListBuilder::GetWidgetLayerManager(
+    nsView** aView) {
+  WindowRenderer* renderer = GetWidgetWindowRenderer();
+  if (renderer) {
+    return renderer->AsWebRender();
+  }
+  return nullptr;
+}
+
+void nsDisplayList::Paint(nsDisplayListBuilder* aBuilder, gfxContext* aCtx,
+                          int32_t aAppUnitsPerDevPixel) {
+  FlattenedDisplayListIterator iter(aBuilder, this);
+  while (iter.HasNext()) {
+    nsPaintedDisplayItem* item = iter.GetNextItem()->AsPaintedDisplayItem();
+    if (!item) {
+      continue;
+    }
+
+    nsRect visible = item->GetClippedBounds(aBuilder);
+    visible = visible.Intersect(item->GetPaintRect(aBuilder, aCtx));
+    if (visible.IsEmpty()) {
+      continue;
+    }
+
+    DisplayItemClip currentClip = item->GetClip();
+    if (currentClip.HasClip()) {
+      aCtx->Save();
+      if (currentClip.IsRectClippedByRoundedCorner(visible)) {
+        currentClip.ApplyTo(aCtx, aAppUnitsPerDevPixel);
+      } else {
+        currentClip.ApplyRectTo(aCtx, aAppUnitsPerDevPixel);
+      }
+    }
+    aCtx->NewPath();
+
+    item->Paint(aBuilder, aCtx);
+
+    if (currentClip.HasClip()) {
+      aCtx->Restore();
+    }
+  }
+}
+
+/**
+ * We paint by executing a layer manager transaction, constructing a
+ * single layer representing the display list, and then making it the
+ * root of the layer manager, drawing into the PaintedLayers.
+ */
+void nsDisplayList::PaintRoot(nsDisplayListBuilder* aBuilder, gfxContext* aCtx,
+                              uint32_t aFlags,
+                              Maybe<double> aDisplayListBuildTime) {
+  AUTO_PROFILER_LABEL("nsDisplayList::PaintRoot", GRAPHICS);
+
+  RefPtr<WebRenderLayerManager> layerManager;
+  WindowRenderer* renderer = nullptr;
+  bool widgetTransaction = false;
+  bool doBeginTransaction = true;
+  nsView* view = nullptr;
+  if (aFlags & PAINT_USE_WIDGET_LAYERS) {
+    renderer = aBuilder->GetWidgetWindowRenderer(&view);
+    if (renderer) {
+      // The fallback renderer doesn't retain any content, so it's
+      // not meaningful to use it when drawing to an external context.
+      if (aCtx && renderer->AsFallback()) {
+        MOZ_ASSERT(!(aFlags & PAINT_EXISTING_TRANSACTION));
+        renderer = nullptr;
+      } else {
+        layerManager = renderer->AsWebRender();
+        doBeginTransaction = !(aFlags & PAINT_EXISTING_TRANSACTION);
+        widgetTransaction = true;
+      }
+    }
+  }
+
+  nsIFrame* frame = aBuilder->RootReferenceFrame();
+  nsPresContext* presContext = frame->PresContext();
+  PresShell* presShell = presContext->PresShell();
+  Document* document = presShell->GetDocument();
+
+  ScopeExit g([&]() {
+    // For layers-free mode, we check the invalidation state bits in the
+    // EndTransaction. So we clear the invalidation state bits after
+    // EndTransaction.
+    if (widgetTransaction ||
+        // SVG-as-an-image docs don't paint as part of the retained layer tree,
+        // but they still need the invalidation state bits cleared in order for
+        // invalidation for CSS/SMIL animation to work properly.
+        (document && document->IsBeingUsedAsImage())) {
+      DL_LOGD("Clearing invalidation state bits");
+      frame->ClearInvalidationStateBits();
+    }
+  });
+
+  if (!renderer) {
+    if (!aCtx) {
+      NS_WARNING("Nowhere to paint into");
+      return;
+    }
+    bool prevIsCompositingCheap = aBuilder->SetIsCompositingCheap(false);
+    Paint(aBuilder, aCtx, presContext->AppUnitsPerDevPixel());
+
+    aBuilder->SetIsCompositingCheap(prevIsCompositingCheap);
+    return;
+  }
+
+  if (renderer->GetBackendType() == LayersBackend::LAYERS_WR) {
+    MOZ_ASSERT(layerManager);
+    if (doBeginTransaction) {
+      if (aCtx) {
+        if (!layerManager->BeginTransactionWithTarget(aCtx, nsCString())) {
+          return;
+        }
+      } else {
+        if (!layerManager->BeginTransaction(nsCString())) {
+          return;
+        }
+      }
+    }
+
+    bool prevIsCompositingCheap = aBuilder->SetIsCompositingCheap(true);
+    layerManager->SetTransactionIdAllocator(presContext->RefreshDriver());
+
+    bool sent = false;
+    if (aFlags & PAINT_IDENTICAL_DISPLAY_LIST) {
+      sent = layerManager->EndEmptyTransaction();
+    }
+
+    if (!sent) {
+      auto* wrManager = static_cast<WebRenderLayerManager*>(layerManager.get());
+
+      nsIDocShell* docShell = presContext->GetDocShell();
+      WrFiltersHolder wrFilters;
+      gfx::Matrix5x4* colorMatrix =
+          nsDocShell::Cast(docShell)->GetColorMatrix();
+      if (colorMatrix) {
+        wrFilters.filters.AppendElement(
+            wr::FilterOp::ColorMatrix(colorMatrix->components));
+      }
+
+      wrManager->EndTransactionWithoutLayer(this, aBuilder,
+                                            std::move(wrFilters), nullptr,
+                                            aDisplayListBuildTime.valueOr(0.0));
+    }
+
+    aBuilder->SetIsCompositingCheap(prevIsCompositingCheap);
+    if (document && widgetTransaction) {
+      TriggerPendingAnimations(*document,
+                               layerManager->GetAnimationReadyTime());
+    }
+
+    if (presContext->RefreshDriver()->HasScheduleFlush()) {
+      presContext->NotifyInvalidation(layerManager->GetLastTransactionId(),
+                                      frame->GetRect());
+    }
+
+    return;
+  }
+
+  FallbackRenderer* fallback = renderer->AsFallback();
+  MOZ_ASSERT(fallback);
+
+  if (doBeginTransaction) {
+    MOZ_ASSERT(!aCtx);
+    if (!fallback->BeginTransaction()) {
+      return;
+    }
+  }
+
+  bool temp = aBuilder->SetIsCompositingCheap(renderer->IsCompositingCheap());
+  fallback->EndTransactionWithList(aBuilder, this,
+                                   presContext->AppUnitsPerDevPixel(),
+                                   WindowRenderer::END_DEFAULT);
+
+  aBuilder->SetIsCompositingCheap(temp);
+
+  if (document && widgetTransaction) {
+    TriggerPendingAnimations(*document, renderer->GetAnimationReadyTime());
+  }
+}
+
+void nsDisplayList::DeleteAll(nsDisplayListBuilder* aBuilder) {
+  for (auto* item : TakeItems()) {
+    item->Destroy(aBuilder);
+  }
+}
+
+static bool IsFrameReceivingPointerEvents(nsIFrame* aFrame) {
+  return aFrame->Style()->PointerEvents() != StylePointerEvents::None;
+}
+
+// A list of frames, and their z depth. Used for sorting
+// the results of hit testing.
+struct FramesWithDepth {
+  explicit FramesWithDepth(float aDepth) : mDepth(aDepth) {}
+
+  bool operator<(const FramesWithDepth& aOther) const {
+    if (!FuzzyEqual(mDepth, aOther.mDepth, 0.1f)) {
+      // We want to sort so that the shallowest item (highest depth value) is
+      // first
+      return mDepth > aOther.mDepth;
+    }
+    return this < &aOther;
+  }
+  bool operator==(const FramesWithDepth& aOther) const {
+    return this == &aOther;
+  }
+
+  float mDepth;
+  nsTArray<nsIFrame*> mFrames;
+};
+
+// Sort the frames by depth and then moves all the contained frames to the
+// destination
+static void FlushFramesArray(nsTArray<FramesWithDepth>& aSource,
+                             nsTArray<nsIFrame*>* aDest) {
+  if (aSource.IsEmpty()) {
+    return;
+  }
+  aSource.Sort();
+  uint32_t length = aSource.Length();
+  for (uint32_t i = 0; i < length; i++) {
+    aDest->AppendElements(std::move(aSource[i].mFrames));
+  }
+  aSource.Clear();
+}
+
+void nsDisplayList::HitTest(nsDisplayListBuilder* aBuilder, const nsRect& aRect,
+                            nsDisplayItem::HitTestState* aState,
+                            nsTArray<nsIFrame*>* aOutFrames) const {
+  nsDisplayItem* item;
+
+  if (aState->mInPreserves3D) {
+    // Collect leaves of the current 3D rendering context.
+    for (nsDisplayItem* item : *this) {
+      auto itemType = item->GetType();
+      if (itemType != DisplayItemType::TYPE_TRANSFORM ||
+          !static_cast<nsDisplayTransform*>(item)->IsLeafOf3DContext()) {
+        item->HitTest(aBuilder, aRect, aState, aOutFrames);
+      } else {
+        // One of leaves in the current 3D rendering context.
+        aState->mItemBuffer.AppendElement(item);
+      }
+    }
+    return;
+  }
+
+  int32_t itemBufferStart = aState->mItemBuffer.Length();
+  for (nsDisplayItem* item : *this) {
+    aState->mItemBuffer.AppendElement(item);
+  }
+
+  AutoTArray<FramesWithDepth, 16> temp;
+  for (int32_t i = aState->mItemBuffer.Length() - 1; i >= itemBufferStart;
+       --i) {
+    // Pop element off the end of the buffer. We want to shorten the buffer
+    // so that recursive calls to HitTest have more buffer space.
+    item = aState->mItemBuffer[i];
+    aState->mItemBuffer.SetLength(i);
+
+    bool snap;
+    nsRect r = item->GetBounds(aBuilder, &snap).Intersect(aRect);
+    auto itemType = item->GetType();
+    bool same3DContext =
+        (itemType == DisplayItemType::TYPE_TRANSFORM &&
+         static_cast<nsDisplayTransform*>(item)->IsParticipating3DContext()) ||
+        (itemType == DisplayItemType::TYPE_PERSPECTIVE &&
+         item->Frame()->Extend3DContext());
+    if (same3DContext &&
+        (itemType != DisplayItemType::TYPE_TRANSFORM ||
+         !static_cast<nsDisplayTransform*>(item)->IsLeafOf3DContext())) {
+      if (!item->GetClip().MayIntersect(aRect)) {
+        continue;
+      }
+      AutoTArray<nsIFrame*, 1> neverUsed;
+      // Start gethering leaves of the 3D rendering context, and
+      // append leaves at the end of mItemBuffer.  Leaves are
+      // processed at following iterations.
+      aState->mInPreserves3D = true;
+      item->HitTest(aBuilder, aRect, aState, &neverUsed);
+      aState->mInPreserves3D = false;
+      i = aState->mItemBuffer.Length();
+      continue;
+    }
+    if (same3DContext || item->GetClip().MayIntersect(r)) {
+      AutoTArray<nsIFrame*, 16> outFrames;
+      item->HitTest(aBuilder, aRect, aState, &outFrames);
+
+      // For 3d transforms with preserve-3d we add hit frames into the temp list
+      // so we can sort them later, otherwise we add them directly to the output
+      // list.
+      nsTArray<nsIFrame*>* writeFrames = aOutFrames;
+      if (item->GetType() == DisplayItemType::TYPE_TRANSFORM &&
+          static_cast<nsDisplayTransform*>(item)->IsLeafOf3DContext()) {
+        if (outFrames.Length()) {
+          nsDisplayTransform* transform =
+              static_cast<nsDisplayTransform*>(item);
+          nsPoint point = aRect.TopLeft();
+          // A 1x1 rect means a point, otherwise use the center of the rect
+          if (aRect.width != 1 || aRect.height != 1) {
+            point = aRect.Center();
+          }
+          temp.AppendElement(
+              FramesWithDepth(transform->GetHitDepthAtPoint(aBuilder, point)));
+          writeFrames = &temp[temp.Length() - 1].mFrames;
+        }
+      } else {
+        // We may have just finished a run of consecutive preserve-3d
+        // transforms, so flush these into the destination array before
+        // processing our frame list.
+        FlushFramesArray(temp, aOutFrames);
+      }
+
+      for (uint32_t j = 0; j < outFrames.Length(); j++) {
+        nsIFrame* f = outFrames.ElementAt(j);
+        // Filter out some frames depending on the type of hittest
+        // we are doing. For visibility tests, pass through all frames.
+        // For pointer tests, only pass through frames that are styled
+        // to receive pointer events.
+        if (aBuilder->HitTestIsForVisibility() ||
+            IsFrameReceivingPointerEvents(f)) {
+          writeFrames->AppendElement(f);
+        }
+      }
+
+      if (aBuilder->HitTestIsForVisibility()) {
+        aState->mHitOccludingItem = [&] {
+          if (aState->mHitOccludingItem) {
+            // We already hit something before.
+            return true;
+          }
+          if (aState->mCurrentOpacity == 1.0f &&
+              item->GetOpaqueRegion(aBuilder, &snap).Contains(aRect)) {
+            // An opaque item always occludes everything. Note that we need to
+            // check wrapping opacity and such as well.
+            return true;
+          }
+          float threshold = aBuilder->VisibilityThreshold();
+          if (threshold == 1.0f) {
+            return false;
+          }
+          float itemOpacity = [&] {
+            switch (item->GetType()) {
+              case DisplayItemType::TYPE_OPACITY:
+                return static_cast<nsDisplayOpacity*>(item)->GetOpacity();
+              case DisplayItemType::TYPE_BACKGROUND_COLOR:
+                return static_cast<nsDisplayBackgroundColor*>(item)
+                    ->GetOpacity();
+              default:
+                // Be conservative and assume it won't occlude other items.
+                return 0.0f;
+            }
+          }();
+          return itemOpacity * aState->mCurrentOpacity >= threshold;
+        }();
+
+        if (aState->mHitOccludingItem) {
+          // We're exiting early, so pop the remaining items off the buffer.
+          aState->mItemBuffer.TruncateLength(itemBufferStart);
+          break;
+        }
+      }
+    }
+  }
+  // Clear any remaining preserve-3d transforms.
+  FlushFramesArray(temp, aOutFrames);
+  NS_ASSERTION(aState->mItemBuffer.Length() == uint32_t(itemBufferStart),
+               "How did we forget to pop some elements?");
+}
+
+static nsIContent* FindContentInDocument(nsDisplayItem* aItem, Document* aDoc) {
+  nsIFrame* f = aItem->Frame();
+  while (f) {
+    nsPresContext* pc = f->PresContext();
+    if (pc->Document() == aDoc) {
+      return f->GetContent();
+    }
+    f = nsLayoutUtils::GetCrossDocParentFrameInProcess(
+        pc->PresShell()->GetRootFrame());
+  }
+  return nullptr;
+}
+
+struct ZSortItem {
+  nsDisplayItem* item;
+  int32_t zIndex;
+
+  explicit ZSortItem(nsDisplayItem* aItem)
+      : item(aItem), zIndex(aItem->ZIndex()) {}
+
+  operator nsDisplayItem*() { return item; }
+};
+
+struct ZOrderComparator {
+  bool operator()(const ZSortItem& aLeft, const ZSortItem& aRight) const {
+    // Note that we can't just take the difference of the two
+    // z-indices here, because that might overflow a 32-bit int.
+    return aLeft.zIndex < aRight.zIndex;
+  }
+};
+
+void nsDisplayList::SortByZOrder() { Sort<ZSortItem>(ZOrderComparator()); }
+
+struct ContentComparator {
+  nsIContent* mCommonAncestor;
+
+  explicit ContentComparator(nsIContent* aCommonAncestor)
+      : mCommonAncestor(aCommonAncestor) {}
+
+  bool operator()(nsDisplayItem* aLeft, nsDisplayItem* aRight) const {
+    // It's possible that the nsIContent for aItem1 or aItem2 is in a
+    // subdocument of commonAncestor, because display items for subdocuments
+    // have been mixed into the same list. Ensure that we're looking at content
+    // in commonAncestor's document.
+    Document* commonAncestorDoc = mCommonAncestor->OwnerDoc();
+    nsIContent* content1 = FindContentInDocument(aLeft, commonAncestorDoc);
+    nsIContent* content2 = FindContentInDocument(aRight, commonAncestorDoc);
+    if (!content1 || !content2) {
+      NS_ERROR("Document trees are mixed up!");
+      // Something weird going on
+      return true;
+    }
+    return nsLayoutUtils::CompareTreePosition(content1, content2,
+                                              mCommonAncestor) < 0;
+  }
+};
+
+void nsDisplayList::SortByContentOrder(nsIContent* aCommonAncestor) {
+  Sort<nsDisplayItem*>(ContentComparator(aCommonAncestor));
+}
+
+#if !defined(DEBUG) && !defined(MOZ_DIAGNOSTIC_ASSERT_ENABLED)
+static_assert(sizeof(nsDisplayItem) <= 176, "nsDisplayItem has grown");
+#endif
+
+nsDisplayItem::nsDisplayItem(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame)
+    : nsDisplayItem(aBuilder, aFrame, aBuilder->CurrentActiveScrolledRoot()) {}
+
+nsDisplayItem::nsDisplayItem(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                             const ActiveScrolledRoot* aActiveScrolledRoot)
+    : mFrame(aFrame), mActiveScrolledRoot(aActiveScrolledRoot) {
+  MOZ_COUNT_CTOR(nsDisplayItem);
+  MOZ_ASSERT(mFrame);
+  if (aBuilder->IsRetainingDisplayList()) {
+    mFrame->AddDisplayItem(this);
+  }
+
+  aBuilder->FindReferenceFrameFor(aFrame, &mToReferenceFrame);
+  NS_ASSERTION(
+      aBuilder->GetVisibleRect().width >= 0 || !aBuilder->IsForPainting(),
+      "visible rect not set");
+
+  mClipChain = aBuilder->ClipState().GetCurrentCombinedClipChain(aBuilder);
+
+  // The visible rect is for mCurrentFrame, so we have to use
+  // mCurrentOffsetToReferenceFrame
+  nsRect visible = aBuilder->GetVisibleRect() +
+                   aBuilder->GetCurrentFrameOffsetToReferenceFrame();
+  SetBuildingRect(visible);
+
+  const nsStyleDisplay* disp = mFrame->StyleDisplay();
+  if (mFrame->BackfaceIsHidden(disp)) {
+    mItemFlags += ItemFlag::BackfaceHidden;
+  }
+  if (mFrame->Combines3DTransformWithAncestors()) {
+    mItemFlags += ItemFlag::Combines3DTransformWithAncestors;
+  }
+}
+
+void nsDisplayItem::SetDeletedFrame() { mItemFlags += ItemFlag::DeletedFrame; }
+
+bool nsDisplayItem::HasDeletedFrame() const {
+  bool retval = mItemFlags.contains(ItemFlag::DeletedFrame) ||
+                (GetType() == DisplayItemType::TYPE_REMOTE &&
+                 !static_cast<const nsDisplayRemote*>(this)->GetFrameLoader());
+  MOZ_ASSERT(retval || mFrame);
+  return retval;
+}
+
+/* static */
+bool nsDisplayItem::ForceActiveLayers() {
+  return StaticPrefs::layers_force_active();
+}
+
+int32_t nsDisplayItem::ZIndex() const { return mFrame->ZIndex().valueOr(0); }
+
+void nsDisplayItem::SetClipChain(const DisplayItemClipChain* aClipChain,
+                                 bool aStore) {
+  mClipChain = aClipChain;
+}
+
+Maybe<nsRect> nsDisplayItem::GetClipWithRespectToASR(
+    nsDisplayListBuilder* aBuilder, const ActiveScrolledRoot* aASR) const {
+  if (const DisplayItemClip* clip =
+          DisplayItemClipChain::ClipForASR(GetClipChain(), aASR)) {
+    return Some(clip->GetClipRect());
+  }
+#ifdef DEBUG
+  MOZ_ASSERT(false, "item should have finite clip with respect to aASR");
+#endif
+  return Nothing();
+}
+
+const DisplayItemClip& nsDisplayItem::GetClip() const {
+  const DisplayItemClip* clip =
+      DisplayItemClipChain::ClipForASR(mClipChain, mActiveScrolledRoot);
+  return clip ? *clip : DisplayItemClip::NoClip();
+}
+
+void nsDisplayItem::IntersectClip(nsDisplayListBuilder* aBuilder,
+                                  const DisplayItemClipChain* aOther,
+                                  bool aStore) {
+  if (!aOther || mClipChain == aOther) {
+    return;
+  }
+
+  // aOther might be a reference to a clip on the stack. We need to make sure
+  // that CreateClipChainIntersection will allocate the actual intersected
+  // clip in the builder's arena, so for the mClipChain == nullptr case,
+  // we supply nullptr as the common ancestor so that
+  // CreateClipChainIntersection clones the whole chain.
+  const DisplayItemClipChain* ancestorClip =
+      mClipChain ? FindCommonAncestorClipForIntersection(mClipChain, aOther)
+                 : nullptr;
+
+  SetClipChain(
+      aBuilder->CreateClipChainIntersection(ancestorClip, mClipChain, aOther),
+      aStore);
+}
+
+nsRect nsDisplayItem::GetClippedBounds(nsDisplayListBuilder* aBuilder) const {
+  bool snap;
+  nsRect r = GetBounds(aBuilder, &snap);
+  return GetClip().ApplyNonRoundedIntersection(r);
+}
+
+nsDisplayContainer::nsDisplayContainer(
+    nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+    const ActiveScrolledRoot* aActiveScrolledRoot, nsDisplayList* aList)
+    : nsDisplayItem(aBuilder, aFrame, aActiveScrolledRoot),
+      mChildren(aBuilder) {
+  MOZ_COUNT_CTOR(nsDisplayContainer);
+  mChildren.AppendToTop(aList);
+  UpdateBounds(aBuilder);
+
+  // Clear and store the clip chain set by nsDisplayItem constructor.
+  nsDisplayItem::SetClipChain(nullptr, true);
+}
+
+nsRect nsDisplayItem::GetPaintRect(nsDisplayListBuilder* aBuilder,
+                                   gfxContext* aCtx) {
+  bool dummy;
+  nsRect result = GetBounds(aBuilder, &dummy);
+  if (aCtx) {
+    result.IntersectRect(result,
+                         nsLayoutUtils::RoundGfxRectToAppRect(
+                             aCtx->GetClipExtents(),
+                             mFrame->PresContext()->AppUnitsPerDevPixel()));
+  }
+  return result;
+}
+
+bool nsDisplayContainer::CreateWebRenderCommands(
+    wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+    const StackingContextHelper& aSc, RenderRootStateManager* aManager,
+    nsDisplayListBuilder* aDisplayListBuilder) {
+  aManager->CommandBuilder().CreateWebRenderCommandsFromDisplayList(
+      GetChildren(), this, aDisplayListBuilder, aSc, aBuilder, aResources,
+      false);
+  return true;
+}
+
+nsRect nsDisplayContainer::GetBounds(nsDisplayListBuilder* aBuilder,
+                                     bool* aSnap) const {
+  *aSnap = false;
+  return mBounds;
+}
+
+nsRect nsDisplayContainer::GetComponentAlphaBounds(
+    nsDisplayListBuilder* aBuilder) const {
+  return mChildren.GetComponentAlphaBounds(aBuilder);
+}
+
+static nsRegion GetOpaqueRegion(nsDisplayListBuilder* aBuilder,
+                                nsDisplayList* aList,
+                                const nsRect& aListBounds) {
+  return aList->GetOpaqueRegion(aBuilder);
+}
+
+nsRegion nsDisplayContainer::GetOpaqueRegion(nsDisplayListBuilder* aBuilder,
+                                             bool* aSnap) const {
+  return ::mozilla::GetOpaqueRegion(aBuilder, GetChildren(),
+                                    GetBounds(aBuilder, aSnap));
+}
+
+Maybe<nsRect> nsDisplayContainer::GetClipWithRespectToASR(
+    nsDisplayListBuilder* aBuilder, const ActiveScrolledRoot* aASR) const {
+  // Our children should have finite bounds with respect to |aASR|.
+  if (aASR == mActiveScrolledRoot) {
+    return Some(mBounds);
+  }
+
+  return Some(mChildren.GetClippedBoundsWithRespectToASR(aBuilder, aASR));
+}
+
+void nsDisplayContainer::HitTest(nsDisplayListBuilder* aBuilder,
+                                 const nsRect& aRect, HitTestState* aState,
+                                 nsTArray<nsIFrame*>* aOutFrames) {
+  mChildren.HitTest(aBuilder, aRect, aState, aOutFrames);
+}
+
+void nsDisplayContainer::UpdateBounds(nsDisplayListBuilder* aBuilder) {
+  // Container item bounds are expected to be clipped.
+  mBounds =
+      mChildren.GetClippedBoundsWithRespectToASR(aBuilder, mActiveScrolledRoot);
+}
+
+nsRect nsDisplaySolidColor::GetBounds(nsDisplayListBuilder* aBuilder,
+                                      bool* aSnap) const {
+  *aSnap = true;
+  return mBounds;
+}
+
+void nsDisplaySolidColor::Paint(nsDisplayListBuilder* aBuilder,
+                                gfxContext* aCtx) {
+  int32_t appUnitsPerDevPixel = mFrame->PresContext()->AppUnitsPerDevPixel();
+  DrawTarget* drawTarget = aCtx->GetDrawTarget();
+  Rect rect = NSRectToSnappedRect(GetPaintRect(aBuilder, aCtx),
+                                  appUnitsPerDevPixel, *drawTarget);
+  drawTarget->FillRect(rect, ColorPattern(ToDeviceColor(mColor)));
+}
+
+void nsDisplaySolidColor::WriteDebugInfo(std::stringstream& aStream) {
+  aStream << " (rgba " << (int)NS_GET_R(mColor) << "," << (int)NS_GET_G(mColor)
+          << "," << (int)NS_GET_B(mColor) << "," << (int)NS_GET_A(mColor)
+          << ")";
+}
+
+bool nsDisplaySolidColor::CreateWebRenderCommands(
+    wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+    const StackingContextHelper& aSc, RenderRootStateManager* aManager,
+    nsDisplayListBuilder* aDisplayListBuilder) {
+  LayoutDeviceRect bounds = LayoutDeviceRect::FromAppUnits(
+      mBounds, mFrame->PresContext()->AppUnitsPerDevPixel());
+  wr::LayoutRect r = wr::ToLayoutRect(bounds);
+  aBuilder.PushRect(r, r, !BackfaceIsHidden(), false, mIsCheckerboardBackground,
+                    wr::ToColorF(ToDeviceColor(mColor)));
+
+  return true;
+}
+
+nsRect nsDisplaySolidColorRegion::GetBounds(nsDisplayListBuilder* aBuilder,
+                                            bool* aSnap) const {
+  *aSnap = true;
+  return mRegion.GetBounds();
+}
+
+void nsDisplaySolidColorRegion::Paint(nsDisplayListBuilder* aBuilder,
+                                      gfxContext* aCtx) {
+  int32_t appUnitsPerDevPixel = mFrame->PresContext()->AppUnitsPerDevPixel();
+  DrawTarget* drawTarget = aCtx->GetDrawTarget();
+  ColorPattern color(ToDeviceColor(mColor));
+  for (auto iter = mRegion.RectIter(); !iter.Done(); iter.Next()) {
+    Rect rect =
+        NSRectToSnappedRect(iter.Get(), appUnitsPerDevPixel, *drawTarget);
+    drawTarget->FillRect(rect, color);
+  }
+}
+
+void nsDisplaySolidColorRegion::WriteDebugInfo(std::stringstream& aStream) {
+  aStream << " (rgba " << int(mColor.r * 255) << "," << int(mColor.g * 255)
+          << "," << int(mColor.b * 255) << "," << mColor.a << ")";
+}
+
+bool nsDisplaySolidColorRegion::CreateWebRenderCommands(
+    wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+    const StackingContextHelper& aSc, RenderRootStateManager* aManager,
+    nsDisplayListBuilder* aDisplayListBuilder) {
+  for (auto iter = mRegion.RectIter(); !iter.Done(); iter.Next()) {
+    nsRect rect = iter.Get();
+    LayoutDeviceRect layerRects = LayoutDeviceRect::FromAppUnits(
+        rect, mFrame->PresContext()->AppUnitsPerDevPixel());
+    wr::LayoutRect r = wr::ToLayoutRect(layerRects);
+    aBuilder.PushRect(r, r, !BackfaceIsHidden(), false, false,
+                      wr::ToColorF(ToDeviceColor(mColor)));
+  }
+
+  return true;
+}
+
+static void RegisterThemeGeometry(nsDisplayListBuilder* aBuilder,
+                                  nsDisplayItem* aItem, nsIFrame* aFrame,
+                                  nsITheme::ThemeGeometryType aType) {
+  if (aBuilder->IsInChromeDocumentOrPopup()) {
+    nsIFrame* displayRoot = nsLayoutUtils::GetDisplayRootFrame(aFrame);
+    bool preservesAxisAlignedRectangles = false;
+    nsRect borderBox = nsLayoutUtils::TransformFrameRectToAncestor(
+        aFrame, aFrame->GetRectRelativeToSelf(), displayRoot,
+        &preservesAxisAlignedRectangles);
+    if (preservesAxisAlignedRectangles) {
+      aBuilder->RegisterThemeGeometry(
+          aType, aItem,
+          LayoutDeviceIntRect::FromUnknownRect(borderBox.ToNearestPixels(
+              aFrame->PresContext()->AppUnitsPerDevPixel())));
+    }
+  }
+}
+
+// Return the bounds of the viewport relative to |aFrame|'s reference frame.
+// Returns Nothing() if transforming into |aFrame|'s coordinate space fails.
+static Maybe<nsRect> GetViewportRectRelativeToReferenceFrame(
+    nsDisplayListBuilder* aBuilder, nsIFrame* aFrame) {
+  nsIFrame* rootFrame = aFrame->PresShell()->GetRootFrame();
+  nsRect rootRect = rootFrame->GetRectRelativeToSelf();
+  if (nsLayoutUtils::TransformRect(rootFrame, aFrame, rootRect) ==
+      nsLayoutUtils::TRANSFORM_SUCCEEDED) {
+    return Some(rootRect + aBuilder->ToReferenceFrame(aFrame));
+  }
+  return Nothing();
+}
+
+/* static */ nsDisplayBackgroundImage::InitData
+nsDisplayBackgroundImage::GetInitData(nsDisplayListBuilder* aBuilder,
+                                      nsIFrame* aFrame, uint16_t aLayer,
+                                      const nsRect& aBackgroundRect,
+                                      const ComputedStyle* aBackgroundStyle) {
+  nsPresContext* presContext = aFrame->PresContext();
+  uint32_t flags = aBuilder->GetBackgroundPaintFlags();
+  const nsStyleImageLayers::Layer& layer =
+      aBackgroundStyle->StyleBackground()->mImage.mLayers[aLayer];
+
+  bool isTransformedFixed;
+  nsBackgroundLayerState state = nsCSSRendering::PrepareImageLayer(
+      presContext, aFrame, flags, aBackgroundRect, aBackgroundRect, layer,
+      &isTransformedFixed);
+
+  // background-attachment:fixed is treated as background-attachment:scroll
+  // if it's affected by a transform.
+  // See https://www.w3.org/Bugs/Public/show_bug.cgi?id=17521.
+  bool shouldTreatAsFixed =
+      layer.mAttachment == StyleImageLayerAttachment::Fixed &&
+      !isTransformedFixed;
+
+  bool shouldFixToViewport = shouldTreatAsFixed && !layer.mImage.IsNone();
+  bool isRasterImage = state.mImageRenderer.IsRasterImage();
+  nsCOMPtr<imgIContainer> image;
+  if (isRasterImage) {
+    image = state.mImageRenderer.GetImage();
+  }
+  return InitData{aBuilder,        aBackgroundStyle, image,
+                  aBackgroundRect, state.mFillArea,  state.mDestArea,
+                  aLayer,          isRasterImage,    shouldFixToViewport};
+}
+
+nsDisplayBackgroundImage::nsDisplayBackgroundImage(
+    nsDisplayListBuilder* aBuilder, nsIFrame* aFrame, const InitData& aInitData,
+    nsIFrame* aFrameForBounds)
+    : nsPaintedDisplayItem(aBuilder, aFrame),
+      mBackgroundStyle(aInitData.backgroundStyle),
+      mImage(aInitData.image),
+      mDependentFrame(nullptr),
+      mBackgroundRect(aInitData.backgroundRect),
+      mFillRect(aInitData.fillArea),
+      mDestRect(aInitData.destArea),
+      mLayer(aInitData.layer),
+      mIsRasterImage(aInitData.isRasterImage),
+      mShouldFixToViewport(aInitData.shouldFixToViewport) {
+  MOZ_COUNT_CTOR(nsDisplayBackgroundImage);
+#ifdef DEBUG
+  if (mBackgroundStyle && mBackgroundStyle != mFrame->Style()) {
+    // If this changes, then you also need to adjust css::ImageLoader to
+    // invalidate mFrame as needed.
+    MOZ_ASSERT(mFrame->IsCanvasFrame() ||
+               mFrame->IsFrameOfType(nsIFrame::eTablePart));
+  }
+#endif
+
+  mBounds = GetBoundsInternal(aInitData.builder, aFrameForBounds);
+  if (mShouldFixToViewport) {
+    // Expand the item's visible rect to cover the entire bounds, limited to the
+    // viewport rect. This is necessary because the background's clip can move
+    // asynchronously.
+    if (Maybe<nsRect> viewportRect = GetViewportRectRelativeToReferenceFrame(
+            aInitData.builder, mFrame)) {
+      SetBuildingRect(mBounds.Intersect(*viewportRect));
+    }
+  }
+}
+
+nsDisplayBackgroundImage::~nsDisplayBackgroundImage() {
+  MOZ_COUNT_DTOR(nsDisplayBackgroundImage);
+  if (mDependentFrame) {
+    mDependentFrame->RemoveDisplayItem(this);
+  }
+}
+
+static nsIFrame* GetBackgroundComputedStyleFrame(nsIFrame* aFrame) {
+  nsIFrame* f = nsCSSRendering::FindBackgroundFrame(aFrame);
+  if (!f) {
+    // We don't want to bail out if moz-appearance is set on a root
+    // node. If it has a parent content node, bail because it's not
+    // a root, other wise keep going in order to let the theme stuff
+    // draw the background. The canvas really should be drawing the
+    // bg, but there's no way to hook that up via css.
+    if (!aFrame->StyleDisplay()->HasAppearance()) {
+      return nullptr;
+    }
+
+    nsIContent* content = aFrame->GetContent();
+    if (!content || content->GetParent()) {
+      return nullptr;
+    }
+
+    f = aFrame;
+  }
+  return f;
+}
+
+static void SetBackgroundClipRegion(
+    DisplayListClipState::AutoSaveRestore& aClipState, nsIFrame* aFrame,
+    const nsStyleImageLayers::Layer& aLayer, const nsRect& aBackgroundRect,
+    bool aWillPaintBorder) {
+  nsCSSRendering::ImageLayerClipState clip;
+  nsCSSRendering::GetImageLayerClip(
+      aLayer, aFrame, *aFrame->StyleBorder(), aBackgroundRect, aBackgroundRect,
+      aWillPaintBorder, aFrame->PresContext()->AppUnitsPerDevPixel(), &clip);
+
+  if (clip.mHasAdditionalBGClipArea) {
+    aClipState.ClipContentDescendants(
+        clip.mAdditionalBGClipArea, clip.mBGClipArea,
+        clip.mHasRoundedCorners ? clip.mRadii : nullptr);
+  } else {
+    aClipState.ClipContentDescendants(
+        clip.mBGClipArea, clip.mHasRoundedCorners ? clip.mRadii : nullptr);
+  }
+}
+
+/**
+ * This is used for the find bar highlighter overlay. It's only accessible
+ * through the AnonymousContent API, so it's not exposed to general web pages.
+ */
+static bool SpecialCutoutRegionCase(nsDisplayListBuilder* aBuilder,
+                                    nsIFrame* aFrame,
+                                    const nsRect& aBackgroundRect,
+                                    nsDisplayList* aList, nscolor aColor) {
+  nsIContent* content = aFrame->GetContent();
+  if (!content) {
+    return false;
+  }
+
+  void* cutoutRegion = content->GetProperty(nsGkAtoms::cutoutregion);
+  if (!cutoutRegion) {
+    return false;
+  }
+
+  if (NS_GET_A(aColor) == 0) {
+    return true;
+  }
+
+  nsRegion region;
+  region.Sub(aBackgroundRect, *static_cast<nsRegion*>(cutoutRegion));
+  region.MoveBy(aBuilder->ToReferenceFrame(aFrame));
+  aList->AppendNewToTop<nsDisplaySolidColorRegion>(aBuilder, aFrame, region,
+                                                   aColor);
+
+  return true;
+}
+
+enum class TableType : uint8_t {
+  Table,
+  TableCol,
+  TableColGroup,
+  TableRow,
+  TableRowGroup,
+  TableCell,
+
+  MAX,
+};
+
+enum class TableTypeBits : uint8_t { Count = 3 };
+
+static_assert(static_cast<uint8_t>(TableType::MAX) <
+                  (1 << (static_cast<uint8_t>(TableTypeBits::Count) + 1)),
+              "TableType cannot fit with TableTypeBits::Count");
+TableType GetTableTypeFromFrame(nsIFrame* aFrame);
+
+static uint16_t CalculateTablePerFrameKey(const uint16_t aIndex,
+                                          const TableType aType) {
+  const uint32_t key = (aIndex << static_cast<uint8_t>(TableTypeBits::Count)) |
+                       static_cast<uint8_t>(aType);
+
+  return static_cast<uint16_t>(key);
+}
+
+static nsDisplayBackgroundImage* CreateBackgroundImage(
+    nsDisplayListBuilder* aBuilder, nsIFrame* aFrame, nsIFrame* aSecondaryFrame,
+    const nsDisplayBackgroundImage::InitData& aBgData) {
+  const auto index = aBgData.layer;
+
+  if (aSecondaryFrame) {
+    const auto tableType = GetTableTypeFromFrame(aFrame);
+    const uint16_t tableItemIndex = CalculateTablePerFrameKey(index, tableType);
+
+    return MakeDisplayItemWithIndex<nsDisplayTableBackgroundImage>(
+        aBuilder, aSecondaryFrame, tableItemIndex, aBgData, aFrame);
+  }
+
+  return MakeDisplayItemWithIndex<nsDisplayBackgroundImage>(aBuilder, aFrame,
+                                                            index, aBgData);
+}
+
+static nsDisplayThemedBackground* CreateThemedBackground(
+    nsDisplayListBuilder* aBuilder, nsIFrame* aFrame, nsIFrame* aSecondaryFrame,
+    nsRect& aBgRect) {
+  if (aSecondaryFrame) {
+    const uint16_t index = static_cast<uint16_t>(GetTableTypeFromFrame(aFrame));
+    return MakeDisplayItemWithIndex<nsDisplayTableThemedBackground>(
+        aBuilder, aSecondaryFrame, index, aBgRect, aFrame);
+  }
+
+  return MakeDisplayItem<nsDisplayThemedBackground>(aBuilder, aFrame, aBgRect);
+}
+
+static nsDisplayBackgroundColor* CreateBackgroundColor(
+    nsDisplayListBuilder* aBuilder, nsIFrame* aFrame, nsIFrame* aSecondaryFrame,
+    nsRect& aBgRect, const ComputedStyle* aBgSC, nscolor aColor) {
+  if (aSecondaryFrame) {
+    const uint16_t index = static_cast<uint16_t>(GetTableTypeFromFrame(aFrame));
+    return MakeDisplayItemWithIndex<nsDisplayTableBackgroundColor>(
+        aBuilder, aSecondaryFrame, index, aBgRect, aBgSC, aColor, aFrame);
+  }
+
+  return MakeDisplayItem<nsDisplayBackgroundColor>(aBuilder, aFrame, aBgRect,
+                                                   aBgSC, aColor);
+}
+
+static void DealWithWindowsAppearanceHacks(nsIFrame* aFrame,
+                                           nsDisplayListBuilder* aBuilder) {
+  const auto& disp = *aFrame->StyleDisplay();
+
+  // We use default appearance rather than effective appearance because we want
+  // to handle when titlebar buttons that have appearance: none.
+  const auto defaultAppearance = disp.mDefaultAppearance;
+  if (MOZ_LIKELY(defaultAppearance == StyleAppearance::None)) {
+    return;
+  }
+
+  if (defaultAppearance == StyleAppearance::MozWinExcludeGlass) {
+    // Check for frames that are marked as a part of the region used in
+    // calculating glass margins on Windows.
+    aBuilder->AddWindowExcludeGlassRegion(
+        aFrame, nsRect(aBuilder->ToReferenceFrame(aFrame), aFrame->GetSize()));
+  }
+
+  if (auto type = disp.GetWindowButtonType()) {
+    if (auto* widget = aFrame->GetNearestWidget()) {
+      auto rect = LayoutDevicePixel::FromAppUnitsToNearest(
+          nsRect(aBuilder->ToReferenceFrame(aFrame), aFrame->GetSize()),
+          aFrame->PresContext()->AppUnitsPerDevPixel());
+      widget->SetWindowButtonRect(*type, rect);
+    }
+  }
+}
+
+/*static*/
+AppendedBackgroundType nsDisplayBackgroundImage::AppendBackgroundItemsToTop(
+    nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+    const nsRect& aBackgroundRect, nsDisplayList* aList,
+    bool aAllowWillPaintBorderOptimization, const nsRect& aBackgroundOriginRect,
+    nsIFrame* aSecondaryReferenceFrame,
+    Maybe<nsDisplayListBuilder::AutoBuildingDisplayList>*
+        aAutoBuildingDisplayList) {
+  const ComputedStyle* bgSC = nullptr;
+  const nsStyleBackground* bg = nullptr;
+  nsRect bgRect = aBackgroundRect;
+  nsRect bgOriginRect = bgRect;
+  if (!aBackgroundOriginRect.IsEmpty()) {
+    bgOriginRect = aBackgroundOriginRect;
+  }
+  const bool isThemed = aFrame->IsThemed();
+  DealWithWindowsAppearanceHacks(aFrame, aBuilder);
+
+  nsIFrame* dependentFrame = nullptr;
+  if (!isThemed) {
+    if (!bgSC) {
+      dependentFrame = GetBackgroundComputedStyleFrame(aFrame);
+      if (dependentFrame) {
+        bgSC = dependentFrame->Style();
+        if (dependentFrame == aFrame) {
+          dependentFrame = nullptr;
+        }
+      }
+    }
+    if (bgSC) {
+      bg = bgSC->StyleBackground();
+    }
+  }
+
+  bool drawBackgroundColor = false;
+  bool drawBackgroundImage = false;
+  nscolor color = NS_RGBA(0, 0, 0, 0);
+  if (bg && !(aFrame->IsCanvasFrame() || aFrame->IsViewportFrame())) {
+    color = nsCSSRendering::DetermineBackgroundColor(
+        aFrame->PresContext(), bgSC, aFrame, drawBackgroundImage,
+        drawBackgroundColor);
+  }
+
+  if (SpecialCutoutRegionCase(aBuilder, aFrame, aBackgroundRect, aList,
+                              color)) {
+    return AppendedBackgroundType::None;
+  }
+
+  const nsStyleBorder* borderStyle = aFrame->StyleBorder();
+  const nsStyleEffects* effectsStyle = aFrame->StyleEffects();
+  bool hasInsetShadow = effectsStyle->HasBoxShadowWithInset(true);
+  bool willPaintBorder = aAllowWillPaintBorderOptimization && !isThemed &&
+                         !hasInsetShadow && borderStyle->HasBorder();
+
+  // An auxiliary list is necessary in case we have background blending; if that
+  // is the case, background items need to be wrapped by a blend container to
+  // isolate blending to the background
+  nsDisplayList bgItemList(aBuilder);
+  // Even if we don't actually have a background color to paint, we may still
+  // need to create an item for hit testing and we still need to create an item
+  // for background-color animations.
+  if ((drawBackgroundColor && color != NS_RGBA(0, 0, 0, 0)) ||
+      aBuilder->IsForEventDelivery() ||
+      EffectCompositor::HasAnimationsForCompositor(
+          aFrame, DisplayItemType::TYPE_BACKGROUND_COLOR)) {
+    if (aAutoBuildingDisplayList && !*aAutoBuildingDisplayList) {
+      nsPoint offset = aBuilder->GetCurrentFrame()->GetOffsetTo(aFrame);
+      aAutoBuildingDisplayList->emplace(aBuilder, aFrame,
+                                        aBuilder->GetVisibleRect() + offset,
+                                        aBuilder->GetDirtyRect() + offset);
+    }
+    Maybe<DisplayListClipState::AutoSaveRestore> clipState;
+    nsRect bgColorRect = bgRect;
+    if (bg && !aBuilder->IsForEventDelivery()) {
+      // Disable the will-paint-border optimization for background
+      // colors with no border-radius. Enabling it for background colors
+      // doesn't help much (there are no tiling issues) and clipping the
+      // background breaks detection of the element's border-box being
+      // opaque. For nonzero border-radius we still need it because we
+      // want to inset the background if possible to avoid antialiasing
+      // artifacts along the rounded corners.
+      bool useWillPaintBorderOptimization =
+          willPaintBorder &&
+          nsLayoutUtils::HasNonZeroCorner(borderStyle->mBorderRadius);
+
+      nsCSSRendering::ImageLayerClipState clip;
+      nsCSSRendering::GetImageLayerClip(
+          bg->BottomLayer(), aFrame, *aFrame->StyleBorder(), bgRect, bgRect,
+          useWillPaintBorderOptimization,
+          aFrame->PresContext()->AppUnitsPerDevPixel(), &clip);
+
+      bgColorRect = bgColorRect.Intersect(clip.mBGClipArea);
+      if (clip.mHasAdditionalBGClipArea) {
+        bgColorRect = bgColorRect.Intersect(clip.mAdditionalBGClipArea);
+      }
+      if (clip.mHasRoundedCorners) {
+        clipState.emplace(aBuilder);
+        clipState->ClipContentDescendants(clip.mBGClipArea, clip.mRadii);
+      }
+    }
+
+    nsDisplayBackgroundColor* bgItem = CreateBackgroundColor(
+        aBuilder, aFrame, aSecondaryReferenceFrame, bgColorRect, bgSC,
+        drawBackgroundColor ? color : NS_RGBA(0, 0, 0, 0));
+
+    if (bgItem) {
+      bgItem->SetDependentFrame(aBuilder, dependentFrame);
+      bgItemList.AppendToTop(bgItem);
+    }
+  }
+
+  if (isThemed) {
+    nsDisplayThemedBackground* bgItem = CreateThemedBackground(
+        aBuilder, aFrame, aSecondaryReferenceFrame, bgRect);
+
+    if (bgItem) {
+      bgItem->Init(aBuilder);
+      bgItemList.AppendToTop(bgItem);
+    }
+
+    if (!bgItemList.IsEmpty()) {
+      aList->AppendToTop(&bgItemList);
+      return AppendedBackgroundType::ThemedBackground;
+    }
+
+    return AppendedBackgroundType::None;
+  }
+
+  if (!bg || !drawBackgroundImage) {
+    if (!bgItemList.IsEmpty()) {
+      aList->AppendToTop(&bgItemList);
+      return AppendedBackgroundType::Background;
+    }
+
+    return AppendedBackgroundType::None;
+  }
+
+  const ActiveScrolledRoot* asr = aBuilder->CurrentActiveScrolledRoot();
+
+  bool needBlendContainer = false;
+
+  // Passing bg == nullptr in this macro will result in one iteration with
+  // i = 0.
+  NS_FOR_VISIBLE_IMAGE_LAYERS_BACK_TO_FRONT(i, bg->mImage) {
+    if (bg->mImage.mLayers[i].mImage.IsNone()) {
+      continue;
+    }
+
+    if (aAutoBuildingDisplayList && !*aAutoBuildingDisplayList) {
+      nsPoint offset = aBuilder->GetCurrentFrame()->GetOffsetTo(aFrame);
+      aAutoBuildingDisplayList->emplace(aBuilder, aFrame,
+                                        aBuilder->GetVisibleRect() + offset,
+                                        aBuilder->GetDirtyRect() + offset);
+    }
+
+    if (bg->mImage.mLayers[i].mBlendMode != StyleBlend::Normal) {
+      needBlendContainer = true;
+    }
+
+    DisplayListClipState::AutoSaveRestore clipState(aBuilder);
+    if (!aBuilder->IsForEventDelivery()) {
+      const nsStyleImageLayers::Layer& layer = bg->mImage.mLayers[i];
+      SetBackgroundClipRegion(clipState, aFrame, layer, bgRect,
+                              willPaintBorder);
+    }
+
+    nsDisplayList thisItemList(aBuilder);
+    nsDisplayBackgroundImage::InitData bgData =
+        nsDisplayBackgroundImage::GetInitData(aBuilder, aFrame, i, bgOriginRect,
+                                              bgSC);
+
+    if (bgData.shouldFixToViewport) {
+      auto* displayData = aBuilder->GetCurrentFixedBackgroundDisplayData();
+      nsDisplayListBuilder::AutoBuildingDisplayList buildingDisplayList(
+          aBuilder, aFrame, aBuilder->GetVisibleRect(),
+          aBuilder->GetDirtyRect());
+
+      nsDisplayListBuilder::AutoCurrentActiveScrolledRootSetter asrSetter(
+          aBuilder);
+      if (displayData) {
+        asrSetter.SetCurrentActiveScrolledRoot(
+            displayData->mContainingBlockActiveScrolledRoot);
+        asrSetter.SetCurrentScrollParentId(displayData->mScrollParentId);
+        if (nsLayoutUtils::UsesAsyncScrolling(aFrame)) {
+          // Override the dirty rect on the builder to be the dirty rect of
+          // the viewport.
+          // displayData->mDirtyRect is relative to the presshell's viewport
+          // frame (the root frame), and we need it to be relative to aFrame.
+          nsIFrame* rootFrame =
+              aBuilder->CurrentPresShellState()->mPresShell->GetRootFrame();
+          // There cannot be any transforms between aFrame and rootFrame
+          // because then bgData.shouldFixToViewport would have been false.
+          nsRect visibleRect =
+              displayData->mVisibleRect + aFrame->GetOffsetTo(rootFrame);
+          aBuilder->SetVisibleRect(visibleRect);
+          nsRect dirtyRect =
+              displayData->mDirtyRect + aFrame->GetOffsetTo(rootFrame);
+          aBuilder->SetDirtyRect(dirtyRect);
+        }
+      }
+
+      nsDisplayBackgroundImage* bgItem = nullptr;
+      {
+        // The clip is captured by the nsDisplayFixedPosition, so clear the
+        // clip for the nsDisplayBackgroundImage inside.
+        DisplayListClipState::AutoSaveRestore bgImageClip(aBuilder);
+        bgImageClip.Clear();
+        bgItem = CreateBackgroundImage(aBuilder, aFrame,
+                                       aSecondaryReferenceFrame, bgData);
+      }
+      if (bgItem) {
+        bgItem->SetDependentFrame(aBuilder, dependentFrame);
+
+        thisItemList.AppendToTop(
+            nsDisplayFixedPosition::CreateForFixedBackground(
+                aBuilder, aFrame, aSecondaryReferenceFrame, bgItem, i, asr));
+      }
+    } else {  // bgData.shouldFixToViewport == false
+      nsDisplayBackgroundImage* bgItem = CreateBackgroundImage(
+          aBuilder, aFrame, aSecondaryReferenceFrame, bgData);
+      if (bgItem) {
+        bgItem->SetDependentFrame(aBuilder, dependentFrame);
+        thisItemList.AppendToTop(bgItem);
+      }
+    }
+
+    if (bg->mImage.mLayers[i].mBlendMode != StyleBlend::Normal) {
+      DisplayListClipState::AutoSaveRestore blendClip(aBuilder);
+      // asr is scrolled. Even if we wrap a fixed background layer, that's
+      // fine, because the item will have a scrolled clip that limits the
+      // item with respect to asr.
+      if (aSecondaryReferenceFrame) {
+        const auto tableType = GetTableTypeFromFrame(aFrame);
+        const uint16_t index = CalculateTablePerFrameKey(i + 1, tableType);
+
+        thisItemList.AppendNewToTopWithIndex<nsDisplayTableBlendMode>(
+            aBuilder, aSecondaryReferenceFrame, index, &thisItemList,
+            bg->mImage.mLayers[i].mBlendMode, asr, aFrame, true);
+      } else {
+        thisItemList.AppendNewToTopWithIndex<nsDisplayBlendMode>(
+            aBuilder, aFrame, i + 1, &thisItemList,
+            bg->mImage.mLayers[i].mBlendMode, asr, true);
+      }
+    }
+    bgItemList.AppendToTop(&thisItemList);
+  }
+
+  if (needBlendContainer) {
+    DisplayListClipState::AutoSaveRestore blendContainerClip(aBuilder);
+
+    bgItemList.AppendToTop(
+        nsDisplayBlendContainer::CreateForBackgroundBlendMode(
+            aBuilder, aFrame, aSecondaryReferenceFrame, &bgItemList, asr));
+  }
+
+  if (!bgItemList.IsEmpty()) {
+    aList->AppendToTop(&bgItemList);
+    return AppendedBackgroundType::Background;
+  }
+
+  return AppendedBackgroundType::None;
+}
+
+// Check that the rounded border of aFrame, added to aToReferenceFrame,
+// intersects aRect.  Assumes that the unrounded border has already
+// been checked for intersection.
+static bool RoundedBorderIntersectsRect(nsIFrame* aFrame,
+                                        const nsPoint& aFrameToReferenceFrame,
+                                        const nsRect& aTestRect) {
+  if (!nsRect(aFrameToReferenceFrame, aFrame->GetSize())
+           .Intersects(aTestRect)) {
+    return false;
+  }
+
+  nscoord radii[8];
+  return !aFrame->GetBorderRadii(radii) ||
+         nsLayoutUtils::RoundedRectIntersectsRect(
+             nsRect(aFrameToReferenceFrame, aFrame->GetSize()), radii,
+             aTestRect);
+}
+
+// Returns TRUE if aContainedRect is guaranteed to be contained in
+// the rounded rect defined by aRoundedRect and aRadii. Complex cases are
+// handled conservatively by returning FALSE in some situations where
+// a more thorough analysis could return TRUE.
+//
+// See also RoundedRectIntersectsRect.
+static bool RoundedRectContainsRect(const nsRect& aRoundedRect,
+                                    const nscoord aRadii[8],
+                                    const nsRect& aContainedRect) {
+  nsRegion rgn = nsLayoutUtils::RoundedRectIntersectRect(aRoundedRect, aRadii,
+                                                         aContainedRect);
+  return rgn.Contains(aContainedRect);
+}
+
+bool nsDisplayBackgroundImage::CanApplyOpacity(
+    WebRenderLayerManager* aManager, nsDisplayListBuilder* aBuilder) const {
+  return CanBuildWebRenderDisplayItems(aManager, aBuilder);
+}
+
+bool nsDisplayBackgroundImage::CanBuildWebRenderDisplayItems(
+    WebRenderLayerManager* aManager, nsDisplayListBuilder* aBuilder) const {
+  return mBackgroundStyle->StyleBackground()->mImage.mLayers[mLayer].mClip !=
+             StyleGeometryBox::Text &&
+         nsCSSRendering::CanBuildWebRenderDisplayItemsForStyleImageLayer(
+             aManager, *StyleFrame()->PresContext(), StyleFrame(),
+             mBackgroundStyle->StyleBackground(), mLayer,
+             aBuilder->GetBackgroundPaintFlags());
+}
+
+bool nsDisplayBackgroundImage::CreateWebRenderCommands(
+    wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+    const StackingContextHelper& aSc, RenderRootStateManager* aManager,
+    nsDisplayListBuilder* aDisplayListBuilder) {
+  if (!CanBuildWebRenderDisplayItems(aManager->LayerManager(),
+                                     aDisplayListBuilder)) {
+    return false;
+  }
+
+  uint32_t paintFlags = aDisplayListBuilder->GetBackgroundPaintFlags();
+  bool dummy;
+  nsCSSRendering::PaintBGParams params =
+      nsCSSRendering::PaintBGParams::ForSingleLayer(
+          *StyleFrame()->PresContext(), GetBounds(aDisplayListBuilder, &dummy),
+          mBackgroundRect, StyleFrame(), paintFlags, mLayer,
+          CompositionOp::OP_OVER, aBuilder.GetInheritedOpacity());
+  params.bgClipRect = &mBounds;
+  ImgDrawResult result =
+      nsCSSRendering::BuildWebRenderDisplayItemsForStyleImageLayer(
+          params, aBuilder, aResources, aSc, aManager, this);
+  if (result == ImgDrawResult::NOT_SUPPORTED) {
+    return false;
+  }
+  return true;
+}
+
+void nsDisplayBackgroundImage::HitTest(nsDisplayListBuilder* aBuilder,
+                                       const nsRect& aRect,
+                                       HitTestState* aState,
+                                       nsTArray<nsIFrame*>* aOutFrames) {
+  if (RoundedBorderIntersectsRect(mFrame, ToReferenceFrame(), aRect)) {
+    aOutFrames->AppendElement(mFrame);
+  }
+}
+
+static nsRect GetInsideClipRect(const nsDisplayItem* aItem,
+                                StyleGeometryBox aClip, const nsRect& aRect,
+                                const nsRect& aBackgroundRect) {
+  if (aRect.IsEmpty()) {
+    return {};
+  }
+
+  nsIFrame* frame = aItem->Frame();
+
+  nsRect clipRect = aBackgroundRect;
+  if (frame->IsCanvasFrame()) {
+    nsCanvasFrame* canvasFrame = static_cast<nsCanvasFrame*>(frame);
+    clipRect = canvasFrame->CanvasArea() + aItem->ToReferenceFrame();
+  } else if (aClip == StyleGeometryBox::PaddingBox ||
+             aClip == StyleGeometryBox::ContentBox) {
+    nsMargin border = frame->GetUsedBorder();
+    if (aClip == StyleGeometryBox::ContentBox) {
+      border += frame->GetUsedPadding();
+    }
+    border.ApplySkipSides(frame->GetSkipSides());
+    clipRect.Deflate(border);
+  }
+
+  return clipRect.Intersect(aRect);
+}
+
+nsRegion nsDisplayBackgroundImage::GetOpaqueRegion(
+    nsDisplayListBuilder* aBuilder, bool* aSnap) const {
+  nsRegion result;
+  *aSnap = false;
+
+  if (!mBackgroundStyle) {
+    return result;
+  }
+
+  *aSnap = true;
+
+  // For StyleBoxDecorationBreak::Slice, don't try to optimize here, since
+  // this could easily lead to O(N^2) behavior inside InlineBackgroundData,
+  // which expects frames to be sent to it in content order, not reverse
+  // content order which we'll produce here.
+  // Of course, if there's only one frame in the flow, it doesn't matter.
+  if (mFrame->StyleBorder()->mBoxDecorationBreak ==
+          StyleBoxDecorationBreak::Clone ||
+      (!mFrame->GetPrevContinuation() && !mFrame->GetNextContinuation())) {
+    const nsStyleImageLayers::Layer& layer =
+        mBackgroundStyle->StyleBackground()->mImage.mLayers[mLayer];
+    if (layer.mImage.IsOpaque() && layer.mBlendMode == StyleBlend::Normal &&
+        layer.mRepeat.mXRepeat != StyleImageLayerRepeat::Space &&
+        layer.mRepeat.mYRepeat != StyleImageLayerRepeat::Space &&
+        layer.mClip != StyleGeometryBox::Text) {
+      result = GetInsideClipRect(this, layer.mClip, mBounds, mBackgroundRect);
+    }
+  }
+
+  return result;
+}
+
+Maybe<nscolor> nsDisplayBackgroundImage::IsUniform(
+    nsDisplayListBuilder* aBuilder) const {
+  if (!mBackgroundStyle) {
+    return Some(NS_RGBA(0, 0, 0, 0));
+  }
+  return Nothing();
+}
+
+nsRect nsDisplayBackgroundImage::GetPositioningArea() const {
+  if (!mBackgroundStyle) {
+    return nsRect();
+  }
+  nsIFrame* attachedToFrame;
+  bool transformedFixed;
+  return nsCSSRendering::ComputeImageLayerPositioningArea(
+             mFrame->PresContext(), mFrame, mBackgroundRect,
+             mBackgroundStyle->StyleBackground()->mImage.mLayers[mLayer],
+             &attachedToFrame, &transformedFixed) +
+         ToReferenceFrame();
+}
+
+bool nsDisplayBackgroundImage::RenderingMightDependOnPositioningAreaSizeChange()
+    const {
+  if (!mBackgroundStyle) {
+    return false;
+  }
+
+  nscoord radii[8];
+  if (mFrame->GetBorderRadii(radii)) {
+    // A change in the size of the positioning area might change the position
+    // of the rounded corners.
+    return true;
+  }
+
+  const nsStyleImageLayers::Layer& layer =
+      mBackgroundStyle->StyleBackground()->mImage.mLayers[mLayer];
+  return layer.RenderingMightDependOnPositioningAreaSizeChange();
+}
+
+void nsDisplayBackgroundImage::Paint(nsDisplayListBuilder* aBuilder,
+                                     gfxContext* aCtx) {
+  PaintInternal(aBuilder, aCtx, GetPaintRect(aBuilder, aCtx), &mBounds);
+}
+
+void nsDisplayBackgroundImage::PaintInternal(nsDisplayListBuilder* aBuilder,
+                                             gfxContext* aCtx,
+                                             const nsRect& aBounds,
+                                             nsRect* aClipRect) {
+  gfxContext* ctx = aCtx;
+  StyleGeometryBox clip =
+      mBackgroundStyle->StyleBackground()->mImage.mLayers[mLayer].mClip;
+
+  if (clip == StyleGeometryBox::Text) {
+    if (!GenerateAndPushTextMask(StyleFrame(), aCtx, mBackgroundRect,
+                                 aBuilder)) {
+      return;
+    }
+  }
+
+  nsCSSRendering::PaintBGParams params =
+      nsCSSRendering::PaintBGParams::ForSingleLayer(
+          *StyleFrame()->PresContext(), aBounds, mBackgroundRect, StyleFrame(),
+          aBuilder->GetBackgroundPaintFlags(), mLayer, CompositionOp::OP_OVER,
+          1.0f);
+  params.bgClipRect = aClipRect;
+  Unused << nsCSSRendering::PaintStyleImageLayer(params, *aCtx);
+
+  if (clip == StyleGeometryBox::Text) {
+    ctx->PopGroupAndBlend();
+  }
+}
+
+void nsDisplayBackgroundImage::ComputeInvalidationRegion(
+    nsDisplayListBuilder* aBuilder, const nsDisplayItemGeometry* aGeometry,
+    nsRegion* aInvalidRegion) const {
+  if (!mBackgroundStyle) {
+    return;
+  }
+
+  const auto* geometry =
+      static_cast<const nsDisplayBackgroundGeometry*>(aGeometry);
+
+  bool snap;
+  nsRect bounds = GetBounds(aBuilder, &snap);
+  nsRect positioningArea = GetPositioningArea();
+  if (positioningArea.TopLeft() != geometry->mPositioningArea.TopLeft() ||
+      (positioningArea.Size() != geometry->mPositioningArea.Size() &&
+       RenderingMightDependOnPositioningAreaSizeChange())) {
+    // Positioning area changed in a way that could cause everything to change,
+    // so invalidate everything (both old and new painting areas).
+    aInvalidRegion->Or(bounds, geometry->mBounds);
+    return;
+  }
+  if (!mDestRect.IsEqualInterior(geometry->mDestRect)) {
+    // Dest area changed in a way that could cause everything to change,
+    // so invalidate everything (both old and new painting areas).
+    aInvalidRegion->Or(bounds, geometry->mBounds);
+    return;
+  }
+  if (!bounds.IsEqualInterior(geometry->mBounds)) {
+    // Positioning area is unchanged, so invalidate just the change in the
+    // painting area.
+    aInvalidRegion->Xor(bounds, geometry->mBounds);
+  }
+}
+
+nsRect nsDisplayBackgroundImage::GetBounds(nsDisplayListBuilder* aBuilder,
+                                           bool* aSnap) const {
+  *aSnap = true;
+  return mBounds;
+}
+
+nsRect nsDisplayBackgroundImage::GetBoundsInternal(
+    nsDisplayListBuilder* aBuilder, nsIFrame* aFrameForBounds) {
+  // This allows nsDisplayTableBackgroundImage to change the frame used for
+  // bounds calculation.
+  nsIFrame* frame = aFrameForBounds ? aFrameForBounds : mFrame;
+
+  nsPresContext* presContext = frame->PresContext();
+
+  if (!mBackgroundStyle) {
+    return nsRect();
+  }
+
+  nsRect clipRect = mBackgroundRect;
+  if (frame->IsCanvasFrame()) {
+    nsCanvasFrame* canvasFrame = static_cast<nsCanvasFrame*>(frame);
+    clipRect = canvasFrame->CanvasArea() + ToReferenceFrame();
+  }
+  const nsStyleImageLayers::Layer& layer =
+      mBackgroundStyle->StyleBackground()->mImage.mLayers[mLayer];
+  return nsCSSRendering::GetBackgroundLayerRect(
+      presContext, frame, mBackgroundRect, clipRect, layer,
+      aBuilder->GetBackgroundPaintFlags());
+}
+
+nsDisplayTableBackgroundImage::nsDisplayTableBackgroundImage(
+    nsDisplayListBuilder* aBuilder, nsIFrame* aFrame, const InitData& aData,
+    nsIFrame* aCellFrame)
+    : nsDisplayBackgroundImage(aBuilder, aFrame, aData, aCellFrame),
+      mStyleFrame(aCellFrame) {
+  if (aBuilder->IsRetainingDisplayList()) {
+    mStyleFrame->AddDisplayItem(this);
+  }
+}
+
+nsDisplayTableBackgroundImage::~nsDisplayTableBackgroundImage() {
+  if (mStyleFrame) {
+    mStyleFrame->RemoveDisplayItem(this);
+  }
+}
+
+bool nsDisplayTableBackgroundImage::IsInvalid(nsRect& aRect) const {
+  bool result = mStyleFrame ? mStyleFrame->IsInvalid(aRect) : false;
+  aRect += ToReferenceFrame();
+  return result;
+}
+
+nsDisplayThemedBackground::nsDisplayThemedBackground(
+    nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+    const nsRect& aBackgroundRect)
+    : nsPaintedDisplayItem(aBuilder, aFrame), mBackgroundRect(aBackgroundRect) {
+  MOZ_COUNT_CTOR(nsDisplayThemedBackground);
+}
+
+void nsDisplayThemedBackground::Init(nsDisplayListBuilder* aBuilder) {
+  const nsStyleDisplay* disp = StyleFrame()->StyleDisplay();
+  mAppearance = disp->EffectiveAppearance();
+  StyleFrame()->IsThemed(disp, &mThemeTransparency);
+
+  // Perform necessary RegisterThemeGeometry
+  nsITheme* theme = StyleFrame()->PresContext()->Theme();
+  nsITheme::ThemeGeometryType type =
+      theme->ThemeGeometryTypeForWidget(StyleFrame(), mAppearance);
+  if (type != nsITheme::eThemeGeometryTypeUnknown) {
+    RegisterThemeGeometry(aBuilder, this, StyleFrame(), type);
+  }
+
+  if (mAppearance == StyleAppearance::MozWinBorderlessGlass) {
+    aBuilder->SetGlassDisplayItem(this);
+  }
+
+  mBounds = GetBoundsInternal();
+}
+
+void nsDisplayThemedBackground::WriteDebugInfo(std::stringstream& aStream) {
+  aStream << " (themed, appearance:" << (int)mAppearance << ")";
+}
+
+void nsDisplayThemedBackground::HitTest(nsDisplayListBuilder* aBuilder,
+                                        const nsRect& aRect,
+                                        HitTestState* aState,
+                                        nsTArray<nsIFrame*>* aOutFrames) {
+  // Assume that any point in our background rect is a hit.
+  if (mBackgroundRect.Intersects(aRect)) {
+    aOutFrames->AppendElement(mFrame);
+  }
+}
+
+nsRegion nsDisplayThemedBackground::GetOpaqueRegion(
+    nsDisplayListBuilder* aBuilder, bool* aSnap) const {
+  nsRegion result;
+  *aSnap = false;
+
+  if (mThemeTransparency == nsITheme::eOpaque) {
+    *aSnap = true;
+    result = mBackgroundRect;
+  }
+  return result;
+}
+
+Maybe<nscolor> nsDisplayThemedBackground::IsUniform(
+    nsDisplayListBuilder* aBuilder) const {
+  if (mAppearance == StyleAppearance::MozWinBorderlessGlass) {
+    return Some(NS_RGBA(0, 0, 0, 0));
+  }
+  return Nothing();
+}
+
+nsRect nsDisplayThemedBackground::GetPositioningArea() const {
+  return mBackgroundRect;
+}
+
+void nsDisplayThemedBackground::Paint(nsDisplayListBuilder* aBuilder,
+                                      gfxContext* aCtx) {
+  PaintInternal(aBuilder, aCtx, GetPaintRect(aBuilder, aCtx), nullptr);
+}
+
+void nsDisplayThemedBackground::PaintInternal(nsDisplayListBuilder* aBuilder,
+                                              gfxContext* aCtx,
+                                              const nsRect& aBounds,
+                                              nsRect* aClipRect) {
+  // XXXzw this ignores aClipRect.
+  nsPresContext* presContext = StyleFrame()->PresContext();
+  nsITheme* theme = presContext->Theme();
+  nsRect drawing(mBackgroundRect);
+  theme->GetWidgetOverflow(presContext->DeviceContext(), StyleFrame(),
+                           mAppearance, &drawing);
+  drawing.IntersectRect(drawing, aBounds);
+  theme->DrawWidgetBackground(aCtx, StyleFrame(), mAppearance, mBackgroundRect,
+                              drawing);
+}
+
+bool nsDisplayThemedBackground::CreateWebRenderCommands(
+    wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+    const StackingContextHelper& aSc, RenderRootStateManager* aManager,
+    nsDisplayListBuilder* aDisplayListBuilder) {
+  nsITheme* theme = StyleFrame()->PresContext()->Theme();
+  return theme->CreateWebRenderCommandsForWidget(aBuilder, aResources, aSc,
+                                                 aManager, StyleFrame(),
+                                                 mAppearance, mBackgroundRect);
+}
+
+bool nsDisplayThemedBackground::IsWindowActive() const {
+  DocumentState docState = mFrame->GetContent()->OwnerDoc()->GetDocumentState();
+  return !docState.HasState(DocumentState::WINDOW_INACTIVE);
+}
+
+void nsDisplayThemedBackground::ComputeInvalidationRegion(
+    nsDisplayListBuilder* aBuilder, const nsDisplayItemGeometry* aGeometry,
+    nsRegion* aInvalidRegion) const {
+  const auto* geometry =
+      static_cast<const nsDisplayThemedBackgroundGeometry*>(aGeometry);
+
+  bool snap;
+  nsRect bounds = GetBounds(aBuilder, &snap);
+  nsRect positioningArea = GetPositioningArea();
+  if (!positioningArea.IsEqualInterior(geometry->mPositioningArea)) {
+    // Invalidate everything (both old and new painting areas).
+    aInvalidRegion->Or(bounds, geometry->mBounds);
+    return;
+  }
+  if (!bounds.IsEqualInterior(geometry->mBounds)) {
+    // Positioning area is unchanged, so invalidate just the change in the
+    // painting area.
+    aInvalidRegion->Xor(bounds, geometry->mBounds);
+  }
+  nsITheme* theme = StyleFrame()->PresContext()->Theme();
+  if (theme->WidgetAppearanceDependsOnWindowFocus(mAppearance) &&
+      IsWindowActive() != geometry->mWindowIsActive) {
+    aInvalidRegion->Or(*aInvalidRegion, bounds);
+  }
+}
+
+nsRect nsDisplayThemedBackground::GetBounds(nsDisplayListBuilder* aBuilder,
+                                            bool* aSnap) const {
+  *aSnap = true;
+  return mBounds;
+}
+
+nsRect nsDisplayThemedBackground::GetBoundsInternal() {
+  nsPresContext* presContext = mFrame->PresContext();
+
+  nsRect r = mBackgroundRect - ToReferenceFrame();
+  presContext->Theme()->GetWidgetOverflow(
+      presContext->DeviceContext(), mFrame,
+      mFrame->StyleDisplay()->EffectiveAppearance(), &r);
+  return r + ToReferenceFrame();
+}
+
+#if defined(MOZ_REFLOW_PERF_DSP) && defined(MOZ_REFLOW_PERF)
+void nsDisplayReflowCount::Paint(nsDisplayListBuilder* aBuilder,
+                                 gfxContext* aCtx) {
+  mFrame->PresShell()->PaintCount(mFrameName, aCtx, mFrame->PresContext(),
+                                  mFrame, ToReferenceFrame(), mColor);
+}
+#endif
+
+bool nsDisplayBackgroundColor::CanApplyOpacity(
+    WebRenderLayerManager* aManager, nsDisplayListBuilder* aBuilder) const {
+  // Don't apply opacity if the background color is animated since the color is
+  // going to be changed on the compositor.
+  return !EffectCompositor::HasAnimationsForCompositor(
+      mFrame, DisplayItemType::TYPE_BACKGROUND_COLOR);
+}
+
+bool nsDisplayBackgroundColor::CreateWebRenderCommands(
+    wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+    const StackingContextHelper& aSc, RenderRootStateManager* aManager,
+    nsDisplayListBuilder* aDisplayListBuilder) {
+  gfx::sRGBColor color = mColor;
+  color.a *= aBuilder.GetInheritedOpacity();
+
+  if (color == sRGBColor() &&
+      !EffectCompositor::HasAnimationsForCompositor(
+          mFrame, DisplayItemType::TYPE_BACKGROUND_COLOR)) {
+    return true;
+  }
+
+  if (HasBackgroundClipText()) {
+    return false;
+  }
+
+  uint64_t animationsId = 0;
+  // We don't support background-color animations on table elements yet.
+  if (GetType() == DisplayItemType::TYPE_BACKGROUND_COLOR) {
+    animationsId =
+        AddAnimationsForWebRender(this, aManager, aDisplayListBuilder);
+  }
+
+  LayoutDeviceRect bounds = LayoutDeviceRect::FromAppUnits(
+      mBackgroundRect, mFrame->PresContext()->AppUnitsPerDevPixel());
+  wr::LayoutRect r = wr::ToLayoutRect(bounds);
+
+  if (animationsId) {
+    wr::WrAnimationProperty prop{
+        wr::WrAnimationType::BackgroundColor,
+        animationsId,
+    };
+    aBuilder.PushRectWithAnimation(r, r, !BackfaceIsHidden(),
+                                   wr::ToColorF(ToDeviceColor(color)), &prop);
+  } else {
+    aBuilder.StartGroup(this);
+    aBuilder.PushRect(r, r, !BackfaceIsHidden(), false, false,
+                      wr::ToColorF(ToDeviceColor(color)));
+    aBuilder.FinishGroup();
+  }
+
+  return true;
+}
+
+void nsDisplayBackgroundColor::PaintWithClip(nsDisplayListBuilder* aBuilder,
+                                             gfxContext* aCtx,
+                                             const DisplayItemClip& aClip) {
+  MOZ_ASSERT(!HasBackgroundClipText());
+
+  if (mColor == sRGBColor()) {
+    return;
+  }
+
+  nsRect fillRect = mBackgroundRect;
+  if (aClip.HasClip()) {
+    fillRect.IntersectRect(fillRect, aClip.GetClipRect());
+  }
+
+  DrawTarget* dt = aCtx->GetDrawTarget();
+  int32_t A2D = mFrame->PresContext()->AppUnitsPerDevPixel();
+  Rect bounds = ToRect(nsLayoutUtils::RectToGfxRect(fillRect, A2D));
+  MaybeSnapToDevicePixels(bounds, *dt);
+  ColorPattern fill(ToDeviceColor(mColor));
+
+  if (aClip.GetRoundedRectCount()) {
+    MOZ_ASSERT(aClip.GetRoundedRectCount() == 1);
+
+    AutoTArray<DisplayItemClip::RoundedRect, 1> roundedRect;
+    aClip.AppendRoundedRects(&roundedRect);
+
+    bool pushedClip = false;
+    if (!fillRect.Contains(roundedRect[0].mRect)) {
+      dt->PushClipRect(bounds);
+      pushedClip = true;
+    }
+
+    RectCornerRadii pixelRadii;
+    nsCSSRendering::ComputePixelRadii(roundedRect[0].mRadii, A2D, &pixelRadii);
+    dt->FillRoundedRect(
+        RoundedRect(NSRectToSnappedRect(roundedRect[0].mRect, A2D, *dt),
+                    pixelRadii),
+        fill);
+    if (pushedClip) {
+      dt->PopClip();
+    }
+  } else {
+    dt->FillRect(bounds, fill);
+  }
+}
+
+void nsDisplayBackgroundColor::Paint(nsDisplayListBuilder* aBuilder,
+                                     gfxContext* aCtx) {
+  if (mColor == sRGBColor()) {
+    return;
+  }
+
+#if 0
+  // See https://bugzilla.mozilla.org/show_bug.cgi?id=1148418#c21 for why this
+  // results in a precision induced rounding issue that makes the rect one
+  // pixel shorter in rare cases. Disabled in favor of the old code for now.
+  // Note that the pref layout.css.devPixelsPerPx needs to be set to 1 to
+  // reproduce the bug.
+  //
+  // TODO:
+  // This new path does not include support for background-clip:text; need to
+  // be fixed if/when we switch to this new code path.
+
+  DrawTarget& aDrawTarget = *aCtx->GetDrawTarget();
+
+  Rect rect = NSRectToSnappedRect(mBackgroundRect,
+                                  mFrame->PresContext()->AppUnitsPerDevPixel(),
+                                  aDrawTarget);
+  ColorPattern color(ToDeviceColor(mColor));
+  aDrawTarget.FillRect(rect, color);
+#else
+  gfxContext* ctx = aCtx;
+  gfxRect bounds = nsLayoutUtils::RectToGfxRect(
+      mBackgroundRect, mFrame->PresContext()->AppUnitsPerDevPixel());
+
+  if (HasBackgroundClipText()) {
+    if (!GenerateAndPushTextMask(mFrame, aCtx, mBackgroundRect, aBuilder)) {
+      return;
+    }
+
+    ctx->SetColor(mColor);
+    ctx->NewPath();
+    ctx->SnappedRectangle(bounds);
+    ctx->Fill();
+    ctx->PopGroupAndBlend();
+    return;
+  }
+
+  ctx->SetColor(mColor);
+  ctx->NewPath();
+  ctx->SnappedRectangle(bounds);
+  ctx->Fill();
+#endif
+}
+
+nsRegion nsDisplayBackgroundColor::GetOpaqueRegion(
+    nsDisplayListBuilder* aBuilder, bool* aSnap) const {
+  *aSnap = false;
+
+  if (mColor.a != 1 ||
+      // Even if the current alpha channel is 1, we treat this item as if it's
+      // non-opaque if there is a background-color animation since the animation
+      // might change the alpha channel.
+      EffectCompositor::HasAnimationsForCompositor(
+          mFrame, DisplayItemType::TYPE_BACKGROUND_COLOR)) {
+    return nsRegion();
+  }
+
+  if (!mHasStyle || HasBackgroundClipText()) {
+    return nsRegion();
+  }
+
+  *aSnap = true;
+  return GetInsideClipRect(this, mBottomLayerClip, mBackgroundRect,
+                           mBackgroundRect);
+}
+
+Maybe<nscolor> nsDisplayBackgroundColor::IsUniform(
+    nsDisplayListBuilder* aBuilder) const {
+  return Some(mColor.ToABGR());
+}
+
+void nsDisplayBackgroundColor::HitTest(nsDisplayListBuilder* aBuilder,
+                                       const nsRect& aRect,
+                                       HitTestState* aState,
+                                       nsTArray<nsIFrame*>* aOutFrames) {
+  if (!RoundedBorderIntersectsRect(mFrame, ToReferenceFrame(), aRect)) {
+    // aRect doesn't intersect our border-radius curve.
+    return;
+  }
+
+  aOutFrames->AppendElement(mFrame);
+}
+
+void nsDisplayBackgroundColor::WriteDebugInfo(std::stringstream& aStream) {
+  aStream << " (rgba " << mColor.r << "," << mColor.g << "," << mColor.b << ","
+          << mColor.a << ")";
+  aStream << " backgroundRect" << mBackgroundRect;
+}
+
+nsRect nsDisplayOutline::GetBounds(nsDisplayListBuilder* aBuilder,
+                                   bool* aSnap) const {
+  *aSnap = false;
+  return mFrame->InkOverflowRectRelativeToSelf() + ToReferenceFrame();
+}
+
+nsRect nsDisplayOutline::GetInnerRect() const {
+  if (nsRect* savedOutlineInnerRect =
+          mFrame->GetProperty(nsIFrame::OutlineInnerRectProperty())) {
+    return *savedOutlineInnerRect;
+  }
+  return mFrame->GetRectRelativeToSelf();
+}
+
+void nsDisplayOutline::Paint(nsDisplayListBuilder* aBuilder, gfxContext* aCtx) {
+  // TODO join outlines together
+  MOZ_ASSERT(mFrame->StyleOutline()->ShouldPaintOutline(),
+             "Should have not created a nsDisplayOutline!");
+
+  nsRect rect = GetInnerRect() + ToReferenceFrame();
+  nsPresContext* pc = mFrame->PresContext();
+  if (IsThemedOutline()) {
+    rect.Inflate(mFrame->StyleOutline()->mOutlineOffset.ToAppUnits());
+    pc->Theme()->DrawWidgetBackground(aCtx, mFrame,
+                                      StyleAppearance::FocusOutline, rect,
+                                      GetPaintRect(aBuilder, aCtx));
+    return;
+  }
+
+  nsCSSRendering::PaintNonThemedOutline(
+      pc, *aCtx, mFrame, GetPaintRect(aBuilder, aCtx), rect, mFrame->Style());
+}
+
+bool nsDisplayOutline::IsThemedOutline() const {
+#ifdef DEBUG
+  nsPresContext* pc = mFrame->PresContext();
+  MOZ_ASSERT(
+      pc->Theme()->ThemeSupportsWidget(pc, mFrame,
+                                       StyleAppearance::FocusOutline),
+      "All of our supported platforms have support for themed focus-outlines");
+#endif
+  return mFrame->StyleOutline()->mOutlineStyle.IsAuto();
+}
+
+bool nsDisplayOutline::CreateWebRenderCommands(
+    wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+    const StackingContextHelper& aSc, RenderRootStateManager* aManager,
+    nsDisplayListBuilder* aDisplayListBuilder) {
+  nsPresContext* pc = mFrame->PresContext();
+  nsRect rect = GetInnerRect() + ToReferenceFrame();
+  if (IsThemedOutline()) {
+    rect.Inflate(mFrame->StyleOutline()->mOutlineOffset.ToAppUnits());
+    return pc->Theme()->CreateWebRenderCommandsForWidget(
+        aBuilder, aResources, aSc, aManager, mFrame,
+        StyleAppearance::FocusOutline, rect);
+  }
+
+  bool dummy;
+  Maybe<nsCSSBorderRenderer> borderRenderer =
+      nsCSSRendering::CreateBorderRendererForNonThemedOutline(
+          pc, /* aDrawTarget = */ nullptr, mFrame,
+          GetBounds(aDisplayListBuilder, &dummy), rect, mFrame->Style());
+
+  if (!borderRenderer) {
+    // No border renderer means "there is no outline".
+    // Paint nothing and return success.
+    return true;
+  }
+
+  borderRenderer->CreateWebRenderCommands(this, aBuilder, aResources, aSc);
+  return true;
+}
+
+bool nsDisplayOutline::HasRadius() const {
+  const auto& radius = mFrame->StyleBorder()->mBorderRadius;
+  return !nsLayoutUtils::HasNonZeroCorner(radius);
+}
+
+bool nsDisplayOutline::IsInvisibleInRect(const nsRect& aRect) const {
+  const nsStyleOutline* outline = mFrame->StyleOutline();
+  nsRect borderBox(ToReferenceFrame(), mFrame->GetSize());
+  if (borderBox.Contains(aRect) && !HasRadius() &&
+      outline->mOutlineOffset.ToCSSPixels() >= 0.0f) {
+    // aRect is entirely inside the border-rect, and the outline isn't rendered
+    // inside the border-rect, so the outline is not visible.
+    return true;
+  }
+  return false;
+}
+
+void nsDisplayEventReceiver::HitTest(nsDisplayListBuilder* aBuilder,
+                                     const nsRect& aRect, HitTestState* aState,
+                                     nsTArray<nsIFrame*>* aOutFrames) {
+  if (!RoundedBorderIntersectsRect(mFrame, ToReferenceFrame(), aRect)) {
+    // aRect doesn't intersect our border-radius curve.
+    return;
+  }
+
+  aOutFrames->AppendElement(mFrame);
+}
+
+bool nsDisplayCompositorHitTestInfo::CreateWebRenderCommands(
+    wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+    const StackingContextHelper& aSc, RenderRootStateManager* aManager,
+    nsDisplayListBuilder* aDisplayListBuilder) {
+  return true;
+}
+
+int32_t nsDisplayCompositorHitTestInfo::ZIndex() const {
+  return mOverrideZIndex ? *mOverrideZIndex : nsDisplayItem::ZIndex();
+}
+
+void nsDisplayCompositorHitTestInfo::SetOverrideZIndex(int32_t aZIndex) {
+  mOverrideZIndex = Some(aZIndex);
+}
+
+nsDisplayCaret::nsDisplayCaret(nsDisplayListBuilder* aBuilder,
+                               nsIFrame* aCaretFrame)
+    : nsPaintedDisplayItem(aBuilder, aCaretFrame),
+      mCaret(aBuilder->GetCaret()),
+      mBounds(aBuilder->GetCaretRect() + ToReferenceFrame()) {
+  MOZ_COUNT_CTOR(nsDisplayCaret);
+  // The presence of a caret doesn't change the overflow rect
+  // of the owning frame, so the normal building rect might not
+  // include the caret at all. We use MarkFrameForDisplay to ensure
+  // we build this item, and here we override the building rect
+  // to cover the pixels we're going to draw.
+  SetBuildingRect(mBounds);
+}
+
+#ifdef NS_BUILD_REFCNT_LOGGING
+nsDisplayCaret::~nsDisplayCaret() { MOZ_COUNT_DTOR(nsDisplayCaret); }
+#endif
+
+nsRect nsDisplayCaret::GetBounds(nsDisplayListBuilder* aBuilder,
+                                 bool* aSnap) const {
+  *aSnap = true;
+  // The caret returns a rect in the coordinates of mFrame.
+  return mBounds;
+}
+
+void nsDisplayCaret::Paint(nsDisplayListBuilder* aBuilder, gfxContext* aCtx) {
+  // Note: Because we exist, we know that the caret is visible, so we don't
+  // need to check for the caret's visibility.
+  mCaret->PaintCaret(*aCtx->GetDrawTarget(), mFrame, ToReferenceFrame());
+}
+
+bool nsDisplayCaret::CreateWebRenderCommands(
+    wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+    const StackingContextHelper& aSc, RenderRootStateManager* aManager,
+    nsDisplayListBuilder* aDisplayListBuilder) {
+  using namespace layers;
+  nsRect caretRect;
+  nsRect hookRect;
+  nscolor caretColor;
+  nsIFrame* frame =
+      mCaret->GetPaintGeometry(&caretRect, &hookRect, &caretColor);
+  MOZ_ASSERT(frame == mFrame, "We're referring different frame");
+  if (!frame) {
+    return true;
+  }
+
+  int32_t appUnitsPerDevPixel = frame->PresContext()->AppUnitsPerDevPixel();
+  gfx::DeviceColor color = ToDeviceColor(caretColor);
+  LayoutDeviceRect devCaretRect = LayoutDeviceRect::FromAppUnits(
+      caretRect + ToReferenceFrame(), appUnitsPerDevPixel);
+  LayoutDeviceRect devHookRect = LayoutDeviceRect::FromAppUnits(
+      hookRect + ToReferenceFrame(), appUnitsPerDevPixel);
+
+  wr::LayoutRect caret = wr::ToLayoutRect(devCaretRect);
+  wr::LayoutRect hook = wr::ToLayoutRect(devHookRect);
+
+  // Note, WR will pixel snap anything that is layout aligned.
+  aBuilder.PushRect(caret, caret, !BackfaceIsHidden(), false, false,
+                    wr::ToColorF(color));
+
+  if (!devHookRect.IsEmpty()) {
+    aBuilder.PushRect(hook, hook, !BackfaceIsHidden(), false, false,
+                      wr::ToColorF(color));
+  }
+  return true;
+}
+
+nsDisplayBorder::nsDisplayBorder(nsDisplayListBuilder* aBuilder,
+                                 nsIFrame* aFrame)
+    : nsPaintedDisplayItem(aBuilder, aFrame) {
+  MOZ_COUNT_CTOR(nsDisplayBorder);
+
+  mBounds = CalculateBounds<nsRect>(*mFrame->StyleBorder());
+}
+
+bool nsDisplayBorder::IsInvisibleInRect(const nsRect& aRect) const {
+  nsRect paddingRect = GetPaddingRect();
+  const nsStyleBorder* styleBorder;
+  if (paddingRect.Contains(aRect) &&
+      !(styleBorder = mFrame->StyleBorder())->IsBorderImageSizeAvailable() &&
+      !nsLayoutUtils::HasNonZeroCorner(styleBorder->mBorderRadius)) {
+    // aRect is entirely inside the content rect, and no part
+    // of the border is rendered inside the content rect, so we are not
+    // visible
+    // Skip this if there's a border-image (which draws a background
+    // too) or if there is a border-radius (which makes the border draw
+    // further in).
+    return true;
+  }
+
+  return false;
+}
+
+nsDisplayItemGeometry* nsDisplayBorder::AllocateGeometry(
+    nsDisplayListBuilder* aBuilder) {
+  return new nsDisplayBorderGeometry(this, aBuilder);
+}
+
+void nsDisplayBorder::ComputeInvalidationRegion(
+    nsDisplayListBuilder* aBuilder, const nsDisplayItemGeometry* aGeometry,
+    nsRegion* aInvalidRegion) const {
+  const auto* geometry = static_cast<const nsDisplayBorderGeometry*>(aGeometry);
+  bool snap;
+
+  if (!geometry->mBounds.IsEqualInterior(GetBounds(aBuilder, &snap))) {
+    // We can probably get away with only invalidating the difference
+    // between the border and padding rects, but the XUL ui at least
+    // is apparently painting a background with this?
+    aInvalidRegion->Or(GetBounds(aBuilder, &snap), geometry->mBounds);
+  }
+}
+
+bool nsDisplayBorder::CreateWebRenderCommands(
+    wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+    const StackingContextHelper& aSc, RenderRootStateManager* aManager,
+    nsDisplayListBuilder* aDisplayListBuilder) {
+  nsRect rect = nsRect(ToReferenceFrame(), mFrame->GetSize());
+
+  ImgDrawResult drawResult = nsCSSRendering::CreateWebRenderCommandsForBorder(
+      this, mFrame, rect, aBuilder, aResources, aSc, aManager,
+      aDisplayListBuilder);
+
+  if (drawResult == ImgDrawResult::NOT_SUPPORTED) {
+    return false;
+  }
+  return true;
+};
+
+void nsDisplayBorder::Paint(nsDisplayListBuilder* aBuilder, gfxContext* aCtx) {
+  nsPoint offset = ToReferenceFrame();
+
+  PaintBorderFlags flags = aBuilder->ShouldSyncDecodeImages()
+                               ? PaintBorderFlags::SyncDecodeImages
+                               : PaintBorderFlags();
+
+  Unused << nsCSSRendering::PaintBorder(
+      mFrame->PresContext(), *aCtx, mFrame, GetPaintRect(aBuilder, aCtx),
+      nsRect(offset, mFrame->GetSize()), mFrame->Style(), flags,
+      mFrame->GetSkipSides());
+}
+
+nsRect nsDisplayBorder::GetBounds(nsDisplayListBuilder* aBuilder,
+                                  bool* aSnap) const {
+  *aSnap = true;
+  return mBounds;
+}
+
+void nsDisplayBoxShadowOuter::Paint(nsDisplayListBuilder* aBuilder,
+                                    gfxContext* aCtx) {
+  nsPoint offset = ToReferenceFrame();
+  nsRect borderRect = mFrame->VisualBorderRectRelativeToSelf() + offset;
+  nsPresContext* presContext = mFrame->PresContext();
+
+  AUTO_PROFILER_LABEL("nsDisplayBoxShadowOuter::Paint", GRAPHICS);
+
+  nsCSSRendering::PaintBoxShadowOuter(presContext, *aCtx, mFrame, borderRect,
+                                      GetPaintRect(aBuilder, aCtx), 1.0f);
+}
+
+nsRect nsDisplayBoxShadowOuter::GetBounds(nsDisplayListBuilder* aBuilder,
+                                          bool* aSnap) const {
+  *aSnap = false;
+  return mBounds;
+}
+
+nsRect nsDisplayBoxShadowOuter::GetBoundsInternal() {
+  return nsLayoutUtils::GetBoxShadowRectForFrame(mFrame, mFrame->GetSize()) +
+         ToReferenceFrame();
+}
+
+bool nsDisplayBoxShadowOuter::IsInvisibleInRect(const nsRect& aRect) const {
+  nsPoint origin = ToReferenceFrame();
+  nsRect frameRect(origin, mFrame->GetSize());
+  if (!frameRect.Contains(aRect)) {
+    return false;
+  }
+
+  // the visible region is entirely inside the border-rect, and box shadows
+  // never render within the border-rect (unless there's a border radius).
+  nscoord twipsRadii[8];
+  bool hasBorderRadii = mFrame->GetBorderRadii(twipsRadii);
+  if (!hasBorderRadii) {
+    return true;
+  }
+
+  return RoundedRectContainsRect(frameRect, twipsRadii, aRect);
+}
+
+bool nsDisplayBoxShadowOuter::CanBuildWebRenderDisplayItems() const {
+  auto shadows = mFrame->StyleEffects()->mBoxShadow.AsSpan();
+  if (shadows.IsEmpty()) {
+    return false;
+  }
+
+  bool hasBorderRadius;
+  // We don't support native themed things yet like box shadows around
+  // input buttons.
+  //
+  // TODO(emilio): The non-native theme could provide the right rect+radius
+  // instead relatively painlessly, if we find this causes performance issues or
+  // what not.
+  return !nsCSSRendering::HasBoxShadowNativeTheme(mFrame, hasBorderRadius);
+}
+
+bool nsDisplayBoxShadowOuter::CreateWebRenderCommands(
+    wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+    const StackingContextHelper& aSc, RenderRootStateManager* aManager,
+    nsDisplayListBuilder* aDisplayListBuilder) {
+  if (!CanBuildWebRenderDisplayItems()) {
+    return false;
+  }
+
+  int32_t appUnitsPerDevPixel = mFrame->PresContext()->AppUnitsPerDevPixel();
+  nsPoint offset = ToReferenceFrame();
+  nsRect borderRect = mFrame->VisualBorderRectRelativeToSelf() + offset;
+  bool snap;
+  nsRect bounds = GetBounds(aDisplayListBuilder, &snap);
+
+  bool hasBorderRadius;
+  bool nativeTheme =
+      nsCSSRendering::HasBoxShadowNativeTheme(mFrame, hasBorderRadius);
+
+  // Don't need the full size of the shadow rect like we do in
+  // nsCSSRendering since WR takes care of calculations for blur
+  // and spread radius.
+  nsRect frameRect =
+      nsCSSRendering::GetShadowRect(borderRect, nativeTheme, mFrame);
+
+  RectCornerRadii borderRadii;
+  if (hasBorderRadius) {
+    hasBorderRadius = nsCSSRendering::GetBorderRadii(frameRect, borderRect,
+                                                     mFrame, borderRadii);
+  }
+
+  // Everything here is in app units, change to device units.
+  LayoutDeviceRect clipRect =
+      LayoutDeviceRect::FromAppUnits(bounds, appUnitsPerDevPixel);
+  auto shadows = mFrame->StyleEffects()->mBoxShadow.AsSpan();
+  MOZ_ASSERT(!shadows.IsEmpty());
+
+  for (const auto& shadow : Reversed(shadows)) {
+    if (shadow.inset) {
+      continue;
+    }
+
+    float blurRadius =
+        float(shadow.base.blur.ToAppUnits()) / float(appUnitsPerDevPixel);
+    gfx::sRGBColor shadowColor = nsCSSRendering::GetShadowColor(
+        shadow.base, mFrame, aBuilder.GetInheritedOpacity());
+
+    // We don't move the shadow rect here since WR does it for us
+    // Now translate everything to device pixels.
+    const nsRect& shadowRect = frameRect;
+    LayoutDevicePoint shadowOffset = LayoutDevicePoint::FromAppUnits(
+        nsPoint(shadow.base.horizontal.ToAppUnits(),
+                shadow.base.vertical.ToAppUnits()),
+        appUnitsPerDevPixel);
+
+    LayoutDeviceRect deviceBox =
+        LayoutDeviceRect::FromAppUnits(shadowRect, appUnitsPerDevPixel);
+    wr::LayoutRect deviceBoxRect = wr::ToLayoutRect(deviceBox);
+    wr::LayoutRect deviceClipRect = wr::ToLayoutRect(clipRect);
+
+    LayoutDeviceSize zeroSize;
+    wr::BorderRadius borderRadius =
+        wr::ToBorderRadius(zeroSize, zeroSize, zeroSize, zeroSize);
+    if (hasBorderRadius) {
+      borderRadius = wr::ToBorderRadius(
+          LayoutDeviceSize::FromUnknownSize(borderRadii.TopLeft()),
+          LayoutDeviceSize::FromUnknownSize(borderRadii.TopRight()),
+          LayoutDeviceSize::FromUnknownSize(borderRadii.BottomLeft()),
+          LayoutDeviceSize::FromUnknownSize(borderRadii.BottomRight()));
+    }
+
+    float spreadRadius =
+        float(shadow.spread.ToAppUnits()) / float(appUnitsPerDevPixel);
+
+    aBuilder.PushBoxShadow(deviceBoxRect, deviceClipRect, !BackfaceIsHidden(),
+                           deviceBoxRect, wr::ToLayoutVector2D(shadowOffset),
+                           wr::ToColorF(ToDeviceColor(shadowColor)), blurRadius,
+                           spreadRadius, borderRadius,
+                           wr::BoxShadowClipMode::Outset);
+  }
+
+  return true;
+}
+
+void nsDisplayBoxShadowOuter::ComputeInvalidationRegion(
+    nsDisplayListBuilder* aBuilder, const nsDisplayItemGeometry* aGeometry,
+    nsRegion* aInvalidRegion) const {
+  const auto* geometry =
+      static_cast<const nsDisplayItemGenericGeometry*>(aGeometry);
+  bool snap;
+  if (!geometry->mBounds.IsEqualInterior(GetBounds(aBuilder, &snap)) ||
+      !geometry->mBorderRect.IsEqualInterior(GetBorderRect())) {
+    nsRegion oldShadow, newShadow;
+    nscoord dontCare[8];
+    bool hasBorderRadius = mFrame->GetBorderRadii(dontCare);
+    if (hasBorderRadius) {
+      // If we have rounded corners then we need to invalidate the frame area
+      // too since we paint into it.
+      oldShadow = geometry->mBounds;
+      newShadow = GetBounds(aBuilder, &snap);
+    } else {
+      oldShadow.Sub(geometry->mBounds, geometry->mBorderRect);
+      newShadow.Sub(GetBounds(aBuilder, &snap), GetBorderRect());
+    }
+    aInvalidRegion->Or(oldShadow, newShadow);
+  }
+}
+
+void nsDisplayBoxShadowInner::Paint(nsDisplayListBuilder* aBuilder,
+                                    gfxContext* aCtx) {
+  nsPoint offset = ToReferenceFrame();
+  nsRect borderRect = nsRect(offset, mFrame->GetSize());
+  nsPresContext* presContext = mFrame->PresContext();
+
+  AUTO_PROFILER_LABEL("nsDisplayBoxShadowInner::Paint", GRAPHICS);
+
+  nsCSSRendering::PaintBoxShadowInner(presContext, *aCtx, mFrame, borderRect);
+}
+
+bool nsDisplayBoxShadowInner::CanCreateWebRenderCommands(
+    nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+    const nsPoint& aReferenceOffset) {
+  auto shadows = aFrame->StyleEffects()->mBoxShadow.AsSpan();
+  if (shadows.IsEmpty()) {
+    // Means we don't have to paint anything
+    return true;
+  }
+
+  bool hasBorderRadius;
+  bool nativeTheme =
+      nsCSSRendering::HasBoxShadowNativeTheme(aFrame, hasBorderRadius);
+
+  // We don't support native themed things yet like box shadows around
+  // input buttons.
+  return !nativeTheme;
+}
+
+/* static */
+void nsDisplayBoxShadowInner::CreateInsetBoxShadowWebRenderCommands(
+    wr::DisplayListBuilder& aBuilder, const StackingContextHelper& aSc,
+    nsRect& aVisibleRect, nsIFrame* aFrame, const nsRect& aBorderRect) {
+  if (!nsCSSRendering::ShouldPaintBoxShadowInner(aFrame)) {
+    return;
+  }
+
+  int32_t appUnitsPerDevPixel = aFrame->PresContext()->AppUnitsPerDevPixel();
+
+  auto shadows = aFrame->StyleEffects()->mBoxShadow.AsSpan();
+
+  LayoutDeviceRect clipRect =
+      LayoutDeviceRect::FromAppUnits(aVisibleRect, appUnitsPerDevPixel);
+
+  for (const auto& shadow : Reversed(shadows)) {
+    if (!shadow.inset) {
+      continue;
+    }
+
+    nsRect shadowRect =
+        nsCSSRendering::GetBoxShadowInnerPaddingRect(aFrame, aBorderRect);
+    RectCornerRadii innerRadii;
+    nsCSSRendering::GetShadowInnerRadii(aFrame, aBorderRect, innerRadii);
+
+    // Now translate everything to device pixels.
+    LayoutDeviceRect deviceBoxRect =
+        LayoutDeviceRect::FromAppUnits(shadowRect, appUnitsPerDevPixel);
+    wr::LayoutRect deviceClipRect = wr::ToLayoutRect(clipRect);
+    sRGBColor shadowColor =
+        nsCSSRendering::GetShadowColor(shadow.base, aFrame, 1.0);
+
+    LayoutDevicePoint shadowOffset = LayoutDevicePoint::FromAppUnits(
+        nsPoint(shadow.base.horizontal.ToAppUnits(),
+                shadow.base.vertical.ToAppUnits()),
+        appUnitsPerDevPixel);
+
+    float blurRadius =
+        float(shadow.base.blur.ToAppUnits()) / float(appUnitsPerDevPixel);
+
+    wr::BorderRadius borderRadius = wr::ToBorderRadius(
+        LayoutDeviceSize::FromUnknownSize(innerRadii.TopLeft()),
+        LayoutDeviceSize::FromUnknownSize(innerRadii.TopRight()),
+        LayoutDeviceSize::FromUnknownSize(innerRadii.BottomLeft()),
+        LayoutDeviceSize::FromUnknownSize(innerRadii.BottomRight()));
+    // NOTE: Any spread radius > 0 will render nothing. WR Bug.
+    float spreadRadius =
+        float(shadow.spread.ToAppUnits()) / float(appUnitsPerDevPixel);
+
+    aBuilder.PushBoxShadow(
+        wr::ToLayoutRect(deviceBoxRect), deviceClipRect,
+        !aFrame->BackfaceIsHidden(), wr::ToLayoutRect(deviceBoxRect),
+        wr::ToLayoutVector2D(shadowOffset),
+        wr::ToColorF(ToDeviceColor(shadowColor)), blurRadius, spreadRadius,
+        borderRadius, wr::BoxShadowClipMode::Inset);
+  }
+}
+
+bool nsDisplayBoxShadowInner::CreateWebRenderCommands(
+    wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+    const StackingContextHelper& aSc, RenderRootStateManager* aManager,
+    nsDisplayListBuilder* aDisplayListBuilder) {
+  if (!CanCreateWebRenderCommands(aDisplayListBuilder, mFrame,
+                                  ToReferenceFrame())) {
+    return false;
+  }
+
+  bool snap;
+  nsRect visible = GetBounds(aDisplayListBuilder, &snap);
+  nsPoint offset = ToReferenceFrame();
+  nsRect borderRect = nsRect(offset, mFrame->GetSize());
+  nsDisplayBoxShadowInner::CreateInsetBoxShadowWebRenderCommands(
+      aBuilder, aSc, visible, mFrame, borderRect);
+
+  return true;
+}
+
+nsDisplayWrapList::nsDisplayWrapList(nsDisplayListBuilder* aBuilder,
+                                     nsIFrame* aFrame, nsDisplayList* aList)
+    : nsDisplayWrapList(aBuilder, aFrame, aList,
+                        aBuilder->CurrentActiveScrolledRoot(), false) {}
+
+nsDisplayWrapList::nsDisplayWrapList(
+    nsDisplayListBuilder* aBuilder, nsIFrame* aFrame, nsDisplayList* aList,
+    const ActiveScrolledRoot* aActiveScrolledRoot, bool aClearClipChain)
+    : nsPaintedDisplayItem(aBuilder, aFrame, aActiveScrolledRoot),
+      mList(aBuilder),
+      mFrameActiveScrolledRoot(aBuilder->CurrentActiveScrolledRoot()),
+      mOverrideZIndex(0),
+      mHasZIndexOverride(false),
+      mClearingClipChain(aClearClipChain) {
+  MOZ_COUNT_CTOR(nsDisplayWrapList);
+
+  mBaseBuildingRect = GetBuildingRect();
+
+  mListPtr = &mList;
+  mListPtr->AppendToTop(aList);
+  mOriginalClipChain = mClipChain;
+  nsDisplayWrapList::UpdateBounds(aBuilder);
+}
+
+nsDisplayWrapList::nsDisplayWrapList(nsDisplayListBuilder* aBuilder,
+                                     nsIFrame* aFrame, nsDisplayItem* aItem)
+    : nsPaintedDisplayItem(aBuilder, aFrame,
+                           aBuilder->CurrentActiveScrolledRoot()),
+      mList(aBuilder),
+      mOverrideZIndex(0),
+      mHasZIndexOverride(false) {
+  MOZ_COUNT_CTOR(nsDisplayWrapList);
+
+  mBaseBuildingRect = GetBuildingRect();
+
+  mListPtr = &mList;
+  mListPtr->AppendToTop(aItem);
+  mOriginalClipChain = mClipChain;
+  nsDisplayWrapList::UpdateBounds(aBuilder);
+
+  if (!aFrame || !aFrame->IsTransformed()) {
+    return;
+  }
+
+  // See the previous nsDisplayWrapList constructor
+  if (aItem->Frame() == aFrame) {
+    mToReferenceFrame = aItem->ToReferenceFrame();
+  }
+
+  nsRect visible = aBuilder->GetVisibleRect() +
+                   aBuilder->GetCurrentFrameOffsetToReferenceFrame();
+
+  SetBuildingRect(visible);
+}
+
+nsDisplayWrapList::~nsDisplayWrapList() { MOZ_COUNT_DTOR(nsDisplayWrapList); }
+
+void nsDisplayWrapList::HitTest(nsDisplayListBuilder* aBuilder,
+                                const nsRect& aRect, HitTestState* aState,
+                                nsTArray<nsIFrame*>* aOutFrames) {
+  mListPtr->HitTest(aBuilder, aRect, aState, aOutFrames);
+}
+
+nsRect nsDisplayWrapList::GetBounds(nsDisplayListBuilder* aBuilder,
+                                    bool* aSnap) const {
+  *aSnap = false;
+  return mBounds;
+}
+
+nsRegion nsDisplayWrapList::GetOpaqueRegion(nsDisplayListBuilder* aBuilder,
+                                            bool* aSnap) const {
+  *aSnap = false;
+  bool snap;
+  return ::mozilla::GetOpaqueRegion(aBuilder, GetChildren(),
+                                    GetBounds(aBuilder, &snap));
+}
+
+Maybe<nscolor> nsDisplayWrapList::IsUniform(
+    nsDisplayListBuilder* aBuilder) const {
+  // We could try to do something but let's conservatively just return Nothing.
+  return Nothing();
+}
+
+void nsDisplayWrapper::Paint(nsDisplayListBuilder* aBuilder, gfxContext* aCtx) {
+  NS_ERROR("nsDisplayWrapper should have been flattened away for painting");
+}
+
+nsRect nsDisplayWrapList::GetComponentAlphaBounds(
+    nsDisplayListBuilder* aBuilder) const {
+  return mListPtr->GetComponentAlphaBounds(aBuilder);
+}
+
+bool nsDisplayWrapList::CreateWebRenderCommandsNewClipListOption(
+    wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+    const StackingContextHelper& aSc, RenderRootStateManager* aManager,
+    nsDisplayListBuilder* aDisplayListBuilder, bool aNewClipList) {
+  aManager->CommandBuilder().CreateWebRenderCommandsFromDisplayList(
+      GetChildren(), this, aDisplayListBuilder, aSc, aBuilder, aResources,
+      aNewClipList);
+  return true;
+}
+
+static nsresult WrapDisplayList(nsDisplayListBuilder* aBuilder,
+                                nsIFrame* aFrame, nsDisplayList* aList,
+                                nsDisplayItemWrapper* aWrapper) {
+  if (!aList->GetTop()) {
+    return NS_OK;
+  }
+  nsDisplayItem* item = aWrapper->WrapList(aBuilder, aFrame, aList);
+  if (!item) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+  // aList was emptied
+  aList->AppendToTop(item);
+  return NS_OK;
+}
+
+static nsresult WrapEachDisplayItem(nsDisplayListBuilder* aBuilder,
+                                    nsDisplayList* aList,
+                                    nsDisplayItemWrapper* aWrapper) {
+  for (nsDisplayItem* item : aList->TakeItems()) {
+    item = aWrapper->WrapItem(aBuilder, item);
+    if (!item) {
+      return NS_ERROR_OUT_OF_MEMORY;
+    }
+    aList->AppendToTop(item);
+  }
+  // aList was emptied
+  return NS_OK;
+}
+
+nsresult nsDisplayItemWrapper::WrapLists(nsDisplayListBuilder* aBuilder,
+                                         nsIFrame* aFrame,
+                                         const nsDisplayListSet& aIn,
+                                         const nsDisplayListSet& aOut) {
+  nsresult rv = WrapListsInPlace(aBuilder, aFrame, aIn);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  if (&aOut == &aIn) {
+    return NS_OK;
+  }
+  aOut.BorderBackground()->AppendToTop(aIn.BorderBackground());
+  aOut.BlockBorderBackgrounds()->AppendToTop(aIn.BlockBorderBackgrounds());
+  aOut.Floats()->AppendToTop(aIn.Floats());
+  aOut.Content()->AppendToTop(aIn.Content());
+  aOut.PositionedDescendants()->AppendToTop(aIn.PositionedDescendants());
+  aOut.Outlines()->AppendToTop(aIn.Outlines());
+  return NS_OK;
+}
+
+nsresult nsDisplayItemWrapper::WrapListsInPlace(
+    nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+    const nsDisplayListSet& aLists) {
+  nsresult rv;
+  if (WrapBorderBackground()) {
+    // Our border-backgrounds are in-flow
+    rv = WrapDisplayList(aBuilder, aFrame, aLists.BorderBackground(), this);
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+  // Our block border-backgrounds are in-flow
+  rv = WrapDisplayList(aBuilder, aFrame, aLists.BlockBorderBackgrounds(), this);
+  NS_ENSURE_SUCCESS(rv, rv);
+  // The floats are not in flow
+  rv = WrapEachDisplayItem(aBuilder, aLists.Floats(), this);
+  NS_ENSURE_SUCCESS(rv, rv);
+  // Our child content is in flow
+  rv = WrapDisplayList(aBuilder, aFrame, aLists.Content(), this);
+  NS_ENSURE_SUCCESS(rv, rv);
+  // The positioned descendants may not be in-flow
+  rv = WrapEachDisplayItem(aBuilder, aLists.PositionedDescendants(), this);
+  NS_ENSURE_SUCCESS(rv, rv);
+  // The outlines may not be in-flow
+  return WrapEachDisplayItem(aBuilder, aLists.Outlines(), this);
+}
+
+nsDisplayOpacity::nsDisplayOpacity(
+    nsDisplayListBuilder* aBuilder, nsIFrame* aFrame, nsDisplayList* aList,
+    const ActiveScrolledRoot* aActiveScrolledRoot, bool aForEventsOnly,
+    bool aNeedsActiveLayer, bool aWrapsBackdropFilter)
+    : nsDisplayWrapList(aBuilder, aFrame, aList, aActiveScrolledRoot, true),
+      mOpacity(aFrame->StyleEffects()->mOpacity),
+      mForEventsOnly(aForEventsOnly),
+      mNeedsActiveLayer(aNeedsActiveLayer),
+      mChildOpacityState(ChildOpacityState::Unknown),
+      mWrapsBackdropFilter(aWrapsBackdropFilter) {
+  MOZ_COUNT_CTOR(nsDisplayOpacity);
+}
+
+void nsDisplayOpacity::HitTest(nsDisplayListBuilder* aBuilder,
+                               const nsRect& aRect,
+                               nsDisplayItem::HitTestState* aState,
+                               nsTArray<nsIFrame*>* aOutFrames) {
+  AutoRestore<float> opacity(aState->mCurrentOpacity);
+  aState->mCurrentOpacity *= mOpacity;
+
+  // TODO(emilio): special-casing zero is a bit arbitrary... Maybe we should
+  // only consider fully opaque items? Or make this configurable somehow?
+  if (aBuilder->HitTestIsForVisibility() && mOpacity == 0.0f) {
+    return;
+  }
+  nsDisplayWrapList::HitTest(aBuilder, aRect, aState, aOutFrames);
+}
+
+nsRegion nsDisplayOpacity::GetOpaqueRegion(nsDisplayListBuilder* aBuilder,
+                                           bool* aSnap) const {
+  *aSnap = false;
+  // The only time where mOpacity == 1.0 should be when we have will-change.
+  // We could report this as opaque then but when the will-change value starts
+  // animating the element would become non opaque and could cause repaints.
+  return nsRegion();
+}
+
+void nsDisplayOpacity::Paint(nsDisplayListBuilder* aBuilder, gfxContext* aCtx) {
+  if (GetOpacity() == 0.0f) {
+    return;
+  }
+
+  if (GetOpacity() == 1.0f) {
+    GetChildren()->Paint(aBuilder, aCtx,
+                         mFrame->PresContext()->AppUnitsPerDevPixel());
+    return;
+  }
+
+  // TODO: Compute a bounds rect to pass to PushLayer for a smaller
+  // allocation.
+  aCtx->GetDrawTarget()->PushLayer(false, GetOpacity(), nullptr, gfx::Matrix());
+  GetChildren()->Paint(aBuilder, aCtx,
+                       mFrame->PresContext()->AppUnitsPerDevPixel());
+  aCtx->GetDrawTarget()->PopLayer();
+}
+
+/* static */
+bool nsDisplayOpacity::NeedsActiveLayer(nsDisplayListBuilder* aBuilder,
+                                        nsIFrame* aFrame) {
+  return EffectCompositor::HasAnimationsForCompositor(
+             aFrame, DisplayItemType::TYPE_OPACITY) ||
+         (ActiveLayerTracker::IsStyleAnimated(
+             aBuilder, aFrame, nsCSSPropertyIDSet::OpacityProperties()));
+}
+
+bool nsDisplayOpacity::CanApplyOpacity(WebRenderLayerManager* aManager,
+                                       nsDisplayListBuilder* aBuilder) const {
+  return !EffectCompositor::HasAnimationsForCompositor(
+      mFrame, DisplayItemType::TYPE_OPACITY);
+}
+
+// Only try folding our opacity down if we have at most |kOpacityMaxChildCount|
+// children that don't overlap and can all apply the opacity to themselves.
+static const size_t kOpacityMaxChildCount = 3;
+
+// |kOpacityMaxListSize| defines an early exit condition for opacity items that
+// are likely have more child items than |kOpacityMaxChildCount|.
+static const size_t kOpacityMaxListSize = kOpacityMaxChildCount * 2;
+
+/**
+ * Recursively iterates through |aList| and collects at most
+ * |kOpacityMaxChildCount| display item pointers to items that return true for
+ * CanApplyOpacity(). The item pointers are added to |aArray|.
+ *
+ * LayerEventRegions and WrapList items are ignored.
+ *
+ * We need to do this recursively, because the child display items might contain
+ * nested nsDisplayWrapLists.
+ *
+ * Returns false if there are more than |kOpacityMaxChildCount| items, or if an
+ * item that returns false for CanApplyOpacity() is encountered.
+ * Otherwise returns true.
+ */
+static bool CollectItemsWithOpacity(WebRenderLayerManager* aManager,
+                                    nsDisplayListBuilder* aBuilder,
+                                    nsDisplayList* aList,
+                                    nsTArray<nsPaintedDisplayItem*>& aArray) {
+  if (aList->Length() > kOpacityMaxListSize) {
+    // Exit early, since |aList| will likely contain more than
+    // |kOpacityMaxChildCount| items.
+    return false;
+  }
+
+  for (nsDisplayItem* i : *aList) {
+    const DisplayItemType type = i->GetType();
+
+    if (type == DisplayItemType::TYPE_COMPOSITOR_HITTEST_INFO) {
+      continue;
+    }
+
+    // Descend only into wraplists.
+    if (type == DisplayItemType::TYPE_WRAP_LIST ||
+        type == DisplayItemType::TYPE_CONTAINER) {
+      // The current display item has children, process them first.
+      if (!CollectItemsWithOpacity(aManager, aBuilder, i->GetChildren(),
+                                   aArray)) {
+        return false;
+      }
+
+      continue;
+    }
+
+    if (aArray.Length() == kOpacityMaxChildCount) {
+      return false;
+    }
+
+    auto* item = i->AsPaintedDisplayItem();
+    if (!item || !item->CanApplyOpacity(aManager, aBuilder)) {
+      return false;
+    }
+
+    aArray.AppendElement(item);
+  }
+
+  return true;
+}
+
+bool nsDisplayOpacity::CanApplyToChildren(WebRenderLayerManager* aManager,
+                                          nsDisplayListBuilder* aBuilder) {
+  if (mChildOpacityState == ChildOpacityState::Deferred) {
+    return false;
+  }
+
+  // Iterate through the child display list and copy at most
+  // |kOpacityMaxChildCount| child display item pointers to a temporary list.
+  AutoTArray<nsPaintedDisplayItem*, kOpacityMaxChildCount> items;
+  if (!CollectItemsWithOpacity(aManager, aBuilder, &mList, items)) {
+    mChildOpacityState = ChildOpacityState::Deferred;
+    return false;
+  }
+
+  struct {
+    nsPaintedDisplayItem* item{};
+    nsRect bounds;
+  } children[kOpacityMaxChildCount];
+
+  bool snap;
+  size_t childCount = 0;
+  for (nsPaintedDisplayItem* item : items) {
+    children[childCount].item = item;
+    children[childCount].bounds = item->GetBounds(aBuilder, &snap);
+    childCount++;
+  }
+
+  for (size_t i = 0; i < childCount; i++) {
+    for (size_t j = i + 1; j < childCount; j++) {
+      if (children[i].bounds.Intersects(children[j].bounds)) {
+        mChildOpacityState = ChildOpacityState::Deferred;
+        return false;
+      }
+    }
+  }
+
+  mChildOpacityState = ChildOpacityState::Applied;
+  return true;
+}
+
+/**
+ * Returns true if this nsDisplayOpacity contains only a filter or a mask item
+ * that has the same frame as the opacity item, and that supports painting with
+ * opacity. In this case the opacity item can be optimized away.
+ */
+bool nsDisplayOpacity::ApplyToMask() {
+  if (mList.Length() != 1) {
+    return false;
+  }
+
+  nsDisplayItem* item = mList.GetBottom();
+  if (item->Frame() != mFrame) {
+    // The effect item needs to have the same frame as the opacity item.
+    return false;
+  }
+
+  const DisplayItemType type = item->GetType();
+  if (type == DisplayItemType::TYPE_MASK) {
+    return true;
+  }
+
+  return false;
+}
+
+bool nsDisplayOpacity::CanApplyOpacityToChildren(
+    WebRenderLayerManager* aManager, nsDisplayListBuilder* aBuilder,
+    float aInheritedOpacity) {
+  if (mFrame->GetPrevContinuation() || mFrame->GetNextContinuation() ||
+      mFrame->HasAnyStateBits(NS_FRAME_PART_OF_IBSPLIT)) {
+    // If we've been split, then we might need to merge, so
+    // don't flatten us away.
+    return false;
+  }
+
+  if (mNeedsActiveLayer || mOpacity == 0.0) {
+    // If our opacity is zero then we'll discard all descendant display items
+    // except for layer event regions, so there's no point in doing this
+    // optimization (and if we do do it, then invalidations of those descendants
+    // might trigger repainting).
+    return false;
+  }
+
+  if (mList.IsEmpty()) {
+    return false;
+  }
+
+  // We can only flatten opacity items into a mask if we haven't
+  // already flattened an earlier ancestor, since the SVG code pulls the opacity
+  // from style directly, and won't know about the outer opacity value.
+  if (aInheritedOpacity == 1.0f && ApplyToMask()) {
+    MOZ_ASSERT(SVGIntegrationUtils::UsingEffectsForFrame(mFrame));
+    mChildOpacityState = ChildOpacityState::Applied;
+    return true;
+  }
+
+  // Return true if we successfully applied opacity to child items.
+  return CanApplyToChildren(aManager, aBuilder);
+}
+
+void nsDisplayOpacity::ComputeInvalidationRegion(
+    nsDisplayListBuilder* aBuilder, const nsDisplayItemGeometry* aGeometry,
+    nsRegion* aInvalidRegion) const {
+  const auto* geometry =
+      static_cast<const nsDisplayOpacityGeometry*>(aGeometry);
+
+  bool snap;
+  if (mOpacity != geometry->mOpacity) {
+    aInvalidRegion->Or(GetBounds(aBuilder, &snap), geometry->mBounds);
+  }
+}
+
+void nsDisplayOpacity::WriteDebugInfo(std::stringstream& aStream) {
+  aStream << " (opacity " << mOpacity << ", mChildOpacityState: ";
+  switch (mChildOpacityState) {
+    case ChildOpacityState::Unknown:
+      aStream << "Unknown";
+      break;
+    case ChildOpacityState::Applied:
+      aStream << "Applied";
+      break;
+    case ChildOpacityState::Deferred:
+      aStream << "Deferred";
+      break;
+    default:
+      break;
+  }
+
+  aStream << ")";
+}
+
+bool nsDisplayOpacity::CreateWebRenderCommands(
+    wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+    const StackingContextHelper& aSc, RenderRootStateManager* aManager,
+    nsDisplayListBuilder* aDisplayListBuilder) {
+  MOZ_ASSERT(mChildOpacityState != ChildOpacityState::Applied);
+  float oldOpacity = aBuilder.GetInheritedOpacity();
+  const DisplayItemClipChain* oldClipChain = aBuilder.GetInheritedClipChain();
+  aBuilder.SetInheritedOpacity(1.0f);
+  aBuilder.SetInheritedClipChain(nullptr);
+  float opacity = mOpacity * oldOpacity;
+  float* opacityForSC = &opacity;
+
+  uint64_t animationsId =
+      AddAnimationsForWebRender(this, aManager, aDisplayListBuilder);
+  wr::WrAnimationProperty prop{
+      wr::WrAnimationType::Opacity,
+      animationsId,
+  };
+
+  wr::StackingContextParams params;
+  params.animation = animationsId ? &prop : nullptr;
+  params.opacity = opacityForSC;
+  params.clip =
+      wr::WrStackingContextClip::ClipChain(aBuilder.CurrentClipChainId());
+  if (mWrapsBackdropFilter) {
+    params.flags |= wr::StackingContextFlags::WRAPS_BACKDROP_FILTER;
+  }
+  StackingContextHelper sc(aSc, GetActiveScrolledRoot(), mFrame, this, aBuilder,
+                           params);
+
+  aManager->CommandBuilder().CreateWebRenderCommandsFromDisplayList(
+      &mList, this, aDisplayListBuilder, sc, aBuilder, aResources);
+  aBuilder.SetInheritedOpacity(oldOpacity);
+  aBuilder.SetInheritedClipChain(oldClipChain);
+  return true;
+}
+
+nsDisplayBlendMode::nsDisplayBlendMode(
+    nsDisplayListBuilder* aBuilder, nsIFrame* aFrame, nsDisplayList* aList,
+    StyleBlend aBlendMode, const ActiveScrolledRoot* aActiveScrolledRoot,
+    const bool aIsForBackground)
+    : nsDisplayWrapList(aBuilder, aFrame, aList, aActiveScrolledRoot, true),
+      mBlendMode(aBlendMode),
+      mIsForBackground(aIsForBackground) {
+  MOZ_COUNT_CTOR(nsDisplayBlendMode);
+}
+
+nsRegion nsDisplayBlendMode::GetOpaqueRegion(nsDisplayListBuilder* aBuilder,
+                                             bool* aSnap) const {
+  *aSnap = false;
+  // We are never considered opaque
+  return nsRegion();
+}
+
+bool nsDisplayBlendMode::CreateWebRenderCommands(
+    wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+    const StackingContextHelper& aSc, RenderRootStateManager* aManager,
+    nsDisplayListBuilder* aDisplayListBuilder) {
+  wr::StackingContextParams params;
+  params.mix_blend_mode =
+      wr::ToMixBlendMode(nsCSSRendering::GetGFXBlendMode(mBlendMode));
+  params.clip =
+      wr::WrStackingContextClip::ClipChain(aBuilder.CurrentClipChainId());
+  StackingContextHelper sc(aSc, GetActiveScrolledRoot(), mFrame, this, aBuilder,
+                           params);
+
+  return nsDisplayWrapList::CreateWebRenderCommands(
+      aBuilder, aResources, sc, aManager, aDisplayListBuilder);
+}
+
+void nsDisplayBlendMode::Paint(nsDisplayListBuilder* aBuilder,
+                               gfxContext* aCtx) {
+  // This should be switched to use PushLayerWithBlend, once it's
+  // been implemented for all DrawTarget backends.
+  DrawTarget* dt = aCtx->GetDrawTarget();
+  int32_t appUnitsPerDevPixel = mFrame->PresContext()->AppUnitsPerDevPixel();
+  Rect rect = NSRectToRect(GetPaintRect(aBuilder, aCtx), appUnitsPerDevPixel);
+  rect.RoundOut();
+
+  // Create a temporary DrawTarget that is clipped to the area that
+  // we're going to draw to. This will include the same transform as
+  // is currently on |dt|.
+  RefPtr<DrawTarget> temp =
+      dt->CreateClippedDrawTarget(rect, SurfaceFormat::B8G8R8A8);
+  if (!temp) {
+    return;
+  }
+
+  RefPtr<gfxContext> ctx = gfxContext::CreatePreservingTransformOrNull(temp);
+
+  GetChildren()->Paint(aBuilder, ctx,
+                       mFrame->PresContext()->AppUnitsPerDevPixel());
+
+  // Draw the temporary DT to the real destination, applying the blend mode, but
+  // no transform.
+  temp->Flush();
+  RefPtr<SourceSurface> surface = temp->Snapshot();
+  gfxContextMatrixAutoSaveRestore saveMatrix(aCtx);
+  dt->SetTransform(Matrix());
+  dt->DrawSurface(
+      surface, Rect(surface->GetRect()), Rect(surface->GetRect()),
+      DrawSurfaceOptions(),
+      DrawOptions(1.0f, nsCSSRendering::GetGFXBlendMode(mBlendMode)));
+}
+
+gfx::CompositionOp nsDisplayBlendMode::BlendMode() {
+  return nsCSSRendering::GetGFXBlendMode(mBlendMode);
+}
+
+bool nsDisplayBlendMode::CanMerge(const nsDisplayItem* aItem) const {
+  // Items for the same content element should be merged into a single
+  // compositing group.
+  if (!HasDifferentFrame(aItem) || !HasSameTypeAndClip(aItem) ||
+      !HasSameContent(aItem)) {
+    return false;
+  }
+
+  const auto* item = static_cast<const nsDisplayBlendMode*>(aItem);
+  if (mIsForBackground || item->mIsForBackground) {
+    // Don't merge background-blend-mode items
+    return false;
+  }
+
+  return true;
+}
+
+/* static */
+nsDisplayBlendContainer* nsDisplayBlendContainer::CreateForMixBlendMode(
+    nsDisplayListBuilder* aBuilder, nsIFrame* aFrame, nsDisplayList* aList,
+    const ActiveScrolledRoot* aActiveScrolledRoot) {
+  return MakeDisplayItem<nsDisplayBlendContainer>(aBuilder, aFrame, aList,
+                                                  aActiveScrolledRoot, false);
+}
+
+/* static */
+nsDisplayBlendContainer* nsDisplayBlendContainer::CreateForBackgroundBlendMode(
+    nsDisplayListBuilder* aBuilder, nsIFrame* aFrame, nsIFrame* aSecondaryFrame,
+    nsDisplayList* aList, const ActiveScrolledRoot* aActiveScrolledRoot) {
+  if (aSecondaryFrame) {
+    auto type = GetTableTypeFromFrame(aFrame);
+    auto index = static_cast<uint16_t>(type);
+
+    return MakeDisplayItemWithIndex<nsDisplayTableBlendContainer>(
+        aBuilder, aSecondaryFrame, index, aList, aActiveScrolledRoot, true,
+        aFrame);
+  }
+
+  return MakeDisplayItemWithIndex<nsDisplayBlendContainer>(
+      aBuilder, aFrame, 1, aList, aActiveScrolledRoot, true);
+}
+
+nsDisplayBlendContainer::nsDisplayBlendContainer(
+    nsDisplayListBuilder* aBuilder, nsIFrame* aFrame, nsDisplayList* aList,
+    const ActiveScrolledRoot* aActiveScrolledRoot, bool aIsForBackground)
+    : nsDisplayWrapList(aBuilder, aFrame, aList, aActiveScrolledRoot, true),
+      mIsForBackground(aIsForBackground) {
+  MOZ_COUNT_CTOR(nsDisplayBlendContainer);
+}
+
+void nsDisplayBlendContainer::Paint(nsDisplayListBuilder* aBuilder,
+                                    gfxContext* aCtx) {
+  aCtx->GetDrawTarget()->PushLayer(false, 1.0, nullptr, gfx::Matrix());
+  GetChildren()->Paint(aBuilder, aCtx,
+                       mFrame->PresContext()->AppUnitsPerDevPixel());
+  aCtx->GetDrawTarget()->PopLayer();
+}
+
+bool nsDisplayBlendContainer::CreateWebRenderCommands(
+    wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+    const StackingContextHelper& aSc, RenderRootStateManager* aManager,
+    nsDisplayListBuilder* aDisplayListBuilder) {
+  wr::StackingContextParams params;
+  params.flags |= wr::StackingContextFlags::IS_BLEND_CONTAINER;
+  params.clip =
+      wr::WrStackingContextClip::ClipChain(aBuilder.CurrentClipChainId());
+  StackingContextHelper sc(aSc, GetActiveScrolledRoot(), mFrame, this, aBuilder,
+                           params);
+
+  return nsDisplayWrapList::CreateWebRenderCommands(
+      aBuilder, aResources, sc, aManager, aDisplayListBuilder);
+}
+
+nsDisplayOwnLayer::nsDisplayOwnLayer(
+    nsDisplayListBuilder* aBuilder, nsIFrame* aFrame, nsDisplayList* aList,
+    const ActiveScrolledRoot* aActiveScrolledRoot,
+    nsDisplayOwnLayerFlags aFlags, const ScrollbarData& aScrollbarData,
+    bool aForceActive, bool aClearClipChain)
+    : nsDisplayWrapList(aBuilder, aFrame, aList, aActiveScrolledRoot,
+                        aClearClipChain),
+      mFlags(aFlags),
+      mScrollbarData(aScrollbarData),
+      mForceActive(aForceActive),
+      mWrAnimationId(0) {
+  MOZ_COUNT_CTOR(nsDisplayOwnLayer);
+}
+
+bool nsDisplayOwnLayer::IsScrollThumbLayer() const {
+  return mScrollbarData.mScrollbarLayerType == ScrollbarLayerType::Thumb;
+}
+
+bool nsDisplayOwnLayer::IsScrollbarContainer() const {
+  return mScrollbarData.mScrollbarLayerType == ScrollbarLayerType::Container;
+}
+
+bool nsDisplayOwnLayer::IsRootScrollbarContainer() const {
+  if (!IsScrollbarContainer()) {
+    return false;
+  }
+
+  return mFrame->PresContext()->IsRootContentDocumentCrossProcess() &&
+         mScrollbarData.mTargetViewId ==
+             nsLayoutUtils::ScrollIdForRootScrollFrame(mFrame->PresContext());
+}
+
+bool nsDisplayOwnLayer::IsZoomingLayer() const {
+  return GetType() == DisplayItemType::TYPE_ASYNC_ZOOM;
+}
+
+bool nsDisplayOwnLayer::IsFixedPositionLayer() const {
+  return GetType() == DisplayItemType::TYPE_FIXED_POSITION;
+}
+
+bool nsDisplayOwnLayer::IsStickyPositionLayer() const {
+  return GetType() == DisplayItemType::TYPE_STICKY_POSITION;
+}
+
+bool nsDisplayOwnLayer::HasDynamicToolbar() const {
+  if (!mFrame->PresContext()->IsRootContentDocumentCrossProcess()) {
+    return false;
+  }
+  return mFrame->PresContext()->HasDynamicToolbar() ||
+         // For tests on Android, this pref is set to simulate the dynamic
+         // toolbar
+         StaticPrefs::apz_fixed_margin_override_enabled();
+}
+
+bool nsDisplayOwnLayer::ShouldFixedAndStickyContentGetAnimationIds() const {
+#if defined(MOZ_WIDGET_ANDROID)
+  return mFrame->PresContext()->IsRootContentDocumentCrossProcess();
+#else
+  return false;
+#endif
+}
+
+bool nsDisplayOwnLayer::CreateWebRenderCommands(
+    wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+    const StackingContextHelper& aSc, RenderRootStateManager* aManager,
+    nsDisplayListBuilder* aDisplayListBuilder) {
+  Maybe<wr::WrAnimationProperty> prop;
+  bool needsProp = aManager->LayerManager()->AsyncPanZoomEnabled() &&
+                   (IsScrollThumbLayer() || IsZoomingLayer() ||
+                    (IsFixedPositionLayer() &&
+                     ShouldFixedAndStickyContentGetAnimationIds()) ||
+                    (IsStickyPositionLayer() &&
+                     ShouldFixedAndStickyContentGetAnimationIds()) ||
+                    (IsRootScrollbarContainer() && HasDynamicToolbar()));
+
+  if (needsProp) {
+    // APZ is enabled and this is a scroll thumb or zooming layer, so we need
+    // to create and set an animation id. That way APZ can adjust the position/
+    // zoom of this content asynchronously as needed.
+    RefPtr<WebRenderAPZAnimationData> animationData =
+        aManager->CommandBuilder()
+            .CreateOrRecycleWebRenderUserData<WebRenderAPZAnimationData>(this);
+    mWrAnimationId = animationData->GetAnimationId();
+
+    prop.emplace();
+    prop->id = mWrAnimationId;
+    prop->key = wr::SpatialKey(uint64_t(mFrame), GetPerFrameKey(),
+                               wr::SpatialKeyKind::APZ);
+    prop->effect_type = wr::WrAnimationType::Transform;
+  }
+
+  wr::StackingContextParams params;
+  params.animation = prop.ptrOr(nullptr);
+  params.clip =
+      wr::WrStackingContextClip::ClipChain(aBuilder.CurrentClipChainId());
+  if (IsScrollbarContainer() && IsRootScrollbarContainer()) {
+    params.prim_flags |= wr::PrimitiveFlags::IS_SCROLLBAR_CONTAINER;
+  }
+  if (IsZoomingLayer() ||
+      ((IsFixedPositionLayer() &&
+        ShouldFixedAndStickyContentGetAnimationIds()) ||
+       (IsStickyPositionLayer() &&
+        ShouldFixedAndStickyContentGetAnimationIds()) ||
+       (IsRootScrollbarContainer() && HasDynamicToolbar()))) {
+    params.is_2d_scale_translation = true;
+    params.should_snap = true;
+  }
+
+  StackingContextHelper sc(aSc, GetActiveScrolledRoot(), mFrame, this, aBuilder,
+                           params);
+
+  nsDisplayWrapList::CreateWebRenderCommands(aBuilder, aResources, sc, aManager,
+                                             aDisplayListBuilder);
+  return true;
+}
+
+bool nsDisplayOwnLayer::UpdateScrollData(WebRenderScrollData* aData,
+                                         WebRenderLayerScrollData* aLayerData) {
+  bool isRelevantToApz =
+      (IsScrollThumbLayer() || IsScrollbarContainer() || IsZoomingLayer() ||
+       (IsFixedPositionLayer() &&
+        ShouldFixedAndStickyContentGetAnimationIds()) ||
+       (IsStickyPositionLayer() &&
+        ShouldFixedAndStickyContentGetAnimationIds()));
+
+  if (!isRelevantToApz) {
+    return false;
+  }
+
+  if (!aLayerData) {
+    return true;
+  }
+
+  if (IsZoomingLayer()) {
+    aLayerData->SetZoomAnimationId(mWrAnimationId);
+    return true;
+  }
+
+  if (IsFixedPositionLayer() && ShouldFixedAndStickyContentGetAnimationIds()) {
+    aLayerData->SetFixedPositionAnimationId(mWrAnimationId);
+    return true;
+  }
+
+  if (IsStickyPositionLayer() && ShouldFixedAndStickyContentGetAnimationIds()) {
+    aLayerData->SetStickyPositionAnimationId(mWrAnimationId);
+    return true;
+  }
+
+  MOZ_ASSERT(IsScrollbarContainer() || IsScrollThumbLayer());
+
+  aLayerData->SetScrollbarData(mScrollbarData);
+
+  if (IsRootScrollbarContainer() && HasDynamicToolbar()) {
+    aLayerData->SetScrollbarAnimationId(mWrAnimationId);
+    return true;
+  }
+
+  if (IsScrollThumbLayer()) {
+    aLayerData->SetScrollbarAnimationId(mWrAnimationId);
+    LayoutDeviceRect bounds = LayoutDeviceIntRect::FromAppUnits(
+        mBounds, mFrame->PresContext()->AppUnitsPerDevPixel());
+    // We use a resolution of 1.0 because this is a WebRender codepath which
+    // always uses containerless scrolling, and so resolution doesn't apply to
+    // scrollbars.
+    LayerIntRect layerBounds =
+        RoundedOut(bounds * LayoutDeviceToLayerScale(1.0f));
+    aLayerData->SetVisibleRegion(LayerIntRegion(layerBounds));
+  }
+  return true;
+}
+
+void nsDisplayOwnLayer::WriteDebugInfo(std::stringstream& aStream) {
+  aStream << nsPrintfCString(" (flags 0x%x) (scrolltarget %" PRIu64 ")",
+                             (int)mFlags, mScrollbarData.mTargetViewId)
+                 .get();
+}
+
+nsDisplaySubDocument::nsDisplaySubDocument(nsDisplayListBuilder* aBuilder,
+                                           nsIFrame* aFrame,
+                                           nsSubDocumentFrame* aSubDocFrame,
+                                           nsDisplayList* aList,
+                                           nsDisplayOwnLayerFlags aFlags)
+    : nsDisplayOwnLayer(aBuilder, aFrame, aList,
+                        aBuilder->CurrentActiveScrolledRoot(), aFlags),
+      mScrollParentId(aBuilder->GetCurrentScrollParentId()),
+      mShouldFlatten(false),
+      mSubDocFrame(aSubDocFrame) {
+  MOZ_COUNT_CTOR(nsDisplaySubDocument);
+
+  if (mSubDocFrame && mSubDocFrame != mFrame) {
+    mSubDocFrame->AddDisplayItem(this);
+  }
+}
+
+nsDisplaySubDocument::~nsDisplaySubDocument() {
+  MOZ_COUNT_DTOR(nsDisplaySubDocument);
+  if (mSubDocFrame) {
+    mSubDocFrame->RemoveDisplayItem(this);
+  }
+}
+
+nsIFrame* nsDisplaySubDocument::FrameForInvalidation() const {
+  return mSubDocFrame ? mSubDocFrame : mFrame;
+}
+
+void nsDisplaySubDocument::RemoveFrame(nsIFrame* aFrame) {
+  if (aFrame == mSubDocFrame) {
+    mSubDocFrame = nullptr;
+    SetDeletedFrame();
+  }
+  nsDisplayOwnLayer::RemoveFrame(aFrame);
+}
+
+static bool UseDisplayPortForViewport(nsDisplayListBuilder* aBuilder,
+                                      nsIFrame* aFrame) {
+  return aBuilder->IsPaintingToWindow() &&
+         DisplayPortUtils::ViewportHasDisplayPort(aFrame->PresContext());
+}
+
+nsRect nsDisplaySubDocument::GetBounds(nsDisplayListBuilder* aBuilder,
+                                       bool* aSnap) const {
+  bool usingDisplayPort = UseDisplayPortForViewport(aBuilder, mFrame);
+
+  if ((mFlags & nsDisplayOwnLayerFlags::GenerateScrollableLayer) &&
+      usingDisplayPort) {
+    *aSnap = false;
+    return mFrame->GetRect() + aBuilder->ToReferenceFrame(mFrame);
+  }
+
+  return nsDisplayOwnLayer::GetBounds(aBuilder, aSnap);
+}
+
+nsRegion nsDisplaySubDocument::GetOpaqueRegion(nsDisplayListBuilder* aBuilder,
+                                               bool* aSnap) const {
+  bool usingDisplayPort = UseDisplayPortForViewport(aBuilder, mFrame);
+
+  if ((mFlags & nsDisplayOwnLayerFlags::GenerateScrollableLayer) &&
+      usingDisplayPort) {
+    *aSnap = false;
+    return nsRegion();
+  }
+
+  return nsDisplayOwnLayer::GetOpaqueRegion(aBuilder, aSnap);
+}
+
+/* static */
+nsDisplayFixedPosition* nsDisplayFixedPosition::CreateForFixedBackground(
+    nsDisplayListBuilder* aBuilder, nsIFrame* aFrame, nsIFrame* aSecondaryFrame,
+    nsDisplayBackgroundImage* aImage, const uint16_t aIndex,
+    const ActiveScrolledRoot* aScrollTargetASR) {
+  nsDisplayList temp(aBuilder);
+  temp.AppendToTop(aImage);
+
+  if (aSecondaryFrame) {
+    auto tableType = GetTableTypeFromFrame(aFrame);
+    const uint16_t index = CalculateTablePerFrameKey(aIndex + 1, tableType);
+    return MakeDisplayItemWithIndex<nsDisplayTableFixedPosition>(
+        aBuilder, aSecondaryFrame, index, &temp, aFrame, aScrollTargetASR);
+  }
+
+  return MakeDisplayItemWithIndex<nsDisplayFixedPosition>(
+      aBuilder, aFrame, aIndex + 1, &temp, aScrollTargetASR);
+}
+
+nsDisplayFixedPosition::nsDisplayFixedPosition(
+    nsDisplayListBuilder* aBuilder, nsIFrame* aFrame, nsDisplayList* aList,
+    const ActiveScrolledRoot* aActiveScrolledRoot,
+    const ActiveScrolledRoot* aScrollTargetASR)
+    : nsDisplayOwnLayer(aBuilder, aFrame, aList, aActiveScrolledRoot),
+      mScrollTargetASR(aScrollTargetASR),
+      mIsFixedBackground(false) {
+  MOZ_COUNT_CTOR(nsDisplayFixedPosition);
+}
+
+nsDisplayFixedPosition::nsDisplayFixedPosition(
+    nsDisplayListBuilder* aBuilder, nsIFrame* aFrame, nsDisplayList* aList,
+    const ActiveScrolledRoot* aScrollTargetASR)
+    : nsDisplayOwnLayer(aBuilder, aFrame, aList,
+                        aBuilder->CurrentActiveScrolledRoot()),
+      // For fixed backgrounds, this is the ASR for the nearest scroll frame.
+      mScrollTargetASR(aScrollTargetASR),
+      mIsFixedBackground(true) {
+  MOZ_COUNT_CTOR(nsDisplayFixedPosition);
+}
+
+ScrollableLayerGuid::ViewID nsDisplayFixedPosition::GetScrollTargetId() {
+  if (mScrollTargetASR &&
+      (mIsFixedBackground || !nsLayoutUtils::IsReallyFixedPos(mFrame))) {
+    return mScrollTargetASR->GetViewId();
+  }
+  return nsLayoutUtils::ScrollIdForRootScrollFrame(mFrame->PresContext());
+}
+
+bool nsDisplayFixedPosition::CreateWebRenderCommands(
+    wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+    const StackingContextHelper& aSc, RenderRootStateManager* aManager,
+    nsDisplayListBuilder* aDisplayListBuilder) {
+  SideBits sides = SideBits::eNone;
+  if (!mIsFixedBackground) {
+    sides = nsLayoutUtils::GetSideBitsForFixedPositionContent(mFrame);
+  }
+
+  // We install this RAII scrolltarget tracker so that any
+  // nsDisplayCompositorHitTestInfo items inside this fixed-pos item (and that
+  // share the same ASR as this item) use the correct scroll target. That way
+  // attempts to scroll on those items will scroll the root scroll frame.
+  wr::DisplayListBuilder::FixedPosScrollTargetTracker tracker(
+      aBuilder, GetActiveScrolledRoot(), GetScrollTargetId(), sides);
+  return nsDisplayOwnLayer::CreateWebRenderCommands(
+      aBuilder, aResources, aSc, aManager, aDisplayListBuilder);
+}
+
+bool nsDisplayFixedPosition::UpdateScrollData(
+    WebRenderScrollData* aData, WebRenderLayerScrollData* aLayerData) {
+  if (aLayerData) {
+    if (!mIsFixedBackground) {
+      aLayerData->SetFixedPositionSides(
+          nsLayoutUtils::GetSideBitsForFixedPositionContent(mFrame));
+    }
+    aLayerData->SetFixedPositionScrollContainerId(GetScrollTargetId());
+  }
+  nsDisplayOwnLayer::UpdateScrollData(aData, aLayerData);
+  return true;
+}
+
+void nsDisplayFixedPosition::WriteDebugInfo(std::stringstream& aStream) {
+  aStream << nsPrintfCString(
+                 " (containerASR %s) (scrolltarget %" PRIu64 ")",
+                 ActiveScrolledRoot::ToString(mScrollTargetASR).get(),
+                 GetScrollTargetId())
+                 .get();
+}
+
+TableType GetTableTypeFromFrame(nsIFrame* aFrame) {
+  if (aFrame->IsTableFrame()) {
+    return TableType::Table;
+  }
+
+  if (aFrame->IsTableColFrame()) {
+    return TableType::TableCol;
+  }
+
+  if (aFrame->IsTableColGroupFrame()) {
+    return TableType::TableColGroup;
+  }
+
+  if (aFrame->IsTableRowFrame()) {
+    return TableType::TableRow;
+  }
+
+  if (aFrame->IsTableRowGroupFrame()) {
+    return TableType::TableRowGroup;
+  }
+
+  if (aFrame->IsTableCellFrame()) {
+    return TableType::TableCell;
+  }
+
+  MOZ_ASSERT_UNREACHABLE("Invalid frame.");
+  return TableType::Table;
+}
+
+nsDisplayTableFixedPosition::nsDisplayTableFixedPosition(
+    nsDisplayListBuilder* aBuilder, nsIFrame* aFrame, nsDisplayList* aList,
+    nsIFrame* aAncestorFrame, const ActiveScrolledRoot* aScrollTargetASR)
+    : nsDisplayFixedPosition(aBuilder, aFrame, aList, aScrollTargetASR),
+      mAncestorFrame(aAncestorFrame) {
+  if (aBuilder->IsRetainingDisplayList()) {
+    mAncestorFrame->AddDisplayItem(this);
+  }
+}
+
+nsDisplayStickyPosition::nsDisplayStickyPosition(
+    nsDisplayListBuilder* aBuilder, nsIFrame* aFrame, nsDisplayList* aList,
+    const ActiveScrolledRoot* aActiveScrolledRoot,
+    const ActiveScrolledRoot* aContainerASR, bool aClippedToDisplayPort)
+    : nsDisplayOwnLayer(aBuilder, aFrame, aList, aActiveScrolledRoot),
+      mContainerASR(aContainerASR),
+      mClippedToDisplayPort(aClippedToDisplayPort),
+      mShouldFlatten(false) {
+  MOZ_COUNT_CTOR(nsDisplayStickyPosition);
+}
+
+// Returns the smallest distance from "0" to the range [min, max] where
+// min <= max. Despite the name, the return value is actually a 1-D vector,
+// and so may be negative if max < 0.
+static nscoord DistanceToRange(nscoord min, nscoord max) {
+  MOZ_ASSERT(min <= max);
+  if (max < 0) {
+    return max;
+  }
+  if (min > 0) {
+    return min;
+  }
+  MOZ_ASSERT(min <= 0 && max >= 0);
+  return 0;
+}
+
+// Returns the magnitude of the part of the range [min, max] that is greater
+// than zero. The return value is always non-negative.
+static nscoord PositivePart(nscoord min, nscoord max) {
+  MOZ_ASSERT(min <= max);
+  if (min >= 0) {
+    return max - min;
+  }
+  if (max > 0) {
+    return max;
+  }
+  return 0;
+}
+
+// Returns the magnitude of the part of the range [min, max] that is less
+// than zero. The return value is always non-negative.
+static nscoord NegativePart(nscoord min, nscoord max) {
+  MOZ_ASSERT(min <= max);
+  if (max <= 0) {
+    return max - min;
+  }
+  if (min < 0) {
+    return 0 - min;
+  }
+  return 0;
+}
+
+StickyScrollContainer* nsDisplayStickyPosition::GetStickyScrollContainer() {
+  StickyScrollContainer* stickyScrollContainer =
+      StickyScrollContainer::GetStickyScrollContainerForFrame(mFrame);
+  if (stickyScrollContainer) {
+    // If there's no ASR for the scrollframe that this sticky item is attached
+    // to, then don't create a WR sticky item for it either. Trying to do so
+    // will end in sadness because WR will interpret some coordinates as
+    // relative to the nearest enclosing scrollframe, which will correspond
+    // to the nearest ancestor ASR on the gecko side. That ASR will not be the
+    // same as the scrollframe this sticky item is actually supposed to be
+    // attached to, thus the sadness.
+    // Not sending WR the sticky item is ok, because the enclosing scrollframe
+    // will never be asynchronously scrolled. Instead we will always position
+    // the sticky items correctly on the gecko side and WR will never need to
+    // adjust their position itself.
+    MOZ_ASSERT(
+        stickyScrollContainer->ScrollFrame()->IsMaybeAsynchronouslyScrolled());
+    if (!stickyScrollContainer->ScrollFrame()
+             ->IsMaybeAsynchronouslyScrolled()) {
+      stickyScrollContainer = nullptr;
+    }
+  }
+  return stickyScrollContainer;
+}
+
+bool nsDisplayStickyPosition::CreateWebRenderCommands(
+    wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+    const StackingContextHelper& aSc, RenderRootStateManager* aManager,
+    nsDisplayListBuilder* aDisplayListBuilder) {
+  StickyScrollContainer* stickyScrollContainer = GetStickyScrollContainer();
+
+  Maybe<wr::SpaceAndClipChainHelper> saccHelper;
+
+  if (stickyScrollContainer) {
+    float auPerDevPixel = mFrame->PresContext()->AppUnitsPerDevPixel();
+
+    bool snap;
+    nsRect itemBounds = GetBounds(aDisplayListBuilder, &snap);
+
+    Maybe<float> topMargin;
+    Maybe<float> rightMargin;
+    Maybe<float> bottomMargin;
+    Maybe<float> leftMargin;
+    wr::StickyOffsetBounds vBounds = {0.0, 0.0};
+    wr::StickyOffsetBounds hBounds = {0.0, 0.0};
+    nsPoint appliedOffset;
+
+    nsRectAbsolute outer;
+    nsRectAbsolute inner;
+    stickyScrollContainer->GetScrollRanges(mFrame, &outer, &inner);
+
+    nsIFrame* scrollFrame = do_QueryFrame(stickyScrollContainer->ScrollFrame());
+    nsPoint offset =
+        scrollFrame->GetOffsetToCrossDoc(Frame()) + ToReferenceFrame();
+
+    // Adjust the scrollPort coordinates to be relative to the reference frame,
+    // so that it is in the same space as everything else.
+    nsRect scrollPort =
+        stickyScrollContainer->ScrollFrame()->GetScrollPortRect();
+    scrollPort += offset;
+
+    // The following computations make more sense upon understanding the
+    // semantics of "inner" and "outer", which is explained in the comment on
+    // SetStickyPositionData in Layers.h.
+
+    if (outer.YMost() != inner.YMost()) {
+      // Question: How far will itemBounds.y be from the top of the scrollport
+      // when we have scrolled from the current scroll position of "0" to
+      // reach the range [inner.YMost(), outer.YMost()] where the item gets
+      // stuck?
+      // Answer: the current distance is "itemBounds.y - scrollPort.y". That
+      // needs to be adjusted by the distance to the range, less any other
+      // sticky ranges that fall between 0 and the range. If the distance is
+      // negative (i.e. inner.YMost() <= outer.YMost() < 0) then we would be
+      // scrolling upwards (decreasing scroll offset) to reach that range,
+      // which would increase itemBounds.y and make it farther away from the
+      // top of the scrollport. So in that case the adjustment is -distance.
+      // If the distance is positive (0 < inner.YMost() <= outer.YMost()) then
+      // we would be scrolling downwards, itemBounds.y would decrease, and we
+      // again need to adjust by -distance. If we are already in the range
+      // then no adjustment is needed and distance is 0 so again using
+      // -distance works. If the distance is positive, and the item has both
+      // top and bottom sticky ranges, then the bottom sticky range may fall
+      // (entirely[1] or partly[2]) between the current scroll position.
+      // [1]: 0 <= outer.Y() <= inner.Y() < inner.YMost() <= outer.YMost()
+      // [2]: outer.Y() < 0 <= inner.Y() < inner.YMost() <= outer.YMost()
+      // In these cases, the item doesn't actually move for that part of the
+      // distance, so we need to subtract out that bit, which can be computed
+      // as the positive portion of the range [outer.Y(), inner.Y()].
+      nscoord distance = DistanceToRange(inner.YMost(), outer.YMost());
+      if (distance > 0) {
+        distance -= PositivePart(outer.Y(), inner.Y());
+      }
+      topMargin = Some(NSAppUnitsToFloatPixels(
+          itemBounds.y - scrollPort.y - distance, auPerDevPixel));
+      // Question: What is the maximum positive ("downward") offset that WR
+      // will have to apply to this item in order to prevent the item from
+      // visually moving?
+      // Answer: Since the item is "sticky" in the range [inner.YMost(),
+      // outer.YMost()], the maximum offset will be the size of the range, which
+      // is outer.YMost() - inner.YMost().
+      vBounds.max =
+          NSAppUnitsToFloatPixels(outer.YMost() - inner.YMost(), auPerDevPixel);
+      // Question: how much of an offset has layout already applied to the item?
+      // Answer: if we are
+      // (a) inside the sticky range (inner.YMost() < 0 <= outer.YMost()), or
+      // (b) past the sticky range (inner.YMost() < outer.YMost() < 0)
+      // then layout has already applied some offset to the position of the
+      // item. The amount of the adjustment is |0 - inner.YMost()| in case (a)
+      // and |outer.YMost() - inner.YMost()| in case (b).
+      if (inner.YMost() < 0) {
+        appliedOffset.y = std::min(0, outer.YMost()) - inner.YMost();
+        MOZ_ASSERT(appliedOffset.y > 0);
+      }
+    }
+    if (outer.Y() != inner.Y()) {
+      // Similar logic as in the previous section, but this time we care about
+      // the distance from itemBounds.YMost() to scrollPort.YMost().
+      nscoord distance = DistanceToRange(outer.Y(), inner.Y());
+      if (distance < 0) {
+        distance += NegativePart(inner.YMost(), outer.YMost());
+      }
+      bottomMargin = Some(NSAppUnitsToFloatPixels(
+          scrollPort.YMost() - itemBounds.YMost() + distance, auPerDevPixel));
+      // And here WR will be moving the item upwards rather than downwards so
+      // again things are inverted from the previous block.
+      vBounds.min =
+          NSAppUnitsToFloatPixels(outer.Y() - inner.Y(), auPerDevPixel);
+      // We can't have appliedOffset be both positive and negative, and the top
+      // adjustment takes priority. So here we only update appliedOffset.y if
+      // it wasn't set by the top-sticky case above.
+      if (appliedOffset.y == 0 && inner.Y() > 0) {
+        appliedOffset.y = std::max(0, outer.Y()) - inner.Y();
+        MOZ_ASSERT(appliedOffset.y < 0);
+      }
+    }
+    // Same as above, but for the x-axis
+    if (outer.XMost() != inner.XMost()) {
+      nscoord distance = DistanceToRange(inner.XMost(), outer.XMost());
+      if (distance > 0) {
+        distance -= PositivePart(outer.X(), inner.X());
+      }
+      leftMargin = Some(NSAppUnitsToFloatPixels(
+          itemBounds.x - scrollPort.x - distance, auPerDevPixel));
+      hBounds.max =
+          NSAppUnitsToFloatPixels(outer.XMost() - inner.XMost(), auPerDevPixel);
+      if (inner.XMost() < 0) {
+        appliedOffset.x = std::min(0, outer.XMost()) - inner.XMost();
+        MOZ_ASSERT(appliedOffset.x > 0);
+      }
+    }
+    if (outer.X() != inner.X()) {
+      nscoord distance = DistanceToRange(outer.X(), inner.X());
+      if (distance < 0) {
+        distance += NegativePart(inner.XMost(), outer.XMost());
+      }
+      rightMargin = Some(NSAppUnitsToFloatPixels(
+          scrollPort.XMost() - itemBounds.XMost() + distance, auPerDevPixel));
+      hBounds.min =
+          NSAppUnitsToFloatPixels(outer.X() - inner.X(), auPerDevPixel);
+      if (appliedOffset.x == 0 && inner.X() > 0) {
+        appliedOffset.x = std::max(0, outer.X()) - inner.X();
+        MOZ_ASSERT(appliedOffset.x < 0);
+      }
+    }
+
+    LayoutDeviceRect bounds =
+        LayoutDeviceRect::FromAppUnits(itemBounds, auPerDevPixel);
+    wr::LayoutVector2D applied = {
+        NSAppUnitsToFloatPixels(appliedOffset.x, auPerDevPixel),
+        NSAppUnitsToFloatPixels(appliedOffset.y, auPerDevPixel)};
+    wr::WrSpatialId spatialId = aBuilder.DefineStickyFrame(
+        wr::ToLayoutRect(bounds), topMargin.ptrOr(nullptr),
+        rightMargin.ptrOr(nullptr), bottomMargin.ptrOr(nullptr),
+        leftMargin.ptrOr(nullptr), vBounds, hBounds, applied,
+        wr::SpatialKey(uint64_t(mFrame), GetPerFrameKey(),
+                       wr::SpatialKeyKind::Sticky));
+
+    saccHelper.emplace(aBuilder, spatialId);
+    aManager->CommandBuilder().PushOverrideForASR(mContainerASR, spatialId);
+  }
+
+  {
+    wr::StackingContextParams params;
+    params.clip =
+        wr::WrStackingContextClip::ClipChain(aBuilder.CurrentClipChainId());
+    StackingContextHelper sc(aSc, GetActiveScrolledRoot(), mFrame, this,
+                             aBuilder, params);
+    nsDisplayOwnLayer::CreateWebRenderCommands(aBuilder, aResources, sc,
+                                               aManager, aDisplayListBuilder);
+  }
+
+  if (stickyScrollContainer) {
+    aManager->CommandBuilder().PopOverrideForASR(mContainerASR);
+  }
+
+  return true;
+}
+
+void nsDisplayStickyPosition::CalculateLayerScrollRanges(
+    StickyScrollContainer* aStickyScrollContainer, float aAppUnitsPerDevPixel,
+    float aScaleX, float aScaleY, LayerRectAbsolute& aStickyOuter,
+    LayerRectAbsolute& aStickyInner) {
+  nsRectAbsolute outer;
+  nsRectAbsolute inner;
+  aStickyScrollContainer->GetScrollRanges(mFrame, &outer, &inner);
+  aStickyOuter.SetBox(
+      NSAppUnitsToFloatPixels(outer.X(), aAppUnitsPerDevPixel) * aScaleX,
+      NSAppUnitsToFloatPixels(outer.Y(), aAppUnitsPerDevPixel) * aScaleY,
+      NSAppUnitsToFloatPixels(outer.XMost(), aAppUnitsPerDevPixel) * aScaleX,
+      NSAppUnitsToFloatPixels(outer.YMost(), aAppUnitsPerDevPixel) * aScaleY);
+  aStickyInner.SetBox(
+      NSAppUnitsToFloatPixels(inner.X(), aAppUnitsPerDevPixel) * aScaleX,
+      NSAppUnitsToFloatPixels(inner.Y(), aAppUnitsPerDevPixel) * aScaleY,
+      NSAppUnitsToFloatPixels(inner.XMost(), aAppUnitsPerDevPixel) * aScaleX,
+      NSAppUnitsToFloatPixels(inner.YMost(), aAppUnitsPerDevPixel) * aScaleY);
+}
+
+bool nsDisplayStickyPosition::UpdateScrollData(
+    WebRenderScrollData* aData, WebRenderLayerScrollData* aLayerData) {
+  bool hasDynamicToolbar = HasDynamicToolbar();
+  if (aLayerData && hasDynamicToolbar) {
+    StickyScrollContainer* stickyScrollContainer = GetStickyScrollContainer();
+    if (stickyScrollContainer) {
+      float auPerDevPixel = mFrame->PresContext()->AppUnitsPerDevPixel();
+      float cumulativeResolution =
+          mFrame->PresShell()->GetCumulativeResolution();
+      LayerRectAbsolute stickyOuter;
+      LayerRectAbsolute stickyInner;
+      CalculateLayerScrollRanges(stickyScrollContainer, auPerDevPixel,
+                                 cumulativeResolution, cumulativeResolution,
+                                 stickyOuter, stickyInner);
+      aLayerData->SetStickyScrollRangeOuter(stickyOuter);
+      aLayerData->SetStickyScrollRangeInner(stickyInner);
+
+      SideBits sides =
+          nsLayoutUtils::GetSideBitsForFixedPositionContent(mFrame);
+      aLayerData->SetFixedPositionSides(sides);
+
+      ScrollableLayerGuid::ViewID scrollId =
+          nsLayoutUtils::FindOrCreateIDFor(stickyScrollContainer->ScrollFrame()
+                                               ->GetScrolledFrame()
+                                               ->GetContent());
+      aLayerData->SetStickyPositionScrollContainerId(scrollId);
+    }
+  }
+  // Return true if either there is a dynamic toolbar affecting this sticky
+  // item or the OwnLayer base implementation returns true for some other
+  // reason.
+  bool ret = hasDynamicToolbar;
+  ret |= nsDisplayOwnLayer::UpdateScrollData(aData, aLayerData);
+  return ret;
+}
+
+nsDisplayScrollInfoLayer::nsDisplayScrollInfoLayer(
+    nsDisplayListBuilder* aBuilder, nsIFrame* aScrolledFrame,
+    nsIFrame* aScrollFrame, const CompositorHitTestInfo& aHitInfo,
+    const nsRect& aHitArea)
+    : nsDisplayWrapList(aBuilder, aScrollFrame),
+      mScrollFrame(aScrollFrame),
+      mScrolledFrame(aScrolledFrame),
+      mScrollParentId(aBuilder->GetCurrentScrollParentId()),
+      mHitInfo(aHitInfo),
+      mHitArea(aHitArea) {
+#ifdef NS_BUILD_REFCNT_LOGGING
+  MOZ_COUNT_CTOR(nsDisplayScrollInfoLayer);
+#endif
+}
+
+UniquePtr<ScrollMetadata> nsDisplayScrollInfoLayer::ComputeScrollMetadata(
+    nsDisplayListBuilder* aBuilder, WebRenderLayerManager* aLayerManager) {
+  ScrollMetadata metadata = nsLayoutUtils::ComputeScrollMetadata(
+      mScrolledFrame, mScrollFrame, mScrollFrame->GetContent(), Frame(),
+      ToReferenceFrame(), aLayerManager, mScrollParentId,
+      mScrollFrame->GetSize(), false);
+  metadata.GetMetrics().SetIsScrollInfoLayer(true);
+  nsIScrollableFrame* scrollableFrame = mScrollFrame->GetScrollTargetFrame();
+  if (scrollableFrame) {
+    aBuilder->AddScrollFrameToNotify(scrollableFrame);
+  }
+
+  return UniquePtr<ScrollMetadata>(new ScrollMetadata(metadata));
+}
+
+bool nsDisplayScrollInfoLayer::UpdateScrollData(
+    WebRenderScrollData* aData, WebRenderLayerScrollData* aLayerData) {
+  if (aLayerData) {
+    UniquePtr<ScrollMetadata> metadata =
+        ComputeScrollMetadata(aData->GetBuilder(), aData->GetManager());
+    MOZ_ASSERT(aData);
+    MOZ_ASSERT(metadata);
+    aLayerData->AppendScrollMetadata(*aData, *metadata);
+  }
+  return true;
+}
+
+bool nsDisplayScrollInfoLayer::CreateWebRenderCommands(
+    wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+    const StackingContextHelper& aSc, RenderRootStateManager* aManager,
+    nsDisplayListBuilder* aDisplayListBuilder) {
+  ScrollableLayerGuid::ViewID scrollId =
+      nsLayoutUtils::FindOrCreateIDFor(mScrollFrame->GetContent());
+
+  const LayoutDeviceRect devRect = LayoutDeviceRect::FromAppUnits(
+      mHitArea, mScrollFrame->PresContext()->AppUnitsPerDevPixel());
+
+  const wr::LayoutRect rect = wr::ToLayoutRect(devRect);
+
+  aBuilder.PushHitTest(rect, rect, !BackfaceIsHidden(), scrollId, mHitInfo,
+                       SideBits::eNone);
+
+  return true;
+}
+
+void nsDisplayScrollInfoLayer::WriteDebugInfo(std::stringstream& aStream) {
+  aStream << " (scrollframe " << mScrollFrame << " scrolledFrame "
+          << mScrolledFrame << ")";
+}
+
+nsDisplayZoom::nsDisplayZoom(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                             nsSubDocumentFrame* aSubDocFrame,
+                             nsDisplayList* aList, int32_t aAPD,
+                             int32_t aParentAPD, nsDisplayOwnLayerFlags aFlags)
+    : nsDisplaySubDocument(aBuilder, aFrame, aSubDocFrame, aList, aFlags),
+      mAPD(aAPD),
+      mParentAPD(aParentAPD) {
+  MOZ_COUNT_CTOR(nsDisplayZoom);
+}
+
+nsRect nsDisplayZoom::GetBounds(nsDisplayListBuilder* aBuilder,
+                                bool* aSnap) const {
+  nsRect bounds = nsDisplaySubDocument::GetBounds(aBuilder, aSnap);
+  *aSnap = false;
+  return bounds.ScaleToOtherAppUnitsRoundOut(mAPD, mParentAPD);
+}
+
+void nsDisplayZoom::HitTest(nsDisplayListBuilder* aBuilder, const nsRect& aRect,
+                            HitTestState* aState,
+                            nsTArray<nsIFrame*>* aOutFrames) {
+  nsRect rect;
+  // A 1x1 rect indicates we are just hit testing a point, so pass down a 1x1
+  // rect as well instead of possibly rounding the width or height to zero.
+  if (aRect.width == 1 && aRect.height == 1) {
+    rect.MoveTo(aRect.TopLeft().ScaleToOtherAppUnits(mParentAPD, mAPD));
+    rect.width = rect.height = 1;
+  } else {
+    rect = aRect.ScaleToOtherAppUnitsRoundOut(mParentAPD, mAPD);
+  }
+  mList.HitTest(aBuilder, rect, aState, aOutFrames);
+}
+
+nsDisplayAsyncZoom::nsDisplayAsyncZoom(
+    nsDisplayListBuilder* aBuilder, nsIFrame* aFrame, nsDisplayList* aList,
+    const ActiveScrolledRoot* aActiveScrolledRoot, FrameMetrics::ViewID aViewID)
+    : nsDisplayOwnLayer(aBuilder, aFrame, aList, aActiveScrolledRoot),
+      mViewID(aViewID) {
+  MOZ_COUNT_CTOR(nsDisplayAsyncZoom);
+}
+
+#ifdef NS_BUILD_REFCNT_LOGGING
+nsDisplayAsyncZoom::~nsDisplayAsyncZoom() {
+  MOZ_COUNT_DTOR(nsDisplayAsyncZoom);
+}
+#endif
+
+void nsDisplayAsyncZoom::HitTest(nsDisplayListBuilder* aBuilder,
+                                 const nsRect& aRect, HitTestState* aState,
+                                 nsTArray<nsIFrame*>* aOutFrames) {
+#ifdef DEBUG
+  nsIScrollableFrame* scrollFrame = do_QueryFrame(mFrame);
+  MOZ_ASSERT(scrollFrame && ViewportUtils::IsZoomedContentRoot(
+                                scrollFrame->GetScrolledFrame()));
+#endif
+  nsRect rect = ViewportUtils::VisualToLayout(aRect, mFrame->PresShell());
+  mList.HitTest(aBuilder, rect, aState, aOutFrames);
+}
+
+bool nsDisplayAsyncZoom::UpdateScrollData(
+    WebRenderScrollData* aData, WebRenderLayerScrollData* aLayerData) {
+  bool ret = nsDisplayOwnLayer::UpdateScrollData(aData, aLayerData);
+  MOZ_ASSERT(ret);
+  if (aLayerData) {
+    aLayerData->SetAsyncZoomContainerId(mViewID);
+  }
+  return ret;
+}
+
+///////////////////////////////////////////////////
+// nsDisplayTransform Implementation
+//
+
+#ifndef DEBUG
+static_assert(sizeof(nsDisplayTransform) <= 512,
+              "nsDisplayTransform has grown");
+#endif
+
+nsDisplayTransform::nsDisplayTransform(nsDisplayListBuilder* aBuilder,
+                                       nsIFrame* aFrame, nsDisplayList* aList,
+                                       const nsRect& aChildrenBuildingRect)
+    : nsPaintedDisplayItem(aBuilder, aFrame),
+      mChildren(aBuilder),
+      mTransform(Some(Matrix4x4())),
+      mChildrenBuildingRect(aChildrenBuildingRect),
+      mPrerenderDecision(PrerenderDecision::No),
+      mIsTransformSeparator(true),
+      mHasTransformGetter(false),
+      mHasAssociatedPerspective(false) {
+  MOZ_COUNT_CTOR(nsDisplayTransform);
+  MOZ_ASSERT(aFrame, "Must have a frame!");
+  Init(aBuilder, aList);
+}
+
+nsDisplayTransform::nsDisplayTransform(nsDisplayListBuilder* aBuilder,
+                                       nsIFrame* aFrame, nsDisplayList* aList,
+                                       const nsRect& aChildrenBuildingRect,
+                                       PrerenderDecision aPrerenderDecision)
+    : nsPaintedDisplayItem(aBuilder, aFrame),
+      mChildren(aBuilder),
+      mChildrenBuildingRect(aChildrenBuildingRect),
+      mPrerenderDecision(aPrerenderDecision),
+      mIsTransformSeparator(false),
+      mHasTransformGetter(false),
+      mHasAssociatedPerspective(false) {
+  MOZ_COUNT_CTOR(nsDisplayTransform);
+  MOZ_ASSERT(aFrame, "Must have a frame!");
+  SetReferenceFrameToAncestor(aBuilder);
+  Init(aBuilder, aList);
+}
+
+nsDisplayTransform::nsDisplayTransform(nsDisplayListBuilder* aBuilder,
+                                       nsIFrame* aFrame, nsDisplayList* aList,
+                                       const nsRect& aChildrenBuildingRect,
+                                       decltype(WithTransformGetter))
+    : nsPaintedDisplayItem(aBuilder, aFrame),
+      mChildren(aBuilder),
+      mChildrenBuildingRect(aChildrenBuildingRect),
+      mPrerenderDecision(PrerenderDecision::No),
+      mIsTransformSeparator(false),
+      mHasTransformGetter(true),
+      mHasAssociatedPerspective(false) {
+  MOZ_COUNT_CTOR(nsDisplayTransform);
+  MOZ_ASSERT(aFrame, "Must have a frame!");
+  MOZ_ASSERT(aFrame->GetTransformGetter());
+  Init(aBuilder, aList);
+}
+
+void nsDisplayTransform::SetReferenceFrameToAncestor(
+    nsDisplayListBuilder* aBuilder) {
+  if (mFrame == aBuilder->RootReferenceFrame()) {
+    return;
+  }
+  // We manually recompute mToReferenceFrame without going through the
+  // builder, since this won't apply the 'additional offset'. Our
+  // children will already be painting with that applied, and we don't
+  // want to include it a second time in our transform. We don't recompute
+  // our visible/building rects, since those should still include the additional
+  // offset.
+  // TODO: Are there are things computed using our ToReferenceFrame that should
+  // have the additional offset applied? Should we instead just manually remove
+  // the offset from our transform instead of this more general value?
+  // Can we instead apply the additional offset to us and not our children, like
+  // we do for all other offsets (and how reference frames are supposed to
+  // work)?
+  nsIFrame* outerFrame = nsLayoutUtils::GetCrossDocParentFrameInProcess(mFrame);
+  const nsIFrame* referenceFrame = aBuilder->FindReferenceFrameFor(outerFrame);
+  mToReferenceFrame = mFrame->GetOffsetToCrossDoc(referenceFrame);
+}
+
+void nsDisplayTransform::Init(nsDisplayListBuilder* aBuilder,
+                              nsDisplayList* aChildren) {
+  mChildren.AppendToTop(aChildren);
+  UpdateBounds(aBuilder);
+}
+
+bool nsDisplayTransform::ShouldFlattenAway(nsDisplayListBuilder* aBuilder) {
+  return false;
+}
+
+/* Returns the delta specified by the transform-origin property.
+ * This is a positive delta, meaning that it indicates the direction to move
+ * to get from (0, 0) of the frame to the transform origin.  This function is
+ * called off the main thread.
+ */
+/* static */
+Point3D nsDisplayTransform::GetDeltaToTransformOrigin(
+    const nsIFrame* aFrame, TransformReferenceBox& aRefBox,
+    float aAppUnitsPerPixel) {
+  MOZ_ASSERT(aFrame, "Can't get delta for a null frame!");
+  MOZ_ASSERT(aFrame->IsTransformed() || aFrame->BackfaceIsHidden() ||
+                 aFrame->Combines3DTransformWithAncestors(),
+             "Shouldn't get a delta for an untransformed frame!");
+
+  if (!aFrame->IsTransformed()) {
+    return Point3D();
+  }
+
+  /* For both of the coordinates, if the value of transform is a
+   * percentage, it's relative to the size of the frame.  Otherwise, if it's
+   * a distance, it's already computed for us!
+   */
+  const nsStyleDisplay* display = aFrame->StyleDisplay();
+
+  const StyleTransformOrigin& transformOrigin = display->mTransformOrigin;
+  CSSPoint origin = nsStyleTransformMatrix::Convert2DPosition(
+      transformOrigin.horizontal, transformOrigin.vertical, aRefBox);
+
+  if (aFrame->HasAnyStateBits(NS_FRAME_SVG_LAYOUT)) {
+    // SVG frames (unlike other frames) have a reference box that can be (and
+    // typically is) offset from the TopLeft() of the frame. We need to account
+    // for that here.
+    origin.x += CSSPixel::FromAppUnits(aRefBox.X());
+    origin.y += CSSPixel::FromAppUnits(aRefBox.Y());
+  }
+
+  float scale = AppUnitsPerCSSPixel() / float(aAppUnitsPerPixel);
+  float z = transformOrigin.depth._0;
+  return Point3D(origin.x * scale, origin.y * scale, z * scale);
+}
+
+/* static */
+bool nsDisplayTransform::ComputePerspectiveMatrix(const nsIFrame* aFrame,
+                                                  float aAppUnitsPerPixel,
+                                                  Matrix4x4& aOutMatrix) {
+  MOZ_ASSERT(aFrame, "Can't get delta for a null frame!");
+  MOZ_ASSERT(aFrame->IsTransformed() || aFrame->BackfaceIsHidden() ||
+                 aFrame->Combines3DTransformWithAncestors(),
+             "Shouldn't get a delta for an untransformed frame!");
+  MOZ_ASSERT(aOutMatrix.IsIdentity(), "Must have a blank output matrix");
+
+  if (!aFrame->IsTransformed()) {
+    return false;
+  }
+
+  // TODO: Is it possible that the perspectiveFrame's bounds haven't been set
+  // correctly yet (similar to the aBoundsOverride case for
+  // GetResultingTransformMatrix)?
+  nsIFrame* perspectiveFrame =
+      aFrame->GetClosestFlattenedTreeAncestorPrimaryFrame();
+  if (!perspectiveFrame) {
+    return false;
+  }
+
+  /* Grab the values for perspective and perspective-origin (if present) */
+  const nsStyleDisplay* perspectiveDisplay = perspectiveFrame->StyleDisplay();
+  if (perspectiveDisplay->mChildPerspective.IsNone()) {
+    return false;
+  }
+
+  MOZ_ASSERT(perspectiveDisplay->mChildPerspective.IsLength());
+  float perspective =
+      perspectiveDisplay->mChildPerspective.AsLength().ToCSSPixels();
+  perspective = std::max(1.0f, perspective);
+  if (perspective < std::numeric_limits<Float>::epsilon()) {
+    return true;
+  }
+
+  TransformReferenceBox refBox(perspectiveFrame);
+
+  Point perspectiveOrigin = nsStyleTransformMatrix::Convert2DPosition(
+      perspectiveDisplay->mPerspectiveOrigin.horizontal,
+      perspectiveDisplay->mPerspectiveOrigin.vertical, refBox,
+      aAppUnitsPerPixel);
+
+  /* GetOffsetTo computes the offset required to move from 0,0 in
+   * perspectiveFrame to 0,0 in aFrame. Although we actually want the inverse of
+   * this, it's faster to compute this way.
+   */
+  nsPoint frameToPerspectiveOffset = -aFrame->GetOffsetTo(perspectiveFrame);
+  Point frameToPerspectiveGfxOffset(
+      NSAppUnitsToFloatPixels(frameToPerspectiveOffset.x, aAppUnitsPerPixel),
+      NSAppUnitsToFloatPixels(frameToPerspectiveOffset.y, aAppUnitsPerPixel));
+
+  /* Move the perspective origin to be relative to aFrame, instead of relative
+   * to the containing block which is how it was specified in the style system.
+   */
+  perspectiveOrigin += frameToPerspectiveGfxOffset;
+
+  aOutMatrix._34 =
+      -1.0 / NSAppUnitsToFloatPixels(CSSPixel::ToAppUnits(perspective),
+                                     aAppUnitsPerPixel);
+
+  aOutMatrix.ChangeBasis(Point3D(perspectiveOrigin.x, perspectiveOrigin.y, 0));
+  return true;
+}
+
+nsDisplayTransform::FrameTransformProperties::FrameTransformProperties(
+    const nsIFrame* aFrame, TransformReferenceBox& aRefBox,
+    float aAppUnitsPerPixel)
+    : mFrame(aFrame),
+      mTranslate(aFrame->StyleDisplay()->mTranslate),
+      mRotate(aFrame->StyleDisplay()->mRotate),
+      mScale(aFrame->StyleDisplay()->mScale),
+      mTransform(aFrame->StyleDisplay()->mTransform),
+      mMotion(MotionPathUtils::ResolveMotionPath(aFrame, aRefBox)),
+      mToTransformOrigin(
+          GetDeltaToTransformOrigin(aFrame, aRefBox, aAppUnitsPerPixel)) {}
+
+/* Wraps up the transform matrix in a change-of-basis matrix pair that
+ * translates from local coordinate space to transform coordinate space, then
+ * hands it back.
+ */
+Matrix4x4 nsDisplayTransform::GetResultingTransformMatrix(
+    const FrameTransformProperties& aProperties, TransformReferenceBox& aRefBox,
+    float aAppUnitsPerPixel) {
+  return GetResultingTransformMatrixInternal(aProperties, aRefBox, nsPoint(),
+                                             aAppUnitsPerPixel, 0);
+}
+
+Matrix4x4 nsDisplayTransform::GetResultingTransformMatrix(
+    const nsIFrame* aFrame, const nsPoint& aOrigin, float aAppUnitsPerPixel,
+    uint32_t aFlags) {
+  TransformReferenceBox refBox(aFrame);
+  FrameTransformProperties props(aFrame, refBox, aAppUnitsPerPixel);
+  return GetResultingTransformMatrixInternal(props, refBox, aOrigin,
+                                             aAppUnitsPerPixel, aFlags);
+}
+
+Matrix4x4 nsDisplayTransform::GetResultingTransformMatrixInternal(
+    const FrameTransformProperties& aProperties, TransformReferenceBox& aRefBox,
+    const nsPoint& aOrigin, float aAppUnitsPerPixel, uint32_t aFlags) {
+  const nsIFrame* frame = aProperties.mFrame;
+  NS_ASSERTION(frame || !(aFlags & INCLUDE_PERSPECTIVE),
+               "Must have a frame to compute perspective!");
+
+  // Get the underlying transform matrix:
+
+  /* Get the matrix, then change its basis to factor in the origin. */
+  Matrix4x4 result;
+  // Call IsSVGTransformed() regardless of the value of
+  // aProperties.HasTransform(), since we still need any
+  // potential parentsChildrenOnlyTransform.
+  Matrix svgTransform, parentsChildrenOnlyTransform;
+  const bool hasSVGTransforms =
+      frame && frame->HasAnyStateBits(NS_FRAME_MAY_BE_TRANSFORMED) &&
+      frame->IsSVGTransformed(&svgTransform, &parentsChildrenOnlyTransform);
+  bool shouldRound = nsLayoutUtils::ShouldSnapToGrid(frame);
+
+  /* Transformed frames always have a transform, or are preserving 3d (and might
+   * still have perspective!) */
+  if (aProperties.HasTransform()) {
+    result = nsStyleTransformMatrix::ReadTransforms(
+        aProperties.mTranslate, aProperties.mRotate, aProperties.mScale,
+        aProperties.mMotion, aProperties.mTransform, aRefBox,
+        aAppUnitsPerPixel);
+  } else if (hasSVGTransforms) {
+    // Correct the translation components for zoom:
+    float pixelsPerCSSPx = AppUnitsPerCSSPixel() / aAppUnitsPerPixel;
+    svgTransform._31 *= pixelsPerCSSPx;
+    svgTransform._32 *= pixelsPerCSSPx;
+    result = Matrix4x4::From2D(svgTransform);
+  }
+
+  // Apply any translation due to 'transform-origin' and/or 'transform-box':
+  result.ChangeBasis(aProperties.mToTransformOrigin);
+
+  // See the comment for SVGContainerFrame::HasChildrenOnlyTransform for
+  // an explanation of what children-only transforms are.
+  const bool parentHasChildrenOnlyTransform =
+      hasSVGTransforms && !parentsChildrenOnlyTransform.IsIdentity();
+
+  if (parentHasChildrenOnlyTransform) {
+    float pixelsPerCSSPx = AppUnitsPerCSSPixel() / aAppUnitsPerPixel;
+    parentsChildrenOnlyTransform._31 *= pixelsPerCSSPx;
+    parentsChildrenOnlyTransform._32 *= pixelsPerCSSPx;
+
+    Point3D frameOffset(
+        NSAppUnitsToFloatPixels(-frame->GetPosition().x, aAppUnitsPerPixel),
+        NSAppUnitsToFloatPixels(-frame->GetPosition().y, aAppUnitsPerPixel), 0);
+    Matrix4x4 parentsChildrenOnlyTransform3D =
+        Matrix4x4::From2D(parentsChildrenOnlyTransform)
+            .ChangeBasis(frameOffset);
+
+    result *= parentsChildrenOnlyTransform3D;
+  }
+
+  Matrix4x4 perspectiveMatrix;
+  bool hasPerspective = aFlags & INCLUDE_PERSPECTIVE;
+  if (hasPerspective) {
+    if (ComputePerspectiveMatrix(frame, aAppUnitsPerPixel, perspectiveMatrix)) {
+      result *= perspectiveMatrix;
+    }
+  }
+
+  if ((aFlags & INCLUDE_PRESERVE3D_ANCESTORS) && frame &&
+      frame->Combines3DTransformWithAncestors()) {
+    // Include the transform set on our parent
+    nsIFrame* parentFrame =
+        frame->GetClosestFlattenedTreeAncestorPrimaryFrame();
+    NS_ASSERTION(parentFrame && parentFrame->IsTransformed() &&
+                     parentFrame->Extend3DContext(),
+                 "Preserve3D mismatch!");
+    TransformReferenceBox refBox(parentFrame);
+    FrameTransformProperties props(parentFrame, refBox, aAppUnitsPerPixel);
+
+    uint32_t flags =
+        aFlags & (INCLUDE_PRESERVE3D_ANCESTORS | INCLUDE_PERSPECTIVE);
+
+    // If this frame isn't transformed (but we exist for backface-visibility),
+    // then we're not a reference frame so no offset to origin will be added.
+    // Otherwise we need to manually translate into our parent's coordinate
+    // space.
+    if (frame->IsTransformed()) {
+      nsLayoutUtils::PostTranslate(result, frame->GetPosition(),
+                                   aAppUnitsPerPixel, shouldRound);
+    }
+    Matrix4x4 parent = GetResultingTransformMatrixInternal(
+        props, refBox, nsPoint(0, 0), aAppUnitsPerPixel, flags);
+    result = result * parent;
+  }
+
+  if (aFlags & OFFSET_BY_ORIGIN) {
+    nsLayoutUtils::PostTranslate(result, aOrigin, aAppUnitsPerPixel,
+                                 shouldRound);
+  }
+
+  return result;
+}
+
+bool nsDisplayOpacity::CanUseAsyncAnimations(nsDisplayListBuilder* aBuilder) {
+  static constexpr nsCSSPropertyIDSet opacitySet =
+      nsCSSPropertyIDSet::OpacityProperties();
+  if (ActiveLayerTracker::IsStyleAnimated(aBuilder, mFrame, opacitySet)) {
+    return true;
+  }
+
+  EffectCompositor::SetPerformanceWarning(
+      mFrame, opacitySet,
+      AnimationPerformanceWarning(
+          AnimationPerformanceWarning::Type::OpacityFrameInactive));
+
+  return false;
+}
+
+bool nsDisplayTransform::CanUseAsyncAnimations(nsDisplayListBuilder* aBuilder) {
+  return mPrerenderDecision != PrerenderDecision::No;
+}
+
+bool nsDisplayBackgroundColor::CanUseAsyncAnimations(
+    nsDisplayListBuilder* aBuilder) {
+  return StaticPrefs::gfx_omta_background_color();
+}
+
+static bool IsInStickyPositionedSubtree(const nsIFrame* aFrame) {
+  for (const nsIFrame* frame = aFrame; frame;
+       frame = nsLayoutUtils::GetCrossDocParentFrameInProcess(frame)) {
+    if (frame->IsStickyPositioned()) {
+      return true;
+    }
+  }
+  return false;
+}
+
+static bool ShouldUsePartialPrerender(const nsIFrame* aFrame) {
+  return StaticPrefs::layout_animation_prerender_partial() &&
+         // Bug 1642547: Support partial prerender for position:sticky elements.
+         !IsInStickyPositionedSubtree(aFrame);
+}
+
+/* static */
+auto nsDisplayTransform::ShouldPrerenderTransformedContent(
+    nsDisplayListBuilder* aBuilder, nsIFrame* aFrame, nsRect* aDirtyRect)
+    -> PrerenderInfo {
+  PrerenderInfo result;
+  // If we are in a preserve-3d tree, and we've disallowed async animations, we
+  // return No prerender decision directly.
+  if ((aFrame->Extend3DContext() ||
+       aFrame->Combines3DTransformWithAncestors()) &&
+      !aBuilder->GetPreserves3DAllowAsyncAnimation()) {
+    return result;
+  }
+
+  // Elements whose transform has been modified recently, or which
+  // have a compositor-animated transform, can be prerendered. An element
+  // might have only just had its transform animated in which case
+  // the ActiveLayerManager may not have been notified yet.
+  static constexpr nsCSSPropertyIDSet transformSet =
+      nsCSSPropertyIDSet::TransformLikeProperties();
+  if (!ActiveLayerTracker::IsTransformMaybeAnimated(aFrame) &&
+      !EffectCompositor::HasAnimationsForCompositor(
+          aFrame, DisplayItemType::TYPE_TRANSFORM)) {
+    EffectCompositor::SetPerformanceWarning(
+        aFrame, transformSet,
+        AnimationPerformanceWarning(
+            AnimationPerformanceWarning::Type::TransformFrameInactive));
+
+    // This case happens when we're sure that the frame is not animated and its
+    // preserve-3d ancestors are not, either. So we don't need to pre-render.
+    // However, this decision shouldn't affect the decisions for other frames in
+    // the preserve-3d context. We need this flag to determine whether we should
+    // block async animations on other frames in the current preserve-3d tree.
+    result.mHasAnimations = false;
+    return result;
+  }
+
+  // We should not allow prerender if any ancestor container element has
+  // mask/clip-path effects.
+  //
+  // With prerender and async transform animation, we do not need to restyle an
+  // animated element to respect position changes, since that transform is done
+  // by layer animation. As a result, the container element is not aware of
+  // position change of that containing element and loses the chance to update
+  // the content of mask/clip-path.
+  //
+  // Why do we need to update a mask? This is relative to how we generate a
+  // mask layer in ContainerState::SetupMaskLayerForCSSMask. While creating a
+  // mask layer, to reduce memory usage, we did not choose the size of the
+  // masked element as mask size. Instead, we read the union of bounds of all
+  // children display items by nsDisplayWrapList::GetBounds, which is smaller
+  // than or equal to the masked element's boundary, and use it as the position
+  // size of the mask layer. That union bounds is actually affected by the
+  // geometry of the animated element. To keep the content of mask up to date,
+  // forbidding of prerender is required.
+  for (nsIFrame* container =
+           nsLayoutUtils::GetCrossDocParentFrameInProcess(aFrame);
+       container;
+       container = nsLayoutUtils::GetCrossDocParentFrameInProcess(container)) {
+    const nsStyleSVGReset* svgReset = container->StyleSVGReset();
+    if (svgReset->HasMask() || svgReset->HasClipPath()) {
+      return result;
+    }
+  }
+
+  // If the incoming dirty rect already contains the entire overflow area,
+  // we are already rendering the entire content.
+  nsRect overflow = aFrame->InkOverflowRectRelativeToSelf();
+  // UntransformRect will not touch the output rect (`&untranformedDirtyRect`)
+  // in cases of non-invertible transforms, so we set `untransformedRect` to
+  // `aDirtyRect` as an initial value for such cases.
+  nsRect untransformedDirtyRect = *aDirtyRect;
+  UntransformRect(*aDirtyRect, overflow, aFrame, &untransformedDirtyRect);
+  if (untransformedDirtyRect.Contains(overflow)) {
+    *aDirtyRect = untransformedDirtyRect;
+    result.mDecision = PrerenderDecision::Full;
+    return result;
+  }
+
+  float viewportRatio =
+      StaticPrefs::layout_animation_prerender_viewport_ratio_limit();
+  uint32_t absoluteLimitX =
+      StaticPrefs::layout_animation_prerender_absolute_limit_x();
+  uint32_t absoluteLimitY =
+      StaticPrefs::layout_animation_prerender_absolute_limit_y();
+  nsSize refSize = aBuilder->RootReferenceFrame()->GetSize();
+
+  float resolution = aFrame->PresShell()->GetCumulativeResolution();
+  if (resolution < 1.0f) {
+    refSize.SizeTo(
+        NSCoordSaturatingNonnegativeMultiply(refSize.width, 1.0f / resolution),
+        NSCoordSaturatingNonnegativeMultiply(refSize.height,
+                                             1.0f / resolution));
+  }
+
+  // Only prerender if the transformed frame's size is <= a multiple of the
+  // reference frame size (~viewport), and less than an absolute limit.
+  // Both the ratio and the absolute limit are configurable.
+  nscoord maxLength = std::max(nscoord(refSize.width * viewportRatio),
+                               nscoord(refSize.height * viewportRatio));
+  nsSize relativeLimit(maxLength, maxLength);
+  nsSize absoluteLimit(
+      aFrame->PresContext()->DevPixelsToAppUnits(absoluteLimitX),
+      aFrame->PresContext()->DevPixelsToAppUnits(absoluteLimitY));
+  nsSize maxSize = Min(relativeLimit, absoluteLimit);
+
+  const auto transform = nsLayoutUtils::GetTransformToAncestor(
+      RelativeTo{aFrame},
+      RelativeTo{nsLayoutUtils::GetDisplayRootFrame(aFrame)});
+  const gfxRect transformedBounds = transform.TransformAndClipBounds(
+      gfxRect(overflow.x, overflow.y, overflow.width, overflow.height),
+      gfxRect::MaxIntRect());
+  const nsSize frameSize =
+      nsSize(transformedBounds.width, transformedBounds.height);
+
+  uint64_t maxLimitArea = uint64_t(maxSize.width) * maxSize.height;
+  uint64_t frameArea = uint64_t(frameSize.width) * frameSize.height;
+  if (frameArea <= maxLimitArea && frameSize <= absoluteLimit) {
+    *aDirtyRect = overflow;
+    result.mDecision = PrerenderDecision::Full;
+    return result;
+  }
+
+  if (ShouldUsePartialPrerender(aFrame)) {
+    *aDirtyRect = nsLayoutUtils::ComputePartialPrerenderArea(
+        aFrame, untransformedDirtyRect, overflow, maxSize);
+    result.mDecision = PrerenderDecision::Partial;
+    return result;
+  }
+
+  if (frameArea > maxLimitArea) {
+    uint64_t appUnitsPerPixel = AppUnitsPerCSSPixel();
+    EffectCompositor::SetPerformanceWarning(
+        aFrame, transformSet,
+        AnimationPerformanceWarning(
+            AnimationPerformanceWarning::Type::ContentTooLargeArea,
+            {
+                int(frameArea / (appUnitsPerPixel * appUnitsPerPixel)),
+                int(maxLimitArea / (appUnitsPerPixel * appUnitsPerPixel)),
+            }));
+  } else {
+    EffectCompositor::SetPerformanceWarning(
+        aFrame, transformSet,
+        AnimationPerformanceWarning(
+            AnimationPerformanceWarning::Type::ContentTooLarge,
+            {
+                nsPresContext::AppUnitsToIntCSSPixels(frameSize.width),
+                nsPresContext::AppUnitsToIntCSSPixels(frameSize.height),
+                nsPresContext::AppUnitsToIntCSSPixels(relativeLimit.width),
+                nsPresContext::AppUnitsToIntCSSPixels(relativeLimit.height),
+                nsPresContext::AppUnitsToIntCSSPixels(absoluteLimit.width),
+                nsPresContext::AppUnitsToIntCSSPixels(absoluteLimit.height),
+            }));
+  }
+
+  return result;
+}
+
+/* If the matrix is singular, or a hidden backface is shown, the frame won't be
+ * visible or hit. */
+static bool IsFrameVisible(nsIFrame* aFrame, const Matrix4x4& aMatrix) {
+  if (aMatrix.IsSingular()) {
+    return false;
+  }
+  if (aFrame->BackfaceIsHidden() && aMatrix.IsBackfaceVisible()) {
+    return false;
+  }
+  return true;
+}
+
+const Matrix4x4Flagged& nsDisplayTransform::GetTransform() const {
+  if (mTransform) {
+    return *mTransform;
+  }
+
+  float scale = mFrame->PresContext()->AppUnitsPerDevPixel();
+
+  if (mHasTransformGetter) {
+    mTransform.emplace((mFrame->GetTransformGetter())(mFrame, scale));
+    Point3D newOrigin =
+        Point3D(NSAppUnitsToFloatPixels(mToReferenceFrame.x, scale),
+                NSAppUnitsToFloatPixels(mToReferenceFrame.y, scale), 0.0f);
+    mTransform->ChangeBasis(newOrigin.x, newOrigin.y, newOrigin.z);
+  } else if (!mIsTransformSeparator) {
+    DebugOnly<bool> isReference = mFrame->IsTransformed() ||
+                                  mFrame->Combines3DTransformWithAncestors() ||
+                                  mFrame->Extend3DContext();
+    MOZ_ASSERT(isReference);
+    mTransform.emplace(
+        GetResultingTransformMatrix(mFrame, ToReferenceFrame(), scale,
+                                    INCLUDE_PERSPECTIVE | OFFSET_BY_ORIGIN));
+  } else {
+    // Use identity matrix
+    mTransform.emplace();
+  }
+
+  return *mTransform;
+}
+
+const Matrix4x4Flagged& nsDisplayTransform::GetInverseTransform() const {
+  if (mInverseTransform) {
+    return *mInverseTransform;
+  }
+
+  MOZ_ASSERT(!GetTransform().IsSingular());
+
+  mInverseTransform.emplace(GetTransform().Inverse());
+
+  return *mInverseTransform;
+}
+
+Matrix4x4 nsDisplayTransform::GetTransformForRendering(
+    LayoutDevicePoint* aOutOrigin) const {
+  if (!mFrame->HasPerspective() || mHasTransformGetter ||
+      mIsTransformSeparator) {
+    if (!mHasTransformGetter && !mIsTransformSeparator && aOutOrigin) {
+      // If aOutOrigin is provided, put the offset to origin into it, because
+      // we need to keep it separate for webrender. The combination of
+      // *aOutOrigin and the returned matrix here should always be equivalent
+      // to what GetTransform() would have returned.
+      float scale = mFrame->PresContext()->AppUnitsPerDevPixel();
+      *aOutOrigin = LayoutDevicePoint::FromAppUnits(ToReferenceFrame(), scale);
+
+      // The rounding behavior should also be the same as GetTransform().
+      if (nsLayoutUtils::ShouldSnapToGrid(mFrame)) {
+        aOutOrigin->Round();
+      }
+      return GetResultingTransformMatrix(mFrame, nsPoint(0, 0), scale,
+                                         INCLUDE_PERSPECTIVE);
+    }
+    return GetTransform().GetMatrix();
+  }
+  MOZ_ASSERT(!mHasTransformGetter);
+
+  float scale = mFrame->PresContext()->AppUnitsPerDevPixel();
+  // Don't include perspective transform, or the offset to origin, since
+  // nsDisplayPerspective will handle both of those.
+  return GetResultingTransformMatrix(mFrame, ToReferenceFrame(), scale, 0);
+}
+
+const Matrix4x4& nsDisplayTransform::GetAccumulatedPreserved3DTransform(
+    nsDisplayListBuilder* aBuilder) {
+  MOZ_ASSERT(!mFrame->Extend3DContext() || IsLeafOf3DContext());
+
+  if (!IsLeafOf3DContext()) {
+    return GetTransform().GetMatrix();
+  }
+
+  if (!mTransformPreserves3D) {
+    const nsIFrame* establisher;  // Establisher of the 3D rendering context.
+    for (establisher = mFrame;
+         establisher && establisher->Combines3DTransformWithAncestors();
+         establisher =
+             establisher->GetClosestFlattenedTreeAncestorPrimaryFrame()) {
+    }
+    const nsIFrame* establisherReference = aBuilder->FindReferenceFrameFor(
+        nsLayoutUtils::GetCrossDocParentFrameInProcess(establisher));
+
+    nsPoint offset = establisher->GetOffsetToCrossDoc(establisherReference);
+    float scale = mFrame->PresContext()->AppUnitsPerDevPixel();
+    uint32_t flags =
+        INCLUDE_PRESERVE3D_ANCESTORS | INCLUDE_PERSPECTIVE | OFFSET_BY_ORIGIN;
+    mTransformPreserves3D = MakeUnique<Matrix4x4>(
+        GetResultingTransformMatrix(mFrame, offset, scale, flags));
+  }
+
+  return *mTransformPreserves3D;
+}
+
+bool nsDisplayTransform::CreateWebRenderCommands(
+    wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+    const StackingContextHelper& aSc, RenderRootStateManager* aManager,
+    nsDisplayListBuilder* aDisplayListBuilder) {
+  // We want to make sure we don't pollute the transform property in the WR
+  // stacking context by including the position of this frame (relative to the
+  // parent reference frame). We need to keep those separate; the position of
+  // this frame goes into the stacking context bounds while the transform goes
+  // into the transform.
+  LayoutDevicePoint position;
+  Matrix4x4 newTransformMatrix = GetTransformForRendering(&position);
+
+  gfx::Matrix4x4* transformForSC = &newTransformMatrix;
+  if (newTransformMatrix.IsIdentity()) {
+    // If the transform is an identity transform, strip it out so that WR
+    // doesn't turn this stacking context into a reference frame, as it
+    // affects positioning. Bug 1345577 tracks a better fix.
+    transformForSC = nullptr;
+
+    // In ChooseScaleAndSetTransform, we round the offset from the reference
+    // frame used to adjust the transform, if there is no transform, or it
+    // is just a translation. We need to do the same here.
+    if (nsLayoutUtils::ShouldSnapToGrid(mFrame)) {
+      position.Round();
+    }
+  }
+
+  auto key = wr::SpatialKey(uint64_t(mFrame), GetPerFrameKey(),
+                            wr::SpatialKeyKind::Transform);
+
+  // We don't send animations for transform separator display items.
+  uint64_t animationsId =
+      mIsTransformSeparator
+          ? 0
+          : AddAnimationsForWebRender(
+                this, aManager, aDisplayListBuilder,
+                IsPartialPrerender() ? Some(position) : Nothing());
+  wr::WrAnimationProperty prop{wr::WrAnimationType::Transform, animationsId,
+                               key};
+
+  nsDisplayTransform* deferredTransformItem = nullptr;
+  if (!mFrame->ChildrenHavePerspective()) {
+    // If it has perspective, we create a new scroll data via the
+    // UpdateScrollData call because that scenario is more complex. Otherwise
+    // we can just stash the transform on the StackingContextHelper and
+    // apply it to any scroll data that are created inside this
+    // nsDisplayTransform.
+    deferredTransformItem = this;
+  }
+
+  // Determine if we're possibly animated (= would need an active layer in FLB).
+  bool animated = !mIsTransformSeparator &&
+                  ActiveLayerTracker::IsTransformMaybeAnimated(Frame());
+
+  wr::StackingContextParams params;
+  params.mBoundTransform = &newTransformMatrix;
+  params.animation = animationsId ? &prop : nullptr;
+
+  wr::WrTransformInfo transform_info;
+  if (transformForSC) {
+    transform_info.transform = wr::ToLayoutTransform(newTransformMatrix);
+    transform_info.key = key;
+    params.mTransformPtr = &transform_info;
+  } else {
+    params.mTransformPtr = nullptr;
+  }
+
+  params.prim_flags = !BackfaceIsHidden()
+                          ? wr::PrimitiveFlags::IS_BACKFACE_VISIBLE
+                          : wr::PrimitiveFlags{0};
+  params.paired_with_perspective = mHasAssociatedPerspective;
+  params.mDeferredTransformItem = deferredTransformItem;
+  params.mAnimated = animated;
+  // Determine if we would have to rasterize any items in local raster space
+  // (i.e. disable subpixel AA). We don't always need to rasterize locally even
+  // if the stacking context is possibly animated (at the cost of potentially
+  // some false negatives with respect to will-change handling), so we pass in
+  // this determination separately to accurately match with when FLB would
+  // normally disable subpixel AA.
+  params.mRasterizeLocally = animated && Frame()->HasAnimationOfTransform();
+  params.SetPreserve3D(mFrame->Extend3DContext() && !mIsTransformSeparator);
+  params.clip =
+      wr::WrStackingContextClip::ClipChain(aBuilder.CurrentClipChainId());
+
+  LayoutDeviceSize boundsSize = LayoutDeviceSize::FromAppUnits(
+      mChildBounds.Size(), mFrame->PresContext()->AppUnitsPerDevPixel());
+
+  StackingContextHelper sc(aSc, GetActiveScrolledRoot(), mFrame, this, aBuilder,
+                           params, LayoutDeviceRect(position, boundsSize));
+
+  aManager->CommandBuilder().CreateWebRenderCommandsFromDisplayList(
+      GetChildren(), this, aDisplayListBuilder, sc, aBuilder, aResources);
+  return true;
+}
+
+bool nsDisplayTransform::UpdateScrollData(
+    WebRenderScrollData* aData, WebRenderLayerScrollData* aLayerData) {
+  if (!mFrame->ChildrenHavePerspective()) {
+    // This case is handled in CreateWebRenderCommands by stashing the transform
+    // on the stacking context.
+    return false;
+  }
+  if (aLayerData) {
+    aLayerData->SetTransform(GetTransform().GetMatrix());
+    aLayerData->SetTransformIsPerspective(true);
+  }
+  return true;
+}
+
+bool nsDisplayTransform::ShouldSkipTransform(
+    nsDisplayListBuilder* aBuilder) const {
+  return (aBuilder->RootReferenceFrame() == mFrame) &&
+         aBuilder->IsForGenerateGlyphMask();
+}
+
+void nsDisplayTransform::Collect3DTransformLeaves(
+    nsDisplayListBuilder* aBuilder, nsTArray<nsDisplayTransform*>& aLeaves) {
+  if (!IsParticipating3DContext() || IsLeafOf3DContext()) {
+    aLeaves.AppendElement(this);
+    return;
+  }
+
+  FlattenedDisplayListIterator iter(aBuilder, &mChildren);
+  while (iter.HasNext()) {
+    nsDisplayItem* item = iter.GetNextItem();
+    if (item->GetType() == DisplayItemType::TYPE_PERSPECTIVE) {
+      auto* perspective = static_cast<nsDisplayPerspective*>(item);
+      if (!perspective->GetChildren()->GetTop()) {
+        continue;
+      }
+      item = perspective->GetChildren()->GetTop();
+    }
+    if (item->GetType() != DisplayItemType::TYPE_TRANSFORM) {
+      gfxCriticalError() << "Invalid child item within 3D transform of type: "
+                         << item->Name();
+      continue;
+    }
+    static_cast<nsDisplayTransform*>(item)->Collect3DTransformLeaves(aBuilder,
+                                                                     aLeaves);
+  }
+}
+
+static RefPtr<gfx::Path> BuildPathFromPolygon(const RefPtr<DrawTarget>& aDT,
+                                              const gfx::Polygon& aPolygon) {
+  MOZ_ASSERT(!aPolygon.IsEmpty());
+
+  RefPtr<PathBuilder> pathBuilder = aDT->CreatePathBuilder();
+  const nsTArray<Point4D>& points = aPolygon.GetPoints();
+
+  pathBuilder->MoveTo(points[0].As2DPoint());
+
+  for (size_t i = 1; i < points.Length(); ++i) {
+    pathBuilder->LineTo(points[i].As2DPoint());
+  }
+
+  pathBuilder->Close();
+  return pathBuilder->Finish();
+}
+
+void nsDisplayTransform::CollectSorted3DTransformLeaves(
+    nsDisplayListBuilder* aBuilder, nsTArray<TransformPolygon>& aLeaves) {
+  std::list<TransformPolygon> inputLayers;
+
+  nsTArray<nsDisplayTransform*> leaves;
+  Collect3DTransformLeaves(aBuilder, leaves);
+  for (nsDisplayTransform* item : leaves) {
+    auto bounds = LayoutDeviceRect::FromAppUnits(
+        item->mChildBounds, item->mFrame->PresContext()->AppUnitsPerDevPixel());
+    Matrix4x4 transform = item->GetAccumulatedPreserved3DTransform(aBuilder);
+
+    if (!IsFrameVisible(item->mFrame, transform)) {
+      continue;
+    }
+    gfx::Polygon polygon =
+        gfx::Polygon::FromRect(gfx::Rect(bounds.ToUnknownRect()));
+
+    polygon.TransformToScreenSpace(transform);
+
+    if (polygon.GetPoints().Length() >= 3) {
+      inputLayers.push_back(TransformPolygon(item, std::move(polygon)));
+    }
+  }
+
+  if (inputLayers.empty()) {
+    return;
+  }
+
+  BSPTree<nsDisplayTransform> tree(inputLayers);
+  nsTArray<TransformPolygon> orderedLayers(tree.GetDrawOrder());
+
+  for (TransformPolygon& polygon : orderedLayers) {
+    Matrix4x4 inverse =
+        polygon.data->GetAccumulatedPreserved3DTransform(aBuilder).Inverse();
+
+    MOZ_ASSERT(polygon.geometry);
+    polygon.geometry->TransformToLayerSpace(inverse);
+  }
+
+  aLeaves = std::move(orderedLayers);
+}
+
+void nsDisplayTransform::Paint(nsDisplayListBuilder* aBuilder,
+                               gfxContext* aCtx) {
+  Paint(aBuilder, aCtx, Nothing());
+}
+
+void nsDisplayTransform::Paint(nsDisplayListBuilder* aBuilder, gfxContext* aCtx,
+                               const Maybe<gfx::Polygon>& aPolygon) {
+  if (IsParticipating3DContext() && !IsLeafOf3DContext()) {
+    MOZ_ASSERT(!aPolygon);
+    nsTArray<TransformPolygon> leaves;
+    CollectSorted3DTransformLeaves(aBuilder, leaves);
+    for (TransformPolygon& item : leaves) {
+      item.data->Paint(aBuilder, aCtx, item.geometry);
+    }
+    return;
+  }
+
+  gfxContextMatrixAutoSaveRestore saveMatrix(aCtx);
+  Matrix4x4 trans = ShouldSkipTransform(aBuilder)
+                        ? Matrix4x4()
+                        : GetAccumulatedPreserved3DTransform(aBuilder);
+  if (!IsFrameVisible(mFrame, trans)) {
+    return;
+  }
+
+  Matrix trans2d;
+  if (trans.CanDraw2D(&trans2d)) {
+    aCtx->Multiply(ThebesMatrix(trans2d));
+
+    if (aPolygon) {
+      RefPtr<gfx::Path> path =
+          BuildPathFromPolygon(aCtx->GetDrawTarget(), *aPolygon);
+      aCtx->GetDrawTarget()->PushClip(path);
+    }
+
+    GetChildren()->Paint(aBuilder, aCtx,
+                         mFrame->PresContext()->AppUnitsPerDevPixel());
+
+    if (aPolygon) {
+      aCtx->GetDrawTarget()->PopClip();
+    }
+    return;
+  }
+
+  // TODO: Implement 3d transform handling, including plane splitting and
+  // sorting. See BasicCompositor.
+  auto pixelBounds = LayoutDeviceRect::FromAppUnitsToOutside(
+      mChildBounds, mFrame->PresContext()->AppUnitsPerDevPixel());
+  RefPtr<DrawTarget> untransformedDT =
+      gfxPlatform::GetPlatform()->CreateOffscreenContentDrawTarget(
+          IntSize(pixelBounds.Width(), pixelBounds.Height()),
+          SurfaceFormat::B8G8R8A8, true);
+  if (!untransformedDT || !untransformedDT->IsValid()) {
+    return;
+  }
+  untransformedDT->SetTransform(
+      Matrix::Translation(-Point(pixelBounds.X(), pixelBounds.Y())));
+
+  RefPtr<gfxContext> groupTarget =
+      gfxContext::CreatePreservingTransformOrNull(untransformedDT);
+
+  if (aPolygon) {
+    RefPtr<gfx::Path> path =
+        BuildPathFromPolygon(aCtx->GetDrawTarget(), *aPolygon);
+    aCtx->GetDrawTarget()->PushClip(path);
+  }
+
+  GetChildren()->Paint(aBuilder, groupTarget,
+                       mFrame->PresContext()->AppUnitsPerDevPixel());
+
+  if (aPolygon) {
+    aCtx->GetDrawTarget()->PopClip();
+  }
+
+  RefPtr<SourceSurface> untransformedSurf = untransformedDT->Snapshot();
+
+  trans.PreTranslate(pixelBounds.X(), pixelBounds.Y(), 0);
+  aCtx->GetDrawTarget()->Draw3DTransformedSurface(untransformedSurf, trans);
+}
+
+bool nsDisplayTransform::MayBeAnimated(nsDisplayListBuilder* aBuilder) const {
+  // If EffectCompositor::HasAnimationsForCompositor() is true then we can
+  // completely bypass the main thread for this animation, so it is always
+  // worthwhile.
+  // For ActiveLayerTracker::IsTransformAnimated() cases the main thread is
+  // already involved so there is less to be gained.
+  // Therefore we check that the *post-transform* bounds of this item are
+  // big enough to justify an active layer.
+  return EffectCompositor::HasAnimationsForCompositor(
+             mFrame, DisplayItemType::TYPE_TRANSFORM) ||
+         (ActiveLayerTracker::IsTransformAnimated(aBuilder, mFrame));
+}
+
+nsRect nsDisplayTransform::TransformUntransformedBounds(
+    nsDisplayListBuilder* aBuilder, const Matrix4x4Flagged& aMatrix) const {
+  bool snap;
+  const nsRect untransformedBounds = GetUntransformedBounds(aBuilder, &snap);
+  // GetTransform always operates in dev pixels.
+  const float factor = mFrame->PresContext()->AppUnitsPerDevPixel();
+  return nsLayoutUtils::MatrixTransformRect(untransformedBounds, aMatrix,
+                                            factor);
+}
+
+/**
+ * Returns the bounds for this transform. The bounds are calculated during
+ * display list building and merging, see |nsDisplayTransform::UpdateBounds()|.
+ */
+nsRect nsDisplayTransform::GetBounds(nsDisplayListBuilder* aBuilder,
+                                     bool* aSnap) const {
+  *aSnap = false;
+  return mBounds;
+}
+
+void nsDisplayTransform::ComputeBounds(nsDisplayListBuilder* aBuilder) {
+  MOZ_ASSERT(mFrame->Extend3DContext() || IsLeafOf3DContext());
+
+  /* Some transforms can get empty bounds in 2D, but might get transformed again
+   * and get non-empty bounds. A simple example of this would be a 180 degree
+   * rotation getting applied twice.
+   * We should not depend on transforming bounds level by level.
+   *
+   * This function collects the bounds of this transform and stores it in
+   * nsDisplayListBuilder. If this is not a leaf of a 3D context, we recurse
+   * down and include the bounds of the child transforms.
+   * The bounds are transformed with the accumulated transformation matrix up to
+   * the 3D context root coordinate space.
+   */
+  nsDisplayListBuilder::AutoAccumulateTransform accTransform(aBuilder);
+  accTransform.Accumulate(GetTransform().GetMatrix());
+
+  // Do not dive into another 3D context.
+  if (!IsLeafOf3DContext()) {
+    for (nsDisplayItem* i : *GetChildren()) {
+      i->DoUpdateBoundsPreserves3D(aBuilder);
+    }
+  }
+
+  /* The child transforms that extend 3D context further will have empty bounds,
+   * so the untransformed bounds here is the bounds of all the non-preserve-3d
+   * content under this transform.
+   */
+  const nsRect rect = TransformUntransformedBounds(
+      aBuilder, accTransform.GetCurrentTransform());
+  aBuilder->AccumulateRect(rect);
+}
+
+void nsDisplayTransform::DoUpdateBoundsPreserves3D(
+    nsDisplayListBuilder* aBuilder) {
+  MOZ_ASSERT(mFrame->Combines3DTransformWithAncestors() ||
+             IsTransformSeparator());
+  // Updating is not going through to child 3D context.
+  ComputeBounds(aBuilder);
+}
+
+void nsDisplayTransform::UpdateBounds(nsDisplayListBuilder* aBuilder) {
+  UpdateUntransformedBounds(aBuilder);
+
+  if (IsTransformSeparator()) {
+    MOZ_ASSERT(GetTransform().IsIdentity());
+    mBounds = mChildBounds;
+    return;
+  }
+
+  if (mFrame->Extend3DContext()) {
+    if (!Combines3DTransformWithAncestors()) {
+      // The transform establishes a 3D context. |UpdateBoundsFor3D()| will
+      // collect the bounds from the child transforms.
+      UpdateBoundsFor3D(aBuilder);
+    } else {
+      // With nested 3D transforms, the 2D bounds might not be useful.
+      mBounds = nsRect();
+    }
+
+    return;
+  }
+
+  MOZ_ASSERT(!mFrame->Extend3DContext());
+
+  // We would like to avoid calculating 2D bounds here for nested 3D transforms,
+  // but mix-blend-mode relies on having bounds set. See bug 1556956.
+
+  // A stand-alone transform.
+  mBounds = TransformUntransformedBounds(aBuilder, GetTransform());
+}
+
+void nsDisplayTransform::UpdateBoundsFor3D(nsDisplayListBuilder* aBuilder) {
+  MOZ_ASSERT(mFrame->Extend3DContext() &&
+             !mFrame->Combines3DTransformWithAncestors() &&
+             !IsTransformSeparator());
+
+  // Always start updating from an establisher of a 3D rendering context.
+  nsDisplayListBuilder::AutoAccumulateRect accRect(aBuilder);
+  nsDisplayListBuilder::AutoAccumulateTransform accTransform(aBuilder);
+  accTransform.StartRoot();
+  ComputeBounds(aBuilder);
+  mBounds = aBuilder->GetAccumulatedRect();
+}
+
+void nsDisplayTransform::UpdateUntransformedBounds(
+    nsDisplayListBuilder* aBuilder) {
+  mChildBounds = GetChildren()->GetClippedBoundsWithRespectToASR(
+      aBuilder, mActiveScrolledRoot);
+}
+
+#ifdef DEBUG_HIT
+#  include <time.h>
+#endif
+
+/* HitTest does some fun stuff with matrix transforms to obtain the answer. */
+void nsDisplayTransform::HitTest(nsDisplayListBuilder* aBuilder,
+                                 const nsRect& aRect, HitTestState* aState,
+                                 nsTArray<nsIFrame*>* aOutFrames) {
+  if (aState->mInPreserves3D) {
+    GetChildren()->HitTest(aBuilder, aRect, aState, aOutFrames);
+    return;
+  }
+
+  /* Here's how this works:
+   * 1. Get the matrix.  If it's singular, abort (clearly we didn't hit
+   *    anything).
+   * 2. Invert the matrix.
+   * 3. Use it to transform the rect into the correct space.
+   * 4. Pass that rect down through to the list's version of HitTest.
+   */
+  // GetTransform always operates in dev pixels.
+  float factor = mFrame->PresContext()->AppUnitsPerDevPixel();
+  Matrix4x4 matrix = GetAccumulatedPreserved3DTransform(aBuilder);
+
+  if (!IsFrameVisible(mFrame, matrix)) {
+    return;
+  }
+
+  const bool oldHitOccludingItem = aState->mHitOccludingItem;
+
+  /* We want to go from transformed-space to regular space.
+   * Thus we have to invert the matrix, which normally does
+   * the reverse operation (e.g. regular->transformed)
+   */
+
+  /* Now, apply the transform and pass it down the channel. */
+  matrix.Invert();
+  nsRect resultingRect;
+  // Magic width/height indicating we're hit testing a point, not a rect
+  const bool testingPoint = aRect.width == 1 && aRect.height == 1;
+  if (testingPoint) {
+    Point4D point =
+        matrix.ProjectPoint(Point(NSAppUnitsToFloatPixels(aRect.x, factor),
+                                  NSAppUnitsToFloatPixels(aRect.y, factor)));
+    if (!point.HasPositiveWCoord()) {
+      return;
+    }
+
+    Point point2d = point.As2DPoint();
+
+    resultingRect =
+        nsRect(NSFloatPixelsToAppUnits(float(point2d.x), factor),
+               NSFloatPixelsToAppUnits(float(point2d.y), factor), 1, 1);
+
+  } else {
+    Rect originalRect(NSAppUnitsToFloatPixels(aRect.x, factor),
+                      NSAppUnitsToFloatPixels(aRect.y, factor),
+                      NSAppUnitsToFloatPixels(aRect.width, factor),
+                      NSAppUnitsToFloatPixels(aRect.height, factor));
+
+    Rect childGfxBounds(NSAppUnitsToFloatPixels(mChildBounds.x, factor),
+                        NSAppUnitsToFloatPixels(mChildBounds.y, factor),
+                        NSAppUnitsToFloatPixels(mChildBounds.width, factor),
+                        NSAppUnitsToFloatPixels(mChildBounds.height, factor));
+
+    Rect rect = matrix.ProjectRectBounds(originalRect, childGfxBounds);
+
+    resultingRect =
+        nsRect(NSFloatPixelsToAppUnits(float(rect.X()), factor),
+               NSFloatPixelsToAppUnits(float(rect.Y()), factor),
+               NSFloatPixelsToAppUnits(float(rect.Width()), factor),
+               NSFloatPixelsToAppUnits(float(rect.Height()), factor));
+  }
+
+  if (resultingRect.IsEmpty()) {
+    return;
+  }
+
+#ifdef DEBUG_HIT
+  printf("Frame: %p\n", dynamic_cast<void*>(mFrame));
+  printf("  Untransformed point: (%f, %f)\n", resultingRect.X(),
+         resultingRect.Y());
+  uint32_t originalFrameCount = aOutFrames.Length();
+#endif
+
+  GetChildren()->HitTest(aBuilder, resultingRect, aState, aOutFrames);
+
+  if (aState->mHitOccludingItem && !testingPoint &&
+      !mChildBounds.Contains(aRect)) {
+    MOZ_ASSERT(aBuilder->HitTestIsForVisibility());
+    // We're hit-testing a rect that's bigger than our child bounds, but
+    // resultingRect is clipped by our bounds (in ProjectRectBounds above), so
+    // we can't stop hit-testing altogether.
+    //
+    // FIXME(emilio): I think this means that theoretically we might include
+    // some frames fully behind other transformed-but-opaque frames? Then again
+    // that's our pre-existing behavior for other untransformed content that
+    // doesn't fill the whole rect. To be fully correct I think we'd need proper
+    // "known occluded region" tracking, but that might be overkill for our
+    // purposes here.
+    aState->mHitOccludingItem = oldHitOccludingItem;
+  }
+
+#ifdef DEBUG_HIT
+  if (originalFrameCount != aOutFrames.Length())
+    printf("  Hit! Time: %f, first frame: %p\n", static_cast<double>(clock()),
+           dynamic_cast<void*>(aOutFrames.ElementAt(0)));
+  printf("=== end of hit test ===\n");
+#endif
+}
+
+float nsDisplayTransform::GetHitDepthAtPoint(nsDisplayListBuilder* aBuilder,
+                                             const nsPoint& aPoint) {
+  // GetTransform always operates in dev pixels.
+  float factor = mFrame->PresContext()->AppUnitsPerDevPixel();
+  Matrix4x4 matrix = GetAccumulatedPreserved3DTransform(aBuilder);
+
+  NS_ASSERTION(IsFrameVisible(mFrame, matrix),
+               "We can't have hit a frame that isn't visible!");
+
+  Matrix4x4 inverse = matrix;
+  inverse.Invert();
+  Point4D point =
+      inverse.ProjectPoint(Point(NSAppUnitsToFloatPixels(aPoint.x, factor),
+                                 NSAppUnitsToFloatPixels(aPoint.y, factor)));
+
+  Point point2d = point.As2DPoint();
+
+  Point3D transformed = matrix.TransformPoint(Point3D(point2d.x, point2d.y, 0));
+  return transformed.z;
+}
+
+/* The transform is opaque iff the transform consists solely of scales and
+ * translations and if the underlying content is opaque.  Thus if the transform
+ * is of the form
+ *
+ * |a c e|
+ * |b d f|
+ * |0 0 1|
+ *
+ * We need b and c to be zero.
+ *
+ * We also need to check whether the underlying opaque content completely fills
+ * our visible rect. We use UntransformRect which expands to the axis-aligned
+ * bounding rect, but that's OK since if
+ * mStoredList.GetVisibleRect().Contains(untransformedVisible), then it
+ * certainly contains the actual (non-axis-aligned) untransformed rect.
+ */
+nsRegion nsDisplayTransform::GetOpaqueRegion(nsDisplayListBuilder* aBuilder,
+                                             bool* aSnap) const {
+  *aSnap = false;
+
+  nsRect untransformedVisible;
+  if (!UntransformBuildingRect(aBuilder, &untransformedVisible)) {
+    return nsRegion();
+  }
+
+  const Matrix4x4Flagged& matrix = GetTransform();
+  Matrix matrix2d;
+  if (!matrix.Is2D(&matrix2d) || !matrix2d.PreservesAxisAlignedRectangles()) {
+    return nsRegion();
+  }
+
+  nsRegion result;
+
+  bool tmpSnap;
+  const nsRect bounds = GetUntransformedBounds(aBuilder, &tmpSnap);
+  const nsRegion opaque =
+      ::mozilla::GetOpaqueRegion(aBuilder, GetChildren(), bounds);
+
+  if (opaque.Contains(untransformedVisible)) {
+    result = GetBuildingRect().Intersect(GetBounds(aBuilder, &tmpSnap));
+  }
+  return result;
+}
+
+nsRect nsDisplayTransform::GetComponentAlphaBounds(
+    nsDisplayListBuilder* aBuilder) const {
+  if (GetChildren()->GetComponentAlphaBounds(aBuilder).IsEmpty()) {
+    return nsRect();
+  }
+
+  bool snap;
+  return GetBounds(aBuilder, &snap);
+}
+
+/* TransformRect takes in as parameters a rectangle (in app space) and returns
+ * the smallest rectangle (in app space) containing the transformed image of
+ * that rectangle.  That is, it takes the four corners of the rectangle,
+ * transforms them according to the matrix associated with the specified frame,
+ * then returns the smallest rectangle containing the four transformed points.
+ *
+ * @param aUntransformedBounds The rectangle (in app units) to transform.
+ * @param aFrame The frame whose transformation should be applied.
+ * @param aOrigin The delta from the frame origin to the coordinate space origin
+ * @return The smallest rectangle containing the image of the transformed
+ *         rectangle.
+ */
+nsRect nsDisplayTransform::TransformRect(const nsRect& aUntransformedBounds,
+                                         const nsIFrame* aFrame,
+                                         TransformReferenceBox& aRefBox) {
+  MOZ_ASSERT(aFrame, "Can't take the transform based on a null frame!");
+
+  float factor = aFrame->PresContext()->AppUnitsPerDevPixel();
+
+  FrameTransformProperties props(aFrame, aRefBox, factor);
+  return nsLayoutUtils::MatrixTransformRect(
+      aUntransformedBounds,
+      GetResultingTransformMatrixInternal(props, aRefBox, nsPoint(), factor,
+                                          kTransformRectFlags),
+      factor);
+}
+
+bool nsDisplayTransform::UntransformRect(const nsRect& aTransformedBounds,
+                                         const nsRect& aChildBounds,
+                                         const nsIFrame* aFrame,
+                                         nsRect* aOutRect) {
+  MOZ_ASSERT(aFrame, "Can't take the transform based on a null frame!");
+
+  float factor = aFrame->PresContext()->AppUnitsPerDevPixel();
+  Matrix4x4 transform = GetResultingTransformMatrix(aFrame, nsPoint(), factor,
+                                                    kTransformRectFlags);
+  return UntransformRect(aTransformedBounds, aChildBounds, transform, factor,
+                         aOutRect);
+}
+
+bool nsDisplayTransform::UntransformRect(const nsRect& aTransformedBounds,
+                                         const nsRect& aChildBounds,
+                                         const Matrix4x4& aMatrix,
+                                         float aAppUnitsPerPixel,
+                                         nsRect* aOutRect) {
+  if (aMatrix.IsSingular()) {
+    return false;
+  }
+
+  RectDouble result(
+      NSAppUnitsToFloatPixels(aTransformedBounds.x, aAppUnitsPerPixel),
+      NSAppUnitsToFloatPixels(aTransformedBounds.y, aAppUnitsPerPixel),
+      NSAppUnitsToFloatPixels(aTransformedBounds.width, aAppUnitsPerPixel),
+      NSAppUnitsToFloatPixels(aTransformedBounds.height, aAppUnitsPerPixel));
+
+  RectDouble childGfxBounds(
+      NSAppUnitsToFloatPixels(aChildBounds.x, aAppUnitsPerPixel),
+      NSAppUnitsToFloatPixels(aChildBounds.y, aAppUnitsPerPixel),
+      NSAppUnitsToFloatPixels(aChildBounds.width, aAppUnitsPerPixel),
+      NSAppUnitsToFloatPixels(aChildBounds.height, aAppUnitsPerPixel));
+
+  result = aMatrix.Inverse().ProjectRectBounds(result, childGfxBounds);
+  *aOutRect = nsLayoutUtils::RoundGfxRectToAppRect(ThebesRect(result),
+                                                   aAppUnitsPerPixel);
+  return true;
+}
+
+bool nsDisplayTransform::UntransformRect(nsDisplayListBuilder* aBuilder,
+                                         const nsRect& aRect,
+                                         nsRect* aOutRect) const {
+  if (GetTransform().IsSingular()) {
+    return false;
+  }
+
+  // GetTransform always operates in dev pixels.
+  float factor = mFrame->PresContext()->AppUnitsPerDevPixel();
+  RectDouble result(NSAppUnitsToFloatPixels(aRect.x, factor),
+                    NSAppUnitsToFloatPixels(aRect.y, factor),
+                    NSAppUnitsToFloatPixels(aRect.width, factor),
+                    NSAppUnitsToFloatPixels(aRect.height, factor));
+
+  bool snap;
+  nsRect childBounds = GetUntransformedBounds(aBuilder, &snap);
+  RectDouble childGfxBounds(
+      NSAppUnitsToFloatPixels(childBounds.x, factor),
+      NSAppUnitsToFloatPixels(childBounds.y, factor),
+      NSAppUnitsToFloatPixels(childBounds.width, factor),
+      NSAppUnitsToFloatPixels(childBounds.height, factor));
+
+  /* We want to untransform the matrix, so invert the transformation first! */
+  result = GetInverseTransform().ProjectRectBounds(result, childGfxBounds);
+
+  *aOutRect = nsLayoutUtils::RoundGfxRectToAppRect(ThebesRect(result), factor);
+
+  return true;
+}
+
+void nsDisplayTransform::WriteDebugInfo(std::stringstream& aStream) {
+  aStream << GetTransform().GetMatrix();
+  if (IsTransformSeparator()) {
+    aStream << " transform-separator";
+  }
+  if (IsLeafOf3DContext()) {
+    aStream << " 3d-context-leaf";
+  }
+  if (mFrame->Extend3DContext()) {
+    aStream << " extends-3d-context";
+  }
+  if (mFrame->Combines3DTransformWithAncestors()) {
+    aStream << " combines-3d-with-ancestors";
+  }
+
+  aStream << " prerender(";
+  switch (mPrerenderDecision) {
+    case PrerenderDecision::No:
+      aStream << "no";
+      break;
+    case PrerenderDecision::Partial:
+      aStream << "partial";
+      break;
+    case PrerenderDecision::Full:
+      aStream << "full";
+      break;
+  }
+  aStream << ")";
+  aStream << " childrenBuildingRect" << mChildrenBuildingRect;
+}
+
+nsDisplayPerspective::nsDisplayPerspective(nsDisplayListBuilder* aBuilder,
+                                           nsIFrame* aFrame,
+                                           nsDisplayList* aList)
+    : nsPaintedDisplayItem(aBuilder, aFrame), mList(aBuilder) {
+  mList.AppendToTop(aList);
+  MOZ_ASSERT(mList.Length() == 1);
+  MOZ_ASSERT(mList.GetTop()->GetType() == DisplayItemType::TYPE_TRANSFORM);
+}
+
+void nsDisplayPerspective::Paint(nsDisplayListBuilder* aBuilder,
+                                 gfxContext* aCtx) {
+  // Just directly recurse into children, since we'll include the persepctive
+  // value in any nsDisplayTransform children.
+  GetChildren()->Paint(aBuilder, aCtx,
+                       mFrame->PresContext()->AppUnitsPerDevPixel());
+}
+
+nsRegion nsDisplayPerspective::GetOpaqueRegion(nsDisplayListBuilder* aBuilder,
+                                               bool* aSnap) const {
+  if (!GetChildren()->GetTop()) {
+    *aSnap = false;
+    return nsRegion();
+  }
+
+  return GetChildren()->GetTop()->GetOpaqueRegion(aBuilder, aSnap);
+}
+
+bool nsDisplayPerspective::CreateWebRenderCommands(
+    wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+    const StackingContextHelper& aSc, RenderRootStateManager* aManager,
+    nsDisplayListBuilder* aDisplayListBuilder) {
+  float appUnitsPerPixel = mFrame->PresContext()->AppUnitsPerDevPixel();
+  Matrix4x4 perspectiveMatrix;
+  DebugOnly<bool> hasPerspective = nsDisplayTransform::ComputePerspectiveMatrix(
+      mFrame, appUnitsPerPixel, perspectiveMatrix);
+  MOZ_ASSERT(hasPerspective, "Why did we create nsDisplayPerspective?");
+
+  /*
+   * ClipListToRange can remove our child after we were created.
+   */
+  if (!GetChildren()->GetTop()) {
+    return false;
+  }
+
+  /*
+   * The resulting matrix is still in the coordinate space of the transformed
+   * frame. Append a translation to the reference frame coordinates.
+   */
+  nsDisplayTransform* transform =
+      static_cast<nsDisplayTransform*>(GetChildren()->GetTop());
+
+  Point3D newOrigin =
+      Point3D(NSAppUnitsToFloatPixels(transform->ToReferenceFrame().x,
+                                      appUnitsPerPixel),
+              NSAppUnitsToFloatPixels(transform->ToReferenceFrame().y,
+                                      appUnitsPerPixel),
+              0.0f);
+  Point3D roundedOrigin(NS_round(newOrigin.x), NS_round(newOrigin.y), 0);
+
+  perspectiveMatrix.PostTranslate(roundedOrigin);
+
+  nsIFrame* perspectiveFrame =
+      mFrame->GetClosestFlattenedTreeAncestorPrimaryFrame();
+
+  // Passing true here is always correct, since perspective always combines
+  // transforms with the descendants. However that'd make WR do a lot of work
+  // that it doesn't really need to do if there aren't other transforms forming
+  // part of the 3D context.
+  //
+  // WR knows how to treat perspective in that case, so the only thing we need
+  // to do is to ensure we pass true when we're involved in a 3d context in any
+  // other way via the transform-style property on either the transformed frame
+  // or the perspective frame in order to not confuse WR's preserve-3d code in
+  // very awful ways.
+  bool preserve3D =
+      mFrame->Extend3DContext() || perspectiveFrame->Extend3DContext();
+
+  wr::StackingContextParams params;
+
+  wr::WrTransformInfo transform_info;
+  transform_info.transform = wr::ToLayoutTransform(perspectiveMatrix);
+  transform_info.key = wr::SpatialKey(uint64_t(mFrame), GetPerFrameKey(),
+                                      wr::SpatialKeyKind::Perspective);
+  params.mTransformPtr = &transform_info;
+
+  params.reference_frame_kind = wr::WrReferenceFrameKind::Perspective;
+  params.prim_flags = !BackfaceIsHidden()
+                          ? wr::PrimitiveFlags::IS_BACKFACE_VISIBLE
+                          : wr::PrimitiveFlags{0};
+  params.SetPreserve3D(preserve3D);
+  params.clip =
+      wr::WrStackingContextClip::ClipChain(aBuilder.CurrentClipChainId());
+
+  Maybe<uint64_t> scrollingRelativeTo;
+  for (const auto* asr = GetActiveScrolledRoot(); asr; asr = asr->mParent) {
+    // In OOP documents, the root scrollable frame of the in-process root
+    // document is always active, so using IsAncestorFrameCrossDocInProcess
+    // should be fine here.
+    if (nsLayoutUtils::IsAncestorFrameCrossDocInProcess(
+            asr->mScrollableFrame->GetScrolledFrame(), perspectiveFrame)) {
+      scrollingRelativeTo.emplace(asr->GetViewId());
+      break;
+    }
+  }
+
+  // We put the perspective reference frame wrapping the transformed frame,
+  // even though there may be arbitrarily nested scroll frames in between.
+  //
+  // We need to know how many ancestor scroll-frames are we nested in, in order
+  // for the async scrolling code in WebRender to calculate the right
+  // transformation for the perspective contents.
+  params.scrolling_relative_to = scrollingRelativeTo.ptrOr(nullptr);
+
+  StackingContextHelper sc(aSc, GetActiveScrolledRoot(), mFrame, this, aBuilder,
+                           params);
+
+  aManager->CommandBuilder().CreateWebRenderCommandsFromDisplayList(
+      GetChildren(), this, aDisplayListBuilder, sc, aBuilder, aResources);
+
+  return true;
+}
+
+nsDisplayText::nsDisplayText(nsDisplayListBuilder* aBuilder,
+                             nsTextFrame* aFrame)
+    : nsPaintedDisplayItem(aBuilder, aFrame),
+      mVisIStartEdge(0),
+      mVisIEndEdge(0) {
+  MOZ_COUNT_CTOR(nsDisplayText);
+  mBounds = mFrame->InkOverflowRectRelativeToSelf() + ToReferenceFrame();
+  // Bug 748228
+  mBounds.Inflate(mFrame->PresContext()->AppUnitsPerDevPixel());
+  mVisibleRect = aBuilder->GetVisibleRect() +
+                 aBuilder->GetCurrentFrameOffsetToReferenceFrame();
+}
+
+bool nsDisplayText::CanApplyOpacity(WebRenderLayerManager* aManager,
+                                    nsDisplayListBuilder* aBuilder) const {
+  auto* f = static_cast<nsTextFrame*>(mFrame);
+
+  if (f->IsSelected()) {
+    return false;
+  }
+
+  const nsStyleText* textStyle = f->StyleText();
+  if (textStyle->HasTextShadow()) {
+    return false;
+  }
+
+  nsTextFrame::TextDecorations decorations;
+  f->GetTextDecorations(f->PresContext(), nsTextFrame::eResolvedColors,
+                        decorations);
+  return !decorations.HasDecorationLines();
+}
+
+void nsDisplayText::Paint(nsDisplayListBuilder* aBuilder, gfxContext* aCtx) {
+  AUTO_PROFILER_LABEL("nsDisplayText::Paint", GRAPHICS);
+  // We don't pass mVisibleRect here, since this can be called from within
+  // the WebRender fallback painting path, and we don't want to issue
+  // recorded commands that are dependent on the visible/building rect.
+  RenderToContext(aCtx, aBuilder, GetPaintRect(aBuilder, aCtx));
+}
+
+bool nsDisplayText::CreateWebRenderCommands(
+    wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+    const StackingContextHelper& aSc, RenderRootStateManager* aManager,
+    nsDisplayListBuilder* aDisplayListBuilder) {
+  auto* f = static_cast<nsTextFrame*>(mFrame);
+  auto appUnitsPerDevPixel = f->PresContext()->AppUnitsPerDevPixel();
+
+  nsRect bounds = f->WebRenderBounds() + ToReferenceFrame();
+  // Bug 748228
+  bounds.Inflate(appUnitsPerDevPixel);
+
+  if (bounds.IsEmpty()) {
+    return true;
+  }
+
+  // For large font sizes, punt to a blob image, to avoid the blurry rendering
+  // that results from WR clamping the glyph size used for rasterization.
+  //
+  // (See FONT_SIZE_LIMIT in webrender/src/glyph_rasterizer/mod.rs.)
+  //
+  // This is not strictly accurate, as final used font sizes might not be the
+  // same as claimed by the fontGroup's style.size (eg: due to font-size-adjust
+  // altering the used size of the font actually used).
+  // It also fails to consider how transforms might affect the device-font-size
+  // that webrender uses (and clamps).
+  // But it should be near enough for practical purposes; the limitations just
+  // mean we might sometimes end up with webrender still applying some bitmap
+  // scaling, or bail out when we didn't really need to.
+  constexpr float kWebRenderFontSizeLimit = 320.0;
+  f->EnsureTextRun(nsTextFrame::eInflated);
+  gfxTextRun* textRun = f->GetTextRun(nsTextFrame::eInflated);
+  if (textRun &&
+      textRun->GetFontGroup()->GetStyle()->size > kWebRenderFontSizeLimit) {
+    return false;
+  }
+
+  gfx::Point deviceOffset =
+      LayoutDevicePoint::FromAppUnits(bounds.TopLeft(), appUnitsPerDevPixel)
+          .ToUnknownPoint();
+
+  // Clipping the bounds to the PaintRect (factoring in what's covered by parent
+  // frames) let's us early reject a bunch of things, but it can produce
+  // incorrect results for shadows, because they can translate things back into
+  // view. Also if we're selected we might have some shadows from the
+  // ::selected and ::inctive-selected pseudo-selectors. So don't do this
+  // optimization if we have shadows or a selection.
+  if (!(f->IsSelected() || f->StyleText()->HasTextShadow())) {
+    nsRect visible = mVisibleRect;
+    visible.Inflate(3 * appUnitsPerDevPixel);
+    bounds = bounds.Intersect(visible);
+  }
+
+  RefPtr<gfxContext> textDrawer = aBuilder.GetTextContext(
+      aResources, aSc, aManager, this, bounds, deviceOffset);
+
+  aBuilder.StartGroup(this);
+
+  RenderToContext(textDrawer, aDisplayListBuilder, mVisibleRect,
+                  aBuilder.GetInheritedOpacity(), true);
+  const bool result = textDrawer->GetTextDrawer()->Finish();
+
+  if (result) {
+    aBuilder.FinishGroup();
+  } else {
+    aBuilder.CancelGroup(true);
+  }
+
+  return result;
+}
+
+void nsDisplayText::RenderToContext(gfxContext* aCtx,
+                                    nsDisplayListBuilder* aBuilder,
+                                    const nsRect& aVisibleRect, float aOpacity,
+                                    bool aIsRecording) {
+  nsTextFrame* f = static_cast<nsTextFrame*>(mFrame);
+
+  // Add 1 pixel of dirty area around mVisibleRect to allow us to paint
+  // antialiased pixels beyond the measured text extents.
+  // This is temporary until we do this in the actual calculation of text
+  // extents.
+  auto A2D = mFrame->PresContext()->AppUnitsPerDevPixel();
+  LayoutDeviceRect extraVisible =
+      LayoutDeviceRect::FromAppUnits(aVisibleRect, A2D);
+  extraVisible.Inflate(1);
+
+  gfxRect pixelVisible(extraVisible.x, extraVisible.y, extraVisible.width,
+                       extraVisible.height);
+  pixelVisible.Inflate(2);
+  pixelVisible.RoundOut();
+
+  bool willClip = !aBuilder->IsForGenerateGlyphMask() && !aIsRecording;
+  if (willClip) {
+    aCtx->Clip(pixelVisible);
+  }
+
+  NS_ASSERTION(mVisIStartEdge >= 0, "illegal start edge");
+  NS_ASSERTION(mVisIEndEdge >= 0, "illegal end edge");
+
+  gfxContextMatrixAutoSaveRestore matrixSR;
+
+  nsPoint framePt = ToReferenceFrame();
+  if (f->Style()->IsTextCombined()) {
+    float scaleFactor = nsTextFrame::GetTextCombineScaleFactor(f);
+    if (scaleFactor != 1.0f) {
+      if (auto* textDrawer = aCtx->GetTextDrawer()) {
+        // WebRender doesn't support scaling text like this yet
+        textDrawer->FoundUnsupportedFeature();
+        return;
+      }
+      matrixSR.SetContext(aCtx);
+      // Setup matrix to compress text for text-combine-upright if
+      // necessary. This is done here because we want selection be
+      // compressed at the same time as text.
+      gfxPoint pt = nsLayoutUtils::PointToGfxPoint(framePt, A2D);
+      gfxMatrix mat = aCtx->CurrentMatrixDouble()
+                          .PreTranslate(pt)
+                          .PreScale(scaleFactor, 1.0)
+                          .PreTranslate(-pt);
+      aCtx->SetMatrixDouble(mat);
+    }
+  }
+  nsTextFrame::PaintTextParams params(aCtx);
+  params.framePt = gfx::Point(framePt.x, framePt.y);
+  params.dirtyRect = extraVisible;
+
+  if (aBuilder->IsForGenerateGlyphMask()) {
+    params.state = nsTextFrame::PaintTextParams::GenerateTextMask;
+  } else {
+    params.state = nsTextFrame::PaintTextParams::PaintText;
+  }
+
+  f->PaintText(params, mVisIStartEdge, mVisIEndEdge, ToReferenceFrame(),
+               f->IsSelected(), aOpacity);
+
+  if (willClip) {
+    aCtx->PopClip();
+  }
+}
+
+// This could go to nsDisplayListInvalidation.h, but
+// |nsTextFrame::TextDecorations| requires including of nsTextFrame.h which
+// would produce circular dependencies.
+class nsDisplayTextGeometry : public nsDisplayItemGenericGeometry {
+ public:
+  nsDisplayTextGeometry(nsDisplayText* aItem, nsDisplayListBuilder* aBuilder)
+      : nsDisplayItemGenericGeometry(aItem, aBuilder),
+        mVisIStartEdge(aItem->VisIStartEdge()),
+        mVisIEndEdge(aItem->VisIEndEdge()) {
+    nsTextFrame* f = static_cast<nsTextFrame*>(aItem->Frame());
+    f->GetTextDecorations(f->PresContext(), nsTextFrame::eResolvedColors,
+                          mDecorations);
+  }
+
+  /**
+   * We store the computed text decorations here since they are
+   * computed using style data from parent frames. Any changes to these
+   * styles will only invalidate the parent frame and not this frame.
+   */
+  nsTextFrame::TextDecorations mDecorations;
+  nscoord mVisIStartEdge;
+  nscoord mVisIEndEdge;
+};
+
+nsDisplayItemGeometry* nsDisplayText::AllocateGeometry(
+    nsDisplayListBuilder* aBuilder) {
+  return new nsDisplayTextGeometry(this, aBuilder);
+}
+
+void nsDisplayText::ComputeInvalidationRegion(
+    nsDisplayListBuilder* aBuilder, const nsDisplayItemGeometry* aGeometry,
+    nsRegion* aInvalidRegion) const {
+  const nsDisplayTextGeometry* geometry =
+      static_cast<const nsDisplayTextGeometry*>(aGeometry);
+  nsTextFrame* f = static_cast<nsTextFrame*>(mFrame);
+
+  nsTextFrame::TextDecorations decorations;
+  f->GetTextDecorations(f->PresContext(), nsTextFrame::eResolvedColors,
+                        decorations);
+
+  bool snap;
+  const nsRect& newRect = geometry->mBounds;
+  nsRect oldRect = GetBounds(aBuilder, &snap);
+  if (decorations != geometry->mDecorations ||
+      mVisIStartEdge != geometry->mVisIStartEdge ||
+      mVisIEndEdge != geometry->mVisIEndEdge ||
+      !oldRect.IsEqualInterior(newRect) ||
+      !geometry->mBorderRect.IsEqualInterior(GetBorderRect())) {
+    aInvalidRegion->Or(oldRect, newRect);
+  }
+}
+
+void nsDisplayText::WriteDebugInfo(std::stringstream& aStream) {
+#ifdef DEBUG
+  aStream << " (\"";
+
+  nsTextFrame* f = static_cast<nsTextFrame*>(mFrame);
+  nsCString buf;
+  f->ToCString(buf);
+
+  aStream << buf.get() << "\")";
+#endif
+}
+
+nsDisplayEffectsBase::nsDisplayEffectsBase(
+    nsDisplayListBuilder* aBuilder, nsIFrame* aFrame, nsDisplayList* aList,
+    const ActiveScrolledRoot* aActiveScrolledRoot, bool aClearClipChain)
+    : nsDisplayWrapList(aBuilder, aFrame, aList, aActiveScrolledRoot,
+                        aClearClipChain) {
+  MOZ_COUNT_CTOR(nsDisplayEffectsBase);
+}
+
+nsDisplayEffectsBase::nsDisplayEffectsBase(nsDisplayListBuilder* aBuilder,
+                                           nsIFrame* aFrame,
+                                           nsDisplayList* aList)
+    : nsDisplayWrapList(aBuilder, aFrame, aList) {
+  MOZ_COUNT_CTOR(nsDisplayEffectsBase);
+}
+
+nsRegion nsDisplayEffectsBase::GetOpaqueRegion(nsDisplayListBuilder* aBuilder,
+                                               bool* aSnap) const {
+  *aSnap = false;
+  return nsRegion();
+}
+
+void nsDisplayEffectsBase::HitTest(nsDisplayListBuilder* aBuilder,
+                                   const nsRect& aRect, HitTestState* aState,
+                                   nsTArray<nsIFrame*>* aOutFrames) {
+  nsPoint rectCenter(aRect.x + aRect.width / 2, aRect.y + aRect.height / 2);
+  if (SVGIntegrationUtils::HitTestFrameForEffects(
+          mFrame, rectCenter - ToReferenceFrame())) {
+    mList.HitTest(aBuilder, aRect, aState, aOutFrames);
+  }
+}
+
+gfxRect nsDisplayEffectsBase::BBoxInUserSpace() const {
+  return SVGUtils::GetBBox(mFrame);
+}
+
+gfxPoint nsDisplayEffectsBase::UserSpaceOffset() const {
+  return SVGUtils::FrameSpaceInCSSPxToUserSpaceOffset(mFrame);
+}
+
+void nsDisplayEffectsBase::ComputeInvalidationRegion(
+    nsDisplayListBuilder* aBuilder, const nsDisplayItemGeometry* aGeometry,
+    nsRegion* aInvalidRegion) const {
+  const auto* geometry =
+      static_cast<const nsDisplaySVGEffectGeometry*>(aGeometry);
+  bool snap;
+  nsRect bounds = GetBounds(aBuilder, &snap);
+  if (geometry->mFrameOffsetToReferenceFrame != ToReferenceFrame() ||
+      geometry->mUserSpaceOffset != UserSpaceOffset() ||
+      !geometry->mBBox.IsEqualInterior(BBoxInUserSpace())) {
+    // Filter and mask output can depend on the location of the frame's user
+    // space and on the frame's BBox. We need to invalidate if either of these
+    // change relative to the reference frame.
+    // Invalidations from our inactive layer manager are not enough to catch
+    // some of these cases because filters can produce output even if there's
+    // nothing in the filter input.
+    aInvalidRegion->Or(bounds, geometry->mBounds);
+  }
+}
+
+bool nsDisplayEffectsBase::ValidateSVGFrame() {
+  const nsIContent* content = mFrame->GetContent();
+  bool hasSVGLayout = mFrame->HasAnyStateBits(NS_FRAME_SVG_LAYOUT);
+  if (hasSVGLayout) {
+    ISVGDisplayableFrame* svgFrame = do_QueryFrame(mFrame);
+    if (!svgFrame || !mFrame->GetContent()->IsSVGElement()) {
+      NS_ASSERTION(false, "why?");
+      return false;
+    }
+    if (!static_cast<const SVGElement*>(content)->HasValidDimensions()) {
+      return false;  // The SVG spec says not to draw filters for this
+    }
+  }
+
+  return true;
+}
+
+using PaintFramesParams = SVGIntegrationUtils::PaintFramesParams;
+
+static void ComputeMaskGeometry(PaintFramesParams& aParams) {
+  // Properties are added lazily and may have been removed by a restyle, so
+  // make sure all applicable ones are set again.
+  nsIFrame* firstFrame =
+      nsLayoutUtils::FirstContinuationOrIBSplitSibling(aParams.frame);
+
+  const nsStyleSVGReset* svgReset = firstFrame->StyleSVGReset();
+
+  nsTArray<SVGMaskFrame*> maskFrames;
+  // XXX check return value?
+  SVGObserverUtils::GetAndObserveMasks(firstFrame, &maskFrames);
+
+  if (maskFrames.Length() == 0) {
+    return;
+  }
+
+  gfxContext& ctx = aParams.ctx;
+  nsIFrame* frame = aParams.frame;
+
+  nsPoint offsetToUserSpace =
+      nsLayoutUtils::ComputeOffsetToUserSpace(aParams.builder, aParams.frame);
+
+  auto cssToDevScale = frame->PresContext()->CSSToDevPixelScale();
+  int32_t appUnitsPerDevPixel = frame->PresContext()->AppUnitsPerDevPixel();
+
+  gfxPoint devPixelOffsetToUserSpace =
+      nsLayoutUtils::PointToGfxPoint(offsetToUserSpace, appUnitsPerDevPixel);
+
+  gfxContextMatrixAutoSaveRestore matSR(&ctx);
+  ctx.SetMatrixDouble(
+      ctx.CurrentMatrixDouble().PreTranslate(devPixelOffsetToUserSpace));
+
+  // Convert boaderArea and dirtyRect to user space.
+  nsRect userSpaceBorderArea = aParams.borderArea - offsetToUserSpace;
+  nsRect userSpaceDirtyRect = aParams.dirtyRect - offsetToUserSpace;
+
+  // Union all mask layer rectangles in user space.
+  LayoutDeviceRect maskInUserSpace;
+  for (size_t i = 0; i < maskFrames.Length(); i++) {
+    SVGMaskFrame* maskFrame = maskFrames[i];
+    LayoutDeviceRect currentMaskSurfaceRect;
+
+    if (maskFrame) {
+      auto rect = maskFrame->GetMaskArea(aParams.frame);
+      currentMaskSurfaceRect =
+          CSSRect::FromUnknownRect(ToRect(rect)) * cssToDevScale;
+    } else {
+      nsCSSRendering::ImageLayerClipState clipState;
+      nsCSSRendering::GetImageLayerClip(
+          svgReset->mMask.mLayers[i], frame, *frame->StyleBorder(),
+          userSpaceBorderArea, userSpaceDirtyRect, false, /* aWillPaintBorder */
+          appUnitsPerDevPixel, &clipState);
+      currentMaskSurfaceRect = LayoutDeviceRect::FromUnknownRect(
+          ToRect(clipState.mDirtyRectInDevPx));
+    }
+
+    maskInUserSpace = maskInUserSpace.Union(currentMaskSurfaceRect);
+  }
+
+  if (!maskInUserSpace.IsEmpty()) {
+    aParams.maskRect = Some(maskInUserSpace);
+  } else {
+    aParams.maskRect = Nothing();
+  }
+}
+
+nsDisplayMasksAndClipPaths::nsDisplayMasksAndClipPaths(
+    nsDisplayListBuilder* aBuilder, nsIFrame* aFrame, nsDisplayList* aList,
+    const ActiveScrolledRoot* aActiveScrolledRoot, bool aWrapsBackdropFilter)
+    : nsDisplayEffectsBase(aBuilder, aFrame, aList, aActiveScrolledRoot, true),
+      mWrapsBackdropFilter(aWrapsBackdropFilter) {
+  MOZ_COUNT_CTOR(nsDisplayMasksAndClipPaths);
+
+  nsPresContext* presContext = mFrame->PresContext();
+  uint32_t flags =
+      aBuilder->GetBackgroundPaintFlags() | nsCSSRendering::PAINTBG_MASK_IMAGE;
+  const nsStyleSVGReset* svgReset = aFrame->StyleSVGReset();
+  NS_FOR_VISIBLE_IMAGE_LAYERS_BACK_TO_FRONT(i, svgReset->mMask) {
+    const auto& layer = svgReset->mMask.mLayers[i];
+    if (!layer.mImage.IsResolved()) {
+      continue;
+    }
+    const nsRect& borderArea = mFrame->GetRectRelativeToSelf();
+    // NOTE(emilio): We only care about the dest rect so we don't bother
+    // computing a clip.
+    bool isTransformedFixed = false;
+    nsBackgroundLayerState state = nsCSSRendering::PrepareImageLayer(
+        presContext, aFrame, flags, borderArea, borderArea, layer,
+        &isTransformedFixed);
+    mDestRects.AppendElement(state.mDestArea);
+  }
+}
+
+static bool CanMergeDisplayMaskFrame(nsIFrame* aFrame) {
+  // Do not merge items for box-decoration-break:clone elements,
+  // since each box should have its own mask in that case.
+  if (aFrame->StyleBorder()->mBoxDecorationBreak ==
+      StyleBoxDecorationBreak::Clone) {
+    return false;
+  }
+
+  // Do not merge if either frame has a mask. Continuation frames should apply
+  // the mask independently (just like nsDisplayBackgroundImage).
+  if (aFrame->StyleSVGReset()->HasMask()) {
+    return false;
+  }
+
+  return true;
+}
+
+bool nsDisplayMasksAndClipPaths::CanMerge(const nsDisplayItem* aItem) const {
+  // Items for the same content element should be merged into a single
+  // compositing group.
+  if (!HasDifferentFrame(aItem) || !HasSameTypeAndClip(aItem) ||
+      !HasSameContent(aItem)) {
+    return false;
+  }
+
+  return CanMergeDisplayMaskFrame(mFrame) &&
+         CanMergeDisplayMaskFrame(aItem->Frame());
+}
+
+bool nsDisplayMasksAndClipPaths::IsValidMask() {
+  if (!ValidateSVGFrame()) {
+    return false;
+  }
+
+  nsIFrame* firstFrame =
+      nsLayoutUtils::FirstContinuationOrIBSplitSibling(mFrame);
+
+  return !(SVGObserverUtils::GetAndObserveClipPath(firstFrame, nullptr) ==
+               SVGObserverUtils::eHasRefsSomeInvalid ||
+           SVGObserverUtils::GetAndObserveMasks(firstFrame, nullptr) ==
+               SVGObserverUtils::eHasRefsSomeInvalid);
+}
+
+bool nsDisplayMasksAndClipPaths::PaintMask(nsDisplayListBuilder* aBuilder,
+                                           gfxContext* aMaskContext,
+                                           bool aHandleOpacity,
+                                           bool* aMaskPainted) {
+  MOZ_ASSERT(aMaskContext->GetDrawTarget()->GetFormat() == SurfaceFormat::A8);
+
+  imgDrawingParams imgParams(aBuilder->GetImageDecodeFlags());
+  nsRect borderArea = nsRect(ToReferenceFrame(), mFrame->GetSize());
+  PaintFramesParams params(*aMaskContext, mFrame, mBounds, borderArea, aBuilder,
+                           aHandleOpacity, imgParams);
+  ComputeMaskGeometry(params);
+  bool maskIsComplete = false;
+  bool painted = SVGIntegrationUtils::PaintMask(params, maskIsComplete);
+  if (aMaskPainted) {
+    *aMaskPainted = painted;
+  }
+
+  return maskIsComplete &&
+         (imgParams.result == ImgDrawResult::SUCCESS ||
+          imgParams.result == ImgDrawResult::SUCCESS_NOT_COMPLETE ||
+          imgParams.result == ImgDrawResult::WRONG_SIZE);
+}
+
+void nsDisplayMasksAndClipPaths::ComputeInvalidationRegion(
+    nsDisplayListBuilder* aBuilder, const nsDisplayItemGeometry* aGeometry,
+    nsRegion* aInvalidRegion) const {
+  nsDisplayEffectsBase::ComputeInvalidationRegion(aBuilder, aGeometry,
+                                                  aInvalidRegion);
+
+  const auto* geometry =
+      static_cast<const nsDisplayMasksAndClipPathsGeometry*>(aGeometry);
+  bool snap;
+  nsRect bounds = GetBounds(aBuilder, &snap);
+
+  if (mDestRects.Length() != geometry->mDestRects.Length()) {
+    aInvalidRegion->Or(bounds, geometry->mBounds);
+  } else {
+    for (size_t i = 0; i < mDestRects.Length(); i++) {
+      if (!mDestRects[i].IsEqualInterior(geometry->mDestRects[i])) {
+        aInvalidRegion->Or(bounds, geometry->mBounds);
+        break;
+      }
+    }
+  }
+}
+
+void nsDisplayMasksAndClipPaths::PaintWithContentsPaintCallback(
+    nsDisplayListBuilder* aBuilder, gfxContext* aCtx,
+    const std::function<void()>& aPaintChildren) {
+  // Clip the drawing target by mVisibleRect, which contains the visible
+  // region of the target frame and its out-of-flow and inflow descendants.
+  gfxContext* context = aCtx;
+
+  Rect bounds = NSRectToRect(GetPaintRect(aBuilder, aCtx),
+                             mFrame->PresContext()->AppUnitsPerDevPixel());
+  bounds.RoundOut();
+  context->Clip(bounds);
+
+  imgDrawingParams imgParams(aBuilder->GetImageDecodeFlags());
+  nsRect borderArea = nsRect(ToReferenceFrame(), mFrame->GetSize());
+  PaintFramesParams params(*aCtx, mFrame, GetPaintRect(aBuilder, aCtx),
+                           borderArea, aBuilder, false, imgParams);
+
+  ComputeMaskGeometry(params);
+
+  SVGIntegrationUtils::PaintMaskAndClipPath(params, aPaintChildren);
+
+  context->PopClip();
+}
+
+void nsDisplayMasksAndClipPaths::Paint(nsDisplayListBuilder* aBuilder,
+                                       gfxContext* aCtx) {
+  if (!IsValidMask()) {
+    return;
+  }
+  PaintWithContentsPaintCallback(aBuilder, aCtx, [&] {
+    GetChildren()->Paint(aBuilder, aCtx,
+                         mFrame->PresContext()->AppUnitsPerDevPixel());
+  });
+}
+
+static Maybe<wr::WrClipChainId> CreateSimpleClipRegion(
+    const nsDisplayMasksAndClipPaths& aDisplayItem,
+    wr::DisplayListBuilder& aBuilder) {
+  nsIFrame* frame = aDisplayItem.Frame();
+  const auto* style = frame->StyleSVGReset();
+  MOZ_ASSERT(style->HasClipPath() || style->HasMask());
+  if (!SVGIntegrationUtils::UsingSimpleClipPathForFrame(frame)) {
+    return Nothing();
+  }
+
+  const auto& clipPath = style->mClipPath;
+  const auto& shape = *clipPath.AsShape()._0;
+
+  auto appUnitsPerDevPixel = frame->PresContext()->AppUnitsPerDevPixel();
+  const nsRect refBox =
+      nsLayoutUtils::ComputeGeometryBox(frame, clipPath.AsShape()._1);
+
+  wr::WrClipId clipId{};
+
+  switch (shape.tag) {
+    case StyleBasicShape::Tag::Inset: {
+      const nsRect insetRect = ShapeUtils::ComputeInsetRect(shape, refBox) +
+                               aDisplayItem.ToReferenceFrame();
+
+      nscoord radii[8] = {0};
+
+      if (ShapeUtils::ComputeInsetRadii(shape, refBox, insetRect, radii)) {
+        clipId = aBuilder.DefineRoundedRectClip(
+            Nothing(),
+            wr::ToComplexClipRegion(insetRect, radii, appUnitsPerDevPixel));
+      } else {
+        clipId = aBuilder.DefineRectClip(
+            Nothing(), wr::ToLayoutRect(LayoutDeviceRect::FromAppUnits(
+                           insetRect, appUnitsPerDevPixel)));
+      }
+
+      break;
+    }
+    case StyleBasicShape::Tag::Ellipse:
+    case StyleBasicShape::Tag::Circle: {
+      nsPoint center = ShapeUtils::ComputeCircleOrEllipseCenter(shape, refBox);
+
+      nsSize radii;
+      if (shape.IsEllipse()) {
+        radii = ShapeUtils::ComputeEllipseRadii(shape, center, refBox);
+      } else {
+        nscoord radius = ShapeUtils::ComputeCircleRadius(shape, center, refBox);
+        radii = {radius, radius};
+      }
+
+      nsRect ellipseRect(aDisplayItem.ToReferenceFrame() + center -
+                             nsPoint(radii.width, radii.height),
+                         radii * 2);
+
+      nscoord ellipseRadii[8];
+      for (const auto corner : AllPhysicalHalfCorners()) {
+        ellipseRadii[corner] =
+            HalfCornerIsX(corner) ? radii.width : radii.height;
+      }
+
+      clipId = aBuilder.DefineRoundedRectClip(
+          Nothing(), wr::ToComplexClipRegion(ellipseRect, ellipseRadii,
+                                             appUnitsPerDevPixel));
+
+      break;
+    }
+    default:
+      // Please don't add more exceptions, try to find a way to define the clip
+      // without using a mask image.
+      //
+      // And if you _really really_ need to add an exception, add it to
+      // SVGIntegrationUtils::UsingSimpleClipPathForFrame
+      MOZ_ASSERT_UNREACHABLE("Unhandled shape id?");
+      return Nothing();
+  }
+
+  wr::WrClipChainId clipChainId = aBuilder.DefineClipChain({clipId}, true);
+
+  return Some(clipChainId);
+}
+
+static void FillPolygonDataForDisplayItem(
+    const nsDisplayMasksAndClipPaths& aDisplayItem,
+    nsTArray<wr::LayoutPoint>& aPoints, wr::FillRule& aFillRule) {
+  nsIFrame* frame = aDisplayItem.Frame();
+  const auto* style = frame->StyleSVGReset();
+  bool isPolygon = style->HasClipPath() && style->mClipPath.IsShape() &&
+                   style->mClipPath.AsShape()._0->IsPolygon();
+  if (!isPolygon) {
+    return;
+  }
+
+  const auto& clipPath = style->mClipPath;
+  const auto& shape = *clipPath.AsShape()._0;
+  const nsRect refBox =
+      nsLayoutUtils::ComputeGeometryBox(frame, clipPath.AsShape()._1);
+
+  // We only fill polygon data for polygons that are below a complexity
+  // limit.
+  nsTArray<nsPoint> vertices =
+      ShapeUtils::ComputePolygonVertices(shape, refBox);
+  if (vertices.Length() > wr::POLYGON_CLIP_VERTEX_MAX) {
+    return;
+  }
+
+  auto appUnitsPerDevPixel = frame->PresContext()->AppUnitsPerDevPixel();
+
+  for (size_t i = 0; i < vertices.Length(); ++i) {
+    wr::LayoutPoint point = wr::ToLayoutPoint(
+        LayoutDevicePoint::FromAppUnits(vertices[i], appUnitsPerDevPixel));
+    aPoints.AppendElement(point);
+  }
+
+  aFillRule = (shape.AsPolygon().fill == StyleFillRule::Nonzero)
+                  ? wr::FillRule::Nonzero
+                  : wr::FillRule::Evenodd;
+}
+
+static Maybe<wr::WrClipChainId> CreateWRClipPathAndMasks(
+    nsDisplayMasksAndClipPaths* aDisplayItem, const LayoutDeviceRect& aBounds,
+    wr::IpcResourceUpdateQueue& aResources, wr::DisplayListBuilder& aBuilder,
+    const StackingContextHelper& aSc, RenderRootStateManager* aManager,
+    nsDisplayListBuilder* aDisplayListBuilder) {
+  if (auto clip = CreateSimpleClipRegion(*aDisplayItem, aBuilder)) {
+    return clip;
+  }
+
+  Maybe<wr::ImageMask> mask = aManager->CommandBuilder().BuildWrMaskImage(
+      aDisplayItem, aBuilder, aResources, aSc, aDisplayListBuilder, aBounds);
+  if (!mask) {
+    return Nothing();
+  }
+
+  // We couldn't create a simple clip region, but before we create an image
+  // mask clip, see if we can get a polygon clip to add to it.
+  nsTArray<wr::LayoutPoint> points;
+  wr::FillRule fillRule = wr::FillRule::Nonzero;
+  FillPolygonDataForDisplayItem(*aDisplayItem, points, fillRule);
+
+  wr::WrClipId clipId =
+      aBuilder.DefineImageMaskClip(mask.ref(), points, fillRule);
+
+  wr::WrClipChainId clipChainId = aBuilder.DefineClipChain({clipId}, true);
+
+  return Some(clipChainId);
+}
+
+bool nsDisplayMasksAndClipPaths::CreateWebRenderCommands(
+    wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+    const StackingContextHelper& aSc, RenderRootStateManager* aManager,
+    nsDisplayListBuilder* aDisplayListBuilder) {
+  bool snap;
+  auto appUnitsPerDevPixel = mFrame->PresContext()->AppUnitsPerDevPixel();
+  nsRect displayBounds = GetBounds(aDisplayListBuilder, &snap);
+  LayoutDeviceRect bounds =
+      LayoutDeviceRect::FromAppUnits(displayBounds, appUnitsPerDevPixel);
+
+  Maybe<wr::WrClipChainId> clip = CreateWRClipPathAndMasks(
+      this, bounds, aResources, aBuilder, aSc, aManager, aDisplayListBuilder);
+
+  float oldOpacity = aBuilder.GetInheritedOpacity();
+
+  Maybe<StackingContextHelper> layer;
+  const StackingContextHelper* sc = &aSc;
+  if (clip) {
+    // Create a new stacking context to attach the mask to, ensuring the mask is
+    // applied to the aggregate, and not the individual elements.
+
+    // The stacking context shouldn't have any offset.
+    bounds.MoveTo(0, 0);
+
+    Maybe<float> opacity =
+        (SVGIntegrationUtils::UsingSimpleClipPathForFrame(mFrame) &&
+         aBuilder.GetInheritedOpacity() != 1.0f)
+            ? Some(aBuilder.GetInheritedOpacity())
+            : Nothing();
+
+    wr::StackingContextParams params;
+    params.clip = wr::WrStackingContextClip::ClipChain(clip->id);
+    params.opacity = opacity.ptrOr(nullptr);
+    if (mWrapsBackdropFilter) {
+      params.flags |= wr::StackingContextFlags::WRAPS_BACKDROP_FILTER;
+    }
+    layer.emplace(aSc, GetActiveScrolledRoot(), mFrame, this, aBuilder, params,
+                  bounds);
+    sc = layer.ptr();
+  }
+
+  aBuilder.SetInheritedOpacity(1.0f);
+  const DisplayItemClipChain* oldClipChain = aBuilder.GetInheritedClipChain();
+  aBuilder.SetInheritedClipChain(nullptr);
+  CreateWebRenderCommandsNewClipListOption(aBuilder, aResources, *sc, aManager,
+                                           aDisplayListBuilder, layer.isSome());
+  aBuilder.SetInheritedOpacity(oldOpacity);
+  aBuilder.SetInheritedClipChain(oldClipChain);
+
+  return true;
+}
+
+Maybe<nsRect> nsDisplayMasksAndClipPaths::GetClipWithRespectToASR(
+    nsDisplayListBuilder* aBuilder, const ActiveScrolledRoot* aASR) const {
+  if (const DisplayItemClip* clip =
+          DisplayItemClipChain::ClipForASR(GetClipChain(), aASR)) {
+    return Some(clip->GetClipRect());
+  }
+  // This item does not have a clip with respect to |aASR|. However, we
+  // might still have finite bounds with respect to |aASR|. Check our
+  // children.
+  nsDisplayList* childList = GetSameCoordinateSystemChildren();
+  if (childList) {
+    return Some(childList->GetClippedBoundsWithRespectToASR(aBuilder, aASR));
+  }
+#ifdef DEBUG
+  MOZ_ASSERT(false, "item should have finite clip with respect to aASR");
+#endif
+  return Nothing();
+}
+
+#ifdef MOZ_DUMP_PAINTING
+void nsDisplayMasksAndClipPaths::PrintEffects(nsACString& aTo) {
+  nsIFrame* firstFrame =
+      nsLayoutUtils::FirstContinuationOrIBSplitSibling(mFrame);
+  bool first = true;
+  aTo += " effects=(";
+  SVGClipPathFrame* clipPathFrame;
+  // XXX Check return value?
+  SVGObserverUtils::GetAndObserveClipPath(firstFrame, &clipPathFrame);
+  if (clipPathFrame) {
+    if (!first) {
+      aTo += ", ";
+    }
+    aTo += nsPrintfCString(
+        "clip(%s)", clipPathFrame->IsTrivial() ? "trivial" : "non-trivial");
+    first = false;
+  } else if (mFrame->StyleSVGReset()->HasClipPath()) {
+    if (!first) {
+      aTo += ", ";
+    }
+    aTo += "clip(basic-shape)";
+    first = false;
+  }
+
+  nsTArray<SVGMaskFrame*> masks;
+  // XXX check return value?
+  SVGObserverUtils::GetAndObserveMasks(firstFrame, &masks);
+  if (!masks.IsEmpty() && masks[0]) {
+    if (!first) {
+      aTo += ", ";
+    }
+    aTo += "mask";
+  }
+  aTo += ")";
+}
+#endif
+
+bool nsDisplayBackdropFilters::CreateWebRenderCommands(
+    wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+    const StackingContextHelper& aSc, RenderRootStateManager* aManager,
+    nsDisplayListBuilder* aDisplayListBuilder) {
+  WrFiltersHolder wrFilters;
+  const ComputedStyle& style = mStyle ? *mStyle : *mFrame->Style();
+  auto filterChain = style.StyleEffects()->mBackdropFilters.AsSpan();
+  bool initialized = true;
+  if (!SVGIntegrationUtils::CreateWebRenderCSSFilters(filterChain, mFrame,
+                                                      wrFilters) &&
+      !SVGIntegrationUtils::BuildWebRenderFilters(mFrame, filterChain,
+                                                  wrFilters, initialized)) {
+    // TODO: If painting backdrop-filters on the content side is implemented,
+    // consider returning false to fall back to that.
+    wrFilters = {};
+  }
+
+  if (!initialized) {
+    wrFilters = {};
+  }
+
+  nsCSSRendering::ImageLayerClipState clip;
+  nsCSSRendering::GetImageLayerClip(
+      style.StyleBackground()->BottomLayer(), mFrame, *style.StyleBorder(),
+      mBackdropRect, mBackdropRect, false,
+      mFrame->PresContext()->AppUnitsPerDevPixel(), &clip);
+
+  LayoutDeviceRect bounds = LayoutDeviceRect::FromAppUnits(
+      mBackdropRect, mFrame->PresContext()->AppUnitsPerDevPixel());
+
+  wr::ComplexClipRegion region =
+      wr::ToComplexClipRegion(clip.mBGClipArea, clip.mRadii,
+                              mFrame->PresContext()->AppUnitsPerDevPixel());
+
+  aBuilder.PushBackdropFilter(wr::ToLayoutRect(bounds), region,
+                              wrFilters.filters, wrFilters.filter_datas,
+                              !BackfaceIsHidden());
+
+  wr::StackingContextParams params;
+  params.clip =
+      wr::WrStackingContextClip::ClipChain(aBuilder.CurrentClipChainId());
+  StackingContextHelper sc(aSc, GetActiveScrolledRoot(), mFrame, this, aBuilder,
+                           params);
+
+  nsDisplayWrapList::CreateWebRenderCommands(aBuilder, aResources, sc, aManager,
+                                             aDisplayListBuilder);
+  return true;
+}
+
+void nsDisplayBackdropFilters::Paint(nsDisplayListBuilder* aBuilder,
+                                     gfxContext* aCtx) {
+  // TODO: Implement backdrop filters
+  GetChildren()->Paint(aBuilder, aCtx,
+                       mFrame->PresContext()->AppUnitsPerDevPixel());
+}
+
+nsRect nsDisplayBackdropFilters::GetBounds(nsDisplayListBuilder* aBuilder,
+                                           bool* aSnap) const {
+  nsRect childBounds = nsDisplayWrapList::GetBounds(aBuilder, aSnap);
+
+  *aSnap = false;
+
+  return mBackdropRect.Union(childBounds);
+}
+
+/* static */
+nsDisplayFilters::nsDisplayFilters(nsDisplayListBuilder* aBuilder,
+                                   nsIFrame* aFrame, nsDisplayList* aList,
+                                   nsIFrame* aStyleFrame,
+                                   bool aWrapsBackdropFilter)
+    : nsDisplayEffectsBase(aBuilder, aFrame, aList),
+      mStyle(aFrame == aStyleFrame ? nullptr : aStyleFrame->Style()),
+      mEffectsBounds(aFrame->InkOverflowRectRelativeToSelf()),
+      mWrapsBackdropFilter(aWrapsBackdropFilter) {
+  MOZ_COUNT_CTOR(nsDisplayFilters);
+  mVisibleRect = aBuilder->GetVisibleRect() +
+                 aBuilder->GetCurrentFrameOffsetToReferenceFrame();
+}
+
+void nsDisplayFilters::Paint(nsDisplayListBuilder* aBuilder, gfxContext* aCtx) {
+  PaintWithContentsPaintCallback(aBuilder, aCtx, [&](gfxContext* aContext) {
+    GetChildren()->Paint(aBuilder, aContext,
+                         mFrame->PresContext()->AppUnitsPerDevPixel());
+  });
+}
+
+void nsDisplayFilters::PaintWithContentsPaintCallback(
+    nsDisplayListBuilder* aBuilder, gfxContext* aCtx,
+    const std::function<void(gfxContext* aContext)>& aPaintChildren) {
+  imgDrawingParams imgParams(aBuilder->GetImageDecodeFlags());
+  nsRect borderArea = nsRect(ToReferenceFrame(), mFrame->GetSize());
+  PaintFramesParams params(*aCtx, mFrame, mVisibleRect, borderArea, aBuilder,
+                           false, imgParams);
+
+  gfxPoint userSpaceToFrameSpaceOffset =
+      SVGIntegrationUtils::GetOffsetToUserSpaceInDevPx(mFrame, params);
+
+  auto filterChain = mStyle ? mStyle->StyleEffects()->mFilters.AsSpan()
+                            : mFrame->StyleEffects()->mFilters.AsSpan();
+  SVGIntegrationUtils::PaintFilter(
+      params, filterChain,
+      [&](gfxContext& aContext, imgDrawingParams&, const gfxMatrix*,
+          const nsIntRect*) {
+        gfxContextMatrixAutoSaveRestore autoSR(&aContext);
+        aContext.SetMatrixDouble(aContext.CurrentMatrixDouble().PreTranslate(
+            -userSpaceToFrameSpaceOffset));
+        aPaintChildren(&aContext);
+      });
+}
+
+bool nsDisplayFilters::CanCreateWebRenderCommands() const {
+  return SVGIntegrationUtils::CanCreateWebRenderFiltersForFrame(mFrame);
+}
+
+bool nsDisplayFilters::CreateWebRenderCommands(
+    wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+    const StackingContextHelper& aSc, RenderRootStateManager* aManager,
+    nsDisplayListBuilder* aDisplayListBuilder) {
+  WrFiltersHolder wrFilters;
+  const ComputedStyle& style = mStyle ? *mStyle : *mFrame->Style();
+  auto filterChain = style.StyleEffects()->mFilters.AsSpan();
+  bool initialized = true;
+  if (!SVGIntegrationUtils::CreateWebRenderCSSFilters(filterChain, mFrame,
+                                                      wrFilters) &&
+      !SVGIntegrationUtils::BuildWebRenderFilters(mFrame, filterChain,
+                                                  wrFilters, initialized)) {
+    if (mStyle) {
+      // TODO(bug 1769223): Support fallback filters in the root code-path,
+      // perhaps. For now treat it the same way as invalid filters.
+      wrFilters = {};
+    } else {
+      // Draw using fallback.
+      return false;
+    }
+  }
+
+  if (!initialized) {
+    // https://drafts.fxtf.org/filter-effects/#typedef-filter-url:
+    //
+    //   If the filter references a non-existent object or the referenced object
+    //   is not a filter element, then the whole filter chain is ignored. No
+    //   filter is applied to the object.
+    //
+    // Note that other engines have a weird discrepancy between SVG and HTML
+    // content here, but the spec is clear.
+    wrFilters = {};
+  }
+
+  uint64_t clipChainId;
+  if (wrFilters.post_filters_clip) {
+    auto devPxRect = LayoutDeviceRect::FromAppUnits(
+        wrFilters.post_filters_clip.value() + ToReferenceFrame(),
+        mFrame->PresContext()->AppUnitsPerDevPixel());
+    auto clipId =
+        aBuilder.DefineRectClip(Nothing(), wr::ToLayoutRect(devPxRect));
+    clipChainId = aBuilder.DefineClipChain({clipId}, true).id;
+  } else {
+    clipChainId = aBuilder.CurrentClipChainId();
+  }
+  wr::WrStackingContextClip clip =
+      wr::WrStackingContextClip::ClipChain(clipChainId);
+
+  float opacity = aBuilder.GetInheritedOpacity();
+  aBuilder.SetInheritedOpacity(1.0f);
+  const DisplayItemClipChain* oldClipChain = aBuilder.GetInheritedClipChain();
+  aBuilder.SetInheritedClipChain(nullptr);
+  wr::StackingContextParams params;
+  params.mFilters = std::move(wrFilters.filters);
+  params.mFilterDatas = std::move(wrFilters.filter_datas);
+  params.opacity = opacity != 1.0f ? &opacity : nullptr;
+  params.clip = clip;
+  if (mWrapsBackdropFilter) {
+    params.flags |= wr::StackingContextFlags::WRAPS_BACKDROP_FILTER;
+  }
+  StackingContextHelper sc(aSc, GetActiveScrolledRoot(), mFrame, this, aBuilder,
+                           params);
+
+  nsDisplayEffectsBase::CreateWebRenderCommands(aBuilder, aResources, sc,
+                                                aManager, aDisplayListBuilder);
+  aBuilder.SetInheritedOpacity(opacity);
+  aBuilder.SetInheritedClipChain(oldClipChain);
+
+  return true;
+}
+
+#ifdef MOZ_DUMP_PAINTING
+void nsDisplayFilters::PrintEffects(nsACString& aTo) {
+  nsIFrame* firstFrame =
+      nsLayoutUtils::FirstContinuationOrIBSplitSibling(mFrame);
+  bool first = true;
+  aTo += " effects=(";
+  // We may exist for a mix of CSS filter functions and/or references to SVG
+  // filters.  If we have invalid references to SVG filters then we paint
+  // nothing, but otherwise we will apply one or more filters.
+  if (SVGObserverUtils::GetAndObserveFilters(firstFrame, nullptr) !=
+      SVGObserverUtils::eHasRefsSomeInvalid) {
+    if (!first) {
+      aTo += ", ";
+    }
+    aTo += "filter";
+  }
+  aTo += ")";
+}
+#endif
+
+nsDisplaySVGWrapper::nsDisplaySVGWrapper(nsDisplayListBuilder* aBuilder,
+                                         nsIFrame* aFrame, nsDisplayList* aList)
+    : nsDisplayWrapList(aBuilder, aFrame, aList) {
+  MOZ_COUNT_CTOR(nsDisplaySVGWrapper);
+}
+
+bool nsDisplaySVGWrapper::ShouldFlattenAway(nsDisplayListBuilder* aBuilder) {
+  return !aBuilder->GetWidgetLayerManager();
+}
+
+bool nsDisplaySVGWrapper::CreateWebRenderCommands(
+    wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+    const StackingContextHelper& aSc, RenderRootStateManager* aManager,
+    nsDisplayListBuilder* aDisplayListBuilder) {
+  return CreateWebRenderCommandsNewClipListOption(
+      aBuilder, aResources, aSc, aManager, aDisplayListBuilder, false);
+}
+
+nsDisplayForeignObject::nsDisplayForeignObject(nsDisplayListBuilder* aBuilder,
+                                               nsIFrame* aFrame,
+                                               nsDisplayList* aList)
+    : nsDisplayWrapList(aBuilder, aFrame, aList) {
+  MOZ_COUNT_CTOR(nsDisplayForeignObject);
+}
+
+#ifdef NS_BUILD_REFCNT_LOGGING
+nsDisplayForeignObject::~nsDisplayForeignObject() {
+  MOZ_COUNT_DTOR(nsDisplayForeignObject);
+}
+#endif
+
+bool nsDisplayForeignObject::ShouldFlattenAway(nsDisplayListBuilder* aBuilder) {
+  return !aBuilder->GetWidgetLayerManager();
+}
+
+bool nsDisplayForeignObject::CreateWebRenderCommands(
+    wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+    const StackingContextHelper& aSc, RenderRootStateManager* aManager,
+    nsDisplayListBuilder* aDisplayListBuilder) {
+  AutoRestore<bool> restoreDoGrouping(aManager->CommandBuilder().mDoGrouping);
+  aManager->CommandBuilder().mDoGrouping = false;
+  return CreateWebRenderCommandsNewClipListOption(
+      aBuilder, aResources, aSc, aManager, aDisplayListBuilder, false);
+}
+
+void nsDisplayLink::Paint(nsDisplayListBuilder* aBuilder, gfxContext* aCtx) {
+  auto appPerDev = mFrame->PresContext()->AppUnitsPerDevPixel();
+  aCtx->GetDrawTarget()->Link(
+      mLinkSpec.get(), NSRectToRect(GetPaintRect(aBuilder, aCtx), appPerDev));
+}
+
+void nsDisplayDestination::Paint(nsDisplayListBuilder* aBuilder,
+                                 gfxContext* aCtx) {
+  auto appPerDev = mFrame->PresContext()->AppUnitsPerDevPixel();
+  aCtx->GetDrawTarget()->Destination(
+      mDestinationName.get(),
+      NSPointToPoint(GetPaintRect(aBuilder, aCtx).TopLeft(), appPerDev));
+}
+
+void nsDisplayListCollection::SerializeWithCorrectZOrder(
+    nsDisplayList* aOutResultList, nsIContent* aContent) {
+  // Sort PositionedDescendants() in CSS 'z-order' order.  The list is already
+  // in content document order and SortByZOrder is a stable sort which
+  // guarantees that boxes produced by the same element are placed together
+  // in the sort. Consider a position:relative inline element that breaks
+  // across lines and has absolutely positioned children; all the abs-pos
+  // children should be z-ordered after all the boxes for the position:relative
+  // element itself.
+  PositionedDescendants()->SortByZOrder();
+
+  // Now follow the rules of http://www.w3.org/TR/CSS21/zindex.html
+  // 1,2: backgrounds and borders
+  aOutResultList->AppendToTop(BorderBackground());
+  // 3: negative z-index children.
+  for (auto* item : PositionedDescendants()->TakeItems()) {
+    if (item->ZIndex() < 0) {
+      aOutResultList->AppendToTop(item);
+    } else {
+      PositionedDescendants()->AppendToTop(item);
+    }
+  }
+
+  // 4: block backgrounds
+  aOutResultList->AppendToTop(BlockBorderBackgrounds());
+  // 5: floats
+  aOutResultList->AppendToTop(Floats());
+  // 7: general content
+  aOutResultList->AppendToTop(Content());
+  // 7.5: outlines, in content tree order. We need to sort by content order
+  // because an element with outline that breaks and has children with outline
+  // might have placed child outline items between its own outline items.
+  // The element's outline items need to all come before any child outline
+  // items.
+  if (aContent) {
+    Outlines()->SortByContentOrder(aContent);
+  }
+  aOutResultList->AppendToTop(Outlines());
+  // 8, 9: non-negative z-index children
+  aOutResultList->AppendToTop(PositionedDescendants());
+}
+
+uint32_t PaintTelemetry::sPaintLevel = 0;
+
+PaintTelemetry::AutoRecordPaint::AutoRecordPaint() {
+  // Don't record nested paints.
+  if (sPaintLevel++ > 0) {
+    return;
+  }
+
+  mStart = TimeStamp::Now();
+}
+
+PaintTelemetry::AutoRecordPaint::~AutoRecordPaint() {
+  MOZ_ASSERT(sPaintLevel != 0);
+  if (--sPaintLevel > 0) {
+    return;
+  }
+
+  // If we're in multi-process mode, don't include paint times for the parent
+  // process.
+  if (gfxVars::BrowserTabsRemoteAutostart() && XRE_IsParentProcess()) {
+    return;
+  }
+
+  double totalMs = (TimeStamp::Now() - mStart).ToMilliseconds();
+
+  // Record the total time.
+  Telemetry::Accumulate(Telemetry::CONTENT_PAINT_TIME,
+                        static_cast<uint32_t>(totalMs));
+}
+
+static nsIFrame* GetSelfOrPlaceholderFor(nsIFrame* aFrame) {
+  if (aFrame->HasAnyStateBits(NS_FRAME_IS_PUSHED_FLOAT)) {
+    return aFrame;
+  }
+
+  if (aFrame->HasAnyStateBits(NS_FRAME_OUT_OF_FLOW) &&
+      !aFrame->GetPrevInFlow()) {
+    return aFrame->GetPlaceholderFrame();
+  }
+
+  return aFrame;
+}
+
+static nsIFrame* GetAncestorFor(nsIFrame* aFrame) {
+  nsIFrame* f = GetSelfOrPlaceholderFor(aFrame);
+  MOZ_ASSERT(f);
+  return nsLayoutUtils::GetCrossDocParentFrameInProcess(f);
+}
+
+nsDisplayListBuilder::AutoBuildingDisplayList::AutoBuildingDisplayList(
+    nsDisplayListBuilder* aBuilder, nsIFrame* aForChild,
+    const nsRect& aVisibleRect, const nsRect& aDirtyRect,
+    const bool aIsTransformed)
+    : mBuilder(aBuilder),
+      mPrevFrame(aBuilder->mCurrentFrame),
+      mPrevReferenceFrame(aBuilder->mCurrentReferenceFrame),
+      mPrevOffset(aBuilder->mCurrentOffsetToReferenceFrame),
+      mPrevAdditionalOffset(aBuilder->mAdditionalOffset),
+      mPrevVisibleRect(aBuilder->mVisibleRect),
+      mPrevDirtyRect(aBuilder->mDirtyRect),
+      mPrevCompositorHitTestInfo(aBuilder->mCompositorHitTestInfo),
+      mPrevAncestorHasApzAwareEventHandler(
+          aBuilder->mAncestorHasApzAwareEventHandler),
+      mPrevBuildingInvisibleItems(aBuilder->mBuildingInvisibleItems),
+      mPrevInInvalidSubtree(aBuilder->mInInvalidSubtree) {
+  if (aIsTransformed) {
+    aBuilder->mCurrentOffsetToReferenceFrame =
+        aBuilder->AdditionalOffset().refOr(nsPoint());
+    aBuilder->mCurrentReferenceFrame = aForChild;
+  } else if (aBuilder->mCurrentFrame == aForChild->GetParent()) {
+    aBuilder->mCurrentOffsetToReferenceFrame += aForChild->GetPosition();
+  } else {
+    aBuilder->mCurrentReferenceFrame = aBuilder->FindReferenceFrameFor(
+        aForChild, &aBuilder->mCurrentOffsetToReferenceFrame);
+  }
+
+  // If aForChild is being visited from a frame other than it's ancestor frame,
+  // mInInvalidSubtree will need to be recalculated the slow way.
+  if (aForChild == mPrevFrame || GetAncestorFor(aForChild) == mPrevFrame) {
+    aBuilder->mInInvalidSubtree =
+        aBuilder->mInInvalidSubtree || aForChild->IsFrameModified();
+  } else {
+    aBuilder->mInInvalidSubtree = AnyContentAncestorModified(aForChild);
+  }
+
+  aBuilder->mCurrentFrame = aForChild;
+  aBuilder->mVisibleRect = aVisibleRect;
+  aBuilder->mDirtyRect =
+      aBuilder->mInInvalidSubtree ? aVisibleRect : aDirtyRect;
+}
+
+}  // namespace mozilla
diff --git a/layout/painting/nsDisplayList.h b/layout/painting/nsDisplayList.h
new file mode 100644
index 0000000000..48a2aa2738
--- /dev/null
+++ b/layout/painting/nsDisplayList.h
@@ -0,0 +1,6842 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+/*
+ * structures that represent things to be painted (ordered in z-order),
+ * used during painting and hit testing
+ */
+
+#ifndef NSDISPLAYLIST_H_
+#define NSDISPLAYLIST_H_
+
+#include "DisplayItemClipChain.h"
+#include "DisplayListClipState.h"
+#include "FrameMetrics.h"
+#include "HitTestInfo.h"
+#include "ImgDrawResult.h"
+#include "LayerState.h"
+#include "RetainedDisplayListHelpers.h"
+#include "Units.h"
+#include "gfxContext.h"
+#include "mozilla/ArenaAllocator.h"
+#include "mozilla/Array.h"
+#include "mozilla/ArrayIterator.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/DebugOnly.h"
+#include "mozilla/EffectCompositor.h"
+#include "mozilla/EnumSet.h"
+#include "mozilla/EnumeratedArray.h"
+#include "mozilla/Logging.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/MotionPathUtils.h"
+#include "mozilla/RefPtr.h"
+#include "mozilla/TemplateLib.h"
+#include "mozilla/TimeStamp.h"
+#include "mozilla/UniquePtr.h"
+#include "mozilla/dom/EffectsInfo.h"
+#include "mozilla/gfx/UserData.h"
+#include "mozilla/layers/BSPTree.h"
+#include "mozilla/layers/ScrollableLayerGuid.h"
+#include "mozilla/layers/ScrollbarData.h"
+#include "nsAutoLayoutPhase.h"
+#include "nsCOMPtr.h"
+#include "nsCSSRenderingBorders.h"
+#include "nsContainerFrame.h"
+#include "nsDisplayItemTypes.h"
+#include "nsDisplayListInvalidation.h"
+#include "nsPoint.h"
+#include "nsPresArena.h"
+#include "nsRect.h"
+#include "nsRegion.h"
+#include "nsClassHashtable.h"
+#include "nsTHashSet.h"
+#include "nsTHashMap.h"
+
+#include <algorithm>
+#include <unordered_set>
+
+// XXX Includes that could be avoided by moving function implementations to the
+// cpp file.
+#include "gfxPlatform.h"
+
+class gfxContext;
+class nsIContent;
+class nsIScrollableFrame;
+class nsSubDocumentFrame;
+class nsCaret;
+struct WrFiltersHolder;
+
+namespace nsStyleTransformMatrix {
+class TransformReferenceBox;
+}
+
+namespace mozilla {
+
+enum class nsDisplayOwnLayerFlags;
+class nsDisplayCompositorHitTestInfo;
+class nsDisplayScrollInfoLayer;
+class PresShell;
+class StickyScrollContainer;
+
+namespace layers {
+struct FrameMetrics;
+class RenderRootStateManager;
+class Layer;
+class ImageContainer;
+class StackingContextHelper;
+class WebRenderScrollData;
+class WebRenderLayerScrollData;
+class WebRenderLayerManager;
+}  // namespace layers
+
+namespace wr {
+class DisplayListBuilder;
+}  // namespace wr
+
+namespace dom {
+class RemoteBrowser;
+class Selection;
+}  // namespace dom
+
+enum class DisplayListArenaObjectId {
+#define DISPLAY_LIST_ARENA_OBJECT(name_) name_,
+#include "nsDisplayListArenaTypes.h"
+#undef DISPLAY_LIST_ARENA_OBJECT
+  COUNT
+};
+
+extern LazyLogModule sContentDisplayListLog;
+extern LazyLogModule sParentDisplayListLog;
+
+LazyLogModule& GetLoggerByProcess();
+
+#define DL_LOG(lvl, ...) MOZ_LOG(GetLoggerByProcess(), lvl, (__VA_ARGS__))
+#define DL_LOGI(...) DL_LOG(LogLevel::Info, __VA_ARGS__)
+#define DL_LOG_TEST(lvl) MOZ_LOG_TEST(GetLoggerByProcess(), lvl)
+
+#ifdef DEBUG
+#  define DL_LOGD(...) DL_LOG(LogLevel::Debug, __VA_ARGS__)
+#  define DL_LOGV(...) DL_LOG(LogLevel::Verbose, __VA_ARGS__)
+#else
+// Disable Debug and Verbose logs for release builds.
+#  define DL_LOGD(...)
+#  define DL_LOGV(...)
+#endif
+
+/*
+ * An nsIFrame can have many different visual parts. For example an image frame
+ * can have a background, border, and outline, the image itself, and a
+ * translucent selection overlay. In general these parts can be drawn at
+ * discontiguous z-levels; see CSS2.1 appendix E:
+ * http://www.w3.org/TR/CSS21/zindex.html
+ *
+ * We construct a display list for a frame tree that contains one item
+ * for each visual part. The display list is itself a tree since some items
+ * are containers for other items; however, its structure does not match
+ * the structure of its source frame tree. The display list items are sorted
+ * by z-order. A display list can be used to paint the frames, to determine
+ * which frame is the target of a mouse event, and to determine what areas
+ * need to be repainted when scrolling. The display lists built for each task
+ * may be different for efficiency; in particular some frames need special
+ * display list items only for event handling, and do not create these items
+ * when the display list will be used for painting (the common case). For
+ * example, when painting we avoid creating nsDisplayBackground items for
+ * frames that don't display a visible background, but for event handling
+ * we need those backgrounds because they are not transparent to events.
+ *
+ * We could avoid constructing an explicit display list by traversing the
+ * frame tree multiple times in clever ways. However, reifying the display list
+ * reduces code complexity and reduces the number of times each frame must be
+ * traversed to one, which seems to be good for performance. It also means
+ * we can share code for painting, event handling and scroll analysis.
+ *
+ * Display lists are short-lived; content and frame trees cannot change
+ * between a display list being created and destroyed. Display lists should
+ * not be created during reflow because the frame tree may be in an
+ * inconsistent state (e.g., a frame's stored overflow-area may not include
+ * the bounds of all its children). However, it should be fine to create
+ * a display list while a reflow is pending, before it starts.
+ *
+ * A display list covers the "extended" frame tree; the display list for
+ * a frame tree containing FRAME/IFRAME elements can include frames from
+ * the subdocuments.
+ *
+ * Display item's coordinates are relative to their nearest reference frame
+ * ancestor. Both the display root and any frame with a transform act as a
+ * reference frame for their frame subtrees.
+ */
+
+/**
+ * An active scrolled root (ASR) is similar to an animated geometry root (AGR).
+ * The differences are:
+ *  - ASRs are only created for async-scrollable scroll frames. This is a
+ *    (hopefully) temporary restriction. In the future we will want to create
+ *    ASRs for all the things that are currently creating AGRs, and then
+ *    replace AGRs with ASRs and rename them from "active scrolled root" to
+ *    "animated geometry root".
+ *  - ASR objects are created during display list construction by the nsIFrames
+ *    that induce ASRs. This is done using AutoCurrentActiveScrolledRootSetter.
+ *    The current ASR is returned by
+ *    nsDisplayListBuilder::CurrentActiveScrolledRoot().
+ *  - There is no way to go from an nsIFrame pointer to the ASR of that frame.
+ *    If you need to look up an ASR after display list construction, you need
+ *    to store it while the AutoCurrentActiveScrolledRootSetter that creates it
+ *    is on the stack.
+ */
+struct ActiveScrolledRoot {
+  static already_AddRefed<ActiveScrolledRoot> CreateASRForFrame(
+      const ActiveScrolledRoot* aParent, nsIScrollableFrame* aScrollableFrame,
+      bool aIsRetained);
+
+  static const ActiveScrolledRoot* PickAncestor(
+      const ActiveScrolledRoot* aOne, const ActiveScrolledRoot* aTwo) {
+    MOZ_ASSERT(IsAncestor(aOne, aTwo) || IsAncestor(aTwo, aOne));
+    return Depth(aOne) <= Depth(aTwo) ? aOne : aTwo;
+  }
+
+  static const ActiveScrolledRoot* PickDescendant(
+      const ActiveScrolledRoot* aOne, const ActiveScrolledRoot* aTwo) {
+    MOZ_ASSERT(IsAncestor(aOne, aTwo) || IsAncestor(aTwo, aOne));
+    return Depth(aOne) >= Depth(aTwo) ? aOne : aTwo;
+  }
+
+  static bool IsAncestor(const ActiveScrolledRoot* aAncestor,
+                         const ActiveScrolledRoot* aDescendant);
+  static bool IsProperAncestor(const ActiveScrolledRoot* aAncestor,
+                               const ActiveScrolledRoot* aDescendant);
+
+  static nsCString ToString(const ActiveScrolledRoot* aActiveScrolledRoot);
+
+  // Call this when inserting an ancestor.
+  void IncrementDepth() { mDepth++; }
+
+  /**
+   * Find the view ID (or generate a new one) for the content element
+   * corresponding to the ASR.
+   */
+  layers::ScrollableLayerGuid::ViewID GetViewId() const {
+    if (!mViewId.isSome()) {
+      mViewId = Some(ComputeViewId());
+    }
+    return *mViewId;
+  }
+
+  RefPtr<const ActiveScrolledRoot> mParent;
+  nsIScrollableFrame* mScrollableFrame;
+
+  NS_INLINE_DECL_REFCOUNTING(ActiveScrolledRoot)
+
+ private:
+  ActiveScrolledRoot()
+      : mScrollableFrame(nullptr), mDepth(0), mRetained(false) {}
+
+  ~ActiveScrolledRoot();
+
+  static void DetachASR(ActiveScrolledRoot* aASR) {
+    aASR->mParent = nullptr;
+    aASR->mScrollableFrame = nullptr;
+    NS_RELEASE(aASR);
+  }
+  NS_DECLARE_FRAME_PROPERTY_WITH_DTOR(ActiveScrolledRootCache,
+                                      ActiveScrolledRoot, DetachASR)
+
+  static uint32_t Depth(const ActiveScrolledRoot* aActiveScrolledRoot) {
+    return aActiveScrolledRoot ? aActiveScrolledRoot->mDepth : 0;
+  }
+
+  layers::ScrollableLayerGuid::ViewID ComputeViewId() const;
+
+  // This field is lazily populated in GetViewId(). We don't want to do the
+  // work of populating if webrender is disabled, because it is often not
+  // needed.
+  mutable Maybe<layers::ScrollableLayerGuid::ViewID> mViewId;
+
+  uint32_t mDepth;
+  bool mRetained;
+};
+
+enum class nsDisplayListBuilderMode : uint8_t {
+  Painting,
+  PaintForPrinting,
+  EventDelivery,
+  FrameVisibility,
+  TransformComputation,
+  GenerateGlyph,
+};
+
+using ListArenaAllocator = ArenaAllocator<4096, 8>;
+
+class nsDisplayItem;
+class nsPaintedDisplayItem;
+class nsDisplayList;
+class nsDisplayWrapList;
+class nsDisplayTableBackgroundSet;
+class nsDisplayTableItem;
+
+class RetainedDisplayList;
+
+/**
+ * This manages a display list and is passed as a parameter to
+ * nsIFrame::BuildDisplayList.
+ * It contains the parameters that don't change from frame to frame and manages
+ * the display list memory using an arena. It also establishes the reference
+ * coordinate system for all display list items. Some of the parameters are
+ * available from the prescontext/presshell, but we copy them into the builder
+ * for faster/more convenient access.
+ */
+class nsDisplayListBuilder {
+  /**
+   * This manages status of a 3d context to collect visible rects of
+   * descendants and passing a dirty rect.
+   *
+   * Since some transforms maybe singular, passing visible rects or
+   * the dirty rect level by level from parent to children may get a
+   * wrong result, being different from the result of appling with
+   * effective transform directly.
+   *
+   * nsIFrame::BuildDisplayListForStackingContext() uses
+   * AutoPreserves3DContext to install an instance on the builder.
+   *
+   * \see AutoAccumulateTransform, AutoAccumulateRect,
+   *      AutoPreserves3DContext, Accumulate, GetCurrentTransform,
+   *      StartRoot.
+   */
+  class Preserves3DContext {
+   public:
+    Preserves3DContext()
+        : mAccumulatedRectLevels(0), mAllowAsyncAnimation(true) {}
+
+    Preserves3DContext(const Preserves3DContext& aOther)
+        : mAccumulatedTransform(),
+          mAccumulatedRect(),
+          mAccumulatedRectLevels(0),
+          mVisibleRect(aOther.mVisibleRect),
+          mAllowAsyncAnimation(aOther.mAllowAsyncAnimation) {}
+
+    // Accmulate transforms of ancestors on the preserves-3d chain.
+    gfx::Matrix4x4 mAccumulatedTransform;
+    // Accmulate visible rect of descendants in the preserves-3d context.
+    nsRect mAccumulatedRect;
+    // How far this frame is from the root of the current 3d context.
+    int mAccumulatedRectLevels;
+    nsRect mVisibleRect;
+    // Allow async animation for this 3D context.
+    bool mAllowAsyncAnimation;
+  };
+
+ public:
+  using ViewID = layers::ScrollableLayerGuid::ViewID;
+
+  /**
+   * @param aReferenceFrame the frame at the root of the subtree; its origin
+   * is the origin of the reference coordinate system for this display list
+   * @param aMode encodes what the builder is being used for.
+   * @param aBuildCaret whether or not we should include the caret in any
+   * display lists that we make.
+   */
+  nsDisplayListBuilder(nsIFrame* aReferenceFrame,
+                       nsDisplayListBuilderMode aMode, bool aBuildCaret,
+                       bool aRetainingDisplayList = false);
+  ~nsDisplayListBuilder();
+
+  void BeginFrame();
+  void EndFrame();
+
+  void AddTemporaryItem(nsDisplayItem* aItem) {
+    mTemporaryItems.AppendElement(aItem);
+  }
+
+  WindowRenderer* GetWidgetWindowRenderer(nsView** aView = nullptr);
+  layers::WebRenderLayerManager* GetWidgetLayerManager(
+      nsView** aView = nullptr);
+
+  /**
+   * @return true if the display is being built in order to determine which
+   * frame is under the mouse position.
+   */
+  bool IsForEventDelivery() const {
+    return mMode == nsDisplayListBuilderMode::EventDelivery;
+  }
+
+  /**
+   * @return true if the display list is being built for painting. This
+   * includes both painting to a window or other buffer and painting to
+   * a print/pdf destination.
+   */
+  bool IsForPainting() const {
+    return mMode == nsDisplayListBuilderMode::Painting ||
+           mMode == nsDisplayListBuilderMode::PaintForPrinting;
+  }
+
+  /**
+   * @return true if the display list is being built specifically for printing.
+   */
+  bool IsForPrinting() const {
+    return mMode == nsDisplayListBuilderMode::PaintForPrinting;
+  }
+
+  /**
+   * @return true if the display list is being built for determining frame
+   * visibility.
+   */
+  bool IsForFrameVisibility() const {
+    return mMode == nsDisplayListBuilderMode::FrameVisibility;
+  }
+
+  /**
+   * @return true if the display list is being built for creating the glyph
+   * mask from text items.
+   */
+  bool IsForGenerateGlyphMask() const {
+    return mMode == nsDisplayListBuilderMode::GenerateGlyph;
+  }
+
+  bool BuildCompositorHitTestInfo() const {
+    return mBuildCompositorHitTestInfo;
+  }
+
+  /**
+   * @return true if "painting is suppressed" during page load and we
+   * should paint only the background of the document.
+   */
+  bool IsBackgroundOnly() {
+    NS_ASSERTION(mPresShellStates.Length() > 0,
+                 "don't call this if we're not in a presshell");
+    return CurrentPresShellState()->mIsBackgroundOnly;
+  }
+
+  /**
+   * @return the root of given frame's (sub)tree, whose origin
+   * establishes the coordinate system for the child display items.
+   */
+  const nsIFrame* FindReferenceFrameFor(const nsIFrame* aFrame,
+                                        nsPoint* aOffset = nullptr) const;
+
+  const Maybe<nsPoint>& AdditionalOffset() const { return mAdditionalOffset; }
+
+  /**
+   * @return the root of the display list's frame (sub)tree, whose origin
+   * establishes the coordinate system for the display list
+   */
+  nsIFrame* RootReferenceFrame() const { return mReferenceFrame; }
+
+  /**
+   * @return a point pt such that adding pt to a coordinate relative to aFrame
+   * makes it relative to ReferenceFrame(), i.e., returns
+   * aFrame->GetOffsetToCrossDoc(ReferenceFrame()). The returned point is in
+   * the appunits of aFrame.
+   */
+  const nsPoint ToReferenceFrame(const nsIFrame* aFrame) const {
+    nsPoint result;
+    FindReferenceFrameFor(aFrame, &result);
+    return result;
+  }
+  /**
+   * When building the display list, the scrollframe aFrame will be "ignored"
+   * for the purposes of clipping, and its scrollbars will be hidden. We use
+   * this to allow RenderOffscreen to render a whole document without beign
+   * clipped by the viewport or drawing the viewport scrollbars.
+   */
+  void SetIgnoreScrollFrame(nsIFrame* aFrame) { mIgnoreScrollFrame = aFrame; }
+  /**
+   * Get the scrollframe to ignore, if any.
+   */
+  nsIFrame* GetIgnoreScrollFrame() { return mIgnoreScrollFrame; }
+  void SetIsRelativeToLayoutViewport();
+  bool IsRelativeToLayoutViewport() const {
+    return mIsRelativeToLayoutViewport;
+  }
+  /**
+   * Get the ViewID of the nearest scrolling ancestor frame.
+   */
+  ViewID GetCurrentScrollParentId() const { return mCurrentScrollParentId; }
+  /**
+   * Get and set the flag that indicates if scroll parents should have layers
+   * forcibly created. This flag is set when a deeply nested scrollframe has
+   * a displayport, and for scroll handoff to work properly the ancestor
+   * scrollframes should also get their own scrollable layers.
+   */
+  void ForceLayerForScrollParent() { mForceLayerForScrollParent = true; }
+  /**
+   * Set the flag that indicates there is a non-minimal display port in the
+   * current subtree. This is used to determine display port expiry.
+   */
+  void SetContainsNonMinimalDisplayPort() {
+    mContainsNonMinimalDisplayPort = true;
+  }
+  /**
+   * Get the ViewID and the scrollbar flags corresponding to the scrollbar for
+   * which we are building display items at the moment.
+   */
+  ViewID GetCurrentScrollbarTarget() const { return mCurrentScrollbarTarget; }
+  Maybe<layers::ScrollDirection> GetCurrentScrollbarDirection() const {
+    return mCurrentScrollbarDirection;
+  }
+  /**
+   * Returns true if building a scrollbar, and the scrollbar will not be
+   * layerized.
+   */
+  bool IsBuildingNonLayerizedScrollbar() const {
+    return mIsBuildingScrollbar && !mCurrentScrollbarWillHaveLayer;
+  }
+  /**
+   * Calling this setter makes us include all out-of-flow descendant
+   * frames in the display list, wherever they may be positioned (even
+   * outside the dirty rects).
+   */
+  void SetIncludeAllOutOfFlows() { mIncludeAllOutOfFlows = true; }
+  bool GetIncludeAllOutOfFlows() const { return mIncludeAllOutOfFlows; }
+  /**
+   * Calling this setter makes us exclude all leaf frames that aren't
+   * selected.
+   */
+  void SetSelectedFramesOnly() { mSelectedFramesOnly = true; }
+  bool GetSelectedFramesOnly() { return mSelectedFramesOnly; }
+  /**
+   * @return Returns true if we should include the caret in any display lists
+   * that we make.
+   */
+  bool IsBuildingCaret() const { return mBuildCaret; }
+
+  bool IsRetainingDisplayList() const { return mRetainingDisplayList; }
+
+  bool IsPartialUpdate() const { return mPartialUpdate; }
+  void SetPartialUpdate(bool aPartial) { mPartialUpdate = aPartial; }
+
+  bool IsBuilding() const { return mIsBuilding; }
+  void SetIsBuilding(bool aIsBuilding) { mIsBuilding = aIsBuilding; }
+
+  bool InInvalidSubtree() const { return mInInvalidSubtree; }
+
+  /**
+   * Allows callers to selectively override the regular paint suppression
+   * checks, so that methods like GetFrameForPoint work when painting is
+   * suppressed.
+   */
+  void IgnorePaintSuppression() { mIgnoreSuppression = true; }
+  /**
+   * @return Returns if this builder will ignore paint suppression.
+   */
+  bool IsIgnoringPaintSuppression() { return mIgnoreSuppression; }
+  /**
+   * Call this if we're doing normal painting to the window.
+   */
+  void SetPaintingToWindow(bool aToWindow) { mIsPaintingToWindow = aToWindow; }
+  bool IsPaintingToWindow() const { return mIsPaintingToWindow; }
+  /**
+   * Call this if we're using high quality scaling for image decoding.
+   * It is also implied by IsPaintingToWindow.
+   */
+  void SetUseHighQualityScaling(bool aUseHighQualityScaling) {
+    mUseHighQualityScaling = aUseHighQualityScaling;
+  }
+  bool UseHighQualityScaling() const {
+    return mIsPaintingToWindow || mUseHighQualityScaling;
+  }
+  /**
+   * Call this if we're doing painting for WebRender
+   */
+  void SetPaintingForWebRender(bool aForWebRender) {
+    mIsPaintingForWebRender = true;
+  }
+  bool IsPaintingForWebRender() const { return mIsPaintingForWebRender; }
+  /**
+   * Call this to prevent descending into subdocuments.
+   */
+  void SetDescendIntoSubdocuments(bool aDescend) {
+    mDescendIntoSubdocuments = aDescend;
+  }
+
+  bool GetDescendIntoSubdocuments() { return mDescendIntoSubdocuments; }
+
+  /**
+   * Get dirty rect relative to current frame (the frame that we're calling
+   * BuildDisplayList on right now).
+   */
+  const nsRect& GetVisibleRect() { return mVisibleRect; }
+  const nsRect& GetDirtyRect() { return mDirtyRect; }
+
+  void SetVisibleRect(const nsRect& aVisibleRect) {
+    mVisibleRect = aVisibleRect;
+  }
+
+  void IntersectVisibleRect(const nsRect& aVisibleRect) {
+    mVisibleRect.IntersectRect(mVisibleRect, aVisibleRect);
+  }
+
+  void SetDirtyRect(const nsRect& aDirtyRect) { mDirtyRect = aDirtyRect; }
+
+  void IntersectDirtyRect(const nsRect& aDirtyRect) {
+    mDirtyRect.IntersectRect(mDirtyRect, aDirtyRect);
+  }
+
+  const nsIFrame* GetCurrentFrame() { return mCurrentFrame; }
+  const nsIFrame* GetCurrentReferenceFrame() { return mCurrentReferenceFrame; }
+
+  const nsPoint& GetCurrentFrameOffsetToReferenceFrame() const {
+    return mCurrentOffsetToReferenceFrame;
+  }
+
+  void Check() { mPool.Check(); }
+
+  /**
+   * Returns true if merging and flattening of display lists should be
+   * performed while computing visibility.
+   */
+  bool AllowMergingAndFlattening() { return mAllowMergingAndFlattening; }
+  void SetAllowMergingAndFlattening(bool aAllow) {
+    mAllowMergingAndFlattening = aAllow;
+  }
+
+  void SetCompositorHitTestInfo(const gfx::CompositorHitTestInfo& aInfo) {
+    mCompositorHitTestInfo = aInfo;
+  }
+
+  const gfx::CompositorHitTestInfo& GetCompositorHitTestInfo() const {
+    return mCompositorHitTestInfo;
+  }
+
+  /**
+   * Builds a new nsDisplayCompositorHitTestInfo for the frame |aFrame| if
+   * needed, and adds it to the top of |aList|.
+   */
+  void BuildCompositorHitTestInfoIfNeeded(nsIFrame* aFrame,
+                                          nsDisplayList* aList);
+
+  bool IsInsidePointerEventsNoneDoc() {
+    return CurrentPresShellState()->mInsidePointerEventsNoneDoc;
+  }
+
+  bool IsTouchEventPrefEnabledDoc() {
+    return CurrentPresShellState()->mTouchEventPrefEnabledDoc;
+  }
+
+  bool GetAncestorHasApzAwareEventHandler() const {
+    return mAncestorHasApzAwareEventHandler;
+  }
+
+  void SetAncestorHasApzAwareEventHandler(bool aValue) {
+    mAncestorHasApzAwareEventHandler = aValue;
+  }
+
+  bool HaveScrollableDisplayPort() const { return mHaveScrollableDisplayPort; }
+  void SetHaveScrollableDisplayPort() { mHaveScrollableDisplayPort = true; }
+  void ClearHaveScrollableDisplayPort() { mHaveScrollableDisplayPort = false; }
+
+  bool SetIsCompositingCheap(bool aCompositingCheap) {
+    bool temp = mIsCompositingCheap;
+    mIsCompositingCheap = aCompositingCheap;
+    return temp;
+  }
+
+  bool IsCompositingCheap() const { return mIsCompositingCheap; }
+  /**
+   * Display the caret if needed.
+   */
+  bool DisplayCaret(nsIFrame* aFrame, nsDisplayList* aList) {
+    nsIFrame* frame = GetCaretFrame();
+    if (aFrame == frame && !IsBackgroundOnly()) {
+      frame->DisplayCaret(this, aList);
+      return true;
+    }
+    return false;
+  }
+  /**
+   * Get the frame that the caret is supposed to draw in.
+   * If the caret is currently invisible, this will be null.
+   */
+  nsIFrame* GetCaretFrame() { return mCaretFrame; }
+  /**
+   * Get the rectangle we're supposed to draw the caret into.
+   */
+  const nsRect& GetCaretRect() { return mCaretRect; }
+  /**
+   * Get the caret associated with the current presshell.
+   */
+  nsCaret* GetCaret();
+
+  /**
+   * Returns the root scroll frame for the current PresShell, if the PresShell
+   * is ignoring viewport scrolling.
+   */
+  nsIFrame* GetPresShellIgnoreScrollFrame() {
+    return CurrentPresShellState()->mPresShellIgnoreScrollFrame;
+  }
+
+  /**
+   * Notify the display list builder that we're entering a presshell.
+   * aReferenceFrame should be a frame in the new presshell.
+   * aPointerEventsNoneDoc should be set to true if the frame generating this
+   * document is pointer-events:none.
+   */
+  void EnterPresShell(const nsIFrame* aReferenceFrame,
+                      bool aPointerEventsNoneDoc = false);
+  /**
+   * For print-preview documents, we sometimes need to build display items for
+   * the same frames multiple times in the same presentation, with different
+   * clipping. Between each such batch of items, call
+   * ResetMarkedFramesForDisplayList to make sure that the results of
+   * MarkFramesForDisplayList do not carry over between batches.
+   */
+  void ResetMarkedFramesForDisplayList(const nsIFrame* aReferenceFrame);
+  /**
+   * Notify the display list builder that we're leaving a presshell.
+   */
+  void LeavePresShell(const nsIFrame* aReferenceFrame,
+                      nsDisplayList* aPaintedContents);
+
+  void IncrementPresShellPaintCount(PresShell* aPresShell);
+
+  /**
+   * Returns true if we're currently building a display list that's
+   * directly or indirectly under an nsDisplayTransform.
+   */
+  bool IsInTransform() const { return mInTransform; }
+
+  bool InEventsOnly() const { return mInEventsOnly; }
+  /**
+   * Indicate whether or not we're directly or indirectly under and
+   * nsDisplayTransform or SVG foreignObject.
+   */
+  void SetInTransform(bool aInTransform) { mInTransform = aInTransform; }
+
+  /**
+   * Returns true if we're currently building a display list that's
+   * under an nsDisplayFilters.
+   */
+  bool IsInFilter() const { return mInFilter; }
+
+  /**
+   * Return true if we're currently building a display list for a
+   * nested presshell.
+   */
+  bool IsInSubdocument() const { return mPresShellStates.Length() > 1; }
+
+  void SetDisablePartialUpdates(bool aDisable) {
+    mDisablePartialUpdates = aDisable;
+  }
+  bool DisablePartialUpdates() const { return mDisablePartialUpdates; }
+
+  void SetPartialBuildFailed(bool aFailed) { mPartialBuildFailed = aFailed; }
+  bool PartialBuildFailed() const { return mPartialBuildFailed; }
+
+  bool IsInActiveDocShell() const { return mIsInActiveDocShell; }
+  void SetInActiveDocShell(bool aActive) { mIsInActiveDocShell = aActive; }
+
+  /**
+   * Return true if we're currently building a display list for the presshell
+   * of a chrome document, or if we're building the display list for a popup.
+   */
+  bool IsInChromeDocumentOrPopup() const {
+    return mIsInChromePresContext || mIsBuildingForPopup;
+  }
+
+  /**
+   * @return true if images have been set to decode synchronously.
+   */
+  bool ShouldSyncDecodeImages() const { return mSyncDecodeImages; }
+
+  /**
+   * Indicates whether we should synchronously decode images. If true, we decode
+   * and draw whatever image data has been loaded. If false, we just draw
+   * whatever has already been decoded.
+   */
+  void SetSyncDecodeImages(bool aSyncDecodeImages) {
+    mSyncDecodeImages = aSyncDecodeImages;
+  }
+
+  nsDisplayTableBackgroundSet* SetTableBackgroundSet(
+      nsDisplayTableBackgroundSet* aTableSet) {
+    nsDisplayTableBackgroundSet* old = mTableBackgroundSet;
+    mTableBackgroundSet = aTableSet;
+    return old;
+  }
+  nsDisplayTableBackgroundSet* GetTableBackgroundSet() const {
+    return mTableBackgroundSet;
+  }
+
+  void FreeClipChains();
+
+  /*
+   * Frees the temporary display items created during merging.
+   */
+  void FreeTemporaryItems();
+
+  /**
+   * Helper method to generate background painting flags based on the
+   * information available in the display list builder.
+   */
+  uint32_t GetBackgroundPaintFlags();
+
+  /**
+   * Helper method to generate nsImageRenderer flags based on the information
+   * available in the display list builder.
+   */
+  uint32_t GetImageRendererFlags() const;
+
+  /**
+   * Helper method to generate image decoding flags based on the
+   * information available in the display list builder.
+   */
+  uint32_t GetImageDecodeFlags() const;
+
+  /**
+   * Subtracts aRegion from *aVisibleRegion. We avoid letting
+   * aVisibleRegion become overcomplex by simplifying it if necessary.
+   */
+  void SubtractFromVisibleRegion(nsRegion* aVisibleRegion,
+                                 const nsRegion& aRegion);
+
+  /**
+   * Mark the frames in aFrames to be displayed if they intersect aDirtyRect
+   * (which is relative to aDirtyFrame). If the frames have placeholders
+   * that might not be displayed, we mark the placeholders and their ancestors
+   * to ensure that display list construction descends into them
+   * anyway. nsDisplayListBuilder will take care of unmarking them when it is
+   * destroyed.
+   */
+  void MarkFramesForDisplayList(nsIFrame* aDirtyFrame,
+                                const nsFrameList& aFrames);
+  void MarkFrameForDisplay(nsIFrame* aFrame, const nsIFrame* aStopAtFrame);
+  void MarkFrameForDisplayIfVisible(nsIFrame* aFrame,
+                                    const nsIFrame* aStopAtFrame);
+  void AddFrameMarkedForDisplayIfVisible(nsIFrame* aFrame);
+
+  void ClearFixedBackgroundDisplayData();
+  /**
+   * Mark all child frames that Preserve3D() as needing display.
+   * Because these frames include transforms set on their parent, dirty rects
+   * for intermediate frames may be empty, yet child frames could still be
+   * visible.
+   */
+  void MarkPreserve3DFramesForDisplayList(nsIFrame* aDirtyFrame);
+
+  /**
+   * Returns true if we need to descend into this frame when building
+   * the display list, even though it doesn't intersect the dirty
+   * rect, because it may have out-of-flows that do so.
+   */
+  bool ShouldDescendIntoFrame(nsIFrame* aFrame, bool aVisible) const {
+    return aFrame->HasAnyStateBits(NS_FRAME_FORCE_DISPLAY_LIST_DESCEND_INTO) ||
+           (aVisible && aFrame->ForceDescendIntoIfVisible()) ||
+           GetIncludeAllOutOfFlows();
+  }
+
+  /**
+   * Returns the list of registered theme geometries.
+   */
+  nsTArray<nsIWidget::ThemeGeometry> GetThemeGeometries() const {
+    nsTArray<nsIWidget::ThemeGeometry> geometries;
+
+    for (const auto& data : mThemeGeometries.Values()) {
+      geometries.AppendElements(*data);
+    }
+
+    return geometries;
+  }
+
+  /**
+   * Notifies the builder that a particular themed widget exists
+   * at the given rectangle within the currently built display list.
+   * For certain appearance values (currently only StyleAppearance::Toolbar and
+   * StyleAppearance::WindowTitlebar) this gets called during every display list
+   * construction, for every themed widget of the right type within the
+   * display list, except for themed widgets which are transformed or have
+   * effects applied to them (e.g. CSS opacity or filters).
+   *
+   * @param aWidgetType the -moz-appearance value for the themed widget
+   * @param aItem the item associated with the theme geometry
+   * @param aRect the device-pixel rect relative to the widget's displayRoot
+   * for the themed widget
+   */
+  void RegisterThemeGeometry(uint8_t aWidgetType, nsDisplayItem* aItem,
+                             const LayoutDeviceIntRect& aRect) {
+    if (!mIsPaintingToWindow) {
+      return;
+    }
+
+    nsTArray<nsIWidget::ThemeGeometry>* geometries =
+        mThemeGeometries.GetOrInsertNew(aItem);
+    geometries->AppendElement(nsIWidget::ThemeGeometry(aWidgetType, aRect));
+  }
+
+  /**
+   * Removes theme geometries associated with the given display item |aItem|.
+   */
+  void UnregisterThemeGeometry(nsDisplayItem* aItem) {
+    mThemeGeometries.Remove(aItem);
+  }
+
+  /**
+   * Adjusts mWindowDraggingRegion to take into account aFrame. If aFrame's
+   * -moz-window-dragging value is |drag|, its border box is added to the
+   * collected dragging region; if the value is |no-drag|, the border box is
+   * subtracted from the region; if the value is |default|, that frame does
+   * not influence the window dragging region.
+   */
+  void AdjustWindowDraggingRegion(nsIFrame* aFrame);
+
+  LayoutDeviceIntRegion GetWindowDraggingRegion() const;
+
+  void RemoveModifiedWindowRegions();
+  void ClearRetainedWindowRegions();
+
+  const nsTHashMap<nsPtrHashKey<dom::RemoteBrowser>, dom::EffectsInfo>&
+  GetEffectUpdates() const {
+    return mEffectsUpdates;
+  }
+
+  void AddEffectUpdate(dom::RemoteBrowser* aBrowser,
+                       const dom::EffectsInfo& aUpdate);
+
+  /**
+   * Allocate memory in our arena. It will only be freed when this display list
+   * builder is destroyed. This memory holds nsDisplayItems and
+   * DisplayItemClipChain objects.
+   *
+   * Destructors are called as soon as the item is no longer used.
+   */
+  void* Allocate(size_t aSize, DisplayListArenaObjectId aId) {
+    return mPool.Allocate(aId, aSize);
+  }
+  void* Allocate(size_t aSize, DisplayItemType aType) {
+#define DECLARE_DISPLAY_ITEM_TYPE(name_, ...)                \
+  static_assert(size_t(DisplayItemType::TYPE_##name_) ==     \
+                    size_t(DisplayListArenaObjectId::name_), \
+                "");
+#include "nsDisplayItemTypesList.h"
+    static_assert(size_t(DisplayItemType::TYPE_MAX) ==
+                      size_t(DisplayListArenaObjectId::CLIPCHAIN),
+                  "");
+    static_assert(size_t(DisplayItemType::TYPE_MAX) + 1 ==
+                      size_t(DisplayListArenaObjectId::LISTNODE),
+                  "");
+#undef DECLARE_DISPLAY_ITEM_TYPE
+    return Allocate(aSize, DisplayListArenaObjectId(size_t(aType)));
+  }
+
+  void Destroy(DisplayListArenaObjectId aId, void* aPtr) {
+    return mPool.Free(aId, aPtr);
+  }
+  void Destroy(DisplayItemType aType, void* aPtr) {
+    return Destroy(DisplayListArenaObjectId(size_t(aType)), aPtr);
+  }
+
+  /**
+   * Allocate a new ActiveScrolledRoot in the arena. Will be cleaned up
+   * automatically when the arena goes away.
+   */
+  ActiveScrolledRoot* AllocateActiveScrolledRoot(
+      const ActiveScrolledRoot* aParent, nsIScrollableFrame* aScrollableFrame);
+
+  /**
+   * Allocate a new DisplayItemClipChain object in the arena. Will be cleaned
+   * up automatically when the arena goes away.
+   */
+  const DisplayItemClipChain* AllocateDisplayItemClipChain(
+      const DisplayItemClip& aClip, const ActiveScrolledRoot* aASR,
+      const DisplayItemClipChain* aParent);
+
+  /**
+   * Intersect two clip chains, allocating the new clip chain items in this
+   * builder's arena. The result is parented to aAncestor, and no intersections
+   * happen past aAncestor's ASR.
+   * That means aAncestor has to be living in this builder's arena already.
+   * aLeafClip1 and aLeafClip2 only need to outlive the call to this function,
+   * their values are copied into the newly-allocated intersected clip chain
+   * and this function does not hold on to any pointers to them.
+   */
+  const DisplayItemClipChain* CreateClipChainIntersection(
+      const DisplayItemClipChain* aAncestor,
+      const DisplayItemClipChain* aLeafClip1,
+      const DisplayItemClipChain* aLeafClip2);
+
+  /**
+   * Same as above, except aAncestor is computed as the nearest common
+   * ancestor of the two provided clips.
+   */
+  const DisplayItemClipChain* CreateClipChainIntersection(
+      const DisplayItemClipChain* aLeafClip1,
+      const DisplayItemClipChain* aLeafClip2);
+
+  /**
+   * Clone the supplied clip chain's chain items into this builder's arena.
+   */
+  const DisplayItemClipChain* CopyWholeChain(
+      const DisplayItemClipChain* aClipChain);
+
+  const ActiveScrolledRoot* GetFilterASR() const { return mFilterASR; }
+
+  /**
+   * Merges the display items in |aMergedItems| and returns a new temporary
+   * display item.
+   * The display items in |aMergedItems| have to be mergeable with each other.
+   */
+  nsDisplayWrapList* MergeItems(nsTArray<nsDisplayItem*>& aItems);
+
+  /**
+   * A helper class used to temporarily set nsDisplayListBuilder properties for
+   * building display items.
+   * aVisibleRect and aDirtyRect are relative to aForChild.
+   */
+  class AutoBuildingDisplayList {
+   public:
+    AutoBuildingDisplayList(nsDisplayListBuilder* aBuilder, nsIFrame* aForChild,
+                            const nsRect& aVisibleRect,
+                            const nsRect& aDirtyRect)
+        : AutoBuildingDisplayList(aBuilder, aForChild, aVisibleRect, aDirtyRect,
+                                  aForChild->IsTransformed()) {}
+
+    AutoBuildingDisplayList(nsDisplayListBuilder* aBuilder, nsIFrame* aForChild,
+                            const nsRect& aVisibleRect,
+                            const nsRect& aDirtyRect,
+                            const bool aIsTransformed);
+
+    void SetReferenceFrameAndCurrentOffset(const nsIFrame* aFrame,
+                                           const nsPoint& aOffset) {
+      mBuilder->mCurrentReferenceFrame = aFrame;
+      mBuilder->mCurrentOffsetToReferenceFrame = aOffset;
+    }
+
+    void SetAdditionalOffset(const nsPoint& aOffset) {
+      MOZ_ASSERT(!mBuilder->mAdditionalOffset);
+      mBuilder->mAdditionalOffset = Some(aOffset);
+
+      mBuilder->mCurrentOffsetToReferenceFrame += aOffset;
+    }
+
+    void RestoreBuildingInvisibleItemsValue() {
+      mBuilder->mBuildingInvisibleItems = mPrevBuildingInvisibleItems;
+    }
+
+    ~AutoBuildingDisplayList() {
+      mBuilder->mCurrentFrame = mPrevFrame;
+      mBuilder->mCurrentReferenceFrame = mPrevReferenceFrame;
+      mBuilder->mCurrentOffsetToReferenceFrame = mPrevOffset;
+      mBuilder->mVisibleRect = mPrevVisibleRect;
+      mBuilder->mDirtyRect = mPrevDirtyRect;
+      mBuilder->mAncestorHasApzAwareEventHandler =
+          mPrevAncestorHasApzAwareEventHandler;
+      mBuilder->mBuildingInvisibleItems = mPrevBuildingInvisibleItems;
+      mBuilder->mInInvalidSubtree = mPrevInInvalidSubtree;
+      mBuilder->mAdditionalOffset = mPrevAdditionalOffset;
+      mBuilder->mCompositorHitTestInfo = mPrevCompositorHitTestInfo;
+    }
+
+   private:
+    nsDisplayListBuilder* mBuilder;
+    const nsIFrame* mPrevFrame;
+    const nsIFrame* mPrevReferenceFrame;
+    nsPoint mPrevOffset;
+    Maybe<nsPoint> mPrevAdditionalOffset;
+    nsRect mPrevVisibleRect;
+    nsRect mPrevDirtyRect;
+    gfx::CompositorHitTestInfo mPrevCompositorHitTestInfo;
+    bool mPrevAncestorHasApzAwareEventHandler;
+    bool mPrevBuildingInvisibleItems;
+    bool mPrevInInvalidSubtree;
+  };
+
+  /**
+   * A helper class to temporarily set the value of mInTransform.
+   */
+  class AutoInTransformSetter {
+   public:
+    AutoInTransformSetter(nsDisplayListBuilder* aBuilder, bool aInTransform)
+        : mBuilder(aBuilder), mOldValue(aBuilder->mInTransform) {
+      aBuilder->mInTransform = aInTransform;
+    }
+
+    ~AutoInTransformSetter() { mBuilder->mInTransform = mOldValue; }
+
+   private:
+    nsDisplayListBuilder* mBuilder;
+    bool mOldValue;
+  };
+
+  class AutoInEventsOnly {
+   public:
+    AutoInEventsOnly(nsDisplayListBuilder* aBuilder, bool aInEventsOnly)
+        : mBuilder(aBuilder), mOldValue(aBuilder->mInEventsOnly) {
+      aBuilder->mInEventsOnly |= aInEventsOnly;
+    }
+
+    ~AutoInEventsOnly() { mBuilder->mInEventsOnly = mOldValue; }
+
+   private:
+    nsDisplayListBuilder* mBuilder;
+    bool mOldValue;
+  };
+
+  /**
+   * A helper class to temporarily set the value of mFilterASR and
+   * mInFilter.
+   */
+  class AutoEnterFilter {
+   public:
+    AutoEnterFilter(nsDisplayListBuilder* aBuilder, bool aUsingFilter)
+        : mBuilder(aBuilder),
+          mOldValue(aBuilder->mFilterASR),
+          mOldInFilter(aBuilder->mInFilter) {
+      if (!aBuilder->mFilterASR && aUsingFilter) {
+        aBuilder->mFilterASR = aBuilder->CurrentActiveScrolledRoot();
+        aBuilder->mInFilter = true;
+      }
+    }
+
+    ~AutoEnterFilter() {
+      mBuilder->mFilterASR = mOldValue;
+      mBuilder->mInFilter = mOldInFilter;
+    }
+
+   private:
+    nsDisplayListBuilder* mBuilder;
+    const ActiveScrolledRoot* mOldValue;
+    bool mOldInFilter;
+  };
+
+  /**
+   * Used to update the current active scrolled root on the display list
+   * builder, and to create new active scrolled roots.
+   */
+  class AutoCurrentActiveScrolledRootSetter {
+   public:
+    explicit AutoCurrentActiveScrolledRootSetter(nsDisplayListBuilder* aBuilder)
+        : mBuilder(aBuilder),
+          mSavedActiveScrolledRoot(aBuilder->mCurrentActiveScrolledRoot),
+          mContentClipASR(aBuilder->ClipState().GetContentClipASR()),
+          mDescendantsStartIndex(aBuilder->mActiveScrolledRoots.Length()),
+          mUsed(false),
+          mOldScrollParentId(aBuilder->mCurrentScrollParentId),
+          mOldForceLayer(aBuilder->mForceLayerForScrollParent),
+          mOldContainsNonMinimalDisplayPort(
+              mBuilder->mContainsNonMinimalDisplayPort),
+          mCanBeScrollParent(false) {}
+
+    void SetCurrentScrollParentId(ViewID aScrollId) {
+      // Update the old scroll parent id.
+      mOldScrollParentId = mBuilder->mCurrentScrollParentId;
+      // If this AutoCurrentActiveScrolledRootSetter has the same aScrollId as
+      // the previous one on the stack, then that means the scrollframe that
+      // created this isn't actually scrollable and cannot participate in
+      // scroll handoff. We set mCanBeScrollParent to false to indicate this.
+      mCanBeScrollParent = (mOldScrollParentId != aScrollId);
+      mBuilder->mCurrentScrollParentId = aScrollId;
+      mBuilder->mForceLayerForScrollParent = false;
+      mBuilder->mContainsNonMinimalDisplayPort = false;
+    }
+
+    bool ShouldForceLayerForScrollParent() const {
+      // Only scrollframes participating in scroll handoff can be forced to
+      // layerize
+      return mCanBeScrollParent && mBuilder->mForceLayerForScrollParent;
+    }
+
+    bool GetContainsNonMinimalDisplayPort() const {
+      // Only for scrollframes participating in scroll handoff can we return
+      // true.
+      return mCanBeScrollParent && mBuilder->mContainsNonMinimalDisplayPort;
+    }
+
+    ~AutoCurrentActiveScrolledRootSetter() {
+      mBuilder->mCurrentActiveScrolledRoot = mSavedActiveScrolledRoot;
+      mBuilder->mCurrentScrollParentId = mOldScrollParentId;
+      if (mCanBeScrollParent) {
+        // If this flag is set, caller code is responsible for having dealt
+        // with the current value of mBuilder->mForceLayerForScrollParent, so
+        // we can just restore the old value.
+        mBuilder->mForceLayerForScrollParent = mOldForceLayer;
+      } else {
+        // Otherwise we need to keep propagating the force-layerization flag
+        // upwards to the next ancestor scrollframe that does participate in
+        // scroll handoff.
+        mBuilder->mForceLayerForScrollParent |= mOldForceLayer;
+      }
+      mBuilder->mContainsNonMinimalDisplayPort |=
+          mOldContainsNonMinimalDisplayPort;
+    }
+
+    void SetCurrentActiveScrolledRoot(
+        const ActiveScrolledRoot* aActiveScrolledRoot);
+
+    void EnterScrollFrame(nsIScrollableFrame* aScrollableFrame) {
+      MOZ_ASSERT(!mUsed);
+      ActiveScrolledRoot* asr = mBuilder->AllocateActiveScrolledRoot(
+          mBuilder->mCurrentActiveScrolledRoot, aScrollableFrame);
+      mBuilder->mCurrentActiveScrolledRoot = asr;
+      mUsed = true;
+    }
+
+    void InsertScrollFrame(nsIScrollableFrame* aScrollableFrame);
+
+   private:
+    nsDisplayListBuilder* mBuilder;
+    /**
+     * The builder's mCurrentActiveScrolledRoot at construction time which
+     * needs to be restored at destruction time.
+     */
+    const ActiveScrolledRoot* mSavedActiveScrolledRoot;
+    /**
+     * If there's a content clip on the builder at construction time, then
+     * mContentClipASR is that content clip's ASR, otherwise null. The
+     * assumption is that the content clip doesn't get relaxed while this
+     * object is on the stack.
+     */
+    const ActiveScrolledRoot* mContentClipASR;
+    /**
+     * InsertScrollFrame needs to mutate existing ASRs (those that were
+     * created while this object was on the stack), and mDescendantsStartIndex
+     * makes it easier to skip ASRs that were created in the past.
+     */
+    size_t mDescendantsStartIndex;
+    /**
+     * Flag to make sure that only one of SetCurrentActiveScrolledRoot /
+     * EnterScrollFrame / InsertScrollFrame is called per instance of this
+     * class.
+     */
+    bool mUsed;
+    ViewID mOldScrollParentId;
+    bool mOldForceLayer;
+    bool mOldContainsNonMinimalDisplayPort;
+    bool mCanBeScrollParent;
+  };
+
+  /**
+   * Keeps track of the innermost ASR that can be used as the ASR for a
+   * container item that wraps all items that were created while this
+   * object was on the stack.
+   * The rule is: all child items of the container item need to have
+   * clipped bounds with respect to the container ASR.
+   */
+  class AutoContainerASRTracker {
+   public:
+    explicit AutoContainerASRTracker(nsDisplayListBuilder* aBuilder);
+
+    const ActiveScrolledRoot* GetContainerASR() {
+      return mBuilder->mCurrentContainerASR;
+    }
+
+    ~AutoContainerASRTracker() {
+      mBuilder->mCurrentContainerASR = ActiveScrolledRoot::PickAncestor(
+          mBuilder->mCurrentContainerASR, mSavedContainerASR);
+    }
+
+   private:
+    nsDisplayListBuilder* mBuilder;
+    const ActiveScrolledRoot* mSavedContainerASR;
+  };
+
+  /**
+   * A helper class to temporarily set the value of mCurrentScrollbarTarget
+   * and mCurrentScrollbarFlags.
+   */
+  class AutoCurrentScrollbarInfoSetter {
+   public:
+    AutoCurrentScrollbarInfoSetter(
+        nsDisplayListBuilder* aBuilder, ViewID aScrollTargetID,
+        const Maybe<layers::ScrollDirection>& aScrollbarDirection,
+        bool aWillHaveLayer)
+        : mBuilder(aBuilder) {
+      aBuilder->mIsBuildingScrollbar = true;
+      aBuilder->mCurrentScrollbarTarget = aScrollTargetID;
+      aBuilder->mCurrentScrollbarDirection = aScrollbarDirection;
+      aBuilder->mCurrentScrollbarWillHaveLayer = aWillHaveLayer;
+    }
+
+    ~AutoCurrentScrollbarInfoSetter() {
+      // No need to restore old values because scrollbars cannot be nested.
+      mBuilder->mIsBuildingScrollbar = false;
+      mBuilder->mCurrentScrollbarTarget =
+          layers::ScrollableLayerGuid::NULL_SCROLL_ID;
+      mBuilder->mCurrentScrollbarDirection.reset();
+      mBuilder->mCurrentScrollbarWillHaveLayer = false;
+    }
+
+   private:
+    nsDisplayListBuilder* mBuilder;
+  };
+
+  /**
+   * A helper class to temporarily set mBuildingExtraPagesForPageNum.
+   */
+  class MOZ_RAII AutoPageNumberSetter {
+   public:
+    AutoPageNumberSetter(nsDisplayListBuilder* aBuilder, const uint8_t aPageNum)
+        : mBuilder(aBuilder),
+          mOldPageNum(aBuilder->GetBuildingExtraPagesForPageNum()) {
+      mBuilder->SetBuildingExtraPagesForPageNum(aPageNum);
+    }
+    ~AutoPageNumberSetter() {
+      mBuilder->SetBuildingExtraPagesForPageNum(mOldPageNum);
+    }
+
+   private:
+    nsDisplayListBuilder* mBuilder;
+    uint8_t mOldPageNum;
+  };
+
+  /**
+   * A helper class to track current effective transform for items.
+   *
+   * For frames that is Combines3DTransformWithAncestors(), we need to
+   * apply all transforms of ancestors on the same preserves3D chain
+   * on the bounds of current frame to the coordination of the 3D
+   * context root.  The 3D context root computes it's bounds from
+   * these transformed bounds.
+   */
+  class AutoAccumulateTransform {
+   public:
+    explicit AutoAccumulateTransform(nsDisplayListBuilder* aBuilder)
+        : mBuilder(aBuilder),
+          mSavedTransform(aBuilder->mPreserves3DCtx.mAccumulatedTransform) {}
+
+    ~AutoAccumulateTransform() {
+      mBuilder->mPreserves3DCtx.mAccumulatedTransform = mSavedTransform;
+    }
+
+    void Accumulate(const gfx::Matrix4x4& aTransform) {
+      mBuilder->mPreserves3DCtx.mAccumulatedTransform =
+          aTransform * mBuilder->mPreserves3DCtx.mAccumulatedTransform;
+    }
+
+    const gfx::Matrix4x4& GetCurrentTransform() {
+      return mBuilder->mPreserves3DCtx.mAccumulatedTransform;
+    }
+
+    void StartRoot() {
+      mBuilder->mPreserves3DCtx.mAccumulatedTransform = gfx::Matrix4x4();
+    }
+
+   private:
+    nsDisplayListBuilder* mBuilder;
+    gfx::Matrix4x4 mSavedTransform;
+  };
+
+  /**
+   * A helper class to collect bounds rects of descendants.
+   *
+   * For a 3D context root, it's bounds is computed from the bounds of
+   * descendants.  If we transform bounds frame by frame applying
+   * transforms, the bounds may turn to empty for any singular
+   * transform on the path, but it is not empty for the accumulated
+   * transform.
+   */
+  class AutoAccumulateRect {
+   public:
+    explicit AutoAccumulateRect(nsDisplayListBuilder* aBuilder)
+        : mBuilder(aBuilder),
+          mSavedRect(aBuilder->mPreserves3DCtx.mAccumulatedRect) {
+      aBuilder->mPreserves3DCtx.mAccumulatedRect = nsRect();
+      aBuilder->mPreserves3DCtx.mAccumulatedRectLevels++;
+    }
+
+    ~AutoAccumulateRect() {
+      mBuilder->mPreserves3DCtx.mAccumulatedRect = mSavedRect;
+      mBuilder->mPreserves3DCtx.mAccumulatedRectLevels--;
+    }
+
+   private:
+    nsDisplayListBuilder* mBuilder;
+    nsRect mSavedRect;
+  };
+
+  void AccumulateRect(const nsRect& aRect) {
+    mPreserves3DCtx.mAccumulatedRect.UnionRect(mPreserves3DCtx.mAccumulatedRect,
+                                               aRect);
+  }
+
+  const nsRect& GetAccumulatedRect() {
+    return mPreserves3DCtx.mAccumulatedRect;
+  }
+
+  /**
+   * The level is increased by one for items establishing 3D rendering
+   * context and starting a new accumulation.
+   */
+  int GetAccumulatedRectLevels() {
+    return mPreserves3DCtx.mAccumulatedRectLevels;
+  }
+
+  struct OutOfFlowDisplayData {
+    OutOfFlowDisplayData(
+        const DisplayItemClipChain* aContainingBlockClipChain,
+        const DisplayItemClipChain* aCombinedClipChain,
+        const ActiveScrolledRoot* aContainingBlockActiveScrolledRoot,
+        const ViewID& aScrollParentId, const nsRect& aVisibleRect,
+        const nsRect& aDirtyRect)
+        : mContainingBlockClipChain(aContainingBlockClipChain),
+          mCombinedClipChain(aCombinedClipChain),
+          mContainingBlockActiveScrolledRoot(
+              aContainingBlockActiveScrolledRoot),
+          mVisibleRect(aVisibleRect),
+          mDirtyRect(aDirtyRect),
+          mScrollParentId(aScrollParentId) {}
+    const DisplayItemClipChain* mContainingBlockClipChain;
+    const DisplayItemClipChain*
+        mCombinedClipChain;  // only necessary for the special case of top layer
+    const ActiveScrolledRoot* mContainingBlockActiveScrolledRoot;
+
+    // If this OutOfFlowDisplayData is associated with the ViewportFrame
+    // of a document that has a resolution (creating separate visual and
+    // layout viewports with their own coordinate spaces), these rects
+    // are in layout coordinates. Similarly, GetVisibleRectForFrame() in
+    // such a case returns a quantity in layout coordinates.
+    nsRect mVisibleRect;
+    nsRect mDirtyRect;
+    ViewID mScrollParentId;
+
+    static nsRect ComputeVisibleRectForFrame(nsDisplayListBuilder* aBuilder,
+                                             nsIFrame* aFrame,
+                                             const nsRect& aVisibleRect,
+                                             const nsRect& aDirtyRect,
+                                             nsRect* aOutDirtyRect);
+
+    nsRect GetVisibleRectForFrame(nsDisplayListBuilder* aBuilder,
+                                  nsIFrame* aFrame, nsRect* aDirtyRect) {
+      return ComputeVisibleRectForFrame(aBuilder, aFrame, mVisibleRect,
+                                        mDirtyRect, aDirtyRect);
+    }
+  };
+
+  NS_DECLARE_FRAME_PROPERTY_DELETABLE(OutOfFlowDisplayDataProperty,
+                                      OutOfFlowDisplayData)
+
+  struct DisplayListBuildingData {
+    nsIFrame* mModifiedAGR = nullptr;
+    nsRect mDirtyRect;
+  };
+  NS_DECLARE_FRAME_PROPERTY_DELETABLE(DisplayListBuildingRect,
+                                      DisplayListBuildingData)
+
+  NS_DECLARE_FRAME_PROPERTY_DELETABLE(DisplayListBuildingDisplayPortRect,
+                                      nsRect)
+
+  static OutOfFlowDisplayData* GetOutOfFlowData(nsIFrame* aFrame) {
+    if (!aFrame->GetParent()) {
+      return nullptr;
+    }
+    return aFrame->GetParent()->GetProperty(OutOfFlowDisplayDataProperty());
+  }
+
+  nsPresContext* CurrentPresContext();
+
+  OutOfFlowDisplayData* GetCurrentFixedBackgroundDisplayData() {
+    auto& displayData = CurrentPresShellState()->mFixedBackgroundDisplayData;
+    return displayData ? displayData.ptr() : nullptr;
+  }
+
+  /**
+   * Accumulates the bounds of box frames that have moz-appearance
+   * -moz-win-exclude-glass style. Used in setting glass margins on
+   * Windows.
+   *
+   * We set the window opaque region (from which glass margins are computed)
+   * to the intersection of the glass region specified here and the opaque
+   * region computed during painting. So the excluded glass region actually
+   * *limits* the extent of the opaque area reported to Windows. We limit it
+   * so that changes to the computed opaque region (which can vary based on
+   * region optimizations and the placement of UI elements) outside the
+   * -moz-win-exclude-glass area don't affect the glass margins reported to
+   * Windows; changing those margins willy-nilly can cause the Windows 7 glass
+   * haze effect to jump around disconcertingly.
+   */
+  void AddWindowExcludeGlassRegion(nsIFrame* aFrame, const nsRect& aBounds) {
+    mWindowExcludeGlassRegion.Add(aFrame, aBounds);
+  }
+
+  /**
+   * Returns the window exclude glass region.
+   */
+  nsRegion GetWindowExcludeGlassRegion() const {
+    return mWindowExcludeGlassRegion.ToRegion();
+  }
+
+  /**
+   * Accumulates opaque stuff into the window opaque region.
+   */
+  void AddWindowOpaqueRegion(nsIFrame* aFrame, const nsRect& aBounds) {
+    if (IsRetainingDisplayList()) {
+      mRetainedWindowOpaqueRegion.Add(aFrame, aBounds);
+      return;
+    }
+    mWindowOpaqueRegion.Or(mWindowOpaqueRegion, aBounds);
+  }
+  /**
+   * Returns the window opaque region built so far. This may be incomplete
+   * since the opaque region is built during layer construction.
+   */
+  const nsRegion GetWindowOpaqueRegion() {
+    return IsRetainingDisplayList() ? mRetainedWindowOpaqueRegion.ToRegion()
+                                    : mWindowOpaqueRegion;
+  }
+
+  void SetGlassDisplayItem(nsDisplayItem* aItem);
+  void ClearGlassDisplayItem() { mGlassDisplayItem = nullptr; }
+  nsDisplayItem* GetGlassDisplayItem() { return mGlassDisplayItem; }
+
+  bool NeedToForceTransparentSurfaceForItem(nsDisplayItem* aItem);
+
+  /**
+   * mContainsBlendMode is true if we processed a display item that
+   * has a blend mode attached. We do this so we can insert a
+   * nsDisplayBlendContainer in the parent stacking context.
+   */
+  void SetContainsBlendMode(bool aContainsBlendMode) {
+    mContainsBlendMode = aContainsBlendMode;
+  }
+  bool ContainsBlendMode() const { return mContainsBlendMode; }
+
+  DisplayListClipState& ClipState() { return mClipState; }
+  const ActiveScrolledRoot* CurrentActiveScrolledRoot() {
+    return mCurrentActiveScrolledRoot;
+  }
+  const ActiveScrolledRoot* CurrentAncestorASRStackingContextContents() {
+    return mCurrentContainerASR;
+  }
+
+  /**
+   * Add the current frame to the will-change budget if possible and
+   * remeber the outcome. Subsequent calls to IsInWillChangeBudget
+   * will return the same value as return here.
+   */
+  bool AddToWillChangeBudget(nsIFrame* aFrame, const nsSize& aSize);
+
+  /**
+   * This will add the current frame to the will-change budget the first
+   * time it is seen. On subsequent calls this will return the same
+   * answer. This effectively implements a first-come, first-served
+   * allocation of the will-change budget.
+   */
+  bool IsInWillChangeBudget(nsIFrame* aFrame, const nsSize& aSize);
+
+  /**
+   * Clears the will-change budget status for the given |aFrame|.
+   * This will also remove the frame from will-change budgets.
+   */
+  void ClearWillChangeBudgetStatus(nsIFrame* aFrame);
+
+  /**
+   * Removes the given |aFrame| from will-change budgets.
+   */
+  void RemoveFromWillChangeBudgets(const nsIFrame* aFrame);
+
+  /**
+   * Clears the will-change budgets.
+   */
+  void ClearWillChangeBudgets();
+
+  void EnterSVGEffectsContents(nsIFrame* aEffectsFrame,
+                               nsDisplayList* aHoistedItemsStorage);
+  void ExitSVGEffectsContents();
+
+  bool ShouldBuildScrollInfoItemsForHoisting() const;
+
+  void AppendNewScrollInfoItemForHoisting(
+      nsDisplayScrollInfoLayer* aScrollInfoItem);
+
+  /**
+   * A helper class to install/restore nsDisplayListBuilder::mPreserves3DCtx.
+   *
+   * mPreserves3DCtx is used by class AutoAccumulateTransform &
+   * AutoAccumulateRect to passing data between frames in the 3D
+   * context.  If a frame create a new 3D context, it should restore
+   * the value of mPreserves3DCtx before returning back to the parent.
+   * This class do it for the users.
+   */
+  class AutoPreserves3DContext {
+   public:
+    explicit AutoPreserves3DContext(nsDisplayListBuilder* aBuilder)
+        : mBuilder(aBuilder), mSavedCtx(aBuilder->mPreserves3DCtx) {}
+
+    ~AutoPreserves3DContext() { mBuilder->mPreserves3DCtx = mSavedCtx; }
+
+   private:
+    nsDisplayListBuilder* mBuilder;
+    Preserves3DContext mSavedCtx;
+  };
+
+  const nsRect GetPreserves3DRect() const {
+    return mPreserves3DCtx.mVisibleRect;
+  }
+
+  void SavePreserves3DRect() { mPreserves3DCtx.mVisibleRect = mVisibleRect; }
+
+  void SavePreserves3DAllowAsyncAnimation(bool aValue) {
+    mPreserves3DCtx.mAllowAsyncAnimation = aValue;
+  }
+
+  bool GetPreserves3DAllowAsyncAnimation() const {
+    return mPreserves3DCtx.mAllowAsyncAnimation;
+  }
+
+  bool IsBuildingInvisibleItems() const { return mBuildingInvisibleItems; }
+
+  void SetBuildingInvisibleItems(bool aBuildingInvisibleItems) {
+    mBuildingInvisibleItems = aBuildingInvisibleItems;
+  }
+
+  void SetBuildingExtraPagesForPageNum(uint8_t aPageNum) {
+    mBuildingExtraPagesForPageNum = aPageNum;
+  }
+  uint8_t GetBuildingExtraPagesForPageNum() const {
+    return mBuildingExtraPagesForPageNum;
+  }
+
+  bool HitTestIsForVisibility() const { return mVisibleThreshold.isSome(); }
+
+  float VisibilityThreshold() const {
+    MOZ_DIAGNOSTIC_ASSERT(HitTestIsForVisibility());
+    return mVisibleThreshold.valueOr(1.0f);
+  }
+
+  void SetHitTestIsForVisibility(float aVisibleThreshold) {
+    mVisibleThreshold = Some(aVisibleThreshold);
+  }
+
+  bool ShouldBuildAsyncZoomContainer() const {
+    return mBuildAsyncZoomContainer;
+  }
+  void UpdateShouldBuildAsyncZoomContainer();
+
+  void UpdateShouldBuildBackdropRootContainer();
+
+  bool ShouldRebuildDisplayListDueToPrefChange();
+
+  /**
+   * Represents a region composed of frame/rect pairs.
+   * WeakFrames are used to track whether a rect still belongs to the region.
+   * Modified frames and rects are removed and re-added to the region if needed.
+   */
+  struct WeakFrameRegion {
+    /**
+     * A wrapper to store WeakFrame and the pointer to the underlying frame.
+     * This is needed because WeakFrame does not store the frame pointer after
+     * the frame has been deleted.
+     */
+    struct WeakFrameWrapper {
+      explicit WeakFrameWrapper(nsIFrame* aFrame)
+          : mWeakFrame(new WeakFrame(aFrame)), mFrame(aFrame) {}
+
+      UniquePtr<WeakFrame> mWeakFrame;
+      void* mFrame;
+    };
+
+    nsTHashSet<void*> mFrameSet;
+    nsTArray<WeakFrameWrapper> mFrames;
+    nsTArray<pixman_box32_t> mRects;
+
+    template <typename RectType>
+    void Add(nsIFrame* aFrame, const RectType& aRect) {
+      if (mFrameSet.Contains(aFrame)) {
+        return;
+      }
+
+      mFrameSet.Insert(aFrame);
+      mFrames.AppendElement(WeakFrameWrapper(aFrame));
+      mRects.AppendElement(nsRegion::RectToBox(aRect));
+    }
+
+    void Clear() {
+      mFrameSet.Clear();
+      mFrames.Clear();
+      mRects.Clear();
+    }
+
+    void RemoveModifiedFramesAndRects();
+
+    size_t SizeOfExcludingThis(MallocSizeOf) const;
+
+    typedef gfx::ArrayView<pixman_box32_t> BoxArrayView;
+
+    nsRegion ToRegion() const { return nsRegion(BoxArrayView(mRects)); }
+
+    LayoutDeviceIntRegion ToLayoutDeviceIntRegion() const {
+      return LayoutDeviceIntRegion(BoxArrayView(mRects));
+    }
+  };
+
+  void AddScrollFrameToNotify(nsIScrollableFrame* aScrollFrame);
+  void NotifyAndClearScrollFrames();
+
+  // Helper class to find what link spec (if any) to associate with a frame,
+  // recording it in the builder, and generate the corresponding DisplayItem.
+  // This also takes care of generating a named destination for internal links
+  // if the element has an id or name attribute.
+  class Linkifier {
+   public:
+    Linkifier(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+              nsDisplayList* aList);
+
+    ~Linkifier() {
+      if (mBuilderToReset) {
+        mBuilderToReset->mLinkSpec.Truncate(0);
+      }
+    }
+
+    void MaybeAppendLink(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame);
+
+   private:
+    nsDisplayListBuilder* mBuilderToReset = nullptr;
+    nsDisplayList* mList;
+  };
+
+  /**
+   * Returns the nearest ancestor frame to aFrame that is considered to have
+   * (or will have) animated geometry. This can return aFrame.
+   */
+  nsIFrame* FindAnimatedGeometryRootFrameFor(nsIFrame* aFrame);
+
+  /**
+   * Returns true if this is a retained builder and reuse stacking contexts
+   * mode is enabled by pref.
+   */
+  bool IsReusingStackingContextItems() const {
+    return mIsReusingStackingContextItems;
+  }
+
+  /**
+   * Adds display item |aItem| to the reuseable display items set.
+   */
+  void AddReusableDisplayItem(nsDisplayItem* aItem);
+
+  /**
+   * Removes display item |aItem| from the reuseable display items set.
+   * This is needed because display items are sometimes deleted during
+   * display list building.
+   * Called by |nsDisplayItem::Destroy()| when the item has been reused.
+   */
+  void RemoveReusedDisplayItem(nsDisplayItem* aItem);
+
+  /**
+   * Clears the reuseable display items set.
+   */
+  void ClearReuseableDisplayItems();
+
+  /**
+   * Marks the given display item |aItem| as reused, and updates the necessary
+   * display list builder state.
+   */
+  void ReuseDisplayItem(nsDisplayItem* aItem);
+
+ private:
+  bool MarkOutOfFlowFrameForDisplay(nsIFrame* aDirtyFrame, nsIFrame* aFrame,
+                                    const nsRect& aVisibleRect,
+                                    const nsRect& aDirtyRect);
+
+  friend class nsDisplayBackgroundImage;
+  friend class RetainedDisplayListBuilder;
+
+  /**
+   * Returns whether a frame acts as an animated geometry root, optionally
+   * returning the next ancestor to check.
+   */
+  bool IsAnimatedGeometryRoot(nsIFrame* aFrame, nsIFrame** aParent = nullptr);
+
+  struct PresShellState {
+    PresShell* mPresShell;
+#ifdef DEBUG
+    Maybe<nsAutoLayoutPhase> mAutoLayoutPhase;
+#endif
+    Maybe<OutOfFlowDisplayData> mFixedBackgroundDisplayData;
+    uint32_t mFirstFrameMarkedForDisplay;
+    uint32_t mFirstFrameWithOOFData;
+    bool mIsBackgroundOnly;
+    // This is a per-document flag turning off event handling for all content
+    // in the document, and is set when we enter a subdocument for a pointer-
+    // events:none frame.
+    bool mInsidePointerEventsNoneDoc;
+    bool mTouchEventPrefEnabledDoc;
+    nsIFrame* mPresShellIgnoreScrollFrame;
+  };
+
+  PresShellState* CurrentPresShellState() {
+    NS_ASSERTION(mPresShellStates.Length() > 0,
+                 "Someone forgot to enter a presshell");
+    return &mPresShellStates[mPresShellStates.Length() - 1];
+  }
+
+  void AddSizeOfExcludingThis(nsWindowSizes&) const;
+
+  struct FrameWillChangeBudget {
+    FrameWillChangeBudget() : mPresContext(nullptr), mUsage(0) {}
+
+    FrameWillChangeBudget(const nsPresContext* aPresContext, uint32_t aUsage)
+        : mPresContext(aPresContext), mUsage(aUsage) {}
+
+    const nsPresContext* mPresContext;
+    uint32_t mUsage;
+  };
+
+  nsIFrame* const mReferenceFrame;
+  nsIFrame* mIgnoreScrollFrame;
+
+  using Arena = nsPresArena<32768, DisplayListArenaObjectId,
+                            size_t(DisplayListArenaObjectId::COUNT)>;
+  Arena mPool;
+
+  AutoTArray<PresShellState, 8> mPresShellStates;
+  AutoTArray<nsIFrame*, 400> mFramesMarkedForDisplay;
+  AutoTArray<nsIFrame*, 40> mFramesMarkedForDisplayIfVisible;
+  AutoTArray<nsIFrame*, 20> mFramesWithOOFData;
+  nsClassHashtable<nsPtrHashKey<nsDisplayItem>,
+                   nsTArray<nsIWidget::ThemeGeometry>>
+      mThemeGeometries;
+  DisplayListClipState mClipState;
+  const ActiveScrolledRoot* mCurrentActiveScrolledRoot;
+  const ActiveScrolledRoot* mCurrentContainerASR;
+  // mCurrentFrame is the frame that we're currently calling (or about to call)
+  // BuildDisplayList on.
+  const nsIFrame* mCurrentFrame;
+  // The reference frame for mCurrentFrame.
+  const nsIFrame* mCurrentReferenceFrame;
+  // The offset from mCurrentFrame to mCurrentReferenceFrame.
+  nsPoint mCurrentOffsetToReferenceFrame;
+
+  Maybe<nsPoint> mAdditionalOffset;
+
+  // will-change budget tracker
+  typedef uint32_t DocumentWillChangeBudget;
+  nsTHashMap<nsPtrHashKey<const nsPresContext>, DocumentWillChangeBudget>
+      mDocumentWillChangeBudgets;
+
+  // Any frame listed in this set is already counted in the budget
+  // and thus is in-budget.
+  nsTHashMap<nsPtrHashKey<const nsIFrame>, FrameWillChangeBudget>
+      mFrameWillChangeBudgets;
+
+  uint8_t mBuildingExtraPagesForPageNum;
+
+  nsTHashMap<nsPtrHashKey<dom::RemoteBrowser>, dom::EffectsInfo>
+      mEffectsUpdates;
+
+  // Relative to mCurrentFrame.
+  nsRect mVisibleRect;
+  nsRect mDirtyRect;
+
+  // Tracked regions used for retained display list.
+  WeakFrameRegion mWindowExcludeGlassRegion;
+  WeakFrameRegion mRetainedWindowDraggingRegion;
+  WeakFrameRegion mRetainedWindowNoDraggingRegion;
+
+  // Window opaque region is calculated during layer building.
+  WeakFrameRegion mRetainedWindowOpaqueRegion;
+
+  // Optimized versions for non-retained display list.
+  LayoutDeviceIntRegion mWindowDraggingRegion;
+  LayoutDeviceIntRegion mWindowNoDraggingRegion;
+  nsRegion mWindowOpaqueRegion;
+
+  // The display item for the Windows window glass background, if any
+  // Set during full display list builds or during display list merging only,
+  // partial display list builds don't touch this.
+  nsDisplayItem* mGlassDisplayItem;
+  // If we've encountered a glass item yet, only used during partial display
+  // list builds.
+  bool mHasGlassItemDuringPartial;
+
+  nsIFrame* mCaretFrame;
+  nsRect mCaretRect;
+
+  // A temporary list that we append scroll info items to while building
+  // display items for the contents of frames with SVG effects.
+  // Only non-null when ShouldBuildScrollInfoItemsForHoisting() is true.
+  // This is a pointer and not a real nsDisplayList value because the
+  // nsDisplayList class is defined below this class, so we can't use it here.
+  nsDisplayList* mScrollInfoItemsForHoisting;
+  nsTArray<RefPtr<ActiveScrolledRoot>> mActiveScrolledRoots;
+  std::unordered_set<const DisplayItemClipChain*, DisplayItemClipChainHasher,
+                     DisplayItemClipChainEqualer>
+      mClipDeduplicator;
+  DisplayItemClipChain* mFirstClipChainToDestroy;
+  nsTArray<nsDisplayItem*> mTemporaryItems;
+  nsDisplayListBuilderMode mMode;
+  nsDisplayTableBackgroundSet* mTableBackgroundSet;
+  ViewID mCurrentScrollParentId;
+  ViewID mCurrentScrollbarTarget;
+  Maybe<layers::ScrollDirection> mCurrentScrollbarDirection;
+  Preserves3DContext mPreserves3DCtx;
+  nsTArray<nsIFrame*> mSVGEffectsFrames;
+  // When we are inside a filter, the current ASR at the time we entered the
+  // filter. Otherwise nullptr.
+  const ActiveScrolledRoot* mFilterASR;
+  std::unordered_set<nsIScrollableFrame*> mScrollFramesToNotify;
+  nsCString mLinkSpec;  // Destination of link currently being emitted, if any.
+  nsTHashSet<nsCString> mDestinations;  // Destination names emitted.
+  bool mContainsBlendMode;
+  bool mIsBuildingScrollbar;
+  bool mCurrentScrollbarWillHaveLayer;
+  bool mBuildCaret;
+  bool mRetainingDisplayList;
+  bool mPartialUpdate;
+  bool mIgnoreSuppression;
+  bool mIncludeAllOutOfFlows;
+  bool mDescendIntoSubdocuments;
+  bool mSelectedFramesOnly;
+  bool mAllowMergingAndFlattening;
+  // True when we're building a display list that's directly or indirectly
+  // under an nsDisplayTransform
+  bool mInTransform;
+  bool mInEventsOnly;
+  bool mInFilter;
+  bool mInPageSequence;
+  bool mIsInChromePresContext;
+  bool mSyncDecodeImages;
+  bool mIsPaintingToWindow;
+  bool mUseHighQualityScaling;
+  bool mIsPaintingForWebRender;
+  bool mIsCompositingCheap;
+  bool mAncestorHasApzAwareEventHandler;
+  // True when the first async-scrollable scroll frame for which we build a
+  // display list has a display port. An async-scrollable scroll frame is one
+  // which WantsAsyncScroll().
+  bool mHaveScrollableDisplayPort;
+  bool mWindowDraggingAllowed;
+  bool mIsBuildingForPopup;
+  bool mForceLayerForScrollParent;
+  bool mContainsNonMinimalDisplayPort;
+  bool mAsyncPanZoomEnabled;
+  bool mBuildingInvisibleItems;
+  bool mIsBuilding;
+  bool mInInvalidSubtree;
+  bool mBuildCompositorHitTestInfo;
+  bool mDisablePartialUpdates;
+  bool mPartialBuildFailed;
+  bool mIsInActiveDocShell;
+  bool mBuildAsyncZoomContainer;
+  bool mIsRelativeToLayoutViewport;
+  bool mUseOverlayScrollbars;
+  bool mAlwaysLayerizeScrollbars;
+
+  Maybe<float> mVisibleThreshold;
+  gfx::CompositorHitTestInfo mCompositorHitTestInfo;
+
+  bool mIsReusingStackingContextItems;
+
+  // Stores reusable items collected during display list preprocessing.
+  nsTHashSet<nsDisplayItem*> mReuseableItems;
+};
+
+// All types are defined in nsDisplayItemTypes.h
+#define NS_DISPLAY_DECL_NAME(n, e)                                           \
+  const char* Name() const override { return n; }                            \
+  constexpr static DisplayItemType ItemType() { return DisplayItemType::e; } \
+                                                                             \
+ private:                                                                    \
+  void* operator new(size_t aSize, nsDisplayListBuilder* aBuilder) {         \
+    return aBuilder->Allocate(aSize, DisplayItemType::e);                    \
+  }                                                                          \
+                                                                             \
+  template <typename T, typename F, typename... Args>                        \
+  friend T* mozilla::MakeDisplayItemWithIndex(                               \
+      nsDisplayListBuilder* aBuilder, F* aFrame, const uint16_t aIndex,      \
+      Args&&... aArgs);                                                      \
+                                                                             \
+ public:
+
+#define NS_DISPLAY_ALLOW_CLONING()                                          \
+  template <typename T>                                                     \
+  friend T* mozilla::MakeClone(nsDisplayListBuilder* aBuilder,              \
+                               const T* aItem);                             \
+                                                                            \
+  nsDisplayWrapList* Clone(nsDisplayListBuilder* aBuilder) const override { \
+    return MakeClone(aBuilder, this);                                       \
+  }
+
+template <typename T>
+MOZ_ALWAYS_INLINE T* MakeClone(nsDisplayListBuilder* aBuilder, const T* aItem) {
+  static_assert(std::is_base_of<nsDisplayWrapList, T>::value,
+                "Display item type should be derived from nsDisplayWrapList");
+  T* item = new (aBuilder) T(aBuilder, *aItem);
+  item->SetType(T::ItemType());
+  return item;
+}
+
+#ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
+void AssertUniqueItem(nsDisplayItem* aItem);
+#endif
+
+/**
+ * Returns true, if a display item of given |aType| needs to be built within
+ * opacity:0 container.
+ */
+bool ShouldBuildItemForEvents(const DisplayItemType aType);
+
+/**
+ * Initializes the hit test information of |aItem| if the item type supports it.
+ */
+void InitializeHitTestInfo(nsDisplayListBuilder* aBuilder,
+                           nsPaintedDisplayItem* aItem,
+                           const DisplayItemType aType);
+
+template <typename T, typename F, typename... Args>
+MOZ_ALWAYS_INLINE T* MakeDisplayItemWithIndex(nsDisplayListBuilder* aBuilder,
+                                              F* aFrame, const uint16_t aIndex,
+                                              Args&&... aArgs) {
+  static_assert(std::is_base_of<nsDisplayItem, T>::value,
+                "Display item type should be derived from nsDisplayItem");
+  static_assert(std::is_base_of<nsIFrame, F>::value,
+                "Frame type should be derived from nsIFrame");
+
+  const DisplayItemType type = T::ItemType();
+  if (aBuilder->InEventsOnly() && !ShouldBuildItemForEvents(type)) {
+    // This item is not needed for events.
+    return nullptr;
+  }
+
+  T* item = new (aBuilder) T(aBuilder, aFrame, std::forward<Args>(aArgs)...);
+
+  if (type != DisplayItemType::TYPE_GENERIC) {
+    item->SetType(type);
+  }
+
+  item->SetPerFrameIndex(aIndex);
+  item->SetExtraPageForPageNum(aBuilder->GetBuildingExtraPagesForPageNum());
+
+  nsPaintedDisplayItem* paintedItem = item->AsPaintedDisplayItem();
+  if (paintedItem) {
+    InitializeHitTestInfo(aBuilder, paintedItem, type);
+  }
+
+  if (aBuilder->InInvalidSubtree() ||
+      item->FrameForInvalidation()->IsFrameModified()) {
+    item->SetModifiedFrame(true);
+  }
+
+#ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
+  if (aBuilder->IsRetainingDisplayList() && aBuilder->IsBuilding()) {
+    AssertUniqueItem(item);
+  }
+
+  // Verify that InInvalidSubtree matches invalidation frame's modified state.
+  if (aBuilder->InInvalidSubtree()) {
+    MOZ_DIAGNOSTIC_ASSERT(
+        AnyContentAncestorModified(item->FrameForInvalidation()));
+  }
+
+  DebugOnly<bool> isContainerType =
+      (GetDisplayItemFlagsForType(type) & TYPE_IS_CONTAINER);
+
+  MOZ_ASSERT(item->HasChildren() == isContainerType,
+             "Container items must have container display item flag set.");
+#endif
+
+  DL_LOGV("Created display item %p (%s) (frame: %p)", item, item->Name(),
+          aFrame);
+
+  return item;
+}
+
+template <typename T, typename F, typename... Args>
+MOZ_ALWAYS_INLINE T* MakeDisplayItem(nsDisplayListBuilder* aBuilder, F* aFrame,
+                                     Args&&... aArgs) {
+  return MakeDisplayItemWithIndex<T>(aBuilder, aFrame, 0,
+                                     std::forward<Args>(aArgs)...);
+}
+
+/*
+ * nsDisplayItemBase is a base-class for all display items. It is mainly
+ * responsible for handling the frame-display item 1:n relationship, as well as
+ * storing the state needed for display list merging.
+ *
+ * Display items are arena-allocated during display list construction.
+ *
+ * Display items can be containers --- i.e., they can perform hit testing
+ * and painting by recursively traversing a list of child items.
+ *
+ * Display items belong to a list at all times (except temporarily as they
+ * move from one list to another).
+ */
+class nsDisplayItem {
+ public:
+  using LayerManager = layers::LayerManager;
+  using WebRenderLayerManager = layers::WebRenderLayerManager;
+  using StackingContextHelper = layers::StackingContextHelper;
+  using ViewID = layers::ScrollableLayerGuid::ViewID;
+
+  /**
+   * Downcasts this item to nsPaintedDisplayItem, if possible.
+   */
+  virtual nsPaintedDisplayItem* AsPaintedDisplayItem() { return nullptr; }
+  virtual const nsPaintedDisplayItem* AsPaintedDisplayItem() const {
+    return nullptr;
+  }
+
+  /**
+   * Downcasts this item to nsDisplayWrapList, if possible.
+   */
+  virtual nsDisplayWrapList* AsDisplayWrapList() { return nullptr; }
+  virtual const nsDisplayWrapList* AsDisplayWrapList() const { return nullptr; }
+
+  /**
+   * Create a clone of this item.
+   */
+  virtual nsDisplayWrapList* Clone(nsDisplayListBuilder* aBuilder) const {
+    return nullptr;
+  }
+
+  /**
+   * Checks if the given display item can be merged with this item.
+   * @return true if the merging is possible, otherwise false.
+   */
+  virtual bool CanMerge(const nsDisplayItem* aItem) const { return false; }
+
+  /**
+   * Frees the memory allocated for this display item.
+   * The given display list builder must have allocated this display item.
+   */
+  virtual void Destroy(nsDisplayListBuilder* aBuilder) {
+    const DisplayItemType type = GetType();
+    DL_LOGV("Destroying display item %p (%s)", this, Name());
+
+    if (IsReusedItem()) {
+      aBuilder->RemoveReusedDisplayItem(this);
+    }
+
+    this->~nsDisplayItem();
+    aBuilder->Destroy(type, this);
+  }
+
+  /**
+   * Returns the frame that this display item was created for.
+   * Never returns null.
+   */
+  inline nsIFrame* Frame() const {
+    MOZ_ASSERT(mFrame, "Trying to use display item after frame deletion!");
+    return mFrame;
+  }
+
+  /**
+   * Called when the display item is prepared for deletion. The display item
+   * should not be used after calling this function.
+   */
+  virtual void RemoveFrame(nsIFrame* aFrame) {
+    MOZ_ASSERT(aFrame);
+
+    if (mFrame && aFrame == mFrame) {
+      mFrame = nullptr;
+      SetDeletedFrame();
+    }
+  }
+
+  /**
+   * A display item can depend on multiple different frames for invalidation.
+   */
+  virtual nsIFrame* GetDependentFrame() { return nullptr; }
+
+  /**
+   * Returns the frame that provides the style data, and should
+   * be checked when deciding if this display item can be reused.
+   */
+  virtual nsIFrame* FrameForInvalidation() const { return Frame(); }
+
+  /**
+   * Display items can override this to communicate that they won't
+   * contribute any visual information (for example fully transparent).
+   */
+  virtual bool IsInvisible() const { return false; }
+
+  /**
+   * Returns the printable name of this display item.
+   */
+  virtual const char* Name() const = 0;
+
+  /**
+   * Some consecutive items should be rendered together as a unit, e.g.,
+   * outlines for the same element. For this, we need a way for items to
+   * identify their type. We use the type for other purposes too.
+   */
+  DisplayItemType GetType() const {
+    MOZ_ASSERT(mType != DisplayItemType::TYPE_ZERO,
+               "Display item should have a valid type!");
+    return mType;
+  }
+
+  /**
+   * Pairing this with the Frame() pointer gives a key that
+   * uniquely identifies this display item in the display item tree.
+   */
+  uint32_t GetPerFrameKey() const {
+    // The top 8 bits are the page index
+    // The middle 16 bits of the per frame key uniquely identify the display
+    // item when there are more than one item of the same type for a frame.
+    // The low 8 bits are the display item type.
+    return (static_cast<uint32_t>(mExtraPageForPageNum)
+            << (TYPE_BITS + (sizeof(mPerFrameIndex) * 8))) |
+           (static_cast<uint32_t>(mPerFrameIndex) << TYPE_BITS) |
+           static_cast<uint32_t>(mType);
+  }
+
+  /**
+   * Returns true if this item was reused during display list merging.
+   */
+  bool IsReused() const { return mItemFlags.contains(ItemFlag::ReusedItem); }
+
+  void SetReused(bool aReused) { SetItemFlag(ItemFlag::ReusedItem, aReused); }
+
+  /**
+   * Returns true if this item can be reused during display list merging.
+   */
+  bool CanBeReused() const {
+    return !mItemFlags.contains(ItemFlag::CantBeReused);
+  }
+
+  void SetCantBeReused() { mItemFlags += ItemFlag::CantBeReused; }
+
+  bool CanBeCached() const {
+    return !mItemFlags.contains(ItemFlag::CantBeCached);
+  }
+
+  void SetCantBeCached() { mItemFlags += ItemFlag::CantBeCached; }
+
+  bool IsOldItem() const { return !!mOldList; }
+
+  /**
+   * Returns true if the frame of this display item is in a modified subtree.
+   */
+  bool HasModifiedFrame() const {
+    return mItemFlags.contains(ItemFlag::ModifiedFrame);
+  }
+
+  void SetModifiedFrame(bool aModified) {
+    SetItemFlag(ItemFlag::ModifiedFrame, aModified);
+  }
+
+  bool HasDeletedFrame() const;
+
+  /**
+   * Set the nsDisplayList that this item belongs to, and what index it is
+   * within that list.
+   * Temporary state for merging used by RetainedDisplayListBuilder.
+   */
+  void SetOldListIndex(nsDisplayList* aList, OldListIndex aIndex,
+                       uint32_t aListKey, uint32_t aNestingDepth) {
+#ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
+    mOldListKey = aListKey;
+    mOldNestingDepth = aNestingDepth;
+#endif
+    mOldList = reinterpret_cast<uintptr_t>(aList);
+    mOldListIndex = aIndex;
+  }
+
+  bool GetOldListIndex(nsDisplayList* aList, uint32_t aListKey,
+                       OldListIndex* aOutIndex) {
+    if (mOldList != reinterpret_cast<uintptr_t>(aList)) {
+#ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
+      MOZ_CRASH_UNSAFE_PRINTF(
+          "Item found was in the wrong list! type %d "
+          "(outer type was %d at depth %d, now is %d)",
+          GetPerFrameKey(), mOldListKey, mOldNestingDepth, aListKey);
+#endif
+      return false;
+    }
+    *aOutIndex = mOldListIndex;
+    return true;
+  }
+
+  /**
+   * Returns the display list containing the children of this display item.
+   * The children may be in a different coordinate system than this item.
+   */
+  virtual RetainedDisplayList* GetChildren() const { return nullptr; }
+  bool HasChildren() const { return GetChildren(); }
+
+  /**
+   * Display items with children may return true here. This causes the
+   * display list iterator to descend into the child display list.
+   */
+  virtual bool ShouldFlattenAway(nsDisplayListBuilder* aBuilder) {
+    return false;
+  }
+
+  virtual bool CreatesStackingContextHelper() { return false; }
+
+  /**
+   * Returns true if this item can be moved asynchronously on the compositor,
+   * see RetainedDisplayListBuilder.cpp comments.
+   */
+  virtual bool CanMoveAsync() { return false; }
+
+ protected:
+  // This is never instantiated directly (it has pure virtual methods), so no
+  // need to count constructors and destructors.
+  nsDisplayItem(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame);
+  nsDisplayItem(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                const ActiveScrolledRoot* aActiveScrolledRoot);
+
+  /**
+   * The custom copy-constructor is implemented to prevent copying the saved
+   * state of the item.
+   * This is currently only used when creating temporary items for merging.
+   */
+  nsDisplayItem(nsDisplayListBuilder* aBuilder, const nsDisplayItem& aOther)
+      : mFrame(aOther.mFrame),
+        mItemFlags(aOther.mItemFlags),
+        mType(aOther.mType),
+        mExtraPageForPageNum(aOther.mExtraPageForPageNum),
+        mPerFrameIndex(aOther.mPerFrameIndex),
+        mBuildingRect(aOther.mBuildingRect),
+        mToReferenceFrame(aOther.mToReferenceFrame),
+        mActiveScrolledRoot(aOther.mActiveScrolledRoot),
+        mClipChain(aOther.mClipChain) {
+    MOZ_COUNT_CTOR(nsDisplayItem);
+    // TODO: It might be better to remove the flags that aren't copied.
+    if (aOther.ForceNotVisible()) {
+      mItemFlags += ItemFlag::ForceNotVisible;
+    }
+    if (mFrame->In3DContextAndBackfaceIsHidden()) {
+      mItemFlags += ItemFlag::BackfaceHidden;
+    }
+    if (aOther.Combines3DTransformWithAncestors()) {
+      mItemFlags += ItemFlag::Combines3DTransformWithAncestors;
+    }
+  }
+
+  virtual ~nsDisplayItem() {
+    MOZ_COUNT_DTOR(nsDisplayItem);
+    if (mFrame) {
+      mFrame->RemoveDisplayItem(this);
+    }
+  }
+
+  void SetType(const DisplayItemType aType) { mType = aType; }
+
+  void SetPerFrameIndex(const uint16_t aIndex) { mPerFrameIndex = aIndex; }
+
+  // Display list building for printing can build duplicate
+  // container display items when they contain a mixture of
+  // OOF and normal content that is spread across multiple
+  // pages. We include the page number for the duplicates
+  // to make our GetPerFrameKey unique.
+  void SetExtraPageForPageNum(const uint8_t aPageNum) {
+    mExtraPageForPageNum = aPageNum;
+  }
+
+  void SetDeletedFrame();
+
+ public:
+  nsDisplayItem() = delete;
+  nsDisplayItem(const nsDisplayItem&) = delete;
+
+  /**
+   * Invalidate cached information that depends on this node's contents, after
+   * a mutation of those contents.
+   *
+   * Specifically, if you mutate an |nsDisplayItem| in a way that would change
+   * the WebRender display list items generated for it, you should call this
+   * method.
+   *
+   * If a |RestoreState| method exists to restore some piece of state, that's a
+   * good indication that modifications to said state should be accompanied by a
+   * call to this method. Opacity flattening's effects on
+   * |nsDisplayBackgroundColor| items are one example.
+   */
+  virtual void InvalidateItemCacheEntry() {}
+
+  struct HitTestState {
+    explicit HitTestState() = default;
+
+    ~HitTestState() {
+      NS_ASSERTION(mItemBuffer.Length() == 0,
+                   "mItemBuffer should have been cleared");
+    }
+
+    // Handling transform items for preserve 3D frames.
+    bool mInPreserves3D = false;
+    // When hit-testing for visibility, we may hit an fully opaque item in a
+    // nested display list. We want to stop at that point, without looking
+    // further on other items.
+    bool mHitOccludingItem = false;
+
+    float mCurrentOpacity = 1.0f;
+
+    AutoTArray<nsDisplayItem*, 100> mItemBuffer;
+  };
+
+  uint8_t GetFlags() const { return GetDisplayItemFlagsForType(GetType()); }
+
+  virtual bool IsContentful() const { return GetFlags() & TYPE_IS_CONTENTFUL; }
+
+  /**
+   * This is called after we've constructed a display list for event handling.
+   * When this is called, we've already ensured that aRect intersects the
+   * item's bounds and that clipping has been taking into account.
+   *
+   * @param aRect the point or rect being tested, relative to the reference
+   * frame. If the width and height are both 1 app unit, it indicates we're
+   * hit testing a point, not a rect.
+   * @param aState must point to a HitTestState. If you don't have one,
+   * just create one with the default constructor and pass it in.
+   * @param aOutFrames each item appends the frame(s) in this display item that
+   * the rect is considered over (if any) to aOutFrames.
+   */
+  virtual void HitTest(nsDisplayListBuilder* aBuilder, const nsRect& aRect,
+                       HitTestState* aState, nsTArray<nsIFrame*>* aOutFrames) {}
+
+  virtual nsIFrame* StyleFrame() const { return mFrame; }
+
+  /**
+   * Compute the used z-index of our frame; returns zero for elements to which
+   * z-index does not apply, and for z-index:auto.
+   * @note This can be overridden, @see nsDisplayWrapList::SetOverrideZIndex.
+   */
+  virtual int32_t ZIndex() const;
+  /**
+   * The default bounds is the frame border rect.
+   * @param aSnap *aSnap is set to true if the returned rect will be
+   * snapped to nearest device pixel edges during actual drawing.
+   * It might be set to false and snap anyway, so code computing the set of
+   * pixels affected by this display item needs to round outwards to pixel
+   * boundaries when *aSnap is set to false.
+   * This does not take the item's clipping into account.
+   * @return a rectangle relative to aBuilder->ReferenceFrame() that
+   * contains the area drawn by this display item
+   */
+  virtual nsRect GetBounds(nsDisplayListBuilder* aBuilder, bool* aSnap) const {
+    *aSnap = false;
+    return nsRect(ToReferenceFrame(), Frame()->GetSize());
+  }
+
+  /**
+   * Returns the untransformed bounds of this display item.
+   */
+  virtual nsRect GetUntransformedBounds(nsDisplayListBuilder* aBuilder,
+                                        bool* aSnap) const {
+    return GetBounds(aBuilder, aSnap);
+  }
+
+  virtual nsRegion GetTightBounds(nsDisplayListBuilder* aBuilder,
+                                  bool* aSnap) const {
+    *aSnap = false;
+    return nsRegion();
+  }
+
+  /**
+   * Returns true if nothing will be rendered inside aRect, false if uncertain.
+   * aRect is assumed to be contained in this item's bounds.
+   */
+  virtual bool IsInvisibleInRect(const nsRect& aRect) const { return false; }
+
+  /**
+   * Returns the result of GetBounds intersected with the item's clip.
+   * The intersection is approximate since rounded corners are not taking into
+   * account.
+   */
+  nsRect GetClippedBounds(nsDisplayListBuilder* aBuilder) const;
+
+  nsRect GetBorderRect() const {
+    return nsRect(ToReferenceFrame(), Frame()->GetSize());
+  }
+
+  nsRect GetPaddingRect() const {
+    return Frame()->GetPaddingRectRelativeToSelf() + ToReferenceFrame();
+  }
+
+  nsRect GetContentRect() const {
+    return Frame()->GetContentRectRelativeToSelf() + ToReferenceFrame();
+  }
+
+  /**
+   * Checks if the frame(s) owning this display item have been marked as
+   * invalid, and needing repainting.
+   */
+  virtual bool IsInvalid(nsRect& aRect) const {
+    bool result = mFrame ? mFrame->IsInvalid(aRect) : false;
+    aRect += ToReferenceFrame();
+    return result;
+  }
+
+  /**
+   * Creates and initializes an nsDisplayItemGeometry object that retains the
+   * current areas covered by this display item. These need to retain enough
+   * information such that they can be compared against a future nsDisplayItem
+   * of the same type, and determine if repainting needs to happen.
+   *
+   * Subclasses wishing to store more information need to override both this
+   * and ComputeInvalidationRegion, as well as implementing an
+   * nsDisplayItemGeometry subclass.
+   *
+   * The default implementation tracks both the display item bounds, and the
+   * frame's border rect.
+   */
+  virtual nsDisplayItemGeometry* AllocateGeometry(
+      nsDisplayListBuilder* aBuilder) {
+    return new nsDisplayItemGenericGeometry(this, aBuilder);
+  }
+
+  /**
+   * Compares an nsDisplayItemGeometry object from a previous paint against the
+   * current item. Computes if the geometry of the item has changed, and the
+   * invalidation area required for correct repainting.
+   *
+   * The existing geometry will have been created from a display item with a
+   * matching GetPerFrameKey()/mFrame pair to the current item.
+   *
+   * The default implementation compares the display item bounds, and the
+   * frame's border rect, and invalidates the entire bounds if either rect
+   * changes.
+   *
+   * @param aGeometry The geometry of the matching display item from the
+   * previous paint.
+   * @param aInvalidRegion Output param, the region to invalidate, or
+   * unchanged if none.
+   */
+  virtual void ComputeInvalidationRegion(nsDisplayListBuilder* aBuilder,
+                                         const nsDisplayItemGeometry* aGeometry,
+                                         nsRegion* aInvalidRegion) const {
+    const nsDisplayItemGenericGeometry* geometry =
+        static_cast<const nsDisplayItemGenericGeometry*>(aGeometry);
+    bool snap;
+    if (!geometry->mBounds.IsEqualInterior(GetBounds(aBuilder, &snap)) ||
+        !geometry->mBorderRect.IsEqualInterior(GetBorderRect())) {
+      aInvalidRegion->Or(GetBounds(aBuilder, &snap), geometry->mBounds);
+    }
+  }
+
+  /**
+   * An alternative default implementation of ComputeInvalidationRegion,
+   * that instead invalidates only the changed area between the two items.
+   */
+  void ComputeInvalidationRegionDifference(
+      nsDisplayListBuilder* aBuilder,
+      const nsDisplayItemBoundsGeometry* aGeometry,
+      nsRegion* aInvalidRegion) const {
+    bool snap;
+    nsRect bounds = GetBounds(aBuilder, &snap);
+
+    if (!aGeometry->mBounds.IsEqualInterior(bounds)) {
+      nscoord radii[8];
+      if (aGeometry->mHasRoundedCorners || Frame()->GetBorderRadii(radii)) {
+        aInvalidRegion->Or(aGeometry->mBounds, bounds);
+      } else {
+        aInvalidRegion->Xor(aGeometry->mBounds, bounds);
+      }
+    }
+  }
+
+  /**
+   * This function is called when an item's list of children has been modified
+   * by RetainedDisplayListBuilder.
+   */
+  virtual void InvalidateCachedChildInfo(nsDisplayListBuilder* aBuilder) {}
+
+  virtual void AddSizeOfExcludingThis(nsWindowSizes&) const {}
+
+  /**
+   * @param aSnap set to true if the edges of the rectangles of the opaque
+   * region would be snapped to device pixels when drawing
+   * @return a region of the item that is opaque --- that is, every pixel
+   * that is visible is painted with an opaque
+   * color. This is useful for determining when one piece
+   * of content completely obscures another so that we can do occlusion
+   * culling.
+   * This does not take clipping into account.
+   * This must return a simple region (1 rect) for painting display lists.
+   * It is only allowed to be a complex region for hit testing.
+   */
+  virtual nsRegion GetOpaqueRegion(nsDisplayListBuilder* aBuilder,
+                                   bool* aSnap) const {
+    *aSnap = false;
+    return nsRegion();
+  }
+  /**
+   * @return Some(nscolor) if the item is guaranteed to paint every pixel in its
+   * bounds with the same (possibly translucent) color
+   */
+  virtual Maybe<nscolor> IsUniform(nsDisplayListBuilder* aBuilder) const {
+    return Nothing();
+  }
+
+  /**
+   * @return true if the contents of this item are rendered fixed relative
+   * to the nearest viewport.
+   */
+  virtual bool ShouldFixToViewport(nsDisplayListBuilder* aBuilder) const {
+    return false;
+  }
+
+  /**
+   * Returns true if all layers that can be active should be forced to be
+   * active. Requires setting the pref layers.force-active=true.
+   */
+  static bool ForceActiveLayers();
+
+#ifdef MOZ_DUMP_PAINTING
+  /**
+   * Mark this display item as being painted via
+   * FrameLayerBuilder::DrawPaintedLayer.
+   */
+  bool Painted() const { return mItemFlags.contains(ItemFlag::Painted); }
+
+  /**
+   * Check if this display item has been painted.
+   */
+  void SetPainted() { mItemFlags += ItemFlag::Painted; }
+#endif
+
+  void SetIsGlassItem() { mItemFlags += ItemFlag::IsGlassItem; }
+  bool IsGlassItem() { return mItemFlags.contains(ItemFlag::IsGlassItem); }
+
+  /**
+   * Function to create the WebRenderCommands.
+   * We should check if the layer state is
+   * active first and have an early return if the layer state is
+   * not active.
+   *
+   * @return true if successfully creating webrender commands.
+   */
+  virtual bool CreateWebRenderCommands(
+      wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+      const StackingContextHelper& aSc,
+      layers::RenderRootStateManager* aManager,
+      nsDisplayListBuilder* aDisplayListBuilder) {
+    return false;
+  }
+
+  /**
+   * Updates the provided aLayerData with any APZ-relevant scroll data
+   * that is specific to this display item. This is stuff that would normally
+   * be put on the layer during BuildLayer, but this is only called in
+   * layers-free webrender mode, where we don't have layers.
+   *
+   * This function returns true if and only if it has APZ-relevant scroll data
+   * to provide. Note that the arguments passed in may be nullptr, in which case
+   * the function should still return true if and only if it has APZ-relevant
+   * scroll data, but obviously in this case it can't actually put the
+   * data onto aLayerData, because there isn't one.
+   *
+   * This function assumes that aData and aLayerData will either both be null,
+   * or will both be non-null. The caller is responsible for enforcing this.
+   */
+  virtual bool UpdateScrollData(layers::WebRenderScrollData* aData,
+                                layers::WebRenderLayerScrollData* aLayerData) {
+    return false;
+  }
+
+  /**
+   * Returns true if this item needs to have its geometry updated, despite
+   * returning empty invalidation region.
+   */
+  virtual bool NeedsGeometryUpdates() const { return false; }
+
+  /**
+   * Some items such as those calling into the native themed widget machinery
+   * have to be painted on the content process. In this case it is best to avoid
+   * allocating layers that serializes and forwards the work to the compositor.
+   */
+  virtual bool MustPaintOnContentSide() const { return false; }
+
+  /**
+   * If this has a child list where the children are in the same coordinate
+   * system as this item (i.e., they have the same reference frame),
+   * return the list.
+   */
+  virtual RetainedDisplayList* GetSameCoordinateSystemChildren() const {
+    return nullptr;
+  }
+
+  virtual void UpdateBounds(nsDisplayListBuilder* aBuilder) {}
+  /**
+   * Do UpdateBounds() for items with frames establishing or extending
+   * 3D rendering context.
+   *
+   * This function is called by UpdateBoundsFor3D() of
+   * nsDisplayTransform(), and it is called by
+   * BuildDisplayListForStackingContext() on transform items
+   * establishing 3D rendering context.
+   *
+   * The bounds of a transform item with the frame establishing 3D
+   * rendering context should be computed by calling
+   * DoUpdateBoundsPreserves3D() on all descendants that participate
+   * the same 3d rendering context.
+   */
+  virtual void DoUpdateBoundsPreserves3D(nsDisplayListBuilder* aBuilder) {}
+
+  /**
+   * Returns the building rectangle used by nsDisplayListBuilder when
+   * this item was constructed.
+   */
+  const nsRect& GetBuildingRect() const { return mBuildingRect; }
+
+  void SetBuildingRect(const nsRect& aBuildingRect) {
+    mBuildingRect = aBuildingRect;
+  }
+
+  /**
+   * Returns the building rect for the children, relative to their
+   * reference frame. Can be different from mBuildingRect for
+   * nsDisplayTransform, since the reference frame for the children is different
+   * from the reference frame for the item itself.
+   */
+  virtual const nsRect& GetBuildingRectForChildren() const {
+    return mBuildingRect;
+  }
+
+  virtual void WriteDebugInfo(std::stringstream& aStream) {}
+
+  /**
+   * Returns the result of aBuilder->ToReferenceFrame(GetUnderlyingFrame())
+   */
+  const nsPoint& ToReferenceFrame() const {
+    NS_ASSERTION(mFrame, "No frame?");
+    return mToReferenceFrame;
+  }
+
+  /**
+   * Returns the reference frame for display item children of this item.
+   */
+  virtual const nsIFrame* ReferenceFrameForChildren() const { return nullptr; }
+
+  /**
+   * Checks if this display item (or any children) contains content that might
+   * be rendered with component alpha (e.g. subpixel antialiasing). Returns the
+   * bounds of the area that needs component alpha, or an empty rect if nothing
+   * in the item does.
+   */
+  virtual nsRect GetComponentAlphaBounds(nsDisplayListBuilder* aBuilder) const {
+    return nsRect();
+  }
+
+  /**
+   * Check if we can add async animations to the layer for this display item.
+   */
+  virtual bool CanUseAsyncAnimations(nsDisplayListBuilder* aBuilder) {
+    return false;
+  }
+
+  virtual bool SupportsOptimizingToImage() const { return false; }
+
+  virtual const DisplayItemClip& GetClip() const;
+  void IntersectClip(nsDisplayListBuilder* aBuilder,
+                     const DisplayItemClipChain* aOther, bool aStore);
+
+  virtual void SetActiveScrolledRoot(
+      const ActiveScrolledRoot* aActiveScrolledRoot) {
+    mActiveScrolledRoot = aActiveScrolledRoot;
+  }
+  const ActiveScrolledRoot* GetActiveScrolledRoot() const {
+    return mActiveScrolledRoot;
+  }
+
+  virtual void SetClipChain(const DisplayItemClipChain* aClipChain,
+                            bool aStore);
+  const DisplayItemClipChain* GetClipChain() const { return mClipChain; }
+
+  bool BackfaceIsHidden() const {
+    return mItemFlags.contains(ItemFlag::BackfaceHidden);
+  }
+
+  bool Combines3DTransformWithAncestors() const {
+    return mItemFlags.contains(ItemFlag::Combines3DTransformWithAncestors);
+  }
+
+  bool ForceNotVisible() const {
+    return mItemFlags.contains(ItemFlag::ForceNotVisible);
+  }
+
+  bool In3DContextAndBackfaceIsHidden() const {
+    return mItemFlags.contains(ItemFlag::BackfaceHidden) &&
+           mItemFlags.contains(ItemFlag::Combines3DTransformWithAncestors);
+  }
+
+  bool HasDifferentFrame(const nsDisplayItem* aOther) const {
+    return mFrame != aOther->mFrame;
+  }
+
+  bool HasHitTestInfo() const {
+    return mItemFlags.contains(ItemFlag::HasHitTestInfo);
+  }
+
+  bool HasSameTypeAndClip(const nsDisplayItem* aOther) const {
+    return GetPerFrameKey() == aOther->GetPerFrameKey() &&
+           GetClipChain() == aOther->GetClipChain();
+  }
+
+  bool HasSameContent(const nsDisplayItem* aOther) const {
+    return mFrame->GetContent() == aOther->Frame()->GetContent();
+  }
+
+  virtual void NotifyUsed(nsDisplayListBuilder* aBuilder) {}
+
+  virtual Maybe<nsRect> GetClipWithRespectToASR(
+      nsDisplayListBuilder* aBuilder, const ActiveScrolledRoot* aASR) const;
+
+  virtual const nsRect& GetUntransformedPaintRect() const {
+    return GetBuildingRect();
+  }
+
+  nsRect GetPaintRect(nsDisplayListBuilder* aBuilder, gfxContext* aCtx);
+
+  virtual const HitTestInfo& GetHitTestInfo() { return HitTestInfo::Empty(); }
+
+  enum class ReuseState : uint8_t {
+    None,
+    // Set during display list building.
+    Reusable,
+    // Set during display list preprocessing.
+    PreProcessed,
+    // Set during partial display list build.
+    Reused,
+  };
+
+  void SetReusable() {
+    MOZ_ASSERT(mReuseState == ReuseState::None ||
+               mReuseState == ReuseState::Reused);
+    mReuseState = ReuseState::Reusable;
+  }
+
+  bool IsReusable() const { return mReuseState == ReuseState::Reusable; }
+
+  void SetPreProcessed() {
+    MOZ_ASSERT(mReuseState == ReuseState::Reusable);
+    mReuseState = ReuseState::PreProcessed;
+  }
+
+  bool IsPreProcessed() const {
+    return mReuseState == ReuseState::PreProcessed;
+  }
+
+  void SetReusedItem() {
+    MOZ_ASSERT(mReuseState == ReuseState::PreProcessed);
+    mReuseState = ReuseState::Reused;
+  }
+
+  bool IsReusedItem() const { return mReuseState == ReuseState::Reused; }
+
+  void ResetReuseState() { mReuseState = ReuseState::None; }
+
+  ReuseState GetReuseState() const { return mReuseState; }
+
+  nsIFrame* mFrame;  // 8
+
+ private:
+  enum class ItemFlag : uint16_t {
+    CantBeReused,
+    CantBeCached,
+    DeletedFrame,
+    ModifiedFrame,
+    ReusedItem,
+#ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
+    MergedItem,
+    PreProcessedItem,
+#endif
+    BackfaceHidden,
+    Combines3DTransformWithAncestors,
+    ForceNotVisible,
+    HasHitTestInfo,
+    IsGlassItem,
+#ifdef MOZ_DUMP_PAINTING
+    // True if this frame has been painted.
+    Painted,
+#endif
+  };
+
+  EnumSet<ItemFlag, uint16_t> mItemFlags;              // 2
+  DisplayItemType mType = DisplayItemType::TYPE_ZERO;  // 1
+  uint8_t mExtraPageForPageNum = 0;                    // 1
+  uint16_t mPerFrameIndex = 0;                         // 2
+  ReuseState mReuseState = ReuseState::None;
+  OldListIndex mOldListIndex;  // 4
+  uintptr_t mOldList = 0;      // 8
+
+  // This is the rectangle that nsDisplayListBuilder was using as the visible
+  // rect to decide which items to construct.
+  nsRect mBuildingRect;
+
+ protected:
+  void SetItemFlag(ItemFlag aFlag, const bool aValue) {
+    if (aValue) {
+      mItemFlags += aFlag;
+    } else {
+      mItemFlags -= aFlag;
+    }
+  }
+
+  void SetHasHitTestInfo() { mItemFlags += ItemFlag::HasHitTestInfo; }
+
+  // Result of ToReferenceFrame(mFrame), if mFrame is non-null
+  nsPoint mToReferenceFrame;
+
+  RefPtr<const ActiveScrolledRoot> mActiveScrolledRoot;
+  RefPtr<const DisplayItemClipChain> mClipChain;
+
+#ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
+ public:
+  bool IsMergedItem() const {
+    return mItemFlags.contains(ItemFlag::MergedItem);
+  }
+
+  bool IsPreProcessedItem() const {
+    return mItemFlags.contains(ItemFlag::PreProcessedItem);
+  }
+
+  void SetMergedPreProcessed(bool aMerged, bool aPreProcessed) {
+    SetItemFlag(ItemFlag::MergedItem, aMerged);
+    SetItemFlag(ItemFlag::PreProcessedItem, aPreProcessed);
+  }
+
+  uint32_t mOldListKey = 0;
+  uint32_t mOldNestingDepth = 0;
+#endif
+};
+
+class nsPaintedDisplayItem : public nsDisplayItem {
+ public:
+  nsPaintedDisplayItem* AsPaintedDisplayItem() final { return this; }
+  const nsPaintedDisplayItem* AsPaintedDisplayItem() const final {
+    return this;
+  }
+
+  /**
+   * Returns true if this display item would return true from ApplyOpacity
+   * without actually applying the opacity. Otherwise returns false.
+   */
+  virtual bool CanApplyOpacity(WebRenderLayerManager* aManager,
+                               nsDisplayListBuilder* aBuilder) const {
+    return false;
+  }
+
+  /**
+   * Returns true if this item supports PaintWithClip, where the clipping
+   * is used directly as the primitive geometry instead of needing an explicit
+   * clip.
+   */
+  virtual bool CanPaintWithClip(const DisplayItemClip& aClip) { return false; }
+
+  /**
+   * Same as |Paint()|, except provides a clip to use the geometry to draw with.
+   * Must not be called unless |CanPaintWithClip()| returned true.
+   */
+  virtual void PaintWithClip(nsDisplayListBuilder* aBuilder, gfxContext* aCtx,
+                             const DisplayItemClip& aClip) {
+    MOZ_ASSERT_UNREACHABLE("PaintWithClip() is not implemented!");
+  }
+
+  /**
+   * Paint this item to some rendering context.
+   */
+  virtual void Paint(nsDisplayListBuilder* aBuilder, gfxContext* aCtx) = 0;
+
+  /**
+   * External storage used by |DisplayItemCache| to avoid hashmap lookups.
+   * If an item is reused and has the cache index set, it means that
+   * |DisplayItemCache| has assigned a cache slot for the item.
+   */
+  Maybe<uint16_t>& CacheIndex() { return mCacheIndex; }
+
+  void InvalidateItemCacheEntry() override {
+    // |nsPaintedDisplayItem|s may have |DisplayItemCache| entries
+    // that no longer match after a mutation. The cache will notice
+    // on its own that the entry is no longer in use, and free it.
+    mCacheIndex = Nothing();
+  }
+
+  const HitTestInfo& GetHitTestInfo() final { return mHitTestInfo; }
+  void InitializeHitTestInfo(nsDisplayListBuilder* aBuilder) {
+    mHitTestInfo.Initialize(aBuilder, Frame());
+    SetHasHitTestInfo();
+  }
+
+ protected:
+  nsPaintedDisplayItem(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame)
+      : nsPaintedDisplayItem(aBuilder, aFrame,
+                             aBuilder->CurrentActiveScrolledRoot()) {}
+
+  nsPaintedDisplayItem(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                       const ActiveScrolledRoot* aActiveScrolledRoot)
+      : nsDisplayItem(aBuilder, aFrame, aActiveScrolledRoot) {}
+
+  nsPaintedDisplayItem(nsDisplayListBuilder* aBuilder,
+                       const nsPaintedDisplayItem& aOther)
+      : nsDisplayItem(aBuilder, aOther), mHitTestInfo(aOther.mHitTestInfo) {}
+
+ protected:
+  HitTestInfo mHitTestInfo;
+  Maybe<uint16_t> mCacheIndex;
+};
+
+template <typename T>
+struct MOZ_HEAP_CLASS LinkedListNode {
+  explicit LinkedListNode(T aValue) : mNext(nullptr), mValue(aValue) {}
+  LinkedListNode* mNext;
+  T mValue;
+};
+
+template <typename T>
+struct LinkedListIterator {
+  using iterator_category = std::forward_iterator_tag;
+  using difference_type = std::ptrdiff_t;
+  using value_type = T;
+  using pointer = T*;
+  using reference = T&;
+  using Node = LinkedListNode<T>;
+
+  explicit LinkedListIterator(Node* aNode = nullptr) : mNode(aNode) {}
+
+  bool HasNext() const { return mNode != nullptr; }
+
+  LinkedListIterator<T>& operator++() {
+    MOZ_ASSERT(mNode);
+    mNode = mNode->mNext;
+    return *this;
+  }
+
+  bool operator==(const LinkedListIterator<T>& aOther) const {
+    return mNode == aOther.mNode;
+  }
+
+  bool operator!=(const LinkedListIterator<T>& aOther) const {
+    return mNode != aOther.mNode;
+  }
+
+  const T operator*() const {
+    MOZ_ASSERT(mNode);
+    return mNode->mValue;
+  }
+
+  T operator*() {
+    MOZ_ASSERT(mNode);
+    return mNode->mValue;
+  }
+
+  Node* mNode;
+};
+
+/**
+ * Manages a singly-linked list of display list items.
+ *
+ * Stepping upward through this list is very fast. Stepping downward is very
+ * slow so we don't support it. The methods that need to step downward
+ * (HitTest()) internally build a temporary array of all
+ * the items while they do the downward traversal, so overall they're still
+ * linear time. We have optimized for efficient AppendToTop() of both
+ * items and lists, with minimal codesize.
+ *
+ * Internal linked list nodes are allocated using arena allocator.
+ * */
+class nsDisplayList {
+ public:
+  using Node = LinkedListNode<nsDisplayItem*>;
+  using iterator = LinkedListIterator<nsDisplayItem*>;
+  using const_iterator = iterator;
+
+  iterator begin() { return iterator(mBottom); }
+  iterator end() { return iterator(nullptr); }
+  const_iterator begin() const { return iterator(mBottom); }
+  const_iterator end() const { return iterator(nullptr); }
+
+  explicit nsDisplayList(nsDisplayListBuilder* aBuilder) : mBuilder(aBuilder) {}
+
+  nsDisplayList() = delete;
+  nsDisplayList(const nsDisplayList&) = delete;
+  nsDisplayList& operator=(const nsDisplayList&) = delete;
+
+  virtual ~nsDisplayList() {
+#ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
+    if (!mAllowNonEmptyDestruction) {
+      MOZ_RELEASE_ASSERT(IsEmpty(), "Nonempty list left over?");
+    }
+#endif
+
+    DeallocateNodes();
+  }
+
+  nsDisplayList(nsDisplayList&& aOther)
+      : mBottom(aOther.mBottom),
+        mTop(aOther.mTop),
+        mLength(aOther.mLength),
+        mBuilder(aOther.mBuilder) {
+    aOther.SetEmpty();
+  }
+
+  nsDisplayList& operator=(nsDisplayList&& aOther) {
+    MOZ_RELEASE_ASSERT(mBuilder == aOther.mBuilder);
+
+    if (this != &aOther) {
+      MOZ_RELEASE_ASSERT(IsEmpty());
+      mBottom = std::move(aOther.mBottom);
+      mTop = std::move(aOther.mTop);
+      mLength = std::move(aOther.mLength);
+      aOther.SetEmpty();
+    }
+    return *this;
+  }
+
+  /**
+   * Append an item to the top of the list.
+   **/
+  void AppendToTop(nsDisplayItem* aItem) {
+    if (!aItem) {
+      return;
+    }
+
+    auto* next = Allocate(aItem);
+    MOZ_ASSERT(next);
+
+    if (IsEmpty()) {
+      mBottom = next;
+      mTop = next;
+    } else {
+      mTop->mNext = next;
+      mTop = next;
+    }
+
+    mLength++;
+
+    MOZ_ASSERT(mBottom && mTop);
+    MOZ_ASSERT(mTop->mNext == nullptr);
+  }
+
+  template <typename T, typename F, typename... Args>
+  void AppendNewToTop(nsDisplayListBuilder* aBuilder, F* aFrame,
+                      Args&&... aArgs) {
+    AppendNewToTopWithIndex<T>(aBuilder, aFrame, 0,
+                               std::forward<Args>(aArgs)...);
+  }
+
+  template <typename T, typename F, typename... Args>
+  void AppendNewToTopWithIndex(nsDisplayListBuilder* aBuilder, F* aFrame,
+                               const uint16_t aIndex, Args&&... aArgs) {
+    nsDisplayItem* item = MakeDisplayItemWithIndex<T>(
+        aBuilder, aFrame, aIndex, std::forward<Args>(aArgs)...);
+    AppendToTop(item);
+  }
+
+  /**
+   * Removes all items from aList and appends them to the top of this list.
+   */
+  void AppendToTop(nsDisplayList* aList) {
+    MOZ_ASSERT(aList != this);
+    MOZ_RELEASE_ASSERT(mBuilder == aList->mBuilder);
+
+    if (aList->IsEmpty()) {
+      return;
+    }
+
+    if (IsEmpty()) {
+      std::swap(mBottom, aList->mBottom);
+      std::swap(mTop, aList->mTop);
+      std::swap(mLength, aList->mLength);
+    } else {
+      MOZ_ASSERT(mTop && mTop->mNext == nullptr);
+      mTop->mNext = aList->mBottom;
+      mTop = aList->mTop;
+      mLength += aList->mLength;
+
+      aList->SetEmpty();
+    }
+  }
+
+  /**
+   * Clears the display list.
+   */
+  void Clear() {
+    DeallocateNodes();
+    SetEmpty();
+  }
+
+  /**
+   * Creates a shallow copy of this display list to |aDestination|.
+   */
+  void CopyTo(nsDisplayList* aDestination) const {
+    for (auto* item : *this) {
+      aDestination->AppendToTop(item);
+    }
+  }
+
+  /**
+   * Calls the function |aFn| for each display item in the display list.
+   */
+  void ForEach(const std::function<void(nsDisplayItem*)>& aFn) {
+    for (auto* item : *this) {
+      aFn(item);
+    }
+  }
+  /**
+   * Remove all items from the list and call their destructors.
+   */
+  virtual void DeleteAll(nsDisplayListBuilder* aBuilder);
+
+  /**
+   * @return the item at the bottom of the list, or null if the list is empty
+   */
+  nsDisplayItem* GetBottom() const {
+    return mBottom ? mBottom->mValue : nullptr;
+  }
+
+  /**
+   * @return the item at the top of the list, or null if the list is empty
+   */
+  nsDisplayItem* GetTop() const { return mTop ? mTop->mValue : nullptr; }
+
+  bool IsEmpty() const { return mBottom == nullptr; }
+
+  /**
+   * @return the number of items in the list
+   */
+  size_t Length() const { return mLength; }
+
+  /**
+   * Stable sort the list by the z-order of Frame() on
+   * each item. 'auto' is counted as zero.
+   * It is assumed that the list is already in content document order.
+   */
+  void SortByZOrder();
+
+  /**
+   * Stable sort the list by the tree order of the content of
+   * Frame() on each item. z-index is ignored.
+   * @param aCommonAncestor a common ancestor of all the content elements
+   * associated with the display items, for speeding up tree order
+   * checks, or nullptr if not known; it's only a hint, if it is not an
+   * ancestor of some elements, then we lose performance but not correctness
+   */
+  void SortByContentOrder(nsIContent* aCommonAncestor);
+
+  /**
+   * Sort the display list using a stable sort.
+   * aComparator(Item item1, Item item2) should return true if item1 should go
+   * before item2.
+   * We sort the items into increasing order.
+   */
+  template <typename Item, typename Comparator>
+  void Sort(const Comparator& aComparator) {
+    if (Length() < 2) {
+      // Only sort lists with more than one item.
+      return;
+    }
+
+    // Some casual local browsing testing suggests that a local preallocated
+    // array of 20 items should be able to avoid a lot of dynamic allocations
+    // here.
+    AutoTArray<Item, 20> items;
+
+    for (nsDisplayItem* item : TakeItems()) {
+      items.AppendElement(Item(item));
+    }
+
+    std::stable_sort(items.begin(), items.end(), aComparator);
+
+    for (Item& item : items) {
+      AppendToTop(item);
+    }
+  }
+
+  nsDisplayList TakeItems() {
+    nsDisplayList list = std::move(*this);
+#ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
+    list.mAllowNonEmptyDestruction = true;
+#endif
+    return list;
+  }
+
+  nsDisplayItem* RemoveBottom() {
+    if (!mBottom) {
+      return nullptr;
+    }
+
+    nsDisplayItem* bottom = mBottom->mValue;
+
+    auto next = mBottom->mNext;
+    Deallocate(mBottom);
+    mBottom = next;
+
+    if (!mBottom) {
+      // No bottom item means no items at all.
+      mTop = nullptr;
+    }
+
+    MOZ_ASSERT(mLength > 0);
+    mLength--;
+
+    return bottom;
+  }
+
+  /**
+   * Paint the list to the rendering context. We assume that (0,0) in aCtx
+   * corresponds to the origin of the reference frame. For best results,
+   * aCtx's current transform should make (0,0) pixel-aligned. The
+   * rectangle in aDirtyRect is painted, which *must* be contained in the
+   * dirty rect used to construct the display list.
+   *
+   * If aFlags contains PAINT_USE_WIDGET_LAYERS and
+   * ShouldUseWidgetLayerManager() is set, then we will paint using
+   * the reference frame's widget's layer manager (and ctx may be null),
+   * otherwise we will use a temporary BasicLayerManager and ctx must
+   * not be null.
+   *
+   * If PAINT_EXISTING_TRANSACTION is set, the reference frame's widget's
+   * layer manager has already had BeginTransaction() called on it and
+   * we should not call it again.
+   *
+   * This must only be called on the root display list of the display list
+   * tree.
+   *
+   * We return the layer manager used for painting --- mainly so that
+   * callers can dump its layer tree if necessary.
+   */
+  enum {
+    PAINT_DEFAULT = 0,
+    PAINT_USE_WIDGET_LAYERS = 0x01,
+    PAINT_EXISTING_TRANSACTION = 0x04,
+    PAINT_IDENTICAL_DISPLAY_LIST = 0x08
+  };
+  void PaintRoot(nsDisplayListBuilder* aBuilder, gfxContext* aCtx,
+                 uint32_t aFlags, Maybe<double> aDisplayListBuildTime);
+
+  void Paint(nsDisplayListBuilder* aBuilder, gfxContext* aCtx,
+             int32_t aAppUnitsPerDevPixel);
+
+  /**
+   * Get the bounds. Takes the union of the bounds of all children.
+   * The result is not cached.
+   */
+  nsRect GetClippedBounds(nsDisplayListBuilder* aBuilder) const;
+
+  /**
+   * Get this list's bounds, respecting clips relative to aASR. The result is
+   * the union of each item's clipped bounds with respect to aASR. That means
+   * that if an item can move asynchronously with an ASR that is a descendant
+   * of aASR, then the clipped bounds with respect to aASR will be the clip of
+   * that item for aASR, because the item can move anywhere inside that clip.
+   * If there is an item in this list which is not bounded with respect to
+   * aASR (i.e. which does not have "finite bounds" with respect to aASR),
+   * then this method trigger an assertion failure.
+   * The optional aBuildingRect out argument can be set to non-null if the
+   * caller is also interested to know the building rect.  This can be used
+   * to get the visible rect efficiently without traversing the display list
+   * twice.
+   */
+  nsRect GetClippedBoundsWithRespectToASR(
+      nsDisplayListBuilder* aBuilder, const ActiveScrolledRoot* aASR,
+      nsRect* aBuildingRect = nullptr) const;
+
+  /**
+   * Returns the opaque region of this display list.
+   */
+  nsRegion GetOpaqueRegion(nsDisplayListBuilder* aBuilder) {
+    nsRegion result;
+    bool snap;
+    for (nsDisplayItem* item : *this) {
+      result.OrWith(item->GetOpaqueRegion(aBuilder, &snap));
+    }
+    return result;
+  }
+
+  /**
+   * Returns the bounds of the area that needs component alpha.
+   */
+  nsRect GetComponentAlphaBounds(nsDisplayListBuilder* aBuilder) const {
+    nsRect bounds;
+    for (nsDisplayItem* item : *this) {
+      bounds.UnionRect(bounds, item->GetComponentAlphaBounds(aBuilder));
+    }
+    return bounds;
+  }
+
+  /**
+   * Find the topmost display item that returns a non-null frame, and return
+   * the frame.
+   */
+  void HitTest(nsDisplayListBuilder* aBuilder, const nsRect& aRect,
+               nsDisplayItem::HitTestState* aState,
+               nsTArray<nsIFrame*>* aOutFrames) const;
+  /**
+   * Compute the union of the visible rects of the items in the list. The
+   * result is not cached.
+   */
+  nsRect GetBuildingRect() const;
+
+ private:
+  inline Node* Allocate(nsDisplayItem* aItem) {
+    void* ptr =
+        mBuilder->Allocate(sizeof(Node), DisplayListArenaObjectId::LISTNODE);
+    return new (ptr) Node(aItem);
+  }
+
+  inline void Deallocate(Node* aNode) {
+    aNode->~Node();
+    mBuilder->Destroy(DisplayListArenaObjectId::LISTNODE, aNode);
+  }
+
+  void DeallocateNodes() {
+    Node* current = mBottom;
+    Node* next = nullptr;
+
+    while (current) {
+      next = current->mNext;
+      Deallocate(current);
+      current = next;
+    }
+  }
+
+  inline void SetEmpty() {
+    mBottom = nullptr;
+    mTop = nullptr;
+    mLength = 0;
+  }
+
+  Node* mBottom = nullptr;
+  Node* mTop = nullptr;
+  size_t mLength = 0;
+  nsDisplayListBuilder* mBuilder = nullptr;
+
+#ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
+  // This checks that the invariant of display lists owning their items is held.
+  bool mAllowNonEmptyDestruction = false;
+#endif
+};
+
+/**
+ * This is passed as a parameter to nsIFrame::BuildDisplayList. That method
+ * will put any generated items onto the appropriate list given here. It's
+ * basically just a collection with one list for each separate stacking layer.
+ * The lists themselves are external to this object and thus can be shared
+ * with others. Some of the list pointers may even refer to the same list.
+ */
+class nsDisplayListSet {
+ public:
+  /**
+   * @return a list where one should place the border and/or background for
+   * this frame (everything from steps 1 and 2 of CSS 2.1 appendix E)
+   */
+  nsDisplayList* BorderBackground() const { return mLists[0]; }
+  /**
+   * @return a list where one should place the borders and/or backgrounds for
+   * block-level in-flow descendants (step 4 of CSS 2.1 appendix E)
+   */
+  nsDisplayList* BlockBorderBackgrounds() const { return mLists[1]; }
+  /**
+   * @return a list where one should place descendant floats (step 5 of
+   * CSS 2.1 appendix E)
+   */
+  nsDisplayList* Floats() const { return mLists[2]; }
+  /**
+   * @return a list where one should place the (pseudo) stacking contexts
+   * for descendants of this frame (everything from steps 3, 7 and 8
+   * of CSS 2.1 appendix E)
+   */
+  nsDisplayList* PositionedDescendants() const { return mLists[3]; }
+  /**
+   * @return a list where one should place the outlines
+   * for this frame and its descendants (step 9 of CSS 2.1 appendix E)
+   */
+  nsDisplayList* Outlines() const { return mLists[4]; }
+  /**
+   * @return a list where one should place all other content
+   */
+  nsDisplayList* Content() const { return mLists[5]; }
+
+  const std::array<nsDisplayList*, 6>& Lists() const { return mLists; }
+
+  /**
+   * Clears all the display lists in the set.
+   */
+  void Clear() {
+    for (auto* list : mLists) {
+      MOZ_ASSERT(list);
+      list->Clear();
+    }
+  }
+
+  /**
+   * Deletes all the display items in the set.
+   */
+  void DeleteAll(nsDisplayListBuilder* aBuilder) {
+    for (auto* list : mLists) {
+      list->DeleteAll(aBuilder);
+    }
+  }
+
+  nsDisplayListSet(nsDisplayList* aBorderBackground,
+                   nsDisplayList* aBlockBorderBackgrounds,
+                   nsDisplayList* aFloats, nsDisplayList* aContent,
+                   nsDisplayList* aPositionedDescendants,
+                   nsDisplayList* aOutlines)
+      : mLists{aBorderBackground, aBlockBorderBackgrounds, aFloats,
+               aContent,          aPositionedDescendants,  aOutlines} {}
+
+  /**
+   * A copy constructor that lets the caller override the BorderBackground
+   * list.
+   */
+  nsDisplayListSet(const nsDisplayListSet& aLists,
+                   nsDisplayList* aBorderBackground)
+      : mLists(aLists.mLists) {
+    mLists[0] = aBorderBackground;
+  }
+
+  /**
+   * Returns true if all the display lists in the display list set are empty.
+   */
+  bool IsEmpty() const {
+    for (auto* list : mLists) {
+      if (!list->IsEmpty()) {
+        return false;
+      }
+    }
+
+    return true;
+  }
+
+  /**
+   * Calls the function |aFn| for each display item in the display list set.
+   */
+  void ForEach(const std::function<void(nsDisplayItem*)>& aFn) const {
+    for (auto* list : mLists) {
+      list->ForEach(aFn);
+    }
+  }
+
+  /**
+   * Creates a shallow copy of this display list set to |aDestination|.
+   */
+  void CopyTo(const nsDisplayListSet& aDestination) const;
+
+  /**
+   * Move all display items in our lists to top of the corresponding lists in
+   * the destination.
+   */
+  void MoveTo(const nsDisplayListSet& aDestination) const;
+
+ private:
+  // This class is only used on stack, so we don't have to worry about leaking
+  // it.  Don't let us be heap-allocated!
+  void* operator new(size_t sz) noexcept(true);
+
+  std::array<nsDisplayList*, 6> mLists;
+};
+
+/**
+ * A specialization of nsDisplayListSet where the lists are actually internal
+ * to the object, and all distinct.
+ */
+struct nsDisplayListCollection : public nsDisplayListSet {
+  explicit nsDisplayListCollection(nsDisplayListBuilder* aBuilder)
+      : nsDisplayListSet(&mLists[0], &mLists[1], &mLists[2], &mLists[3],
+                         &mLists[4], &mLists[5]),
+        mLists{nsDisplayList{aBuilder}, nsDisplayList{aBuilder},
+               nsDisplayList{aBuilder}, nsDisplayList{aBuilder},
+               nsDisplayList{aBuilder}, nsDisplayList{aBuilder}} {}
+
+  /**
+   * Sort all lists by content order.
+   */
+  void SortAllByContentOrder(nsIContent* aCommonAncestor) {
+    for (auto& mList : mLists) {
+      mList.SortByContentOrder(aCommonAncestor);
+    }
+  }
+
+  /**
+   * Serialize this display list collection into a display list with the items
+   * in the correct Z order.
+   * @param aOutList the result display list
+   * @param aContent the content element to use for content ordering
+   */
+  void SerializeWithCorrectZOrder(nsDisplayList* aOutResultList,
+                                  nsIContent* aContent);
+
+ private:
+  // This class is only used on stack, so we don't have to worry about leaking
+  // it.  Don't let us be heap-allocated!
+  void* operator new(size_t sz) noexcept(true);
+
+  nsDisplayList mLists[6];
+};
+
+/**
+ * A display list that also retains the partial build
+ * information (in the form of a DAG) used to create it.
+ *
+ * Display lists built from a partial list aren't necessarily
+ * in the same order as a full build, and the DAG retains
+ * the information needing to interpret the current
+ * order correctly.
+ */
+class RetainedDisplayList : public nsDisplayList {
+ public:
+  explicit RetainedDisplayList(nsDisplayListBuilder* aBuilder)
+      : nsDisplayList(aBuilder) {}
+
+  RetainedDisplayList(RetainedDisplayList&& aOther)
+      : nsDisplayList(std::move(aOther)), mDAG(std::move(aOther.mDAG)) {}
+
+  RetainedDisplayList(const RetainedDisplayList&) = delete;
+  RetainedDisplayList& operator=(const RetainedDisplayList&) = delete;
+
+  ~RetainedDisplayList() override {
+    MOZ_ASSERT(mOldItems.IsEmpty(), "Must empty list before destroying");
+  }
+
+  RetainedDisplayList& operator=(RetainedDisplayList&& aOther) {
+    MOZ_ASSERT(IsEmpty(), "Can only move into an empty list!");
+    MOZ_ASSERT(mOldItems.IsEmpty(), "Can only move into an empty list!");
+
+    nsDisplayList::operator=(std::move(aOther));
+    mDAG = std::move(aOther.mDAG);
+    mOldItems = std::move(aOther.mOldItems);
+    return *this;
+  }
+
+  RetainedDisplayList& operator=(nsDisplayList&& aOther) {
+    MOZ_ASSERT(IsEmpty(), "Can only move into an empty list!");
+    MOZ_ASSERT(mOldItems.IsEmpty(), "Can only move into an empty list!");
+    nsDisplayList::operator=(std::move(aOther));
+    return *this;
+  }
+
+  void DeleteAll(nsDisplayListBuilder* aBuilder) override {
+    for (OldItemInfo& i : mOldItems) {
+      if (i.mItem && i.mOwnsItem) {
+        i.mItem->Destroy(aBuilder);
+        MOZ_ASSERT(!GetBottom(),
+                   "mOldItems should not be owning items if we also have items "
+                   "in the normal list");
+      }
+    }
+    mOldItems.Clear();
+    mDAG.Clear();
+    nsDisplayList::DeleteAll(aBuilder);
+  }
+
+  void AddSizeOfExcludingThis(nsWindowSizes&) const;
+
+  DirectedAcyclicGraph<MergedListUnits> mDAG;
+
+  // Temporary state initialized during the preprocess pass
+  // of RetainedDisplayListBuilder and then used during merging.
+  nsTArray<OldItemInfo> mOldItems;
+};
+
+class nsDisplayContainer final : public nsDisplayItem {
+ public:
+  nsDisplayContainer(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                     const ActiveScrolledRoot* aActiveScrolledRoot,
+                     nsDisplayList* aList);
+
+  ~nsDisplayContainer() override { MOZ_COUNT_DTOR(nsDisplayContainer); }
+
+  NS_DISPLAY_DECL_NAME("nsDisplayContainer", TYPE_CONTAINER)
+
+  void Destroy(nsDisplayListBuilder* aBuilder) override {
+    mChildren.DeleteAll(aBuilder);
+    nsDisplayItem::Destroy(aBuilder);
+  }
+
+  bool CreateWebRenderCommands(
+      wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+      const StackingContextHelper& aSc,
+      layers::RenderRootStateManager* aManager,
+      nsDisplayListBuilder* aDisplayListBuilder) override;
+
+  nsRect GetBounds(nsDisplayListBuilder* aBuilder, bool* aSnap) const override;
+
+  nsRect GetComponentAlphaBounds(nsDisplayListBuilder* aBuilder) const override;
+
+  nsRegion GetOpaqueRegion(nsDisplayListBuilder* aBuilder,
+                           bool* aSnap) const override;
+
+  Maybe<nscolor> IsUniform(nsDisplayListBuilder* aBuilder) const override {
+    return Nothing();
+  }
+
+  RetainedDisplayList* GetChildren() const override { return &mChildren; }
+  RetainedDisplayList* GetSameCoordinateSystemChildren() const override {
+    return GetChildren();
+  }
+
+  Maybe<nsRect> GetClipWithRespectToASR(
+      nsDisplayListBuilder* aBuilder,
+      const ActiveScrolledRoot* aASR) const override;
+
+  void HitTest(nsDisplayListBuilder* aBuilder, const nsRect& aRect,
+               HitTestState* aState, nsTArray<nsIFrame*>* aOutFrames) override;
+
+  bool ShouldFlattenAway(nsDisplayListBuilder* aBuilder) override {
+    return true;
+  }
+
+  void SetClipChain(const DisplayItemClipChain* aClipChain,
+                    bool aStore) override {
+    MOZ_ASSERT_UNREACHABLE("nsDisplayContainer does not support clipping");
+  }
+
+  void UpdateBounds(nsDisplayListBuilder* aBuilder) override;
+
+ private:
+  mutable RetainedDisplayList mChildren;
+  nsRect mBounds;
+};
+
+/**
+ * Use this class to implement not-very-frequently-used display items
+ * that are not opaque, do not receive events, and are bounded by a frame's
+ * border-rect.
+ *
+ * This should not be used for display items which are created frequently,
+ * because each item is one or two pointers bigger than an item from a
+ * custom display item class could be, and fractionally slower. However it does
+ * save code size. We use this for infrequently-used item types.
+ */
+class nsDisplayGeneric : public nsPaintedDisplayItem {
+ public:
+  typedef void (*PaintCallback)(nsIFrame* aFrame, gfx::DrawTarget* aDrawTarget,
+                                const nsRect& aDirtyRect, nsPoint aFramePt);
+
+  // XXX: should be removed eventually
+  typedef void (*OldPaintCallback)(nsIFrame* aFrame, gfxContext* aCtx,
+                                   const nsRect& aDirtyRect, nsPoint aFramePt);
+
+  nsDisplayGeneric(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                   PaintCallback aPaint, const char* aName,
+                   DisplayItemType aType)
+      : nsPaintedDisplayItem(aBuilder, aFrame),
+        mPaint(aPaint),
+        mOldPaint(nullptr),
+        mName(aName) {
+    MOZ_COUNT_CTOR(nsDisplayGeneric);
+    SetType(aType);
+  }
+
+  // XXX: should be removed eventually
+  nsDisplayGeneric(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                   OldPaintCallback aOldPaint, const char* aName,
+                   DisplayItemType aType)
+      : nsPaintedDisplayItem(aBuilder, aFrame),
+        mPaint(nullptr),
+        mOldPaint(aOldPaint),
+        mName(aName) {
+    MOZ_COUNT_CTOR(nsDisplayGeneric);
+    SetType(aType);
+  }
+
+  constexpr static DisplayItemType ItemType() {
+    return DisplayItemType::TYPE_GENERIC;
+  }
+
+  MOZ_COUNTED_DTOR_OVERRIDE(nsDisplayGeneric)
+
+  void Paint(nsDisplayListBuilder* aBuilder, gfxContext* aCtx) override {
+    MOZ_ASSERT(!!mPaint != !!mOldPaint);
+    if (mPaint) {
+      mPaint(mFrame, aCtx->GetDrawTarget(), GetPaintRect(aBuilder, aCtx),
+             ToReferenceFrame());
+    } else {
+      mOldPaint(mFrame, aCtx, GetPaintRect(aBuilder, aCtx), ToReferenceFrame());
+    }
+  }
+
+  const char* Name() const override { return mName; }
+
+  // This override is needed because GetType() for nsDisplayGeneric subclasses
+  // does not match TYPE_GENERIC that was used to allocate the object.
+  void Destroy(nsDisplayListBuilder* aBuilder) override {
+    this->~nsDisplayGeneric();
+    aBuilder->Destroy(DisplayItemType::TYPE_GENERIC, this);
+  }
+
+ protected:
+  void* operator new(size_t aSize, nsDisplayListBuilder* aBuilder) {
+    return aBuilder->Allocate(aSize, DisplayItemType::TYPE_GENERIC);
+  }
+
+  template <typename T, typename F, typename... Args>
+  friend T* MakeDisplayItemWithIndex(nsDisplayListBuilder* aBuilder, F* aFrame,
+                                     const uint16_t aIndex, Args&&... aArgs);
+
+  PaintCallback mPaint;
+  OldPaintCallback mOldPaint;  // XXX: should be removed eventually
+  const char* mName;
+};
+
+#if defined(MOZ_REFLOW_PERF_DSP) && defined(MOZ_REFLOW_PERF)
+/**
+ * This class implements painting of reflow counts.  Ideally, we would simply
+ * make all the frame names be those returned by nsIFrame::GetFrameName
+ * (except that tosses in the content tag name!)  and support only one color
+ * and eliminate this class altogether in favor of nsDisplayGeneric, but for
+ * the time being we can't pass args to a PaintCallback, so just have a
+ * separate class to do the right thing.  Sadly, this alsmo means we need to
+ * hack all leaf frame classes to handle this.
+ *
+ * XXXbz the color thing is a bit of a mess, but 0 basically means "not set"
+ * here...  I could switch it all to nscolor, but why bother?
+ */
+class nsDisplayReflowCount : public nsPaintedDisplayItem {
+ public:
+  nsDisplayReflowCount(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                       const char* aFrameName, uint32_t aColor = 0)
+      : nsPaintedDisplayItem(aBuilder, aFrame),
+        mFrameName(aFrameName),
+        mColor(aColor) {
+    MOZ_COUNT_CTOR(nsDisplayReflowCount);
+  }
+
+  MOZ_COUNTED_DTOR_OVERRIDE(nsDisplayReflowCount)
+
+  NS_DISPLAY_DECL_NAME("nsDisplayReflowCount", TYPE_REFLOW_COUNT)
+
+  void Paint(nsDisplayListBuilder* aBuilder, gfxContext* aCtx) override;
+
+ protected:
+  const char* mFrameName;
+  nscolor mColor;
+};
+
+#  define DO_GLOBAL_REFLOW_COUNT_DSP(_name)                                 \
+    PR_BEGIN_MACRO                                                          \
+    if (!aBuilder->IsBackgroundOnly() && !aBuilder->IsForEventDelivery() && \
+        PresShell()->IsPaintingFrameCounts()) {                             \
+      aLists.Outlines()->AppendNewToTop<mozilla::nsDisplayReflowCount>(     \
+          aBuilder, this, _name);                                           \
+    }                                                                       \
+    PR_END_MACRO
+
+#  define DO_GLOBAL_REFLOW_COUNT_DSP_COLOR(_name, _color)                   \
+    PR_BEGIN_MACRO                                                          \
+    if (!aBuilder->IsBackgroundOnly() && !aBuilder->IsForEventDelivery() && \
+        PresShell()->IsPaintingFrameCounts()) {                             \
+      aLists.Outlines()->AppendNewToTop<mozilla::nsDisplayReflowCount>(     \
+          aBuilder, this, _name, _color);                                   \
+    }                                                                       \
+    PR_END_MACRO
+
+/*
+  Macro to be used for classes that don't actually implement BuildDisplayList
+ */
+#  define DECL_DO_GLOBAL_REFLOW_COUNT_DSP(_class, _super)     \
+    void BuildDisplayList(nsDisplayListBuilder* aBuilder,     \
+                          const nsRect& aDirtyRect,           \
+                          const nsDisplayListSet& aLists) {   \
+      DO_GLOBAL_REFLOW_COUNT_DSP(#_class);                    \
+      _super::BuildDisplayList(aBuilder, aDirtyRect, aLists); \
+    }
+
+#else  // MOZ_REFLOW_PERF_DSP && MOZ_REFLOW_PERF
+
+#  define DO_GLOBAL_REFLOW_COUNT_DSP(_name)
+#  define DO_GLOBAL_REFLOW_COUNT_DSP_COLOR(_name, _color)
+#  define DECL_DO_GLOBAL_REFLOW_COUNT_DSP(_class, _super)
+
+#endif  // MOZ_REFLOW_PERF_DSP && MOZ_REFLOW_PERF
+
+class nsDisplayCaret : public nsPaintedDisplayItem {
+ public:
+  nsDisplayCaret(nsDisplayListBuilder* aBuilder, nsIFrame* aCaretFrame);
+
+#ifdef NS_BUILD_REFCNT_LOGGING
+  ~nsDisplayCaret() override;
+#endif
+
+  NS_DISPLAY_DECL_NAME("Caret", TYPE_CARET)
+
+  nsRect GetBounds(nsDisplayListBuilder* aBuilder, bool* aSnap) const override;
+  void Paint(nsDisplayListBuilder* aBuilder, gfxContext* aCtx) override;
+  bool CreateWebRenderCommands(
+      wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+      const StackingContextHelper& aSc,
+      layers::RenderRootStateManager* aManager,
+      nsDisplayListBuilder* aDisplayListBuilder) override;
+
+ protected:
+  RefPtr<nsCaret> mCaret;
+  nsRect mBounds;
+};
+
+/**
+ * The standard display item to paint the CSS borders of a frame.
+ */
+class nsDisplayBorder : public nsPaintedDisplayItem {
+ public:
+  nsDisplayBorder(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame);
+
+  MOZ_COUNTED_DTOR_OVERRIDE(nsDisplayBorder)
+
+  NS_DISPLAY_DECL_NAME("Border", TYPE_BORDER)
+
+  bool IsInvisibleInRect(const nsRect& aRect) const override;
+  nsRect GetBounds(nsDisplayListBuilder* aBuilder, bool* aSnap) const override;
+  bool CreateWebRenderCommands(
+      wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+      const StackingContextHelper& aSc,
+      layers::RenderRootStateManager* aManager,
+      nsDisplayListBuilder* aDisplayListBuilder) override;
+  void Paint(nsDisplayListBuilder* aBuilder, gfxContext* aCtx) override;
+  nsDisplayItemGeometry* AllocateGeometry(
+      nsDisplayListBuilder* aBuilder) override;
+  void ComputeInvalidationRegion(nsDisplayListBuilder* aBuilder,
+                                 const nsDisplayItemGeometry* aGeometry,
+                                 nsRegion* aInvalidRegion) const override;
+
+  nsRegion GetTightBounds(nsDisplayListBuilder* aBuilder,
+                          bool* aSnap) const override {
+    *aSnap = true;
+    return CalculateBounds<nsRegion>(*mFrame->StyleBorder());
+  }
+
+ protected:
+  template <typename T>
+  T CalculateBounds(const nsStyleBorder& aStyleBorder) const {
+    nsRect borderBounds(ToReferenceFrame(), mFrame->GetSize());
+    if (aStyleBorder.IsBorderImageSizeAvailable()) {
+      borderBounds.Inflate(aStyleBorder.GetImageOutset());
+      return borderBounds;
+    }
+
+    nsMargin border = aStyleBorder.GetComputedBorder();
+    T result;
+    if (border.top > 0) {
+      result = nsRect(borderBounds.X(), borderBounds.Y(), borderBounds.Width(),
+                      border.top);
+    }
+    if (border.right > 0) {
+      result.OrWith(nsRect(borderBounds.XMost() - border.right,
+                           borderBounds.Y(), border.right,
+                           borderBounds.Height()));
+    }
+    if (border.bottom > 0) {
+      result.OrWith(nsRect(borderBounds.X(),
+                           borderBounds.YMost() - border.bottom,
+                           borderBounds.Width(), border.bottom));
+    }
+    if (border.left > 0) {
+      result.OrWith(nsRect(borderBounds.X(), borderBounds.Y(), border.left,
+                           borderBounds.Height()));
+    }
+
+    nscoord radii[8];
+    if (mFrame->GetBorderRadii(radii)) {
+      if (border.left > 0 || border.top > 0) {
+        nsSize cornerSize(radii[eCornerTopLeftX], radii[eCornerTopLeftY]);
+        result.OrWith(nsRect(borderBounds.TopLeft(), cornerSize));
+      }
+      if (border.top > 0 || border.right > 0) {
+        nsSize cornerSize(radii[eCornerTopRightX], radii[eCornerTopRightY]);
+        result.OrWith(
+            nsRect(borderBounds.TopRight() - nsPoint(cornerSize.width, 0),
+                   cornerSize));
+      }
+      if (border.right > 0 || border.bottom > 0) {
+        nsSize cornerSize(radii[eCornerBottomRightX],
+                          radii[eCornerBottomRightY]);
+        result.OrWith(nsRect(borderBounds.BottomRight() -
+                                 nsPoint(cornerSize.width, cornerSize.height),
+                             cornerSize));
+      }
+      if (border.bottom > 0 || border.left > 0) {
+        nsSize cornerSize(radii[eCornerBottomLeftX], radii[eCornerBottomLeftY]);
+        result.OrWith(
+            nsRect(borderBounds.BottomLeft() - nsPoint(0, cornerSize.height),
+                   cornerSize));
+      }
+    }
+    return result;
+  }
+
+  nsRect mBounds;
+};
+
+/**
+ * A simple display item that just renders a solid color across the
+ * specified bounds. For canvas frames (in the CSS sense) we split off the
+ * drawing of the background color into this class (from nsDisplayBackground
+ * via nsDisplayCanvasBackground). This is done so that we can always draw a
+ * background color to avoid ugly flashes of white when we can't draw a full
+ * frame tree (ie when a page is loading). The bounds can differ from the
+ * frame's bounds -- this is needed when a frame/iframe is loading and there
+ * is not yet a frame tree to go in the frame/iframe so we use the subdoc
+ * frame of the parent document as a standin.
+ */
+class nsDisplaySolidColorBase : public nsPaintedDisplayItem {
+ public:
+  nsDisplaySolidColorBase(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                          nscolor aColor)
+      : nsPaintedDisplayItem(aBuilder, aFrame), mColor(aColor) {}
+
+  nsDisplayItemGeometry* AllocateGeometry(
+      nsDisplayListBuilder* aBuilder) override {
+    return new nsDisplaySolidColorGeometry(this, aBuilder, mColor);
+  }
+
+  void ComputeInvalidationRegion(nsDisplayListBuilder* aBuilder,
+                                 const nsDisplayItemGeometry* aGeometry,
+                                 nsRegion* aInvalidRegion) const override {
+    const nsDisplaySolidColorGeometry* geometry =
+        static_cast<const nsDisplaySolidColorGeometry*>(aGeometry);
+    if (mColor != geometry->mColor) {
+      bool dummy;
+      aInvalidRegion->Or(geometry->mBounds, GetBounds(aBuilder, &dummy));
+      return;
+    }
+    ComputeInvalidationRegionDifference(aBuilder, geometry, aInvalidRegion);
+  }
+
+  nsRegion GetOpaqueRegion(nsDisplayListBuilder* aBuilder,
+                           bool* aSnap) const override {
+    *aSnap = false;
+    nsRegion result;
+    if (NS_GET_A(mColor) == 255) {
+      result = GetBounds(aBuilder, aSnap);
+    }
+    return result;
+  }
+
+  Maybe<nscolor> IsUniform(nsDisplayListBuilder* aBuilder) const override {
+    return Some(mColor);
+  }
+
+ protected:
+  nscolor mColor;
+};
+
+class nsDisplaySolidColor : public nsDisplaySolidColorBase {
+ public:
+  nsDisplaySolidColor(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                      const nsRect& aBounds, nscolor aColor,
+                      bool aCanBeReused = true)
+      : nsDisplaySolidColorBase(aBuilder, aFrame, aColor),
+        mBounds(aBounds),
+        mIsCheckerboardBackground(false) {
+    NS_ASSERTION(NS_GET_A(aColor) > 0,
+                 "Don't create invisible nsDisplaySolidColors!");
+    MOZ_COUNT_CTOR(nsDisplaySolidColor);
+    if (!aCanBeReused) {
+      SetCantBeReused();
+    }
+  }
+
+  MOZ_COUNTED_DTOR_OVERRIDE(nsDisplaySolidColor)
+
+  NS_DISPLAY_DECL_NAME("SolidColor", TYPE_SOLID_COLOR)
+
+  nsRect GetBounds(nsDisplayListBuilder* aBuilder, bool* aSnap) const override;
+  void Paint(nsDisplayListBuilder* aBuilder, gfxContext* aCtx) override;
+  void WriteDebugInfo(std::stringstream& aStream) override;
+  void SetIsCheckerboardBackground() { mIsCheckerboardBackground = true; }
+  bool CreateWebRenderCommands(
+      wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+      const StackingContextHelper& aSc,
+      layers::RenderRootStateManager* aManager,
+      nsDisplayListBuilder* aDisplayListBuilder) override;
+
+  int32_t ZIndex() const override {
+    if (mOverrideZIndex) {
+      return mOverrideZIndex.value();
+    }
+    return nsDisplaySolidColorBase::ZIndex();
+  }
+
+  void SetOverrideZIndex(int32_t aZIndex) { mOverrideZIndex = Some(aZIndex); }
+
+ private:
+  nsRect mBounds;
+  bool mIsCheckerboardBackground;
+  Maybe<int32_t> mOverrideZIndex;
+};
+
+/**
+ * A display item that renders a solid color over a region. This is not
+ * exposed through CSS, its only purpose is efficient invalidation of
+ * the find bar highlighter dimmer.
+ */
+class nsDisplaySolidColorRegion : public nsPaintedDisplayItem {
+ public:
+  nsDisplaySolidColorRegion(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                            const nsRegion& aRegion, nscolor aColor)
+      : nsPaintedDisplayItem(aBuilder, aFrame),
+        mRegion(aRegion),
+        mColor(gfx::sRGBColor::FromABGR(aColor)) {
+    NS_ASSERTION(NS_GET_A(aColor) > 0,
+                 "Don't create invisible nsDisplaySolidColorRegions!");
+    MOZ_COUNT_CTOR(nsDisplaySolidColorRegion);
+  }
+
+  MOZ_COUNTED_DTOR_OVERRIDE(nsDisplaySolidColorRegion)
+
+  NS_DISPLAY_DECL_NAME("SolidColorRegion", TYPE_SOLID_COLOR_REGION)
+
+  nsDisplayItemGeometry* AllocateGeometry(
+      nsDisplayListBuilder* aBuilder) override {
+    return new nsDisplaySolidColorRegionGeometry(this, aBuilder, mRegion,
+                                                 mColor);
+  }
+
+  void ComputeInvalidationRegion(nsDisplayListBuilder* aBuilder,
+                                 const nsDisplayItemGeometry* aGeometry,
+                                 nsRegion* aInvalidRegion) const override {
+    const nsDisplaySolidColorRegionGeometry* geometry =
+        static_cast<const nsDisplaySolidColorRegionGeometry*>(aGeometry);
+    if (mColor == geometry->mColor) {
+      aInvalidRegion->Xor(geometry->mRegion, mRegion);
+    } else {
+      aInvalidRegion->Or(geometry->mRegion.GetBounds(), mRegion.GetBounds());
+    }
+  }
+
+  bool CreateWebRenderCommands(
+      wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+      const StackingContextHelper& aSc,
+      layers::RenderRootStateManager* aManager,
+      nsDisplayListBuilder* aDisplayListBuilder) override;
+
+ protected:
+  nsRect GetBounds(nsDisplayListBuilder* aBuilder, bool* aSnap) const override;
+  void Paint(nsDisplayListBuilder* aBuilder, gfxContext* aCtx) override;
+  void WriteDebugInfo(std::stringstream& aStream) override;
+
+ private:
+  nsRegion mRegion;
+  gfx::sRGBColor mColor;
+};
+
+enum class AppendedBackgroundType : uint8_t {
+  None,
+  Background,
+  ThemedBackground,
+};
+
+/**
+ * A display item to paint one background-image for a frame. Each background
+ * image layer gets its own nsDisplayBackgroundImage.
+ */
+class nsDisplayBackgroundImage : public nsPaintedDisplayItem {
+ public:
+  struct InitData {
+    nsDisplayListBuilder* builder;
+    const ComputedStyle* backgroundStyle;
+    nsCOMPtr<imgIContainer> image;
+    nsRect backgroundRect;
+    nsRect fillArea;
+    nsRect destArea;
+    uint32_t layer;
+    bool isRasterImage;
+    bool shouldFixToViewport;
+  };
+
+  /**
+   * aLayer signifies which background layer this item represents.
+   * aIsThemed should be the value of aFrame->IsThemed.
+   * aBackgroundStyle should be the result of
+   * nsCSSRendering::FindBackground, or null if FindBackground returned false.
+   * aBackgroundRect is relative to aFrame.
+   */
+  static InitData GetInitData(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                              uint16_t aLayer, const nsRect& aBackgroundRect,
+                              const ComputedStyle* aBackgroundStyle);
+
+  explicit nsDisplayBackgroundImage(nsDisplayListBuilder* aBuilder,
+                                    nsIFrame* aFrame, const InitData& aInitData,
+                                    nsIFrame* aFrameForBounds = nullptr);
+  ~nsDisplayBackgroundImage() override;
+
+  NS_DISPLAY_DECL_NAME("Background", TYPE_BACKGROUND)
+
+  /**
+   * This will create and append new items for all the layers of the
+   * background. Returns the type of background that was appended.
+   * aAllowWillPaintBorderOptimization should usually be left at true, unless
+   * aFrame has special border drawing that causes opaque borders to not
+   * actually be opaque.
+   */
+  static AppendedBackgroundType AppendBackgroundItemsToTop(
+      nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+      const nsRect& aBackgroundRect, nsDisplayList* aList,
+      bool aAllowWillPaintBorderOptimization = true,
+      const nsRect& aBackgroundOriginRect = nsRect(),
+      nsIFrame* aSecondaryReferenceFrame = nullptr,
+      Maybe<nsDisplayListBuilder::AutoBuildingDisplayList>*
+          aAutoBuildingDisplayList = nullptr);
+
+  bool CreateWebRenderCommands(
+      wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+      const StackingContextHelper& aSc,
+      layers::RenderRootStateManager* aManager,
+      nsDisplayListBuilder* aDisplayListBuilder) override;
+  void HitTest(nsDisplayListBuilder* aBuilder, const nsRect& aRect,
+               HitTestState* aState, nsTArray<nsIFrame*>* aOutFrames) override;
+  nsRegion GetOpaqueRegion(nsDisplayListBuilder* aBuilder,
+                           bool* aSnap) const override;
+  Maybe<nscolor> IsUniform(nsDisplayListBuilder* aBuilder) const override;
+
+  bool CanApplyOpacity(WebRenderLayerManager* aManager,
+                       nsDisplayListBuilder* aBuilder) const override;
+
+  /**
+   * GetBounds() returns the background painting area.
+   */
+  nsRect GetBounds(nsDisplayListBuilder* aBuilder, bool* aSnap) const override;
+
+  void Paint(nsDisplayListBuilder* aBuilder, gfxContext* aCtx) override;
+
+  /**
+   * Return the background positioning area.
+   * (GetBounds() returns the background painting area.)
+   * Can be called only when mBackgroundStyle is non-null.
+   */
+  nsRect GetPositioningArea() const;
+
+  /**
+   * Returns true if existing rendered pixels of this display item may need
+   * to be redrawn if the positioning area size changes but its position does
+   * not.
+   * If false, only the changed painting area needs to be redrawn when the
+   * positioning area size changes but its position does not.
+   */
+  bool RenderingMightDependOnPositioningAreaSizeChange() const;
+
+  nsDisplayItemGeometry* AllocateGeometry(
+      nsDisplayListBuilder* aBuilder) override {
+    return new nsDisplayBackgroundGeometry(this, aBuilder);
+  }
+
+  void ComputeInvalidationRegion(nsDisplayListBuilder* aBuilder,
+                                 const nsDisplayItemGeometry* aGeometry,
+                                 nsRegion* aInvalidRegion) const override;
+  bool ShouldFixToViewport(nsDisplayListBuilder* aBuilder) const override {
+    return mShouldFixToViewport;
+  }
+
+  nsRect GetDestRect() const { return mDestRect; }
+
+  nsIFrame* GetDependentFrame() override { return mDependentFrame; }
+
+  void SetDependentFrame(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame) {
+    if (!aBuilder->IsRetainingDisplayList() || mDependentFrame == aFrame) {
+      return;
+    }
+    mDependentFrame = aFrame;
+    if (aFrame) {
+      mDependentFrame->AddDisplayItem(this);
+    }
+  }
+
+  void RemoveFrame(nsIFrame* aFrame) override {
+    if (aFrame == mDependentFrame) {
+      mDependentFrame = nullptr;
+    }
+    nsPaintedDisplayItem::RemoveFrame(aFrame);
+  }
+
+  // Match https://w3c.github.io/paint-timing/#contentful-image
+  bool IsContentful() const override {
+    const auto& styleImage =
+        mBackgroundStyle->StyleBackground()->mImage.mLayers[mLayer].mImage;
+
+    return styleImage.IsSizeAvailable() && styleImage.FinalImage().IsUrl();
+  }
+
+ protected:
+  bool CanBuildWebRenderDisplayItems(layers::WebRenderLayerManager* aManager,
+                                     nsDisplayListBuilder* aBuilder) const;
+  nsRect GetBoundsInternal(nsDisplayListBuilder* aBuilder,
+                           nsIFrame* aFrameForBounds = nullptr);
+
+  void PaintInternal(nsDisplayListBuilder* aBuilder, gfxContext* aCtx,
+                     const nsRect& aBounds, nsRect* aClipRect);
+
+  // Cache the result of nsCSSRendering::FindBackground. Always null if
+  // mIsThemed is true or if FindBackground returned false.
+  RefPtr<const ComputedStyle> mBackgroundStyle;
+  nsCOMPtr<imgIContainer> mImage;
+  nsIFrame* mDependentFrame;
+  nsRect mBackgroundRect;  // relative to the reference frame
+  nsRect mFillRect;
+  nsRect mDestRect;
+  /* Bounds of this display item */
+  nsRect mBounds;
+  uint16_t mLayer;
+  bool mIsRasterImage;
+  /* Whether the image should be treated as fixed to the viewport. */
+  bool mShouldFixToViewport;
+};
+
+/**
+ * A display item to paint background image for table. For table parts, such
+ * as row, row group, col, col group, when drawing its background, we'll
+ * create separate background image display item for its containning cell.
+ * Those background image display items will reference to same DisplayItemData
+ * if we keep the mFrame point to cell's ancestor frame. We don't want to this
+ * happened bacause share same DisplatItemData will cause many bugs. So that
+ * we let mFrame point to cell frame and store the table type of the ancestor
+ * frame. And use mFrame and table type as key to generate DisplayItemData to
+ * avoid sharing DisplayItemData.
+ *
+ * Also store ancestor frame as mStyleFrame for all rendering informations.
+ */
+class nsDisplayTableBackgroundImage : public nsDisplayBackgroundImage {
+ public:
+  nsDisplayTableBackgroundImage(nsDisplayListBuilder* aBuilder,
+                                nsIFrame* aFrame, const InitData& aData,
+                                nsIFrame* aCellFrame);
+  ~nsDisplayTableBackgroundImage() override;
+
+  NS_DISPLAY_DECL_NAME("TableBackgroundImage", TYPE_TABLE_BACKGROUND_IMAGE)
+
+  bool IsInvalid(nsRect& aRect) const override;
+
+  nsIFrame* FrameForInvalidation() const override { return mStyleFrame; }
+
+  void RemoveFrame(nsIFrame* aFrame) override {
+    if (aFrame == mStyleFrame) {
+      mStyleFrame = nullptr;
+      SetDeletedFrame();
+    }
+    nsDisplayBackgroundImage::RemoveFrame(aFrame);
+  }
+
+ protected:
+  nsIFrame* StyleFrame() const override { return mStyleFrame; }
+  nsIFrame* mStyleFrame;
+};
+
+/**
+ * A display item to paint the native theme background for a frame.
+ */
+class nsDisplayThemedBackground : public nsPaintedDisplayItem {
+ public:
+  nsDisplayThemedBackground(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                            const nsRect& aBackgroundRect);
+
+  MOZ_COUNTED_DTOR_OVERRIDE(nsDisplayThemedBackground)
+
+  NS_DISPLAY_DECL_NAME("ThemedBackground", TYPE_THEMED_BACKGROUND)
+
+  void Init(nsDisplayListBuilder* aBuilder);
+
+  void Destroy(nsDisplayListBuilder* aBuilder) override {
+    aBuilder->UnregisterThemeGeometry(this);
+    nsPaintedDisplayItem::Destroy(aBuilder);
+  }
+
+  void HitTest(nsDisplayListBuilder* aBuilder, const nsRect& aRect,
+               HitTestState* aState, nsTArray<nsIFrame*>* aOutFrames) override;
+  nsRegion GetOpaqueRegion(nsDisplayListBuilder* aBuilder,
+                           bool* aSnap) const override;
+  Maybe<nscolor> IsUniform(nsDisplayListBuilder* aBuilder) const override;
+  bool CreateWebRenderCommands(
+      wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+      const StackingContextHelper& aSc,
+      layers::RenderRootStateManager* aManager,
+      nsDisplayListBuilder* aDisplayListBuilder) override;
+
+  bool MustPaintOnContentSide() const override { return true; }
+
+  /**
+   * GetBounds() returns the background painting area.
+   */
+  nsRect GetBounds(nsDisplayListBuilder* aBuilder, bool* aSnap) const override;
+
+  void Paint(nsDisplayListBuilder* aBuilder, gfxContext* aCtx) override;
+
+  /**
+   * Return the background positioning area.
+   * (GetBounds() returns the background painting area.)
+   * Can be called only when mBackgroundStyle is non-null.
+   */
+  nsRect GetPositioningArea() const;
+
+  /**
+   * Return whether our frame's document does not have the state
+   * NS_DOCUMENT_STATE_WINDOW_INACTIVE.
+   */
+  bool IsWindowActive() const;
+
+  nsDisplayItemGeometry* AllocateGeometry(
+      nsDisplayListBuilder* aBuilder) override {
+    return new nsDisplayThemedBackgroundGeometry(this, aBuilder);
+  }
+
+  void ComputeInvalidationRegion(nsDisplayListBuilder* aBuilder,
+                                 const nsDisplayItemGeometry* aGeometry,
+                                 nsRegion* aInvalidRegion) const override;
+
+  void WriteDebugInfo(std::stringstream& aStream) override;
+
+ protected:
+  nsRect GetBoundsInternal();
+
+  void PaintInternal(nsDisplayListBuilder* aBuilder, gfxContext* aCtx,
+                     const nsRect& aBounds, nsRect* aClipRect);
+
+  nsRect mBackgroundRect;
+  nsRect mBounds;
+  nsITheme::Transparency mThemeTransparency;
+  StyleAppearance mAppearance;
+};
+
+class nsDisplayTableThemedBackground : public nsDisplayThemedBackground {
+ public:
+  nsDisplayTableThemedBackground(nsDisplayListBuilder* aBuilder,
+                                 nsIFrame* aFrame,
+                                 const nsRect& aBackgroundRect,
+                                 nsIFrame* aAncestorFrame)
+      : nsDisplayThemedBackground(aBuilder, aFrame, aBackgroundRect),
+        mAncestorFrame(aAncestorFrame) {
+    if (aBuilder->IsRetainingDisplayList()) {
+      mAncestorFrame->AddDisplayItem(this);
+    }
+  }
+
+  ~nsDisplayTableThemedBackground() override {
+    if (mAncestorFrame) {
+      mAncestorFrame->RemoveDisplayItem(this);
+    }
+  }
+
+  NS_DISPLAY_DECL_NAME("TableThemedBackground",
+                       TYPE_TABLE_THEMED_BACKGROUND_IMAGE)
+
+  nsIFrame* FrameForInvalidation() const override { return mAncestorFrame; }
+
+  void RemoveFrame(nsIFrame* aFrame) override {
+    if (aFrame == mAncestorFrame) {
+      mAncestorFrame = nullptr;
+      SetDeletedFrame();
+    }
+    nsDisplayThemedBackground::RemoveFrame(aFrame);
+  }
+
+ protected:
+  nsIFrame* StyleFrame() const override { return mAncestorFrame; }
+  nsIFrame* mAncestorFrame;
+};
+
+class nsDisplayBackgroundColor : public nsPaintedDisplayItem {
+ public:
+  nsDisplayBackgroundColor(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                           const nsRect& aBackgroundRect,
+                           const ComputedStyle* aBackgroundStyle,
+                           const nscolor& aColor)
+      : nsPaintedDisplayItem(aBuilder, aFrame),
+        mBackgroundRect(aBackgroundRect),
+        mHasStyle(aBackgroundStyle),
+        mDependentFrame(nullptr),
+        mColor(gfx::sRGBColor::FromABGR(aColor)) {
+    if (mHasStyle) {
+      mBottomLayerClip =
+          aBackgroundStyle->StyleBackground()->BottomLayer().mClip;
+    } else {
+      MOZ_ASSERT(aBuilder->IsForEventDelivery());
+    }
+  }
+
+  ~nsDisplayBackgroundColor() override {
+    if (mDependentFrame) {
+      mDependentFrame->RemoveDisplayItem(this);
+    }
+  }
+
+  NS_DISPLAY_DECL_NAME("BackgroundColor", TYPE_BACKGROUND_COLOR)
+
+  bool HasBackgroundClipText() const {
+    MOZ_ASSERT(mHasStyle);
+    return mBottomLayerClip == StyleGeometryBox::Text;
+  }
+
+  void Paint(nsDisplayListBuilder* aBuilder, gfxContext* aCtx) override;
+  void PaintWithClip(nsDisplayListBuilder* aBuilder, gfxContext* aCtx,
+                     const DisplayItemClip& aClip) override;
+  bool CreateWebRenderCommands(
+      wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+      const StackingContextHelper& aSc,
+      layers::RenderRootStateManager* aManager,
+      nsDisplayListBuilder* aDisplayListBuilder) override;
+  nsRegion GetOpaqueRegion(nsDisplayListBuilder* aBuilder,
+                           bool* aSnap) const override;
+  Maybe<nscolor> IsUniform(nsDisplayListBuilder* aBuilder) const override;
+  void HitTest(nsDisplayListBuilder* aBuilder, const nsRect& aRect,
+               HitTestState* aState, nsTArray<nsIFrame*>* aOutFrames) override;
+  bool CanApplyOpacity(WebRenderLayerManager* aManager,
+                       nsDisplayListBuilder* aBuilder) const override;
+
+  float GetOpacity() const { return mColor.a; }
+
+  nsRect GetBounds(nsDisplayListBuilder* aBuilder, bool* aSnap) const override {
+    *aSnap = true;
+    return mBackgroundRect;
+  }
+
+  bool CanPaintWithClip(const DisplayItemClip& aClip) override {
+    if (HasBackgroundClipText()) {
+      return false;
+    }
+
+    if (aClip.GetRoundedRectCount() > 1) {
+      return false;
+    }
+
+    return true;
+  }
+
+  nsDisplayItemGeometry* AllocateGeometry(
+      nsDisplayListBuilder* aBuilder) override {
+    return new nsDisplaySolidColorGeometry(this, aBuilder, mColor.ToABGR());
+  }
+
+  void ComputeInvalidationRegion(nsDisplayListBuilder* aBuilder,
+                                 const nsDisplayItemGeometry* aGeometry,
+                                 nsRegion* aInvalidRegion) const override {
+    const nsDisplaySolidColorGeometry* geometry =
+        static_cast<const nsDisplaySolidColorGeometry*>(aGeometry);
+
+    if (mColor.ToABGR() != geometry->mColor) {
+      bool dummy;
+      aInvalidRegion->Or(geometry->mBounds, GetBounds(aBuilder, &dummy));
+      return;
+    }
+    ComputeInvalidationRegionDifference(aBuilder, geometry, aInvalidRegion);
+  }
+
+  nsIFrame* GetDependentFrame() override { return mDependentFrame; }
+
+  void SetDependentFrame(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame) {
+    if (!aBuilder->IsRetainingDisplayList() || mDependentFrame == aFrame) {
+      return;
+    }
+    mDependentFrame = aFrame;
+    if (aFrame) {
+      mDependentFrame->AddDisplayItem(this);
+    }
+  }
+
+  void RemoveFrame(nsIFrame* aFrame) override {
+    if (aFrame == mDependentFrame) {
+      mDependentFrame = nullptr;
+    }
+
+    nsPaintedDisplayItem::RemoveFrame(aFrame);
+  }
+
+  void WriteDebugInfo(std::stringstream& aStream) override;
+
+  bool CanUseAsyncAnimations(nsDisplayListBuilder* aBuilder) override;
+
+ protected:
+  const nsRect mBackgroundRect;
+  const bool mHasStyle;
+  StyleGeometryBox mBottomLayerClip;
+  nsIFrame* mDependentFrame;
+  gfx::sRGBColor mColor;
+};
+
+class nsDisplayTableBackgroundColor : public nsDisplayBackgroundColor {
+ public:
+  nsDisplayTableBackgroundColor(nsDisplayListBuilder* aBuilder,
+                                nsIFrame* aFrame, const nsRect& aBackgroundRect,
+                                const ComputedStyle* aBackgroundStyle,
+                                const nscolor& aColor, nsIFrame* aAncestorFrame)
+      : nsDisplayBackgroundColor(aBuilder, aFrame, aBackgroundRect,
+                                 aBackgroundStyle, aColor),
+        mAncestorFrame(aAncestorFrame) {
+    if (aBuilder->IsRetainingDisplayList()) {
+      mAncestorFrame->AddDisplayItem(this);
+    }
+  }
+
+  ~nsDisplayTableBackgroundColor() override {
+    if (mAncestorFrame) {
+      mAncestorFrame->RemoveDisplayItem(this);
+    }
+  }
+
+  NS_DISPLAY_DECL_NAME("TableBackgroundColor", TYPE_TABLE_BACKGROUND_COLOR)
+
+  nsIFrame* FrameForInvalidation() const override { return mAncestorFrame; }
+
+  void RemoveFrame(nsIFrame* aFrame) override {
+    if (aFrame == mAncestorFrame) {
+      mAncestorFrame = nullptr;
+      SetDeletedFrame();
+    }
+    nsDisplayBackgroundColor::RemoveFrame(aFrame);
+  }
+
+  bool CanUseAsyncAnimations(nsDisplayListBuilder* aBuilder) override {
+    return false;
+  }
+
+ protected:
+  nsIFrame* mAncestorFrame;
+};
+
+/**
+ * The standard display item to paint the outer CSS box-shadows of a frame.
+ */
+class nsDisplayBoxShadowOuter final : public nsPaintedDisplayItem {
+ public:
+  nsDisplayBoxShadowOuter(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame)
+      : nsPaintedDisplayItem(aBuilder, aFrame) {
+    MOZ_COUNT_CTOR(nsDisplayBoxShadowOuter);
+    mBounds = GetBoundsInternal();
+  }
+
+  MOZ_COUNTED_DTOR_OVERRIDE(nsDisplayBoxShadowOuter)
+
+  NS_DISPLAY_DECL_NAME("BoxShadowOuter", TYPE_BOX_SHADOW_OUTER)
+
+  void Paint(nsDisplayListBuilder* aBuilder, gfxContext* aCtx) override;
+  nsRect GetBounds(nsDisplayListBuilder* aBuilder, bool* aSnap) const override;
+  bool IsInvisibleInRect(const nsRect& aRect) const override;
+  void ComputeInvalidationRegion(nsDisplayListBuilder* aBuilder,
+                                 const nsDisplayItemGeometry* aGeometry,
+                                 nsRegion* aInvalidRegion) const override;
+
+  bool CanApplyOpacity(WebRenderLayerManager* aManager,
+                       nsDisplayListBuilder* aBuilder) const override {
+    return CanBuildWebRenderDisplayItems();
+  }
+
+  bool CanBuildWebRenderDisplayItems() const;
+  bool CreateWebRenderCommands(
+      wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+      const StackingContextHelper& aSc,
+      layers::RenderRootStateManager* aManager,
+      nsDisplayListBuilder* aDisplayListBuilder) override;
+  nsRect GetBoundsInternal();
+
+ private:
+  nsRect mBounds;
+};
+
+/**
+ * The standard display item to paint the inner CSS box-shadows of a frame.
+ */
+class nsDisplayBoxShadowInner : public nsPaintedDisplayItem {
+ public:
+  nsDisplayBoxShadowInner(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame)
+      : nsPaintedDisplayItem(aBuilder, aFrame) {
+    MOZ_COUNT_CTOR(nsDisplayBoxShadowInner);
+  }
+
+  MOZ_COUNTED_DTOR_OVERRIDE(nsDisplayBoxShadowInner)
+
+  NS_DISPLAY_DECL_NAME("BoxShadowInner", TYPE_BOX_SHADOW_INNER)
+
+  void Paint(nsDisplayListBuilder* aBuilder, gfxContext* aCtx) override;
+
+  nsDisplayItemGeometry* AllocateGeometry(
+      nsDisplayListBuilder* aBuilder) override {
+    return new nsDisplayBoxShadowInnerGeometry(this, aBuilder);
+  }
+
+  void ComputeInvalidationRegion(nsDisplayListBuilder* aBuilder,
+                                 const nsDisplayItemGeometry* aGeometry,
+                                 nsRegion* aInvalidRegion) const override {
+    const nsDisplayBoxShadowInnerGeometry* geometry =
+        static_cast<const nsDisplayBoxShadowInnerGeometry*>(aGeometry);
+    if (!geometry->mPaddingRect.IsEqualInterior(GetPaddingRect())) {
+      // nsDisplayBoxShadowInner is based around the padding rect, but it can
+      // touch pixels outside of this. We should invalidate the entire bounds.
+      bool snap;
+      aInvalidRegion->Or(geometry->mBounds, GetBounds(aBuilder, &snap));
+    }
+  }
+
+  static bool CanCreateWebRenderCommands(nsDisplayListBuilder* aBuilder,
+                                         nsIFrame* aFrame,
+                                         const nsPoint& aReferenceOffset);
+  static void CreateInsetBoxShadowWebRenderCommands(
+      wr::DisplayListBuilder& aBuilder, const StackingContextHelper& aSc,
+      nsRect& aVisibleRect, nsIFrame* aFrame, const nsRect& aBorderRect);
+  bool CreateWebRenderCommands(
+      wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+      const StackingContextHelper& aSc,
+      layers::RenderRootStateManager* aManager,
+      nsDisplayListBuilder* aDisplayListBuilder) override;
+};
+
+/**
+ * The standard display item to paint the CSS outline of a frame.
+ */
+class nsDisplayOutline final : public nsPaintedDisplayItem {
+ public:
+  nsDisplayOutline(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame)
+      : nsPaintedDisplayItem(aBuilder, aFrame) {
+    MOZ_COUNT_CTOR(nsDisplayOutline);
+  }
+
+  MOZ_COUNTED_DTOR_OVERRIDE(nsDisplayOutline)
+
+  NS_DISPLAY_DECL_NAME("Outline", TYPE_OUTLINE)
+
+  bool MustPaintOnContentSide() const override {
+    MOZ_ASSERT(IsThemedOutline(),
+               "The only fallback path we have is for themed outlines");
+    return true;
+  }
+
+  bool CreateWebRenderCommands(
+      wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+      const StackingContextHelper& aSc,
+      layers::RenderRootStateManager* aManager,
+      nsDisplayListBuilder* aDisplayListBuilder) override;
+  bool IsInvisibleInRect(const nsRect& aRect) const override;
+  nsRect GetBounds(nsDisplayListBuilder* aBuilder, bool* aSnap) const override;
+  void Paint(nsDisplayListBuilder* aBuilder, gfxContext* aCtx) override;
+
+ private:
+  nsRect GetInnerRect() const;
+  bool IsThemedOutline() const;
+  bool HasRadius() const;
+};
+
+/**
+ * A class that lets you receive events within the frame bounds but never
+ * paints.
+ */
+class nsDisplayEventReceiver final : public nsDisplayItem {
+ public:
+  nsDisplayEventReceiver(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame)
+      : nsDisplayItem(aBuilder, aFrame) {
+    MOZ_COUNT_CTOR(nsDisplayEventReceiver);
+  }
+
+  MOZ_COUNTED_DTOR_FINAL(nsDisplayEventReceiver)
+
+  NS_DISPLAY_DECL_NAME("EventReceiver", TYPE_EVENT_RECEIVER)
+
+  void HitTest(nsDisplayListBuilder* aBuilder, const nsRect& aRect,
+               HitTestState* aState, nsTArray<nsIFrame*>* aOutFrames) final;
+};
+
+/**
+ * Similar to nsDisplayEventReceiver in that it is used for hit-testing. However
+ * this gets built when we're doing widget painting and we need to send the
+ * compositor some hit-test info for a frame. This is effectively a dummy item
+ * whose sole purpose is to carry the hit-test info to the compositor.
+ */
+class nsDisplayCompositorHitTestInfo final : public nsDisplayItem {
+ public:
+  nsDisplayCompositorHitTestInfo(nsDisplayListBuilder* aBuilder,
+                                 nsIFrame* aFrame)
+      : nsDisplayItem(aBuilder, aFrame) {
+    MOZ_COUNT_CTOR(nsDisplayCompositorHitTestInfo);
+    mHitTestInfo.Initialize(aBuilder, aFrame);
+    SetHasHitTestInfo();
+  }
+
+  nsDisplayCompositorHitTestInfo(
+      nsDisplayListBuilder* aBuilder, nsIFrame* aFrame, const nsRect& aArea,
+      const gfx::CompositorHitTestInfo& aHitTestFlags)
+      : nsDisplayItem(aBuilder, aFrame) {
+    MOZ_COUNT_CTOR(nsDisplayCompositorHitTestInfo);
+    mHitTestInfo.SetAreaAndInfo(aArea, aHitTestFlags);
+    mHitTestInfo.InitializeScrollTarget(aBuilder);
+    SetHasHitTestInfo();
+  }
+
+  MOZ_COUNTED_DTOR_OVERRIDE(nsDisplayCompositorHitTestInfo)
+
+  NS_DISPLAY_DECL_NAME("CompositorHitTestInfo", TYPE_COMPOSITOR_HITTEST_INFO)
+
+  bool CreateWebRenderCommands(
+      wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+      const StackingContextHelper& aSc,
+      layers::RenderRootStateManager* aManager,
+      nsDisplayListBuilder* aDisplayListBuilder) override;
+
+  bool isInvisible() const { return true; }
+
+  int32_t ZIndex() const override;
+  void SetOverrideZIndex(int32_t aZIndex);
+
+  nsRect GetBounds(nsDisplayListBuilder* aBuilder, bool* aSnap) const override {
+    *aSnap = false;
+    return nsRect();
+  }
+
+  const HitTestInfo& GetHitTestInfo() final { return mHitTestInfo; }
+
+ private:
+  HitTestInfo mHitTestInfo;
+  Maybe<int32_t> mOverrideZIndex;
+};
+
+class nsDisplayWrapper;
+
+/**
+ * A class that lets you wrap a display list as a display item.
+ *
+ * GetUnderlyingFrame() is troublesome for wrapped lists because if the wrapped
+ * list has many items, it's not clear which one has the 'underlying frame'.
+ * Thus we force the creator to specify what the underlying frame is. The
+ * underlying frame should be the root of a stacking context, because sorting
+ * a list containing this item will not get at the children.
+ *
+ * In some cases (e.g., clipping) we want to wrap a list but we don't have a
+ * particular underlying frame that is a stacking context root. In that case
+ * we allow the frame to be nullptr. Callers to GetUnderlyingFrame must
+ * detect and handle this case.
+ */
+class nsDisplayWrapList : public nsPaintedDisplayItem {
+ public:
+  /**
+   * Takes all the items from aList and puts them in our list.
+   */
+  nsDisplayWrapList(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                    nsDisplayList* aList);
+
+  nsDisplayWrapList(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                    nsDisplayItem* aItem);
+
+  nsDisplayWrapList(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                    nsDisplayList* aList,
+                    const ActiveScrolledRoot* aActiveScrolledRoot,
+                    bool aClearClipChain = false);
+
+  nsDisplayWrapList(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame)
+      : nsPaintedDisplayItem(aBuilder, aFrame),
+        mList(aBuilder),
+        mFrameActiveScrolledRoot(aBuilder->CurrentActiveScrolledRoot()),
+        mOverrideZIndex(0),
+        mHasZIndexOverride(false) {
+    MOZ_COUNT_CTOR(nsDisplayWrapList);
+    mBaseBuildingRect = GetBuildingRect();
+    mListPtr = &mList;
+    mOriginalClipChain = mClipChain;
+  }
+
+  nsDisplayWrapList() = delete;
+
+  /**
+   * A custom copy-constructor that does not copy mList, as this would mutate
+   * the other item.
+   */
+  nsDisplayWrapList(const nsDisplayWrapList& aOther) = delete;
+  nsDisplayWrapList(nsDisplayListBuilder* aBuilder,
+                    const nsDisplayWrapList& aOther)
+      : nsPaintedDisplayItem(aBuilder, aOther),
+        mList(aBuilder),
+        mListPtr(&mList),
+        mFrameActiveScrolledRoot(aOther.mFrameActiveScrolledRoot),
+        mMergedFrames(aOther.mMergedFrames.Clone()),
+        mBounds(aOther.mBounds),
+        mBaseBuildingRect(aOther.mBaseBuildingRect),
+        mOriginalClipChain(aOther.mClipChain),
+        mOverrideZIndex(aOther.mOverrideZIndex),
+        mHasZIndexOverride(aOther.mHasZIndexOverride),
+        mClearingClipChain(aOther.mClearingClipChain) {
+    MOZ_COUNT_CTOR(nsDisplayWrapList);
+  }
+
+  ~nsDisplayWrapList() override;
+
+  const nsDisplayWrapList* AsDisplayWrapList() const final { return this; }
+  nsDisplayWrapList* AsDisplayWrapList() final { return this; }
+
+  void Destroy(nsDisplayListBuilder* aBuilder) override {
+    mList.DeleteAll(aBuilder);
+    nsPaintedDisplayItem::Destroy(aBuilder);
+  }
+
+  /**
+   * Creates a new nsDisplayWrapper that holds a pointer to the display list
+   * owned by the given nsDisplayItem.
+   */
+  nsDisplayWrapper* CreateShallowCopy(nsDisplayListBuilder* aBuilder);
+
+  /**
+   * Call this if the wrapped list is changed.
+   */
+  void UpdateBounds(nsDisplayListBuilder* aBuilder) override {
+    // Clear the clip chain up to the asr, but don't store it, so that we'll
+    // recover it when we reuse the item.
+    if (mClearingClipChain) {
+      const DisplayItemClipChain* clip = mOriginalClipChain;
+      while (clip && ActiveScrolledRoot::IsAncestor(GetActiveScrolledRoot(),
+                                                    clip->mASR)) {
+        clip = clip->mParent;
+      }
+      SetClipChain(clip, false);
+    }
+
+    nsRect buildingRect;
+    mBounds = mListPtr->GetClippedBoundsWithRespectToASR(
+        aBuilder, mActiveScrolledRoot, &buildingRect);
+    // The display list may contain content that's visible outside the visible
+    // rect (i.e. the current dirty rect) passed in when the item was created.
+    // This happens when the dirty rect has been restricted to the visual
+    // overflow rect of a frame for some reason (e.g. when setting up dirty
+    // rects in nsDisplayListBuilder::MarkOutOfFlowFrameForDisplay), but that
+    // frame contains placeholders for out-of-flows that aren't descendants of
+    // the frame.
+    buildingRect.UnionRect(mBaseBuildingRect, buildingRect);
+    SetBuildingRect(buildingRect);
+  }
+
+  void SetClipChain(const DisplayItemClipChain* aClipChain,
+                    bool aStore) override {
+    nsDisplayItem::SetClipChain(aClipChain, aStore);
+
+    if (aStore) {
+      mOriginalClipChain = mClipChain;
+    }
+  }
+
+  void HitTest(nsDisplayListBuilder* aBuilder, const nsRect& aRect,
+               HitTestState* aState, nsTArray<nsIFrame*>* aOutFrames) override;
+  nsRect GetBounds(nsDisplayListBuilder* aBuilder, bool* aSnap) const override;
+  nsRegion GetOpaqueRegion(nsDisplayListBuilder* aBuilder,
+                           bool* aSnap) const override;
+  Maybe<nscolor> IsUniform(nsDisplayListBuilder* aBuilder) const override;
+
+  /**
+   * Try to merge with the other item (which is below us in the display
+   * list). This gets used by nsDisplayClip to coalesce clipping operations
+   * (optimization), by nsDisplayOpacity to merge rendering for the same
+   * content element into a single opacity group (correctness), and will be
+   * used by nsDisplayOutline to merge multiple outlines for the same element
+   * (also for correctness).
+   */
+  virtual void Merge(const nsDisplayItem* aItem) {
+    MOZ_ASSERT(CanMerge(aItem));
+    MOZ_ASSERT(Frame() != aItem->Frame());
+    MergeFromTrackingMergedFrames(static_cast<const nsDisplayWrapList*>(aItem));
+  }
+
+  /**
+   * Returns the underlying frames of all display items that have been
+   * merged into this one (excluding this item's own underlying frame)
+   * to aFrames.
+   */
+  const nsTArray<nsIFrame*>& GetMergedFrames() const { return mMergedFrames; }
+
+  bool HasMergedFrames() const { return !mMergedFrames.IsEmpty(); }
+
+  bool ShouldFlattenAway(nsDisplayListBuilder* aBuilder) override {
+    return true;
+  }
+
+  bool IsInvalid(nsRect& aRect) const override {
+    if (mFrame->IsInvalid(aRect) && aRect.IsEmpty()) {
+      return true;
+    }
+    nsRect temp;
+    for (uint32_t i = 0; i < mMergedFrames.Length(); i++) {
+      if (mMergedFrames[i]->IsInvalid(temp) && temp.IsEmpty()) {
+        aRect.SetEmpty();
+        return true;
+      }
+      aRect = aRect.Union(temp);
+    }
+    aRect += ToReferenceFrame();
+    return !aRect.IsEmpty();
+  }
+
+  nsRect GetComponentAlphaBounds(nsDisplayListBuilder* aBuilder) const override;
+
+  RetainedDisplayList* GetSameCoordinateSystemChildren() const override {
+    return mListPtr;
+  }
+
+  RetainedDisplayList* GetChildren() const override { return mListPtr; }
+
+  int32_t ZIndex() const override {
+    return (mHasZIndexOverride) ? mOverrideZIndex
+                                : nsPaintedDisplayItem::ZIndex();
+  }
+
+  void SetOverrideZIndex(int32_t aZIndex) {
+    mHasZIndexOverride = true;
+    mOverrideZIndex = aZIndex;
+  }
+
+  /**
+   * This creates a copy of this item, but wrapping aItem instead of
+   * our existing list. Only gets called if this item returned nullptr
+   * for GetUnderlyingFrame(). aItem is guaranteed to return non-null from
+   * GetUnderlyingFrame().
+   */
+  nsDisplayWrapList* WrapWithClone(nsDisplayListBuilder* aBuilder,
+                                   nsDisplayItem* aItem) {
+    MOZ_ASSERT_UNREACHABLE("We never returned nullptr for GetUnderlyingFrame!");
+    return nullptr;
+  }
+
+  bool CreateWebRenderCommands(
+      wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+      const StackingContextHelper& aSc,
+      layers::RenderRootStateManager* aManager,
+      nsDisplayListBuilder* aDisplayListBuilder) override {
+    return CreateWebRenderCommandsNewClipListOption(
+        aBuilder, aResources, aSc, aManager, aDisplayListBuilder, true);
+  }
+
+  // Same as the above but with the option to pass the aNewClipList argument to
+  // WebRenderCommandBuilder::CreateWebRenderCommandsFromDisplayList.
+  bool CreateWebRenderCommandsNewClipListOption(
+      wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+      const StackingContextHelper& aSc,
+      layers::RenderRootStateManager* aManager,
+      nsDisplayListBuilder* aDisplayListBuilder, bool aNewClipList);
+
+  const ActiveScrolledRoot* GetFrameActiveScrolledRoot() {
+    return mFrameActiveScrolledRoot;
+  }
+
+ protected:
+  void MergeFromTrackingMergedFrames(const nsDisplayWrapList* aOther) {
+    mBounds.UnionRect(mBounds, aOther->mBounds);
+    nsRect buildingRect;
+    buildingRect.UnionRect(GetBuildingRect(), aOther->GetBuildingRect());
+    SetBuildingRect(buildingRect);
+    mMergedFrames.AppendElement(aOther->mFrame);
+    mMergedFrames.AppendElements(aOther->mMergedFrames.Clone());
+  }
+
+  RetainedDisplayList mList;
+  RetainedDisplayList* mListPtr;
+  // The active scrolled root for the frame that created this
+  // wrap list.
+  RefPtr<const ActiveScrolledRoot> mFrameActiveScrolledRoot;
+  // The frames from items that have been merged into this item, excluding
+  // this item's own frame.
+  nsTArray<nsIFrame*> mMergedFrames;
+  nsRect mBounds;
+  // Displaylist building rect contributed by this display item itself.
+  // Our mBuildingRect may include the visible areas of children.
+  nsRect mBaseBuildingRect;
+  RefPtr<const DisplayItemClipChain> mOriginalClipChain;
+  int32_t mOverrideZIndex;
+  bool mHasZIndexOverride;
+  bool mClearingClipChain = false;
+};
+
+class nsDisplayWrapper : public nsDisplayWrapList {
+ public:
+  NS_DISPLAY_DECL_NAME("WrapList", TYPE_WRAP_LIST)
+
+  nsDisplayWrapper(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                   nsDisplayList* aList,
+                   const ActiveScrolledRoot* aActiveScrolledRoot,
+                   bool aClearClipChain = false)
+      : nsDisplayWrapList(aBuilder, aFrame, aList, aActiveScrolledRoot,
+                          aClearClipChain) {}
+
+  nsDisplayWrapper(const nsDisplayWrapper& aOther) = delete;
+  nsDisplayWrapper(nsDisplayListBuilder* aBuilder,
+                   const nsDisplayWrapList& aOther)
+      : nsDisplayWrapList(aBuilder, aOther) {}
+
+  void Paint(nsDisplayListBuilder* aBuilder, gfxContext* aCtx) override;
+
+ private:
+  NS_DISPLAY_ALLOW_CLONING()
+  friend class nsDisplayListBuilder;
+  friend class nsDisplayWrapList;
+};
+
+/**
+ * We call WrapDisplayList on the in-flow lists: BorderBackground(),
+ * BlockBorderBackgrounds() and Content().
+ * We call WrapDisplayItem on each item of Outlines(), PositionedDescendants(),
+ * and Floats(). This is done to support special wrapping processing for frames
+ * that may not be in-flow descendants of the current frame.
+ */
+class nsDisplayItemWrapper {
+ public:
+  // This is never instantiated directly (it has pure virtual methods), so no
+  // need to count constructors and destructors.
+
+  bool WrapBorderBackground() { return true; }
+  virtual nsDisplayItem* WrapList(nsDisplayListBuilder* aBuilder,
+                                  nsIFrame* aFrame, nsDisplayList* aList) = 0;
+  virtual nsDisplayItem* WrapItem(nsDisplayListBuilder* aBuilder,
+                                  nsDisplayItem* aItem) = 0;
+
+  nsresult WrapLists(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                     const nsDisplayListSet& aIn, const nsDisplayListSet& aOut);
+  nsresult WrapListsInPlace(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                            const nsDisplayListSet& aLists);
+
+ protected:
+  nsDisplayItemWrapper() = default;
+};
+
+/**
+ * The standard display item to paint a stacking context with translucency
+ * set by the stacking context root frame's 'opacity' style.
+ */
+class nsDisplayOpacity : public nsDisplayWrapList {
+ public:
+  nsDisplayOpacity(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                   nsDisplayList* aList,
+                   const ActiveScrolledRoot* aActiveScrolledRoot,
+                   bool aForEventsOnly, bool aNeedsActiveLayer,
+                   bool aWrapsBackdropFilter);
+
+  nsDisplayOpacity(nsDisplayListBuilder* aBuilder,
+                   const nsDisplayOpacity& aOther)
+      : nsDisplayWrapList(aBuilder, aOther),
+        mOpacity(aOther.mOpacity),
+        mForEventsOnly(aOther.mForEventsOnly),
+        mNeedsActiveLayer(aOther.mNeedsActiveLayer),
+        mChildOpacityState(ChildOpacityState::Unknown),
+        mWrapsBackdropFilter(aOther.mWrapsBackdropFilter) {
+    MOZ_COUNT_CTOR(nsDisplayOpacity);
+    // We should not try to merge flattened opacities.
+    MOZ_ASSERT(aOther.mChildOpacityState != ChildOpacityState::Applied);
+  }
+
+  void HitTest(nsDisplayListBuilder* aBuilder, const nsRect& aRect,
+               HitTestState* aState, nsTArray<nsIFrame*>* aOutFrames) override;
+
+  MOZ_COUNTED_DTOR_OVERRIDE(nsDisplayOpacity)
+
+  NS_DISPLAY_DECL_NAME("Opacity", TYPE_OPACITY)
+
+  void InvalidateCachedChildInfo(nsDisplayListBuilder* aBuilder) override {
+    mChildOpacityState = ChildOpacityState::Unknown;
+  }
+
+  nsRegion GetOpaqueRegion(nsDisplayListBuilder* aBuilder,
+                           bool* aSnap) const override;
+  void Paint(nsDisplayListBuilder* aBuilder, gfxContext* aCtx) override;
+
+  bool CanMerge(const nsDisplayItem* aItem) const override {
+    // items for the same content element should be merged into a single
+    // compositing group
+    // aItem->GetUnderlyingFrame() returns non-null because it's
+    // nsDisplayOpacity
+    return HasDifferentFrame(aItem) && HasSameTypeAndClip(aItem) &&
+           HasSameContent(aItem);
+  }
+
+  nsDisplayItemGeometry* AllocateGeometry(
+      nsDisplayListBuilder* aBuilder) override {
+    return new nsDisplayOpacityGeometry(this, aBuilder, mOpacity);
+  }
+
+  void ComputeInvalidationRegion(nsDisplayListBuilder* aBuilder,
+                                 const nsDisplayItemGeometry* aGeometry,
+                                 nsRegion* aInvalidRegion) const override;
+
+  bool IsInvalid(nsRect& aRect) const override {
+    if (mForEventsOnly) {
+      return false;
+    }
+    return nsDisplayWrapList::IsInvalid(aRect);
+  }
+  bool CanApplyOpacity(WebRenderLayerManager* aManager,
+                       nsDisplayListBuilder* aBuilder) const override;
+  bool ShouldFlattenAway(nsDisplayListBuilder* aBuilder) override {
+    return false;
+  }
+
+  bool CanApplyOpacityToChildren(WebRenderLayerManager* aManager,
+                                 nsDisplayListBuilder* aBuilder,
+                                 float aInheritedOpacity);
+
+  bool NeedsGeometryUpdates() const override {
+    // For flattened nsDisplayOpacity items, ComputeInvalidationRegion() only
+    // handles invalidation for changed |mOpacity|. In order to keep track of
+    // the current bounds of the item for invalidation, nsDisplayOpacityGeometry
+    // for the corresponding DisplayItemData needs to be updated, even if the
+    // reported invalidation region is empty.
+    return mChildOpacityState == ChildOpacityState::Deferred;
+  }
+
+  /**
+   * Returns true if ShouldFlattenAway() applied opacity to children.
+   */
+  bool OpacityAppliedToChildren() const {
+    return mChildOpacityState == ChildOpacityState::Applied;
+  }
+
+  static bool NeedsActiveLayer(nsDisplayListBuilder* aBuilder,
+                               nsIFrame* aFrame);
+  void WriteDebugInfo(std::stringstream& aStream) override;
+  bool CanUseAsyncAnimations(nsDisplayListBuilder* aBuilder) override;
+  bool CreateWebRenderCommands(
+      wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+      const StackingContextHelper& aSc,
+      layers::RenderRootStateManager* aManager,
+      nsDisplayListBuilder* aDisplayListBuilder) override;
+
+  float GetOpacity() const { return mOpacity; }
+
+  bool CreatesStackingContextHelper() override { return true; }
+
+ private:
+  NS_DISPLAY_ALLOW_CLONING()
+
+  bool CanApplyToChildren(WebRenderLayerManager* aManager,
+                          nsDisplayListBuilder* aBuilder);
+  bool ApplyToMask();
+
+  float mOpacity;
+  bool mForEventsOnly : 1;
+  enum class ChildOpacityState : uint8_t {
+    // Our child list has changed since the last time ApplyToChildren was
+    // called.
+    Unknown,
+    // Our children defer opacity handling to us.
+    Deferred,
+    // Opacity is applied to our children.
+    Applied
+  };
+  bool mNeedsActiveLayer : 1;
+#ifndef __GNUC__
+  ChildOpacityState mChildOpacityState : 2;
+#else
+  ChildOpacityState mChildOpacityState;
+#endif
+  bool mWrapsBackdropFilter;
+};
+
+class nsDisplayBlendMode : public nsDisplayWrapList {
+ public:
+  nsDisplayBlendMode(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                     nsDisplayList* aList, StyleBlend aBlendMode,
+                     const ActiveScrolledRoot* aActiveScrolledRoot,
+                     const bool aIsForBackground);
+  nsDisplayBlendMode(nsDisplayListBuilder* aBuilder,
+                     const nsDisplayBlendMode& aOther)
+      : nsDisplayWrapList(aBuilder, aOther),
+        mBlendMode(aOther.mBlendMode),
+        mIsForBackground(aOther.mIsForBackground) {
+    MOZ_COUNT_CTOR(nsDisplayBlendMode);
+  }
+
+  MOZ_COUNTED_DTOR_OVERRIDE(nsDisplayBlendMode)
+
+  NS_DISPLAY_DECL_NAME("BlendMode", TYPE_BLEND_MODE)
+
+  nsRegion GetOpaqueRegion(nsDisplayListBuilder* aBuilder,
+                           bool* aSnap) const override;
+  void ComputeInvalidationRegion(nsDisplayListBuilder* aBuilder,
+                                 const nsDisplayItemGeometry* aGeometry,
+                                 nsRegion* aInvalidRegion) const override {
+    // We don't need to compute an invalidation region since we have
+    // LayerTreeInvalidation
+  }
+
+  bool CreateWebRenderCommands(
+      wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+      const StackingContextHelper& aSc,
+      layers::RenderRootStateManager* aManager,
+      nsDisplayListBuilder* aDisplayListBuilder) override;
+  void Paint(nsDisplayListBuilder* aBuilder, gfxContext* aCtx) override;
+
+  bool CanMerge(const nsDisplayItem* aItem) const override;
+
+  bool ShouldFlattenAway(nsDisplayListBuilder* aBuilder) override {
+    return false;
+  }
+
+  gfx::CompositionOp BlendMode();
+
+  bool CreatesStackingContextHelper() override { return true; }
+
+ protected:
+  StyleBlend mBlendMode;
+  bool mIsForBackground;
+
+ private:
+  NS_DISPLAY_ALLOW_CLONING()
+};
+
+class nsDisplayTableBlendMode : public nsDisplayBlendMode {
+ public:
+  nsDisplayTableBlendMode(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                          nsDisplayList* aList, StyleBlend aBlendMode,
+                          const ActiveScrolledRoot* aActiveScrolledRoot,
+                          nsIFrame* aAncestorFrame, const bool aIsForBackground)
+      : nsDisplayBlendMode(aBuilder, aFrame, aList, aBlendMode,
+                           aActiveScrolledRoot, aIsForBackground),
+        mAncestorFrame(aAncestorFrame) {
+    if (aBuilder->IsRetainingDisplayList()) {
+      mAncestorFrame->AddDisplayItem(this);
+    }
+  }
+
+  nsDisplayTableBlendMode(nsDisplayListBuilder* aBuilder,
+                          const nsDisplayTableBlendMode& aOther)
+      : nsDisplayBlendMode(aBuilder, aOther),
+        mAncestorFrame(aOther.mAncestorFrame) {
+    if (aBuilder->IsRetainingDisplayList()) {
+      mAncestorFrame->AddDisplayItem(this);
+    }
+  }
+
+  ~nsDisplayTableBlendMode() override {
+    if (mAncestorFrame) {
+      mAncestorFrame->RemoveDisplayItem(this);
+    }
+  }
+
+  NS_DISPLAY_DECL_NAME("TableBlendMode", TYPE_TABLE_BLEND_MODE)
+
+  nsIFrame* FrameForInvalidation() const override { return mAncestorFrame; }
+
+  void RemoveFrame(nsIFrame* aFrame) override {
+    if (aFrame == mAncestorFrame) {
+      mAncestorFrame = nullptr;
+      SetDeletedFrame();
+    }
+    nsDisplayBlendMode::RemoveFrame(aFrame);
+  }
+
+ protected:
+  nsIFrame* mAncestorFrame;
+
+ private:
+  NS_DISPLAY_ALLOW_CLONING()
+};
+
+class nsDisplayBlendContainer : public nsDisplayWrapList {
+ public:
+  static nsDisplayBlendContainer* CreateForMixBlendMode(
+      nsDisplayListBuilder* aBuilder, nsIFrame* aFrame, nsDisplayList* aList,
+      const ActiveScrolledRoot* aActiveScrolledRoot);
+
+  static nsDisplayBlendContainer* CreateForBackgroundBlendMode(
+      nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+      nsIFrame* aSecondaryFrame, nsDisplayList* aList,
+      const ActiveScrolledRoot* aActiveScrolledRoot);
+
+  MOZ_COUNTED_DTOR_OVERRIDE(nsDisplayBlendContainer)
+
+  NS_DISPLAY_DECL_NAME("BlendContainer", TYPE_BLEND_CONTAINER)
+
+  void Paint(nsDisplayListBuilder* aBuilder, gfxContext* aCtx) override;
+  bool CreateWebRenderCommands(
+      wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+      const StackingContextHelper& aSc,
+      layers::RenderRootStateManager* aManager,
+      nsDisplayListBuilder* aDisplayListBuilder) override;
+
+  bool CanMerge(const nsDisplayItem* aItem) const override {
+    // Items for the same content element should be merged into a single
+    // compositing group.
+    return HasDifferentFrame(aItem) && HasSameTypeAndClip(aItem) &&
+           HasSameContent(aItem) &&
+           mIsForBackground ==
+               static_cast<const nsDisplayBlendContainer*>(aItem)
+                   ->mIsForBackground;
+  }
+
+  bool ShouldFlattenAway(nsDisplayListBuilder* aBuilder) override {
+    return false;
+  }
+
+  bool CreatesStackingContextHelper() override { return true; }
+
+ protected:
+  nsDisplayBlendContainer(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                          nsDisplayList* aList,
+                          const ActiveScrolledRoot* aActiveScrolledRoot,
+                          bool aIsForBackground);
+  nsDisplayBlendContainer(nsDisplayListBuilder* aBuilder,
+                          const nsDisplayBlendContainer& aOther)
+      : nsDisplayWrapList(aBuilder, aOther),
+        mIsForBackground(aOther.mIsForBackground) {
+    MOZ_COUNT_CTOR(nsDisplayBlendContainer);
+  }
+
+  // Used to distinguish containers created at building stacking
+  // context or appending background.
+  bool mIsForBackground;
+
+ private:
+  NS_DISPLAY_ALLOW_CLONING()
+};
+
+class nsDisplayTableBlendContainer : public nsDisplayBlendContainer {
+ public:
+  NS_DISPLAY_DECL_NAME("TableBlendContainer", TYPE_TABLE_BLEND_CONTAINER)
+
+  nsIFrame* FrameForInvalidation() const override { return mAncestorFrame; }
+
+  void RemoveFrame(nsIFrame* aFrame) override {
+    if (aFrame == mAncestorFrame) {
+      mAncestorFrame = nullptr;
+      SetDeletedFrame();
+    }
+    nsDisplayBlendContainer::RemoveFrame(aFrame);
+  }
+
+ protected:
+  nsDisplayTableBlendContainer(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                               nsDisplayList* aList,
+                               const ActiveScrolledRoot* aActiveScrolledRoot,
+                               bool aIsForBackground, nsIFrame* aAncestorFrame)
+      : nsDisplayBlendContainer(aBuilder, aFrame, aList, aActiveScrolledRoot,
+                                aIsForBackground),
+        mAncestorFrame(aAncestorFrame) {
+    if (aBuilder->IsRetainingDisplayList()) {
+      mAncestorFrame->AddDisplayItem(this);
+    }
+  }
+
+  nsDisplayTableBlendContainer(nsDisplayListBuilder* aBuilder,
+                               const nsDisplayTableBlendContainer& aOther)
+      : nsDisplayBlendContainer(aBuilder, aOther),
+        mAncestorFrame(aOther.mAncestorFrame) {}
+
+  ~nsDisplayTableBlendContainer() override {
+    if (mAncestorFrame) {
+      mAncestorFrame->RemoveDisplayItem(this);
+    }
+  }
+
+  nsIFrame* mAncestorFrame;
+
+ private:
+  NS_DISPLAY_ALLOW_CLONING()
+};
+
+/**
+ * nsDisplayOwnLayer constructor flags. If we nest this class inside
+ * nsDisplayOwnLayer then we can't forward-declare it up at the top of this
+ * file and that makes it hard to use in all the places that we need to use it.
+ */
+enum class nsDisplayOwnLayerFlags {
+  None = 0,
+  GenerateSubdocInvalidations = 1 << 0,
+  GenerateScrollableLayer = 1 << 1,
+};
+
+MOZ_MAKE_ENUM_CLASS_BITWISE_OPERATORS(nsDisplayOwnLayerFlags)
+
+/**
+ * A display item that has no purpose but to ensure its contents get
+ * their own layer.
+ */
+class nsDisplayOwnLayer : public nsDisplayWrapList {
+ public:
+  enum OwnLayerType {
+    OwnLayerForTransformWithRoundedClip,
+    OwnLayerForStackingContext,
+    OwnLayerForImageBoxFrame,
+    OwnLayerForScrollbar,
+    OwnLayerForScrollThumb,
+    OwnLayerForSubdoc,
+    OwnLayerForBoxFrame
+  };
+
+  /**
+   * @param aFlags eGenerateSubdocInvalidations :
+   * Add UserData to the created ContainerLayer, so that invalidations
+   * for this layer are send to our nsPresContext.
+   * eGenerateScrollableLayer : only valid on nsDisplaySubDocument (and
+   * subclasses), indicates this layer is to be a scrollable layer, so call
+   * ComputeFrameMetrics, etc.
+   * @param aScrollTarget when eVerticalScrollbar or eHorizontalScrollbar
+   * is set in the flags, this parameter should be the ViewID of the
+   * scrollable content this scrollbar is for.
+   */
+  nsDisplayOwnLayer(
+      nsDisplayListBuilder* aBuilder, nsIFrame* aFrame, nsDisplayList* aList,
+      const ActiveScrolledRoot* aActiveScrolledRoot,
+      nsDisplayOwnLayerFlags aFlags = nsDisplayOwnLayerFlags::None,
+      const layers::ScrollbarData& aScrollbarData = layers::ScrollbarData{},
+      bool aForceActive = true, bool aClearClipChain = false);
+
+  nsDisplayOwnLayer(nsDisplayListBuilder* aBuilder,
+                    const nsDisplayOwnLayer& aOther)
+      : nsDisplayWrapList(aBuilder, aOther),
+        mFlags(aOther.mFlags),
+        mScrollbarData(aOther.mScrollbarData),
+        mForceActive(aOther.mForceActive),
+        mWrAnimationId(aOther.mWrAnimationId) {
+    MOZ_COUNT_CTOR(nsDisplayOwnLayer);
+  }
+
+  MOZ_COUNTED_DTOR_OVERRIDE(nsDisplayOwnLayer)
+
+  NS_DISPLAY_DECL_NAME("OwnLayer", TYPE_OWN_LAYER)
+
+  bool CreateWebRenderCommands(
+      wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+      const StackingContextHelper& aSc,
+      layers::RenderRootStateManager* aManager,
+      nsDisplayListBuilder* aDisplayListBuilder) override;
+  bool UpdateScrollData(layers::WebRenderScrollData* aData,
+                        layers::WebRenderLayerScrollData* aLayerData) override;
+  void Paint(nsDisplayListBuilder* aBuilder, gfxContext* aCtx) override {
+    GetChildren()->Paint(aBuilder, aCtx,
+                         mFrame->PresContext()->AppUnitsPerDevPixel());
+  }
+
+  bool CanMerge(const nsDisplayItem* aItem) const override {
+    // Don't allow merging, each sublist must have its own layer
+    return false;
+  }
+
+  bool ShouldFlattenAway(nsDisplayListBuilder* aBuilder) override {
+    return false;
+  }
+
+  void WriteDebugInfo(std::stringstream& aStream) override;
+  nsDisplayOwnLayerFlags GetFlags() { return mFlags; }
+  bool IsScrollThumbLayer() const;
+  bool IsScrollbarContainer() const;
+  bool IsRootScrollbarContainer() const;
+  bool IsZoomingLayer() const;
+  bool IsFixedPositionLayer() const;
+  bool IsStickyPositionLayer() const;
+  bool HasDynamicToolbar() const;
+  bool ShouldFixedAndStickyContentGetAnimationIds() const;
+
+  bool CreatesStackingContextHelper() override { return true; }
+
+ protected:
+  nsDisplayOwnLayerFlags mFlags;
+
+  /**
+   * If this nsDisplayOwnLayer represents a scroll thumb layer or a
+   * scrollbar container layer, mScrollbarData stores information
+   * about the scrollbar. Otherwise, mScrollbarData will be
+   * default-constructed (in particular with mDirection == Nothing())
+   * and can be ignored.
+   */
+  layers::ScrollbarData mScrollbarData;
+  bool mForceActive;
+  uint64_t mWrAnimationId;
+};
+
+/**
+ * A display item for subdocuments. This is more or less the same as
+ * nsDisplayOwnLayer, except that it always populates the FrameMetrics instance
+ * on the ContainerLayer it builds.
+ */
+class nsDisplaySubDocument : public nsDisplayOwnLayer {
+ public:
+  nsDisplaySubDocument(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                       nsSubDocumentFrame* aSubDocFrame, nsDisplayList* aList,
+                       nsDisplayOwnLayerFlags aFlags);
+  ~nsDisplaySubDocument() override;
+
+  NS_DISPLAY_DECL_NAME("SubDocument", TYPE_SUBDOCUMENT)
+
+  nsRect GetBounds(nsDisplayListBuilder* aBuilder, bool* aSnap) const override;
+
+  virtual nsSubDocumentFrame* SubDocumentFrame() { return mSubDocFrame; }
+
+  bool ShouldFlattenAway(nsDisplayListBuilder* aBuilder) override {
+    return mShouldFlatten;
+  }
+
+  void SetShouldFlattenAway(bool aShouldFlatten) {
+    mShouldFlatten = aShouldFlatten;
+  }
+
+  nsRegion GetOpaqueRegion(nsDisplayListBuilder* aBuilder,
+                           bool* aSnap) const override;
+
+  nsIFrame* FrameForInvalidation() const override;
+  void RemoveFrame(nsIFrame* aFrame) override;
+
+ protected:
+  ViewID mScrollParentId;
+  bool mForceDispatchToContentRegion{};
+  bool mShouldFlatten;
+  nsSubDocumentFrame* mSubDocFrame;
+};
+
+/**
+ * A display item used to represent sticky position elements. The contents
+ * gets its own layer and creates a stacking context, and the layer will have
+ * position-related metadata set on it.
+ */
+class nsDisplayStickyPosition : public nsDisplayOwnLayer {
+ public:
+  nsDisplayStickyPosition(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                          nsDisplayList* aList,
+                          const ActiveScrolledRoot* aActiveScrolledRoot,
+                          const ActiveScrolledRoot* aContainerASR,
+                          bool aClippedToDisplayPort);
+  nsDisplayStickyPosition(nsDisplayListBuilder* aBuilder,
+                          const nsDisplayStickyPosition& aOther)
+      : nsDisplayOwnLayer(aBuilder, aOther),
+        mContainerASR(aOther.mContainerASR),
+        mClippedToDisplayPort(aOther.mClippedToDisplayPort),
+        mShouldFlatten(false) {
+    MOZ_COUNT_CTOR(nsDisplayStickyPosition);
+  }
+
+  MOZ_COUNTED_DTOR_OVERRIDE(nsDisplayStickyPosition)
+
+  const DisplayItemClip& GetClip() const override {
+    return DisplayItemClip::NoClip();
+  }
+  bool IsClippedToDisplayPort() const { return mClippedToDisplayPort; }
+
+  NS_DISPLAY_DECL_NAME("StickyPosition", TYPE_STICKY_POSITION)
+  void Paint(nsDisplayListBuilder* aBuilder, gfxContext* aCtx) override {
+    GetChildren()->Paint(aBuilder, aCtx,
+                         mFrame->PresContext()->AppUnitsPerDevPixel());
+  }
+
+  bool CreateWebRenderCommands(
+      wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+      const StackingContextHelper& aSc,
+      layers::RenderRootStateManager* aManager,
+      nsDisplayListBuilder* aDisplayListBuilder) override;
+
+  bool UpdateScrollData(layers::WebRenderScrollData* aData,
+                        layers::WebRenderLayerScrollData* aLayerData) override;
+
+  const ActiveScrolledRoot* GetContainerASR() const { return mContainerASR; }
+
+  bool CreatesStackingContextHelper() override { return true; }
+
+  bool CanMoveAsync() override { return true; }
+
+  void SetShouldFlatten(bool aShouldFlatten) {
+    mShouldFlatten = aShouldFlatten;
+  }
+
+  bool ShouldFlattenAway(nsDisplayListBuilder* aBuilder) final {
+    return mShouldFlatten;
+  }
+
+ private:
+  NS_DISPLAY_ALLOW_CLONING()
+
+  void CalculateLayerScrollRanges(StickyScrollContainer* aStickyScrollContainer,
+                                  float aAppUnitsPerDevPixel, float aScaleX,
+                                  float aScaleY,
+                                  LayerRectAbsolute& aStickyOuter,
+                                  LayerRectAbsolute& aStickyInner);
+
+  StickyScrollContainer* GetStickyScrollContainer();
+
+  // This stores the ASR that this sticky container item would have assuming it
+  // has no fixed descendants. This may be the same as the ASR returned by
+  // GetActiveScrolledRoot(), or it may be a descendant of that.
+  RefPtr<const ActiveScrolledRoot> mContainerASR;
+  // This flag tracks if this sticky item is just clipped to the enclosing
+  // scrollframe's displayport, or if there are additional clips in play. In
+  // the former case, we can skip setting the displayport clip as the scrolled-
+  // clip of the corresponding layer. This allows sticky items to remain
+  // unclipped when the enclosing scrollframe is scrolled past the displayport.
+  // i.e. when the rest of the scrollframe checkerboards, the sticky item will
+  // not. This makes sense to do because the sticky item has abnormal scrolling
+  // behavior and may still be visible even if the rest of the scrollframe is
+  // checkerboarded. Note that the sticky item will still be subject to the
+  // scrollport clip.
+  bool mClippedToDisplayPort;
+
+  // True if this item should be flattened away.
+  bool mShouldFlatten;
+};
+
+class nsDisplayFixedPosition : public nsDisplayOwnLayer {
+ public:
+  nsDisplayFixedPosition(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                         nsDisplayList* aList,
+                         const ActiveScrolledRoot* aActiveScrolledRoot,
+                         const ActiveScrolledRoot* aScrollTargetASR);
+  nsDisplayFixedPosition(nsDisplayListBuilder* aBuilder,
+                         const nsDisplayFixedPosition& aOther)
+      : nsDisplayOwnLayer(aBuilder, aOther),
+        mScrollTargetASR(aOther.mScrollTargetASR),
+        mIsFixedBackground(aOther.mIsFixedBackground) {
+    MOZ_COUNT_CTOR(nsDisplayFixedPosition);
+  }
+
+  static nsDisplayFixedPosition* CreateForFixedBackground(
+      nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+      nsIFrame* aSecondaryFrame, nsDisplayBackgroundImage* aImage,
+      const uint16_t aIndex, const ActiveScrolledRoot* aScrollTargetASR);
+
+  MOZ_COUNTED_DTOR_OVERRIDE(nsDisplayFixedPosition)
+
+  NS_DISPLAY_DECL_NAME("FixedPosition", TYPE_FIXED_POSITION)
+
+  void Paint(nsDisplayListBuilder* aBuilder, gfxContext* aCtx) override {
+    GetChildren()->Paint(aBuilder, aCtx,
+                         mFrame->PresContext()->AppUnitsPerDevPixel());
+  }
+
+  bool ShouldFixToViewport(nsDisplayListBuilder* aBuilder) const override {
+    return mIsFixedBackground;
+  }
+
+  bool CreateWebRenderCommands(
+      wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+      const StackingContextHelper& aSc,
+      layers::RenderRootStateManager* aManager,
+      nsDisplayListBuilder* aDisplayListBuilder) override;
+  bool UpdateScrollData(layers::WebRenderScrollData* aData,
+                        layers::WebRenderLayerScrollData* aLayerData) override;
+  void WriteDebugInfo(std::stringstream& aStream) override;
+
+ protected:
+  // For background-attachment:fixed
+  nsDisplayFixedPosition(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                         nsDisplayList* aList,
+                         const ActiveScrolledRoot* aScrollTargetASR);
+  ViewID GetScrollTargetId();
+
+  RefPtr<const ActiveScrolledRoot> mScrollTargetASR;
+  bool mIsFixedBackground;
+
+ private:
+  NS_DISPLAY_ALLOW_CLONING()
+};
+
+class nsDisplayTableFixedPosition : public nsDisplayFixedPosition {
+ public:
+  NS_DISPLAY_DECL_NAME("TableFixedPosition", TYPE_TABLE_FIXED_POSITION)
+
+  nsIFrame* FrameForInvalidation() const override { return mAncestorFrame; }
+
+  void RemoveFrame(nsIFrame* aFrame) override {
+    if (aFrame == mAncestorFrame) {
+      mAncestorFrame = nullptr;
+      SetDeletedFrame();
+    }
+    nsDisplayFixedPosition::RemoveFrame(aFrame);
+  }
+
+ protected:
+  nsDisplayTableFixedPosition(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                              nsDisplayList* aList, nsIFrame* aAncestorFrame,
+                              const ActiveScrolledRoot* aScrollTargetASR);
+
+  nsDisplayTableFixedPosition(nsDisplayListBuilder* aBuilder,
+                              const nsDisplayTableFixedPosition& aOther)
+      : nsDisplayFixedPosition(aBuilder, aOther),
+        mAncestorFrame(aOther.mAncestorFrame) {}
+
+  ~nsDisplayTableFixedPosition() override {
+    if (mAncestorFrame) {
+      mAncestorFrame->RemoveDisplayItem(this);
+    }
+  }
+
+  nsIFrame* mAncestorFrame;
+
+ private:
+  NS_DISPLAY_ALLOW_CLONING()
+};
+
+/**
+ * This creates an empty scrollable layer. It has no child layers.
+ * It is used to record the existence of a scrollable frame in the layer
+ * tree.
+ */
+class nsDisplayScrollInfoLayer : public nsDisplayWrapList {
+ public:
+  nsDisplayScrollInfoLayer(nsDisplayListBuilder* aBuilder,
+                           nsIFrame* aScrolledFrame, nsIFrame* aScrollFrame,
+                           const gfx::CompositorHitTestInfo& aHitInfo,
+                           const nsRect& aHitArea);
+
+  MOZ_COUNTED_DTOR_OVERRIDE(nsDisplayScrollInfoLayer)
+
+  NS_DISPLAY_DECL_NAME("ScrollInfoLayer", TYPE_SCROLL_INFO_LAYER)
+
+  nsRegion GetOpaqueRegion(nsDisplayListBuilder* aBuilder,
+                           bool* aSnap) const override {
+    *aSnap = false;
+    return nsRegion();
+  }
+
+  void Paint(nsDisplayListBuilder* aBuilder, gfxContext* aCtx) override {
+    return;
+  }
+
+  bool ShouldFlattenAway(nsDisplayListBuilder* aBuilder) override {
+    return false;
+  }
+
+  void WriteDebugInfo(std::stringstream& aStream) override;
+  UniquePtr<layers::ScrollMetadata> ComputeScrollMetadata(
+      nsDisplayListBuilder* aBuilder,
+      layers::WebRenderLayerManager* aLayerManager);
+  bool UpdateScrollData(layers::WebRenderScrollData* aData,
+                        layers::WebRenderLayerScrollData* aLayerData) override;
+  bool CreateWebRenderCommands(
+      wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+      const StackingContextHelper& aSc,
+      layers::RenderRootStateManager* aManager,
+      nsDisplayListBuilder* aDisplayListBuilder) override;
+
+ protected:
+  nsIFrame* mScrollFrame;
+  nsIFrame* mScrolledFrame;
+  ViewID mScrollParentId;
+  gfx::CompositorHitTestInfo mHitInfo;
+  nsRect mHitArea;
+};
+
+/**
+ * nsDisplayZoom is used for subdocuments that have a different full zoom than
+ * their parent documents. This item creates a container layer.
+ */
+class nsDisplayZoom : public nsDisplaySubDocument {
+ public:
+  /**
+   * @param aFrame is the root frame of the subdocument.
+   * @param aList contains the display items for the subdocument.
+   * @param aAPD is the app units per dev pixel ratio of the subdocument.
+   * @param aParentAPD is the app units per dev pixel ratio of the parent
+   * document.
+   * @param aFlags eGenerateSubdocInvalidations :
+   * Add UserData to the created ContainerLayer, so that invalidations
+   * for this layer are send to our nsPresContext.
+   */
+  nsDisplayZoom(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                nsSubDocumentFrame* aSubDocFrame, nsDisplayList* aList,
+                int32_t aAPD, int32_t aParentAPD,
+                nsDisplayOwnLayerFlags aFlags = nsDisplayOwnLayerFlags::None);
+
+  MOZ_COUNTED_DTOR_OVERRIDE(nsDisplayZoom)
+
+  NS_DISPLAY_DECL_NAME("Zoom", TYPE_ZOOM)
+
+  nsRect GetBounds(nsDisplayListBuilder* aBuilder, bool* aSnap) const override;
+  void HitTest(nsDisplayListBuilder* aBuilder, const nsRect& aRect,
+               HitTestState* aState, nsTArray<nsIFrame*>* aOutFrames) override;
+  // Get the app units per dev pixel ratio of the child document.
+  int32_t GetChildAppUnitsPerDevPixel() { return mAPD; }
+  // Get the app units per dev pixel ratio of the parent document.
+  int32_t GetParentAppUnitsPerDevPixel() { return mParentAPD; }
+
+ private:
+  int32_t mAPD, mParentAPD;
+};
+
+/**
+ * nsDisplayAsyncZoom is used for APZ zooming. It wraps the contents of the
+ * root content document's scroll frame, including fixed position content. It
+ * does not contain the scroll frame's scrollbars. It is clipped to the scroll
+ * frame's scroll port clip. It is not scrolled; only its non-fixed contents
+ * are scrolled. This item creates a container layer.
+ */
+class nsDisplayAsyncZoom : public nsDisplayOwnLayer {
+ public:
+  nsDisplayAsyncZoom(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                     nsDisplayList* aList,
+                     const ActiveScrolledRoot* aActiveScrolledRoot,
+                     layers::FrameMetrics::ViewID aViewID);
+  nsDisplayAsyncZoom(nsDisplayListBuilder* aBuilder,
+                     const nsDisplayAsyncZoom& aOther)
+      : nsDisplayOwnLayer(aBuilder, aOther), mViewID(aOther.mViewID) {
+    MOZ_COUNT_CTOR(nsDisplayAsyncZoom);
+  }
+
+#ifdef NS_BUILD_REFCNT_LOGGING
+  virtual ~nsDisplayAsyncZoom();
+#endif
+
+  NS_DISPLAY_DECL_NAME("AsyncZoom", TYPE_ASYNC_ZOOM)
+
+  void HitTest(nsDisplayListBuilder* aBuilder, const nsRect& aRect,
+               HitTestState* aState, nsTArray<nsIFrame*>* aOutFrames) override;
+  bool UpdateScrollData(layers::WebRenderScrollData* aData,
+                        layers::WebRenderLayerScrollData* aLayerData) override;
+
+ protected:
+  layers::FrameMetrics::ViewID mViewID;
+};
+
+/**
+ * A base class for different effects types.
+ */
+class nsDisplayEffectsBase : public nsDisplayWrapList {
+ public:
+  nsDisplayEffectsBase(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                       nsDisplayList* aList,
+                       const ActiveScrolledRoot* aActiveScrolledRoot,
+                       bool aClearClipChain = false);
+  nsDisplayEffectsBase(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                       nsDisplayList* aList);
+
+  nsDisplayEffectsBase(nsDisplayListBuilder* aBuilder,
+                       const nsDisplayEffectsBase& aOther)
+      : nsDisplayWrapList(aBuilder, aOther),
+        mEffectsBounds(aOther.mEffectsBounds) {
+    MOZ_COUNT_CTOR(nsDisplayEffectsBase);
+  }
+
+  MOZ_COUNTED_DTOR_OVERRIDE(nsDisplayEffectsBase)
+
+  nsRegion GetOpaqueRegion(nsDisplayListBuilder* aBuilder,
+                           bool* aSnap) const override;
+  void HitTest(nsDisplayListBuilder* aBuilder, const nsRect& aRect,
+               HitTestState* aState, nsTArray<nsIFrame*>* aOutFrames) override;
+
+  bool ShouldFlattenAway(nsDisplayListBuilder* aBuilder) override {
+    return false;
+  }
+
+  gfxRect BBoxInUserSpace() const;
+  gfxPoint UserSpaceOffset() const;
+
+  void ComputeInvalidationRegion(nsDisplayListBuilder* aBuilder,
+                                 const nsDisplayItemGeometry* aGeometry,
+                                 nsRegion* aInvalidRegion) const override;
+
+ protected:
+  bool ValidateSVGFrame();
+
+  // relative to mFrame
+  nsRect mEffectsBounds;
+};
+
+/**
+ * A display item to paint a stacking context with 'mask' and 'clip-path'
+ * effects set by the stacking context root frame's style.  The 'mask' and
+ * 'clip-path' properties may both contain multiple masks and clip paths,
+ * respectively.
+ *
+ * Note that 'mask' and 'clip-path' may just contain CSS simple-images and CSS
+ * basic shapes, respectively.  That is, they don't necessarily reference
+ * resources such as SVG 'mask' and 'clipPath' elements.
+ */
+class nsDisplayMasksAndClipPaths : public nsDisplayEffectsBase {
+ public:
+  nsDisplayMasksAndClipPaths(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                             nsDisplayList* aList,
+                             const ActiveScrolledRoot* aActiveScrolledRoot,
+                             bool aWrapsBackdropFilter);
+  nsDisplayMasksAndClipPaths(nsDisplayListBuilder* aBuilder,
+                             const nsDisplayMasksAndClipPaths& aOther)
+      : nsDisplayEffectsBase(aBuilder, aOther),
+        mDestRects(aOther.mDestRects.Clone()),
+        mWrapsBackdropFilter(aOther.mWrapsBackdropFilter) {
+    MOZ_COUNT_CTOR(nsDisplayMasksAndClipPaths);
+  }
+
+  MOZ_COUNTED_DTOR_OVERRIDE(nsDisplayMasksAndClipPaths)
+
+  NS_DISPLAY_DECL_NAME("Mask", TYPE_MASK)
+
+  bool CanMerge(const nsDisplayItem* aItem) const override;
+
+  void Merge(const nsDisplayItem* aItem) override {
+    nsDisplayWrapList::Merge(aItem);
+
+    const nsDisplayMasksAndClipPaths* other =
+        static_cast<const nsDisplayMasksAndClipPaths*>(aItem);
+    mEffectsBounds.UnionRect(
+        mEffectsBounds,
+        other->mEffectsBounds + other->mFrame->GetOffsetTo(mFrame));
+  }
+
+  void Paint(nsDisplayListBuilder* aBuilder, gfxContext* aCtx) override;
+
+  nsDisplayItemGeometry* AllocateGeometry(
+      nsDisplayListBuilder* aBuilder) override {
+    return new nsDisplayMasksAndClipPathsGeometry(this, aBuilder);
+  }
+
+  void ComputeInvalidationRegion(nsDisplayListBuilder* aBuilder,
+                                 const nsDisplayItemGeometry* aGeometry,
+                                 nsRegion* aInvalidRegion) const override;
+#ifdef MOZ_DUMP_PAINTING
+  void PrintEffects(nsACString& aTo);
+#endif
+
+  bool IsValidMask();
+
+  void PaintWithContentsPaintCallback(
+      nsDisplayListBuilder* aBuilder, gfxContext* aCtx,
+      const std::function<void()>& aPaintChildren);
+
+  /*
+   * Paint mask onto aMaskContext in mFrame's coordinate space and
+   * return whether the mask layer was painted successfully.
+   */
+  bool PaintMask(nsDisplayListBuilder* aBuilder, gfxContext* aMaskContext,
+                 bool aHandleOpacity, bool* aMaskPainted = nullptr);
+
+  const nsTArray<nsRect>& GetDestRects() { return mDestRects; }
+
+  bool CreateWebRenderCommands(
+      wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+      const StackingContextHelper& aSc,
+      layers::RenderRootStateManager* aManager,
+      nsDisplayListBuilder* aDisplayListBuilder) override;
+
+  Maybe<nsRect> GetClipWithRespectToASR(
+      nsDisplayListBuilder* aBuilder,
+      const ActiveScrolledRoot* aASR) const override;
+
+  bool CreatesStackingContextHelper() override { return true; }
+
+ private:
+  NS_DISPLAY_ALLOW_CLONING()
+
+  nsTArray<nsRect> mDestRects;
+  bool mWrapsBackdropFilter;
+};
+
+class nsDisplayBackdropFilters : public nsDisplayWrapList {
+ public:
+  nsDisplayBackdropFilters(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                           nsDisplayList* aList, const nsRect& aBackdropRect,
+                           nsIFrame* aStyleFrame)
+      : nsDisplayWrapList(aBuilder, aFrame, aList),
+        mStyle(aFrame == aStyleFrame ? nullptr : aStyleFrame->Style()),
+        mBackdropRect(aBackdropRect) {
+    MOZ_COUNT_CTOR(nsDisplayBackdropFilters);
+  }
+
+  MOZ_COUNTED_DTOR_OVERRIDE(nsDisplayBackdropFilters)
+
+  NS_DISPLAY_DECL_NAME("BackdropFilter", TYPE_BACKDROP_FILTER)
+
+  bool CreateWebRenderCommands(
+      wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+      const StackingContextHelper& aSc,
+      layers::RenderRootStateManager* aManager,
+      nsDisplayListBuilder* aDisplayListBuilder) override;
+  void Paint(nsDisplayListBuilder* aBuilder, gfxContext* aCtx) override;
+
+  bool ShouldFlattenAway(nsDisplayListBuilder* aBuilder) override {
+    return !aBuilder->IsPaintingForWebRender();
+  }
+
+  bool CreatesStackingContextHelper() override { return true; }
+
+  nsRect GetBounds(nsDisplayListBuilder* aBuilder, bool* aSnap) const override;
+
+ private:
+  RefPtr<ComputedStyle> mStyle;
+  nsRect mBackdropRect;
+};
+
+/**
+ * A display item to paint a stacking context with filter effects set by the
+ * stacking context root frame's style.
+ *
+ * Note that the filters may just be simple CSS filter functions.  That is,
+ * they won't necessarily be references to SVG 'filter' elements.
+ */
+class nsDisplayFilters : public nsDisplayEffectsBase {
+ public:
+  nsDisplayFilters(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                   nsDisplayList* aList, nsIFrame* aStyleFrame,
+                   bool aWrapsBackdropFilter);
+
+  nsDisplayFilters(nsDisplayListBuilder* aBuilder,
+                   const nsDisplayFilters& aOther)
+      : nsDisplayEffectsBase(aBuilder, aOther),
+        mStyle(aOther.mStyle),
+        mEffectsBounds(aOther.mEffectsBounds),
+        mWrapsBackdropFilter(aOther.mWrapsBackdropFilter) {
+    MOZ_COUNT_CTOR(nsDisplayFilters);
+  }
+
+  MOZ_COUNTED_DTOR_OVERRIDE(nsDisplayFilters)
+
+  NS_DISPLAY_DECL_NAME("Filter", TYPE_FILTER)
+
+  bool CanMerge(const nsDisplayItem* aItem) const override {
+    // Items for the same content element should be merged into a single
+    // compositing group.
+    return HasDifferentFrame(aItem) && HasSameTypeAndClip(aItem) &&
+           HasSameContent(aItem);
+  }
+
+  void Merge(const nsDisplayItem* aItem) override {
+    nsDisplayWrapList::Merge(aItem);
+
+    const nsDisplayFilters* other = static_cast<const nsDisplayFilters*>(aItem);
+    mEffectsBounds.UnionRect(
+        mEffectsBounds,
+        other->mEffectsBounds + other->mFrame->GetOffsetTo(mFrame));
+  }
+
+  void Paint(nsDisplayListBuilder* aBuilder, gfxContext* aCtx) override;
+
+  nsRect GetBounds(nsDisplayListBuilder* aBuilder, bool* aSnap) const override {
+    *aSnap = false;
+    return mEffectsBounds + ToReferenceFrame();
+  }
+
+  nsDisplayItemGeometry* AllocateGeometry(
+      nsDisplayListBuilder* aBuilder) override {
+    return new nsDisplaySVGEffectGeometry(this, aBuilder);
+  }
+
+#ifdef MOZ_DUMP_PAINTING
+  void PrintEffects(nsACString& aTo);
+#endif
+
+  void PaintWithContentsPaintCallback(
+      nsDisplayListBuilder* aBuilder, gfxContext* aCtx,
+      const std::function<void(gfxContext* aContext)>& aPaintChildren);
+
+  bool CreateWebRenderCommands(
+      wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+      const StackingContextHelper& aSc,
+      layers::RenderRootStateManager* aManager,
+      nsDisplayListBuilder* aDisplayListBuilder) override;
+  bool CanCreateWebRenderCommands() const;
+
+  bool CanApplyOpacity(WebRenderLayerManager* aManager,
+                       nsDisplayListBuilder* aBuilder) const override {
+    return CanCreateWebRenderCommands();
+  }
+
+  bool CreatesStackingContextHelper() override { return true; }
+
+ private:
+  NS_DISPLAY_ALLOW_CLONING()
+
+  RefPtr<ComputedStyle> mStyle;
+  // relative to mFrame
+  nsRect mEffectsBounds;
+  nsRect mVisibleRect;
+  bool mWrapsBackdropFilter;
+};
+
+/* A display item that applies a transformation to all of its descendant
+ * elements.  This wrapper should only be used if there is a transform applied
+ * to the root element.
+ *
+ * The reason that a "bounds" rect is involved in transform calculations is
+ * because CSS-transforms allow percentage values for the x and y components
+ * of <translation-value>s, where percentages are percentages of the element's
+ * border box.
+ *
+ * INVARIANT: The wrapped frame is transformed or we supplied a transform getter
+ * function.
+ * INVARIANT: The wrapped frame is non-null.
+ */
+class nsDisplayTransform : public nsPaintedDisplayItem {
+  using Matrix4x4 = gfx::Matrix4x4;
+  using Matrix4x4Flagged = gfx::Matrix4x4Flagged;
+  using TransformReferenceBox = nsStyleTransformMatrix::TransformReferenceBox;
+
+ public:
+  enum class PrerenderDecision : uint8_t { No, Full, Partial };
+
+  enum {
+    WithTransformGetter,
+  };
+
+  /* Constructor accepts a display list, empties it, and wraps it up.  It also
+   * ferries the underlying frame to the nsDisplayItem constructor.
+   */
+  nsDisplayTransform(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                     nsDisplayList* aList, const nsRect& aChildrenBuildingRect);
+
+  nsDisplayTransform(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                     nsDisplayList* aList, const nsRect& aChildrenBuildingRect,
+                     PrerenderDecision aPrerenderDecision);
+
+  nsDisplayTransform(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                     nsDisplayList* aList, const nsRect& aChildrenBuildingRect,
+                     decltype(WithTransformGetter));
+
+  MOZ_COUNTED_DTOR_OVERRIDE(nsDisplayTransform)
+
+  NS_DISPLAY_DECL_NAME("nsDisplayTransform", TYPE_TRANSFORM)
+
+  void UpdateBounds(nsDisplayListBuilder* aBuilder) override;
+
+  /**
+   * This function updates bounds for items with a frame establishing
+   * 3D rendering context.
+   */
+  void UpdateBoundsFor3D(nsDisplayListBuilder* aBuilder);
+
+  void DoUpdateBoundsPreserves3D(nsDisplayListBuilder* aBuilder) override;
+
+  void Destroy(nsDisplayListBuilder* aBuilder) override {
+    GetChildren()->DeleteAll(aBuilder);
+    nsPaintedDisplayItem::Destroy(aBuilder);
+  }
+
+  nsRect GetComponentAlphaBounds(nsDisplayListBuilder* aBuilder) const override;
+
+  RetainedDisplayList* GetChildren() const override { return &mChildren; }
+
+  nsRect GetUntransformedBounds(nsDisplayListBuilder* aBuilder,
+                                bool* aSnap) const override {
+    *aSnap = false;
+    return mChildBounds;
+  }
+
+  const nsRect& GetUntransformedPaintRect() const override {
+    return mChildrenBuildingRect;
+  }
+
+  bool ShouldFlattenAway(nsDisplayListBuilder* aBuilder) override;
+
+  void HitTest(nsDisplayListBuilder* aBuilder, const nsRect& aRect,
+               HitTestState* aState, nsTArray<nsIFrame*>* aOutFrames) override;
+  nsRect GetBounds(nsDisplayListBuilder* aBuilder, bool* aSnap) const override;
+  nsRegion GetOpaqueRegion(nsDisplayListBuilder* aBuilder,
+                           bool* aSnap) const override;
+  void Paint(nsDisplayListBuilder* aBuilder, gfxContext* aCtx) override;
+  void Paint(nsDisplayListBuilder* aBuilder, gfxContext* aCtx,
+             const Maybe<gfx::Polygon>& aPolygon);
+  bool CreateWebRenderCommands(
+      wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+      const StackingContextHelper& aSc,
+      layers::RenderRootStateManager* aManager,
+      nsDisplayListBuilder* aDisplayListBuilder) override;
+  bool UpdateScrollData(layers::WebRenderScrollData* aData,
+                        layers::WebRenderLayerScrollData* aLayerData) override;
+
+  nsDisplayItemGeometry* AllocateGeometry(
+      nsDisplayListBuilder* aBuilder) override {
+    return new nsDisplayTransformGeometry(
+        this, aBuilder, GetTransformForRendering(),
+        mFrame->PresContext()->AppUnitsPerDevPixel());
+  }
+
+  void ComputeInvalidationRegion(nsDisplayListBuilder* aBuilder,
+                                 const nsDisplayItemGeometry* aGeometry,
+                                 nsRegion* aInvalidRegion) const override {
+    const nsDisplayTransformGeometry* geometry =
+        static_cast<const nsDisplayTransformGeometry*>(aGeometry);
+
+    // This code is only called for flattened, inactive transform items.
+    // Only check if the transform has changed. The bounds invalidation should
+    // be handled by the children themselves.
+    if (!geometry->mTransform.FuzzyEqual(GetTransformForRendering())) {
+      bool snap;
+      aInvalidRegion->Or(GetBounds(aBuilder, &snap), geometry->mBounds);
+    }
+  }
+
+  const nsIFrame* ReferenceFrameForChildren() const override {
+    // If we were created using a transform-getter, then we don't
+    // belong to a transformed frame, and aren't a reference frame
+    // for our children.
+    if (!mHasTransformGetter) {
+      return mFrame;
+    }
+    return nsPaintedDisplayItem::ReferenceFrameForChildren();
+  }
+
+  const nsRect& GetBuildingRectForChildren() const override {
+    return mChildrenBuildingRect;
+  }
+
+  enum { INDEX_MAX = UINT32_MAX >> TYPE_BITS };
+
+  /**
+   * We include the perspective matrix from our containing block for the
+   * purposes of visibility calculations, but we exclude it from the transform
+   * we set on the layer (for rendering), since there will be an
+   * nsDisplayPerspective created for that.
+   */
+  const Matrix4x4Flagged& GetTransform() const;
+  const Matrix4x4Flagged& GetInverseTransform() const;
+
+  bool ShouldSkipTransform(nsDisplayListBuilder* aBuilder) const;
+  Matrix4x4 GetTransformForRendering(
+      LayoutDevicePoint* aOutOrigin = nullptr) const;
+
+  /**
+   * Return the transform that is aggregation of all transform on the
+   * preserves3d chain.
+   */
+  const Matrix4x4& GetAccumulatedPreserved3DTransform(
+      nsDisplayListBuilder* aBuilder);
+
+  float GetHitDepthAtPoint(nsDisplayListBuilder* aBuilder,
+                           const nsPoint& aPoint);
+  /**
+   * TransformRect takes in as parameters a rectangle (in aFrame's coordinate
+   * space) and returns the smallest rectangle (in aFrame's coordinate space)
+   * containing the transformed image of that rectangle.  That is, it takes
+   * the four corners of the rectangle, transforms them according to the
+   * matrix associated with the specified frame, then returns the smallest
+   * rectangle containing the four transformed points.
+   *
+   * @param untransformedBounds The rectangle (in app units) to transform.
+   * @param aFrame The frame whose transformation should be applied.  This
+   *        function raises an assertion if aFrame is null or doesn't have a
+   *        transform applied to it.
+   * @param aRefBox the reference box to use, which would usually be just
+   *        TransformReferemceBox(aFrame), but callers may override it if
+   *        needed.
+   */
+  static nsRect TransformRect(const nsRect& aUntransformedBounds,
+                              const nsIFrame* aFrame,
+                              TransformReferenceBox& aRefBox);
+
+  /* UntransformRect is like TransformRect, except that it inverts the
+   * transform.
+   */
+  static bool UntransformRect(const nsRect& aTransformedBounds,
+                              const nsRect& aChildBounds,
+                              const nsIFrame* aFrame, nsRect* aOutRect);
+  static bool UntransformRect(const nsRect& aTransformedBounds,
+                              const nsRect& aChildBounds,
+                              const Matrix4x4& aMatrix, float aAppUnitsPerPixel,
+                              nsRect* aOutRect);
+
+  bool UntransformRect(nsDisplayListBuilder* aBuilder, const nsRect& aRect,
+                       nsRect* aOutRect) const;
+
+  bool UntransformBuildingRect(nsDisplayListBuilder* aBuilder,
+                               nsRect* aOutRect) const {
+    return UntransformRect(aBuilder, GetBuildingRect(), aOutRect);
+  }
+
+  static gfx::Point3D GetDeltaToTransformOrigin(const nsIFrame* aFrame,
+                                                TransformReferenceBox&,
+                                                float aAppUnitsPerPixel);
+
+  /*
+   * Returns true if aFrame has perspective applied from its containing
+   * block.
+   * Returns the matrix to append to apply the persective (taking
+   * perspective-origin into account), relative to aFrames coordinate
+   * space).
+   * aOutMatrix is assumed to be the identity matrix, and isn't explicitly
+   * cleared.
+   */
+  static bool ComputePerspectiveMatrix(const nsIFrame* aFrame,
+                                       float aAppUnitsPerPixel,
+                                       Matrix4x4& aOutMatrix);
+
+  struct MOZ_STACK_CLASS FrameTransformProperties {
+    FrameTransformProperties(const nsIFrame* aFrame,
+                             TransformReferenceBox& aRefBox,
+                             float aAppUnitsPerPixel);
+    FrameTransformProperties(const StyleTranslate& aTranslate,
+                             const StyleRotate& aRotate,
+                             const StyleScale& aScale,
+                             const StyleTransform& aTransform,
+                             const Maybe<ResolvedMotionPathData>& aMotion,
+                             const gfx::Point3D& aToTransformOrigin)
+        : mFrame(nullptr),
+          mTranslate(aTranslate),
+          mRotate(aRotate),
+          mScale(aScale),
+          mTransform(aTransform),
+          mMotion(aMotion),
+          mToTransformOrigin(aToTransformOrigin) {}
+
+    bool HasTransform() const {
+      return !mTranslate.IsNone() || !mRotate.IsNone() || !mScale.IsNone() ||
+             !mTransform.IsNone() || mMotion.isSome();
+    }
+
+    const nsIFrame* mFrame;
+    const StyleTranslate& mTranslate;
+    const StyleRotate& mRotate;
+    const StyleScale& mScale;
+    const StyleTransform& mTransform;
+    const Maybe<ResolvedMotionPathData> mMotion;
+    const gfx::Point3D mToTransformOrigin;
+  };
+
+  /**
+   * Given a frame with the transform property or an SVG transform,
+   * returns the transformation matrix for that frame.
+   *
+   * @param aFrame The frame to get the matrix from.
+   * @param aOrigin Relative to which point this transform should be applied.
+   * @param aAppUnitsPerPixel The number of app units per graphics unit.
+   * @param aBoundsOverride [optional] If this is nullptr (the default), the
+   *        computation will use the value of TransformReferenceBox(aFrame).
+   *        Otherwise, it will use the value of aBoundsOverride.  This is
+   *        mostly for internal use and in most cases you will not need to
+   *        specify a value.
+   * @param aFlags OFFSET_BY_ORIGIN The resulting matrix will be translated
+   *        by aOrigin. This translation is applied *before* the CSS transform.
+   * @param aFlags INCLUDE_PRESERVE3D_ANCESTORS The computed transform will
+   *        include the transform of any ancestors participating in the same
+   *        3d rendering context.
+   * @param aFlags INCLUDE_PERSPECTIVE The resulting matrix will include the
+   *        perspective transform from the containing block if applicable.
+   */
+  enum {
+    OFFSET_BY_ORIGIN = 1 << 0,
+    INCLUDE_PRESERVE3D_ANCESTORS = 1 << 1,
+    INCLUDE_PERSPECTIVE = 1 << 2,
+  };
+  static constexpr uint32_t kTransformRectFlags =
+      INCLUDE_PERSPECTIVE | OFFSET_BY_ORIGIN | INCLUDE_PRESERVE3D_ANCESTORS;
+  static Matrix4x4 GetResultingTransformMatrix(const nsIFrame* aFrame,
+                                               const nsPoint& aOrigin,
+                                               float aAppUnitsPerPixel,
+                                               uint32_t aFlags);
+  static Matrix4x4 GetResultingTransformMatrix(
+      const FrameTransformProperties& aProperties, TransformReferenceBox&,
+      float aAppUnitsPerPixel);
+
+  struct PrerenderInfo {
+    bool CanUseAsyncAnimations() const {
+      return mDecision != PrerenderDecision::No && mHasAnimations;
+    }
+    PrerenderDecision mDecision = PrerenderDecision::No;
+    bool mHasAnimations = true;
+  };
+  /**
+   * Decide whether we should prerender some or all of the contents of the
+   * transformed frame even when it's not completely visible (yet).
+   * Return PrerenderDecision::Full if the entire contents should be
+   * prerendered, PrerenderDecision::Partial if some but not all of the
+   * contents should be prerendered, or PrerenderDecision::No if only the
+   * visible area should be rendered.
+   * |mNoAffectDecisionInPreserve3D| is set if the prerender decision should not
+   * affect the decision on other frames in the preserve 3d tree.
+   * |aDirtyRect| is updated to the area that should be prerendered.
+   */
+  static PrerenderInfo ShouldPrerenderTransformedContent(
+      nsDisplayListBuilder* aBuilder, nsIFrame* aFrame, nsRect* aDirtyRect);
+
+  bool CanUseAsyncAnimations(nsDisplayListBuilder* aBuilder) override;
+
+  bool MayBeAnimated(nsDisplayListBuilder* aBuilder) const;
+
+  void WriteDebugInfo(std::stringstream& aStream) override;
+
+  bool CanMoveAsync() override {
+    return EffectCompositor::HasAnimationsForCompositor(
+        mFrame, DisplayItemType::TYPE_TRANSFORM);
+  }
+
+  /**
+   * This item is an additional item as the boundary between parent
+   * and child 3D rendering context.
+   * \see nsIFrame::BuildDisplayListForStackingContext().
+   */
+  bool IsTransformSeparator() const { return mIsTransformSeparator; }
+  /**
+   * This item is the boundary between parent and child 3D rendering
+   * context.
+   */
+  bool IsLeafOf3DContext() const {
+    return (IsTransformSeparator() ||
+            (!mFrame->Extend3DContext() && Combines3DTransformWithAncestors()));
+  }
+  /**
+   * The backing frame of this item participates a 3D rendering
+   * context.
+   */
+  bool IsParticipating3DContext() const {
+    return mFrame->Extend3DContext() || Combines3DTransformWithAncestors();
+  }
+
+  bool IsPartialPrerender() const {
+    return mPrerenderDecision == PrerenderDecision::Partial;
+  }
+
+  /**
+   * Mark this item as created together with `nsDisplayPerspective`.
+   * \see nsIFrame::BuildDisplayListForStackingContext().
+   */
+  void MarkWithAssociatedPerspective() { mHasAssociatedPerspective = true; }
+
+  void AddSizeOfExcludingThis(nsWindowSizes&) const override;
+
+  bool CreatesStackingContextHelper() override { return true; }
+
+ private:
+  void ComputeBounds(nsDisplayListBuilder* aBuilder);
+  nsRect TransformUntransformedBounds(nsDisplayListBuilder* aBuilder,
+                                      const Matrix4x4Flagged& aMatrix) const;
+  void UpdateUntransformedBounds(nsDisplayListBuilder* aBuilder);
+
+  void SetReferenceFrameToAncestor(nsDisplayListBuilder* aBuilder);
+  void Init(nsDisplayListBuilder* aBuilder, nsDisplayList* aChildren);
+
+  static Matrix4x4 GetResultingTransformMatrixInternal(
+      const FrameTransformProperties& aProperties,
+      TransformReferenceBox& aRefBox, const nsPoint& aOrigin,
+      float aAppUnitsPerPixel, uint32_t aFlags);
+
+  void Collect3DTransformLeaves(nsDisplayListBuilder* aBuilder,
+                                nsTArray<nsDisplayTransform*>& aLeaves);
+  using TransformPolygon = layers::BSPPolygon<nsDisplayTransform>;
+  void CollectSorted3DTransformLeaves(nsDisplayListBuilder* aBuilder,
+                                      nsTArray<TransformPolygon>& aLeaves);
+
+  mutable RetainedDisplayList mChildren;
+  mutable Maybe<Matrix4x4Flagged> mTransform;
+  mutable Maybe<Matrix4x4Flagged> mInverseTransform;
+  // Accumulated transform of ancestors on the preserves-3d chain.
+  UniquePtr<Matrix4x4> mTransformPreserves3D;
+  nsRect mChildrenBuildingRect;
+
+  // The untransformed bounds of |mChildren|.
+  nsRect mChildBounds;
+  // The transformed bounds of this display item.
+  nsRect mBounds;
+  PrerenderDecision mPrerenderDecision : 8;
+  // This item is a separator between 3D rendering contexts, and
+  // mTransform have been presetted by the constructor.
+  // This also forces us not to extend the 3D context.  Since we don't create a
+  // transform item, a container layer, for every frame in a preserves3d
+  // context, the transform items of a child preserves3d context may extend the
+  // parent context unintendedly if the root of the child preserves3d context
+  // doesn't create a transform item.
+  bool mIsTransformSeparator : 1;
+  // True if we have a transform getter.
+  bool mHasTransformGetter : 1;
+  // True if this item is created together with `nsDisplayPerspective`
+  // from the same CSS stacking context.
+  bool mHasAssociatedPerspective : 1;
+};
+
+/* A display item that applies a perspective transformation to a single
+ * nsDisplayTransform child item. We keep this as a separate item since the
+ * perspective-origin is relative to an ancestor of the transformed frame, and
+ * APZ can scroll the child separately.
+ */
+class nsDisplayPerspective : public nsPaintedDisplayItem {
+ public:
+  nsDisplayPerspective(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                       nsDisplayList* aList);
+  ~nsDisplayPerspective() override = default;
+
+  NS_DISPLAY_DECL_NAME("nsDisplayPerspective", TYPE_PERSPECTIVE)
+
+  void Destroy(nsDisplayListBuilder* aBuilder) override {
+    mList.DeleteAll(aBuilder);
+    nsPaintedDisplayItem::Destroy(aBuilder);
+  }
+
+  void HitTest(nsDisplayListBuilder* aBuilder, const nsRect& aRect,
+               HitTestState* aState, nsTArray<nsIFrame*>* aOutFrames) override {
+    return GetChildren()->HitTest(aBuilder, aRect, aState, aOutFrames);
+  }
+
+  nsRect GetBounds(nsDisplayListBuilder* aBuilder, bool* aSnap) const override {
+    *aSnap = false;
+    return GetChildren()->GetClippedBoundsWithRespectToASR(aBuilder,
+                                                           mActiveScrolledRoot);
+  }
+
+  void ComputeInvalidationRegion(nsDisplayListBuilder* aBuilder,
+                                 const nsDisplayItemGeometry* aGeometry,
+                                 nsRegion* aInvalidRegion) const override {}
+
+  nsRegion GetOpaqueRegion(nsDisplayListBuilder* aBuilder,
+                           bool* aSnap) const override;
+
+  bool CreateWebRenderCommands(
+      wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+      const StackingContextHelper& aSc,
+      layers::RenderRootStateManager* aManager,
+      nsDisplayListBuilder* aDisplayListBuilder) override;
+
+  void Paint(nsDisplayListBuilder* aBuilder, gfxContext* aCtx) override;
+
+  RetainedDisplayList* GetSameCoordinateSystemChildren() const override {
+    return &mList;
+  }
+
+  RetainedDisplayList* GetChildren() const override { return &mList; }
+
+  nsRect GetComponentAlphaBounds(
+      nsDisplayListBuilder* aBuilder) const override {
+    return GetChildren()->GetComponentAlphaBounds(aBuilder);
+  }
+
+  void DoUpdateBoundsPreserves3D(nsDisplayListBuilder* aBuilder) override {
+    if (GetChildren()->GetTop()) {
+      static_cast<nsDisplayTransform*>(GetChildren()->GetTop())
+          ->DoUpdateBoundsPreserves3D(aBuilder);
+    }
+  }
+
+  bool CreatesStackingContextHelper() override { return true; }
+
+ private:
+  mutable RetainedDisplayList mList;
+};
+
+class nsDisplayTextGeometry;
+
+/**
+ * This class adds basic support for limiting the rendering (in the inline axis
+ * of the writing mode) to the part inside the specified edges.
+ * The two members, mVisIStartEdge and mVisIEndEdge, are relative to the edges
+ * of the frame's scrollable overflow rectangle and are the amount to suppress
+ * on each side.
+ *
+ * Setting none, both or only one edge is allowed.
+ * The values must be non-negative.
+ * The default value for both edges is zero, which means everything is painted.
+ */
+class nsDisplayText final : public nsPaintedDisplayItem {
+ public:
+  nsDisplayText(nsDisplayListBuilder* aBuilder, nsTextFrame* aFrame);
+  MOZ_COUNTED_DTOR_OVERRIDE(nsDisplayText)
+
+  NS_DISPLAY_DECL_NAME("Text", TYPE_TEXT)
+
+  nsRect GetBounds(nsDisplayListBuilder* aBuilder, bool* aSnap) const final {
+    *aSnap = false;
+    return mBounds;
+  }
+
+  void HitTest(nsDisplayListBuilder* aBuilder, const nsRect& aRect,
+               HitTestState* aState, nsTArray<nsIFrame*>* aOutFrames) final {
+    if (nsRect(ToReferenceFrame(), mFrame->GetSize()).Intersects(aRect)) {
+      aOutFrames->AppendElement(mFrame);
+    }
+  }
+
+  bool CreateWebRenderCommands(wr::DisplayListBuilder& aBuilder,
+                               wr::IpcResourceUpdateQueue& aResources,
+                               const StackingContextHelper& aSc,
+                               layers::RenderRootStateManager* aManager,
+                               nsDisplayListBuilder* aDisplayListBuilder) final;
+  void Paint(nsDisplayListBuilder* aBuilder, gfxContext* aCtx) final;
+
+  nsRect GetComponentAlphaBounds(nsDisplayListBuilder* aBuilder) const final {
+    if (gfxPlatform::GetPlatform()->RespectsFontStyleSmoothing()) {
+      // On OS X, web authors can turn off subpixel text rendering using the
+      // CSS property -moz-osx-font-smoothing. If they do that, we don't need
+      // to use component alpha layers for the affected text.
+      if (mFrame->StyleFont()->mFont.smoothing == NS_FONT_SMOOTHING_GRAYSCALE) {
+        return nsRect();
+      }
+    }
+    bool snap;
+    return GetBounds(aBuilder, &snap);
+  }
+
+  nsDisplayItemGeometry* AllocateGeometry(nsDisplayListBuilder* aBuilder) final;
+
+  void ComputeInvalidationRegion(nsDisplayListBuilder* aBuilder,
+                                 const nsDisplayItemGeometry* aGeometry,
+                                 nsRegion* aInvalidRegion) const final;
+
+  void RenderToContext(gfxContext* aCtx, nsDisplayListBuilder* aBuilder,
+                       const nsRect& aVisibleRect, float aOpacity = 1.0f,
+                       bool aIsRecording = false);
+
+  bool CanApplyOpacity(WebRenderLayerManager* aManager,
+                       nsDisplayListBuilder* aBuilder) const final;
+
+  void WriteDebugInfo(std::stringstream& aStream) final;
+
+  static nsDisplayText* CheckCast(nsDisplayItem* aItem) {
+    return (aItem->GetType() == DisplayItemType::TYPE_TEXT)
+               ? static_cast<nsDisplayText*>(aItem)
+               : nullptr;
+  }
+
+  nscoord& VisIStartEdge() { return mVisIStartEdge; }
+  nscoord& VisIEndEdge() { return mVisIEndEdge; }
+
+ private:
+  nsRect mBounds;
+  nsRect mVisibleRect;
+
+  // Lengths measured from the visual inline start and end sides
+  // (i.e. left and right respectively in horizontal writing modes,
+  // regardless of bidi directionality; top and bottom in vertical modes).
+  nscoord mVisIStartEdge;
+  nscoord mVisIEndEdge;
+};
+
+/**
+ * A display item that for webrender to handle SVG
+ */
+class nsDisplaySVGWrapper : public nsDisplayWrapList {
+ public:
+  nsDisplaySVGWrapper(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                      nsDisplayList* aList);
+
+  MOZ_COUNTED_DTOR_OVERRIDE(nsDisplaySVGWrapper)
+
+  NS_DISPLAY_DECL_NAME("SVGWrapper", TYPE_SVG_WRAPPER)
+
+  void Paint(nsDisplayListBuilder* aBuilder, gfxContext* aCtx) override {
+    GetChildren()->Paint(aBuilder, aCtx,
+                         mFrame->PresContext()->AppUnitsPerDevPixel());
+  }
+  bool ShouldFlattenAway(nsDisplayListBuilder* aBuilder) override;
+  bool CreateWebRenderCommands(
+      wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+      const StackingContextHelper& aSc,
+      layers::RenderRootStateManager* aManager,
+      nsDisplayListBuilder* aDisplayListBuilder) override;
+};
+
+/**
+ * A display item for webrender to handle SVG foreign object
+ */
+class nsDisplayForeignObject : public nsDisplayWrapList {
+ public:
+  nsDisplayForeignObject(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                         nsDisplayList* aList);
+#ifdef NS_BUILD_REFCNT_LOGGING
+  virtual ~nsDisplayForeignObject();
+#endif
+
+  NS_DISPLAY_DECL_NAME("ForeignObject", TYPE_FOREIGN_OBJECT)
+
+  virtual bool ShouldFlattenAway(nsDisplayListBuilder* aBuilder) override;
+  void Paint(nsDisplayListBuilder* aBuilder, gfxContext* aCtx) override {
+    GetChildren()->Paint(aBuilder, aCtx,
+                         mFrame->PresContext()->AppUnitsPerDevPixel());
+  }
+
+  bool CreateWebRenderCommands(
+      wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
+      const StackingContextHelper& aSc,
+      layers::RenderRootStateManager* aManager,
+      nsDisplayListBuilder* aDisplayListBuilder) override;
+};
+
+/**
+ * A display item to represent a hyperlink.
+ */
+class nsDisplayLink : public nsPaintedDisplayItem {
+ public:
+  nsDisplayLink(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                const char* aLinkSpec, const nsRect& aRect)
+      : nsPaintedDisplayItem(aBuilder, aFrame),
+        mLinkSpec(aLinkSpec),
+        mRect(aRect) {}
+
+  NS_DISPLAY_DECL_NAME("Link", TYPE_LINK)
+
+  void Paint(nsDisplayListBuilder* aBuilder, gfxContext* aCtx) override;
+
+ private:
+  nsCString mLinkSpec;
+  nsRect mRect;
+};
+
+/**
+ * A display item to represent a destination within the document.
+ */
+class nsDisplayDestination : public nsPaintedDisplayItem {
+ public:
+  nsDisplayDestination(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                       const char* aDestinationName, const nsPoint& aPosition)
+      : nsPaintedDisplayItem(aBuilder, aFrame),
+        mDestinationName(aDestinationName),
+        mPosition(aPosition) {}
+
+  NS_DISPLAY_DECL_NAME("Destination", TYPE_DESTINATION)
+
+  void Paint(nsDisplayListBuilder* aBuilder, gfxContext* aCtx) override;
+
+ private:
+  nsCString mDestinationName;
+  nsPoint mPosition;
+};
+
+class FlattenedDisplayListIterator {
+ public:
+  FlattenedDisplayListIterator(nsDisplayListBuilder* aBuilder,
+                               nsDisplayList* aList)
+      : mBuilder(aBuilder), mStart(aList->begin()), mEnd(aList->end()) {
+    ResolveFlattening();
+  }
+
+  bool HasNext() const { return !AtEndOfCurrentList(); }
+
+  nsDisplayItem* GetNextItem() {
+    MOZ_ASSERT(HasNext());
+
+    nsDisplayItem* current = NextItem();
+    Advance();
+
+    if (!AtEndOfCurrentList() && current->CanMerge(NextItem())) {
+      // Since we can merge at least two display items, create an array and
+      // collect mergeable display items there.
+      AutoTArray<nsDisplayItem*, 2> willMerge{current};
+
+      auto it = mStart;
+      while (it != mEnd) {
+        nsDisplayItem* next = *it;
+        if (current->CanMerge(next)) {
+          willMerge.AppendElement(next);
+          ++it;
+        } else {
+          break;
+        }
+      }
+      mStart = it;
+
+      current = mBuilder->MergeItems(willMerge);
+    }
+
+    ResolveFlattening();
+    return current;
+  }
+
+ protected:
+  void Advance() { ++mStart; }
+
+  bool AtEndOfNestedList() const {
+    return AtEndOfCurrentList() && mStack.Length() > 0;
+  }
+
+  bool AtEndOfCurrentList() const { return mStart == mEnd; }
+
+  nsDisplayItem* NextItem() {
+    MOZ_ASSERT(HasNext());
+    return *mStart;
+  }
+
+  bool ShouldFlattenNextItem() {
+    return HasNext() && NextItem()->ShouldFlattenAway(mBuilder);
+  }
+
+  void ResolveFlattening() {
+    // Handle the case where we reach the end of a nested list, or the current
+    // item should start a new nested list. Repeat this until we find an actual
+    // item, or the very end of the outer list.
+    while (AtEndOfNestedList() || ShouldFlattenNextItem()) {
+      if (AtEndOfNestedList()) {
+        // We reached the end of the list, pop the next list from the stack.
+        std::tie(mStart, mEnd) = mStack.PopLastElement();
+      } else {
+        // The next item wants to be flattened. This means that we will skip the
+        // flattened item and directly iterate over its sublist.
+        MOZ_ASSERT(ShouldFlattenNextItem());
+
+        nsDisplayList* sublist = NextItem()->GetChildren();
+        MOZ_ASSERT(sublist);
+
+        // Skip the flattened item.
+        Advance();
+
+        // Store the current position on the stack.
+        if (!AtEndOfCurrentList()) {
+          mStack.AppendElement(std::make_pair(mStart, mEnd));
+        }
+
+        // Iterate over the sublist.
+        mStart = sublist->begin();
+        mEnd = sublist->end();
+      }
+    }
+  }
+
+ private:
+  nsDisplayListBuilder* mBuilder;
+  nsDisplayList::iterator mStart;
+  nsDisplayList::iterator mEnd;
+  nsTArray<std::pair<nsDisplayList::iterator, nsDisplayList::iterator>> mStack;
+};
+
+class PaintTelemetry {
+ public:
+  class AutoRecordPaint {
+   public:
+    AutoRecordPaint();
+    ~AutoRecordPaint();
+
+   private:
+    TimeStamp mStart;
+  };
+
+ private:
+  static uint32_t sPaintLevel;
+};
+
+}  // namespace mozilla
+
+#endif /*NSDISPLAYLIST_H_*/
diff --git a/layout/painting/nsDisplayListArenaTypes.h b/layout/painting/nsDisplayListArenaTypes.h
new file mode 100644
index 0000000000..79d04b298a
--- /dev/null
+++ b/layout/painting/nsDisplayListArenaTypes.h
@@ -0,0 +1,15 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/* a list of all types that can be allocated in the display list's nsPresArena,
+   for preprocessing */
+
+#define DECLARE_DISPLAY_ITEM_TYPE(name_, ...) DISPLAY_LIST_ARENA_OBJECT(name_)
+DISPLAY_LIST_ARENA_OBJECT(UNUSED)  // DisplayItemType::TYPE_ZERO
+#include "nsDisplayItemTypesList.h"
+#undef DECLARE_DISPLAY_ITEM_TYPE
+DISPLAY_LIST_ARENA_OBJECT(CLIPCHAIN)
+DISPLAY_LIST_ARENA_OBJECT(LISTNODE)
diff --git a/layout/painting/nsDisplayListInvalidation.cpp b/layout/painting/nsDisplayListInvalidation.cpp
new file mode 100644
index 0000000000..e5696d14c7
--- /dev/null
+++ b/layout/painting/nsDisplayListInvalidation.cpp
@@ -0,0 +1,124 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsDisplayListInvalidation.h"
+#include "nsDisplayList.h"
+#include "nsIFrame.h"
+#include "nsTableFrame.h"
+
+namespace mozilla {
+
+nsDisplayItemGeometry::nsDisplayItemGeometry(nsDisplayItem* aItem,
+                                             nsDisplayListBuilder* aBuilder) {
+  MOZ_COUNT_CTOR(nsDisplayItemGeometry);
+  bool snap;
+  mBounds = aItem->GetBounds(aBuilder, &snap);
+}
+
+nsDisplayItemGeometry::~nsDisplayItemGeometry() {
+  MOZ_COUNT_DTOR(nsDisplayItemGeometry);
+}
+
+nsDisplayItemGenericGeometry::nsDisplayItemGenericGeometry(
+    nsDisplayItem* aItem, nsDisplayListBuilder* aBuilder)
+    : nsDisplayItemGeometry(aItem, aBuilder),
+      mBorderRect(aItem->GetBorderRect()) {}
+
+bool ShouldSyncDecodeImages(nsDisplayListBuilder* aBuilder) {
+  return aBuilder->ShouldSyncDecodeImages();
+}
+
+nsDisplayItemGeometry* GetPreviousGeometry(nsDisplayItem* aItem) {
+  if (RefPtr<layers::WebRenderFallbackData> data =
+          layers::GetWebRenderUserData<layers::WebRenderFallbackData>(
+              aItem->Frame(), aItem->GetPerFrameKey())) {
+    return data->GetGeometry();
+  }
+  return nullptr;
+}
+
+void nsDisplayItemGenericGeometry::MoveBy(const nsPoint& aOffset) {
+  nsDisplayItemGeometry::MoveBy(aOffset);
+  mBorderRect.MoveBy(aOffset);
+}
+
+nsDisplayItemBoundsGeometry::nsDisplayItemBoundsGeometry(
+    nsDisplayItem* aItem, nsDisplayListBuilder* aBuilder)
+    : nsDisplayItemGeometry(aItem, aBuilder) {
+  nscoord radii[8];
+  mHasRoundedCorners = aItem->Frame()->GetBorderRadii(radii);
+}
+
+nsDisplayBorderGeometry::nsDisplayBorderGeometry(nsDisplayItem* aItem,
+                                                 nsDisplayListBuilder* aBuilder)
+    : nsDisplayItemGeometry(aItem, aBuilder) {}
+
+nsDisplayBackgroundGeometry::nsDisplayBackgroundGeometry(
+    nsDisplayBackgroundImage* aItem, nsDisplayListBuilder* aBuilder)
+    : nsDisplayItemGeometry(aItem, aBuilder),
+      mPositioningArea(aItem->GetPositioningArea()),
+      mDestRect(aItem->GetDestRect()) {}
+
+void nsDisplayBackgroundGeometry::MoveBy(const nsPoint& aOffset) {
+  nsDisplayItemGeometry::MoveBy(aOffset);
+  mPositioningArea.MoveBy(aOffset);
+  mDestRect.MoveBy(aOffset);
+}
+
+nsDisplayThemedBackgroundGeometry::nsDisplayThemedBackgroundGeometry(
+    nsDisplayThemedBackground* aItem, nsDisplayListBuilder* aBuilder)
+    : nsDisplayItemGeometry(aItem, aBuilder),
+      mPositioningArea(aItem->GetPositioningArea()),
+      mWindowIsActive(aItem->IsWindowActive()) {}
+
+void nsDisplayThemedBackgroundGeometry::MoveBy(const nsPoint& aOffset) {
+  nsDisplayItemGeometry::MoveBy(aOffset);
+  mPositioningArea.MoveBy(aOffset);
+}
+
+nsDisplayBoxShadowInnerGeometry::nsDisplayBoxShadowInnerGeometry(
+    nsDisplayItem* aItem, nsDisplayListBuilder* aBuilder)
+    : nsDisplayItemGeometry(aItem, aBuilder),
+      mPaddingRect(aItem->GetPaddingRect()) {}
+
+void nsDisplayBoxShadowInnerGeometry::MoveBy(const nsPoint& aOffset) {
+  nsDisplayItemGeometry::MoveBy(aOffset);
+  mPaddingRect.MoveBy(aOffset);
+}
+
+void nsDisplaySolidColorRegionGeometry::MoveBy(const nsPoint& aOffset) {
+  nsDisplayItemGeometry::MoveBy(aOffset);
+  mRegion.MoveBy(aOffset);
+}
+
+nsDisplaySVGEffectGeometry::nsDisplaySVGEffectGeometry(
+    nsDisplayEffectsBase* aItem, nsDisplayListBuilder* aBuilder)
+    : nsDisplayItemGeometry(aItem, aBuilder),
+      mBBox(aItem->BBoxInUserSpace()),
+      mUserSpaceOffset(aItem->UserSpaceOffset()),
+      mFrameOffsetToReferenceFrame(aItem->ToReferenceFrame()) {}
+
+void nsDisplaySVGEffectGeometry::MoveBy(const nsPoint& aOffset) {
+  mBounds.MoveBy(aOffset);
+  mFrameOffsetToReferenceFrame += aOffset;
+}
+
+nsDisplayMasksAndClipPathsGeometry::nsDisplayMasksAndClipPathsGeometry(
+    nsDisplayMasksAndClipPaths* aItem, nsDisplayListBuilder* aBuilder)
+    : nsDisplaySVGEffectGeometry(aItem, aBuilder),
+      mDestRects(aItem->GetDestRects().Clone()) {}
+
+nsDisplayFiltersGeometry::nsDisplayFiltersGeometry(
+    nsDisplayFilters* aItem, nsDisplayListBuilder* aBuilder)
+    : nsDisplaySVGEffectGeometry(aItem, aBuilder) {}
+
+nsDisplayTableItemGeometry::nsDisplayTableItemGeometry(
+    nsDisplayTableItem* aItem, nsDisplayListBuilder* aBuilder,
+    const nsPoint& aFrameOffsetToViewport)
+    : nsDisplayItemGenericGeometry(aItem, aBuilder),
+      mFrameOffsetToViewport(aFrameOffsetToViewport) {}
+
+}  // namespace mozilla
diff --git a/layout/painting/nsDisplayListInvalidation.h b/layout/painting/nsDisplayListInvalidation.h
new file mode 100644
index 0000000000..3e07713301
--- /dev/null
+++ b/layout/painting/nsDisplayListInvalidation.h
@@ -0,0 +1,236 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef NSDISPLAYLISTINVALIDATION_H_
+#define NSDISPLAYLISTINVALIDATION_H_
+
+#include "mozilla/Attributes.h"
+#include "mozilla/layers/WebRenderUserData.h"
+#include "ImgDrawResult.h"
+#include "nsRect.h"
+#include "nsColor.h"
+#include "gfxRect.h"
+#include "mozilla/gfx/MatrixFwd.h"
+
+namespace mozilla {
+class nsDisplayBackgroundImage;
+class nsCharClipDisplayItem;
+class nsDisplayItem;
+class nsDisplayListBuilder;
+class nsDisplayTableItem;
+class nsDisplayThemedBackground;
+class nsDisplayEffectsBase;
+class nsDisplayMasksAndClipPaths;
+class nsDisplayFilters;
+
+namespace gfx {
+struct sRGBColor;
+}
+
+/**
+ * This stores the geometry of an nsDisplayItem, and the area
+ * that will be affected when painting the item.
+ *
+ * It is used to retain information about display items so they
+ * can be compared against new display items in the next paint.
+ */
+class nsDisplayItemGeometry {
+ public:
+  nsDisplayItemGeometry(nsDisplayItem* aItem, nsDisplayListBuilder* aBuilder);
+  virtual ~nsDisplayItemGeometry();
+
+  /**
+   * Compute the area required to be invalidated if this
+   * display item is removed.
+   */
+  const nsRect& ComputeInvalidationRegion() { return mBounds; }
+
+  /**
+   * Shifts all retained areas of the nsDisplayItemGeometry by the given offset.
+   *
+   * This is used to compensate for scrolling, since the destination buffer
+   * can scroll without requiring a full repaint.
+   *
+   * @param aOffset Offset to shift by.
+   */
+  virtual void MoveBy(const nsPoint& aOffset) { mBounds.MoveBy(aOffset); }
+
+  /**
+   * Bounds of the display item
+   */
+  nsRect mBounds;
+};
+
+/**
+ * A default geometry implementation, used by nsDisplayItem. Retains
+ * and compares the bounds, and border rect.
+ *
+ * This should be sufficient for the majority of display items.
+ */
+class nsDisplayItemGenericGeometry : public nsDisplayItemGeometry {
+ public:
+  nsDisplayItemGenericGeometry(nsDisplayItem* aItem,
+                               nsDisplayListBuilder* aBuilder);
+
+  void MoveBy(const nsPoint& aOffset) override;
+
+  nsRect mBorderRect;
+};
+
+bool ShouldSyncDecodeImages(nsDisplayListBuilder* aBuilder);
+
+nsDisplayItemGeometry* GetPreviousGeometry(nsDisplayItem*);
+
+class nsDisplayItemBoundsGeometry : public nsDisplayItemGeometry {
+ public:
+  nsDisplayItemBoundsGeometry(nsDisplayItem* aItem,
+                              nsDisplayListBuilder* aBuilder);
+
+  bool mHasRoundedCorners;
+};
+
+class nsDisplayBorderGeometry : public nsDisplayItemGeometry {
+ public:
+  nsDisplayBorderGeometry(nsDisplayItem* aItem, nsDisplayListBuilder* aBuilder);
+};
+
+class nsDisplayBackgroundGeometry : public nsDisplayItemGeometry {
+ public:
+  nsDisplayBackgroundGeometry(nsDisplayBackgroundImage* aItem,
+                              nsDisplayListBuilder* aBuilder);
+
+  void MoveBy(const nsPoint& aOffset) override;
+
+  nsRect mPositioningArea;
+  nsRect mDestRect;
+};
+
+class nsDisplayThemedBackgroundGeometry : public nsDisplayItemGeometry {
+ public:
+  nsDisplayThemedBackgroundGeometry(nsDisplayThemedBackground* aItem,
+                                    nsDisplayListBuilder* aBuilder);
+
+  void MoveBy(const nsPoint& aOffset) override;
+
+  nsRect mPositioningArea;
+  bool mWindowIsActive;
+};
+
+class nsDisplayTreeBodyGeometry : public nsDisplayItemGenericGeometry {
+ public:
+  nsDisplayTreeBodyGeometry(nsDisplayItem* aItem,
+                            nsDisplayListBuilder* aBuilder,
+                            bool aWindowIsActive)
+      : nsDisplayItemGenericGeometry(aItem, aBuilder),
+        mWindowIsActive(aWindowIsActive) {}
+
+  bool mWindowIsActive = false;
+};
+
+class nsDisplayBoxShadowInnerGeometry : public nsDisplayItemGeometry {
+ public:
+  nsDisplayBoxShadowInnerGeometry(nsDisplayItem* aItem,
+                                  nsDisplayListBuilder* aBuilder);
+
+  void MoveBy(const nsPoint& aOffset) override;
+
+  nsRect mPaddingRect;
+};
+
+class nsDisplaySolidColorGeometry : public nsDisplayItemBoundsGeometry {
+ public:
+  nsDisplaySolidColorGeometry(nsDisplayItem* aItem,
+                              nsDisplayListBuilder* aBuilder, nscolor aColor)
+      : nsDisplayItemBoundsGeometry(aItem, aBuilder), mColor(aColor) {}
+
+  nscolor mColor;
+};
+
+class nsDisplaySolidColorRegionGeometry : public nsDisplayItemBoundsGeometry {
+ public:
+  nsDisplaySolidColorRegionGeometry(nsDisplayItem* aItem,
+                                    nsDisplayListBuilder* aBuilder,
+                                    const nsRegion& aRegion,
+                                    mozilla::gfx::sRGBColor aColor)
+      : nsDisplayItemBoundsGeometry(aItem, aBuilder),
+        mRegion(aRegion),
+        mColor(aColor) {}
+
+  void MoveBy(const nsPoint& aOffset) override;
+
+  nsRegion mRegion;
+  mozilla::gfx::sRGBColor mColor;
+};
+
+class nsDisplaySVGEffectGeometry : public nsDisplayItemGeometry {
+ public:
+  nsDisplaySVGEffectGeometry(nsDisplayEffectsBase* aItem,
+                             nsDisplayListBuilder* aBuilder);
+
+  void MoveBy(const nsPoint& aOffset) override;
+
+  gfxRect mBBox;
+  gfxPoint mUserSpaceOffset;
+  nsPoint mFrameOffsetToReferenceFrame;
+  bool mHandleOpacity;
+};
+
+class nsDisplayMasksAndClipPathsGeometry : public nsDisplaySVGEffectGeometry {
+ public:
+  nsDisplayMasksAndClipPathsGeometry(nsDisplayMasksAndClipPaths* aItem,
+                                     nsDisplayListBuilder* aBuilder);
+
+  nsTArray<nsRect> mDestRects;
+};
+
+class nsDisplayFiltersGeometry : public nsDisplaySVGEffectGeometry {
+ public:
+  nsDisplayFiltersGeometry(nsDisplayFilters* aItem,
+                           nsDisplayListBuilder* aBuilder);
+};
+
+class nsDisplayTableItemGeometry : public nsDisplayItemGenericGeometry {
+ public:
+  nsDisplayTableItemGeometry(nsDisplayTableItem* aItem,
+                             nsDisplayListBuilder* aBuilder,
+                             const nsPoint& aFrameOffsetToViewport);
+
+  nsPoint mFrameOffsetToViewport;
+};
+
+class nsDisplayOpacityGeometry : public nsDisplayItemGenericGeometry {
+ public:
+  nsDisplayOpacityGeometry(nsDisplayItem* aItem, nsDisplayListBuilder* aBuilder,
+                           float aOpacity)
+      : nsDisplayItemGenericGeometry(aItem, aBuilder), mOpacity(aOpacity) {}
+
+  float mOpacity;
+};
+
+class nsDisplayTransformGeometry : public nsDisplayItemGeometry {
+ public:
+  nsDisplayTransformGeometry(nsDisplayItem* aItem,
+                             nsDisplayListBuilder* aBuilder,
+                             const mozilla::gfx::Matrix4x4Flagged& aTransform,
+                             int32_t aAppUnitsPerDevPixel)
+      : nsDisplayItemGeometry(aItem, aBuilder),
+        mTransform(aTransform),
+        mAppUnitsPerDevPixel(aAppUnitsPerDevPixel) {}
+
+  void MoveBy(const nsPoint& aOffset) override {
+    nsDisplayItemGeometry::MoveBy(aOffset);
+    mTransform.PostTranslate(
+        NSAppUnitsToFloatPixels(aOffset.x, mAppUnitsPerDevPixel),
+        NSAppUnitsToFloatPixels(aOffset.y, mAppUnitsPerDevPixel), 0.0f);
+  }
+
+  mozilla::gfx::Matrix4x4Flagged mTransform;
+  int32_t mAppUnitsPerDevPixel;
+};
+
+}  // namespace mozilla
+
+#endif /*NSDISPLAYLISTINVALIDATION_H_*/
diff --git a/layout/painting/nsImageRenderer.cpp b/layout/painting/nsImageRenderer.cpp
new file mode 100644
index 0000000000..7ff27c1937
--- /dev/null
+++ b/layout/painting/nsImageRenderer.cpp
@@ -0,0 +1,1074 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/* utility code for drawing images as CSS borders, backgrounds, and shapes. */
+
+#include "nsImageRenderer.h"
+
+#include "mozilla/webrender/WebRenderAPI.h"
+
+#include "gfxContext.h"
+#include "gfxDrawable.h"
+#include "ImageOps.h"
+#include "ImageRegion.h"
+#include "mozilla/image/WebRenderImageProvider.h"
+#include "mozilla/layers/RenderRootStateManager.h"
+#include "mozilla/layers/StackingContextHelper.h"
+#include "mozilla/layers/WebRenderLayerManager.h"
+#include "nsContentUtils.h"
+#include "nsCSSRendering.h"
+#include "nsCSSRenderingGradients.h"
+#include "nsDeviceContext.h"
+#include "nsIFrame.h"
+#include "nsLayoutUtils.h"
+#include "nsStyleStructInlines.h"
+#include "mozilla/StaticPrefs_image.h"
+#include "mozilla/ISVGDisplayableFrame.h"
+#include "mozilla/SVGIntegrationUtils.h"
+#include "mozilla/SVGPaintServerFrame.h"
+#include "mozilla/SVGObserverUtils.h"
+
+using namespace mozilla;
+using namespace mozilla::gfx;
+using namespace mozilla::image;
+using namespace mozilla::layers;
+
+nsSize CSSSizeOrRatio::ComputeConcreteSize() const {
+  NS_ASSERTION(CanComputeConcreteSize(), "Cannot compute");
+  if (mHasWidth && mHasHeight) {
+    return nsSize(mWidth, mHeight);
+  }
+  if (mHasWidth) {
+    return nsSize(mWidth, mRatio.Inverted().ApplyTo(mWidth));
+  }
+
+  MOZ_ASSERT(mHasHeight);
+  return nsSize(mRatio.ApplyTo(mHeight), mHeight);
+}
+
+nsImageRenderer::nsImageRenderer(nsIFrame* aForFrame, const StyleImage* aImage,
+                                 uint32_t aFlags)
+    : mForFrame(aForFrame),
+      mImage(&aImage->FinalImage()),
+      mImageResolution(aImage->GetResolution()),
+      mType(mImage->tag),
+      mImageContainer(nullptr),
+      mGradientData(nullptr),
+      mPaintServerFrame(nullptr),
+      mPrepareResult(ImgDrawResult::NOT_READY),
+      mSize(0, 0),
+      mFlags(aFlags),
+      mExtendMode(ExtendMode::CLAMP),
+      mMaskOp(StyleMaskMode::MatchSource) {}
+
+bool nsImageRenderer::PrepareImage() {
+  if (mImage->IsNone()) {
+    mPrepareResult = ImgDrawResult::BAD_IMAGE;
+    return false;
+  }
+
+  const bool isImageRequest = mImage->IsImageRequestType();
+  MOZ_ASSERT_IF(!isImageRequest, !mImage->GetImageRequest());
+  imgRequestProxy* request = nullptr;
+  if (isImageRequest) {
+    request = mImage->GetImageRequest();
+    if (!request) {
+      // request could be null here if the StyleImage refused
+      // to load a same-document URL, or the url was invalid, for example.
+      mPrepareResult = ImgDrawResult::BAD_IMAGE;
+      return false;
+    }
+  }
+
+  if (!mImage->IsComplete()) {
+    MOZ_DIAGNOSTIC_ASSERT(isImageRequest);
+
+    // Make sure the image is actually decoding.
+    bool frameComplete = request->StartDecodingWithResult(
+        imgIContainer::FLAG_ASYNC_NOTIFY |
+        imgIContainer::FLAG_AVOID_REDECODE_FOR_SIZE);
+
+    // Boost the loading priority since we know we want to draw the image.
+    if (mFlags & nsImageRenderer::FLAG_PAINTING_TO_WINDOW) {
+      request->BoostPriority(imgIRequest::CATEGORY_DISPLAY);
+    }
+
+    // Check again to see if we finished.
+    // We cannot prepare the image for rendering if it is not fully loaded.
+    if (!frameComplete && !mImage->IsComplete()) {
+      uint32_t imageStatus = 0;
+      request->GetImageStatus(&imageStatus);
+      if (imageStatus & imgIRequest::STATUS_ERROR) {
+        mPrepareResult = ImgDrawResult::BAD_IMAGE;
+        return false;
+      }
+
+      // If not errored, and we requested a sync decode, and the image has
+      // loaded, push on through because the Draw() will do a sync decode then.
+      const bool syncDecodeWillComplete =
+          (mFlags & FLAG_SYNC_DECODE_IMAGES) &&
+          (imageStatus & imgIRequest::STATUS_LOAD_COMPLETE);
+
+      bool canDrawPartial =
+          (mFlags & nsImageRenderer::FLAG_DRAW_PARTIAL_FRAMES) &&
+          isImageRequest && mImage->IsSizeAvailable() && !mImage->IsRect();
+
+      // If we are drawing a partial frame then we want to make sure there are
+      // some pixels to draw, otherwise we waste effort pushing through to draw
+      // nothing.
+      if (!syncDecodeWillComplete && canDrawPartial) {
+        nsCOMPtr<imgIContainer> image;
+        canDrawPartial =
+            canDrawPartial &&
+            NS_SUCCEEDED(request->GetImage(getter_AddRefs(image))) && image &&
+            image->GetType() == imgIContainer::TYPE_RASTER &&
+            image->HasDecodedPixels();
+      }
+
+      // If we can draw partial then proceed if we at least have the size
+      // available.
+      if (!(syncDecodeWillComplete || canDrawPartial)) {
+        mPrepareResult = ImgDrawResult::NOT_READY;
+        return false;
+      }
+    }
+  }
+
+  if (isImageRequest) {
+    nsCOMPtr<imgIContainer> srcImage;
+    nsresult rv = request->GetImage(getter_AddRefs(srcImage));
+    MOZ_ASSERT(NS_SUCCEEDED(rv) && srcImage,
+               "If GetImage() is failing, mImage->IsComplete() "
+               "should have returned false");
+    if (!NS_SUCCEEDED(rv)) {
+      srcImage = nullptr;
+    }
+
+    if (srcImage) {
+      StyleImageOrientation orientation =
+          mForFrame->StyleVisibility()->UsedImageOrientation(request);
+      srcImage = nsLayoutUtils::OrientImage(srcImage, orientation);
+    }
+
+    if (!mImage->IsRect()) {
+      mImageContainer.swap(srcImage);
+    } else {
+      auto croprect = mImage->ComputeActualCropRect();
+      if (!croprect || croprect->mRect.IsEmpty()) {
+        // The cropped image has zero size
+        mPrepareResult = ImgDrawResult::BAD_IMAGE;
+        return false;
+      }
+      if (croprect->mIsEntireImage) {
+        // The cropped image is identical to the source image
+        mImageContainer.swap(srcImage);
+      } else {
+        nsCOMPtr<imgIContainer> subImage =
+            ImageOps::Clip(srcImage, croprect->mRect, Nothing());
+        mImageContainer.swap(subImage);
+      }
+    }
+    mPrepareResult = ImgDrawResult::SUCCESS;
+  } else if (mImage->IsGradient()) {
+    mGradientData = &*mImage->AsGradient();
+    mPrepareResult = ImgDrawResult::SUCCESS;
+  } else if (mImage->IsElement()) {
+    dom::Element* paintElement =  // may be null
+        SVGObserverUtils::GetAndObserveBackgroundImage(
+            mForFrame->FirstContinuation(), mImage->AsElement().AsAtom());
+    // If the referenced element is an <img>, <canvas>, or <video> element,
+    // prefer SurfaceFromElement as it's more reliable.
+    mImageElementSurface = nsLayoutUtils::SurfaceFromElement(paintElement);
+
+    if (!mImageElementSurface.GetSourceSurface()) {
+      nsIFrame* paintServerFrame =
+          paintElement ? paintElement->GetPrimaryFrame() : nullptr;
+      // If there's no referenced frame, or the referenced frame is
+      // non-displayable SVG, then we have nothing valid to paint.
+      if (!paintServerFrame ||
+          (paintServerFrame->IsFrameOfType(nsIFrame::eSVG) &&
+           !static_cast<SVGPaintServerFrame*>(
+               do_QueryFrame(paintServerFrame)) &&
+           !static_cast<ISVGDisplayableFrame*>(
+               do_QueryFrame(paintServerFrame)))) {
+        mPrepareResult = ImgDrawResult::BAD_IMAGE;
+        return false;
+      }
+      mPaintServerFrame = paintServerFrame;
+    }
+
+    mPrepareResult = ImgDrawResult::SUCCESS;
+  } else if (mImage->IsCrossFade()) {
+    // See bug 546052 - cross-fade implementation still being worked
+    // on.
+    mPrepareResult = ImgDrawResult::BAD_IMAGE;
+    return false;
+  } else {
+    MOZ_ASSERT(mImage->IsNone(), "Unknown image type?");
+  }
+
+  return IsReady();
+}
+
+CSSSizeOrRatio nsImageRenderer::ComputeIntrinsicSize() {
+  NS_ASSERTION(IsReady(),
+               "Ensure PrepareImage() has returned true "
+               "before calling me");
+
+  CSSSizeOrRatio result;
+  switch (mType) {
+    case StyleImage::Tag::Rect:
+    case StyleImage::Tag::Url: {
+      bool haveWidth, haveHeight;
+      CSSIntSize imageIntSize;
+      nsLayoutUtils::ComputeSizeForDrawing(mImageContainer, mImageResolution,
+                                           imageIntSize, result.mRatio,
+                                           haveWidth, haveHeight);
+      if (haveWidth) {
+        result.SetWidth(CSSPixel::ToAppUnits(imageIntSize.width));
+      }
+      if (haveHeight) {
+        result.SetHeight(CSSPixel::ToAppUnits(imageIntSize.height));
+      }
+
+      // If we know the aspect ratio and one of the dimensions,
+      // we can compute the other missing width or height.
+      if (!haveHeight && haveWidth && result.mRatio) {
+        nscoord intrinsicHeight =
+            result.mRatio.Inverted().ApplyTo(imageIntSize.width);
+        result.SetHeight(nsPresContext::CSSPixelsToAppUnits(intrinsicHeight));
+      } else if (haveHeight && !haveWidth && result.mRatio) {
+        nscoord intrinsicWidth = result.mRatio.ApplyTo(imageIntSize.height);
+        result.SetWidth(nsPresContext::CSSPixelsToAppUnits(intrinsicWidth));
+      }
+
+      break;
+    }
+    case StyleImage::Tag::Element: {
+      // XXX element() should have the width/height of the referenced element,
+      //     and that element's ratio, if it matches.  If it doesn't match, it
+      //     should have no width/height or ratio.  See element() in CSS images:
+      //     <http://dev.w3.org/csswg/css-images-4/#element-notation>.
+      //     Make sure to change nsStyleImageLayers::Size::DependsOnFrameSize
+      //     when fixing this!
+      if (mPaintServerFrame) {
+        // SVG images have no intrinsic size
+        if (!mPaintServerFrame->IsFrameOfType(nsIFrame::eSVG)) {
+          // The intrinsic image size for a generic nsIFrame paint server is
+          // the union of the border-box rects of all of its continuations,
+          // rounded to device pixels.
+          int32_t appUnitsPerDevPixel =
+              mForFrame->PresContext()->AppUnitsPerDevPixel();
+          result.SetSize(IntSizeToAppUnits(
+              SVGIntegrationUtils::GetContinuationUnionSize(mPaintServerFrame)
+                  .ToNearestPixels(appUnitsPerDevPixel),
+              appUnitsPerDevPixel));
+        }
+      } else {
+        NS_ASSERTION(mImageElementSurface.GetSourceSurface(),
+                     "Surface should be ready.");
+        IntSize surfaceSize = mImageElementSurface.mSize;
+        result.SetSize(
+            nsSize(nsPresContext::CSSPixelsToAppUnits(surfaceSize.width),
+                   nsPresContext::CSSPixelsToAppUnits(surfaceSize.height)));
+      }
+      break;
+    }
+    case StyleImage::Tag::ImageSet:
+      MOZ_FALLTHROUGH_ASSERT("image-set should be resolved already");
+    // Bug 546052 cross-fade not yet implemented.
+    case StyleImage::Tag::CrossFade:
+    // Per <http://dev.w3.org/csswg/css3-images/#gradients>, gradients have no
+    // intrinsic dimensions.
+    case StyleImage::Tag::Gradient:
+    case StyleImage::Tag::None:
+      break;
+  }
+
+  return result;
+}
+
+/* static */
+nsSize nsImageRenderer::ComputeConcreteSize(
+    const CSSSizeOrRatio& aSpecifiedSize, const CSSSizeOrRatio& aIntrinsicSize,
+    const nsSize& aDefaultSize) {
+  // The specified size is fully specified, just use that
+  if (aSpecifiedSize.IsConcrete()) {
+    return aSpecifiedSize.ComputeConcreteSize();
+  }
+
+  MOZ_ASSERT(!aSpecifiedSize.mHasWidth || !aSpecifiedSize.mHasHeight);
+
+  if (!aSpecifiedSize.mHasWidth && !aSpecifiedSize.mHasHeight) {
+    // no specified size, try using the intrinsic size
+    if (aIntrinsicSize.CanComputeConcreteSize()) {
+      return aIntrinsicSize.ComputeConcreteSize();
+    }
+
+    if (aIntrinsicSize.mHasWidth) {
+      return nsSize(aIntrinsicSize.mWidth, aDefaultSize.height);
+    }
+    if (aIntrinsicSize.mHasHeight) {
+      return nsSize(aDefaultSize.width, aIntrinsicSize.mHeight);
+    }
+
+    // couldn't use the intrinsic size either, revert to using the default size
+    return ComputeConstrainedSize(aDefaultSize, aIntrinsicSize.mRatio, CONTAIN);
+  }
+
+  MOZ_ASSERT(aSpecifiedSize.mHasWidth || aSpecifiedSize.mHasHeight);
+
+  // The specified height is partial, try to compute the missing part.
+  if (aSpecifiedSize.mHasWidth) {
+    nscoord height;
+    if (aIntrinsicSize.HasRatio()) {
+      height = aIntrinsicSize.mRatio.Inverted().ApplyTo(aSpecifiedSize.mWidth);
+    } else if (aIntrinsicSize.mHasHeight) {
+      height = aIntrinsicSize.mHeight;
+    } else {
+      height = aDefaultSize.height;
+    }
+    return nsSize(aSpecifiedSize.mWidth, height);
+  }
+
+  MOZ_ASSERT(aSpecifiedSize.mHasHeight);
+  nscoord width;
+  if (aIntrinsicSize.HasRatio()) {
+    width = aIntrinsicSize.mRatio.ApplyTo(aSpecifiedSize.mHeight);
+  } else if (aIntrinsicSize.mHasWidth) {
+    width = aIntrinsicSize.mWidth;
+  } else {
+    width = aDefaultSize.width;
+  }
+  return nsSize(width, aSpecifiedSize.mHeight);
+}
+
+/* static */
+nsSize nsImageRenderer::ComputeConstrainedSize(
+    const nsSize& aConstrainingSize, const AspectRatio& aIntrinsicRatio,
+    FitType aFitType) {
+  if (!aIntrinsicRatio) {
+    return aConstrainingSize;
+  }
+
+  // Suppose we're doing a "contain" fit. If the image's aspect ratio has a
+  // "fatter" shape than the constraint area, then we need to use the
+  // constraint area's full width, and we need to use the aspect ratio to
+  // produce a height. On the other hand, if the aspect ratio is "skinnier", we
+  // use the constraint area's full height, and we use the aspect ratio to
+  // produce a width. (If instead we're doing a "cover" fit, then it can easily
+  // be seen that we should do precisely the opposite.)
+  //
+  // We check if the image's aspect ratio is "fatter" than the constraint area
+  // by simply applying the aspect ratio to the constraint area's height, to
+  // produce a "hypothetical width", and we check whether that
+  // aspect-ratio-provided "hypothetical width" is wider than the constraint
+  // area's actual width. If it is, then the aspect ratio is fatter than the
+  // constraint area.
+  //
+  // This is equivalent to the more descriptive alternative:
+  //
+  //   AspectRatio::FromSize(aConstrainingSize) < aIntrinsicRatio
+  //
+  // But gracefully handling the case where one of the two dimensions from
+  // aConstrainingSize is zero. This is easy to prove since:
+  //
+  //   aConstrainingSize.width / aConstrainingSize.height < aIntrinsicRatio
+  //
+  // Is trivially equivalent to:
+  //
+  //   aIntrinsicRatio.width < aIntrinsicRatio * aConstrainingSize.height
+  //
+  // For the cases where height is not zero.
+  //
+  // We use float math here to avoid losing precision for very large backgrounds
+  // since we use saturating nscoord math otherwise.
+  const float constraintWidth = float(aConstrainingSize.width);
+  const float hypotheticalWidth =
+      aIntrinsicRatio.ApplyToFloat(aConstrainingSize.height);
+
+  nsSize size;
+  if ((aFitType == CONTAIN) == (constraintWidth < hypotheticalWidth)) {
+    size.width = aConstrainingSize.width;
+    size.height = aIntrinsicRatio.Inverted().ApplyTo(aConstrainingSize.width);
+    // If we're reducing the size by less than one css pixel, then just use the
+    // constraining size.
+    if (aFitType == CONTAIN &&
+        aConstrainingSize.height - size.height < AppUnitsPerCSSPixel()) {
+      size.height = aConstrainingSize.height;
+    }
+  } else {
+    size.height = aConstrainingSize.height;
+    size.width = aIntrinsicRatio.ApplyTo(aConstrainingSize.height);
+    if (aFitType == CONTAIN &&
+        aConstrainingSize.width - size.width < AppUnitsPerCSSPixel()) {
+      size.width = aConstrainingSize.width;
+    }
+  }
+  return size;
+}
+
+/**
+ * mSize is the image's "preferred" size for this particular rendering, while
+ * the drawn (aka concrete) size is the actual rendered size after accounting
+ * for background-size etc..  The preferred size is most often the image's
+ * intrinsic dimensions.  But for images with incomplete intrinsic dimensions,
+ * the preferred size varies, depending on the specified and default sizes, see
+ * nsImageRenderer::Compute*Size.
+ *
+ * This distinction is necessary because the components of a vector image are
+ * specified with respect to its preferred size for a rendering situation, not
+ * to its actual rendered size.  For example, consider a 4px wide background
+ * vector image with no height which contains a left-aligned
+ * 2px wide black rectangle with height 100%.  If the background-size width is
+ * auto (or 4px), the vector image will render 4px wide, and the black rectangle
+ * will be 2px wide.  If the background-size width is 8px, the vector image will
+ * render 8px wide, and the black rectangle will be 4px wide -- *not* 2px wide.
+ * In both cases mSize.width will be 4px; but in the first case the returned
+ * width will be 4px, while in the second case the returned width will be 8px.
+ */
+void nsImageRenderer::SetPreferredSize(const CSSSizeOrRatio& aIntrinsicSize,
+                                       const nsSize& aDefaultSize) {
+  mSize.width =
+      aIntrinsicSize.mHasWidth ? aIntrinsicSize.mWidth : aDefaultSize.width;
+  mSize.height =
+      aIntrinsicSize.mHasHeight ? aIntrinsicSize.mHeight : aDefaultSize.height;
+}
+
+// Convert from nsImageRenderer flags to the flags we want to use for drawing in
+// the imgIContainer namespace.
+static uint32_t ConvertImageRendererToDrawFlags(uint32_t aImageRendererFlags) {
+  uint32_t drawFlags = imgIContainer::FLAG_ASYNC_NOTIFY;
+  if (aImageRendererFlags & nsImageRenderer::FLAG_SYNC_DECODE_IMAGES) {
+    drawFlags |= imgIContainer::FLAG_SYNC_DECODE;
+  }
+  if (aImageRendererFlags & (nsImageRenderer::FLAG_PAINTING_TO_WINDOW |
+                             nsImageRenderer::FLAG_HIGH_QUALITY_SCALING)) {
+    drawFlags |= imgIContainer::FLAG_HIGH_QUALITY_SCALING;
+  }
+  return drawFlags;
+}
+
+ImgDrawResult nsImageRenderer::Draw(nsPresContext* aPresContext,
+                                    gfxContext& aRenderingContext,
+                                    const nsRect& aDirtyRect,
+                                    const nsRect& aDest, const nsRect& aFill,
+                                    const nsPoint& aAnchor,
+                                    const nsSize& aRepeatSize,
+                                    const CSSIntRect& aSrc, float aOpacity) {
+  if (!IsReady()) {
+    MOZ_ASSERT_UNREACHABLE(
+        "Ensure PrepareImage() has returned true before "
+        "calling me");
+    return ImgDrawResult::TEMPORARY_ERROR;
+  }
+
+  if (aDest.IsEmpty() || aFill.IsEmpty() || mSize.width <= 0 ||
+      mSize.height <= 0) {
+    return ImgDrawResult::SUCCESS;
+  }
+
+  SamplingFilter samplingFilter =
+      nsLayoutUtils::GetSamplingFilterForFrame(mForFrame);
+  ImgDrawResult result = ImgDrawResult::SUCCESS;
+  RefPtr<gfxContext> ctx = &aRenderingContext;
+  IntRect tmpDTRect;
+
+  if (ctx->CurrentOp() != CompositionOp::OP_OVER ||
+      mMaskOp == StyleMaskMode::Luminance) {
+    gfxRect clipRect = ctx->GetClipExtents(gfxContext::eDeviceSpace);
+    tmpDTRect = RoundedOut(ToRect(clipRect));
+    if (tmpDTRect.IsEmpty()) {
+      return ImgDrawResult::SUCCESS;
+    }
+    RefPtr<DrawTarget> tempDT = ctx->GetDrawTarget()->CreateSimilarDrawTarget(
+        tmpDTRect.Size(), SurfaceFormat::B8G8R8A8);
+    if (!tempDT || !tempDT->IsValid()) {
+      gfxDevCrash(LogReason::InvalidContext)
+          << "ImageRenderer::Draw problem " << gfx::hexa(tempDT);
+      return ImgDrawResult::TEMPORARY_ERROR;
+    }
+    tempDT->SetTransform(ctx->GetDrawTarget()->GetTransform() *
+                         Matrix::Translation(-tmpDTRect.TopLeft()));
+    ctx = gfxContext::CreatePreservingTransformOrNull(tempDT);
+    if (!ctx) {
+      gfxDevCrash(LogReason::InvalidContext)
+          << "ImageRenderer::Draw problem " << gfx::hexa(tempDT);
+      return ImgDrawResult::TEMPORARY_ERROR;
+    }
+  }
+
+  switch (mType) {
+    case StyleImage::Tag::Rect:
+    case StyleImage::Tag::Url: {
+      result = nsLayoutUtils::DrawBackgroundImage(
+          *ctx, mForFrame, aPresContext, mImageContainer, samplingFilter, aDest,
+          aFill, aRepeatSize, aAnchor, aDirtyRect,
+          ConvertImageRendererToDrawFlags(mFlags), mExtendMode, aOpacity);
+      break;
+    }
+    case StyleImage::Tag::Gradient: {
+      nsCSSGradientRenderer renderer = nsCSSGradientRenderer::Create(
+          aPresContext, mForFrame->Style(), *mGradientData, mSize);
+
+      renderer.Paint(*ctx, aDest, aFill, aRepeatSize, aSrc, aDirtyRect,
+                     aOpacity);
+      break;
+    }
+    case StyleImage::Tag::Element: {
+      RefPtr<gfxDrawable> drawable = DrawableForElement(aDest, *ctx);
+      if (!drawable) {
+        NS_WARNING("Could not create drawable for element");
+        return ImgDrawResult::TEMPORARY_ERROR;
+      }
+
+      nsCOMPtr<imgIContainer> image(ImageOps::CreateFromDrawable(drawable));
+      result = nsLayoutUtils::DrawImage(
+          *ctx, mForFrame->Style(), aPresContext, image, samplingFilter, aDest,
+          aFill, aAnchor, aDirtyRect, ConvertImageRendererToDrawFlags(mFlags),
+          aOpacity);
+      break;
+    }
+    case StyleImage::Tag::ImageSet:
+      MOZ_FALLTHROUGH_ASSERT("image-set should be resolved already");
+    // See bug 546052 - cross-fade implementation still being worked
+    // on.
+    case StyleImage::Tag::CrossFade:
+    case StyleImage::Tag::None:
+      break;
+  }
+
+  if (!tmpDTRect.IsEmpty()) {
+    DrawTarget* dt = aRenderingContext.GetDrawTarget();
+    Matrix oldTransform = dt->GetTransform();
+    dt->SetTransform(Matrix());
+    if (mMaskOp == StyleMaskMode::Luminance) {
+      RefPtr<SourceSurface> surf = ctx->GetDrawTarget()->IntoLuminanceSource(
+          LuminanceType::LUMINANCE, 1.0f);
+      dt->MaskSurface(ColorPattern(DeviceColor(0, 0, 0, 1.0f)), surf,
+                      tmpDTRect.TopLeft(),
+                      DrawOptions(1.0f, aRenderingContext.CurrentOp()));
+    } else {
+      RefPtr<SourceSurface> surf = ctx->GetDrawTarget()->Snapshot();
+      dt->DrawSurface(
+          surf,
+          Rect(tmpDTRect.x, tmpDTRect.y, tmpDTRect.width, tmpDTRect.height),
+          Rect(0, 0, tmpDTRect.width, tmpDTRect.height),
+          DrawSurfaceOptions(SamplingFilter::POINT),
+          DrawOptions(1.0f, aRenderingContext.CurrentOp()));
+    }
+
+    dt->SetTransform(oldTransform);
+  }
+
+  if (!mImage->IsComplete()) {
+    result &= ImgDrawResult::SUCCESS_NOT_COMPLETE;
+  }
+
+  return result;
+}
+
+ImgDrawResult nsImageRenderer::BuildWebRenderDisplayItems(
+    nsPresContext* aPresContext, mozilla::wr::DisplayListBuilder& aBuilder,
+    mozilla::wr::IpcResourceUpdateQueue& aResources,
+    const mozilla::layers::StackingContextHelper& aSc,
+    mozilla::layers::RenderRootStateManager* aManager, nsDisplayItem* aItem,
+    const nsRect& aDirtyRect, const nsRect& aDest, const nsRect& aFill,
+    const nsPoint& aAnchor, const nsSize& aRepeatSize, const CSSIntRect& aSrc,
+    float aOpacity) {
+  if (!IsReady()) {
+    MOZ_ASSERT_UNREACHABLE(
+        "Ensure PrepareImage() has returned true before "
+        "calling me");
+    return ImgDrawResult::NOT_READY;
+  }
+
+  if (aDest.IsEmpty() || aFill.IsEmpty() || mSize.width <= 0 ||
+      mSize.height <= 0) {
+    return ImgDrawResult::SUCCESS;
+  }
+
+  ImgDrawResult drawResult = ImgDrawResult::SUCCESS;
+  switch (mType) {
+    case StyleImage::Tag::Gradient: {
+      nsCSSGradientRenderer renderer = nsCSSGradientRenderer::Create(
+          aPresContext, mForFrame->Style(), *mGradientData, mSize);
+
+      renderer.BuildWebRenderDisplayItems(aBuilder, aSc, aDest, aFill,
+                                          aRepeatSize, aSrc,
+                                          !aItem->BackfaceIsHidden(), aOpacity);
+      break;
+    }
+    case StyleImage::Tag::Rect:
+    case StyleImage::Tag::Url: {
+      ExtendMode extendMode = mExtendMode;
+      if (aDest.Contains(aFill)) {
+        extendMode = ExtendMode::CLAMP;
+      }
+
+      uint32_t containerFlags = ConvertImageRendererToDrawFlags(mFlags);
+      if (extendMode == ExtendMode::CLAMP &&
+          StaticPrefs::image_svg_blob_image() &&
+          mImageContainer->GetType() == imgIContainer::TYPE_VECTOR) {
+        containerFlags |= imgIContainer::FLAG_RECORD_BLOB;
+      }
+
+      CSSIntSize destCSSSize{
+          nsPresContext::AppUnitsToIntCSSPixels(aDest.width),
+          nsPresContext::AppUnitsToIntCSSPixels(aDest.height)};
+
+      SVGImageContext svgContext(Some(destCSSSize));
+      Maybe<ImageIntRegion> region;
+
+      const int32_t appUnitsPerDevPixel =
+          mForFrame->PresContext()->AppUnitsPerDevPixel();
+      LayoutDeviceRect destRect =
+          LayoutDeviceRect::FromAppUnits(aDest, appUnitsPerDevPixel);
+      LayoutDeviceRect clipRect =
+          LayoutDeviceRect::FromAppUnits(aFill, appUnitsPerDevPixel);
+      auto stretchSize = wr::ToLayoutSize(destRect.Size());
+
+      gfx::IntSize decodeSize =
+          nsLayoutUtils::ComputeImageContainerDrawingParameters(
+              mImageContainer, mForFrame, destRect, clipRect, aSc,
+              containerFlags, svgContext, region);
+
+      RefPtr<image::WebRenderImageProvider> provider;
+      drawResult = mImageContainer->GetImageProvider(
+          aManager->LayerManager(), decodeSize, svgContext, region,
+          containerFlags, getter_AddRefs(provider));
+
+      Maybe<wr::ImageKey> key =
+          aManager->CommandBuilder().CreateImageProviderKey(
+              aItem, provider, drawResult, aResources);
+      if (key.isNothing()) {
+        break;
+      }
+
+      auto rendering =
+          wr::ToImageRendering(aItem->Frame()->UsedImageRendering());
+      wr::LayoutRect clip = wr::ToLayoutRect(clipRect);
+
+      // If we provided a region to the provider, then it already took the
+      // dest rect into account when it did the recording.
+      wr::LayoutRect dest = region ? clip : wr::ToLayoutRect(destRect);
+
+      if (extendMode == ExtendMode::CLAMP) {
+        // The image is not repeating. Just push as a regular image.
+        aBuilder.PushImage(dest, clip, !aItem->BackfaceIsHidden(), false,
+                           rendering, key.value(), true,
+                           wr::ColorF{1.0f, 1.0f, 1.0f, aOpacity});
+      } else {
+        nsPoint firstTilePos = nsLayoutUtils::GetBackgroundFirstTilePos(
+            aDest.TopLeft(), aFill.TopLeft(), aRepeatSize);
+        LayoutDeviceRect fillRect = LayoutDeviceRect::FromAppUnits(
+            nsRect(firstTilePos.x, firstTilePos.y,
+                   aFill.XMost() - firstTilePos.x,
+                   aFill.YMost() - firstTilePos.y),
+            appUnitsPerDevPixel);
+        wr::LayoutRect fill = wr::ToLayoutRect(fillRect);
+
+        switch (extendMode) {
+          case ExtendMode::REPEAT_Y:
+            fill.min.x = dest.min.x;
+            fill.max.x = dest.max.x;
+            stretchSize.width = dest.width();
+            break;
+          case ExtendMode::REPEAT_X:
+            fill.min.y = dest.min.y;
+            fill.max.y = dest.max.y;
+            stretchSize.height = dest.height();
+            break;
+          default:
+            break;
+        }
+
+        LayoutDeviceSize gapSize = LayoutDeviceSize::FromAppUnits(
+            aRepeatSize - aDest.Size(), appUnitsPerDevPixel);
+
+        aBuilder.PushRepeatingImage(fill, clip, !aItem->BackfaceIsHidden(),
+                                    stretchSize, wr::ToLayoutSize(gapSize),
+                                    rendering, key.value(), true,
+                                    wr::ColorF{1.0f, 1.0f, 1.0f, aOpacity});
+      }
+      break;
+    }
+    default:
+      break;
+  }
+
+  if (!mImage->IsComplete() && drawResult == ImgDrawResult::SUCCESS) {
+    return ImgDrawResult::SUCCESS_NOT_COMPLETE;
+  }
+  return drawResult;
+}
+
+already_AddRefed<gfxDrawable> nsImageRenderer::DrawableForElement(
+    const nsRect& aImageRect, gfxContext& aContext) {
+  NS_ASSERTION(mType == StyleImage::Tag::Element,
+               "DrawableForElement only makes sense if backed by an element");
+  if (mPaintServerFrame) {
+    // XXX(seth): In order to not pass FLAG_SYNC_DECODE_IMAGES here,
+    // DrawableFromPaintServer would have to return a ImgDrawResult indicating
+    // whether any images could not be painted because they weren't fully
+    // decoded. Even always passing FLAG_SYNC_DECODE_IMAGES won't eliminate all
+    // problems, as it won't help if there are image which haven't finished
+    // loading, but it's better than nothing.
+    int32_t appUnitsPerDevPixel =
+        mForFrame->PresContext()->AppUnitsPerDevPixel();
+    nsRect destRect = aImageRect - aImageRect.TopLeft();
+    nsIntSize roundedOut = destRect.ToOutsidePixels(appUnitsPerDevPixel).Size();
+    IntSize imageSize(roundedOut.width, roundedOut.height);
+
+    RefPtr<gfxDrawable> drawable;
+
+    SurfaceFormat format = aContext.GetDrawTarget()->GetFormat();
+    // Don't allow creating images that are too big
+    if (aContext.GetDrawTarget()->CanCreateSimilarDrawTarget(imageSize,
+                                                             format)) {
+      drawable = SVGIntegrationUtils::DrawableFromPaintServer(
+          mPaintServerFrame, mForFrame, mSize, imageSize,
+          aContext.GetDrawTarget(), aContext.CurrentMatrixDouble(),
+          SVGIntegrationUtils::FLAG_SYNC_DECODE_IMAGES);
+    }
+
+    return drawable.forget();
+  }
+  NS_ASSERTION(mImageElementSurface.GetSourceSurface(),
+               "Surface should be ready.");
+  RefPtr<gfxDrawable> drawable =
+      new gfxSurfaceDrawable(mImageElementSurface.GetSourceSurface().get(),
+                             mImageElementSurface.mSize);
+  return drawable.forget();
+}
+
+ImgDrawResult nsImageRenderer::DrawLayer(
+    nsPresContext* aPresContext, gfxContext& aRenderingContext,
+    const nsRect& aDest, const nsRect& aFill, const nsPoint& aAnchor,
+    const nsRect& aDirty, const nsSize& aRepeatSize, float aOpacity) {
+  if (!IsReady()) {
+    MOZ_ASSERT_UNREACHABLE(
+        "Ensure PrepareImage() has returned true before "
+        "calling me");
+    return ImgDrawResult::TEMPORARY_ERROR;
+  }
+
+  if (aDest.IsEmpty() || aFill.IsEmpty() || mSize.width <= 0 ||
+      mSize.height <= 0) {
+    return ImgDrawResult::SUCCESS;
+  }
+
+  return Draw(
+      aPresContext, aRenderingContext, aDirty, aDest, aFill, aAnchor,
+      aRepeatSize,
+      CSSIntRect(0, 0, nsPresContext::AppUnitsToIntCSSPixels(mSize.width),
+                 nsPresContext::AppUnitsToIntCSSPixels(mSize.height)),
+      aOpacity);
+}
+
+ImgDrawResult nsImageRenderer::BuildWebRenderDisplayItemsForLayer(
+    nsPresContext* aPresContext, mozilla::wr::DisplayListBuilder& aBuilder,
+    mozilla::wr::IpcResourceUpdateQueue& aResources,
+    const mozilla::layers::StackingContextHelper& aSc,
+    mozilla::layers::RenderRootStateManager* aManager, nsDisplayItem* aItem,
+    const nsRect& aDest, const nsRect& aFill, const nsPoint& aAnchor,
+    const nsRect& aDirty, const nsSize& aRepeatSize, float aOpacity) {
+  if (!IsReady()) {
+    MOZ_ASSERT_UNREACHABLE(
+        "Ensure PrepareImage() has returned true before "
+        "calling me");
+    return mPrepareResult;
+  }
+
+  CSSIntRect srcRect(0, 0, nsPresContext::AppUnitsToIntCSSPixels(mSize.width),
+                     nsPresContext::AppUnitsToIntCSSPixels(mSize.height));
+
+  if (aDest.IsEmpty() || aFill.IsEmpty() || srcRect.IsEmpty()) {
+    return ImgDrawResult::SUCCESS;
+  }
+  return BuildWebRenderDisplayItems(aPresContext, aBuilder, aResources, aSc,
+                                    aManager, aItem, aDirty, aDest, aFill,
+                                    aAnchor, aRepeatSize, srcRect, aOpacity);
+}
+
+/**
+ * Compute the size and position of the master copy of the image. I.e., a single
+ * tile used to fill the dest rect.
+ * aFill The destination rect to be filled
+ * aHFill and aVFill are the repeat patterns for the component -
+ * StyleBorderImageRepeat - i.e., how a tiling unit is used to fill aFill
+ * aUnitSize The size of the source rect in dest coords.
+ */
+static nsRect ComputeTile(nsRect& aFill, StyleBorderImageRepeat aHFill,
+                          StyleBorderImageRepeat aVFill,
+                          const nsSize& aUnitSize, nsSize& aRepeatSize) {
+  nsRect tile;
+  switch (aHFill) {
+    case StyleBorderImageRepeat::Stretch:
+      tile.x = aFill.x;
+      tile.width = aFill.width;
+      aRepeatSize.width = tile.width;
+      break;
+    case StyleBorderImageRepeat::Repeat:
+      tile.x = aFill.x + aFill.width / 2 - aUnitSize.width / 2;
+      tile.width = aUnitSize.width;
+      aRepeatSize.width = tile.width;
+      break;
+    case StyleBorderImageRepeat::Round:
+      tile.x = aFill.x;
+      tile.width =
+          nsCSSRendering::ComputeRoundedSize(aUnitSize.width, aFill.width);
+      aRepeatSize.width = tile.width;
+      break;
+    case StyleBorderImageRepeat::Space: {
+      nscoord space;
+      aRepeatSize.width = nsCSSRendering::ComputeBorderSpacedRepeatSize(
+          aUnitSize.width, aFill.width, space);
+      tile.x = aFill.x + space;
+      tile.width = aUnitSize.width;
+      aFill.x = tile.x;
+      aFill.width = aFill.width - space * 2;
+    } break;
+    default:
+      MOZ_ASSERT_UNREACHABLE("unrecognized border-image fill style");
+  }
+
+  switch (aVFill) {
+    case StyleBorderImageRepeat::Stretch:
+      tile.y = aFill.y;
+      tile.height = aFill.height;
+      aRepeatSize.height = tile.height;
+      break;
+    case StyleBorderImageRepeat::Repeat:
+      tile.y = aFill.y + aFill.height / 2 - aUnitSize.height / 2;
+      tile.height = aUnitSize.height;
+      aRepeatSize.height = tile.height;
+      break;
+    case StyleBorderImageRepeat::Round:
+      tile.y = aFill.y;
+      tile.height =
+          nsCSSRendering::ComputeRoundedSize(aUnitSize.height, aFill.height);
+      aRepeatSize.height = tile.height;
+      break;
+    case StyleBorderImageRepeat::Space: {
+      nscoord space;
+      aRepeatSize.height = nsCSSRendering::ComputeBorderSpacedRepeatSize(
+          aUnitSize.height, aFill.height, space);
+      tile.y = aFill.y + space;
+      tile.height = aUnitSize.height;
+      aFill.y = tile.y;
+      aFill.height = aFill.height - space * 2;
+    } break;
+    default:
+      MOZ_ASSERT_UNREACHABLE("unrecognized border-image fill style");
+  }
+
+  return tile;
+}
+
+/**
+ * Returns true if the given set of arguments will require the tiles which fill
+ * the dest rect to be scaled from the source tile. See comment on ComputeTile
+ * for argument descriptions.
+ */
+static bool RequiresScaling(const nsRect& aFill, StyleBorderImageRepeat aHFill,
+                            StyleBorderImageRepeat aVFill,
+                            const nsSize& aUnitSize) {
+  // If we have no tiling in either direction, we can skip the intermediate
+  // scaling step.
+  return (aHFill != StyleBorderImageRepeat::Stretch ||
+          aVFill != StyleBorderImageRepeat::Stretch) &&
+         (aUnitSize.width != aFill.width || aUnitSize.height != aFill.height);
+}
+
+ImgDrawResult nsImageRenderer::DrawBorderImageComponent(
+    nsPresContext* aPresContext, gfxContext& aRenderingContext,
+    const nsRect& aDirtyRect, const nsRect& aFill, const CSSIntRect& aSrc,
+    StyleBorderImageRepeat aHFill, StyleBorderImageRepeat aVFill,
+    const nsSize& aUnitSize, uint8_t aIndex,
+    const Maybe<nsSize>& aSVGViewportSize, const bool aHasIntrinsicRatio) {
+  if (!IsReady()) {
+    MOZ_ASSERT_UNREACHABLE(
+        "Ensure PrepareImage() has returned true before "
+        "calling me");
+    return ImgDrawResult::BAD_ARGS;
+  }
+
+  if (aFill.IsEmpty() || aSrc.IsEmpty()) {
+    return ImgDrawResult::SUCCESS;
+  }
+
+  const bool isRequestBacked =
+      mType == StyleImage::Tag::Url || mType == StyleImage::Tag::Rect;
+  MOZ_ASSERT(isRequestBacked == mImage->IsImageRequestType());
+
+  if (isRequestBacked || mType == StyleImage::Tag::Element) {
+    nsCOMPtr<imgIContainer> subImage;
+
+    // To draw one portion of an image into a border component, we stretch that
+    // portion to match the size of that border component and then draw onto.
+    // However, preserveAspectRatio attribute of a SVG image may break this
+    // rule. To get correct rendering result, we add
+    // FLAG_FORCE_PRESERVEASPECTRATIO_NONE flag here, to tell mImage to ignore
+    // preserveAspectRatio attribute, and always do non-uniform stretch.
+    uint32_t drawFlags = ConvertImageRendererToDrawFlags(mFlags) |
+                         imgIContainer::FLAG_FORCE_PRESERVEASPECTRATIO_NONE;
+    // For those SVG image sources which don't have fixed aspect ratio (i.e.
+    // without viewport size and viewBox), we should scale the source uniformly
+    // after the viewport size is decided by "Default Sizing Algorithm".
+    if (!aHasIntrinsicRatio) {
+      drawFlags = drawFlags | imgIContainer::FLAG_FORCE_UNIFORM_SCALING;
+    }
+    // Retrieve or create the subimage we'll draw.
+    nsIntRect srcRect(aSrc.x, aSrc.y, aSrc.width, aSrc.height);
+    if (isRequestBacked) {
+      CachedBorderImageData* cachedData =
+          mForFrame->GetProperty(nsIFrame::CachedBorderImageDataProperty());
+      if (!cachedData) {
+        cachedData = new CachedBorderImageData();
+        mForFrame->AddProperty(nsIFrame::CachedBorderImageDataProperty(),
+                               cachedData);
+      }
+      if (!(subImage = cachedData->GetSubImage(aIndex))) {
+        subImage = ImageOps::Clip(mImageContainer, srcRect, aSVGViewportSize);
+        cachedData->SetSubImage(aIndex, subImage);
+      }
+    } else {
+      // This path, for eStyleImageType_Element, is currently slower than it
+      // needs to be because we don't cache anything. (In particular, if we have
+      // to draw to a temporary surface inside ClippedImage, we don't cache that
+      // temporary surface since we immediately throw the ClippedImage we create
+      // here away.) However, if we did cache, we'd need to know when to
+      // invalidate that cache, and it's not clear that it's worth the trouble
+      // since using border-image with -moz-element is rare.
+
+      RefPtr<gfxDrawable> drawable =
+          DrawableForElement(nsRect(nsPoint(), mSize), aRenderingContext);
+      if (!drawable) {
+        NS_WARNING("Could not create drawable for element");
+        return ImgDrawResult::TEMPORARY_ERROR;
+      }
+
+      nsCOMPtr<imgIContainer> image(ImageOps::CreateFromDrawable(drawable));
+      subImage = ImageOps::Clip(image, srcRect, aSVGViewportSize);
+    }
+
+    MOZ_ASSERT(!aSVGViewportSize ||
+               subImage->GetType() == imgIContainer::TYPE_VECTOR);
+
+    SamplingFilter samplingFilter =
+        nsLayoutUtils::GetSamplingFilterForFrame(mForFrame);
+
+    if (!RequiresScaling(aFill, aHFill, aVFill, aUnitSize)) {
+      ImgDrawResult result = nsLayoutUtils::DrawSingleImage(
+          aRenderingContext, aPresContext, subImage, samplingFilter, aFill,
+          aDirtyRect, SVGImageContext(), drawFlags);
+
+      if (!mImage->IsComplete()) {
+        result &= ImgDrawResult::SUCCESS_NOT_COMPLETE;
+      }
+
+      return result;
+    }
+
+    nsSize repeatSize;
+    nsRect fillRect(aFill);
+    nsRect tile = ComputeTile(fillRect, aHFill, aVFill, aUnitSize, repeatSize);
+
+    ImgDrawResult result = nsLayoutUtils::DrawBackgroundImage(
+        aRenderingContext, mForFrame, aPresContext, subImage, samplingFilter,
+        tile, fillRect, repeatSize, tile.TopLeft(), aDirtyRect, drawFlags,
+        ExtendMode::CLAMP, 1.0);
+
+    if (!mImage->IsComplete()) {
+      result &= ImgDrawResult::SUCCESS_NOT_COMPLETE;
+    }
+
+    return result;
+  }
+
+  nsSize repeatSize(aFill.Size());
+  nsRect fillRect(aFill);
+  nsRect destTile =
+      RequiresScaling(fillRect, aHFill, aVFill, aUnitSize)
+          ? ComputeTile(fillRect, aHFill, aVFill, aUnitSize, repeatSize)
+          : fillRect;
+
+  return Draw(aPresContext, aRenderingContext, aDirtyRect, destTile, fillRect,
+              destTile.TopLeft(), repeatSize, aSrc);
+}
+
+ImgDrawResult nsImageRenderer::DrawShapeImage(nsPresContext* aPresContext,
+                                              gfxContext& aRenderingContext) {
+  if (!IsReady()) {
+    MOZ_ASSERT_UNREACHABLE(
+        "Ensure PrepareImage() has returned true before "
+        "calling me");
+    return ImgDrawResult::NOT_READY;
+  }
+
+  if (mSize.width <= 0 || mSize.height <= 0) {
+    return ImgDrawResult::SUCCESS;
+  }
+
+  if (mImage->IsImageRequestType()) {
+    uint32_t drawFlags =
+        ConvertImageRendererToDrawFlags(mFlags) | imgIContainer::FRAME_FIRST;
+    nsRect dest(nsPoint(0, 0), mSize);
+    // We have a tricky situation in our choice of SamplingFilter. Shape
+    // images define a float area based on the alpha values in the rendered
+    // pixels. When multiple device pixels are used for one css pixel, the
+    // sampling can change crisp edges into aliased edges. For visual pixels,
+    // that's usually the right choice. For defining a float area, it can
+    // cause problems. If a style is using a shape-image-threshold value that
+    // is less than the alpha of the edge pixels, any filtering may smear the
+    // alpha into adjacent pixels and expand the float area in a confusing
+    // way. Since the alpha threshold can be set precisely in CSS, and since a
+    // web author may be counting on that threshold to define a precise float
+    // area from an image, it is least confusing to have the rendered pixels
+    // have unfiltered alpha. We use SamplingFilter::POINT to ensure that each
+    // rendered pixel has an alpha that precisely matches the alpha of the
+    // closest pixel in the image.
+    return nsLayoutUtils::DrawSingleImage(
+        aRenderingContext, aPresContext, mImageContainer, SamplingFilter::POINT,
+        dest, dest, SVGImageContext(), drawFlags);
+  }
+
+  if (mImage->IsGradient()) {
+    nsCSSGradientRenderer renderer = nsCSSGradientRenderer::Create(
+        aPresContext, mForFrame->Style(), *mGradientData, mSize);
+    nsRect dest(nsPoint(0, 0), mSize);
+    renderer.Paint(aRenderingContext, dest, dest, mSize,
+                   CSSIntRect::FromAppUnitsRounded(dest), dest, 1.0);
+    return ImgDrawResult::SUCCESS;
+  }
+
+  // Unsupported image type.
+  return ImgDrawResult::BAD_IMAGE;
+}
+
+bool nsImageRenderer::IsRasterImage() {
+  return mImageContainer &&
+         mImageContainer->GetType() == imgIContainer::TYPE_RASTER;
+}
+
+already_AddRefed<imgIContainer> nsImageRenderer::GetImage() {
+  return do_AddRef(mImageContainer);
+}
+
+void nsImageRenderer::PurgeCacheForViewportChange(
+    const Maybe<nsSize>& aSVGViewportSize, const bool aHasIntrinsicRatio) {
+  // Check if we should flush the cached data - only vector images need to do
+  // the check since they might not have fixed ratio.
+  if (mImageContainer &&
+      mImageContainer->GetType() == imgIContainer::TYPE_VECTOR) {
+    if (auto* cachedData =
+            mForFrame->GetProperty(nsIFrame::CachedBorderImageDataProperty())) {
+      cachedData->PurgeCacheForViewportChange(aSVGViewportSize,
+                                              aHasIntrinsicRatio);
+    }
+  }
+}
diff --git a/layout/painting/nsImageRenderer.h b/layout/painting/nsImageRenderer.h
new file mode 100644
index 0000000000..7689295a4b
--- /dev/null
+++ b/layout/painting/nsImageRenderer.h
@@ -0,0 +1,315 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef nsImageRenderer_h__
+#define nsImageRenderer_h__
+
+#include "nsStyleStruct.h"
+#include "Units.h"
+#include "mozilla/AspectRatio.h"
+#include "mozilla/SurfaceFromElementResult.h"
+
+class gfxDrawable;
+
+namespace mozilla {
+class nsDisplayItem;
+
+namespace layers {
+class StackingContextHelper;
+class WebRenderParentCommand;
+class RenderRootStateManager;
+}  // namespace layers
+
+namespace wr {
+class DisplayListBuilder;
+class IpcResourceUpdateQueue;
+}  // namespace wr
+
+// A CSSSizeOrRatio represents a (possibly partially specified) size for use
+// in computing image sizes. Either or both of the width and height might be
+// given. A ratio of width to height may also be given. If we at least two
+// of these then we can compute a concrete size, that is a width and height.
+struct CSSSizeOrRatio {
+  CSSSizeOrRatio()
+      : mWidth(0), mHeight(0), mHasWidth(false), mHasHeight(false) {}
+
+  bool CanComputeConcreteSize() const {
+    return mHasWidth + mHasHeight + HasRatio() >= 2;
+  }
+  bool IsConcrete() const { return mHasWidth && mHasHeight; }
+  bool HasRatio() const { return !!mRatio; }
+  bool IsEmpty() const {
+    return (mHasWidth && mWidth <= 0) || (mHasHeight && mHeight <= 0) ||
+           !mRatio;
+  }
+
+  // CanComputeConcreteSize must return true when ComputeConcreteSize is
+  // called.
+  nsSize ComputeConcreteSize() const;
+
+  void SetWidth(nscoord aWidth) {
+    mWidth = aWidth;
+    mHasWidth = true;
+    if (mHasHeight) {
+      mRatio = AspectRatio::FromSize(mWidth, mHeight);
+    }
+  }
+  void SetHeight(nscoord aHeight) {
+    mHeight = aHeight;
+    mHasHeight = true;
+    if (mHasWidth) {
+      mRatio = AspectRatio::FromSize(mWidth, mHeight);
+    }
+  }
+  void SetSize(const nsSize& aSize) {
+    mWidth = aSize.width;
+    mHeight = aSize.height;
+    mHasWidth = true;
+    mHasHeight = true;
+    mRatio = AspectRatio::FromSize(mWidth, mHeight);
+  }
+  void SetRatio(const AspectRatio& aRatio) {
+    MOZ_ASSERT(
+        !mHasWidth || !mHasHeight,
+        "Probably shouldn't be setting a ratio if we have a concrete size");
+    mRatio = aRatio;
+  }
+
+  AspectRatio mRatio;
+  nscoord mWidth;
+  nscoord mHeight;
+  bool mHasWidth;
+  bool mHasHeight;
+};
+
+/**
+ * This is a small wrapper class to encapsulate image drawing that can draw an
+ * StyleImage image, which may internally be a real image, a sub image, or a CSS
+ * gradient, etc...
+ *
+ * @note Always call the member functions in the order of PrepareImage(),
+ * SetSize(), and Draw*().
+ */
+class nsImageRenderer {
+ public:
+  typedef mozilla::image::ImgDrawResult ImgDrawResult;
+  typedef mozilla::layers::ImageContainer ImageContainer;
+
+  enum {
+    FLAG_SYNC_DECODE_IMAGES = 0x01,
+    FLAG_PAINTING_TO_WINDOW = 0x02,
+    FLAG_HIGH_QUALITY_SCALING = 0x04,
+    FLAG_DRAW_PARTIAL_FRAMES = 0x08
+  };
+  enum FitType { CONTAIN, COVER };
+
+  nsImageRenderer(nsIFrame* aForFrame, const mozilla::StyleImage* aImage,
+                  uint32_t aFlags);
+  ~nsImageRenderer() = default;
+  /**
+   * Populates member variables to get ready for rendering.
+   * @return true iff the image is ready, and there is at least a pixel to
+   * draw.
+   */
+  bool PrepareImage();
+
+  /**
+   * The three Compute*Size functions correspond to the sizing algorthms and
+   * definitions from the CSS Image Values and Replaced Content spec. See
+   * http://dev.w3.org/csswg/css-images-3/#sizing .
+   */
+
+  /**
+   * Compute the intrinsic size of the image as defined in the CSS Image Values
+   * spec. The intrinsic size is the unscaled size which the image would ideally
+   * like to be in app units.
+   */
+  mozilla::CSSSizeOrRatio ComputeIntrinsicSize();
+
+  /**
+   * Computes the placement for a background image, or for the image data
+   * inside of a replaced element.
+   *
+   * @param aPos The CSS <position> value that specifies the image's position.
+   * @param aOriginBounds The box to which the tiling position should be
+   *          relative. For background images, this should correspond to
+   *          'background-origin' for the frame, except when painting on the
+   *          canvas, in which case the origin bounds should be the bounds
+   *          of the root element's frame. For a replaced element, this should
+   *          be the element's content-box.
+   * @param aTopLeft [out] The top-left corner where an image tile should be
+   *          drawn.
+   * @param aAnchorPoint [out] A point which should be pixel-aligned by
+   *          nsLayoutUtils::DrawImage. This is the same as aTopLeft, unless
+   *          CSS specifies a percentage (including 'right' or 'bottom'), in
+   *          which case it's that percentage within of aOriginBounds. So
+   *          'right' would set aAnchorPoint.x to aOriginBounds.XMost().
+   *
+   * Points are returned relative to aOriginBounds.
+   */
+  static void ComputeObjectAnchorPoint(const mozilla::Position& aPos,
+                                       const nsSize& aOriginBounds,
+                                       const nsSize& aImageSize,
+                                       nsPoint* aTopLeft,
+                                       nsPoint* aAnchorPoint);
+
+  /**
+   * Compute the size of the rendered image using either the 'cover' or
+   * 'contain' constraints (aFitType).
+   */
+  static nsSize ComputeConstrainedSize(
+      const nsSize& aConstrainingSize,
+      const mozilla::AspectRatio& aIntrinsicRatio, FitType aFitType);
+  /**
+   * Compute the size of the rendered image (the concrete size) where no cover/
+   * contain constraints are given. The 'default algorithm' from the CSS Image
+   * Values spec.
+   */
+  static nsSize ComputeConcreteSize(
+      const mozilla::CSSSizeOrRatio& aSpecifiedSize,
+      const mozilla::CSSSizeOrRatio& aIntrinsicSize,
+      const nsSize& aDefaultSize);
+
+  /**
+   * Set this image's preferred size. This will be its intrinsic size where
+   * specified and the default size where it is not. Used as the unscaled size
+   * when rendering the image.
+   */
+  void SetPreferredSize(const mozilla::CSSSizeOrRatio& aIntrinsicSize,
+                        const nsSize& aDefaultSize);
+
+  /**
+   * Draws the image to the target rendering context using
+   * {background|mask}-specific arguments.
+   * @see nsLayoutUtils::DrawImage() for parameters.
+   */
+  ImgDrawResult DrawLayer(nsPresContext* aPresContext,
+                          gfxContext& aRenderingContext, const nsRect& aDest,
+                          const nsRect& aFill, const nsPoint& aAnchor,
+                          const nsRect& aDirty, const nsSize& aRepeatSize,
+                          float aOpacity);
+
+  /**
+   * Builds WebRender DisplayItems for an image using
+   * {background|mask}-specific arguments.
+   * @see nsLayoutUtils::DrawImage() for parameters.
+   */
+  ImgDrawResult BuildWebRenderDisplayItemsForLayer(
+      nsPresContext* aPresContext, mozilla::wr::DisplayListBuilder& aBuilder,
+      mozilla::wr::IpcResourceUpdateQueue& aResource,
+      const mozilla::layers::StackingContextHelper& aSc,
+      mozilla::layers::RenderRootStateManager* aManager, nsDisplayItem* aItem,
+      const nsRect& aDest, const nsRect& aFill, const nsPoint& aAnchor,
+      const nsRect& aDirty, const nsSize& aRepeatSize, float aOpacity);
+
+  /**
+   * Draw the image to a single component of a border-image style rendering.
+   * aFill The destination rect to be drawn into
+   * aSrc is the part of the image to be rendered into a tile (aUnitSize in
+   * aFill), if aSrc and the dest tile are different sizes, the image will be
+   * scaled to map aSrc onto the dest tile.
+   * aHFill and aVFill are the repeat patterns for the component -
+   * NS_STYLE_BORDER_IMAGE_REPEAT_*
+   * aUnitSize The scaled size of a single source rect (in destination coords)
+   * aIndex identifies the component: 0 1 2
+   *                                  3 4 5
+   *                                  6 7 8
+   * aSVGViewportSize The image size evaluated by default sizing algorithm.
+   * Pass Nothing() if we can read a valid viewport size or aspect-ratio from
+   * the drawing image directly, otherwise, pass Some() with viewport size
+   * evaluated from default sizing algorithm.
+   * aHasIntrinsicRatio is used to record if the source image has fixed
+   * intrinsic ratio.
+   */
+  ImgDrawResult DrawBorderImageComponent(
+      nsPresContext* aPresContext, gfxContext& aRenderingContext,
+      const nsRect& aDirtyRect, const nsRect& aFill,
+      const mozilla::CSSIntRect& aSrc, mozilla::StyleBorderImageRepeat aHFill,
+      mozilla::StyleBorderImageRepeat aVFill, const nsSize& aUnitSize,
+      uint8_t aIndex, const mozilla::Maybe<nsSize>& aSVGViewportSize,
+      const bool aHasIntrinsicRatio);
+
+  /**
+   * Draw the image to aRenderingContext which can be used to define the
+   * float area in the presence of "shape-outside: <image>".
+   */
+  ImgDrawResult DrawShapeImage(nsPresContext* aPresContext,
+                               gfxContext& aRenderingContext);
+
+  bool IsRasterImage();
+
+  /// Retrieves the image associated with this nsImageRenderer, if there is one.
+  already_AddRefed<imgIContainer> GetImage();
+
+  bool IsReady() const { return mPrepareResult == ImgDrawResult::SUCCESS; }
+  ImgDrawResult PrepareResult() const { return mPrepareResult; }
+  void SetExtendMode(mozilla::gfx::ExtendMode aMode) { mExtendMode = aMode; }
+  void SetMaskOp(mozilla::StyleMaskMode aMaskOp) { mMaskOp = aMaskOp; }
+  void PurgeCacheForViewportChange(
+      const mozilla::Maybe<nsSize>& aSVGViewportSize, const bool aHasRatio);
+  const nsSize& GetSize() const { return mSize; }
+  mozilla::StyleImage::Tag GetType() const { return mType; }
+  const mozilla::StyleGradient* GetGradientData() const {
+    return mGradientData;
+  }
+
+ private:
+  /**
+   * Draws the image to the target rendering context.
+   * aSrc is a rect on the source image which will be mapped to aDest; it's
+   * currently only used for gradients.
+   *
+   * @see nsLayoutUtils::DrawImage() for other parameters.
+   */
+  ImgDrawResult Draw(nsPresContext* aPresContext, gfxContext& aRenderingContext,
+                     const nsRect& aDirtyRect, const nsRect& aDest,
+                     const nsRect& aFill, const nsPoint& aAnchor,
+                     const nsSize& aRepeatSize, const mozilla::CSSIntRect& aSrc,
+                     float aOpacity = 1.0);
+
+  /**
+   * Builds WebRender DisplayItems for the image.
+   * aSrc is a rect on the source image which will be mapped to aDest; it's
+   * currently only used for gradients.
+   *
+   * @see nsLayoutUtils::DrawImage() for other parameters.
+   */
+  ImgDrawResult BuildWebRenderDisplayItems(
+      nsPresContext* aPresContext, mozilla::wr::DisplayListBuilder& aBuilder,
+      mozilla::wr::IpcResourceUpdateQueue& aResources,
+      const mozilla::layers::StackingContextHelper& aSc,
+      mozilla::layers::RenderRootStateManager* aManager, nsDisplayItem* aItem,
+      const nsRect& aDirtyRect, const nsRect& aDest, const nsRect& aFill,
+      const nsPoint& aAnchor, const nsSize& aRepeatSize,
+      const mozilla::CSSIntRect& aSrc, float aOpacity = 1.0);
+
+  /**
+   * Helper method for creating a gfxDrawable from mPaintServerFrame or
+   * mImageElementSurface.
+   * Requires mType to be Element.
+   * Returns null if we cannot create the drawable.
+   */
+  already_AddRefed<gfxDrawable> DrawableForElement(const nsRect& aImageRect,
+                                                   gfxContext& aContext);
+
+  nsIFrame* mForFrame;
+  const mozilla::StyleImage* mImage;
+  ImageResolution mImageResolution;
+  mozilla::StyleImage::Tag mType;
+  nsCOMPtr<imgIContainer> mImageContainer;
+  const mozilla::StyleGradient* mGradientData;
+  nsIFrame* mPaintServerFrame;
+  SurfaceFromElementResult mImageElementSurface;
+  ImgDrawResult mPrepareResult;
+  nsSize mSize;  // unscaled size of the image, in app units
+  uint32_t mFlags;
+  mozilla::gfx::ExtendMode mExtendMode;
+  mozilla::StyleMaskMode mMaskOp;
+};
+
+}  // namespace mozilla
+
+#endif /* nsImageRenderer_h__ */