Adding upstream version 124.0.1.upstream/124.0.1

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

1 files changed, 12724 insertions, 0 deletions

diff --git a/layout/generic/nsIFrame.cpp b/layout/generic/nsIFrame.cpp
new file mode 100644
index 0000000000..81109151ff
--- /dev/null
+++ b/layout/generic/nsIFrame.cpp
@@ -0,0 +1,12724 @@
+/* -*- 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/. */
+
+/* base class of all rendering objects */
+
+#include "nsIFrame.h"
+
+#include <stdarg.h>
+#include <algorithm>
+
+#include "gfx2DGlue.h"
+#include "gfxUtils.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/CaretAssociationHint.h"
+#include "mozilla/ComputedStyle.h"
+#include "mozilla/DebugOnly.h"
+#include "mozilla/DisplayPortUtils.h"
+#include "mozilla/EventForwards.h"
+#include "mozilla/dom/CSSAnimation.h"
+#include "mozilla/dom/CSSTransition.h"
+#include "mozilla/dom/ContentVisibilityAutoStateChangeEvent.h"
+#include "mozilla/dom/DocumentInlines.h"
+#include "mozilla/dom/AncestorIterator.h"
+#include "mozilla/dom/ElementInlines.h"
+#include "mozilla/dom/ImageTracker.h"
+#include "mozilla/dom/Selection.h"
+#include "mozilla/gfx/2D.h"
+#include "mozilla/gfx/PathHelpers.h"
+#include "mozilla/IntegerRange.h"
+#include "mozilla/intl/BidiEmbeddingLevel.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/PresShell.h"
+#include "mozilla/PresShellInlines.h"
+#include "mozilla/ResultExtensions.h"
+#include "mozilla/SelectionMovementUtils.h"
+#include "mozilla/Sprintf.h"
+#include "mozilla/StaticAnalysisFunctions.h"
+#include "mozilla/StaticPrefs_layout.h"
+#include "mozilla/StaticPrefs_print.h"
+#include "mozilla/StaticPrefs_ui.h"
+#include "mozilla/SVGMaskFrame.h"
+#include "mozilla/SVGObserverUtils.h"
+#include "mozilla/SVGTextFrame.h"
+#include "mozilla/SVGIntegrationUtils.h"
+#include "mozilla/SVGUtils.h"
+#include "mozilla/TextControlElement.h"
+#include "mozilla/ToString.h"
+#include "mozilla/Try.h"
+#include "mozilla/ViewportUtils.h"
+
+#include "nsCOMPtr.h"
+#include "nsFieldSetFrame.h"
+#include "nsFlexContainerFrame.h"
+#include "nsFocusManager.h"
+#include "nsFrameList.h"
+#include "nsPlaceholderFrame.h"
+#include "nsIBaseWindow.h"
+#include "nsIContent.h"
+#include "nsIContentInlines.h"
+#include "nsContentUtils.h"
+#include "nsCSSFrameConstructor.h"
+#include "nsCSSProps.h"
+#include "nsCSSPseudoElements.h"
+#include "nsCSSRendering.h"
+#include "nsAtom.h"
+#include "nsString.h"
+#include "nsReadableUtils.h"
+#include "nsTableWrapperFrame.h"
+#include "nsView.h"
+#include "nsViewManager.h"
+#include "nsIScrollableFrame.h"
+#include "nsPresContext.h"
+#include "nsPresContextInlines.h"
+#include "nsStyleConsts.h"
+#include "mozilla/Logging.h"
+#include "nsLayoutUtils.h"
+#include "LayoutLogging.h"
+#include "mozilla/RestyleManager.h"
+#include "nsImageFrame.h"
+#include "nsInlineFrame.h"
+#include "nsFrameSelection.h"
+#include "nsGkAtoms.h"
+#include "nsGridContainerFrame.h"
+#include "nsGfxScrollFrame.h"
+#include "nsCSSAnonBoxes.h"
+#include "nsCanvasFrame.h"
+
+#include "nsFieldSetFrame.h"
+#include "nsFrameTraversal.h"
+#include "nsRange.h"
+#include "nsITextControlFrame.h"
+#include "nsNameSpaceManager.h"
+#include "nsIPercentBSizeObserver.h"
+#include "nsStyleStructInlines.h"
+
+#include "nsBidiPresUtils.h"
+#include "RubyUtils.h"
+#include "TextOverflow.h"
+#include "nsAnimationManager.h"
+
+// For triple-click pref
+#include "imgIRequest.h"
+#include "nsError.h"
+#include "nsContainerFrame.h"
+#include "nsBlockFrame.h"
+#include "nsDisplayList.h"
+#include "nsChangeHint.h"
+#include "nsSubDocumentFrame.h"
+#include "RetainedDisplayListBuilder.h"
+
+#include "gfxContext.h"
+#include "nsAbsoluteContainingBlock.h"
+#include "ScrollSnap.h"
+#include "StickyScrollContainer.h"
+#include "nsFontInflationData.h"
+#include "nsRegion.h"
+#include "nsIFrameInlines.h"
+#include "nsStyleChangeList.h"
+#include "nsWindowSizes.h"
+
+#ifdef ACCESSIBILITY
+#  include "nsAccessibilityService.h"
+#endif
+
+#include "mozilla/AsyncEventDispatcher.h"
+#include "mozilla/CSSClipPathInstance.h"
+#include "mozilla/EffectCompositor.h"
+#include "mozilla/EffectSet.h"
+#include "mozilla/EventListenerManager.h"
+#include "mozilla/EventStateManager.h"
+#include "mozilla/Preferences.h"
+#include "mozilla/LookAndFeel.h"
+#include "mozilla/MouseEvents.h"
+#include "mozilla/ServoStyleSet.h"
+#include "mozilla/ServoStyleSetInlines.h"
+#include "mozilla/css/ImageLoader.h"
+#include "mozilla/dom/HTMLBodyElement.h"
+#include "mozilla/dom/SVGPathData.h"
+#include "mozilla/dom/TouchEvent.h"
+#include "mozilla/gfx/Tools.h"
+#include "mozilla/layers/WebRenderUserData.h"
+#include "mozilla/layout/ScrollAnchorContainer.h"
+#include "nsPrintfCString.h"
+#include "ActiveLayerTracker.h"
+
+#include "nsITheme.h"
+
+using namespace mozilla;
+using namespace mozilla::css;
+using namespace mozilla::dom;
+using namespace mozilla::gfx;
+using namespace mozilla::layers;
+using namespace mozilla::layout;
+typedef nsAbsoluteContainingBlock::AbsPosReflowFlags AbsPosReflowFlags;
+using nsStyleTransformMatrix::TransformReferenceBox;
+
+nsIFrame* nsILineIterator::LineInfo::GetLastFrameOnLine() const {
+  if (!mNumFramesOnLine) {
+    return nullptr;  // empty line, not illegal
+  }
+  MOZ_ASSERT(mFirstFrameOnLine);
+  nsIFrame* maybeLastFrame = mFirstFrameOnLine;
+  for ([[maybe_unused]] int32_t i : IntegerRange(mNumFramesOnLine - 1)) {
+    maybeLastFrame = maybeLastFrame->GetNextSibling();
+    if (NS_WARN_IF(!maybeLastFrame)) {
+      return nullptr;
+    }
+  }
+  return maybeLastFrame;
+}
+
+#ifdef HAVE_64BIT_BUILD
+static_assert(sizeof(nsIFrame) == 120, "nsIFrame should remain small");
+#else
+static_assert(sizeof(void*) == 4, "Odd build config?");
+// FIXME(emilio): Investigate why win32 and android-arm32 have bigger sizes (80)
+// than Linux32 (76).
+static_assert(sizeof(nsIFrame) <= 80, "nsIFrame should remain small");
+#endif
+
+const mozilla::LayoutFrameType nsIFrame::sLayoutFrameTypes[kFrameClassCount] = {
+#define FRAME_ID(class_, type_, ...) mozilla::LayoutFrameType::type_,
+#define ABSTRACT_FRAME_ID(...)
+#include "mozilla/FrameIdList.h"
+#undef FRAME_ID
+#undef ABSTRACT_FRAME_ID
+};
+
+const nsIFrame::ClassFlags nsIFrame::sLayoutFrameClassFlags[kFrameClassCount] =
+    {
+#define FRAME_ID(class_, type_, flags_, ...) flags_,
+#define ABSTRACT_FRAME_ID(...)
+#include "mozilla/FrameIdList.h"
+#undef FRAME_ID
+#undef ABSTRACT_FRAME_ID
+};
+
+std::ostream& operator<<(std::ostream& aStream, const nsDirection& aDirection) {
+  return aStream << (aDirection == eDirNext ? "eDirNext" : "eDirPrevious");
+}
+
+struct nsContentAndOffset {
+  nsIContent* mContent = nullptr;
+  int32_t mOffset = 0;
+};
+
+#include "nsILineIterator.h"
+#include "prenv.h"
+
+// Utility function to set a nsRect-valued property table entry on aFrame,
+// reusing the existing storage if the property happens to be already set.
+template <typename T>
+static void SetOrUpdateRectValuedProperty(
+    nsIFrame* aFrame, FrameProperties::Descriptor<T> aProperty,
+    const nsRect& aNewValue) {
+  bool found;
+  nsRect* rectStorage = aFrame->GetProperty(aProperty, &found);
+  if (!found) {
+    rectStorage = new nsRect(aNewValue);
+    aFrame->AddProperty(aProperty, rectStorage);
+  } else {
+    *rectStorage = aNewValue;
+  }
+}
+
+FrameDestroyContext::~FrameDestroyContext() {
+  for (auto& content : mozilla::Reversed(mAnonymousContent)) {
+    mPresShell->NativeAnonymousContentRemoved(content);
+    content->UnbindFromTree();
+  }
+}
+
+// Formerly the nsIFrameDebug interface
+
+std::ostream& operator<<(std::ostream& aStream, const nsReflowStatus& aStatus) {
+  char complete = 'Y';
+  if (aStatus.IsIncomplete()) {
+    complete = 'N';
+  } else if (aStatus.IsOverflowIncomplete()) {
+    complete = 'O';
+  }
+
+  char brk = 'N';
+  if (aStatus.IsInlineBreakBefore()) {
+    brk = 'B';
+  } else if (aStatus.IsInlineBreakAfter()) {
+    brk = 'A';
+  }
+
+  aStream << "["
+          << "Complete=" << complete << ","
+          << "NIF=" << (aStatus.NextInFlowNeedsReflow() ? 'Y' : 'N') << ","
+          << "Break=" << brk << ","
+          << "FirstLetter=" << (aStatus.FirstLetterComplete() ? 'Y' : 'N')
+          << "]";
+  return aStream;
+}
+
+#ifdef DEBUG
+
+/**
+ * Note: the log module is created during library initialization which
+ * means that you cannot perform logging before then.
+ */
+mozilla::LazyLogModule nsIFrame::sFrameLogModule("frame");
+
+#endif
+
+NS_DECLARE_FRAME_PROPERTY_DELETABLE(AbsoluteContainingBlockProperty,
+                                    nsAbsoluteContainingBlock)
+
+bool nsIFrame::HasAbsolutelyPositionedChildren() const {
+  return IsAbsoluteContainer() &&
+         GetAbsoluteContainingBlock()->HasAbsoluteFrames();
+}
+
+nsAbsoluteContainingBlock* nsIFrame::GetAbsoluteContainingBlock() const {
+  NS_ASSERTION(IsAbsoluteContainer(),
+               "The frame is not marked as an abspos container correctly");
+  nsAbsoluteContainingBlock* absCB =
+      GetProperty(AbsoluteContainingBlockProperty());
+  NS_ASSERTION(absCB,
+               "The frame is marked as an abspos container but doesn't have "
+               "the property");
+  return absCB;
+}
+
+void nsIFrame::MarkAsAbsoluteContainingBlock() {
+  MOZ_ASSERT(HasAnyStateBits(NS_FRAME_CAN_HAVE_ABSPOS_CHILDREN));
+  NS_ASSERTION(!GetProperty(AbsoluteContainingBlockProperty()),
+               "Already has an abs-pos containing block property?");
+  NS_ASSERTION(!HasAnyStateBits(NS_FRAME_HAS_ABSPOS_CHILDREN),
+               "Already has NS_FRAME_HAS_ABSPOS_CHILDREN state bit?");
+  AddStateBits(NS_FRAME_HAS_ABSPOS_CHILDREN);
+  SetProperty(AbsoluteContainingBlockProperty(),
+              new nsAbsoluteContainingBlock(GetAbsoluteListID()));
+}
+
+void nsIFrame::MarkAsNotAbsoluteContainingBlock() {
+  NS_ASSERTION(!HasAbsolutelyPositionedChildren(), "Think of the children!");
+  NS_ASSERTION(GetProperty(AbsoluteContainingBlockProperty()),
+               "Should have an abs-pos containing block property");
+  NS_ASSERTION(HasAnyStateBits(NS_FRAME_HAS_ABSPOS_CHILDREN),
+               "Should have NS_FRAME_HAS_ABSPOS_CHILDREN state bit");
+  MOZ_ASSERT(HasAnyStateBits(NS_FRAME_CAN_HAVE_ABSPOS_CHILDREN));
+  RemoveStateBits(NS_FRAME_HAS_ABSPOS_CHILDREN);
+  RemoveProperty(AbsoluteContainingBlockProperty());
+}
+
+bool nsIFrame::CheckAndClearPaintedState() {
+  bool result = HasAnyStateBits(NS_FRAME_PAINTED_THEBES);
+  RemoveStateBits(NS_FRAME_PAINTED_THEBES);
+
+  for (const auto& childList : ChildLists()) {
+    for (nsIFrame* child : childList.mList) {
+      if (child->CheckAndClearPaintedState()) {
+        result = true;
+      }
+    }
+  }
+  return result;
+}
+
+bool nsIFrame::CheckAndClearDisplayListState() {
+  bool result = BuiltDisplayList();
+  SetBuiltDisplayList(false);
+
+  for (const auto& childList : ChildLists()) {
+    for (nsIFrame* child : childList.mList) {
+      if (child->CheckAndClearDisplayListState()) {
+        result = true;
+      }
+    }
+  }
+  return result;
+}
+
+bool nsIFrame::IsVisibleConsideringAncestors(uint32_t aFlags) const {
+  if (!StyleVisibility()->IsVisible()) {
+    return false;
+  }
+
+  if (PresShell()->IsUnderHiddenEmbedderElement()) {
+    return false;
+  }
+
+  const nsIFrame* frame = this;
+  while (frame) {
+    nsView* view = frame->GetView();
+    if (view && view->GetVisibility() == ViewVisibility::Hide) {
+      return false;
+    }
+
+    if (frame->StyleUIReset()->mMozSubtreeHiddenOnlyVisually) {
+      return false;
+    }
+
+    // This method is used to determine if a frame is focusable, because it's
+    // called by nsIFrame::IsFocusable. `content-visibility: auto` should not
+    // force this frame to be unfocusable, so we only take into account
+    // `content-visibility: hidden` here.
+    if (this != frame &&
+        frame->HidesContent(IncludeContentVisibility::Hidden)) {
+      return false;
+    }
+
+    if (nsIFrame* parent = frame->GetParent()) {
+      frame = parent;
+    } else {
+      parent = nsLayoutUtils::GetCrossDocParentFrameInProcess(frame);
+      if (!parent) break;
+
+      if ((aFlags & nsIFrame::VISIBILITY_CROSS_CHROME_CONTENT_BOUNDARY) == 0 &&
+          parent->PresContext()->IsChrome() &&
+          !frame->PresContext()->IsChrome()) {
+        break;
+      }
+
+      frame = parent;
+    }
+  }
+
+  return true;
+}
+
+void nsIFrame::FindCloserFrameForSelection(
+    const nsPoint& aPoint, FrameWithDistance* aCurrentBestFrame) {
+  if (nsLayoutUtils::PointIsCloserToRect(aPoint, mRect,
+                                         aCurrentBestFrame->mXDistance,
+                                         aCurrentBestFrame->mYDistance)) {
+    aCurrentBestFrame->mFrame = this;
+  }
+}
+
+void nsIFrame::ElementStateChanged(mozilla::dom::ElementState aStates) {}
+
+void WeakFrame::Clear(mozilla::PresShell* aPresShell) {
+  if (aPresShell) {
+    aPresShell->RemoveWeakFrame(this);
+  }
+  mFrame = nullptr;
+}
+
+AutoWeakFrame::AutoWeakFrame(const WeakFrame& aOther)
+    : mPrev(nullptr), mFrame(nullptr) {
+  Init(aOther.GetFrame());
+}
+
+void AutoWeakFrame::Clear(mozilla::PresShell* aPresShell) {
+  if (aPresShell) {
+    aPresShell->RemoveAutoWeakFrame(this);
+  }
+  mFrame = nullptr;
+  mPrev = nullptr;
+}
+
+AutoWeakFrame::~AutoWeakFrame() {
+  Clear(mFrame ? mFrame->PresContext()->GetPresShell() : nullptr);
+}
+
+void AutoWeakFrame::Init(nsIFrame* aFrame) {
+  Clear(mFrame ? mFrame->PresContext()->GetPresShell() : nullptr);
+  mFrame = aFrame;
+  if (mFrame) {
+    mozilla::PresShell* presShell = mFrame->PresContext()->GetPresShell();
+    NS_WARNING_ASSERTION(presShell, "Null PresShell in AutoWeakFrame!");
+    if (presShell) {
+      presShell->AddAutoWeakFrame(this);
+    } else {
+      mFrame = nullptr;
+    }
+  }
+}
+
+void WeakFrame::Init(nsIFrame* aFrame) {
+  Clear(mFrame ? mFrame->PresContext()->GetPresShell() : nullptr);
+  mFrame = aFrame;
+  if (mFrame) {
+    mozilla::PresShell* presShell = mFrame->PresContext()->GetPresShell();
+    MOZ_ASSERT(presShell, "Null PresShell in WeakFrame!");
+    if (presShell) {
+      presShell->AddWeakFrame(this);
+    } else {
+      mFrame = nullptr;
+    }
+  }
+}
+
+nsIFrame* NS_NewEmptyFrame(PresShell* aPresShell, ComputedStyle* aStyle) {
+  return new (aPresShell) nsIFrame(aStyle, aPresShell->GetPresContext());
+}
+
+nsIFrame::~nsIFrame() {
+  MOZ_COUNT_DTOR(nsIFrame);
+
+  MOZ_ASSERT(GetVisibility() != Visibility::ApproximatelyVisible,
+             "Visible nsFrame is being destroyed");
+}
+
+NS_IMPL_FRAMEARENA_HELPERS(nsIFrame)
+
+// Dummy operator delete.  Will never be called, but must be defined
+// to satisfy some C++ ABIs.
+void nsIFrame::operator delete(void*, size_t) {
+  MOZ_CRASH("nsIFrame::operator delete should never be called");
+}
+
+NS_QUERYFRAME_HEAD(nsIFrame)
+  NS_QUERYFRAME_ENTRY(nsIFrame)
+NS_QUERYFRAME_TAIL_INHERITANCE_ROOT
+
+/////////////////////////////////////////////////////////////////////////////
+// nsIFrame
+
+static bool IsFontSizeInflationContainer(nsIFrame* aFrame,
+                                         const nsStyleDisplay* aStyleDisplay) {
+  /*
+   * Font size inflation is built around the idea that we're inflating
+   * the fonts for a pan-and-zoom UI so that when the user scales up a
+   * block or other container to fill the width of the device, the fonts
+   * will be readable.  To do this, we need to pick what counts as a
+   * container.
+   *
+   * From a code perspective, the only hard requirement is that frames
+   * that are line participants (nsIFrame::IsLineParticipant) are never
+   * containers, since line layout assumes that the inflation is consistent
+   * within a line.
+   *
+   * This is not an imposition, since we obviously want a bunch of text
+   * (possibly with inline elements) flowing within a block to count the
+   * block (or higher) as its container.
+   *
+   * We also want form controls, including the text in the anonymous
+   * content inside of them, to match each other and the text next to
+   * them, so they and their anonymous content should also not be a
+   * container.
+   *
+   * However, because we can't reliably compute sizes across XUL during
+   * reflow, any XUL frame with a XUL parent is always a container.
+   *
+   * There are contexts where it would be nice if some blocks didn't
+   * count as a container, so that, for example, an indented quotation
+   * didn't end up with a smaller font size.  However, it's hard to
+   * distinguish these situations where we really do want the indented
+   * thing to count as a container, so we don't try, and blocks are
+   * always containers.
+   */
+
+  // The root frame should always be an inflation container.
+  if (!aFrame->GetParent()) {
+    return true;
+  }
+
+  nsIContent* content = aFrame->GetContent();
+  if (content && content->IsInNativeAnonymousSubtree()) {
+    // Native anonymous content shouldn't be a font inflation root,
+    // except for the canvas custom content container.
+    nsCanvasFrame* canvas = aFrame->PresShell()->GetCanvasFrame();
+    return canvas && canvas->GetCustomContentContainer() == content;
+  }
+
+  LayoutFrameType frameType = aFrame->Type();
+  bool isInline =
+      aFrame->GetDisplay().IsInlineFlow() || RubyUtils::IsRubyBox(frameType) ||
+      (aStyleDisplay->IsFloatingStyle() &&
+       frameType == LayoutFrameType::Letter) ||
+      // Given multiple frames for the same node, only the
+      // outer one should be considered a container.
+      // (Important, e.g., for nsSelectsAreaFrame.)
+      (aFrame->GetParent()->GetContent() == content) ||
+      (content &&
+       // Form controls shouldn't become inflation containers.
+       (content->IsAnyOfHTMLElements(nsGkAtoms::option, nsGkAtoms::optgroup,
+                                     nsGkAtoms::select, nsGkAtoms::input,
+                                     nsGkAtoms::button, nsGkAtoms::textarea)));
+  NS_ASSERTION(!aFrame->IsLineParticipant() || isInline ||
+                   // br frames and mathml frames report being line
+                   // participants even when their position or display is
+                   // set
+                   aFrame->IsBrFrame() || aFrame->IsMathMLFrame(),
+               "line participants must not be containers");
+  return !isInline;
+}
+
+static void MaybeScheduleReflowSVGNonDisplayText(nsIFrame* aFrame) {
+  if (!aFrame->IsInSVGTextSubtree()) {
+    return;
+  }
+
+  // We need to ensure that any non-display SVGTextFrames get reflowed when a
+  // child text frame gets new style. Thus we need to schedule a reflow in
+  // |DidSetComputedStyle|. We also need to call it from |DestroyFrom|,
+  // because otherwise we won't get notified when style changes to
+  // "display:none".
+  SVGTextFrame* svgTextFrame = static_cast<SVGTextFrame*>(
+      nsLayoutUtils::GetClosestFrameOfType(aFrame, LayoutFrameType::SVGText));
+  nsIFrame* anonBlock = svgTextFrame->PrincipalChildList().FirstChild();
+
+  // Note that we must check NS_FRAME_FIRST_REFLOW on our SVGTextFrame's
+  // anonymous block frame rather than our aFrame, since NS_FRAME_FIRST_REFLOW
+  // may be set on us if we're a new frame that has been inserted after the
+  // document's first reflow. (In which case this DidSetComputedStyle call may
+  // be happening under frame construction under a Reflow() call.)
+  if (!anonBlock || anonBlock->HasAnyStateBits(NS_FRAME_FIRST_REFLOW)) {
+    return;
+  }
+
+  if (!svgTextFrame->HasAnyStateBits(NS_FRAME_IS_NONDISPLAY) ||
+      svgTextFrame->HasAnyStateBits(NS_STATE_SVG_TEXT_IN_REFLOW)) {
+    return;
+  }
+
+  svgTextFrame->ScheduleReflowSVGNonDisplayText(
+      IntrinsicDirty::FrameAncestorsAndDescendants);
+}
+
+bool nsIFrame::IsPrimaryFrameOfRootOrBodyElement() const {
+  if (!IsPrimaryFrame()) {
+    return false;
+  }
+  nsIContent* content = GetContent();
+  Document* document = content->OwnerDoc();
+  return content == document->GetRootElement() ||
+         content == document->GetBodyElement();
+}
+
+bool nsIFrame::IsRenderedLegend() const {
+  if (auto* parent = GetParent(); parent && parent->IsFieldSetFrame()) {
+    return static_cast<nsFieldSetFrame*>(parent)->GetLegend() == this;
+  }
+  return false;
+}
+
+void nsIFrame::Init(nsIContent* aContent, nsContainerFrame* aParent,
+                    nsIFrame* aPrevInFlow) {
+  MOZ_ASSERT(nsQueryFrame::FrameIID(mClass) == GetFrameId());
+  MOZ_ASSERT(!mContent, "Double-initing a frame?");
+
+  mContent = aContent;
+  mParent = aParent;
+  MOZ_DIAGNOSTIC_ASSERT(!mParent || PresShell() == mParent->PresShell());
+
+  if (aPrevInFlow) {
+    mWritingMode = aPrevInFlow->GetWritingMode();
+
+    // Copy some state bits from prev-in-flow (the bits that should apply
+    // throughout a continuation chain). The bits are sorted according to their
+    // order in nsFrameStateBits.h.
+
+    // clang-format off
+    AddStateBits(aPrevInFlow->GetStateBits() &
+                 (NS_FRAME_GENERATED_CONTENT |
+                  NS_FRAME_OUT_OF_FLOW |
+                  NS_FRAME_CAN_HAVE_ABSPOS_CHILDREN |
+                  NS_FRAME_INDEPENDENT_SELECTION |
+                  NS_FRAME_PART_OF_IBSPLIT |
+                  NS_FRAME_MAY_BE_TRANSFORMED |
+                  NS_FRAME_HAS_MULTI_COLUMN_ANCESTOR));
+    // clang-format on
+
+    // Copy other bits in nsIFrame from prev-in-flow.
+    mHasColumnSpanSiblings = aPrevInFlow->HasColumnSpanSiblings();
+  } else {
+    PresContext()->ConstructedFrame();
+  }
+
+  if (GetParent()) {
+    if (MOZ_UNLIKELY(mContent == PresContext()->Document()->GetRootElement() &&
+                     mContent == GetParent()->GetContent())) {
+      // Our content is the root element and we have the same content as our
+      // parent. That is, we are the internal anonymous frame of the root
+      // element. Copy the used mWritingMode from our parent because
+      // mDocElementContainingBlock gets its mWritingMode from <body>.
+      mWritingMode = GetParent()->GetWritingMode();
+    }
+
+    // Copy some state bits from our parent (the bits that should apply
+    // recursively throughout a subtree). The bits are sorted according to their
+    // order in nsFrameStateBits.h.
+
+    // clang-format off
+    AddStateBits(GetParent()->GetStateBits() &
+                 (NS_FRAME_GENERATED_CONTENT |
+                  NS_FRAME_INDEPENDENT_SELECTION |
+                  NS_FRAME_IS_SVG_TEXT |
+                  NS_FRAME_IN_POPUP |
+                  NS_FRAME_IS_NONDISPLAY));
+    // clang-format on
+
+    if (HasAnyStateBits(NS_FRAME_IN_POPUP) && TrackingVisibility()) {
+      // Assume all frames in popups are visible.
+      IncApproximateVisibleCount();
+    }
+  }
+  if (aPrevInFlow) {
+    mMayHaveOpacityAnimation = aPrevInFlow->MayHaveOpacityAnimation();
+    mMayHaveTransformAnimation = aPrevInFlow->MayHaveTransformAnimation();
+  } else if (mContent) {
+    // It's fine to fetch the EffectSet for the style frame here because in the
+    // following code we take care of the case where animations may target
+    // a different frame.
+    EffectSet* effectSet = EffectSet::GetForStyleFrame(this);
+    if (effectSet) {
+      mMayHaveOpacityAnimation = effectSet->MayHaveOpacityAnimation();
+
+      if (effectSet->MayHaveTransformAnimation()) {
+        // If we are the inner table frame for display:table content, then
+        // transform animations should go on our parent frame (the table wrapper
+        // frame).
+        //
+        // We do this when initializing the child frame (table inner frame),
+        // because when initializng the table wrapper frame, we don't yet have
+        // access to its children so we can't tell if we have transform
+        // animations or not.
+        if (SupportsCSSTransforms()) {
+          mMayHaveTransformAnimation = true;
+          AddStateBits(NS_FRAME_MAY_BE_TRANSFORMED);
+        } else if (aParent && nsLayoutUtils::GetStyleFrame(aParent) == this) {
+          MOZ_ASSERT(
+              aParent->SupportsCSSTransforms(),
+              "Style frames that don't support transforms should have parents"
+              " that do");
+          aParent->mMayHaveTransformAnimation = true;
+          aParent->AddStateBits(NS_FRAME_MAY_BE_TRANSFORMED);
+        }
+      }
+    }
+  }
+
+  const nsStyleDisplay* disp = StyleDisplay();
+  if (disp->HasTransform(this)) {
+    // If 'transform' dynamically changes, RestyleManager takes care of
+    // updating this bit.
+    AddStateBits(NS_FRAME_MAY_BE_TRANSFORMED);
+  }
+
+  if (nsLayoutUtils::FontSizeInflationEnabled(PresContext()) ||
+      !GetParent()
+#ifdef DEBUG
+      // We have assertions that check inflation invariants even when
+      // font size inflation is not enabled.
+      || true
+#endif
+  ) {
+    if (IsFontSizeInflationContainer(this, disp)) {
+      AddStateBits(NS_FRAME_FONT_INFLATION_CONTAINER);
+      if (!GetParent() ||
+          // I'd use NS_FRAME_OUT_OF_FLOW, but it's not set yet.
+          disp->IsFloating(this) || disp->IsAbsolutelyPositioned(this) ||
+          GetParent()->IsFlexContainerFrame() ||
+          GetParent()->IsGridContainerFrame()) {
+        AddStateBits(NS_FRAME_FONT_INFLATION_FLOW_ROOT);
+      }
+    }
+    NS_ASSERTION(
+        GetParent() || HasAnyStateBits(NS_FRAME_FONT_INFLATION_CONTAINER),
+        "root frame should always be a container");
+  }
+
+  if (TrackingVisibility() && PresShell()->AssumeAllFramesVisible()) {
+    IncApproximateVisibleCount();
+  }
+
+  DidSetComputedStyle(nullptr);
+
+  // For a newly created frame, we need to update this frame's visibility state.
+  // Usually we update the state when the frame is restyled and has a
+  // VisibilityChange change hint but we don't generate any change hints for
+  // newly created frames.
+  // Note: We don't need to do this for placeholders since placeholders have
+  // different styles so that the styles don't have visibility:hidden even if
+  // the parent has visibility:hidden style. We also don't need to update the
+  // state when creating continuations because its visibility is the same as its
+  // prev-in-flow, and the animation code cares only primary frames.
+  if (!IsPlaceholderFrame() && !aPrevInFlow) {
+    UpdateVisibleDescendantsState();
+  }
+
+  if (!aPrevInFlow && HasAnyStateBits(NS_FRAME_IS_NONDISPLAY)) {
+    // We aren't going to get a reflow, so nothing else will call
+    // InvalidateRenderingObservers, we have to do it here.
+    SVGObserverUtils::InvalidateRenderingObservers(this);
+  }
+}
+
+void nsIFrame::InitPrimaryFrame() {
+  MOZ_ASSERT(IsPrimaryFrame());
+  HandlePrimaryFrameStyleChange(nullptr);
+}
+
+void nsIFrame::HandlePrimaryFrameStyleChange(ComputedStyle* aOldStyle) {
+  const nsStyleDisplay* disp = StyleDisplay();
+  const nsStyleDisplay* oldDisp =
+      aOldStyle ? aOldStyle->StyleDisplay() : nullptr;
+
+  const bool wasQueryContainer = oldDisp && oldDisp->IsQueryContainer();
+  const bool isQueryContainer = disp->IsQueryContainer();
+  if (wasQueryContainer != isQueryContainer) {
+    auto* pc = PresContext();
+    if (isQueryContainer) {
+      pc->RegisterContainerQueryFrame(this);
+    } else {
+      pc->UnregisterContainerQueryFrame(this);
+    }
+  }
+
+  const auto cv = disp->ContentVisibility(*this);
+  if (!oldDisp || oldDisp->ContentVisibility(*this) != cv) {
+    if (cv == StyleContentVisibility::Auto) {
+      PresShell()->RegisterContentVisibilityAutoFrame(this);
+    } else {
+      if (auto* element = Element::FromNodeOrNull(GetContent())) {
+        element->ClearContentRelevancy();
+      }
+      PresShell()->UnregisterContentVisibilityAutoFrame(this);
+    }
+    PresContext()->SetNeedsToUpdateHiddenByContentVisibilityForAnimations();
+  }
+
+  HandleLastRememberedSize();
+}
+
+void nsIFrame::Destroy(DestroyContext& aContext) {
+  NS_ASSERTION(!nsContentUtils::IsSafeToRunScript(),
+               "destroy called on frame while scripts not blocked");
+  NS_ASSERTION(!GetNextSibling() && !GetPrevSibling(),
+               "Frames should be removed before destruction.");
+  MOZ_ASSERT(!HasAbsolutelyPositionedChildren());
+  MOZ_ASSERT(!HasAnyStateBits(NS_FRAME_PART_OF_IBSPLIT),
+             "NS_FRAME_PART_OF_IBSPLIT set on non-nsContainerFrame?");
+
+  MaybeScheduleReflowSVGNonDisplayText(this);
+
+  SVGObserverUtils::InvalidateDirectRenderingObservers(this);
+
+  const auto* disp = StyleDisplay();
+  if (disp->mPosition == StylePositionProperty::Sticky) {
+    if (auto* ssc =
+            StickyScrollContainer::GetStickyScrollContainerForFrame(this)) {
+      ssc->RemoveFrame(this);
+    }
+  }
+
+  if (HasAnyStateBits(NS_FRAME_OUT_OF_FLOW)) {
+    if (nsPlaceholderFrame* placeholder = GetPlaceholderFrame()) {
+      placeholder->SetOutOfFlowFrame(nullptr);
+    }
+  }
+
+  nsPresContext* pc = PresContext();
+  mozilla::PresShell* ps = pc->GetPresShell();
+  if (IsPrimaryFrame()) {
+    if (disp->IsQueryContainer()) {
+      pc->UnregisterContainerQueryFrame(this);
+    }
+    if (disp->ContentVisibility(*this) == StyleContentVisibility::Auto) {
+      ps->UnregisterContentVisibilityAutoFrame(this);
+    }
+    // This needs to happen before we clear our Properties() table.
+    ActiveLayerTracker::TransferActivityToContent(this, mContent);
+  }
+
+  ScrollAnchorContainer* anchor = nullptr;
+  if (IsScrollAnchor(&anchor)) {
+    anchor->InvalidateAnchor();
+  }
+
+  if (HasCSSAnimations() || HasCSSTransitions() ||
+      // It's fine to look up the style frame here since if we're destroying the
+      // frames for display:table content we should be destroying both wrapper
+      // and inner frame.
+      EffectSet::GetForStyleFrame(this)) {
+    // If no new frame for this element is created by the end of the
+    // restyling process, stop animations and transitions for this frame
+    RestyleManager::AnimationsWithDestroyedFrame* adf =
+        pc->RestyleManager()->GetAnimationsWithDestroyedFrame();
+    // AnimationsWithDestroyedFrame only lives during the restyling process.
+    if (adf) {
+      adf->Put(mContent, mComputedStyle);
+    }
+  }
+
+  // Disable visibility tracking. Note that we have to do this before we clear
+  // frame properties and lose track of whether we were previously visible.
+  // XXX(seth): It'd be ideal to assert that we're already marked nonvisible
+  // here, but it's unfortunately tricky to guarantee in the face of things like
+  // frame reconstruction induced by style changes.
+  DisableVisibilityTracking();
+
+  // Ensure that we're not in the approximately visible list anymore.
+  ps->RemoveFrameFromApproximatelyVisibleList(this);
+
+  ps->NotifyDestroyingFrame(this);
+
+  if (HasAnyStateBits(NS_FRAME_EXTERNAL_REFERENCE)) {
+    ps->ClearFrameRefs(this);
+  }
+
+  nsView* view = GetView();
+  if (view) {
+    view->SetFrame(nullptr);
+    view->Destroy();
+  }
+
+  // Make sure that our deleted frame can't be returned from GetPrimaryFrame()
+  if (IsPrimaryFrame()) {
+    mContent->SetPrimaryFrame(nullptr);
+
+    // Pass the root of a generated content subtree (e.g. ::after/::before) to
+    // aPostDestroyData to unbind it after frame destruction is done.
+    if (HasAnyStateBits(NS_FRAME_GENERATED_CONTENT) &&
+        mContent->IsRootOfNativeAnonymousSubtree()) {
+      aContext.AddAnonymousContent(mContent.forget());
+    }
+  }
+
+  // Remove all properties attached to the frame, to ensure any property
+  // destructors that need the frame pointer are handled properly.
+  RemoveAllProperties();
+
+  // Must retrieve the object ID before calling destructors, so the
+  // vtable is still valid.
+  //
+  // Note to future tweakers: having the method that returns the
+  // object size call the destructor will not avoid an indirect call;
+  // the compiler cannot devirtualize the call to the destructor even
+  // if it's from a method defined in the same class.
+
+  nsQueryFrame::FrameIID id = GetFrameId();
+  this->~nsIFrame();
+
+#ifdef DEBUG
+  {
+    nsIFrame* rootFrame = ps->GetRootFrame();
+    MOZ_ASSERT(rootFrame);
+    if (this != rootFrame) {
+      auto* builder = nsLayoutUtils::GetRetainedDisplayListBuilder(rootFrame);
+      auto* data = builder ? builder->Data() : nullptr;
+
+      const bool inData =
+          data && (data->IsModified(this) || data->HasProps(this));
+
+      if (inData) {
+        DL_LOG(LogLevel::Warning, "Frame %p found in retained data", this);
+      }
+
+      MOZ_ASSERT(!inData, "Deleted frame in retained data!");
+    }
+  }
+#endif
+
+  // Now that we're totally cleaned out, we need to add ourselves to
+  // the presshell's recycler.
+  ps->FreeFrame(id, this);
+}
+
+std::pair<int32_t, int32_t> nsIFrame::GetOffsets() const {
+  return std::make_pair(0, 0);
+}
+
+static void CompareLayers(
+    const nsStyleImageLayers* aFirstLayers,
+    const nsStyleImageLayers* aSecondLayers,
+    const std::function<void(imgRequestProxy* aReq)>& aCallback) {
+  NS_FOR_VISIBLE_IMAGE_LAYERS_BACK_TO_FRONT(i, (*aFirstLayers)) {
+    const auto& image = aFirstLayers->mLayers[i].mImage;
+    if (!image.IsImageRequestType() || !image.IsResolved()) {
+      continue;
+    }
+
+    // aCallback is called when the style image in aFirstLayers is thought to
+    // be different with the corresponded one in aSecondLayers
+    if (!aSecondLayers || i >= aSecondLayers->mImageCount ||
+        (!aSecondLayers->mLayers[i].mImage.IsResolved() ||
+         image.GetImageRequest() !=
+             aSecondLayers->mLayers[i].mImage.GetImageRequest())) {
+      if (imgRequestProxy* req = image.GetImageRequest()) {
+        aCallback(req);
+      }
+    }
+  }
+}
+
+static void AddAndRemoveImageAssociations(
+    ImageLoader& aImageLoader, nsIFrame* aFrame,
+    const nsStyleImageLayers* aOldLayers,
+    const nsStyleImageLayers* aNewLayers) {
+  // If the old context had a background-image image, or mask-image image,
+  // and new context does not have the same image, clear the image load
+  // notifier (which keeps the image loading, if it still is) for the frame.
+  // We want to do this conservatively because some frames paint their
+  // backgrounds from some other frame's style data, and we don't want
+  // to clear those notifiers unless we have to.  (They'll be reset
+  // when we paint, although we could miss a notification in that
+  // interval.)
+  if (aOldLayers && aFrame->HasImageRequest()) {
+    CompareLayers(aOldLayers, aNewLayers, [&](imgRequestProxy* aReq) {
+      aImageLoader.DisassociateRequestFromFrame(aReq, aFrame);
+    });
+  }
+
+  CompareLayers(aNewLayers, aOldLayers, [&](imgRequestProxy* aReq) {
+    aImageLoader.AssociateRequestToFrame(aReq, aFrame);
+  });
+}
+
+void nsIFrame::AddDisplayItem(nsDisplayItem* aItem) {
+  MOZ_DIAGNOSTIC_ASSERT(!mDisplayItems.Contains(aItem));
+  mDisplayItems.AppendElement(aItem);
+#ifdef ACCESSIBILITY
+  if (nsAccessibilityService* accService = GetAccService()) {
+    accService->NotifyOfPossibleBoundsChange(PresShell(), mContent);
+  }
+#endif
+}
+
+bool nsIFrame::RemoveDisplayItem(nsDisplayItem* aItem) {
+  return mDisplayItems.RemoveElement(aItem);
+}
+
+bool nsIFrame::HasDisplayItems() { return !mDisplayItems.IsEmpty(); }
+
+bool nsIFrame::HasDisplayItem(nsDisplayItem* aItem) {
+  return mDisplayItems.Contains(aItem);
+}
+
+bool nsIFrame::HasDisplayItem(uint32_t aKey) {
+  for (nsDisplayItem* i : mDisplayItems) {
+    if (i->GetPerFrameKey() == aKey) {
+      return true;
+    }
+  }
+  return false;
+}
+
+template <typename Condition>
+static void DiscardDisplayItems(nsIFrame* aFrame, Condition aCondition) {
+  for (nsDisplayItem* i : aFrame->DisplayItems()) {
+    // Only discard items that are invalidated by this frame, as we're only
+    // guaranteed to rebuild those items. Table background items are created by
+    // the relevant table part, but have the cell frame as the primary frame,
+    // and we don't want to remove them if this is the cell.
+    if (aCondition(i) && i->FrameForInvalidation() == aFrame) {
+      i->SetCantBeReused();
+    }
+  }
+}
+
+static void DiscardOldItems(nsIFrame* aFrame) {
+  DiscardDisplayItems(aFrame,
+                      [](nsDisplayItem* aItem) { return aItem->IsOldItem(); });
+}
+
+void nsIFrame::RemoveDisplayItemDataForDeletion() {
+  // Destroying a WebRenderUserDataTable can cause destruction of other objects
+  // which can remove frame properties in their destructor. If we delete a frame
+  // property it runs the destructor of the stored object in the middle of
+  // updating the frame property table, so if the destruction of that object
+  // causes another update to the frame property table it would leave the frame
+  // property table in an inconsistent state. So we remove it from the table and
+  // then destroy it. (bug 1530657)
+  WebRenderUserDataTable* userDataTable =
+      TakeProperty(WebRenderUserDataProperty::Key());
+  if (userDataTable) {
+    for (const auto& data : userDataTable->Values()) {
+      data->RemoveFromTable();
+    }
+    delete userDataTable;
+  }
+
+  if (!nsLayoutUtils::AreRetainedDisplayListsEnabled()) {
+    // Retained display lists are disabled, no need to update
+    // RetainedDisplayListData.
+    return;
+  }
+
+  auto* builder = nsLayoutUtils::GetRetainedDisplayListBuilder(this);
+  if (!builder) {
+    MOZ_ASSERT(DisplayItems().IsEmpty());
+    MOZ_ASSERT(!IsFrameModified());
+    return;
+  }
+
+  for (nsDisplayItem* i : DisplayItems()) {
+    if (i->GetDependentFrame() == this && !i->HasDeletedFrame()) {
+      i->Frame()->MarkNeedsDisplayItemRebuild();
+    }
+    i->RemoveFrame(this);
+  }
+
+  DisplayItems().Clear();
+
+  nsAutoString name;
+#ifdef DEBUG_FRAME_DUMP
+  if (DL_LOG_TEST(LogLevel::Debug)) {
+    GetFrameName(name);
+  }
+#endif
+  DL_LOGV("Removing display item data for frame %p (%s)", this,
+          NS_ConvertUTF16toUTF8(name).get());
+
+  auto* data = builder->Data();
+  if (MayHaveWillChangeBudget()) {
+    // Keep the frame in list, so it can be removed from the will-change budget.
+    data->Flags(this) = RetainedDisplayListData::FrameFlag::HadWillChange;
+  } else {
+    data->Remove(this);
+  }
+}
+
+void nsIFrame::MarkNeedsDisplayItemRebuild() {
+  if (!nsLayoutUtils::AreRetainedDisplayListsEnabled() || IsFrameModified() ||
+      HasAnyStateBits(NS_FRAME_IN_POPUP)) {
+    // Skip frames that are already marked modified.
+    return;
+  }
+
+  if (Type() == LayoutFrameType::Placeholder) {
+    nsIFrame* oof = static_cast<nsPlaceholderFrame*>(this)->GetOutOfFlowFrame();
+    if (oof) {
+      oof->MarkNeedsDisplayItemRebuild();
+    }
+    // Do not mark placeholder frames modified.
+    return;
+  }
+
+#ifdef ACCESSIBILITY
+  if (nsAccessibilityService* accService = GetAccService()) {
+    accService->NotifyOfPossibleBoundsChange(PresShell(), mContent);
+  }
+#endif
+
+  nsIFrame* rootFrame = PresShell()->GetRootFrame();
+
+  if (rootFrame->IsFrameModified()) {
+    // The whole frame tree is modified.
+    return;
+  }
+
+  auto* builder = nsLayoutUtils::GetRetainedDisplayListBuilder(this);
+  if (!builder) {
+    MOZ_ASSERT(DisplayItems().IsEmpty());
+    return;
+  }
+
+  RetainedDisplayListData* data = builder->Data();
+  MOZ_ASSERT(data);
+
+  if (data->AtModifiedFrameLimit()) {
+    // This marks the whole frame tree modified.
+    // See |RetainedDisplayListBuilder::ShouldBuildPartial()|.
+    data->AddModifiedFrame(rootFrame);
+    return;
+  }
+
+  nsAutoString name;
+#ifdef DEBUG_FRAME_DUMP
+  if (DL_LOG_TEST(LogLevel::Debug)) {
+    GetFrameName(name);
+  }
+#endif
+
+  DL_LOGV("RDL - Rebuilding display items for frame %p (%s)", this,
+          NS_ConvertUTF16toUTF8(name).get());
+
+  data->AddModifiedFrame(this);
+
+  MOZ_ASSERT(
+      PresContext()->LayoutPhaseCount(nsLayoutPhase::DisplayListBuilding) == 0);
+
+  // Hopefully this is cheap, but we could use a frame state bit to note
+  // the presence of dependencies to speed it up.
+  for (nsDisplayItem* i : DisplayItems()) {
+    if (i->HasDeletedFrame() || i->Frame() == this) {
+      // Ignore the items with deleted frames, and the items with |this| as
+      // the primary frame.
+      continue;
+    }
+
+    if (i->GetDependentFrame() == this) {
+      // For items with |this| as a dependent frame, mark the primary frame
+      // for rebuild.
+      i->Frame()->MarkNeedsDisplayItemRebuild();
+    }
+  }
+}
+
+// Subclass hook for style post processing
+/* virtual */
+void nsIFrame::DidSetComputedStyle(ComputedStyle* aOldComputedStyle) {
+#ifdef ACCESSIBILITY
+  // Don't notify for reconstructed frames here, since the frame is still being
+  // constructed at this point and so LocalAccessible::GetFrame() will return
+  // null. Style changes for reconstructed frames are handled in
+  // DocAccessible::PruneOrInsertSubtree.
+  if (aOldComputedStyle) {
+    if (nsAccessibilityService* accService = GetAccService()) {
+      accService->NotifyOfComputedStyleChange(PresShell(), mContent);
+    }
+  }
+#endif
+
+  MaybeScheduleReflowSVGNonDisplayText(this);
+
+  Document* doc = PresContext()->Document();
+  ImageLoader* loader = doc->StyleImageLoader();
+  // Continuing text frame doesn't initialize its continuation pointer before
+  // reaching here for the first time, so we have to exclude text frames. This
+  // doesn't affect correctness because text can't match selectors.
+  //
+  // FIXME(emilio): We should consider fixing that.
+  //
+  // TODO(emilio): Can we avoid doing some / all of the image stuff when
+  // isNonTextFirstContinuation is false? We should consider doing this just for
+  // primary frames and pseudos, but the first-line reparenting code makes it
+  // all bad, should get around to bug 1465474 eventually :(
+  const bool isNonText = !IsTextFrame();
+  if (isNonText) {
+    mComputedStyle->StartImageLoads(*doc, aOldComputedStyle);
+  }
+
+  const nsStyleImageLayers* oldLayers =
+      aOldComputedStyle ? &aOldComputedStyle->StyleBackground()->mImage
+                        : nullptr;
+  const nsStyleImageLayers* newLayers = &StyleBackground()->mImage;
+  AddAndRemoveImageAssociations(*loader, this, oldLayers, newLayers);
+
+  oldLayers =
+      aOldComputedStyle ? &aOldComputedStyle->StyleSVGReset()->mMask : nullptr;
+  newLayers = &StyleSVGReset()->mMask;
+  AddAndRemoveImageAssociations(*loader, this, oldLayers, newLayers);
+
+  const nsStyleDisplay* disp = StyleDisplay();
+  bool handleStickyChange = false;
+  if (aOldComputedStyle) {
+    // Detect style changes that should trigger a scroll anchor adjustment
+    // suppression.
+    // https://drafts.csswg.org/css-scroll-anchoring/#suppression-triggers
+    bool needAnchorSuppression = false;
+
+    const nsStyleMargin* oldMargin = aOldComputedStyle->StyleMargin();
+    if (oldMargin->mMargin != StyleMargin()->mMargin) {
+      needAnchorSuppression = true;
+    }
+
+    const nsStylePadding* oldPadding = aOldComputedStyle->StylePadding();
+    if (oldPadding->mPadding != StylePadding()->mPadding) {
+      SetHasPaddingChange(true);
+      needAnchorSuppression = true;
+    }
+
+    const nsStyleDisplay* oldDisp = aOldComputedStyle->StyleDisplay();
+    if (oldDisp->mOverflowAnchor != disp->mOverflowAnchor) {
+      if (auto* container = ScrollAnchorContainer::FindFor(this)) {
+        container->InvalidateAnchor();
+      }
+      if (nsIScrollableFrame* scrollableFrame = do_QueryFrame(this)) {
+        scrollableFrame->Anchor()->InvalidateAnchor();
+      }
+    }
+
+    if (mInScrollAnchorChain) {
+      const nsStylePosition* pos = StylePosition();
+      const nsStylePosition* oldPos = aOldComputedStyle->StylePosition();
+      if (!needAnchorSuppression &&
+          (oldPos->mOffset != pos->mOffset || oldPos->mWidth != pos->mWidth ||
+           oldPos->mMinWidth != pos->mMinWidth ||
+           oldPos->mMaxWidth != pos->mMaxWidth ||
+           oldPos->mHeight != pos->mHeight ||
+           oldPos->mMinHeight != pos->mMinHeight ||
+           oldPos->mMaxHeight != pos->mMaxHeight ||
+           oldDisp->mPosition != disp->mPosition ||
+           oldDisp->mTransform != disp->mTransform)) {
+        needAnchorSuppression = true;
+      }
+
+      if (needAnchorSuppression &&
+          StaticPrefs::layout_css_scroll_anchoring_suppressions_enabled()) {
+        ScrollAnchorContainer::FindFor(this)->SuppressAdjustments();
+      }
+    }
+
+    if (disp->mPosition != oldDisp->mPosition) {
+      if (!disp->IsRelativelyOrStickyPositionedStyle() &&
+          oldDisp->IsRelativelyOrStickyPositionedStyle()) {
+        RemoveProperty(NormalPositionProperty());
+      }
+
+      handleStickyChange = disp->mPosition == StylePositionProperty::Sticky ||
+                           oldDisp->mPosition == StylePositionProperty::Sticky;
+    }
+    if (disp->mScrollSnapAlign != oldDisp->mScrollSnapAlign) {
+      ScrollSnapUtils::PostPendingResnapFor(this);
+    }
+    if (aOldComputedStyle->IsRootElementStyle() &&
+        disp->mScrollSnapType != oldDisp->mScrollSnapType) {
+      if (nsIScrollableFrame* scrollableFrame =
+              PresShell()->GetRootScrollFrameAsScrollable()) {
+        scrollableFrame->PostPendingResnap();
+      }
+    }
+    if (StyleUIReset()->mMozSubtreeHiddenOnlyVisually &&
+        !aOldComputedStyle->StyleUIReset()->mMozSubtreeHiddenOnlyVisually) {
+      PresShell::ClearMouseCapture(this);
+    }
+  } else {  // !aOldComputedStyle
+    handleStickyChange = disp->mPosition == StylePositionProperty::Sticky;
+  }
+
+  if (handleStickyChange && !HasAnyStateBits(NS_FRAME_IS_NONDISPLAY) &&
+      !GetPrevInFlow()) {
+    // Note that we only add first continuations, but we really only
+    // want to add first continuation-or-ib-split-siblings. But since we don't
+    // yet know if we're a later part of a block-in-inline split, we'll just
+    // add later members of a block-in-inline split here, and then
+    // StickyScrollContainer will remove them later.
+    if (auto* ssc =
+            StickyScrollContainer::GetStickyScrollContainerForFrame(this)) {
+      if (disp->mPosition == StylePositionProperty::Sticky) {
+        ssc->AddFrame(this);
+      } else {
+        ssc->RemoveFrame(this);
+      }
+    }
+  }
+
+  imgIRequest* oldBorderImage =
+      aOldComputedStyle
+          ? aOldComputedStyle->StyleBorder()->GetBorderImageRequest()
+          : nullptr;
+  imgIRequest* newBorderImage = StyleBorder()->GetBorderImageRequest();
+  // FIXME (Bug 759996): The following is no longer true.
+  // For border-images, we can't be as conservative (we need to set the
+  // new loaders if there has been any change) since the CalcDifference
+  // call depended on the result of GetComputedBorder() and that result
+  // depends on whether the image has loaded, start the image load now
+  // so that we'll get notified when it completes loading and can do a
+  // restyle.  Otherwise, the image might finish loading from the
+  // network before we start listening to its notifications, and then
+  // we'll never know that it's finished loading.  Likewise, we want to
+  // do this for freshly-created frames to prevent a similar race if the
+  // image loads between reflow (which can depend on whether the image
+  // is loaded) and paint.  We also don't really care about any callers who try
+  // to paint borders with a different style, because they won't have the
+  // correct size for the border either.
+  if (oldBorderImage != newBorderImage) {
+    // stop and restart the image loading/notification
+    if (oldBorderImage && HasImageRequest()) {
+      loader->DisassociateRequestFromFrame(oldBorderImage, this);
+    }
+    if (newBorderImage) {
+      loader->AssociateRequestToFrame(newBorderImage, this);
+    }
+  }
+
+  auto GetShapeImageRequest = [](const ComputedStyle* aStyle) -> imgIRequest* {
+    if (!aStyle) {
+      return nullptr;
+    }
+    auto& shape = aStyle->StyleDisplay()->mShapeOutside;
+    if (!shape.IsImage()) {
+      return nullptr;
+    }
+    return shape.AsImage().GetImageRequest();
+  };
+
+  imgIRequest* oldShapeImage = GetShapeImageRequest(aOldComputedStyle);
+  imgIRequest* newShapeImage = GetShapeImageRequest(Style());
+  if (oldShapeImage != newShapeImage) {
+    if (oldShapeImage && HasImageRequest()) {
+      loader->DisassociateRequestFromFrame(oldShapeImage, this);
+    }
+    if (newShapeImage) {
+      loader->AssociateRequestToFrame(
+          newShapeImage, this,
+          ImageLoader::Flags::
+              RequiresReflowOnFirstFrameCompleteAndLoadEventBlocking);
+    }
+  }
+
+  // SVGObserverUtils::GetEffectProperties() asserts that we only invoke it with
+  // the first continuation so we need to check that in advance.
+  const bool isNonTextFirstContinuation = isNonText && !GetPrevContinuation();
+  if (isNonTextFirstContinuation) {
+    // Kick off loading of external SVG resources referenced from properties if
+    // any. This currently includes filter, clip-path, and mask.
+    SVGObserverUtils::InitiateResourceDocLoads(this);
+  }
+
+  // If the page contains markup that overrides text direction, and
+  // does not contain any characters that would activate the Unicode
+  // bidi algorithm, we need to call |SetBidiEnabled| on the pres
+  // context before reflow starts.  See bug 115921.
+  if (StyleVisibility()->mDirection == StyleDirection::Rtl) {
+    PresContext()->SetBidiEnabled();
+  }
+
+  // The following part is for caching offset-path:path(). We cache the
+  // flatten gfx path, so we don't have to rebuild and re-flattern it at
+  // each cycle if we have animations on offset-* with a fixed offset-path.
+  const StyleOffsetPath* oldPath =
+      aOldComputedStyle ? &aOldComputedStyle->StyleDisplay()->mOffsetPath
+                        : nullptr;
+  const StyleOffsetPath& newPath = StyleDisplay()->mOffsetPath;
+  if (!oldPath || *oldPath != newPath) {
+    // FIXME: Bug 1837042. Cache all basic shapes.
+    if (newPath.IsPath()) {
+      RefPtr<gfx::PathBuilder> builder = MotionPathUtils::GetPathBuilder();
+      RefPtr<gfx::Path> path =
+          MotionPathUtils::BuildSVGPath(newPath.AsSVGPathData(), builder);
+      if (path) {
+        // The newPath could be path('') (i.e. empty path), so its gfx path
+        // could be nullptr, and so we only set property for a non-empty path.
+        SetProperty(nsIFrame::OffsetPathCache(), path.forget().take());
+      } else {
+        // May have an old cached path, so we have to delete it.
+        RemoveProperty(nsIFrame::OffsetPathCache());
+      }
+    } else if (oldPath) {
+      RemoveProperty(nsIFrame::OffsetPathCache());
+    }
+  }
+
+  if (IsPrimaryFrame()) {
+    MOZ_ASSERT(aOldComputedStyle);
+    HandlePrimaryFrameStyleChange(aOldComputedStyle);
+  }
+
+  RemoveStateBits(NS_FRAME_SIMPLE_EVENT_REGIONS | NS_FRAME_SIMPLE_DISPLAYLIST);
+
+  mMayHaveRoundedCorners = true;
+}
+
+void nsIFrame::HandleLastRememberedSize() {
+  MOZ_ASSERT(IsPrimaryFrame());
+  // Storing a last remembered size requires contain-intrinsic-size, and using
+  // a previously stored last remembered size requires content-visibility.
+  if (!StaticPrefs::layout_css_contain_intrinsic_size_enabled() ||
+      !StaticPrefs::layout_css_content_visibility_enabled()) {
+    return;
+  }
+  auto* element = Element::FromNodeOrNull(mContent);
+  if (!element) {
+    return;
+  }
+  const WritingMode wm = GetWritingMode();
+  const nsStylePosition* stylePos = StylePosition();
+  bool canRememberBSize = stylePos->ContainIntrinsicBSize(wm).HasAuto();
+  bool canRememberISize = stylePos->ContainIntrinsicISize(wm).HasAuto();
+  if (!canRememberBSize) {
+    element->RemoveLastRememberedBSize();
+  }
+  if (!canRememberISize) {
+    element->RemoveLastRememberedISize();
+  }
+  if ((canRememberBSize || canRememberISize) && !HidesContent()) {
+    bool isNonReplacedInline = IsLineParticipant() && !IsReplaced();
+    if (!isNonReplacedInline) {
+      PresContext()->Document()->ObserveForLastRememberedSize(*element);
+      return;
+    }
+  }
+  PresContext()->Document()->UnobserveForLastRememberedSize(*element);
+}
+
+#ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
+void nsIFrame::AssertNewStyleIsSane(ComputedStyle& aNewStyle) {
+  MOZ_DIAGNOSTIC_ASSERT(
+      aNewStyle.GetPseudoType() == mComputedStyle->GetPseudoType() ||
+      // ::first-line continuations are weird, this should probably be fixed via
+      // bug 1465474.
+      (mComputedStyle->GetPseudoType() == PseudoStyleType::firstLine &&
+       aNewStyle.GetPseudoType() == PseudoStyleType::mozLineFrame) ||
+      // ::first-letter continuations are broken, in particular floating ones,
+      // see bug 1490281. The construction code tries to fix this up after the
+      // fact, then restyling undoes it...
+      (mComputedStyle->GetPseudoType() == PseudoStyleType::mozText &&
+       aNewStyle.GetPseudoType() == PseudoStyleType::firstLetterContinuation) ||
+      (mComputedStyle->GetPseudoType() ==
+           PseudoStyleType::firstLetterContinuation &&
+       aNewStyle.GetPseudoType() == PseudoStyleType::mozText));
+}
+#endif
+
+void nsIFrame::ReparentFrameViewTo(nsViewManager* aViewManager,
+                                   nsView* aNewParentView) {
+  if (HasView()) {
+    if (IsMenuPopupFrame()) {
+      // This view must be parented by the root view, don't reparent it.
+      return;
+    }
+    nsView* view = GetView();
+    aViewManager->RemoveChild(view);
+
+    // The view will remember the Z-order and other attributes that have been
+    // set on it.
+    nsView* insertBefore =
+        nsLayoutUtils::FindSiblingViewFor(aNewParentView, this);
+    aViewManager->InsertChild(aNewParentView, view, insertBefore,
+                              insertBefore != nullptr);
+  } else if (HasAnyStateBits(NS_FRAME_HAS_CHILD_WITH_VIEW)) {
+    for (const auto& childList : ChildLists()) {
+      // Iterate the child frames, and check each child frame to see if it has
+      // a view
+      for (nsIFrame* child : childList.mList) {
+        child->ReparentFrameViewTo(aViewManager, aNewParentView);
+      }
+    }
+  }
+}
+
+void nsIFrame::SyncFrameViewProperties(nsView* aView) {
+  if (!aView) {
+    aView = GetView();
+    if (!aView) {
+      return;
+    }
+  }
+
+  nsViewManager* vm = aView->GetViewManager();
+
+  // Make sure visibility is correct. This only affects nsSubDocumentFrame.
+  if (!SupportsVisibilityHidden()) {
+    // See if the view should be hidden or visible
+    ComputedStyle* sc = Style();
+    vm->SetViewVisibility(aView, sc->StyleVisibility()->IsVisible()
+                                     ? ViewVisibility::Show
+                                     : ViewVisibility::Hide);
+  }
+
+  const auto zIndex = ZIndex();
+  const bool autoZIndex = !zIndex;
+  vm->SetViewZIndex(aView, autoZIndex, zIndex.valueOr(0));
+}
+
+void nsIFrame::CreateView() {
+  MOZ_ASSERT(!HasView());
+
+  nsView* parentView = GetParent()->GetClosestView();
+  MOZ_ASSERT(parentView, "no parent with view");
+
+  nsViewManager* viewManager = parentView->GetViewManager();
+  MOZ_ASSERT(viewManager, "null view manager");
+
+  nsView* view = viewManager->CreateView(GetRect(), parentView);
+  SyncFrameViewProperties(view);
+
+  nsView* insertBefore = nsLayoutUtils::FindSiblingViewFor(parentView, this);
+  // we insert this view 'above' the insertBefore view, unless insertBefore is
+  // null, in which case we want to call with aAbove == false to insert at the
+  // beginning in document order
+  viewManager->InsertChild(parentView, view, insertBefore,
+                           insertBefore != nullptr);
+
+  // REVIEW: Don't create a widget for fixed-pos elements anymore.
+  // ComputeRepaintRegionForCopy will calculate the right area to repaint
+  // when we scroll.
+  // Reparent views on any child frames (or their descendants) to this
+  // view. We can just call ReparentFrameViewTo on this frame because
+  // we know this frame has no view, so it will crawl the children. Also,
+  // we know that any descendants with views must have 'parentView' as their
+  // parent view.
+  ReparentFrameViewTo(viewManager, view);
+
+  // Remember our view
+  SetView(view);
+
+  NS_FRAME_LOG(NS_FRAME_TRACE_CALLS,
+               ("nsIFrame::CreateView: frame=%p view=%p", this, view));
+}
+
+/* virtual */
+nsMargin nsIFrame::GetUsedMargin() const {
+  nsMargin margin;
+  if (((mState & NS_FRAME_FIRST_REFLOW) && !(mState & NS_FRAME_IN_REFLOW)) ||
+      IsInSVGTextSubtree()) {
+    return margin;
+  }
+
+  if (nsMargin* m = GetProperty(UsedMarginProperty())) {
+    margin = *m;
+  } else if (!StyleMargin()->GetMargin(margin)) {
+    // If we get here, our caller probably shouldn't be calling us...
+    NS_ERROR(
+        "Returning bogus 0-sized margin, because this margin "
+        "depends on layout & isn't cached!");
+  }
+  return margin;
+}
+
+/* virtual */
+nsMargin nsIFrame::GetUsedBorder() const {
+  if (((mState & NS_FRAME_FIRST_REFLOW) && !(mState & NS_FRAME_IN_REFLOW)) ||
+      IsInSVGTextSubtree()) {
+    return {};
+  }
+
+  const nsStyleDisplay* disp = StyleDisplay();
+  if (IsThemed(disp)) {
+    // Theme methods don't use const-ness.
+    auto* mutable_this = const_cast<nsIFrame*>(this);
+    nsPresContext* pc = PresContext();
+    LayoutDeviceIntMargin widgetBorder = pc->Theme()->GetWidgetBorder(
+        pc->DeviceContext(), mutable_this, disp->EffectiveAppearance());
+    return LayoutDevicePixel::ToAppUnits(widgetBorder,
+                                         pc->AppUnitsPerDevPixel());
+  }
+
+  return StyleBorder()->GetComputedBorder();
+}
+
+/* virtual */
+nsMargin nsIFrame::GetUsedPadding() const {
+  nsMargin padding;
+  if (((mState & NS_FRAME_FIRST_REFLOW) && !(mState & NS_FRAME_IN_REFLOW)) ||
+      IsInSVGTextSubtree()) {
+    return padding;
+  }
+
+  const nsStyleDisplay* disp = StyleDisplay();
+  if (IsThemed(disp)) {
+    // Theme methods don't use const-ness.
+    nsIFrame* mutable_this = const_cast<nsIFrame*>(this);
+    nsPresContext* pc = PresContext();
+    LayoutDeviceIntMargin widgetPadding;
+    if (pc->Theme()->GetWidgetPadding(pc->DeviceContext(), mutable_this,
+                                      disp->EffectiveAppearance(),
+                                      &widgetPadding)) {
+      return LayoutDevicePixel::ToAppUnits(widgetPadding,
+                                           pc->AppUnitsPerDevPixel());
+    }
+  }
+
+  if (nsMargin* p = GetProperty(UsedPaddingProperty())) {
+    padding = *p;
+  } else if (!StylePadding()->GetPadding(padding)) {
+    // If we get here, our caller probably shouldn't be calling us...
+    NS_ERROR(
+        "Returning bogus 0-sized padding, because this padding "
+        "depends on layout & isn't cached!");
+  }
+  return padding;
+}
+
+nsIFrame::Sides nsIFrame::GetSkipSides() const {
+  if (MOZ_UNLIKELY(StyleBorder()->mBoxDecorationBreak ==
+                   StyleBoxDecorationBreak::Clone) &&
+      !HasAnyStateBits(NS_FRAME_IS_OVERFLOW_CONTAINER)) {
+    return Sides();
+  }
+
+  // Convert the logical skip sides to physical sides using the frame's
+  // writing mode
+  WritingMode writingMode = GetWritingMode();
+  LogicalSides logicalSkip = GetLogicalSkipSides();
+  Sides skip;
+
+  if (logicalSkip.BStart()) {
+    if (writingMode.IsVertical()) {
+      skip |= writingMode.IsVerticalLR() ? SideBits::eLeft : SideBits::eRight;
+    } else {
+      skip |= SideBits::eTop;
+    }
+  }
+
+  if (logicalSkip.BEnd()) {
+    if (writingMode.IsVertical()) {
+      skip |= writingMode.IsVerticalLR() ? SideBits::eRight : SideBits::eLeft;
+    } else {
+      skip |= SideBits::eBottom;
+    }
+  }
+
+  if (logicalSkip.IStart()) {
+    if (writingMode.IsVertical()) {
+      skip |= SideBits::eTop;
+    } else {
+      skip |= writingMode.IsBidiLTR() ? SideBits::eLeft : SideBits::eRight;
+    }
+  }
+
+  if (logicalSkip.IEnd()) {
+    if (writingMode.IsVertical()) {
+      skip |= SideBits::eBottom;
+    } else {
+      skip |= writingMode.IsBidiLTR() ? SideBits::eRight : SideBits::eLeft;
+    }
+  }
+  return skip;
+}
+
+nsRect nsIFrame::GetPaddingRectRelativeToSelf() const {
+  nsMargin border = GetUsedBorder().ApplySkipSides(GetSkipSides());
+  nsRect r(0, 0, mRect.width, mRect.height);
+  r.Deflate(border);
+  return r;
+}
+
+nsRect nsIFrame::GetPaddingRect() const {
+  return GetPaddingRectRelativeToSelf() + GetPosition();
+}
+
+WritingMode nsIFrame::WritingModeForLine(WritingMode aSelfWM,
+                                         nsIFrame* aSubFrame) const {
+  MOZ_ASSERT(aSelfWM == GetWritingMode());
+  WritingMode writingMode = aSelfWM;
+
+  if (StyleTextReset()->mUnicodeBidi == StyleUnicodeBidi::Plaintext) {
+    mozilla::intl::BidiEmbeddingLevel frameLevel =
+        nsBidiPresUtils::GetFrameBaseLevel(aSubFrame);
+    writingMode.SetDirectionFromBidiLevel(frameLevel);
+  }
+
+  return writingMode;
+}
+
+nsRect nsIFrame::GetMarginRect() const {
+  return GetMarginRectRelativeToSelf() + GetPosition();
+}
+
+nsRect nsIFrame::GetMarginRectRelativeToSelf() const {
+  nsMargin m = GetUsedMargin().ApplySkipSides(GetSkipSides());
+  nsRect r(0, 0, mRect.width, mRect.height);
+  r.Inflate(m);
+  return r;
+}
+
+bool nsIFrame::IsTransformed() const {
+  if (!HasAnyStateBits(NS_FRAME_MAY_BE_TRANSFORMED)) {
+    MOZ_ASSERT(!IsCSSTransformed());
+    MOZ_ASSERT(!IsSVGTransformed());
+    return false;
+  }
+  return IsCSSTransformed() || IsSVGTransformed();
+}
+
+bool nsIFrame::IsCSSTransformed() const {
+  return HasAnyStateBits(NS_FRAME_MAY_BE_TRANSFORMED) &&
+         (StyleDisplay()->HasTransform(this) || HasAnimationOfTransform());
+}
+
+bool nsIFrame::HasAnimationOfTransform() const {
+  return IsPrimaryFrame() &&
+         nsLayoutUtils::HasAnimationOfTransformAndMotionPath(this) &&
+         SupportsCSSTransforms();
+}
+
+bool nsIFrame::ChildrenHavePerspective(
+    const nsStyleDisplay* aStyleDisplay) const {
+  MOZ_ASSERT(aStyleDisplay == StyleDisplay());
+  return aStyleDisplay->HasPerspective(this);
+}
+
+bool nsIFrame::HasAnimationOfOpacity(EffectSet* aEffectSet) const {
+  return ((nsLayoutUtils::IsPrimaryStyleFrame(this) ||
+           nsLayoutUtils::FirstContinuationOrIBSplitSibling(this)
+               ->IsPrimaryFrame()) &&
+          nsLayoutUtils::HasAnimationOfPropertySet(
+              this, nsCSSPropertyIDSet::OpacityProperties(), aEffectSet));
+}
+
+bool nsIFrame::HasOpacityInternal(float aThreshold,
+                                  const nsStyleDisplay* aStyleDisplay,
+                                  const nsStyleEffects* aStyleEffects,
+                                  EffectSet* aEffectSet) const {
+  MOZ_ASSERT(0.0 <= aThreshold && aThreshold <= 1.0, "Invalid argument");
+  if (aStyleEffects->mOpacity < aThreshold ||
+      aStyleDisplay->mWillChange.bits & StyleWillChangeBits::OPACITY) {
+    return true;
+  }
+
+  if (!mMayHaveOpacityAnimation) {
+    return false;
+  }
+
+  return HasAnimationOfOpacity(aEffectSet);
+}
+
+bool nsIFrame::IsSVGTransformed(gfx::Matrix* aOwnTransforms,
+                                gfx::Matrix* aFromParentTransforms) const {
+  return false;
+}
+
+bool nsIFrame::Extend3DContext(const nsStyleDisplay* aStyleDisplay,
+                               const nsStyleEffects* aStyleEffects,
+                               mozilla::EffectSet* aEffectSetForOpacity) const {
+  if (!HasAnyStateBits(NS_FRAME_MAY_BE_TRANSFORMED)) {
+    return false;
+  }
+  const nsStyleDisplay* disp = StyleDisplayWithOptionalParam(aStyleDisplay);
+  if (disp->mTransformStyle != StyleTransformStyle::Preserve3d ||
+      !SupportsCSSTransforms()) {
+    return false;
+  }
+
+  // If we're all scroll frame, then all descendants will be clipped, so we
+  // can't preserve 3d.
+  if (IsScrollFrame()) {
+    return false;
+  }
+
+  const nsStyleEffects* effects = StyleEffectsWithOptionalParam(aStyleEffects);
+  if (HasOpacity(disp, effects, aEffectSetForOpacity)) {
+    return false;
+  }
+
+  return ShouldApplyOverflowClipping(disp) == PhysicalAxes::None &&
+         !GetClipPropClipRect(disp, effects, GetSize()) &&
+         !SVGIntegrationUtils::UsingEffectsForFrame(this) &&
+         !effects->HasMixBlendMode() &&
+         disp->mIsolation != StyleIsolation::Isolate;
+}
+
+bool nsIFrame::Combines3DTransformWithAncestors() const {
+  // Check these first as they are faster then both calls below and are we are
+  // likely to hit the early return (backface hidden is uncommon and
+  // GetReferenceFrame is a hot caller of this which only calls this if
+  // IsCSSTransformed is false).
+  if (!IsCSSTransformed() && !BackfaceIsHidden()) {
+    return false;
+  }
+  nsIFrame* parent = GetClosestFlattenedTreeAncestorPrimaryFrame();
+  return parent && parent->Extend3DContext();
+}
+
+bool nsIFrame::In3DContextAndBackfaceIsHidden() const {
+  // While both tests fail most of the time, test BackfaceIsHidden()
+  // first since it's likely to fail faster.
+  return BackfaceIsHidden() && Combines3DTransformWithAncestors();
+}
+
+bool nsIFrame::HasPerspective() const {
+  if (!IsCSSTransformed()) {
+    return false;
+  }
+  nsIFrame* parent = GetClosestFlattenedTreeAncestorPrimaryFrame();
+  if (!parent) {
+    return false;
+  }
+  return parent->ChildrenHavePerspective();
+}
+
+nsRect nsIFrame::GetContentRectRelativeToSelf() const {
+  nsMargin bp = GetUsedBorderAndPadding().ApplySkipSides(GetSkipSides());
+  nsRect r(0, 0, mRect.width, mRect.height);
+  r.Deflate(bp);
+  return r;
+}
+
+nsRect nsIFrame::GetContentRect() const {
+  return GetContentRectRelativeToSelf() + GetPosition();
+}
+
+bool nsIFrame::ComputeBorderRadii(const BorderRadius& aBorderRadius,
+                                  const nsSize& aFrameSize,
+                                  const nsSize& aBorderArea, Sides aSkipSides,
+                                  nscoord aRadii[8]) {
+  // Percentages are relative to whichever side they're on.
+  for (const auto i : mozilla::AllPhysicalHalfCorners()) {
+    const LengthPercentage& c = aBorderRadius.Get(i);
+    nscoord axis = HalfCornerIsX(i) ? aFrameSize.width : aFrameSize.height;
+    aRadii[i] = std::max(0, c.Resolve(axis));
+  }
+
+  if (aSkipSides.Top()) {
+    aRadii[eCornerTopLeftX] = 0;
+    aRadii[eCornerTopLeftY] = 0;
+    aRadii[eCornerTopRightX] = 0;
+    aRadii[eCornerTopRightY] = 0;
+  }
+
+  if (aSkipSides.Right()) {
+    aRadii[eCornerTopRightX] = 0;
+    aRadii[eCornerTopRightY] = 0;
+    aRadii[eCornerBottomRightX] = 0;
+    aRadii[eCornerBottomRightY] = 0;
+  }
+
+  if (aSkipSides.Bottom()) {
+    aRadii[eCornerBottomRightX] = 0;
+    aRadii[eCornerBottomRightY] = 0;
+    aRadii[eCornerBottomLeftX] = 0;
+    aRadii[eCornerBottomLeftY] = 0;
+  }
+
+  if (aSkipSides.Left()) {
+    aRadii[eCornerBottomLeftX] = 0;
+    aRadii[eCornerBottomLeftY] = 0;
+    aRadii[eCornerTopLeftX] = 0;
+    aRadii[eCornerTopLeftY] = 0;
+  }
+
+  // css3-background specifies this algorithm for reducing
+  // corner radii when they are too big.
+  bool haveRadius = false;
+  double ratio = 1.0f;
+  for (const auto side : mozilla::AllPhysicalSides()) {
+    uint32_t hc1 = SideToHalfCorner(side, false, true);
+    uint32_t hc2 = SideToHalfCorner(side, true, true);
+    nscoord length =
+        SideIsVertical(side) ? aBorderArea.height : aBorderArea.width;
+    nscoord sum = aRadii[hc1] + aRadii[hc2];
+    if (sum) {
+      haveRadius = true;
+      // avoid floating point division in the normal case
+      if (length < sum) {
+        ratio = std::min(ratio, double(length) / sum);
+      }
+    }
+  }
+  if (ratio < 1.0) {
+    for (const auto corner : mozilla::AllPhysicalHalfCorners()) {
+      aRadii[corner] *= ratio;
+    }
+  }
+
+  return haveRadius;
+}
+
+void nsIFrame::AdjustBorderRadii(nscoord aRadii[8], const nsMargin& aOffsets) {
+  auto AdjustOffset = [](const uint32_t aRadius, const nscoord aOffset) {
+    // Implement the cubic formula to adjust offset when aOffset > 0 and
+    // aRadius / aOffset < 1.
+    // https://drafts.csswg.org/css-shapes/#valdef-shape-box-margin-box
+    if (aOffset > 0) {
+      const double ratio = aRadius / double(aOffset);
+      if (ratio < 1.0) {
+        return nscoord(aOffset * (1.0 + std::pow(ratio - 1, 3)));
+      }
+    }
+    return aOffset;
+  };
+
+  for (const auto side : mozilla::AllPhysicalSides()) {
+    const nscoord offset = aOffsets.Side(side);
+    const uint32_t hc1 = SideToHalfCorner(side, false, false);
+    const uint32_t hc2 = SideToHalfCorner(side, true, false);
+    if (aRadii[hc1] > 0) {
+      const nscoord offset1 = AdjustOffset(aRadii[hc1], offset);
+      aRadii[hc1] = std::max(0, aRadii[hc1] + offset1);
+    }
+    if (aRadii[hc2] > 0) {
+      const nscoord offset2 = AdjustOffset(aRadii[hc2], offset);
+      aRadii[hc2] = std::max(0, aRadii[hc2] + offset2);
+    }
+  }
+}
+
+static inline bool RadiiAreDefinitelyZero(const BorderRadius& aBorderRadius) {
+  for (const auto corner : mozilla::AllPhysicalHalfCorners()) {
+    if (!aBorderRadius.Get(corner).IsDefinitelyZero()) {
+      return false;
+    }
+  }
+  return true;
+}
+
+/* virtual */
+bool nsIFrame::GetBorderRadii(const nsSize& aFrameSize,
+                              const nsSize& aBorderArea, Sides aSkipSides,
+                              nscoord aRadii[8]) const {
+  if (!mMayHaveRoundedCorners) {
+    memset(aRadii, 0, sizeof(nscoord) * 8);
+    return false;
+  }
+
+  if (IsThemed()) {
+    // When we're themed, the native theme code draws the border and
+    // background, and therefore it doesn't make sense to tell other
+    // code that's interested in border-radius that we have any radii.
+    //
+    // In an ideal world, we might have a way for the them to tell us an
+    // border radius, but since we don't, we're better off assuming
+    // zero.
+    for (const auto corner : mozilla::AllPhysicalHalfCorners()) {
+      aRadii[corner] = 0;
+    }
+    return false;
+  }
+
+  const auto& radii = StyleBorder()->mBorderRadius;
+  const bool hasRadii =
+      ComputeBorderRadii(radii, aFrameSize, aBorderArea, aSkipSides, aRadii);
+  if (!hasRadii) {
+    // TODO(emilio): Maybe we can just remove this bit and do the
+    // IsDefinitelyZero check unconditionally. That should still avoid most of
+    // the work, though maybe not the cache miss of going through the style and
+    // the border struct.
+    const_cast<nsIFrame*>(this)->mMayHaveRoundedCorners =
+        !RadiiAreDefinitelyZero(radii);
+  }
+  return hasRadii;
+}
+
+bool nsIFrame::GetBorderRadii(nscoord aRadii[8]) const {
+  nsSize sz = GetSize();
+  return GetBorderRadii(sz, sz, GetSkipSides(), aRadii);
+}
+
+bool nsIFrame::GetMarginBoxBorderRadii(nscoord aRadii[8]) const {
+  return GetBoxBorderRadii(aRadii, GetUsedMargin());
+}
+
+bool nsIFrame::GetPaddingBoxBorderRadii(nscoord aRadii[8]) const {
+  return GetBoxBorderRadii(aRadii, -GetUsedBorder());
+}
+
+bool nsIFrame::GetContentBoxBorderRadii(nscoord aRadii[8]) const {
+  return GetBoxBorderRadii(aRadii, -GetUsedBorderAndPadding());
+}
+
+bool nsIFrame::GetBoxBorderRadii(nscoord aRadii[8],
+                                 const nsMargin& aOffsets) const {
+  if (!GetBorderRadii(aRadii)) {
+    return false;
+  }
+  AdjustBorderRadii(aRadii, aOffsets);
+  for (const auto corner : mozilla::AllPhysicalHalfCorners()) {
+    if (aRadii[corner]) {
+      return true;
+    }
+  }
+  return false;
+}
+
+bool nsIFrame::GetShapeBoxBorderRadii(nscoord aRadii[8]) const {
+  using Tag = StyleShapeOutside::Tag;
+  auto& shapeOutside = StyleDisplay()->mShapeOutside;
+  auto box = StyleShapeBox::MarginBox;
+  switch (shapeOutside.tag) {
+    case Tag::Image:
+    case Tag::None:
+      return false;
+    case Tag::Box:
+      box = shapeOutside.AsBox();
+      break;
+    case Tag::Shape:
+      box = shapeOutside.AsShape()._1;
+      break;
+  }
+
+  switch (box) {
+    case StyleShapeBox::ContentBox:
+      return GetContentBoxBorderRadii(aRadii);
+    case StyleShapeBox::PaddingBox:
+      return GetPaddingBoxBorderRadii(aRadii);
+    case StyleShapeBox::BorderBox:
+      return GetBorderRadii(aRadii);
+    case StyleShapeBox::MarginBox:
+      return GetMarginBoxBorderRadii(aRadii);
+    default:
+      MOZ_ASSERT_UNREACHABLE("Unexpected box value");
+      return false;
+  }
+}
+
+ComputedStyle* nsIFrame::GetAdditionalComputedStyle(int32_t aIndex) const {
+  MOZ_ASSERT(aIndex >= 0, "invalid index number");
+  return nullptr;
+}
+
+void nsIFrame::SetAdditionalComputedStyle(int32_t aIndex,
+                                          ComputedStyle* aComputedStyle) {
+  MOZ_ASSERT(aIndex >= 0, "invalid index number");
+}
+
+nscoord nsIFrame::SynthesizeFallbackBaseline(
+    WritingMode aWM, BaselineSharingGroup aBaselineGroup) const {
+  const auto margin = GetLogicalUsedMargin(aWM);
+  NS_ASSERTION(!IsSubtreeDirty(), "frame must not be dirty");
+  if (aWM.IsCentralBaseline()) {
+    return (BSize(aWM) + GetLogicalUsedMargin(aWM).BEnd(aWM)) / 2;
+  }
+  // Baseline for inverted line content is the top (block-start) margin edge,
+  // as the frame is in effect "flipped" for alignment purposes.
+  if (aWM.IsLineInverted()) {
+    const auto marginStart = margin.BStart(aWM);
+    return aBaselineGroup == BaselineSharingGroup::First
+               ? -marginStart
+               : BSize(aWM) + marginStart;
+  }
+  // Otherwise, the bottom margin edge, per CSS2.1's definition of the
+  // 'baseline' value of 'vertical-align'.
+  const auto marginEnd = margin.BEnd(aWM);
+  return aBaselineGroup == BaselineSharingGroup::First ? BSize(aWM) + marginEnd
+                                                       : -marginEnd;
+}
+
+nscoord nsIFrame::GetLogicalBaseline(WritingMode aWM) const {
+  return GetLogicalBaseline(aWM, GetDefaultBaselineSharingGroup(),
+                            BaselineExportContext::LineLayout);
+}
+
+nscoord nsIFrame::GetLogicalBaseline(
+    WritingMode aWM, BaselineSharingGroup aBaselineGroup,
+    BaselineExportContext aExportContext) const {
+  const auto result =
+      GetNaturalBaselineBOffset(aWM, aBaselineGroup, aExportContext)
+          .valueOrFrom([this, aWM, aBaselineGroup]() {
+            return SynthesizeFallbackBaseline(aWM, aBaselineGroup);
+          });
+  if (aBaselineGroup == BaselineSharingGroup::Last) {
+    return BSize(aWM) - result;
+  }
+  return result;
+}
+
+const nsFrameList& nsIFrame::GetChildList(ChildListID aListID) const {
+  if (IsAbsoluteContainer() && aListID == GetAbsoluteListID()) {
+    return GetAbsoluteContainingBlock()->GetChildList();
+  } else {
+    return nsFrameList::EmptyList();
+  }
+}
+
+void nsIFrame::GetChildLists(nsTArray<ChildList>* aLists) const {
+  if (IsAbsoluteContainer()) {
+    const nsFrameList& absoluteList =
+        GetAbsoluteContainingBlock()->GetChildList();
+    absoluteList.AppendIfNonempty(aLists, GetAbsoluteListID());
+  }
+}
+
+AutoTArray<nsIFrame::ChildList, 4> nsIFrame::CrossDocChildLists() {
+  AutoTArray<ChildList, 4> childLists;
+  nsSubDocumentFrame* subdocumentFrame = do_QueryFrame(this);
+  if (subdocumentFrame) {
+    // Descend into the subdocument
+    nsIFrame* root = subdocumentFrame->GetSubdocumentRootFrame();
+    if (root) {
+      childLists.EmplaceBack(
+          nsFrameList(root, nsLayoutUtils::GetLastSibling(root)),
+          FrameChildListID::Principal);
+    }
+  }
+
+  GetChildLists(&childLists);
+  return childLists;
+}
+
+nsIFrame::CaretBlockAxisMetrics nsIFrame::GetCaretBlockAxisMetrics(
+    mozilla::WritingMode aWM, const nsFontMetrics& aFM) const {
+  // Note(dshin): Ultimately, this does something highly similar (But still
+  // different) to `nsLayoutUtils::GetFirstLinePosition`.
+  const auto baseline = GetCaretBaseline();
+  nscoord ascent = 0, descent = 0;
+  ascent = aFM.MaxAscent();
+  descent = aFM.MaxDescent();
+  const nscoord height = ascent + descent;
+  if (aWM.IsVertical() && aWM.IsLineInverted()) {
+    return CaretBlockAxisMetrics{.mOffset = baseline - descent,
+                                 .mExtent = height};
+  }
+  return CaretBlockAxisMetrics{.mOffset = baseline - ascent, .mExtent = height};
+}
+
+const nsAtom* nsIFrame::ComputePageValue() const {
+  const nsAtom* value = nsGkAtoms::_empty;
+  const nsIFrame* frame = this;
+  // Find what CSS page name value this frame's subtree has, if any.
+  // Starting with this frame, check if a page name other than auto is present,
+  // and record it if so. Then, if the current frame is a container frame, find
+  // the first non-placeholder child and repeat.
+  // This will find the most deeply nested first in-flow child of this frame's
+  // subtree, and return its page name (with auto resolved if applicable, and
+  // subtrees with no page-names returning the empty atom rather than null).
+  do {
+    if (const nsAtom* maybePageName = frame->GetStylePageName()) {
+      value = maybePageName;
+    }
+    // Get the next frame to read from.
+    const nsIFrame* firstNonPlaceholderFrame = nullptr;
+    // If this is a container frame, inspect its in-flow children.
+    if (const nsContainerFrame* containerFrame = do_QueryFrame(frame)) {
+      for (const nsIFrame* childFrame : containerFrame->PrincipalChildList()) {
+        if (!childFrame->IsPlaceholderFrame()) {
+          firstNonPlaceholderFrame = childFrame;
+          break;
+        }
+      }
+    }
+    frame = firstNonPlaceholderFrame;
+  } while (frame);
+  return value;
+}
+
+Visibility nsIFrame::GetVisibility() const {
+  if (!HasAnyStateBits(NS_FRAME_VISIBILITY_IS_TRACKED)) {
+    return Visibility::Untracked;
+  }
+
+  bool isSet = false;
+  uint32_t visibleCount = GetProperty(VisibilityStateProperty(), &isSet);
+
+  MOZ_ASSERT(isSet,
+             "Should have a VisibilityStateProperty value "
+             "if NS_FRAME_VISIBILITY_IS_TRACKED is set");
+
+  return visibleCount > 0 ? Visibility::ApproximatelyVisible
+                          : Visibility::ApproximatelyNonVisible;
+}
+
+void nsIFrame::UpdateVisibilitySynchronously() {
+  mozilla::PresShell* presShell = PresShell();
+  if (!presShell) {
+    return;
+  }
+
+  if (presShell->AssumeAllFramesVisible()) {
+    presShell->EnsureFrameInApproximatelyVisibleList(this);
+    return;
+  }
+
+  bool visible = StyleVisibility()->IsVisible();
+  nsIFrame* f = GetParent();
+  nsRect rect = GetRectRelativeToSelf();
+  nsIFrame* rectFrame = this;
+  while (f && visible) {
+    nsIScrollableFrame* sf = do_QueryFrame(f);
+    if (sf) {
+      nsRect transformedRect =
+          nsLayoutUtils::TransformFrameRectToAncestor(rectFrame, rect, f);
+      if (!sf->IsRectNearlyVisible(transformedRect)) {
+        visible = false;
+        break;
+      }
+
+      // In this code we're trying to synchronously update *approximate*
+      // visibility. (In the future we may update precise visibility here as
+      // well, which is why the method name does not contain 'approximate'.) The
+      // IsRectNearlyVisible() check above tells us that the rect we're checking
+      // is approximately visible within the scrollframe, but we still need to
+      // ensure that, even if it was scrolled into view, it'd be visible when we
+      // consider the rest of the document. To do that, we move transformedRect
+      // to be contained in the scrollport as best we can (it might not fit) to
+      // pretend that it was scrolled into view.
+      rect = transformedRect.MoveInsideAndClamp(sf->GetScrollPortRect());
+      rectFrame = f;
+    }
+    nsIFrame* parent = f->GetParent();
+    if (!parent) {
+      parent = nsLayoutUtils::GetCrossDocParentFrameInProcess(f);
+      if (parent && parent->PresContext()->IsChrome()) {
+        break;
+      }
+    }
+    f = parent;
+  }
+
+  if (visible) {
+    presShell->EnsureFrameInApproximatelyVisibleList(this);
+  } else {
+    presShell->RemoveFrameFromApproximatelyVisibleList(this);
+  }
+}
+
+void nsIFrame::EnableVisibilityTracking() {
+  if (HasAnyStateBits(NS_FRAME_VISIBILITY_IS_TRACKED)) {
+    return;  // Nothing to do.
+  }
+
+  MOZ_ASSERT(!HasProperty(VisibilityStateProperty()),
+             "Shouldn't have a VisibilityStateProperty value "
+             "if NS_FRAME_VISIBILITY_IS_TRACKED is not set");
+
+  // Add the state bit so we know to track visibility for this frame, and
+  // initialize the frame property.
+  AddStateBits(NS_FRAME_VISIBILITY_IS_TRACKED);
+  SetProperty(VisibilityStateProperty(), 0);
+
+  mozilla::PresShell* presShell = PresShell();
+  if (!presShell) {
+    return;
+  }
+
+  // Schedule a visibility update. This method will virtually always be called
+  // when layout has changed anyway, so it's very unlikely that any additional
+  // visibility updates will be triggered by this, but this way we guarantee
+  // that if this frame is currently visible we'll eventually find out.
+  presShell->ScheduleApproximateFrameVisibilityUpdateSoon();
+}
+
+void nsIFrame::DisableVisibilityTracking() {
+  if (!HasAnyStateBits(NS_FRAME_VISIBILITY_IS_TRACKED)) {
+    return;  // Nothing to do.
+  }
+
+  bool isSet = false;
+  uint32_t visibleCount = TakeProperty(VisibilityStateProperty(), &isSet);
+
+  MOZ_ASSERT(isSet,
+             "Should have a VisibilityStateProperty value "
+             "if NS_FRAME_VISIBILITY_IS_TRACKED is set");
+
+  RemoveStateBits(NS_FRAME_VISIBILITY_IS_TRACKED);
+
+  if (visibleCount == 0) {
+    return;  // We were nonvisible.
+  }
+
+  // We were visible, so send an OnVisibilityChange() notification.
+  OnVisibilityChange(Visibility::ApproximatelyNonVisible);
+}
+
+void nsIFrame::DecApproximateVisibleCount(
+    const Maybe<OnNonvisible>& aNonvisibleAction
+    /* = Nothing() */) {
+  MOZ_ASSERT(HasAnyStateBits(NS_FRAME_VISIBILITY_IS_TRACKED));
+
+  bool isSet = false;
+  uint32_t visibleCount = GetProperty(VisibilityStateProperty(), &isSet);
+
+  MOZ_ASSERT(isSet,
+             "Should have a VisibilityStateProperty value "
+             "if NS_FRAME_VISIBILITY_IS_TRACKED is set");
+  MOZ_ASSERT(visibleCount > 0,
+             "Frame is already nonvisible and we're "
+             "decrementing its visible count?");
+
+  visibleCount--;
+  SetProperty(VisibilityStateProperty(), visibleCount);
+  if (visibleCount > 0) {
+    return;
+  }
+
+  // We just became nonvisible, so send an OnVisibilityChange() notification.
+  OnVisibilityChange(Visibility::ApproximatelyNonVisible, aNonvisibleAction);
+}
+
+void nsIFrame::IncApproximateVisibleCount() {
+  MOZ_ASSERT(HasAnyStateBits(NS_FRAME_VISIBILITY_IS_TRACKED));
+
+  bool isSet = false;
+  uint32_t visibleCount = GetProperty(VisibilityStateProperty(), &isSet);
+
+  MOZ_ASSERT(isSet,
+             "Should have a VisibilityStateProperty value "
+             "if NS_FRAME_VISIBILITY_IS_TRACKED is set");
+
+  visibleCount++;
+  SetProperty(VisibilityStateProperty(), visibleCount);
+  if (visibleCount > 1) {
+    return;
+  }
+
+  // We just became visible, so send an OnVisibilityChange() notification.
+  OnVisibilityChange(Visibility::ApproximatelyVisible);
+}
+
+void nsIFrame::OnVisibilityChange(Visibility aNewVisibility,
+                                  const Maybe<OnNonvisible>& aNonvisibleAction
+                                  /* = Nothing() */) {
+  // XXX(seth): In bug 1218990 we'll implement visibility tracking for CSS
+  // images here.
+}
+
+static nsIFrame* GetActiveSelectionFrame(nsPresContext* aPresContext,
+                                         nsIFrame* aFrame) {
+  nsIContent* capturingContent = PresShell::GetCapturingContent();
+  if (capturingContent) {
+    nsIFrame* activeFrame = aPresContext->GetPrimaryFrameFor(capturingContent);
+    return activeFrame ? activeFrame : aFrame;
+  }
+
+  return aFrame;
+}
+
+int16_t nsIFrame::DetermineDisplaySelection() {
+  int16_t selType = nsISelectionController::SELECTION_OFF;
+
+  nsCOMPtr<nsISelectionController> selCon;
+  nsresult result =
+      GetSelectionController(PresContext(), getter_AddRefs(selCon));
+  if (NS_SUCCEEDED(result) && selCon) {
+    result = selCon->GetDisplaySelection(&selType);
+    if (NS_SUCCEEDED(result) &&
+        (selType != nsISelectionController::SELECTION_OFF)) {
+      // Check whether style allows selection.
+      if (!IsSelectable(nullptr)) {
+        selType = nsISelectionController::SELECTION_OFF;
+      }
+    }
+  }
+  return selType;
+}
+
+static Element* FindElementAncestorForMozSelection(nsIContent* aContent) {
+  NS_ENSURE_TRUE(aContent, nullptr);
+  while (aContent && aContent->IsInNativeAnonymousSubtree()) {
+    aContent = aContent->GetClosestNativeAnonymousSubtreeRootParentOrHost();
+  }
+  NS_ASSERTION(aContent, "aContent isn't in non-anonymous tree?");
+  return aContent ? aContent->GetAsElementOrParentElement() : nullptr;
+}
+
+already_AddRefed<ComputedStyle> nsIFrame::ComputeSelectionStyle(
+    int16_t aSelectionStatus) const {
+  // Just bail out if not a selection-status that ::selection applies to.
+  if (aSelectionStatus != nsISelectionController::SELECTION_ON &&
+      aSelectionStatus != nsISelectionController::SELECTION_DISABLED) {
+    return nullptr;
+  }
+  Element* element = FindElementAncestorForMozSelection(GetContent());
+  if (!element) {
+    return nullptr;
+  }
+  RefPtr<ComputedStyle> pseudoStyle =
+      PresContext()->StyleSet()->ProbePseudoElementStyle(
+          *element, PseudoStyleType::selection, nullptr, Style());
+  if (!pseudoStyle) {
+    return nullptr;
+  }
+  // When in high-contrast mode, the style system ends up ignoring the color
+  // declarations, which means that the ::selection style becomes the inherited
+  // color, and default background. That's no good.
+  // When force-color-adjust is set to none allow using the color styles,
+  // as they will not be replaced.
+  if (PresContext()->ForcingColors() &&
+      pseudoStyle->StyleText()->mForcedColorAdjust !=
+          StyleForcedColorAdjust::None) {
+    return nullptr;
+  }
+  return do_AddRef(pseudoStyle);
+}
+
+already_AddRefed<ComputedStyle> nsIFrame::ComputeHighlightSelectionStyle(
+    nsAtom* aHighlightName) {
+  Element* element = FindElementAncestorForMozSelection(GetContent());
+  if (!element) {
+    return nullptr;
+  }
+  return PresContext()->StyleSet()->ProbePseudoElementStyle(
+      *element, PseudoStyleType::highlight, aHighlightName, Style());
+}
+
+template <typename SizeOrMaxSize>
+static inline bool IsIntrinsicKeyword(const SizeOrMaxSize& aSize) {
+  // All keywords other than auto/none/-moz-available depend on intrinsic sizes.
+  return aSize.IsMaxContent() || aSize.IsMinContent() || aSize.IsFitContent() ||
+         aSize.IsFitContentFunction();
+}
+
+bool nsIFrame::CanBeDynamicReflowRoot() const {
+  const auto& display = *StyleDisplay();
+  if (IsLineParticipant() || display.mDisplay.IsRuby() ||
+      display.IsInnerTableStyle() ||
+      display.DisplayInside() == StyleDisplayInside::Table) {
+    // We have a display type where 'width' and 'height' don't actually set the
+    // width or height (i.e., the size depends on content).
+    MOZ_ASSERT(!HasAnyStateBits(NS_FRAME_DYNAMIC_REFLOW_ROOT),
+               "should not have dynamic reflow root bit");
+    return false;
+  }
+
+  // In general, frames that have contain:layout+size can be reflow roots.
+  // (One exception: table-wrapper frames don't work well as reflow roots,
+  // because their inner-table ReflowInput init path tries to reuse & deref
+  // the wrapper's containing block's reflow input, which may be null if we
+  // initiate reflow from the table-wrapper itself.)
+  //
+  // Changes to `contain` force frame reconstructions, so we used to use
+  // NS_FRAME_REFLOW_ROOT, this bit could be set for the whole lifetime of
+  // this frame. But after the support of `content-visibility: auto` which
+  // is with contain layout + size when it's not relevant to user, and only
+  // with contain layout when it is relevant. The frame does not reconstruct
+  // when the relevancy changes. So we use NS_FRAME_DYNAMIC_REFLOW_ROOT instead.
+  //
+  // We place it above the pref check on purpose, to make sure it works for
+  // containment even with the pref disabled.
+  if (display.IsContainLayout() && GetContainSizeAxes().IsBoth()) {
+    return true;
+  }
+
+  if (!StaticPrefs::layout_dynamic_reflow_roots_enabled()) {
+    return false;
+  }
+
+  // We can't serve as a dynamic reflow root if our used 'width' and 'height'
+  // might be influenced by content.
+  //
+  // FIXME: For display:block, we should probably optimize inline-size: auto.
+  // FIXME: Other flex and grid cases?
+  const auto& pos = *StylePosition();
+  const auto& width = pos.mWidth;
+  const auto& height = pos.mHeight;
+  if (!width.IsLengthPercentage() || width.HasPercent() ||
+      !height.IsLengthPercentage() || height.HasPercent() ||
+      IsIntrinsicKeyword(pos.mMinWidth) || IsIntrinsicKeyword(pos.mMaxWidth) ||
+      IsIntrinsicKeyword(pos.mMinHeight) ||
+      IsIntrinsicKeyword(pos.mMaxHeight) ||
+      ((pos.mMinWidth.IsAuto() || pos.mMinHeight.IsAuto()) &&
+       IsFlexOrGridItem())) {
+    return false;
+  }
+
+  // If our flex-basis is 'auto', it'll defer to 'width' (or 'height') which
+  // we've already checked. Otherwise, it preempts them, so we need to
+  // perform the same "could-this-value-be-influenced-by-content" checks that
+  // we performed for 'width' and 'height' above.
+  if (IsFlexItem()) {
+    const auto& flexBasis = pos.mFlexBasis;
+    if (!flexBasis.IsAuto()) {
+      if (!flexBasis.IsSize() || !flexBasis.AsSize().IsLengthPercentage() ||
+          flexBasis.AsSize().HasPercent()) {
+        return false;
+      }
+    }
+  }
+
+  if (!IsFixedPosContainingBlock()) {
+    // We can't treat this frame as a reflow root, since dynamic changes
+    // to absolutely-positioned frames inside of it require that we
+    // reflow the placeholder before we reflow the absolutely positioned
+    // frame.
+    // FIXME:  Alternatively, we could sort the reflow roots in
+    // PresShell::ProcessReflowCommands by depth in the tree, from
+    // deepest to least deep.  However, for performance (FIXME) we
+    // should really be sorting them in the opposite order!
+    return false;
+  }
+
+  // If we participate in a container's block reflow context, or margins
+  // can collapse through us, we can't be a dynamic reflow root.
+  if (IsBlockFrameOrSubclass() && !HasAnyStateBits(NS_BLOCK_BFC_STATE_BITS)) {
+    return false;
+  }
+
+  // Subgrids are never reflow roots, but 'contain:layout/paint' prevents
+  // creating a subgrid in the first place.
+  if (pos.mGridTemplateColumns.IsSubgrid() ||
+      pos.mGridTemplateRows.IsSubgrid()) {
+    // NOTE: we could check that 'display' of our parent's primary frame is
+    // '[inline-]grid' here but that's probably not worth it in practice.
+    if (!display.IsContainLayout() && !display.IsContainPaint()) {
+      return false;
+    }
+  }
+
+  // If we are split, we can't be a dynamic reflow root. Our reflow status may
+  // change after reflow, and our parent is responsible to create or delete our
+  // next-in-flow.
+  if (GetPrevContinuation() || GetNextContinuation()) {
+    return false;
+  }
+
+  return true;
+}
+
+/********************************************************
+ * Refreshes each content's frame
+ *********************************************************/
+
+void nsIFrame::DisplayOutlineUnconditional(nsDisplayListBuilder* aBuilder,
+                                           const nsDisplayListSet& aLists) {
+  // Per https://drafts.csswg.org/css-tables-3/#global-style-overrides:
+  // "All css properties of table-column and table-column-group boxes are
+  // ignored, except when explicitly specified by this specification."
+  // CSS outlines fall into this category, so we skip them on these boxes.
+  MOZ_ASSERT(!IsTableColGroupFrame() && !IsTableColFrame());
+  const auto& outline = *StyleOutline();
+
+  if (!outline.ShouldPaintOutline()) {
+    return;
+  }
+
+  // Outlines are painted by the table wrapper frame.
+  if (IsTableFrame()) {
+    return;
+  }
+
+  if (HasAnyStateBits(NS_FRAME_PART_OF_IBSPLIT) &&
+      ScrollableOverflowRect().IsEmpty()) {
+    // Skip parts of IB-splits with an empty overflow rect, see bug 434301.
+    // We may still want to fix some of the overflow area calculations over in
+    // that bug.
+    return;
+  }
+
+  // We don't display outline-style: auto on themed frames that have their own
+  // focus indicators.
+  if (outline.mOutlineStyle.IsAuto()) {
+    auto* disp = StyleDisplay();
+    if (IsThemed(disp) && PresContext()->Theme()->ThemeDrawsFocusForWidget(
+                              this, disp->EffectiveAppearance())) {
+      return;
+    }
+  }
+
+  aLists.Outlines()->AppendNewToTop<nsDisplayOutline>(aBuilder, this);
+}
+
+void nsIFrame::DisplayOutline(nsDisplayListBuilder* aBuilder,
+                              const nsDisplayListSet& aLists) {
+  if (!IsVisibleForPainting()) return;
+
+  DisplayOutlineUnconditional(aBuilder, aLists);
+}
+
+void nsIFrame::DisplayInsetBoxShadowUnconditional(
+    nsDisplayListBuilder* aBuilder, nsDisplayList* aList) {
+  // XXXbz should box-shadow for rows/rowgroups/columns/colgroups get painted
+  // just because we're visible?  Or should it depend on the cell visibility
+  // when we're not the whole table?
+  const auto* effects = StyleEffects();
+  if (effects->HasBoxShadowWithInset(true)) {
+    aList->AppendNewToTop<nsDisplayBoxShadowInner>(aBuilder, this);
+  }
+}
+
+void nsIFrame::DisplayInsetBoxShadow(nsDisplayListBuilder* aBuilder,
+                                     nsDisplayList* aList) {
+  if (!IsVisibleForPainting()) return;
+
+  DisplayInsetBoxShadowUnconditional(aBuilder, aList);
+}
+
+void nsIFrame::DisplayOutsetBoxShadowUnconditional(
+    nsDisplayListBuilder* aBuilder, nsDisplayList* aList) {
+  // XXXbz should box-shadow for rows/rowgroups/columns/colgroups get painted
+  // just because we're visible?  Or should it depend on the cell visibility
+  // when we're not the whole table?
+  const auto* effects = StyleEffects();
+  if (effects->HasBoxShadowWithInset(false)) {
+    aList->AppendNewToTop<nsDisplayBoxShadowOuter>(aBuilder, this);
+  }
+}
+
+void nsIFrame::DisplayOutsetBoxShadow(nsDisplayListBuilder* aBuilder,
+                                      nsDisplayList* aList) {
+  if (!IsVisibleForPainting()) return;
+
+  DisplayOutsetBoxShadowUnconditional(aBuilder, aList);
+}
+
+void nsIFrame::DisplayCaret(nsDisplayListBuilder* aBuilder,
+                            nsDisplayList* aList) {
+  if (!IsVisibleForPainting()) return;
+
+  aList->AppendNewToTop<nsDisplayCaret>(aBuilder, this);
+}
+
+nscolor nsIFrame::GetCaretColorAt(int32_t aOffset) {
+  return nsLayoutUtils::GetColor(this, &nsStyleUI::mCaretColor);
+}
+
+auto nsIFrame::ComputeShouldPaintBackground() const -> ShouldPaintBackground {
+  nsPresContext* pc = PresContext();
+  ShouldPaintBackground settings{pc->GetBackgroundColorDraw(),
+                                 pc->GetBackgroundImageDraw()};
+  if (settings.mColor && settings.mImage) {
+    return settings;
+  }
+
+  if (StyleVisibility()->mPrintColorAdjust == StylePrintColorAdjust::Exact) {
+    return {true, true};
+  }
+
+  return settings;
+}
+
+bool nsIFrame::DisplayBackgroundUnconditional(nsDisplayListBuilder* aBuilder,
+                                              const nsDisplayListSet& aLists) {
+  if (aBuilder->IsForEventDelivery() && !aBuilder->HitTestIsForVisibility()) {
+    // For hit-testing, we generally just need a light-weight data structure
+    // like nsDisplayEventReceiver. But if the hit-testing is for visibility,
+    // then we need to know the opaque region in order to determine whether to
+    // stop or not.
+    aLists.BorderBackground()->AppendNewToTop<nsDisplayEventReceiver>(aBuilder,
+                                                                      this);
+    return false;
+  }
+
+  const AppendedBackgroundType result =
+      nsDisplayBackgroundImage::AppendBackgroundItemsToTop(
+          aBuilder, this,
+          GetRectRelativeToSelf() + aBuilder->ToReferenceFrame(this),
+          aLists.BorderBackground());
+
+  if (result == AppendedBackgroundType::None) {
+    aBuilder->BuildCompositorHitTestInfoIfNeeded(this,
+                                                 aLists.BorderBackground());
+  }
+
+  return result == AppendedBackgroundType::ThemedBackground;
+}
+
+void nsIFrame::DisplayBorderBackgroundOutline(nsDisplayListBuilder* aBuilder,
+                                              const nsDisplayListSet& aLists) {
+  // The visibility check belongs here since child elements have the
+  // opportunity to override the visibility property and display even if
+  // their parent is hidden.
+  if (!IsVisibleForPainting()) {
+    return;
+  }
+
+  DisplayOutsetBoxShadowUnconditional(aBuilder, aLists.BorderBackground());
+
+  bool bgIsThemed = DisplayBackgroundUnconditional(aBuilder, aLists);
+  DisplayInsetBoxShadowUnconditional(aBuilder, aLists.BorderBackground());
+
+  // If there's a themed background, we should not create a border item.
+  // It won't be rendered.
+  // Don't paint borders for tables here, since they paint them in a different
+  // order.
+  if (!bgIsThemed && StyleBorder()->HasBorder() && !IsTableFrame()) {
+    aLists.BorderBackground()->AppendNewToTop<nsDisplayBorder>(aBuilder, this);
+  }
+
+  DisplayOutlineUnconditional(aBuilder, aLists);
+}
+
+inline static bool IsSVGContentWithCSSClip(const nsIFrame* aFrame) {
+  // The CSS spec says that the 'clip' property only applies to absolutely
+  // positioned elements, whereas the SVG spec says that it applies to SVG
+  // elements regardless of the value of the 'position' property. Here we obey
+  // the CSS spec for outer-<svg> (since that's what we generally do), but
+  // obey the SVG spec for other SVG elements to which 'clip' applies.
+  return aFrame->HasAnyStateBits(NS_FRAME_SVG_LAYOUT) &&
+         aFrame->GetContent()->IsAnyOfSVGElements(nsGkAtoms::svg,
+                                                  nsGkAtoms::foreignObject);
+}
+
+Maybe<nsRect> nsIFrame::GetClipPropClipRect(const nsStyleDisplay* aDisp,
+                                            const nsStyleEffects* aEffects,
+                                            const nsSize& aSize) const {
+  if (aEffects->mClip.IsAuto() ||
+      !(aDisp->IsAbsolutelyPositioned(this) || IsSVGContentWithCSSClip(this))) {
+    return Nothing();
+  }
+
+  auto& clipRect = aEffects->mClip.AsRect();
+  nsRect rect = clipRect.ToLayoutRect();
+  if (MOZ_LIKELY(StyleBorder()->mBoxDecorationBreak ==
+                 StyleBoxDecorationBreak::Slice)) {
+    // The clip applies to the joined boxes so it's relative the first
+    // continuation.
+    nscoord y = 0;
+    for (nsIFrame* f = GetPrevContinuation(); f; f = f->GetPrevContinuation()) {
+      y += f->GetRect().height;
+    }
+    rect.MoveBy(nsPoint(0, -y));
+  }
+
+  if (clipRect.right.IsAuto()) {
+    rect.width = aSize.width - rect.x;
+  }
+  if (clipRect.bottom.IsAuto()) {
+    rect.height = aSize.height - rect.y;
+  }
+  return Some(rect);
+}
+
+/**
+ * If the CSS 'overflow' property applies to this frame, and is not
+ * handled by constructing a dedicated nsHTML/XULScrollFrame, set up clipping
+ * for that overflow in aBuilder->ClipState() to clip all containing-block
+ * descendants.
+ */
+static void ApplyOverflowClipping(
+    nsDisplayListBuilder* aBuilder, const nsIFrame* aFrame,
+    nsIFrame::PhysicalAxes aClipAxes,
+    DisplayListClipState::AutoClipMultiple& aClipState) {
+  // Only 'clip' is handled here (and 'hidden' for table frames, and any
+  // non-'visible' value for blocks in a paginated context).
+  // We allow 'clip' to apply to any kind of frame. This is required by
+  // comboboxes which make their display text (an inline frame) have clipping.
+  MOZ_ASSERT(aClipAxes != nsIFrame::PhysicalAxes::None);
+  MOZ_ASSERT(aFrame->ShouldApplyOverflowClipping(aFrame->StyleDisplay()) ==
+             aClipAxes);
+
+  nsRect clipRect;
+  bool haveRadii = false;
+  nscoord radii[8];
+  auto* disp = aFrame->StyleDisplay();
+  // Only deflate the padding if we clip to the content-box in that axis.
+  auto wm = aFrame->GetWritingMode();
+  bool cbH = (wm.IsVertical() ? disp->mOverflowClipBoxBlock
+                              : disp->mOverflowClipBoxInline) ==
+             StyleOverflowClipBox::ContentBox;
+  bool cbV = (wm.IsVertical() ? disp->mOverflowClipBoxInline
+                              : disp->mOverflowClipBoxBlock) ==
+             StyleOverflowClipBox::ContentBox;
+
+  nsMargin boxMargin = -aFrame->GetUsedPadding();
+  if (!cbH) {
+    boxMargin.left = boxMargin.right = nscoord(0);
+  }
+  if (!cbV) {
+    boxMargin.top = boxMargin.bottom = nscoord(0);
+  }
+
+  auto clipMargin = aFrame->OverflowClipMargin(aClipAxes);
+
+  boxMargin -= aFrame->GetUsedBorder();
+  boxMargin += nsMargin(clipMargin.height, clipMargin.width, clipMargin.height,
+                        clipMargin.width);
+  boxMargin.ApplySkipSides(aFrame->GetSkipSides());
+
+  nsRect rect(nsPoint(0, 0), aFrame->GetSize());
+  rect.Inflate(boxMargin);
+  if (MOZ_UNLIKELY(!(aClipAxes & nsIFrame::PhysicalAxes::Horizontal))) {
+    // NOTE(mats) We shouldn't be clipping at all in this dimension really,
+    // but clipping in just one axis isn't supported by our GFX APIs so we
+    // clip to our visual overflow rect instead.
+    nsRect o = aFrame->InkOverflowRect();
+    rect.x = o.x;
+    rect.width = o.width;
+  }
+  if (MOZ_UNLIKELY(!(aClipAxes & nsIFrame::PhysicalAxes::Vertical))) {
+    // See the note above.
+    nsRect o = aFrame->InkOverflowRect();
+    rect.y = o.y;
+    rect.height = o.height;
+  }
+  clipRect = rect + aBuilder->ToReferenceFrame(aFrame);
+  haveRadii = aFrame->GetBoxBorderRadii(radii, boxMargin);
+  aClipState.ClipContainingBlockDescendantsExtra(clipRect,
+                                                 haveRadii ? radii : nullptr);
+}
+
+nsSize nsIFrame::OverflowClipMargin(PhysicalAxes aClipAxes) const {
+  nsSize result;
+  if (aClipAxes == PhysicalAxes::None) {
+    return result;
+  }
+  const auto& margin = StyleMargin()->mOverflowClipMargin;
+  if (margin.IsZero()) {
+    return result;
+  }
+  nscoord marginAu = margin.ToAppUnits();
+  if (aClipAxes & PhysicalAxes::Horizontal) {
+    result.width = marginAu;
+  }
+  if (aClipAxes & PhysicalAxes::Vertical) {
+    result.height = marginAu;
+  }
+  return result;
+}
+
+/**
+ * Returns whether a display item that gets created with the builder's current
+ * state will have a scrolled clip, i.e. a clip that is scrolled by a scroll
+ * frame which does not move the item itself.
+ */
+static bool BuilderHasScrolledClip(nsDisplayListBuilder* aBuilder) {
+  const DisplayItemClipChain* currentClip =
+      aBuilder->ClipState().GetCurrentCombinedClipChain(aBuilder);
+  if (!currentClip) {
+    return false;
+  }
+
+  const ActiveScrolledRoot* currentClipASR = currentClip->mASR;
+  const ActiveScrolledRoot* currentASR = aBuilder->CurrentActiveScrolledRoot();
+  return ActiveScrolledRoot::PickDescendant(currentClipASR, currentASR) !=
+         currentASR;
+}
+
+class AutoSaveRestoreContainsBlendMode {
+  nsDisplayListBuilder& mBuilder;
+  bool mSavedContainsBlendMode;
+
+ public:
+  explicit AutoSaveRestoreContainsBlendMode(nsDisplayListBuilder& aBuilder)
+      : mBuilder(aBuilder),
+        mSavedContainsBlendMode(aBuilder.ContainsBlendMode()) {}
+
+  ~AutoSaveRestoreContainsBlendMode() {
+    mBuilder.SetContainsBlendMode(mSavedContainsBlendMode);
+  }
+};
+
+static bool IsFrameOrAncestorApzAware(nsIFrame* aFrame) {
+  nsIContent* node = aFrame->GetContent();
+  if (!node) {
+    return false;
+  }
+
+  do {
+    if (node->IsNodeApzAware()) {
+      return true;
+    }
+    nsIContent* shadowRoot = node->GetShadowRoot();
+    if (shadowRoot && shadowRoot->IsNodeApzAware()) {
+      return true;
+    }
+
+    // Even if the node owning aFrame doesn't have apz-aware event listeners
+    // itself, its shadow root or display: contents ancestors (which have no
+    // frames) might, so we need to account for them too.
+  } while ((node = node->GetFlattenedTreeParent()) && node->IsElement() &&
+           node->AsElement()->IsDisplayContents());
+
+  return false;
+}
+
+static void CheckForApzAwareEventHandlers(nsDisplayListBuilder* aBuilder,
+                                          nsIFrame* aFrame) {
+  if (aBuilder->GetAncestorHasApzAwareEventHandler()) {
+    return;
+  }
+
+  if (IsFrameOrAncestorApzAware(aFrame)) {
+    aBuilder->SetAncestorHasApzAwareEventHandler(true);
+  }
+}
+
+static void UpdateCurrentHitTestInfo(nsDisplayListBuilder* aBuilder,
+                                     nsIFrame* aFrame) {
+  if (!aBuilder->BuildCompositorHitTestInfo()) {
+    // Compositor hit test info is not used.
+    return;
+  }
+
+  CheckForApzAwareEventHandlers(aBuilder, aFrame);
+
+  const CompositorHitTestInfo info = aFrame->GetCompositorHitTestInfo(aBuilder);
+  aBuilder->SetCompositorHitTestInfo(info);
+}
+
+/**
+ * True if aDescendant participates the context aAncestor participating.
+ */
+static bool FrameParticipatesIn3DContext(nsIFrame* aAncestor,
+                                         nsIFrame* aDescendant) {
+  MOZ_ASSERT(aAncestor != aDescendant);
+  MOZ_ASSERT(aAncestor->GetContent() != aDescendant->GetContent());
+  MOZ_ASSERT(aAncestor->Extend3DContext());
+
+  nsIFrame* ancestor = aAncestor->FirstContinuation();
+  MOZ_ASSERT(ancestor->IsPrimaryFrame());
+
+  nsIFrame* frame;
+  for (frame = aDescendant->GetClosestFlattenedTreeAncestorPrimaryFrame();
+       frame && ancestor != frame;
+       frame = frame->GetClosestFlattenedTreeAncestorPrimaryFrame()) {
+    if (!frame->Extend3DContext()) {
+      return false;
+    }
+  }
+
+  MOZ_ASSERT(frame == ancestor);
+  return true;
+}
+
+static bool ItemParticipatesIn3DContext(nsIFrame* aAncestor,
+                                        nsDisplayItem* aItem) {
+  auto type = aItem->GetType();
+  const bool isContainer = type == DisplayItemType::TYPE_WRAP_LIST ||
+                           type == DisplayItemType::TYPE_CONTAINER;
+
+  if (isContainer && aItem->GetChildren()->Length() == 1) {
+    // If the wraplist has only one child item, use the type of that item.
+    type = aItem->GetChildren()->GetBottom()->GetType();
+  }
+
+  if (type != DisplayItemType::TYPE_TRANSFORM &&
+      type != DisplayItemType::TYPE_PERSPECTIVE) {
+    return false;
+  }
+  nsIFrame* transformFrame = aItem->Frame();
+  if (aAncestor->GetContent() == transformFrame->GetContent()) {
+    return true;
+  }
+  return FrameParticipatesIn3DContext(aAncestor, transformFrame);
+}
+
+static void WrapSeparatorTransform(nsDisplayListBuilder* aBuilder,
+                                   nsIFrame* aFrame,
+                                   nsDisplayList* aNonParticipants,
+                                   nsDisplayList* aParticipants, int aIndex,
+                                   nsDisplayItem** aSeparator) {
+  if (aNonParticipants->IsEmpty()) {
+    return;
+  }
+
+  nsDisplayTransform* item = MakeDisplayItemWithIndex<nsDisplayTransform>(
+      aBuilder, aFrame, aIndex, aNonParticipants, aBuilder->GetVisibleRect());
+
+  if (*aSeparator == nullptr && item) {
+    *aSeparator = item;
+  }
+
+  aParticipants->AppendToTop(item);
+}
+
+// Try to compute a clip rect to bound the contents of the mask item
+// that will be built for |aMaskedFrame|. If we're not able to compute
+// one, return an empty Maybe.
+// The returned clip rect, if there is one, is relative to |aMaskedFrame|.
+static Maybe<nsRect> ComputeClipForMaskItem(
+    nsDisplayListBuilder* aBuilder, nsIFrame* aMaskedFrame,
+    const SVGUtils::MaskUsage& aMaskUsage) {
+  const nsStyleSVGReset* svgReset = aMaskedFrame->StyleSVGReset();
+
+  nsPoint offsetToUserSpace =
+      nsLayoutUtils::ComputeOffsetToUserSpace(aBuilder, aMaskedFrame);
+  int32_t devPixelRatio = aMaskedFrame->PresContext()->AppUnitsPerDevPixel();
+  gfxPoint devPixelOffsetToUserSpace =
+      nsLayoutUtils::PointToGfxPoint(offsetToUserSpace, devPixelRatio);
+  CSSToLayoutDeviceScale cssToDevScale =
+      aMaskedFrame->PresContext()->CSSToDevPixelScale();
+
+  nsPoint toReferenceFrame;
+  aBuilder->FindReferenceFrameFor(aMaskedFrame, &toReferenceFrame);
+
+  Maybe<gfxRect> combinedClip;
+  if (aMaskUsage.ShouldApplyBasicShapeOrPath()) {
+    Maybe<Rect> result =
+        CSSClipPathInstance::GetBoundingRectForBasicShapeOrPathClip(
+            aMaskedFrame, svgReset->mClipPath);
+    if (result) {
+      combinedClip = Some(ThebesRect(*result));
+    }
+  } else if (aMaskUsage.ShouldApplyClipPath()) {
+    gfxRect result = SVGUtils::GetBBox(
+        aMaskedFrame,
+        SVGUtils::eBBoxIncludeClipped | SVGUtils::eBBoxIncludeFill |
+            SVGUtils::eBBoxIncludeMarkers | SVGUtils::eBBoxIncludeStroke |
+            SVGUtils::eDoNotClipToBBoxOfContentInsideClipPath);
+    combinedClip = Some(
+        ThebesRect((CSSRect::FromUnknownRect(ToRect(result)) * cssToDevScale)
+                       .ToUnknownRect()));
+  } else {
+    // The code for this case is adapted from ComputeMaskGeometry().
+
+    nsRect borderArea(toReferenceFrame, aMaskedFrame->GetSize());
+    borderArea -= offsetToUserSpace;
+
+    // Use an infinite dirty rect to pass into nsCSSRendering::
+    // GetImageLayerClip() because we don't have an actual dirty rect to
+    // pass in. This is fine because the only time GetImageLayerClip() will
+    // not intersect the incoming dirty rect with something is in the "NoClip"
+    // case, and we handle that specially.
+    nsRect dirtyRect(nscoord_MIN / 2, nscoord_MIN / 2, nscoord_MAX,
+                     nscoord_MAX);
+
+    nsIFrame* firstFrame =
+        nsLayoutUtils::FirstContinuationOrIBSplitSibling(aMaskedFrame);
+    nsTArray<SVGMaskFrame*> maskFrames;
+    // XXX check return value?
+    SVGObserverUtils::GetAndObserveMasks(firstFrame, &maskFrames);
+
+    for (uint32_t i = 0; i < maskFrames.Length(); ++i) {
+      gfxRect clipArea;
+      if (maskFrames[i]) {
+        clipArea = maskFrames[i]->GetMaskArea(aMaskedFrame);
+        clipArea = ThebesRect(
+            (CSSRect::FromUnknownRect(ToRect(clipArea)) * cssToDevScale)
+                .ToUnknownRect());
+      } else {
+        const auto& layer = svgReset->mMask.mLayers[i];
+        if (layer.mClip == StyleGeometryBox::NoClip) {
+          return Nothing();
+        }
+
+        nsCSSRendering::ImageLayerClipState clipState;
+        nsCSSRendering::GetImageLayerClip(
+            layer, aMaskedFrame, *aMaskedFrame->StyleBorder(), borderArea,
+            dirtyRect, false /* aWillPaintBorder */, devPixelRatio, &clipState);
+        clipArea = clipState.mDirtyRectInDevPx;
+      }
+      combinedClip = UnionMaybeRects(combinedClip, Some(clipArea));
+    }
+  }
+  if (combinedClip) {
+    if (combinedClip->IsEmpty()) {
+      // *clipForMask might be empty if all mask references are not resolvable
+      // or the size of them are empty. We still need to create a transparent
+      // mask before bug 1276834 fixed, so don't clip ctx by an empty rectangle
+      // for for now.
+      return Nothing();
+    }
+
+    // Convert to user space.
+    *combinedClip += devPixelOffsetToUserSpace;
+
+    // Round the clip out. In FrameLayerBuilder we round clips to nearest
+    // pixels, and if we have a really thin clip here, that can cause the
+    // clip to become empty if we didn't round out here.
+    // The rounding happens in coordinates that are relative to the reference
+    // frame, which matches what FrameLayerBuilder does.
+    combinedClip->RoundOut();
+
+    // Convert to app units.
+    nsRect result =
+        nsLayoutUtils::RoundGfxRectToAppRect(*combinedClip, devPixelRatio);
+
+    // The resulting clip is relative to the reference frame, but the caller
+    // expects it to be relative to the masked frame, so adjust it.
+    result -= toReferenceFrame;
+    return Some(result);
+  }
+  return Nothing();
+}
+
+struct AutoCheckBuilder {
+  explicit AutoCheckBuilder(nsDisplayListBuilder* aBuilder)
+      : mBuilder(aBuilder) {
+    aBuilder->Check();
+  }
+
+  ~AutoCheckBuilder() { mBuilder->Check(); }
+
+  nsDisplayListBuilder* mBuilder;
+};
+
+/**
+ * Tries to reuse a top-level stacking context item from the previous paint.
+ * Returns true if an item was reused, otherwise false.
+ */
+bool TryToReuseStackingContextItem(nsDisplayListBuilder* aBuilder,
+                                   nsDisplayList* aList, nsIFrame* aFrame) {
+  if (!aBuilder->IsForPainting() || !aBuilder->IsPartialUpdate() ||
+      aBuilder->InInvalidSubtree()) {
+    return false;
+  }
+
+  if (aFrame->IsFrameModified() || aFrame->HasModifiedDescendants()) {
+    return false;
+  }
+
+  auto& items = aFrame->DisplayItems();
+  auto* res = std::find_if(
+      items.begin(), items.end(),
+      [](nsDisplayItem* aItem) { return aItem->IsPreProcessed(); });
+
+  if (res == items.end()) {
+    return false;
+  }
+
+  nsDisplayItem* container = *res;
+  MOZ_ASSERT(container->Frame() == aFrame);
+  DL_LOGD("RDL - Found SC item %p (%s) (frame: %p)", container,
+          container->Name(), container->Frame());
+
+  aList->AppendToTop(container);
+  aBuilder->ReuseDisplayItem(container);
+  return true;
+}
+
+void nsIFrame::BuildDisplayListForStackingContext(
+    nsDisplayListBuilder* aBuilder, nsDisplayList* aList,
+    bool* aCreatedContainerItem) {
+#ifdef DEBUG
+  DL_LOGV("BuildDisplayListForStackingContext (%p) <", this);
+  ScopeExit e(
+      [this]() { DL_LOGV("> BuildDisplayListForStackingContext (%p)", this); });
+#endif
+
+  AutoCheckBuilder check(aBuilder);
+
+  if (aBuilder->IsReusingStackingContextItems() &&
+      TryToReuseStackingContextItem(aBuilder, aList, this)) {
+    if (aCreatedContainerItem) {
+      *aCreatedContainerItem = true;
+    }
+    return;
+  }
+
+  if (HasAnyStateBits(NS_FRAME_TOO_DEEP_IN_FRAME_TREE)) {
+    return;
+  }
+
+  const auto& style = *Style();
+  const nsStyleDisplay* disp = style.StyleDisplay();
+  const nsStyleEffects* effects = style.StyleEffects();
+  EffectSet* effectSetForOpacity =
+      EffectSet::GetForFrame(this, nsCSSPropertyIDSet::OpacityProperties());
+  // We can stop right away if this is a zero-opacity stacking context and
+  // we're painting, and we're not animating opacity.
+  bool needHitTestInfo = aBuilder->BuildCompositorHitTestInfo() &&
+                         Style()->PointerEvents() != StylePointerEvents::None;
+  bool opacityItemForEventsOnly = false;
+  if (effects->IsTransparent() && aBuilder->IsForPainting() &&
+      !(disp->mWillChange.bits & StyleWillChangeBits::OPACITY) &&
+      !nsLayoutUtils::HasAnimationOfPropertySet(
+          this, nsCSSPropertyIDSet::OpacityProperties(), effectSetForOpacity)) {
+    if (needHitTestInfo) {
+      opacityItemForEventsOnly = true;
+    } else {
+      return;
+    }
+  }
+
+  if (aBuilder->IsForPainting() && disp->mWillChange.bits) {
+    aBuilder->AddToWillChangeBudget(this, GetSize());
+  }
+
+  // For preserves3d, use the dirty rect already installed on the
+  // builder, since aDirtyRect maybe distorted for transforms along
+  // the chain.
+  nsRect visibleRect = aBuilder->GetVisibleRect();
+  nsRect dirtyRect = aBuilder->GetDirtyRect();
+
+  // We build an opacity item if it's not going to be drawn by SVG content.
+  // We could in principle skip creating an nsDisplayOpacity item if
+  // nsDisplayOpacity::NeedsActiveLayer returns false and usingSVGEffects is
+  // true (the nsDisplayFilter/nsDisplayMasksAndClipPaths could handle the
+  // opacity). Since SVG has perf issues where we sometimes spend a lot of
+  // time creating display list items that might be helpful.  We'd need to
+  // restore our mechanism to do that (changed in bug 1482403), and we'd
+  // need to invalidate the frame if the value that would be return from
+  // NeedsActiveLayer was to change, which we don't currently do.
+  const bool useOpacity =
+      HasVisualOpacity(disp, effects, effectSetForOpacity) &&
+      !SVGUtils::CanOptimizeOpacity(this);
+
+  const bool isTransformed = IsTransformed();
+  const bool hasPerspective = isTransformed && HasPerspective();
+  const bool extend3DContext =
+      Extend3DContext(disp, effects, effectSetForOpacity);
+  const bool combines3DTransformWithAncestors =
+      (extend3DContext || isTransformed) && Combines3DTransformWithAncestors();
+
+  Maybe<nsDisplayListBuilder::AutoPreserves3DContext> autoPreserves3DContext;
+  if (extend3DContext && !combines3DTransformWithAncestors) {
+    // Start a new preserves3d context to keep informations on
+    // nsDisplayListBuilder.
+    autoPreserves3DContext.emplace(aBuilder);
+    // Save dirty rect on the builder to avoid being distorted for
+    // multiple transforms along the chain.
+    aBuilder->SavePreserves3DRect();
+
+    // We rebuild everything within preserve-3d and don't try
+    // to retain, so override the dirty rect now.
+    if (aBuilder->IsRetainingDisplayList()) {
+      dirtyRect = visibleRect;
+      aBuilder->SetDisablePartialUpdates(true);
+    }
+  }
+
+  const bool useBlendMode = effects->mMixBlendMode != StyleBlend::Normal;
+  if (useBlendMode) {
+    aBuilder->SetContainsBlendMode(true);
+  }
+
+  // reset blend mode so we can keep track if this stacking context needs have
+  // a nsDisplayBlendContainer. Set the blend mode back when the routine exits
+  // so we keep track if the parent stacking context needs a container too.
+  AutoSaveRestoreContainsBlendMode autoRestoreBlendMode(*aBuilder);
+  aBuilder->SetContainsBlendMode(false);
+
+  // NOTE: When changing this condition make sure to tweak nsGfxScrollFrame as
+  // well.
+  bool usingBackdropFilter = effects->HasBackdropFilters() &&
+                             IsVisibleForPainting() &&
+                             !style.IsRootElementStyle();
+
+  nsRect visibleRectOutsideTransform = visibleRect;
+  nsDisplayTransform::PrerenderInfo prerenderInfo;
+  bool inTransform = aBuilder->IsInTransform();
+  if (isTransformed) {
+    prerenderInfo = nsDisplayTransform::ShouldPrerenderTransformedContent(
+        aBuilder, this, &visibleRect);
+
+    switch (prerenderInfo.mDecision) {
+      case nsDisplayTransform::PrerenderDecision::Full:
+      case nsDisplayTransform::PrerenderDecision::Partial:
+        dirtyRect = visibleRect;
+        break;
+      case nsDisplayTransform::PrerenderDecision::No: {
+        // If we didn't prerender an animated frame in a preserve-3d context,
+        // then we want disable async animations for the rest of the preserve-3d
+        // (especially ancestors).
+        if ((extend3DContext || combines3DTransformWithAncestors) &&
+            prerenderInfo.mHasAnimations) {
+          aBuilder->SavePreserves3DAllowAsyncAnimation(false);
+        }
+
+        const nsRect overflow = InkOverflowRectRelativeToSelf();
+        if (overflow.IsEmpty() && !extend3DContext) {
+          return;
+        }
+
+        // If we're in preserve-3d then grab the dirty rect that was given to
+        // the root and transform using the combined transform.
+        if (combines3DTransformWithAncestors) {
+          visibleRect = dirtyRect = aBuilder->GetPreserves3DRect();
+        }
+
+        float appPerDev = PresContext()->AppUnitsPerDevPixel();
+        auto transform = nsDisplayTransform::GetResultingTransformMatrix(
+            this, nsPoint(), appPerDev,
+            nsDisplayTransform::kTransformRectFlags);
+        nsRect untransformedDirtyRect;
+        if (nsDisplayTransform::UntransformRect(dirtyRect, overflow, transform,
+                                                appPerDev,
+                                                &untransformedDirtyRect)) {
+          dirtyRect = untransformedDirtyRect;
+          nsDisplayTransform::UntransformRect(visibleRect, overflow, transform,
+                                              appPerDev, &visibleRect);
+        } else {
+          // This should only happen if the transform is singular, in which case
+          // nothing is visible anyway
+          dirtyRect.SetEmpty();
+          visibleRect.SetEmpty();
+        }
+      }
+    }
+    inTransform = true;
+  } else if (IsFixedPosContainingBlock()) {
+    // Restict the building area to the overflow rect for these frames, since
+    // RetainedDisplayListBuilder uses it to know if the size of the stacking
+    // context changed.
+    visibleRect.IntersectRect(visibleRect, InkOverflowRect());
+    dirtyRect.IntersectRect(dirtyRect, InkOverflowRect());
+  }
+
+  bool hasOverrideDirtyRect = false;
+  // If we're doing a partial build, we're not invalid and we're capable
+  // of having an override building rect (stacking context and fixed pos
+  // containing block), then we should assume we have one.
+  // Either we have an explicit one, or nothing in our subtree changed and
+  // we have an implicit empty rect.
+  //
+  // These conditions should match |CanStoreDisplayListBuildingRect()| in
+  // RetainedDisplayListBuilder.cpp
+  if (!aBuilder->IsReusingStackingContextItems() &&
+      aBuilder->IsPartialUpdate() && !aBuilder->InInvalidSubtree() &&
+      !IsFrameModified() && IsFixedPosContainingBlock() &&
+      !GetPrevContinuation() && !GetNextContinuation()) {
+    dirtyRect = nsRect();
+    if (HasOverrideDirtyRegion()) {
+      nsDisplayListBuilder::DisplayListBuildingData* data =
+          GetProperty(nsDisplayListBuilder::DisplayListBuildingRect());
+      if (data) {
+        dirtyRect = data->mDirtyRect.Intersect(visibleRect);
+        hasOverrideDirtyRect = true;
+      }
+    }
+  }
+
+  bool usingFilter = effects->HasFilters() && !style.IsRootElementStyle();
+  SVGUtils::MaskUsage maskUsage = SVGUtils::DetermineMaskUsage(this, false);
+  bool usingMask = maskUsage.UsingMaskOrClipPath();
+  bool usingSVGEffects = usingFilter || usingMask;
+
+  nsRect visibleRectOutsideSVGEffects = visibleRect;
+  nsDisplayList hoistedScrollInfoItemsStorage(aBuilder);
+  if (usingSVGEffects) {
+    dirtyRect =
+        SVGIntegrationUtils::GetRequiredSourceForInvalidArea(this, dirtyRect);
+    visibleRect =
+        SVGIntegrationUtils::GetRequiredSourceForInvalidArea(this, visibleRect);
+    aBuilder->EnterSVGEffectsContents(this, &hoistedScrollInfoItemsStorage);
+  }
+
+  bool useStickyPosition = disp->mPosition == StylePositionProperty::Sticky;
+
+  bool useFixedPosition =
+      disp->mPosition == StylePositionProperty::Fixed &&
+      (DisplayPortUtils::IsFixedPosFrameInDisplayPort(this) ||
+       BuilderHasScrolledClip(aBuilder));
+
+  nsDisplayListBuilder::AutoBuildingDisplayList buildingDisplayList(
+      aBuilder, this, visibleRect, dirtyRect, isTransformed);
+
+  UpdateCurrentHitTestInfo(aBuilder, this);
+
+  // Depending on the effects that are applied to this frame, we can create
+  // multiple container display items and wrap them around our contents.
+  // This enum lists all the potential container display items, in the order
+  // outside to inside.
+  enum class ContainerItemType : uint8_t {
+    None = 0,
+    OwnLayerIfNeeded,
+    BlendMode,
+    FixedPosition,
+    OwnLayerForTransformWithRoundedClip,
+    Perspective,
+    Transform,
+    SeparatorTransforms,
+    Opacity,
+    Filter,
+    BlendContainer
+  };
+
+  nsDisplayListBuilder::AutoContainerASRTracker contASRTracker(aBuilder);
+
+  auto cssClip = GetClipPropClipRect(disp, effects, GetSize());
+  auto ApplyClipProp = [&](DisplayListClipState::AutoSaveRestore& aClipState) {
+    if (!cssClip) {
+      return;
+    }
+    nsPoint offset = aBuilder->GetCurrentFrameOffsetToReferenceFrame();
+    aBuilder->IntersectDirtyRect(*cssClip);
+    aBuilder->IntersectVisibleRect(*cssClip);
+    aClipState.ClipContentDescendants(*cssClip + offset);
+  };
+
+  // The CSS clip property is effectively inside the transform, but outside the
+  // filters. So if we're not transformed we can apply it just here for
+  // simplicity, instead of on each of the places that handle clipCapturedBy.
+  DisplayListClipState::AutoSaveRestore untransformedCssClip(aBuilder);
+  if (!isTransformed) {
+    ApplyClipProp(untransformedCssClip);
+  }
+
+  // If there is a current clip, then depending on the container items we
+  // create, different things can happen to it. Some container items simply
+  // propagate the clip to their children and aren't clipped themselves.
+  // But other container items, especially those that establish a different
+  // geometry for their contents (e.g. transforms), capture the clip on
+  // themselves and unset the clip for their contents. If we create more than
+  // one of those container items, the clip will be captured on the outermost
+  // one and the inner container items will be unclipped.
+  ContainerItemType clipCapturedBy = ContainerItemType::None;
+  if (useFixedPosition) {
+    clipCapturedBy = ContainerItemType::FixedPosition;
+  } else if (isTransformed) {
+    const DisplayItemClipChain* currentClip =
+        aBuilder->ClipState().GetCurrentCombinedClipChain(aBuilder);
+    if ((hasPerspective || extend3DContext) &&
+        (currentClip && currentClip->HasRoundedCorners())) {
+      // If we're creating an nsDisplayTransform item that is going to combine
+      // its transform with its children (preserve-3d or perspective), then we
+      // can't have an intermediate surface. Mask layers force an intermediate
+      // surface, so if we're going to need both then create a separate
+      // wrapping layer for the mask.
+      clipCapturedBy = ContainerItemType::OwnLayerForTransformWithRoundedClip;
+    } else if (hasPerspective) {
+      clipCapturedBy = ContainerItemType::Perspective;
+    } else {
+      clipCapturedBy = ContainerItemType::Transform;
+    }
+  } else if (usingFilter) {
+    clipCapturedBy = ContainerItemType::Filter;
+  }
+
+  DisplayListClipState::AutoSaveRestore clipState(aBuilder);
+  if (clipCapturedBy != ContainerItemType::None) {
+    clipState.Clear();
+  }
+
+  DisplayListClipState::AutoSaveRestore transformedCssClip(aBuilder);
+  if (isTransformed) {
+    // FIXME(emilio, bug 1525159): In the case we have a both a transform _and_
+    // filters, this clips the input to the filters as well, which is not
+    // correct (clipping by the `clip` property is supposed to happen after
+    // applying the filter effects, per [1].
+    //
+    // This is not a regression though, since we used to do that anyway before
+    // bug 1514384, and even without the transform we get it wrong.
+    //
+    // [1]: https://drafts.fxtf.org/css-masking/#placement
+    ApplyClipProp(transformedCssClip);
+  }
+
+  nsDisplayListCollection set(aBuilder);
+  Maybe<nsRect> clipForMask;
+  {
+    DisplayListClipState::AutoSaveRestore nestedClipState(aBuilder);
+    nsDisplayListBuilder::AutoInTransformSetter inTransformSetter(aBuilder,
+                                                                  inTransform);
+    nsDisplayListBuilder::AutoEnterFilter filterASRSetter(aBuilder,
+                                                          usingFilter);
+    nsDisplayListBuilder::AutoInEventsOnly inEventsSetter(
+        aBuilder, opacityItemForEventsOnly);
+
+    // If we have a mask, compute a clip to bound the masked content.
+    // This is necessary in case the content moves with an ancestor
+    // ASR of the mask.
+    // Don't do this if we also have a filter, because then the clip
+    // would be applied before the filter, violating
+    // https://www.w3.org/TR/filter-effects-1/#placement.
+    // Filters are a containing block for fixed and absolute descendants,
+    // so the masked content cannot move with an ancestor ASR.
+    if (usingMask && !usingFilter) {
+      clipForMask = ComputeClipForMaskItem(aBuilder, this, maskUsage);
+      if (clipForMask) {
+        aBuilder->IntersectDirtyRect(*clipForMask);
+        aBuilder->IntersectVisibleRect(*clipForMask);
+        nestedClipState.ClipContentDescendants(
+            *clipForMask + aBuilder->GetCurrentFrameOffsetToReferenceFrame());
+      }
+    }
+
+    // extend3DContext also guarantees that applyAbsPosClipping and
+    // usingSVGEffects are false We only modify the preserve-3d rect if we are
+    // the top of a preserve-3d heirarchy
+    if (extend3DContext) {
+      // Mark these first so MarkAbsoluteFramesForDisplayList knows if we are
+      // going to be forced to descend into frames.
+      aBuilder->MarkPreserve3DFramesForDisplayList(this);
+    }
+
+    aBuilder->AdjustWindowDraggingRegion(this);
+
+    MarkAbsoluteFramesForDisplayList(aBuilder);
+    aBuilder->Check();
+    BuildDisplayList(aBuilder, set);
+    SetBuiltDisplayList(true);
+    aBuilder->Check();
+    aBuilder->DisplayCaret(this, set.Outlines());
+
+    // Blend modes are a real pain for retained display lists. We build a blend
+    // container item if the built list contains any blend mode items within
+    // the current stacking context. This can change without an invalidation
+    // to the stacking context frame, or the blend mode frame (e.g. by moving
+    // an intermediate frame).
+    // When we gain/remove a blend container item, we need to mark this frame
+    // as invalid and have the full display list for merging to track
+    // the change correctly.
+    // It seems really hard to track this in advance, as the bookkeeping
+    // required to note which stacking contexts have blend descendants
+    // is complex and likely to be buggy.
+    // Instead we're doing the sad thing, detecting it afterwards, and just
+    // repeating display list building if it changed.
+    // We have to repeat building for the entire display list (or at least
+    // the outer stacking context), since we need to mark this frame as invalid
+    // to remove any existing content that isn't wrapped in the blend container,
+    // and then we need to build content infront/behind the blend container
+    // to get correct positioning during merging.
+    if (aBuilder->ContainsBlendMode() && aBuilder->IsRetainingDisplayList()) {
+      if (aBuilder->IsPartialUpdate()) {
+        aBuilder->SetPartialBuildFailed(true);
+      } else {
+        aBuilder->SetDisablePartialUpdates(true);
+      }
+    }
+  }
+
+  if (aBuilder->IsBackgroundOnly()) {
+    set.BlockBorderBackgrounds()->DeleteAll(aBuilder);
+    set.Floats()->DeleteAll(aBuilder);
+    set.Content()->DeleteAll(aBuilder);
+    set.PositionedDescendants()->DeleteAll(aBuilder);
+    set.Outlines()->DeleteAll(aBuilder);
+  }
+
+  if (hasOverrideDirtyRect &&
+      StaticPrefs::layout_display_list_show_rebuild_area()) {
+    nsDisplaySolidColor* color = MakeDisplayItem<nsDisplaySolidColor>(
+        aBuilder, this,
+        dirtyRect + aBuilder->GetCurrentFrameOffsetToReferenceFrame(),
+        NS_RGBA(255, 0, 0, 64), false);
+    if (color) {
+      color->SetOverrideZIndex(INT32_MAX);
+      set.PositionedDescendants()->AppendToTop(color);
+    }
+  }
+
+  nsIContent* content = GetContent();
+  if (!content) {
+    content = PresContext()->Document()->GetRootElement();
+  }
+
+  nsDisplayList resultList(aBuilder);
+  set.SerializeWithCorrectZOrder(&resultList, content);
+
+  // Get the ASR to use for the container items that we create here.
+  const ActiveScrolledRoot* containerItemASR = contASRTracker.GetContainerASR();
+
+  bool createdContainer = false;
+
+  // If adding both a nsDisplayBlendContainer and a nsDisplayBlendMode to the
+  // same list, the nsDisplayBlendContainer should be added first. This only
+  // happens when the element creating this stacking context has mix-blend-mode
+  // and also contains a child which has mix-blend-mode.
+  // The nsDisplayBlendContainer must be added to the list first, so it does not
+  // isolate the containing element blending as well.
+  if (aBuilder->ContainsBlendMode()) {
+    resultList.AppendToTop(nsDisplayBlendContainer::CreateForMixBlendMode(
+        aBuilder, this, &resultList, containerItemASR));
+    createdContainer = true;
+  }
+
+  if (usingBackdropFilter) {
+    nsRect backdropRect =
+        GetRectRelativeToSelf() + aBuilder->ToReferenceFrame(this);
+    resultList.AppendNewToTop<nsDisplayBackdropFilters>(
+        aBuilder, this, &resultList, backdropRect, this);
+    createdContainer = true;
+  }
+
+  // If there are any SVG effects, wrap the list up in an SVG effects item
+  // (which also handles CSS group opacity). Note that we create an SVG effects
+  // item even if resultList is empty, since a filter can produce graphical
+  // output even if the element being filtered wouldn't otherwise do so.
+  if (usingSVGEffects) {
+    MOZ_ASSERT(usingFilter || usingMask,
+               "Beside filter & mask/clip-path, what else effect do we have?");
+
+    if (clipCapturedBy == ContainerItemType::Filter) {
+      clipState.Restore();
+    }
+    // Revert to the post-filter dirty rect.
+    aBuilder->SetVisibleRect(visibleRectOutsideSVGEffects);
+
+    // Skip all filter effects while generating glyph mask.
+    if (usingFilter && !aBuilder->IsForGenerateGlyphMask()) {
+      /* List now emptied, so add the new list to the top. */
+      resultList.AppendNewToTop<nsDisplayFilters>(aBuilder, this, &resultList,
+                                                  this, usingBackdropFilter);
+      createdContainer = true;
+    }
+
+    if (usingMask) {
+      // The mask should move with aBuilder->CurrentActiveScrolledRoot(), so
+      // that's the ASR we prefer to use for the mask item. However, we can
+      // only do this if the mask if clipped with respect to that ASR, because
+      // an item always needs to have finite bounds with respect to its ASR.
+      // If we weren't able to compute a clip for the mask, we fall back to
+      // using containerItemASR, which is the lowest common ancestor clip of
+      // the mask's contents. That's not entirely correct, but it satisfies
+      // the base requirement of the ASR system (that items have finite bounds
+      // wrt. their ASR).
+      const ActiveScrolledRoot* maskASR =
+          clipForMask.isSome() ? aBuilder->CurrentActiveScrolledRoot()
+                               : containerItemASR;
+      /* List now emptied, so add the new list to the top. */
+      resultList.AppendNewToTop<nsDisplayMasksAndClipPaths>(
+          aBuilder, this, &resultList, maskASR, usingBackdropFilter);
+      createdContainer = true;
+    }
+
+    // TODO(miko): We could probably create a wraplist here and avoid creating
+    // it later in |BuildDisplayListForChild()|.
+    createdContainer = false;
+
+    // Also add the hoisted scroll info items. We need those for APZ scrolling
+    // because nsDisplayMasksAndClipPaths items can't build active layers.
+    aBuilder->ExitSVGEffectsContents();
+    resultList.AppendToTop(&hoistedScrollInfoItemsStorage);
+  }
+
+  // If the list is non-empty and there is CSS group opacity without SVG
+  // effects, wrap it up in an opacity item.
+  if (useOpacity) {
+    const bool needsActiveOpacityLayer =
+        nsDisplayOpacity::NeedsActiveLayer(aBuilder, this);
+    resultList.AppendNewToTop<nsDisplayOpacity>(
+        aBuilder, this, &resultList, containerItemASR, opacityItemForEventsOnly,
+        needsActiveOpacityLayer, usingBackdropFilter);
+    createdContainer = true;
+  }
+
+  // If we're going to apply a transformation and don't have preserve-3d set,
+  // wrap everything in an nsDisplayTransform. If there's nothing in the list,
+  // don't add anything.
+  //
+  // For the preserve-3d case we want to individually wrap every child in the
+  // list with a separate nsDisplayTransform instead. When the child is already
+  // an nsDisplayTransform, we can skip this step, as the computed transform
+  // will already include our own.
+  //
+  // We also traverse into sublists created by nsDisplayWrapList, so that we
+  // find all the correct children.
+  if (isTransformed && extend3DContext) {
+    // Install dummy nsDisplayTransform as a leaf containing
+    // descendants not participating this 3D rendering context.
+    nsDisplayList nonparticipants(aBuilder);
+    nsDisplayList participants(aBuilder);
+    int index = 1;
+
+    nsDisplayItem* separator = nullptr;
+
+    // TODO: This can be simplified: |participants| is just |resultList|.
+    for (nsDisplayItem* item : resultList.TakeItems()) {
+      if (ItemParticipatesIn3DContext(this, item) &&
+          !item->GetClip().HasClip()) {
+        // The frame of this item participates the same 3D context.
+        WrapSeparatorTransform(aBuilder, this, &nonparticipants, &participants,
+                               index++, &separator);
+
+        participants.AppendToTop(item);
+      } else {
+        // The frame of the item doesn't participate the current
+        // context, or has no transform.
+        //
+        // For items participating but not transformed, they are add
+        // to nonparticipants to get a separator layer for handling
+        // clips, if there is, on an intermediate surface.
+        // \see ContainerLayer::DefaultComputeEffectiveTransforms().
+        nonparticipants.AppendToTop(item);
+      }
+    }
+    WrapSeparatorTransform(aBuilder, this, &nonparticipants, &participants,
+                           index++, &separator);
+
+    if (separator) {
+      createdContainer = true;
+    }
+
+    resultList.AppendToTop(&participants);
+  }
+
+  if (isTransformed) {
+    transformedCssClip.Restore();
+    if (clipCapturedBy == ContainerItemType::Transform) {
+      // Restore clip state now so nsDisplayTransform is clipped properly.
+      clipState.Restore();
+    }
+    // Revert to the dirtyrect coming in from the parent, without our transform
+    // taken into account.
+    aBuilder->SetVisibleRect(visibleRectOutsideTransform);
+
+    if (this != aBuilder->RootReferenceFrame()) {
+      // Revert to the outer reference frame and offset because all display
+      // items we create from now on are outside the transform.
+      nsPoint toOuterReferenceFrame;
+      const nsIFrame* outerReferenceFrame =
+          aBuilder->FindReferenceFrameFor(GetParent(), &toOuterReferenceFrame);
+      toOuterReferenceFrame += GetPosition();
+
+      buildingDisplayList.SetReferenceFrameAndCurrentOffset(
+          outerReferenceFrame, toOuterReferenceFrame);
+    }
+
+    // We would like to block async animations for ancestors of ones not
+    // prerendered in the preserve-3d tree. Now that we've finished processing
+    // all descendants, update allowAsyncAnimation to take their prerender
+    // state into account
+    // FIXME: We don't block async animations for previous siblings because
+    // their prerender decisions have been made. We may have to figure out a
+    // better way to rollback their prerender decisions.
+    // Alternatively we could not block animations for later siblings, and only
+    // block them for ancestors of a blocked one.
+    if ((extend3DContext || combines3DTransformWithAncestors) &&
+        prerenderInfo.CanUseAsyncAnimations() &&
+        !aBuilder->GetPreserves3DAllowAsyncAnimation()) {
+      // aBuilder->GetPreserves3DAllowAsyncAnimation() means the inner or
+      // previous silbing frames are allowed/disallowed for async animations.
+      prerenderInfo.mDecision = nsDisplayTransform::PrerenderDecision::No;
+    }
+
+    nsDisplayTransform* transformItem = MakeDisplayItem<nsDisplayTransform>(
+        aBuilder, this, &resultList, visibleRect, prerenderInfo.mDecision);
+    if (transformItem) {
+      resultList.AppendToTop(transformItem);
+      createdContainer = true;
+    }
+
+    if (hasPerspective) {
+      transformItem->MarkWithAssociatedPerspective();
+
+      if (clipCapturedBy == ContainerItemType::Perspective) {
+        clipState.Restore();
+      }
+      resultList.AppendNewToTop<nsDisplayPerspective>(aBuilder, this,
+                                                      &resultList);
+      createdContainer = true;
+    }
+  }
+
+  if (clipCapturedBy ==
+      ContainerItemType::OwnLayerForTransformWithRoundedClip) {
+    clipState.Restore();
+    resultList.AppendNewToTopWithIndex<nsDisplayOwnLayer>(
+        aBuilder, this,
+        /* aIndex = */ nsDisplayOwnLayer::OwnLayerForTransformWithRoundedClip,
+        &resultList, aBuilder->CurrentActiveScrolledRoot(),
+        nsDisplayOwnLayerFlags::None, ScrollbarData{},
+        /* aForceActive = */ false, false);
+    createdContainer = true;
+  }
+
+  // If we have sticky positioning, wrap it in a sticky position item.
+  if (useFixedPosition) {
+    if (clipCapturedBy == ContainerItemType::FixedPosition) {
+      clipState.Restore();
+    }
+    // The ASR for the fixed item should be the ASR of our containing block,
+    // which has been set as the builder's current ASR, unless this frame is
+    // invisible and we hadn't saved display item data for it. In that case,
+    // we need to take the containerItemASR since we might have fixed children.
+    // For WebRender, we want to the know what |containerItemASR| is for the
+    // case where the fixed-pos item is not a "real" fixed-pos item (e.g. it's
+    // nested inside a scrolling transform), so we stash that on the display
+    // item as well.
+    const ActiveScrolledRoot* fixedASR = ActiveScrolledRoot::PickAncestor(
+        containerItemASR, aBuilder->CurrentActiveScrolledRoot());
+    resultList.AppendNewToTop<nsDisplayFixedPosition>(
+        aBuilder, this, &resultList, fixedASR, containerItemASR);
+    createdContainer = true;
+  } else if (useStickyPosition) {
+    // For position:sticky, the clip needs to be applied both to the sticky
+    // container item and to the contents. The container item needs the clip
+    // because a scrolled clip needs to move independently from the sticky
+    // contents, and the contents need the clip so that they have finite
+    // clipped bounds with respect to the container item's ASR. The latter is
+    // a little tricky in the case where the sticky item has both fixed and
+    // non-fixed descendants, because that means that the sticky container
+    // item's ASR is the ASR of the fixed descendant.
+    // For WebRender display list building, though, we still want to know the
+    // the ASR that the sticky container item would normally have, so we stash
+    // that on the display item as the "container ASR" (i.e. the normal ASR of
+    // the container item, excluding the special behaviour induced by fixed
+    // descendants).
+    const ActiveScrolledRoot* stickyASR = ActiveScrolledRoot::PickAncestor(
+        containerItemASR, aBuilder->CurrentActiveScrolledRoot());
+
+    auto* stickyItem = MakeDisplayItem<nsDisplayStickyPosition>(
+        aBuilder, this, &resultList, stickyASR,
+        aBuilder->CurrentActiveScrolledRoot(),
+        clipState.IsClippedToDisplayPort());
+
+    bool shouldFlatten = true;
+
+    StickyScrollContainer* stickyScrollContainer =
+        StickyScrollContainer::GetStickyScrollContainerForFrame(this);
+    if (stickyScrollContainer &&
+        stickyScrollContainer->ScrollFrame()->IsMaybeAsynchronouslyScrolled()) {
+      shouldFlatten = false;
+    }
+
+    stickyItem->SetShouldFlatten(shouldFlatten);
+
+    resultList.AppendToTop(stickyItem);
+    createdContainer = true;
+
+    // If the sticky element is inside a filter, annotate the scroll frame that
+    // scrolls the filter as having out-of-flow content inside a filter (this
+    // inhibits paint skipping).
+    if (aBuilder->GetFilterASR() && aBuilder->GetFilterASR() == stickyASR) {
+      aBuilder->GetFilterASR()
+          ->mScrollableFrame->SetHasOutOfFlowContentInsideFilter();
+    }
+  }
+
+  // If there's blending, wrap up the list in a blend-mode item. Note that
+  // opacity can be applied before blending as the blend color is not affected
+  // by foreground opacity (only background alpha).
+  if (useBlendMode) {
+    DisplayListClipState::AutoSaveRestore blendModeClipState(aBuilder);
+    resultList.AppendNewToTop<nsDisplayBlendMode>(aBuilder, this, &resultList,
+                                                  effects->mMixBlendMode,
+                                                  containerItemASR, false);
+    createdContainer = true;
+  }
+
+  if (aBuilder->IsReusingStackingContextItems()) {
+    if (resultList.IsEmpty()) {
+      return;
+    }
+
+    nsDisplayItem* container = resultList.GetBottom();
+    if (resultList.Length() > 1 || container->Frame() != this) {
+      container = MakeDisplayItem<nsDisplayContainer>(
+          aBuilder, this, containerItemASR, &resultList);
+    } else {
+      MOZ_ASSERT(resultList.Length() == 1);
+      resultList.Clear();
+    }
+
+    // Mark the outermost display item as reusable. These display items and
+    // their chidren can be reused during the next paint if no ancestor or
+    // descendant frames have been modified.
+    if (!container->IsReusedItem()) {
+      container->SetReusable();
+    }
+    aList->AppendToTop(container);
+    createdContainer = true;
+  } else {
+    aList->AppendToTop(&resultList);
+  }
+
+  if (aCreatedContainerItem) {
+    *aCreatedContainerItem = createdContainer;
+  }
+}
+
+static nsDisplayItem* WrapInWrapList(nsDisplayListBuilder* aBuilder,
+                                     nsIFrame* aFrame, nsDisplayList* aList,
+                                     const ActiveScrolledRoot* aContainerASR,
+                                     bool aBuiltContainerItem = false) {
+  nsDisplayItem* item = aList->GetBottom();
+  if (!item) {
+    return nullptr;
+  }
+
+  // We need a wrap list if there are multiple items, or if the single
+  // item has a different frame. This can change in a partial build depending
+  // on which items we build, so we need to ensure that we don't transition
+  // to/from a wrap list without invalidating correctly.
+  bool needsWrapList =
+      aList->Length() > 1 || item->Frame() != aFrame || item->GetChildren();
+
+  // If we have an explicit container item (that can't change without an
+  // invalidation) or we're doing a full build and don't need a wrap list, then
+  // we can skip adding one.
+  if (aBuiltContainerItem || (!aBuilder->IsPartialUpdate() && !needsWrapList)) {
+    MOZ_ASSERT(aList->Length() == 1);
+    aList->Clear();
+    return item;
+  }
+
+  // If we're doing a partial build and we didn't need a wrap list
+  // previously then we can try to work from there.
+  if (aBuilder->IsPartialUpdate() &&
+      !aFrame->HasDisplayItem(uint32_t(DisplayItemType::TYPE_CONTAINER))) {
+    // If we now need a wrap list, we must previously have had no display items
+    // or a single one belonging to this frame. Mark the item itself as
+    // discarded so that RetainedDisplayListBuilder uses the ones we just built.
+    // We don't want to mark the frame as modified as that would invalidate
+    // positioned descendants that might be outside of this list, and might not
+    // have been rebuilt this time.
+    if (needsWrapList) {
+      DiscardOldItems(aFrame);
+    } else {
+      MOZ_ASSERT(aList->Length() == 1);
+      aList->Clear();
+      return item;
+    }
+  }
+
+  // The last case we could try to handle is when we previously had a wrap list,
+  // but no longer need it. Unfortunately we can't differentiate this case from
+  // a partial build where other children exist but we just didn't build them
+  // this time.
+  // TODO:RetainedDisplayListBuilder's merge phase has the full list and
+  // could strip them out.
+
+  return MakeDisplayItem<nsDisplayContainer>(aBuilder, aFrame, aContainerASR,
+                                             aList);
+}
+
+/**
+ * Check if a frame should be visited for building display list.
+ */
+static bool DescendIntoChild(nsDisplayListBuilder* aBuilder,
+                             const nsIFrame* aChild, const nsRect& aVisible,
+                             const nsRect& aDirty) {
+  if (aChild->HasAnyStateBits(NS_FRAME_FORCE_DISPLAY_LIST_DESCEND_INTO)) {
+    return true;
+  }
+
+  // If the child is a scrollframe that we want to ignore, then we need
+  // to descend into it because its scrolled child may intersect the dirty
+  // area even if the scrollframe itself doesn't.
+  if (aChild == aBuilder->GetIgnoreScrollFrame()) {
+    return true;
+  }
+
+  // There are cases where the "ignore scroll frame" on the builder is not set
+  // correctly, and so we additionally want to catch cases where the child is
+  // a root scrollframe and we are ignoring scrolling on the viewport.
+  if (aChild == aBuilder->GetPresShellIgnoreScrollFrame()) {
+    return true;
+  }
+
+  nsRect overflow = aChild->InkOverflowRect();
+
+  // On mobile, there may be a dynamic toolbar. The root content document's
+  // root scroll frame's ink overflow rect does not include the toolbar
+  // height, but if the toolbar is hidden, we still want to be able to target
+  // content underneath the toolbar, so expand the overflow rect here to
+  // allow display list building to descend into the scroll frame.
+  if (aBuilder->IsForEventDelivery() &&
+      aChild == aChild->PresShell()->GetRootScrollFrame() &&
+      aChild->PresContext()->IsRootContentDocumentCrossProcess() &&
+      aChild->PresContext()->HasDynamicToolbar()) {
+    overflow.SizeTo(nsLayoutUtils::ExpandHeightForDynamicToolbar(
+        aChild->PresContext(), overflow.Size()));
+  }
+
+  if (aDirty.Intersects(overflow)) {
+    return true;
+  }
+
+  if (aChild->ForceDescendIntoIfVisible() && aVisible.Intersects(overflow)) {
+    return true;
+  }
+
+  if (aChild->IsTablePart()) {
+    // Relative positioning and transforms can cause table parts to move, but we
+    // will still paint the backgrounds for their ancestor parts under them at
+    // their 'normal' position. That means that we must consider the overflow
+    // rects at both positions.
+
+    // We convert the overflow rect into the nsTableFrame's coordinate
+    // space, applying the normal position offset at each step. Then we
+    // compare that against the builder's cached dirty rect in table
+    // coordinate space.
+    const nsIFrame* f = aChild;
+    nsRect normalPositionOverflowRelativeToTable = overflow;
+
+    while (f->IsTablePart()) {
+      normalPositionOverflowRelativeToTable += f->GetNormalPosition();
+      f = f->GetParent();
+    }
+
+    nsDisplayTableBackgroundSet* tableBGs = aBuilder->GetTableBackgroundSet();
+    if (tableBGs && tableBGs->GetDirtyRect().Intersects(
+                        normalPositionOverflowRelativeToTable)) {
+      return true;
+    }
+  }
+
+  return false;
+}
+
+void nsIFrame::BuildDisplayListForSimpleChild(nsDisplayListBuilder* aBuilder,
+                                              nsIFrame* aChild,
+                                              const nsDisplayListSet& aLists) {
+  // This is the shortcut for frames been handled along the common
+  // path, the most common one of THE COMMON CASE mentioned later.
+  MOZ_ASSERT(aChild->Type() != LayoutFrameType::Placeholder);
+  MOZ_ASSERT(!aBuilder->GetSelectedFramesOnly() &&
+                 !aBuilder->GetIncludeAllOutOfFlows(),
+             "It should be held for painting to window");
+  MOZ_ASSERT(aChild->HasAnyStateBits(NS_FRAME_SIMPLE_DISPLAYLIST));
+
+  const nsPoint offset = aChild->GetOffsetTo(this);
+  const nsRect visible = aBuilder->GetVisibleRect() - offset;
+  const nsRect dirty = aBuilder->GetDirtyRect() - offset;
+
+  if (!DescendIntoChild(aBuilder, aChild, visible, dirty)) {
+    DL_LOGV("Skipped frame %p", aChild);
+    return;
+  }
+
+  // Child cannot be transformed since it is not a stacking context.
+  nsDisplayListBuilder::AutoBuildingDisplayList buildingForChild(
+      aBuilder, aChild, visible, dirty, false);
+
+  UpdateCurrentHitTestInfo(aBuilder, aChild);
+
+  aChild->MarkAbsoluteFramesForDisplayList(aBuilder);
+  aBuilder->AdjustWindowDraggingRegion(aChild);
+  aBuilder->Check();
+  aChild->BuildDisplayList(aBuilder, aLists);
+  aChild->SetBuiltDisplayList(true);
+  aBuilder->Check();
+  aBuilder->DisplayCaret(aChild, aLists.Outlines());
+}
+
+static bool ShouldSkipFrame(nsDisplayListBuilder* aBuilder,
+                            const nsIFrame* aFrame) {
+  // If painting is restricted to just the background of the top level frame,
+  // then we have nothing to do here.
+  if (aBuilder->IsBackgroundOnly()) {
+    return true;
+  }
+  if (aBuilder->IsForGenerateGlyphMask() &&
+      (!aFrame->IsTextFrame() && aFrame->IsLeaf())) {
+    return true;
+  }
+  // The placeholder frame should have the same content as the OOF frame.
+  if (aBuilder->GetSelectedFramesOnly() &&
+      (aFrame->IsLeaf() && !aFrame->IsSelected())) {
+    return true;
+  }
+  static const nsFrameState skipFlags =
+      (NS_FRAME_TOO_DEEP_IN_FRAME_TREE | NS_FRAME_IS_NONDISPLAY);
+  if (aFrame->HasAnyStateBits(skipFlags)) {
+    return true;
+  }
+  return aFrame->StyleUIReset()->mMozSubtreeHiddenOnlyVisually;
+}
+
+void nsIFrame::BuildDisplayListForChild(nsDisplayListBuilder* aBuilder,
+                                        nsIFrame* aChild,
+                                        const nsDisplayListSet& aLists,
+                                        DisplayChildFlags aFlags) {
+  AutoCheckBuilder check(aBuilder);
+#ifdef DEBUG
+  DL_LOGV("BuildDisplayListForChild (%p) <", aChild);
+  ScopeExit e(
+      [aChild]() { DL_LOGV("> BuildDisplayListForChild (%p)", aChild); });
+#endif
+
+  if (ShouldSkipFrame(aBuilder, aChild)) {
+    return;
+  }
+
+  if (HidesContent()) {
+    return;
+  }
+
+  // If we're generating a display list for printing, include Link items for
+  // frames that correspond to HTML link elements so that we can have active
+  // links in saved PDF output. Note that the state of "within a link" is
+  // set on the display-list builder, such that all descendants of the link
+  // element will generate display-list links.
+  // TODO: we should be able to optimize this so as to avoid creating links
+  // for the same destination that entirely overlap each other, which adds
+  // nothing useful to the final PDF.
+  Maybe<nsDisplayListBuilder::Linkifier> linkifier;
+  if (StaticPrefs::print_save_as_pdf_links_enabled() &&
+      aBuilder->IsForPrinting()) {
+    linkifier.emplace(aBuilder, aChild, aLists.Content());
+    linkifier->MaybeAppendLink(aBuilder, aChild);
+  }
+
+  nsIFrame* child = aChild;
+  auto* placeholder = child->IsPlaceholderFrame()
+                          ? static_cast<nsPlaceholderFrame*>(child)
+                          : nullptr;
+  nsIFrame* childOrOutOfFlow =
+      placeholder ? placeholder->GetOutOfFlowFrame() : child;
+
+  nsIFrame* parent = childOrOutOfFlow->GetParent();
+  const auto* parentDisplay = parent->StyleDisplay();
+  const auto overflowClipAxes =
+      parent->ShouldApplyOverflowClipping(parentDisplay);
+
+  const bool isPaintingToWindow = aBuilder->IsPaintingToWindow();
+  const bool doingShortcut =
+      isPaintingToWindow &&
+      child->HasAnyStateBits(NS_FRAME_SIMPLE_DISPLAYLIST) &&
+      // Animations may change the stacking context state.
+      // ShouldApplyOverflowClipping is affected by the parent style, which does
+      // not invalidate the NS_FRAME_SIMPLE_DISPLAYLIST bit.
+      !(overflowClipAxes != PhysicalAxes::None ||
+        child->MayHaveTransformAnimation() || child->MayHaveOpacityAnimation());
+
+  if (aBuilder->IsForPainting()) {
+    aBuilder->ClearWillChangeBudgetStatus(child);
+  }
+
+  if (StaticPrefs::layout_css_scroll_anchoring_highlight()) {
+    if (child->FirstContinuation()->IsScrollAnchor()) {
+      nsRect bounds = child->GetContentRectRelativeToSelf() +
+                      aBuilder->ToReferenceFrame(child);
+      nsDisplaySolidColor* color = MakeDisplayItem<nsDisplaySolidColor>(
+          aBuilder, child, bounds, NS_RGBA(255, 0, 255, 64));
+      if (color) {
+        color->SetOverrideZIndex(INT32_MAX);
+        aLists.PositionedDescendants()->AppendToTop(color);
+      }
+    }
+  }
+
+  if (doingShortcut) {
+    BuildDisplayListForSimpleChild(aBuilder, child, aLists);
+    return;
+  }
+
+  // dirty rect in child-relative coordinates
+  NS_ASSERTION(aBuilder->GetCurrentFrame() == this, "Wrong coord space!");
+  const nsPoint offset = child->GetOffsetTo(this);
+  nsRect visible = aBuilder->GetVisibleRect() - offset;
+  nsRect dirty = aBuilder->GetDirtyRect() - offset;
+
+  nsDisplayListBuilder::OutOfFlowDisplayData* savedOutOfFlowData = nullptr;
+  if (placeholder) {
+    if (placeholder->HasAnyStateBits(PLACEHOLDER_FOR_TOPLAYER)) {
+      // If the out-of-flow frame is in the top layer, the viewport frame
+      // will paint it. Skip it here. Note that, only out-of-flow frames
+      // with this property should be skipped, because non-HTML elements
+      // may stop their children from being out-of-flow. Those frames
+      // should still be handled in the normal in-flow path.
+      return;
+    }
+
+    child = childOrOutOfFlow;
+    if (aBuilder->IsForPainting()) {
+      aBuilder->ClearWillChangeBudgetStatus(child);
+    }
+
+    // If 'child' is a pushed float then it's owned by a block that's not an
+    // ancestor of the placeholder, and it will be painted by that block and
+    // should not be painted through the placeholder. Also recheck
+    // NS_FRAME_TOO_DEEP_IN_FRAME_TREE and NS_FRAME_IS_NONDISPLAY.
+    static const nsFrameState skipFlags =
+        (NS_FRAME_IS_PUSHED_FLOAT | NS_FRAME_TOO_DEEP_IN_FRAME_TREE |
+         NS_FRAME_IS_NONDISPLAY);
+    if (child->HasAnyStateBits(skipFlags) || nsLayoutUtils::IsPopup(child)) {
+      return;
+    }
+
+    MOZ_ASSERT(child->HasAnyStateBits(NS_FRAME_OUT_OF_FLOW));
+    savedOutOfFlowData = nsDisplayListBuilder::GetOutOfFlowData(child);
+
+    if (aBuilder->GetIncludeAllOutOfFlows()) {
+      visible = child->InkOverflowRect();
+      dirty = child->InkOverflowRect();
+    } else if (savedOutOfFlowData) {
+      visible =
+          savedOutOfFlowData->GetVisibleRectForFrame(aBuilder, child, &dirty);
+    } else {
+      // The out-of-flow frame did not intersect the dirty area. We may still
+      // need to traverse into it, since it may contain placeholders we need
+      // to enter to reach other out-of-flow frames that are visible.
+      visible.SetEmpty();
+      dirty.SetEmpty();
+    }
+  }
+
+  NS_ASSERTION(!child->IsPlaceholderFrame(),
+               "Should have dealt with placeholders already");
+
+  if (!DescendIntoChild(aBuilder, child, visible, dirty)) {
+    DL_LOGV("Skipped frame %p", child);
+    return;
+  }
+
+  const bool isSVG = child->HasAnyStateBits(NS_FRAME_SVG_LAYOUT);
+
+  // This flag is raised if the control flow strays off the common path.
+  // The common path is the most common one of THE COMMON CASE mentioned later.
+  bool awayFromCommonPath = !isPaintingToWindow;
+
+  // true if this is a real or pseudo stacking context
+  bool pseudoStackingContext =
+      aFlags.contains(DisplayChildFlag::ForcePseudoStackingContext);
+
+  if (!pseudoStackingContext && !isSVG &&
+      aFlags.contains(DisplayChildFlag::Inline) &&
+      !child->IsLineParticipant()) {
+    // child is a non-inline frame in an inline context, i.e.,
+    // it acts like inline-block or inline-table. Therefore it is a
+    // pseudo-stacking-context.
+    pseudoStackingContext = true;
+  }
+
+  const nsStyleDisplay* ourDisp = StyleDisplay();
+  // Don't paint our children if the theme object is a leaf.
+  if (IsThemed(ourDisp) && !PresContext()->Theme()->WidgetIsContainer(
+                               ourDisp->EffectiveAppearance())) {
+    return;
+  }
+
+  // Since we're now sure that we're adding this frame to the display list
+  // (which means we're painting it, modulo occlusion), mark it as visible
+  // within the displayport.
+  if (isPaintingToWindow && child->TrackingVisibility() &&
+      child->IsVisibleForPainting()) {
+    child->PresShell()->EnsureFrameInApproximatelyVisibleList(child);
+    awayFromCommonPath = true;
+  }
+
+  // Child is composited if it's transformed, partially transparent, or has
+  // SVG effects or a blend mode..
+  const nsStyleDisplay* disp = child->StyleDisplay();
+  const nsStyleEffects* effects = child->StyleEffects();
+
+  const bool isPositioned = disp->IsPositionedStyle();
+  const bool isStackingContext =
+      aFlags.contains(DisplayChildFlag::ForceStackingContext) ||
+      child->IsStackingContext(disp, effects);
+
+  if (pseudoStackingContext || isStackingContext || isPositioned ||
+      placeholder || (!isSVG && disp->IsFloating(child)) ||
+      (isSVG && effects->mClip.IsRect() && IsSVGContentWithCSSClip(child))) {
+    pseudoStackingContext = true;
+    awayFromCommonPath = true;
+  }
+
+  NS_ASSERTION(!isStackingContext || pseudoStackingContext,
+               "Stacking contexts must also be pseudo-stacking-contexts");
+
+  nsDisplayListBuilder::AutoBuildingDisplayList buildingForChild(
+      aBuilder, child, visible, dirty);
+
+  UpdateCurrentHitTestInfo(aBuilder, child);
+
+  DisplayListClipState::AutoClipMultiple clipState(aBuilder);
+  nsDisplayListBuilder::AutoCurrentActiveScrolledRootSetter asrSetter(aBuilder);
+
+  if (savedOutOfFlowData) {
+    aBuilder->SetBuildingInvisibleItems(false);
+
+    clipState.SetClipChainForContainingBlockDescendants(
+        savedOutOfFlowData->mContainingBlockClipChain);
+    asrSetter.SetCurrentActiveScrolledRoot(
+        savedOutOfFlowData->mContainingBlockActiveScrolledRoot);
+    asrSetter.SetCurrentScrollParentId(savedOutOfFlowData->mScrollParentId);
+    MOZ_ASSERT(awayFromCommonPath,
+               "It is impossible when savedOutOfFlowData is true");
+  } else if (HasAnyStateBits(NS_FRAME_FORCE_DISPLAY_LIST_DESCEND_INTO) &&
+             placeholder) {
+    NS_ASSERTION(visible.IsEmpty(), "should have empty visible rect");
+    // Every item we build from now until we descent into an out of flow that
+    // does have saved out of flow data should be invisible. This state gets
+    // restored when AutoBuildingDisplayList gets out of scope.
+    aBuilder->SetBuildingInvisibleItems(true);
+
+    // If we have nested out-of-flow frames and the outer one isn't visible
+    // then we won't have stored clip data for it. We can just clear the clip
+    // instead since we know we won't render anything, and the inner out-of-flow
+    // frame will setup the correct clip for itself.
+    clipState.SetClipChainForContainingBlockDescendants(nullptr);
+  }
+
+  // Setup clipping for the parent's overflow:clip,
+  // or overflow:hidden on elements that don't support scrolling (and therefore
+  // don't create nsHTML/XULScrollFrame). This clipping needs to not clip
+  // anything directly rendered by the parent, only the rendering of its
+  // children.
+  // Don't use overflowClip to restrict the dirty rect, since some of the
+  // descendants may not be clipped by it. Even if we end up with unnecessary
+  // display items, they'll be pruned during ComputeVisibility.
+  //
+  // FIXME(emilio): Why can't we handle this more similarly to `clip` (on the
+  // parent, rather than on the children)? Would ClipContentDescendants do what
+  // we want?
+  if (overflowClipAxes != PhysicalAxes::None) {
+    ApplyOverflowClipping(aBuilder, parent, overflowClipAxes, clipState);
+    awayFromCommonPath = true;
+  }
+
+  nsDisplayList list(aBuilder);
+  nsDisplayList extraPositionedDescendants(aBuilder);
+  const ActiveScrolledRoot* wrapListASR;
+  bool builtContainerItem = false;
+  if (isStackingContext) {
+    // True stacking context.
+    // For stacking contexts, BuildDisplayListForStackingContext handles
+    // clipping and MarkAbsoluteFramesForDisplayList.
+    nsDisplayListBuilder::AutoContainerASRTracker contASRTracker(aBuilder);
+    child->BuildDisplayListForStackingContext(aBuilder, &list,
+                                              &builtContainerItem);
+    wrapListASR = contASRTracker.GetContainerASR();
+    if (!aBuilder->IsReusingStackingContextItems() &&
+        aBuilder->GetCaretFrame() == child) {
+      builtContainerItem = false;
+    }
+  } else {
+    Maybe<nsRect> clipPropClip =
+        child->GetClipPropClipRect(disp, effects, child->GetSize());
+    if (clipPropClip) {
+      aBuilder->IntersectVisibleRect(*clipPropClip);
+      aBuilder->IntersectDirtyRect(*clipPropClip);
+      clipState.ClipContentDescendants(*clipPropClip +
+                                       aBuilder->ToReferenceFrame(child));
+      awayFromCommonPath = true;
+    }
+
+    child->MarkAbsoluteFramesForDisplayList(aBuilder);
+    child->SetBuiltDisplayList(true);
+
+    // Some SVG frames might change opacity without invalidating the frame, so
+    // exclude them from the fast-path.
+    if (!awayFromCommonPath && !child->IsSVGFrame()) {
+      // The shortcut is available for the child for next time.
+      child->AddStateBits(NS_FRAME_SIMPLE_DISPLAYLIST);
+    }
+
+    if (!pseudoStackingContext) {
+      // THIS IS THE COMMON CASE.
+      // Not a pseudo or real stacking context. Do the simple thing and
+      // return early.
+      aBuilder->AdjustWindowDraggingRegion(child);
+      aBuilder->Check();
+      child->BuildDisplayList(aBuilder, aLists);
+      aBuilder->Check();
+      aBuilder->DisplayCaret(child, aLists.Outlines());
+      return;
+    }
+
+    // A pseudo-stacking context (e.g., a positioned element with z-index auto).
+    // We allow positioned descendants of the child to escape to our parent
+    // stacking context's positioned descendant list, because they might be
+    // z-index:non-auto
+    nsDisplayListCollection pseudoStack(aBuilder);
+
+    aBuilder->AdjustWindowDraggingRegion(child);
+    nsDisplayListBuilder::AutoContainerASRTracker contASRTracker(aBuilder);
+    aBuilder->Check();
+    child->BuildDisplayList(aBuilder, pseudoStack);
+    aBuilder->Check();
+    if (aBuilder->DisplayCaret(child, pseudoStack.Outlines())) {
+      builtContainerItem = false;
+    }
+    wrapListASR = contASRTracker.GetContainerASR();
+
+    list.AppendToTop(pseudoStack.BorderBackground());
+    list.AppendToTop(pseudoStack.BlockBorderBackgrounds());
+    list.AppendToTop(pseudoStack.Floats());
+    list.AppendToTop(pseudoStack.Content());
+    list.AppendToTop(pseudoStack.Outlines());
+    extraPositionedDescendants.AppendToTop(pseudoStack.PositionedDescendants());
+  }
+
+  buildingForChild.RestoreBuildingInvisibleItemsValue();
+
+  if (!list.IsEmpty()) {
+    if (isPositioned || isStackingContext) {
+      // Genuine stacking contexts, and positioned pseudo-stacking-contexts,
+      // go in this level.
+      nsDisplayItem* item = WrapInWrapList(aBuilder, child, &list, wrapListASR,
+                                           builtContainerItem);
+      if (isSVG) {
+        aLists.Content()->AppendToTop(item);
+      } else {
+        aLists.PositionedDescendants()->AppendToTop(item);
+      }
+    } else if (!isSVG && disp->IsFloating(child)) {
+      aLists.Floats()->AppendToTop(
+          WrapInWrapList(aBuilder, child, &list, wrapListASR));
+    } else {
+      aLists.Content()->AppendToTop(&list);
+    }
+  }
+  // We delay placing the positioned descendants of positioned frames to here,
+  // because in the absence of z-index this is the correct order for them.
+  // This doesn't affect correctness because the positioned descendants list
+  // is sorted by z-order and content in BuildDisplayListForStackingContext,
+  // but it means that sort routine needs to do less work.
+  aLists.PositionedDescendants()->AppendToTop(&extraPositionedDescendants);
+}
+
+void nsIFrame::MarkAbsoluteFramesForDisplayList(
+    nsDisplayListBuilder* aBuilder) {
+  if (IsAbsoluteContainer()) {
+    aBuilder->MarkFramesForDisplayList(
+        this, GetAbsoluteContainingBlock()->GetChildList());
+  }
+}
+
+nsresult nsIFrame::GetContentForEvent(const WidgetEvent* aEvent,
+                                      nsIContent** aContent) {
+  nsIFrame* f = nsLayoutUtils::GetNonGeneratedAncestor(this);
+  *aContent = f->GetContent();
+  NS_IF_ADDREF(*aContent);
+  return NS_OK;
+}
+
+void nsIFrame::FireDOMEvent(const nsAString& aDOMEventName,
+                            nsIContent* aContent) {
+  nsIContent* target = aContent ? aContent : GetContent();
+
+  if (target) {
+    RefPtr<AsyncEventDispatcher> asyncDispatcher = new AsyncEventDispatcher(
+        target, aDOMEventName, CanBubble::eYes, ChromeOnlyDispatch::eNo);
+    DebugOnly<nsresult> rv = asyncDispatcher->PostDOMEvent();
+    NS_ASSERTION(NS_SUCCEEDED(rv), "AsyncEventDispatcher failed to dispatch");
+  }
+}
+
+nsresult nsIFrame::HandleEvent(nsPresContext* aPresContext,
+                               WidgetGUIEvent* aEvent,
+                               nsEventStatus* aEventStatus) {
+  if (aEvent->mMessage == eMouseMove) {
+    // XXX If the second argument of HandleDrag() is WidgetMouseEvent,
+    //     the implementation becomes simpler.
+    return HandleDrag(aPresContext, aEvent, aEventStatus);
+  }
+
+  if ((aEvent->mClass == eMouseEventClass &&
+       aEvent->AsMouseEvent()->mButton == MouseButton::ePrimary) ||
+      aEvent->mClass == eTouchEventClass) {
+    if (aEvent->mMessage == eMouseDown || aEvent->mMessage == eTouchStart) {
+      HandlePress(aPresContext, aEvent, aEventStatus);
+    } else if (aEvent->mMessage == eMouseUp || aEvent->mMessage == eTouchEnd) {
+      HandleRelease(aPresContext, aEvent, aEventStatus);
+    }
+    return NS_OK;
+  }
+
+  // When secondary buttion is down, we need to move selection to make users
+  // possible to paste something at click point quickly.
+  // When middle button is down, we need to just move selection and focus at
+  // the clicked point.  Note that even if middle click paste is not enabled,
+  // Chrome moves selection at middle mouse button down.  So, we should follow
+  // the behavior for the compatibility.
+  if (aEvent->mMessage == eMouseDown) {
+    WidgetMouseEvent* mouseEvent = aEvent->AsMouseEvent();
+    if (mouseEvent && (mouseEvent->mButton == MouseButton::eSecondary ||
+                       mouseEvent->mButton == MouseButton::eMiddle)) {
+      if (*aEventStatus == nsEventStatus_eConsumeNoDefault) {
+        return NS_OK;
+      }
+      return MoveCaretToEventPoint(aPresContext, mouseEvent, aEventStatus);
+    }
+  }
+
+  return NS_OK;
+}
+
+nsresult nsIFrame::GetDataForTableSelection(
+    const nsFrameSelection* aFrameSelection, mozilla::PresShell* aPresShell,
+    WidgetMouseEvent* aMouseEvent, nsIContent** aParentContent,
+    int32_t* aContentOffset, TableSelectionMode* aTarget) {
+  if (!aFrameSelection || !aPresShell || !aMouseEvent || !aParentContent ||
+      !aContentOffset || !aTarget)
+    return NS_ERROR_NULL_POINTER;
+
+  *aParentContent = nullptr;
+  *aContentOffset = 0;
+  *aTarget = TableSelectionMode::None;
+
+  int16_t displaySelection = aPresShell->GetSelectionFlags();
+
+  bool selectingTableCells = aFrameSelection->IsInTableSelectionMode();
+
+  // DISPLAY_ALL means we're in an editor.
+  // If already in cell selection mode,
+  //  continue selecting with mouse drag or end on mouse up,
+  //  or when using shift key to extend block of cells
+  //  (Mouse down does normal selection unless Ctrl/Cmd is pressed)
+  bool doTableSelection =
+      displaySelection == nsISelectionDisplay::DISPLAY_ALL &&
+      selectingTableCells &&
+      (aMouseEvent->mMessage == eMouseMove ||
+       (aMouseEvent->mMessage == eMouseUp &&
+        aMouseEvent->mButton == MouseButton::ePrimary) ||
+       aMouseEvent->IsShift());
+
+  if (!doTableSelection) {
+    // In Browser, special 'table selection' key must be pressed for table
+    // selection or when just Shift is pressed and we're already in table/cell
+    // selection mode
+#ifdef XP_MACOSX
+    doTableSelection = aMouseEvent->IsMeta() ||
+                       (aMouseEvent->IsShift() && selectingTableCells);
+#else
+    doTableSelection = aMouseEvent->IsControl() ||
+                       (aMouseEvent->IsShift() && selectingTableCells);
+#endif
+  }
+  if (!doTableSelection) return NS_OK;
+
+  // Get the cell frame or table frame (or parent) of the current content node
+  nsIFrame* frame = this;
+  bool foundCell = false;
+  bool foundTable = false;
+
+  // Get the limiting node to stop parent frame search
+  nsIContent* limiter = aFrameSelection->GetLimiter();
+
+  // If our content node is an ancestor of the limiting node,
+  // we should stop the search right now.
+  if (limiter && limiter->IsInclusiveDescendantOf(GetContent())) return NS_OK;
+
+  // We don't initiate row/col selection from here now,
+  //  but we may in future
+  // bool selectColumn = false;
+  // bool selectRow = false;
+
+  while (frame) {
+    // Check for a table cell by querying to a known CellFrame interface
+    nsITableCellLayout* cellElement = do_QueryFrame(frame);
+    if (cellElement) {
+      foundCell = true;
+      // TODO: If we want to use proximity to top or left border
+      //      for row and column selection, this is the place to do it
+      break;
+    } else {
+      // If not a cell, check for table
+      // This will happen when starting frame is the table or child of a table,
+      //  such as a row (we were inbetween cells or in table border)
+      nsTableWrapperFrame* tableFrame = do_QueryFrame(frame);
+      if (tableFrame) {
+        foundTable = true;
+        // TODO: How can we select row when along left table edge
+        //  or select column when along top edge?
+        break;
+      } else {
+        frame = frame->GetParent();
+        // Stop if we have hit the selection's limiting content node
+        if (frame && frame->GetContent() == limiter) break;
+      }
+    }
+  }
+  // We aren't in a cell or table
+  if (!foundCell && !foundTable) return NS_OK;
+
+  nsIContent* tableOrCellContent = frame->GetContent();
+  if (!tableOrCellContent) return NS_ERROR_FAILURE;
+
+  nsCOMPtr<nsIContent> parentContent = tableOrCellContent->GetParent();
+  if (!parentContent) return NS_ERROR_FAILURE;
+
+  const int32_t offset =
+      parentContent->ComputeIndexOf_Deprecated(tableOrCellContent);
+  // Not likely?
+  if (offset < 0) {
+    return NS_ERROR_FAILURE;
+  }
+
+  // Everything is OK -- set the return values
+  parentContent.forget(aParentContent);
+
+  *aContentOffset = offset;
+
+#if 0
+  if (selectRow)
+    *aTarget = TableSelectionMode::Row;
+  else if (selectColumn)
+    *aTarget = TableSelectionMode::Column;
+  else
+#endif
+  if (foundCell) {
+    *aTarget = TableSelectionMode::Cell;
+  } else if (foundTable) {
+    *aTarget = TableSelectionMode::Table;
+  }
+
+  return NS_OK;
+}
+
+static bool IsEditingHost(const nsIFrame* aFrame) {
+  nsIContent* content = aFrame->GetContent();
+  return content && content->IsEditingHost();
+}
+
+static StyleUserSelect UsedUserSelect(const nsIFrame* aFrame) {
+  if (aFrame->IsGeneratedContentFrame()) {
+    return StyleUserSelect::None;
+  }
+
+  // Per https://drafts.csswg.org/css-ui-4/#content-selection:
+  //
+  // The used value is the same as the computed value, except:
+  //
+  //    1 - on editable elements where the used value is always 'contain'
+  //        regardless of the computed value
+  //    2 - when the computed value is auto, in which case the used value is one
+  //        of the other values...
+  //
+  // See https://github.com/w3c/csswg-drafts/issues/3344 to see why we do this
+  // at used-value time instead of at computed-value time.
+
+  if (aFrame->IsTextInputFrame() || IsEditingHost(aFrame)) {
+    // We don't implement 'contain' itself, but we make 'text' behave as
+    // 'contain' for contenteditable and <input> / <textarea> elements anyway so
+    // this is ok.
+    return StyleUserSelect::Text;
+  }
+
+  auto style = aFrame->Style()->UserSelect();
+  if (style != StyleUserSelect::Auto) {
+    return style;
+  }
+
+  auto* parent = nsLayoutUtils::GetParentOrPlaceholderFor(aFrame);
+  return parent ? UsedUserSelect(parent) : StyleUserSelect::Text;
+}
+
+bool nsIFrame::IsSelectable(StyleUserSelect* aSelectStyle) const {
+  auto style = UsedUserSelect(this);
+  if (aSelectStyle) {
+    *aSelectStyle = style;
+  }
+  return style != StyleUserSelect::None;
+}
+
+bool nsIFrame::ShouldHaveLineIfEmpty() const {
+  if (Style()->IsPseudoOrAnonBox() &&
+      Style()->GetPseudoType() != PseudoStyleType::scrolledContent) {
+    return false;
+  }
+  return IsEditingHost(this);
+}
+
+/**
+ * Handles the Mouse Press Event for the frame
+ */
+NS_IMETHODIMP
+nsIFrame::HandlePress(nsPresContext* aPresContext, WidgetGUIEvent* aEvent,
+                      nsEventStatus* aEventStatus) {
+  NS_ENSURE_ARG_POINTER(aEventStatus);
+  if (nsEventStatus_eConsumeNoDefault == *aEventStatus) {
+    return NS_OK;
+  }
+
+  NS_ENSURE_ARG_POINTER(aEvent);
+  if (aEvent->mClass == eTouchEventClass) {
+    return NS_OK;
+  }
+
+  return MoveCaretToEventPoint(aPresContext, aEvent->AsMouseEvent(),
+                               aEventStatus);
+}
+
+nsresult nsIFrame::MoveCaretToEventPoint(nsPresContext* aPresContext,
+                                         WidgetMouseEvent* aMouseEvent,
+                                         nsEventStatus* aEventStatus) {
+  MOZ_ASSERT(aPresContext);
+  MOZ_ASSERT(aMouseEvent);
+  MOZ_ASSERT(aMouseEvent->mMessage == eMouseDown);
+  MOZ_ASSERT(aEventStatus);
+  MOZ_ASSERT(nsEventStatus_eConsumeNoDefault != *aEventStatus);
+
+  mozilla::PresShell* presShell = aPresContext->GetPresShell();
+  if (!presShell) {
+    return NS_ERROR_FAILURE;
+  }
+
+  // We often get out of sync state issues with mousedown events that
+  // get interrupted by alerts/dialogs.
+  // Check with the ESM to see if we should process this one
+  if (!aPresContext->EventStateManager()->EventStatusOK(aMouseEvent)) {
+    return NS_OK;
+  }
+
+  const nsPoint pt = nsLayoutUtils::GetEventCoordinatesRelativeTo(
+      aMouseEvent, RelativeTo{this});
+
+  // When not using `alt`, and clicking on a draggable, but non-editable
+  // element, don't do anything, and let d&d handle the event.
+  //
+  // See bug 48876, bug 388659 and bug 55921 for context here.
+  //
+  // FIXME(emilio): The .Contains(pt) check looks a bit fishy. When would it be
+  // false given we're the event target? If it is needed, why not checking the
+  // actual draggable node rect instead?
+  if (!aMouseEvent->IsAlt() && GetRectRelativeToSelf().Contains(pt)) {
+    for (nsIContent* content = mContent; content;
+         content = content->GetFlattenedTreeParent()) {
+      if (nsContentUtils::ContentIsDraggable(content) &&
+          !content->IsEditable()) {
+        return NS_OK;
+      }
+    }
+  }
+
+  // If we are in Navigator and the click is in a draggable node, we don't want
+  // to start selection because we don't want to interfere with a potential
+  // drag of said node and steal all its glory.
+  const bool isEditor =
+      presShell->GetSelectionFlags() == nsISelectionDisplay::DISPLAY_ALL;
+
+  // Don't do something if it's middle button down event.
+  const bool isPrimaryButtonDown =
+      aMouseEvent->mButton == MouseButton::ePrimary;
+
+  // check whether style allows selection
+  // if not, don't tell selection the mouse event even occurred.
+  StyleUserSelect selectStyle;
+  // check for select: none
+  if (!IsSelectable(&selectStyle)) {
+    return NS_OK;
+  }
+
+  if (isPrimaryButtonDown) {
+    // If the mouse is dragged outside the nearest enclosing scrollable area
+    // while making a selection, the area will be scrolled. To do this, capture
+    // the mouse on the nearest scrollable frame. If there isn't a scrollable
+    // frame, or something else is already capturing the mouse, there's no
+    // reason to capture.
+    if (!PresShell::GetCapturingContent()) {
+      nsIScrollableFrame* scrollFrame =
+          nsLayoutUtils::GetNearestScrollableFrame(
+              this, nsLayoutUtils::SCROLLABLE_SAME_DOC |
+                        nsLayoutUtils::SCROLLABLE_INCLUDE_HIDDEN);
+      if (scrollFrame) {
+        nsIFrame* capturingFrame = do_QueryFrame(scrollFrame);
+        PresShell::SetCapturingContent(capturingFrame->GetContent(),
+                                       CaptureFlags::IgnoreAllowedState);
+      }
+    }
+  }
+
+  // XXX This is screwy; it really should use the selection frame, not the
+  // event frame
+  const nsFrameSelection* frameselection =
+      selectStyle == StyleUserSelect::Text ? GetConstFrameSelection()
+                                           : presShell->ConstFrameSelection();
+
+  if (!frameselection || frameselection->GetDisplaySelection() ==
+                             nsISelectionController::SELECTION_OFF) {
+    return NS_OK;  // nothing to do we cannot affect selection from here
+  }
+
+#ifdef XP_MACOSX
+  // If Control key is pressed on macOS, it should be treated as right click.
+  // So, don't change selection.
+  if (aMouseEvent->IsControl()) {
+    return NS_OK;
+  }
+  const bool control = aMouseEvent->IsMeta();
+#else
+  const bool control = aMouseEvent->IsControl();
+#endif
+
+  RefPtr<nsFrameSelection> fc = const_cast<nsFrameSelection*>(frameselection);
+  if (isPrimaryButtonDown && aMouseEvent->mClickCount > 1) {
+    // These methods aren't const but can't actually delete anything,
+    // so no need for AutoWeakFrame.
+    fc->SetDragState(true);
+    return HandleMultiplePress(aPresContext, aMouseEvent, aEventStatus,
+                               control);
+  }
+
+  ContentOffsets offsets = GetContentOffsetsFromPoint(pt, SKIP_HIDDEN);
+
+  if (!offsets.content) {
+    return NS_ERROR_FAILURE;
+  }
+
+  const bool isSecondaryButton =
+      aMouseEvent->mButton == MouseButton::eSecondary;
+  if (isSecondaryButton &&
+      !MovingCaretToEventPointAllowedIfSecondaryButtonEvent(
+          *frameselection, *aMouseEvent, *offsets.content,
+          // When we collapse selection in nsFrameSelection::TakeFocus,
+          // we always collapse selection to the start offset.  Therefore,
+          // we can ignore the end offset here.  E.g., when an <img> is clicked,
+          // set the primary offset to after it, but the the secondary offset
+          // may be before it, see OffsetsForSingleFrame for the detail.
+          offsets.StartOffset())) {
+    return NS_OK;
+  }
+
+  if (aMouseEvent->mMessage == eMouseDown &&
+      aMouseEvent->mButton == MouseButton::eMiddle &&
+      !offsets.content->IsEditable()) {
+    // However, some users don't like the Chrome compatible behavior of
+    // middle mouse click.  They want to keep selection after starting
+    // autoscroll.  However, the selection change is important for middle
+    // mouse past.  Therefore, we should allow users to take the traditional
+    // behavior back by themselves unless middle click paste is enabled or
+    // autoscrolling is disabled.
+    if (!Preferences::GetBool("middlemouse.paste", false) &&
+        Preferences::GetBool("general.autoScroll", false) &&
+        Preferences::GetBool("general.autoscroll.prevent_to_collapse_selection_"
+                             "by_middle_mouse_down",
+                             false)) {
+      return NS_OK;
+    }
+  }
+
+  if (isPrimaryButtonDown) {
+    // Let Ctrl/Cmd + left mouse down do table selection instead of drag
+    // initiation.
+    nsCOMPtr<nsIContent> parentContent;
+    int32_t contentOffset;
+    TableSelectionMode target;
+    nsresult rv = GetDataForTableSelection(
+        frameselection, presShell, aMouseEvent, getter_AddRefs(parentContent),
+        &contentOffset, &target);
+    if (NS_SUCCEEDED(rv) && parentContent) {
+      fc->SetDragState(true);
+      return fc->HandleTableSelection(parentContent, contentOffset, target,
+                                      aMouseEvent);
+    }
+  }
+
+  fc->SetDelayedCaretData(0);
+
+  if (isPrimaryButtonDown) {
+    // Check if any part of this frame is selected, and if the user clicked
+    // inside the selected region, and if it's the left button. If so, we delay
+    // starting a new selection since the user may be trying to drag the
+    // selected region to some other app.
+
+    if (GetContent() && GetContent()->IsMaybeSelected()) {
+      bool inSelection = false;
+      UniquePtr<SelectionDetails> details = frameselection->LookUpSelection(
+          offsets.content, 0, offsets.EndOffset(), false);
+
+      //
+      // If there are any details, check to see if the user clicked
+      // within any selected region of the frame.
+      //
+
+      for (SelectionDetails* curDetail = details.get(); curDetail;
+           curDetail = curDetail->mNext.get()) {
+        //
+        // If the user clicked inside a selection, then just
+        // return without doing anything. We will handle placing
+        // the caret later on when the mouse is released. We ignore
+        // the spellcheck, find and url formatting selections.
+        //
+        if (curDetail->mSelectionType != SelectionType::eSpellCheck &&
+            curDetail->mSelectionType != SelectionType::eFind &&
+            curDetail->mSelectionType != SelectionType::eURLSecondary &&
+            curDetail->mSelectionType != SelectionType::eURLStrikeout &&
+            curDetail->mSelectionType != SelectionType::eHighlight &&
+            curDetail->mStart <= offsets.StartOffset() &&
+            offsets.EndOffset() <= curDetail->mEnd) {
+          inSelection = true;
+        }
+      }
+
+      if (inSelection) {
+        fc->SetDragState(false);
+        fc->SetDelayedCaretData(aMouseEvent);
+        return NS_OK;
+      }
+    }
+
+    fc->SetDragState(true);
+  }
+
+  // Do not touch any nsFrame members after this point without adding
+  // weakFrame checks.
+  const nsFrameSelection::FocusMode focusMode = [&]() {
+    // If "Shift" and "Ctrl" are both pressed, "Shift" is given precedence. This
+    // mimics the old behaviour.
+    const bool isShift =
+        aMouseEvent->IsShift() &&
+        // If Shift + secondary button press shoud open context menu without a
+        // contextmenu event, user wants to open context menu like as a
+        // secondary button press without Shift key.
+        !(isSecondaryButton &&
+          StaticPrefs::dom_event_contextmenu_shift_suppresses_event());
+    if (isShift) {
+      // If clicked in a link when focused content is editable, we should
+      // collapse selection in the link for compatibility with Blink.
+      if (isEditor) {
+        for (Element* element : mContent->InclusiveAncestorsOfType<Element>()) {
+          if (element->IsLink()) {
+            return nsFrameSelection::FocusMode::kCollapseToNewPoint;
+          }
+        }
+      }
+      return nsFrameSelection::FocusMode::kExtendSelection;
+    }
+
+    if (isPrimaryButtonDown && control) {
+      return nsFrameSelection::FocusMode::kMultiRangeSelection;
+    }
+
+    return nsFrameSelection::FocusMode::kCollapseToNewPoint;
+  }();
+
+  nsresult rv = fc->HandleClick(
+      MOZ_KnownLive(offsets.content) /* bug 1636889 */, offsets.StartOffset(),
+      offsets.EndOffset(), focusMode, offsets.associate);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  // We don't handle mouse button up if it's middle button.
+  if (isPrimaryButtonDown && offsets.offset != offsets.secondaryOffset) {
+    fc->MaintainSelection();
+  }
+
+  if (isPrimaryButtonDown && isEditor && !aMouseEvent->IsShift() &&
+      (offsets.EndOffset() - offsets.StartOffset()) == 1) {
+    // A single node is selected and we aren't extending an existing selection,
+    // which means the user clicked directly on an object (either
+    // `user-select: all` or a non-text node without children). Therefore,
+    // disable selection extension during mouse moves.
+    // XXX This is a bit hacky; shouldn't editor be able to deal with this?
+    fc->SetDragState(false);
+  }
+
+  return NS_OK;
+}
+
+bool nsIFrame::MovingCaretToEventPointAllowedIfSecondaryButtonEvent(
+    const nsFrameSelection& aFrameSelection,
+    WidgetMouseEvent& aSecondaryButtonEvent,
+    const nsIContent& aContentAtEventPoint, int32_t aOffsetAtEventPoint) const {
+  MOZ_ASSERT(aSecondaryButtonEvent.mButton == MouseButton::eSecondary);
+
+  if (NS_WARN_IF(aOffsetAtEventPoint < 0)) {
+    return false;
+  }
+
+  const bool contentIsEditable = aContentAtEventPoint.IsEditable();
+  const TextControlElement* const contentAsTextControl =
+      TextControlElement::FromNodeOrNull(
+          aContentAtEventPoint.IsTextControlElement()
+              ? &aContentAtEventPoint
+              : aContentAtEventPoint.GetClosestNativeAnonymousSubtreeRoot());
+  if (Selection* selection =
+          aFrameSelection.GetSelection(SelectionType::eNormal)) {
+    const bool selectionIsCollapsed = selection->IsCollapsed();
+    // If right click in a selection range, we should not collapse selection.
+    if (!selectionIsCollapsed &&
+        nsContentUtils::IsPointInSelection(
+            *selection, aContentAtEventPoint,
+            static_cast<uint32_t>(aOffsetAtEventPoint))) {
+      return false;
+    }
+    const bool wantToPreventMoveCaret =
+        StaticPrefs::
+            ui_mouse_right_click_move_caret_stop_if_in_focused_editable_node() &&
+        selectionIsCollapsed && (contentIsEditable || contentAsTextControl);
+    const bool wantToPreventCollapseSelection =
+        StaticPrefs::
+            ui_mouse_right_click_collapse_selection_stop_if_non_collapsed_selection() &&
+        !selectionIsCollapsed;
+    if (wantToPreventMoveCaret || wantToPreventCollapseSelection) {
+      // If currently selection is limited in an editing host, we should not
+      // collapse selection nor move caret if the clicked point is in the
+      // ancestor limiter.  Otherwise, this mouse click moves focus from the
+      // editing host to different one or blur the editing host.  In this case,
+      // we need to update selection because keeping current selection in the
+      // editing host looks like it's not blurred.
+      // FIXME: If the active editing host is the document element, editor
+      // does not set ancestor limiter properly.  Fix it in the editor side.
+      if (nsIContent* ancestorLimiter = selection->GetAncestorLimiter()) {
+        MOZ_ASSERT(ancestorLimiter->IsEditable());
+        return !aContentAtEventPoint.IsInclusiveDescendantOf(ancestorLimiter);
+      }
+    }
+    // If selection is editable and `stop_if_in_focused_editable_node` pref is
+    // set to true, user does not want to move caret to right click place if
+    // clicked in the focused text control element.
+    if (wantToPreventMoveCaret && contentAsTextControl &&
+        contentAsTextControl == nsFocusManager::GetFocusedElementStatic()) {
+      return false;
+    }
+    // If currently selection is not limited in an editing host, we should
+    // collapse selection only when this click moves focus to an editing
+    // host because we need to update selection in this case.
+    if (wantToPreventCollapseSelection && !contentIsEditable) {
+      return false;
+    }
+  }
+
+  return !StaticPrefs::
+             ui_mouse_right_click_collapse_selection_stop_if_non_editable_node() ||
+         // The user does not want to collapse selection into non-editable
+         // content by a right button click.
+         contentIsEditable ||
+         // Treat clicking in a text control as always clicked on editable
+         // content because we want a hack only for clicking in normal text
+         // nodes which is outside any editing hosts.
+         contentAsTextControl;
+}
+
+nsresult nsIFrame::SelectByTypeAtPoint(nsPresContext* aPresContext,
+                                       const nsPoint& aPoint,
+                                       nsSelectionAmount aBeginAmountType,
+                                       nsSelectionAmount aEndAmountType,
+                                       uint32_t aSelectFlags) {
+  NS_ENSURE_ARG_POINTER(aPresContext);
+
+  // No point in selecting if selection is turned off
+  if (DetermineDisplaySelection() == nsISelectionController::SELECTION_OFF) {
+    return NS_OK;
+  }
+
+  ContentOffsets offsets = GetContentOffsetsFromPoint(
+      aPoint, SKIP_HIDDEN | IGNORE_NATIVE_ANONYMOUS_SUBTREE);
+  if (!offsets.content) {
+    return NS_ERROR_FAILURE;
+  }
+
+  uint32_t offset;
+  nsIFrame* frame = SelectionMovementUtils::GetFrameForNodeOffset(
+      offsets.content, offsets.offset, offsets.associate, &offset);
+  if (!frame) {
+    return NS_ERROR_FAILURE;
+  }
+  return frame->PeekBackwardAndForward(
+      aBeginAmountType, aEndAmountType, static_cast<int32_t>(offset),
+      aBeginAmountType != eSelectWord, aSelectFlags);
+}
+
+/**
+ * Multiple Mouse Press -- line or paragraph selection -- for the frame.
+ * Wouldn't it be nice if this didn't have to be hardwired into Frame code?
+ */
+NS_IMETHODIMP
+nsIFrame::HandleMultiplePress(nsPresContext* aPresContext,
+                              WidgetGUIEvent* aEvent,
+                              nsEventStatus* aEventStatus, bool aControlHeld) {
+  NS_ENSURE_ARG_POINTER(aEvent);
+  NS_ENSURE_ARG_POINTER(aEventStatus);
+
+  if (nsEventStatus_eConsumeNoDefault == *aEventStatus ||
+      DetermineDisplaySelection() == nsISelectionController::SELECTION_OFF) {
+    return NS_OK;
+  }
+
+  // Find out whether we're doing line or paragraph selection.
+  // If browser.triple_click_selects_paragraph is true, triple-click selects
+  // paragraph. Otherwise, triple-click selects line, and quadruple-click
+  // selects paragraph (on platforms that support quadruple-click).
+  nsSelectionAmount beginAmount, endAmount;
+  WidgetMouseEvent* mouseEvent = aEvent->AsMouseEvent();
+  if (!mouseEvent) {
+    return NS_OK;
+  }
+
+  if (mouseEvent->mClickCount == 4) {
+    beginAmount = endAmount = eSelectParagraph;
+  } else if (mouseEvent->mClickCount == 3) {
+    if (Preferences::GetBool("browser.triple_click_selects_paragraph")) {
+      beginAmount = endAmount = eSelectParagraph;
+    } else {
+      beginAmount = eSelectBeginLine;
+      endAmount = eSelectEndLine;
+    }
+  } else if (mouseEvent->mClickCount == 2) {
+    // We only want inline frames; PeekBackwardAndForward dislikes blocks
+    beginAmount = endAmount = eSelectWord;
+  } else {
+    return NS_OK;
+  }
+
+  nsPoint relPoint = nsLayoutUtils::GetEventCoordinatesRelativeTo(
+      mouseEvent, RelativeTo{this});
+  return SelectByTypeAtPoint(aPresContext, relPoint, beginAmount, endAmount,
+                             (aControlHeld ? SELECT_ACCUMULATE : 0));
+}
+
+nsresult nsIFrame::PeekBackwardAndForward(nsSelectionAmount aAmountBack,
+                                          nsSelectionAmount aAmountForward,
+                                          int32_t aStartPos, bool aJumpLines,
+                                          uint32_t aSelectFlags) {
+  nsIFrame* baseFrame = this;
+  int32_t baseOffset = aStartPos;
+  nsresult rv;
+
+  PeekOffsetOptions peekOffsetOptions{PeekOffsetOption::StopAtScroller};
+  if (aJumpLines) {
+    peekOffsetOptions += PeekOffsetOption::JumpLines;
+  }
+
+  if (aAmountBack == eSelectWord) {
+    // To avoid selecting the previous word when at start of word,
+    // first move one character forward.
+    PeekOffsetStruct pos(eSelectCharacter, eDirNext, aStartPos, nsPoint(0, 0),
+                         peekOffsetOptions);
+    rv = PeekOffset(&pos);
+    if (NS_SUCCEEDED(rv)) {
+      baseFrame = pos.mResultFrame;
+      baseOffset = pos.mContentOffset;
+    }
+  }
+
+  // Search backward for a boundary.
+  PeekOffsetStruct startpos(aAmountBack, eDirPrevious, baseOffset,
+                            nsPoint(0, 0), peekOffsetOptions);
+  rv = baseFrame->PeekOffset(&startpos);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  // If the backward search stayed within the same frame, search forward from
+  // that position for the end boundary; but if it crossed out to a sibling or
+  // ancestor, start from the original position.
+  if (startpos.mResultFrame == baseFrame) {
+    baseOffset = startpos.mContentOffset;
+  } else {
+    baseFrame = this;
+    baseOffset = aStartPos;
+  }
+
+  PeekOffsetStruct endpos(aAmountForward, eDirNext, baseOffset, nsPoint(0, 0),
+                          peekOffsetOptions);
+  rv = baseFrame->PeekOffset(&endpos);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  // Keep frameSelection alive.
+  RefPtr<nsFrameSelection> frameSelection = GetFrameSelection();
+
+  const nsFrameSelection::FocusMode focusMode =
+      (aSelectFlags & SELECT_ACCUMULATE)
+          ? nsFrameSelection::FocusMode::kMultiRangeSelection
+          : nsFrameSelection::FocusMode::kCollapseToNewPoint;
+  rv = frameSelection->HandleClick(
+      MOZ_KnownLive(startpos.mResultContent) /* bug 1636889 */,
+      startpos.mContentOffset, startpos.mContentOffset, focusMode,
+      CaretAssociationHint::After);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  rv = frameSelection->HandleClick(
+      MOZ_KnownLive(endpos.mResultContent) /* bug 1636889 */,
+      endpos.mContentOffset, endpos.mContentOffset,
+      nsFrameSelection::FocusMode::kExtendSelection,
+      CaretAssociationHint::Before);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+  if (aAmountBack == eSelectWord) {
+    frameSelection->SetIsDoubleClickSelection(true);
+  }
+
+  // maintain selection
+  return frameSelection->MaintainSelection(aAmountBack);
+}
+
+NS_IMETHODIMP nsIFrame::HandleDrag(nsPresContext* aPresContext,
+                                   WidgetGUIEvent* aEvent,
+                                   nsEventStatus* aEventStatus) {
+  MOZ_ASSERT(aEvent->mClass == eMouseEventClass,
+             "HandleDrag can only handle mouse event");
+
+  NS_ENSURE_ARG_POINTER(aEventStatus);
+
+  RefPtr<nsFrameSelection> frameselection = GetFrameSelection();
+  if (!frameselection) {
+    return NS_OK;
+  }
+
+  bool mouseDown = frameselection->GetDragState();
+  if (!mouseDown) {
+    return NS_OK;
+  }
+
+  nsIFrame* scrollbar =
+      nsLayoutUtils::GetClosestFrameOfType(this, LayoutFrameType::Scrollbar);
+  if (!scrollbar) {
+    // XXX Do we really need to exclude non-selectable content here?
+    // GetContentOffsetsFromPoint can handle it just fine, although some
+    // other stuff might not like it.
+    // NOTE: DetermineDisplaySelection() returns SELECTION_OFF for
+    // non-selectable frames.
+    if (DetermineDisplaySelection() == nsISelectionController::SELECTION_OFF) {
+      return NS_OK;
+    }
+  }
+
+  frameselection->StopAutoScrollTimer();
+
+  // Check if we are dragging in a table cell
+  nsCOMPtr<nsIContent> parentContent;
+  int32_t contentOffset;
+  TableSelectionMode target;
+  WidgetMouseEvent* mouseEvent = aEvent->AsMouseEvent();
+  mozilla::PresShell* presShell = aPresContext->PresShell();
+  nsresult result;
+  result = GetDataForTableSelection(frameselection, presShell, mouseEvent,
+                                    getter_AddRefs(parentContent),
+                                    &contentOffset, &target);
+
+  AutoWeakFrame weakThis = this;
+  if (NS_SUCCEEDED(result) && parentContent) {
+    result = frameselection->HandleTableSelection(parentContent, contentOffset,
+                                                  target, mouseEvent);
+    if (NS_WARN_IF(NS_FAILED(result))) {
+      return result;
+    }
+  } else {
+    nsPoint pt = nsLayoutUtils::GetEventCoordinatesRelativeTo(mouseEvent,
+                                                              RelativeTo{this});
+    frameselection->HandleDrag(this, pt);
+  }
+
+  // The frameselection object notifies selection listeners synchronously above
+  // which might have killed us.
+  if (!weakThis.IsAlive()) {
+    return NS_OK;
+  }
+
+  // get the nearest scrollframe
+  nsIScrollableFrame* scrollFrame = nsLayoutUtils::GetNearestScrollableFrame(
+      this, nsLayoutUtils::SCROLLABLE_SAME_DOC |
+                nsLayoutUtils::SCROLLABLE_INCLUDE_HIDDEN);
+
+  if (scrollFrame) {
+    nsIFrame* capturingFrame = scrollFrame->GetScrolledFrame();
+    if (capturingFrame) {
+      nsPoint pt = nsLayoutUtils::GetEventCoordinatesRelativeTo(
+          mouseEvent, RelativeTo{capturingFrame});
+      frameselection->StartAutoScrollTimer(capturingFrame, pt, 30);
+    }
+  }
+
+  return NS_OK;
+}
+
+/**
+ * This static method handles part of the nsIFrame::HandleRelease in a way
+ * which doesn't rely on the nsFrame object to stay alive.
+ */
+MOZ_CAN_RUN_SCRIPT_BOUNDARY static nsresult HandleFrameSelection(
+    nsFrameSelection* aFrameSelection, nsIFrame::ContentOffsets& aOffsets,
+    bool aHandleTableSel, int32_t aContentOffsetForTableSel,
+    TableSelectionMode aTargetForTableSel,
+    nsIContent* aParentContentForTableSel, WidgetGUIEvent* aEvent,
+    const nsEventStatus* aEventStatus) {
+  if (!aFrameSelection) {
+    return NS_OK;
+  }
+
+  nsresult rv = NS_OK;
+
+  if (nsEventStatus_eConsumeNoDefault != *aEventStatus) {
+    if (!aHandleTableSel) {
+      if (!aOffsets.content || !aFrameSelection->HasDelayedCaretData()) {
+        return NS_ERROR_FAILURE;
+      }
+
+      // We are doing this to simulate what we would have done on HandlePress.
+      // We didn't do it there to give the user an opportunity to drag
+      // the text, but since they didn't drag, we want to place the
+      // caret.
+      // However, we'll use the mouse position from the release, since:
+      //  * it's easier
+      //  * that's the normal click position to use (although really, in
+      //    the normal case, small movements that don't count as a drag
+      //    can do selection)
+      aFrameSelection->SetDragState(true);
+
+      const nsFrameSelection::FocusMode focusMode =
+          aFrameSelection->IsShiftDownInDelayedCaretData()
+              ? nsFrameSelection::FocusMode::kExtendSelection
+              : nsFrameSelection::FocusMode::kCollapseToNewPoint;
+      rv = aFrameSelection->HandleClick(
+          MOZ_KnownLive(aOffsets.content) /* bug 1636889 */,
+          aOffsets.StartOffset(), aOffsets.EndOffset(), focusMode,
+          aOffsets.associate);
+      if (NS_FAILED(rv)) {
+        return rv;
+      }
+    } else if (aParentContentForTableSel) {
+      aFrameSelection->SetDragState(false);
+      rv = aFrameSelection->HandleTableSelection(
+          aParentContentForTableSel, aContentOffsetForTableSel,
+          aTargetForTableSel, aEvent->AsMouseEvent());
+      if (NS_FAILED(rv)) {
+        return rv;
+      }
+    }
+    aFrameSelection->SetDelayedCaretData(0);
+  }
+
+  aFrameSelection->SetDragState(false);
+  aFrameSelection->StopAutoScrollTimer();
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP nsIFrame::HandleRelease(nsPresContext* aPresContext,
+                                      WidgetGUIEvent* aEvent,
+                                      nsEventStatus* aEventStatus) {
+  if (aEvent->mClass != eMouseEventClass) {
+    return NS_OK;
+  }
+
+  nsIFrame* activeFrame = GetActiveSelectionFrame(aPresContext, this);
+
+  nsCOMPtr<nsIContent> captureContent = PresShell::GetCapturingContent();
+
+  bool selectionOff =
+      (DetermineDisplaySelection() == nsISelectionController::SELECTION_OFF);
+
+  RefPtr<nsFrameSelection> frameselection;
+  ContentOffsets offsets;
+  nsCOMPtr<nsIContent> parentContent;
+  int32_t contentOffsetForTableSel = 0;
+  TableSelectionMode targetForTableSel = TableSelectionMode::None;
+  bool handleTableSelection = true;
+
+  if (!selectionOff) {
+    frameselection = GetFrameSelection();
+    if (nsEventStatus_eConsumeNoDefault != *aEventStatus && frameselection) {
+      // Check if the frameselection recorded the mouse going down.
+      // If not, the user must have clicked in a part of the selection.
+      // Place the caret before continuing!
+
+      if (frameselection->MouseDownRecorded()) {
+        nsPoint pt = nsLayoutUtils::GetEventCoordinatesRelativeTo(
+            aEvent, RelativeTo{this});
+        offsets = GetContentOffsetsFromPoint(pt, SKIP_HIDDEN);
+        handleTableSelection = false;
+      } else {
+        GetDataForTableSelection(frameselection, PresShell(),
+                                 aEvent->AsMouseEvent(),
+                                 getter_AddRefs(parentContent),
+                                 &contentOffsetForTableSel, &targetForTableSel);
+      }
+    }
+  }
+
+  // We might be capturing in some other document and the event just happened to
+  // trickle down here. Make sure that document's frame selection is notified.
+  // Note, this may cause the current nsFrame object to be deleted, bug 336592.
+  RefPtr<nsFrameSelection> frameSelection;
+  if (activeFrame != this && activeFrame->DetermineDisplaySelection() !=
+                                 nsISelectionController::SELECTION_OFF) {
+    frameSelection = activeFrame->GetFrameSelection();
+  }
+
+  // Also check the selection of the capturing content which might be in a
+  // different document.
+  if (!frameSelection && captureContent) {
+    if (Document* doc = captureContent->GetComposedDoc()) {
+      mozilla::PresShell* capturingPresShell = doc->GetPresShell();
+      if (capturingPresShell &&
+          capturingPresShell != PresContext()->GetPresShell()) {
+        frameSelection = capturingPresShell->FrameSelection();
+      }
+    }
+  }
+
+  if (frameSelection) {
+    AutoWeakFrame wf(this);
+    frameSelection->SetDragState(false);
+    frameSelection->StopAutoScrollTimer();
+    if (wf.IsAlive()) {
+      nsIScrollableFrame* scrollFrame =
+          nsLayoutUtils::GetNearestScrollableFrame(
+              this, nsLayoutUtils::SCROLLABLE_SAME_DOC |
+                        nsLayoutUtils::SCROLLABLE_INCLUDE_HIDDEN);
+      if (scrollFrame) {
+        // Perform any additional scrolling needed to maintain CSS snap point
+        // requirements when autoscrolling is over.
+        scrollFrame->ScrollSnap();
+      }
+    }
+  }
+
+  // Do not call any methods of the current object after this point!!!
+  // The object is perhaps dead!
+
+  return selectionOff ? NS_OK
+                      : HandleFrameSelection(
+                            frameselection, offsets, handleTableSelection,
+                            contentOffsetForTableSel, targetForTableSel,
+                            parentContent, aEvent, aEventStatus);
+}
+
+struct MOZ_STACK_CLASS FrameContentRange {
+  FrameContentRange(nsIContent* aContent, int32_t aStart, int32_t aEnd)
+      : content(aContent), start(aStart), end(aEnd) {}
+  nsCOMPtr<nsIContent> content;
+  int32_t start;
+  int32_t end;
+};
+
+// Retrieve the content offsets of a frame
+static FrameContentRange GetRangeForFrame(const nsIFrame* aFrame) {
+  nsIContent* content = aFrame->GetContent();
+  if (!content) {
+    NS_WARNING("Frame has no content");
+    return FrameContentRange(nullptr, -1, -1);
+  }
+
+  LayoutFrameType type = aFrame->Type();
+  if (type == LayoutFrameType::Text) {
+    auto [offset, offsetEnd] = aFrame->GetOffsets();
+    return FrameContentRange(content, offset, offsetEnd);
+  }
+
+  if (type == LayoutFrameType::Br) {
+    nsIContent* parent = content->GetParent();
+    const int32_t beginOffset = parent->ComputeIndexOf_Deprecated(content);
+    return FrameContentRange(parent, beginOffset, beginOffset);
+  }
+
+  while (content->IsRootOfNativeAnonymousSubtree()) {
+    content = content->GetParent();
+  }
+
+  nsIContent* parent = content->GetParent();
+  if (aFrame->IsBlockOutside() || !parent) {
+    return FrameContentRange(content, 0, content->GetChildCount());
+  }
+
+  // TODO(emilio): Revise this in presence of Shadow DOM / display: contents,
+  // it's likely that we don't want to just walk the light tree, and we need to
+  // change the representation of FrameContentRange.
+  const int32_t index = parent->ComputeIndexOf_Deprecated(content);
+  MOZ_ASSERT(index >= 0);
+  return FrameContentRange(parent, index, index + 1);
+}
+
+// The FrameTarget represents the closest frame to a point that can be selected
+// The frame is the frame represented, frameEdge says whether one end of the
+// frame is the result (in which case different handling is needed), and
+// afterFrame says which end is represented if frameEdge is true
+struct FrameTarget {
+  explicit operator bool() const { return !!frame; }
+
+  nsIFrame* frame = nullptr;
+  bool frameEdge = false;
+  bool afterFrame = false;
+};
+
+// See function implementation for information
+static FrameTarget GetSelectionClosestFrame(nsIFrame* aFrame,
+                                            const nsPoint& aPoint,
+                                            uint32_t aFlags);
+
+static bool SelfIsSelectable(nsIFrame* aFrame, uint32_t aFlags) {
+  if ((aFlags & nsIFrame::SKIP_HIDDEN) &&
+      !aFrame->StyleVisibility()->IsVisible()) {
+    return false;
+  }
+  return !aFrame->IsGeneratedContentFrame() &&
+         aFrame->Style()->UserSelect() != StyleUserSelect::None;
+}
+
+static bool FrameContentCanHaveParentSelectionRange(nsIFrame* aFrame) {
+  // If we are only near (not directly over) then don't traverse
+  // frames with independent selection (e.g. text and list controls, see bug
+  // 268497).  Note that this prevents any of the users of this method from
+  // entering form controls.
+  // XXX We might want some way to allow using the up-arrow to go into a form
+  // control, but the focus didn't work right anyway; it'd probably be enough
+  // if the left and right arrows could enter textboxes (which I don't believe
+  // they can at the moment)
+  if (aFrame->IsTextInputFrame() || aFrame->IsListControlFrame()) {
+    MOZ_ASSERT(aFrame->HasAnyStateBits(NS_FRAME_INDEPENDENT_SELECTION));
+    return false;
+  }
+
+  // Failure in this assertion means a new type of frame forms the root of an
+  // NS_FRAME_INDEPENDENT_SELECTION subtree. In such case, the condition above
+  // should be changed to handle it.
+  MOZ_ASSERT_IF(
+      aFrame->HasAnyStateBits(NS_FRAME_INDEPENDENT_SELECTION),
+      aFrame->GetParent()->HasAnyStateBits(NS_FRAME_INDEPENDENT_SELECTION));
+
+  return !aFrame->IsGeneratedContentFrame();
+}
+
+static bool SelectionDescendToKids(nsIFrame* aFrame) {
+  if (!FrameContentCanHaveParentSelectionRange(aFrame)) {
+    return false;
+  }
+  auto style = aFrame->Style()->UserSelect();
+  return style != StyleUserSelect::All && style != StyleUserSelect::None;
+}
+
+static FrameTarget GetSelectionClosestFrameForChild(nsIFrame* aChild,
+                                                    const nsPoint& aPoint,
+                                                    uint32_t aFlags) {
+  nsIFrame* parent = aChild->GetParent();
+  if (SelectionDescendToKids(aChild)) {
+    nsPoint pt = aPoint - aChild->GetOffsetTo(parent);
+    return GetSelectionClosestFrame(aChild, pt, aFlags);
+  }
+  return FrameTarget{aChild, false, false};
+}
+
+// When the cursor needs to be at the beginning of a block, it shouldn't be
+// before the first child.  A click on a block whose first child is a block
+// should put the cursor in the child.  The cursor shouldn't be between the
+// blocks, because that's not where it's expected.
+// Note that this method is guaranteed to succeed.
+static FrameTarget DrillDownToSelectionFrame(nsIFrame* aFrame, bool aEndFrame,
+                                             uint32_t aFlags) {
+  if (SelectionDescendToKids(aFrame)) {
+    nsIFrame* result = nullptr;
+    nsIFrame* frame = aFrame->PrincipalChildList().FirstChild();
+    if (!aEndFrame) {
+      while (frame && (!SelfIsSelectable(frame, aFlags) || frame->IsEmpty()))
+        frame = frame->GetNextSibling();
+      if (frame) result = frame;
+    } else {
+      // Because the frame tree is singly linked, to find the last frame,
+      // we have to iterate through all the frames
+      // XXX I have a feeling this could be slow for long blocks, although
+      //     I can't find any slowdowns
+      while (frame) {
+        if (!frame->IsEmpty() && SelfIsSelectable(frame, aFlags))
+          result = frame;
+        frame = frame->GetNextSibling();
+      }
+    }
+    if (result) return DrillDownToSelectionFrame(result, aEndFrame, aFlags);
+  }
+  // If the current frame has no targetable children, target the current frame
+  return FrameTarget{aFrame, true, aEndFrame};
+}
+
+// This method finds the closest valid FrameTarget on a given line; if there is
+// no valid FrameTarget on the line, it returns a null FrameTarget
+static FrameTarget GetSelectionClosestFrameForLine(
+    nsBlockFrame* aParent, nsBlockFrame::LineIterator aLine,
+    const nsPoint& aPoint, uint32_t aFlags) {
+  // Account for end of lines (any iterator from the block is valid)
+  if (aLine == aParent->LinesEnd())
+    return DrillDownToSelectionFrame(aParent, true, aFlags);
+  nsIFrame* frame = aLine->mFirstChild;
+  nsIFrame* closestFromIStart = nullptr;
+  nsIFrame* closestFromIEnd = nullptr;
+  nscoord closestIStart = aLine->IStart(), closestIEnd = aLine->IEnd();
+  WritingMode wm = aLine->mWritingMode;
+  LogicalPoint pt(wm, aPoint, aLine->mContainerSize);
+  bool canSkipBr = false;
+  bool lastFrameWasEditable = false;
+  for (int32_t n = aLine->GetChildCount(); n;
+       --n, frame = frame->GetNextSibling()) {
+    // Skip brFrames. Can only skip if the line contains at least
+    // one selectable and non-empty frame before. Also, avoid skipping brs if
+    // the previous thing had a different editableness than us, since then we
+    // may end up not being able to select after it if the br is the last thing
+    // on the line.
+    if (!SelfIsSelectable(frame, aFlags) || frame->IsEmpty() ||
+        (canSkipBr && frame->IsBrFrame() &&
+         lastFrameWasEditable == frame->GetContent()->IsEditable())) {
+      continue;
+    }
+    canSkipBr = true;
+    lastFrameWasEditable =
+        frame->GetContent() && frame->GetContent()->IsEditable();
+    LogicalRect frameRect =
+        LogicalRect(wm, frame->GetRect(), aLine->mContainerSize);
+    if (pt.I(wm) >= frameRect.IStart(wm)) {
+      if (pt.I(wm) < frameRect.IEnd(wm)) {
+        return GetSelectionClosestFrameForChild(frame, aPoint, aFlags);
+      }
+      if (frameRect.IEnd(wm) >= closestIStart) {
+        closestFromIStart = frame;
+        closestIStart = frameRect.IEnd(wm);
+      }
+    } else {
+      if (frameRect.IStart(wm) <= closestIEnd) {
+        closestFromIEnd = frame;
+        closestIEnd = frameRect.IStart(wm);
+      }
+    }
+  }
+  if (!closestFromIStart && !closestFromIEnd) {
+    // We should only get here if there are no selectable frames on a line
+    // XXX Do we need more elaborate handling here?
+    return FrameTarget();
+  }
+  if (closestFromIStart &&
+      (!closestFromIEnd ||
+       (abs(pt.I(wm) - closestIStart) <= abs(pt.I(wm) - closestIEnd)))) {
+    return GetSelectionClosestFrameForChild(closestFromIStart, aPoint, aFlags);
+  }
+  return GetSelectionClosestFrameForChild(closestFromIEnd, aPoint, aFlags);
+}
+
+// This method is for the special handling we do for block frames; they're
+// special because they represent paragraphs and because they are organized
+// into lines, which have bounds that are not stored elsewhere in the
+// frame tree.  Returns a null FrameTarget for frames which are not
+// blocks or blocks with no lines except editable one.
+static FrameTarget GetSelectionClosestFrameForBlock(nsIFrame* aFrame,
+                                                    const nsPoint& aPoint,
+                                                    uint32_t aFlags) {
+  nsBlockFrame* bf = do_QueryFrame(aFrame);
+  if (!bf) {
+    return FrameTarget();
+  }
+
+  // This code searches for the correct line
+  nsBlockFrame::LineIterator end = bf->LinesEnd();
+  nsBlockFrame::LineIterator curLine = bf->LinesBegin();
+  nsBlockFrame::LineIterator closestLine = end;
+
+  if (curLine != end) {
+    // Convert aPoint into a LogicalPoint in the writing-mode of this block
+    WritingMode wm = curLine->mWritingMode;
+    LogicalPoint pt(wm, aPoint, curLine->mContainerSize);
+    do {
+      // Check to see if our point lies within the line's block-direction bounds
+      nscoord BCoord = pt.B(wm) - curLine->BStart();
+      nscoord BSize = curLine->BSize();
+      if (BCoord >= 0 && BCoord < BSize) {
+        closestLine = curLine;
+        break;  // We found the line; stop looking
+      }
+      if (BCoord < 0) break;
+      ++curLine;
+    } while (curLine != end);
+
+    if (closestLine == end) {
+      nsBlockFrame::LineIterator prevLine = curLine.prev();
+      nsBlockFrame::LineIterator nextLine = curLine;
+      // Avoid empty lines
+      while (nextLine != end && nextLine->IsEmpty()) ++nextLine;
+      while (prevLine != end && prevLine->IsEmpty()) --prevLine;
+
+      // This hidden pref dictates whether a point above or below all lines
+      // comes up with a line or the beginning or end of the frame; 0 on
+      // Windows, 1 on other platforms by default at the writing of this code
+      int32_t dragOutOfFrame =
+          Preferences::GetInt("browser.drag_out_of_frame_style");
+
+      if (prevLine == end) {
+        if (dragOutOfFrame == 1 || nextLine == end)
+          return DrillDownToSelectionFrame(aFrame, false, aFlags);
+        closestLine = nextLine;
+      } else if (nextLine == end) {
+        if (dragOutOfFrame == 1)
+          return DrillDownToSelectionFrame(aFrame, true, aFlags);
+        closestLine = prevLine;
+      } else {  // Figure out which line is closer
+        if (pt.B(wm) - prevLine->BEnd() < nextLine->BStart() - pt.B(wm))
+          closestLine = prevLine;
+        else
+          closestLine = nextLine;
+      }
+    }
+  }
+
+  do {
+    if (auto target =
+            GetSelectionClosestFrameForLine(bf, closestLine, aPoint, aFlags)) {
+      return target;
+    }
+    ++closestLine;
+  } while (closestLine != end);
+
+  // Fall back to just targeting the last targetable place
+  return DrillDownToSelectionFrame(aFrame, true, aFlags);
+}
+
+// Use frame edge for grid, flex, table, and non-editable images. Choose the
+// edge based on the point position past the frame rect. If past the middle,
+// caret should be at end, otherwise at start. This behavior matches Blink.
+//
+// TODO(emilio): Can we use this code path for other replaced elements other
+// than images? Or even all other frames? We only get there when we didn't find
+// selectable children... At least one XUL test fails if we make this apply to
+// XUL labels. Also, editable images need _not_ to use the frame edge, see
+// below.
+static bool UseFrameEdge(nsIFrame* aFrame) {
+  if (aFrame->IsFlexOrGridContainer() || aFrame->IsTableFrame()) {
+    return true;
+  }
+  const nsImageFrame* image = do_QueryFrame(aFrame);
+  if (image && !aFrame->GetContent()->IsEditable()) {
+    // Editable images are a special-case because editing relies on clicking on
+    // an editable image selecting it, for it to show resizers.
+    return true;
+  }
+  return false;
+}
+
+static FrameTarget LastResortFrameTargetForFrame(nsIFrame* aFrame,
+                                                 const nsPoint& aPoint) {
+  if (!UseFrameEdge(aFrame)) {
+    return {aFrame, false, false};
+  }
+  const auto& rect = aFrame->GetRectRelativeToSelf();
+  nscoord reference;
+  nscoord middle;
+  if (aFrame->GetWritingMode().IsVertical()) {
+    reference = aPoint.y;
+    middle = rect.Height() / 2;
+  } else {
+    reference = aPoint.x;
+    middle = rect.Width() / 2;
+  }
+  const bool afterFrame = reference > middle;
+  return {aFrame, true, afterFrame};
+}
+
+// GetSelectionClosestFrame is the helper function that calculates the closest
+// frame to the given point.
+// It doesn't completely account for offset styles, so needs to be used in
+// restricted environments.
+// Cannot handle overlapping frames correctly, so it should receive the output
+// of GetFrameForPoint
+// Guaranteed to return a valid FrameTarget.
+// aPoint is relative to aFrame.
+static FrameTarget GetSelectionClosestFrame(nsIFrame* aFrame,
+                                            const nsPoint& aPoint,
+                                            uint32_t aFlags) {
+  // Handle blocks; if the frame isn't a block, the method fails
+  if (auto target = GetSelectionClosestFrameForBlock(aFrame, aPoint, aFlags)) {
+    return target;
+  }
+
+  if (aFlags & nsIFrame::IGNORE_NATIVE_ANONYMOUS_SUBTREE &&
+      !FrameContentCanHaveParentSelectionRange(aFrame)) {
+    return LastResortFrameTargetForFrame(aFrame, aPoint);
+  }
+
+  if (nsIFrame* kid = aFrame->PrincipalChildList().FirstChild()) {
+    // Go through all the child frames to find the closest one
+    nsIFrame::FrameWithDistance closest = {nullptr, nscoord_MAX, nscoord_MAX};
+    for (; kid; kid = kid->GetNextSibling()) {
+      if (!SelfIsSelectable(kid, aFlags) || kid->IsEmpty()) {
+        continue;
+      }
+
+      kid->FindCloserFrameForSelection(aPoint, &closest);
+    }
+    if (closest.mFrame) {
+      if (closest.mFrame->IsInSVGTextSubtree())
+        return FrameTarget{closest.mFrame, false, false};
+      return GetSelectionClosestFrameForChild(closest.mFrame, aPoint, aFlags);
+    }
+  }
+
+  return LastResortFrameTargetForFrame(aFrame, aPoint);
+}
+
+static nsIFrame::ContentOffsets OffsetsForSingleFrame(nsIFrame* aFrame,
+                                                      const nsPoint& aPoint) {
+  nsIFrame::ContentOffsets offsets;
+  FrameContentRange range = GetRangeForFrame(aFrame);
+  offsets.content = range.content;
+  // If there are continuations (meaning it's not one rectangle), this is the
+  // best this function can do
+  if (aFrame->GetNextContinuation() || aFrame->GetPrevContinuation()) {
+    offsets.offset = range.start;
+    offsets.secondaryOffset = range.end;
+    offsets.associate = CaretAssociationHint::After;
+    return offsets;
+  }
+
+  // Figure out whether the offsets should be over, after, or before the frame
+  nsRect rect(nsPoint(0, 0), aFrame->GetSize());
+
+  bool isBlock = !aFrame->StyleDisplay()->IsInlineFlow();
+  bool isRtl = (aFrame->StyleVisibility()->mDirection == StyleDirection::Rtl);
+  if ((isBlock && rect.y < aPoint.y) ||
+      (!isBlock && ((isRtl && rect.x + rect.width / 2 > aPoint.x) ||
+                    (!isRtl && rect.x + rect.width / 2 < aPoint.x)))) {
+    offsets.offset = range.end;
+    if (rect.Contains(aPoint))
+      offsets.secondaryOffset = range.start;
+    else
+      offsets.secondaryOffset = range.end;
+  } else {
+    offsets.offset = range.start;
+    if (rect.Contains(aPoint))
+      offsets.secondaryOffset = range.end;
+    else
+      offsets.secondaryOffset = range.start;
+  }
+  offsets.associate = offsets.offset == range.start
+                          ? CaretAssociationHint::After
+                          : CaretAssociationHint::Before;
+  return offsets;
+}
+
+static nsIFrame* AdjustFrameForSelectionStyles(nsIFrame* aFrame) {
+  nsIFrame* adjustedFrame = aFrame;
+  for (nsIFrame* frame = aFrame; frame; frame = frame->GetParent()) {
+    // These are the conditions that make all children not able to handle
+    // a cursor.
+    auto userSelect = frame->Style()->UserSelect();
+    if (userSelect != StyleUserSelect::Auto &&
+        userSelect != StyleUserSelect::All) {
+      break;
+    }
+    if (userSelect == StyleUserSelect::All ||
+        frame->IsGeneratedContentFrame()) {
+      adjustedFrame = frame;
+    }
+  }
+  return adjustedFrame;
+}
+
+nsIFrame::ContentOffsets nsIFrame::GetContentOffsetsFromPoint(
+    const nsPoint& aPoint, uint32_t aFlags) {
+  nsIFrame* adjustedFrame;
+  if (aFlags & IGNORE_SELECTION_STYLE) {
+    adjustedFrame = this;
+  } else {
+    // This section of code deals with special selection styles.  Note that
+    // -moz-all exists, even though it doesn't need to be explicitly handled.
+    //
+    // The offset is forced not to end up in generated content; content offsets
+    // cannot represent content outside of the document's content tree.
+
+    adjustedFrame = AdjustFrameForSelectionStyles(this);
+
+    // `user-select: all` needs special handling, because clicking on it should
+    // lead to the whole frame being selected.
+    if (adjustedFrame->Style()->UserSelect() == StyleUserSelect::All) {
+      nsPoint adjustedPoint = aPoint + GetOffsetTo(adjustedFrame);
+      return OffsetsForSingleFrame(adjustedFrame, adjustedPoint);
+    }
+
+    // For other cases, try to find a closest frame starting from the parent of
+    // the unselectable frame
+    if (adjustedFrame != this) {
+      adjustedFrame = adjustedFrame->GetParent();
+    }
+  }
+
+  nsPoint adjustedPoint = aPoint + GetOffsetTo(adjustedFrame);
+
+  FrameTarget closest =
+      GetSelectionClosestFrame(adjustedFrame, adjustedPoint, aFlags);
+
+  // If the correct offset is at one end of a frame, use offset-based
+  // calculation method
+  if (closest.frameEdge) {
+    ContentOffsets offsets;
+    FrameContentRange range = GetRangeForFrame(closest.frame);
+    offsets.content = range.content;
+    if (closest.afterFrame)
+      offsets.offset = range.end;
+    else
+      offsets.offset = range.start;
+    offsets.secondaryOffset = offsets.offset;
+    offsets.associate = offsets.offset == range.start
+                            ? CaretAssociationHint::After
+                            : CaretAssociationHint::Before;
+    return offsets;
+  }
+
+  nsPoint pt;
+  if (closest.frame != this) {
+    if (closest.frame->IsInSVGTextSubtree()) {
+      pt = nsLayoutUtils::TransformAncestorPointToFrame(
+          RelativeTo{closest.frame}, aPoint, RelativeTo{this});
+    } else {
+      pt = aPoint - closest.frame->GetOffsetTo(this);
+    }
+  } else {
+    pt = aPoint;
+  }
+  return closest.frame->CalcContentOffsetsFromFramePoint(pt);
+
+  // XXX should I add some kind of offset standardization?
+  // consider <b>xxxxx</b><i>zzzzz</i>; should any click between the last
+  // x and first z put the cursor in the same logical position in addition
+  // to the same visual position?
+}
+
+nsIFrame::ContentOffsets nsIFrame::CalcContentOffsetsFromFramePoint(
+    const nsPoint& aPoint) {
+  return OffsetsForSingleFrame(this, aPoint);
+}
+
+bool nsIFrame::AssociateImage(const StyleImage& aImage) {
+  imgRequestProxy* req = aImage.GetImageRequest();
+  if (!req) {
+    return false;
+  }
+
+  mozilla::css::ImageLoader* loader =
+      PresContext()->Document()->StyleImageLoader();
+
+  loader->AssociateRequestToFrame(req, this);
+  return true;
+}
+
+void nsIFrame::DisassociateImage(const StyleImage& aImage) {
+  imgRequestProxy* req = aImage.GetImageRequest();
+  if (!req) {
+    return;
+  }
+
+  mozilla::css::ImageLoader* loader =
+      PresContext()->Document()->StyleImageLoader();
+
+  loader->DisassociateRequestFromFrame(req, this);
+}
+
+StyleImageRendering nsIFrame::UsedImageRendering() const {
+  ComputedStyle* style;
+  if (IsCanvasFrame()) {
+    // XXXdholbert Maybe we should use FindCanvasBackground here (instead of
+    // FindBackground), since we're inside an IsCanvasFrame check? Though then
+    // we'd also have to copypaste or abstract-away the multi-part root-frame
+    // lookup that the canvas-flavored API requires.
+    style = nsCSSRendering::FindBackground(this);
+  } else {
+    style = Style();
+  }
+  return style->StyleVisibility()->mImageRendering;
+}
+
+// The touch-action CSS property applies to: all elements except: non-replaced
+// inline elements, table rows, row groups, table columns, and column groups.
+StyleTouchAction nsIFrame::UsedTouchAction() const {
+  if (IsLineParticipant()) {
+    return StyleTouchAction::AUTO;
+  }
+  auto& disp = *StyleDisplay();
+  if (disp.IsInternalTableStyleExceptCell()) {
+    return StyleTouchAction::AUTO;
+  }
+  return disp.mTouchAction;
+}
+
+nsIFrame::Cursor nsIFrame::GetCursor(const nsPoint&) {
+  StyleCursorKind kind = StyleUI()->Cursor().keyword;
+  if (kind == StyleCursorKind::Auto) {
+    // If this is editable, I-beam cursor is better for most elements.
+    kind = (mContent && mContent->IsEditable()) ? StyleCursorKind::Text
+                                                : StyleCursorKind::Default;
+  }
+  if (kind == StyleCursorKind::Text && GetWritingMode().IsVertical()) {
+    // Per CSS UI spec, UA may treat value 'text' as
+    // 'vertical-text' for vertical text.
+    kind = StyleCursorKind::VerticalText;
+  }
+
+  return Cursor{kind, AllowCustomCursorImage::Yes};
+}
+
+// Resize and incremental reflow
+
+/* virtual */
+void nsIFrame::MarkIntrinsicISizesDirty() {
+  // If we're a flex item, clear our flex-item-specific cached measurements
+  // (which likely depended on our now-stale intrinsic isize).
+  if (IsFlexItem()) {
+    nsFlexContainerFrame::MarkCachedFlexMeasurementsDirty(this);
+  }
+
+  if (HasAnyStateBits(NS_FRAME_FONT_INFLATION_FLOW_ROOT)) {
+    nsFontInflationData::MarkFontInflationDataTextDirty(this);
+  }
+
+  RemoveProperty(nsGridContainerFrame::CachedBAxisMeasurement::Prop());
+}
+
+void nsIFrame::MarkSubtreeDirty() {
+  if (HasAnyStateBits(NS_FRAME_IS_DIRTY)) {
+    return;
+  }
+  // Unconditionally mark given frame dirty.
+  AddStateBits(NS_FRAME_IS_DIRTY);
+
+  // Mark all descendants dirty, unless:
+  // - Already dirty.
+  // - TableColGroup
+  AutoTArray<nsIFrame*, 32> stack;
+  for (const auto& childLists : ChildLists()) {
+    for (nsIFrame* kid : childLists.mList) {
+      stack.AppendElement(kid);
+    }
+  }
+  while (!stack.IsEmpty()) {
+    nsIFrame* f = stack.PopLastElement();
+    if (f->HasAnyStateBits(NS_FRAME_IS_DIRTY) || f->IsTableColGroupFrame()) {
+      continue;
+    }
+
+    f->AddStateBits(NS_FRAME_IS_DIRTY);
+
+    for (const auto& childLists : f->ChildLists()) {
+      for (nsIFrame* kid : childLists.mList) {
+        stack.AppendElement(kid);
+      }
+    }
+  }
+}
+
+/* virtual */
+nscoord nsIFrame::GetMinISize(gfxContext* aRenderingContext) {
+  nscoord result = 0;
+  DISPLAY_MIN_INLINE_SIZE(this, result);
+  return result;
+}
+
+/* virtual */
+nscoord nsIFrame::GetPrefISize(gfxContext* aRenderingContext) {
+  nscoord result = 0;
+  DISPLAY_PREF_INLINE_SIZE(this, result);
+  return result;
+}
+
+/* virtual */
+void nsIFrame::AddInlineMinISize(gfxContext* aRenderingContext,
+                                 nsIFrame::InlineMinISizeData* aData) {
+  nscoord isize = nsLayoutUtils::IntrinsicForContainer(
+      aRenderingContext, this, IntrinsicISizeType::MinISize);
+  aData->DefaultAddInlineMinISize(this, isize);
+}
+
+/* virtual */
+void nsIFrame::AddInlinePrefISize(gfxContext* aRenderingContext,
+                                  nsIFrame::InlinePrefISizeData* aData) {
+  nscoord isize = nsLayoutUtils::IntrinsicForContainer(
+      aRenderingContext, this, IntrinsicISizeType::PrefISize);
+  aData->DefaultAddInlinePrefISize(isize);
+}
+
+void nsIFrame::InlineMinISizeData::DefaultAddInlineMinISize(nsIFrame* aFrame,
+                                                            nscoord aISize,
+                                                            bool aAllowBreak) {
+  auto parent = aFrame->GetParent();
+  MOZ_ASSERT(parent, "Must have a parent if we get here!");
+  const bool mayBreak = aAllowBreak && !aFrame->CanContinueTextRun() &&
+                        !parent->Style()->ShouldSuppressLineBreak() &&
+                        parent->StyleText()->WhiteSpaceCanWrap(parent);
+  if (mayBreak) {
+    OptionallyBreak();
+  }
+  mTrailingWhitespace = 0;
+  mSkipWhitespace = false;
+  mCurrentLine += aISize;
+  mAtStartOfLine = false;
+  if (mayBreak) {
+    OptionallyBreak();
+  }
+}
+
+void nsIFrame::InlinePrefISizeData::DefaultAddInlinePrefISize(nscoord aISize) {
+  mCurrentLine = NSCoordSaturatingAdd(mCurrentLine, aISize);
+  mTrailingWhitespace = 0;
+  mSkipWhitespace = false;
+  mLineIsEmpty = false;
+}
+
+void nsIFrame::InlineMinISizeData::ForceBreak() {
+  mCurrentLine -= mTrailingWhitespace;
+  mPrevLines = std::max(mPrevLines, mCurrentLine);
+  mCurrentLine = mTrailingWhitespace = 0;
+
+  for (uint32_t i = 0, i_end = mFloats.Length(); i != i_end; ++i) {
+    nscoord float_min = mFloats[i].Width();
+    if (float_min > mPrevLines) mPrevLines = float_min;
+  }
+  mFloats.Clear();
+  mSkipWhitespace = true;
+}
+
+void nsIFrame::InlineMinISizeData::OptionallyBreak(nscoord aHyphenWidth) {
+  // If we can fit more content into a smaller width by staying on this
+  // line (because we're still at a negative offset due to negative
+  // text-indent or negative margin), don't break.  Otherwise, do the
+  // same as ForceBreak.  it doesn't really matter when we accumulate
+  // floats.
+  if (mCurrentLine + aHyphenWidth < 0 || mAtStartOfLine) return;
+  mCurrentLine += aHyphenWidth;
+  ForceBreak();
+}
+
+void nsIFrame::InlinePrefISizeData::ForceBreak(StyleClear aClearType) {
+  // If this force break is not clearing any float, we can leave all the
+  // floats to the next force break.
+  if (!mFloats.IsEmpty() && aClearType != StyleClear::None) {
+    // preferred widths accumulated for floats that have already
+    // been cleared past
+    nscoord floats_done = 0,
+            // preferred widths accumulated for floats that have not yet
+            // been cleared past
+        floats_cur_left = 0, floats_cur_right = 0;
+
+    for (const FloatInfo& floatInfo : mFloats) {
+      const nsStyleDisplay* floatDisp = floatInfo.Frame()->StyleDisplay();
+      StyleClear clearType = floatDisp->mClear;
+      if (clearType == StyleClear::Left || clearType == StyleClear::Right ||
+          clearType == StyleClear::Both) {
+        nscoord floats_cur =
+            NSCoordSaturatingAdd(floats_cur_left, floats_cur_right);
+        if (floats_cur > floats_done) {
+          floats_done = floats_cur;
+        }
+        if (clearType != StyleClear::Right) {
+          floats_cur_left = 0;
+        }
+        if (clearType != StyleClear::Left) {
+          floats_cur_right = 0;
+        }
+      }
+
+      StyleFloat floatStyle = floatDisp->mFloat;
+      nscoord& floats_cur =
+          floatStyle == StyleFloat::Left ? floats_cur_left : floats_cur_right;
+      nscoord floatWidth = floatInfo.Width();
+      // Negative-width floats don't change the available space so they
+      // shouldn't change our intrinsic line width either.
+      floats_cur = NSCoordSaturatingAdd(floats_cur, std::max(0, floatWidth));
+    }
+
+    nscoord floats_cur =
+        NSCoordSaturatingAdd(floats_cur_left, floats_cur_right);
+    if (floats_cur > floats_done) floats_done = floats_cur;
+
+    mCurrentLine = NSCoordSaturatingAdd(mCurrentLine, floats_done);
+
+    if (aClearType == StyleClear::Both) {
+      mFloats.Clear();
+    } else {
+      // If the break type does not clear all floats, it means there may
+      // be some floats whose isize should contribute to the intrinsic
+      // isize of the next line. The code here scans the current mFloats
+      // and keeps floats which are not cleared by this break. Note that
+      // floats may be cleared directly or indirectly. See below.
+      nsTArray<FloatInfo> newFloats;
+      MOZ_ASSERT(
+          aClearType == StyleClear::Left || aClearType == StyleClear::Right,
+          "Other values should have been handled in other branches");
+      StyleFloat clearFloatType =
+          aClearType == StyleClear::Left ? StyleFloat::Left : StyleFloat::Right;
+      // Iterate the array in reverse so that we can stop when there are
+      // no longer any floats we need to keep. See below.
+      for (FloatInfo& floatInfo : Reversed(mFloats)) {
+        const nsStyleDisplay* floatDisp = floatInfo.Frame()->StyleDisplay();
+        if (floatDisp->mFloat != clearFloatType) {
+          newFloats.AppendElement(floatInfo);
+        } else {
+          // This is a float on the side that this break directly clears
+          // which means we're not keeping it in mFloats. However, if
+          // this float clears floats on the opposite side (via a value
+          // of either 'both' or one of 'left'/'right'), any remaining
+          // (earlier) floats on that side would be indirectly cleared
+          // as well. Thus, we should break out of this loop and stop
+          // considering earlier floats to be kept in mFloats.
+          StyleClear clearType = floatDisp->mClear;
+          if (clearType != aClearType && clearType != StyleClear::None) {
+            break;
+          }
+        }
+      }
+      newFloats.Reverse();
+      mFloats = std::move(newFloats);
+    }
+  }
+
+  mCurrentLine =
+      NSCoordSaturatingSubtract(mCurrentLine, mTrailingWhitespace, nscoord_MAX);
+  mPrevLines = std::max(mPrevLines, mCurrentLine);
+  mCurrentLine = mTrailingWhitespace = 0;
+  mSkipWhitespace = true;
+  mLineIsEmpty = true;
+}
+
+static nscoord ResolveMargin(const LengthPercentageOrAuto& aStyle,
+                             nscoord aPercentageBasis) {
+  if (aStyle.IsAuto()) {
+    return nscoord(0);
+  }
+  return nsLayoutUtils::ResolveToLength<false>(aStyle.AsLengthPercentage(),
+                                               aPercentageBasis);
+}
+
+static nscoord ResolvePadding(const LengthPercentage& aStyle,
+                              nscoord aPercentageBasis) {
+  return nsLayoutUtils::ResolveToLength<true>(aStyle, aPercentageBasis);
+}
+
+static nsIFrame::IntrinsicSizeOffsetData IntrinsicSizeOffsets(
+    nsIFrame* aFrame, nscoord aPercentageBasis, bool aForISize) {
+  nsIFrame::IntrinsicSizeOffsetData result;
+  WritingMode wm = aFrame->GetWritingMode();
+  const auto& margin = aFrame->StyleMargin()->mMargin;
+  bool verticalAxis = aForISize == wm.IsVertical();
+  if (verticalAxis) {
+    result.margin += ResolveMargin(margin.Get(eSideTop), aPercentageBasis);
+    result.margin += ResolveMargin(margin.Get(eSideBottom), aPercentageBasis);
+  } else {
+    result.margin += ResolveMargin(margin.Get(eSideLeft), aPercentageBasis);
+    result.margin += ResolveMargin(margin.Get(eSideRight), aPercentageBasis);
+  }
+
+  const auto& padding = aFrame->StylePadding()->mPadding;
+  if (verticalAxis) {
+    result.padding += ResolvePadding(padding.Get(eSideTop), aPercentageBasis);
+    result.padding +=
+        ResolvePadding(padding.Get(eSideBottom), aPercentageBasis);
+  } else {
+    result.padding += ResolvePadding(padding.Get(eSideLeft), aPercentageBasis);
+    result.padding += ResolvePadding(padding.Get(eSideRight), aPercentageBasis);
+  }
+
+  const nsStyleBorder* styleBorder = aFrame->StyleBorder();
+  if (verticalAxis) {
+    result.border += styleBorder->GetComputedBorderWidth(eSideTop);
+    result.border += styleBorder->GetComputedBorderWidth(eSideBottom);
+  } else {
+    result.border += styleBorder->GetComputedBorderWidth(eSideLeft);
+    result.border += styleBorder->GetComputedBorderWidth(eSideRight);
+  }
+
+  const nsStyleDisplay* disp = aFrame->StyleDisplay();
+  if (aFrame->IsThemed(disp)) {
+    nsPresContext* presContext = aFrame->PresContext();
+
+    LayoutDeviceIntMargin border = presContext->Theme()->GetWidgetBorder(
+        presContext->DeviceContext(), aFrame, disp->EffectiveAppearance());
+    result.border = presContext->DevPixelsToAppUnits(
+        verticalAxis ? border.TopBottom() : border.LeftRight());
+
+    LayoutDeviceIntMargin padding;
+    if (presContext->Theme()->GetWidgetPadding(
+            presContext->DeviceContext(), aFrame, disp->EffectiveAppearance(),
+            &padding)) {
+      result.padding = presContext->DevPixelsToAppUnits(
+          verticalAxis ? padding.TopBottom() : padding.LeftRight());
+    }
+  }
+  return result;
+}
+
+/* virtual */ nsIFrame::IntrinsicSizeOffsetData nsIFrame::IntrinsicISizeOffsets(
+    nscoord aPercentageBasis) {
+  return IntrinsicSizeOffsets(this, aPercentageBasis, true);
+}
+
+nsIFrame::IntrinsicSizeOffsetData nsIFrame::IntrinsicBSizeOffsets(
+    nscoord aPercentageBasis) {
+  return IntrinsicSizeOffsets(this, aPercentageBasis, false);
+}
+
+/* virtual */
+IntrinsicSize nsIFrame::GetIntrinsicSize() {
+  return IntrinsicSize();  // default is width/height set to eStyleUnit_None
+}
+
+AspectRatio nsIFrame::GetAspectRatio() const {
+  // Per spec, 'aspect-ratio' property applies to all elements except inline
+  // boxes and internal ruby or table boxes.
+  // https://drafts.csswg.org/css-sizing-4/#aspect-ratio
+  // For those frame types that don't support aspect-ratio, they must not have
+  // the natural ratio, so this early return is fine.
+  if (!SupportsAspectRatio()) {
+    return AspectRatio();
+  }
+
+  const StyleAspectRatio& aspectRatio = StylePosition()->mAspectRatio;
+  // If aspect-ratio is zero or infinite, it's a degenerate ratio and behaves
+  // as auto.
+  // https://drafts.csswg.org/css-sizing-4/#valdef-aspect-ratio-ratio
+  if (!aspectRatio.BehavesAsAuto()) {
+    // Non-auto. Return the preferred aspect ratio from the aspect-ratio style.
+    return aspectRatio.ratio.AsRatio().ToLayoutRatio(UseBoxSizing::Yes);
+  }
+
+  // The rest of the cases are when aspect-ratio has 'auto'.
+  if (auto intrinsicRatio = GetIntrinsicRatio()) {
+    return intrinsicRatio;
+  }
+
+  if (aspectRatio.HasRatio()) {
+    // If it's a degenerate ratio, this returns 0. Just the same as the auto
+    // case.
+    return aspectRatio.ratio.AsRatio().ToLayoutRatio(UseBoxSizing::No);
+  }
+
+  return AspectRatio();
+}
+
+/* virtual */
+AspectRatio nsIFrame::GetIntrinsicRatio() const { return AspectRatio(); }
+
+static bool ShouldApplyAutomaticMinimumOnInlineAxis(
+    WritingMode aWM, const nsStyleDisplay* aDisplay,
+    const nsStylePosition* aPosition) {
+  // Apply the automatic minimum size for aspect ratio:
+  // Note: The replaced elements shouldn't be here, so we only check the scroll
+  // container.
+  // https://drafts.csswg.org/css-sizing-4/#aspect-ratio-minimum
+  return !aDisplay->IsScrollableOverflow() && aPosition->MinISize(aWM).IsAuto();
+}
+
+struct MinMaxSize {
+  nscoord mMinSize = 0;
+  nscoord mMaxSize = NS_UNCONSTRAINEDSIZE;
+
+  nscoord ClampSizeToMinAndMax(nscoord aSize) const {
+    return NS_CSS_MINMAX(aSize, mMinSize, mMaxSize);
+  }
+};
+static MinMaxSize ComputeTransferredMinMaxInlineSize(
+    const WritingMode aWM, const AspectRatio& aAspectRatio,
+    const MinMaxSize& aMinMaxBSize, const LogicalSize& aBoxSizingAdjustment) {
+  // Note: the spec mentions that
+  // 1. This transferred minimum is capped by any definite preferred or maximum
+  //    size in the destination axis.
+  // 2. This transferred maximum is floored by any definite preferred or minimum
+  //    size in the destination axis
+  //
+  // https://drafts.csswg.org/css-sizing-4/#aspect-ratio
+  //
+  // The spec requires us to clamp these by the specified size (it calls it the
+  // preferred size). However, we actually don't need to worry about that,
+  // because we only use this if the inline size is indefinite.
+  //
+  // We do not need to clamp the transferred minimum and maximum as long as we
+  // always apply the transferred min/max size before the explicit min/max size,
+  // the result will be identical.
+
+  MinMaxSize transferredISize;
+
+  if (aMinMaxBSize.mMinSize > 0) {
+    transferredISize.mMinSize = aAspectRatio.ComputeRatioDependentSize(
+        LogicalAxis::eLogicalAxisInline, aWM, aMinMaxBSize.mMinSize,
+        aBoxSizingAdjustment);
+  }
+
+  if (aMinMaxBSize.mMaxSize != NS_UNCONSTRAINEDSIZE) {
+    transferredISize.mMaxSize = aAspectRatio.ComputeRatioDependentSize(
+        LogicalAxis::eLogicalAxisInline, aWM, aMinMaxBSize.mMaxSize,
+        aBoxSizingAdjustment);
+  }
+
+  // Minimum size wins over maximum size.
+  transferredISize.mMaxSize =
+      std::max(transferredISize.mMinSize, transferredISize.mMaxSize);
+  return transferredISize;
+}
+
+/* virtual */
+nsIFrame::SizeComputationResult nsIFrame::ComputeSize(
+    gfxContext* aRenderingContext, WritingMode aWM, const LogicalSize& aCBSize,
+    nscoord aAvailableISize, const LogicalSize& aMargin,
+    const LogicalSize& aBorderPadding, const StyleSizeOverrides& aSizeOverrides,
+    ComputeSizeFlags aFlags) {
+  MOZ_ASSERT(!GetIntrinsicRatio(),
+             "Please override this method and call "
+             "nsContainerFrame::ComputeSizeWithIntrinsicDimensions instead.");
+  LogicalSize result =
+      ComputeAutoSize(aRenderingContext, aWM, aCBSize, aAvailableISize, aMargin,
+                      aBorderPadding, aSizeOverrides, aFlags);
+  const nsStylePosition* stylePos = StylePosition();
+  const nsStyleDisplay* disp = StyleDisplay();
+  auto aspectRatioUsage = AspectRatioUsage::None;
+
+  const auto boxSizingAdjust = stylePos->mBoxSizing == StyleBoxSizing::Border
+                                   ? aBorderPadding
+                                   : LogicalSize(aWM);
+  nscoord boxSizingToMarginEdgeISize = aMargin.ISize(aWM) +
+                                       aBorderPadding.ISize(aWM) -
+                                       boxSizingAdjust.ISize(aWM);
+
+  const auto& styleISize = aSizeOverrides.mStyleISize
+                               ? *aSizeOverrides.mStyleISize
+                               : stylePos->ISize(aWM);
+  const auto& styleBSize = aSizeOverrides.mStyleBSize
+                               ? *aSizeOverrides.mStyleBSize
+                               : stylePos->BSize(aWM);
+  const auto& aspectRatio = aSizeOverrides.mAspectRatio
+                                ? *aSizeOverrides.mAspectRatio
+                                : GetAspectRatio();
+
+  auto parentFrame = GetParent();
+  auto alignCB = parentFrame;
+  bool isGridItem = IsGridItem();
+  const bool isSubgrid = IsSubgrid();
+  if (parentFrame && parentFrame->IsTableWrapperFrame() && IsTableFrame()) {
+    // An inner table frame is sized as a grid item if its table wrapper is,
+    // because they actually have the same CB (the wrapper's CB).
+    // @see ReflowInput::InitCBReflowInput
+    auto tableWrapper = GetParent();
+    auto grandParent = tableWrapper->GetParent();
+    isGridItem = grandParent->IsGridContainerFrame() &&
+                 !tableWrapper->HasAnyStateBits(NS_FRAME_OUT_OF_FLOW);
+    if (isGridItem) {
+      // When resolving justify/align-self below, we want to use the grid
+      // container's justify/align-items value and WritingMode.
+      alignCB = grandParent;
+    }
+  }
+  const bool isFlexItem =
+      IsFlexItem() && !parentFrame->HasAnyStateBits(
+                          NS_STATE_FLEX_IS_EMULATING_LEGACY_WEBKIT_BOX);
+  // This variable only gets set (and used) if isFlexItem is true.  It
+  // indicates which axis (in this frame's own WM) corresponds to its
+  // flex container's main axis.
+  LogicalAxis flexMainAxis =
+      eLogicalAxisInline;  // (init to make valgrind happy)
+  if (isFlexItem) {
+    flexMainAxis = nsFlexContainerFrame::IsItemInlineAxisMainAxis(this)
+                       ? eLogicalAxisInline
+                       : eLogicalAxisBlock;
+  }
+
+  const bool isOrthogonal = aWM.IsOrthogonalTo(alignCB->GetWritingMode());
+  const bool isAutoISize = styleISize.IsAuto();
+  const bool isAutoBSize =
+      nsLayoutUtils::IsAutoBSize(styleBSize, aCBSize.BSize(aWM));
+
+  // Compute inline-axis size
+  const bool isSubgriddedInInlineAxis =
+      isSubgrid && static_cast<nsGridContainerFrame*>(this)->IsColSubgrid();
+
+  // Per https://drafts.csswg.org/css-grid/#subgrid-box-alignment, if we are
+  // subgridded in the inline-axis, ignore our style inline-size, and stretch to
+  // fill the CB.
+  const bool shouldComputeISize = !isAutoISize && !isSubgriddedInInlineAxis;
+  if (shouldComputeISize) {
+    auto iSizeResult = ComputeISizeValue(
+        aRenderingContext, aWM, aCBSize, boxSizingAdjust,
+        boxSizingToMarginEdgeISize, styleISize, aSizeOverrides, aFlags);
+    result.ISize(aWM) = iSizeResult.mISize;
+    aspectRatioUsage = iSizeResult.mAspectRatioUsage;
+  } else if (MOZ_UNLIKELY(isGridItem) && !IsTrueOverflowContainer()) {
+    // 'auto' inline-size for grid-level box - fill the CB for 'stretch' /
+    // 'normal' and clamp it to the CB if requested:
+    bool stretch = false;
+    bool mayUseAspectRatio = aspectRatio && !isAutoBSize;
+    if (!aFlags.contains(ComputeSizeFlag::ShrinkWrap) &&
+        !StyleMargin()->HasInlineAxisAuto(aWM) &&
+        !alignCB->IsMasonry(isOrthogonal ? eLogicalAxisBlock
+                                         : eLogicalAxisInline)) {
+      auto inlineAxisAlignment =
+          isOrthogonal ? StylePosition()->UsedAlignSelf(alignCB->Style())._0
+                       : StylePosition()->UsedJustifySelf(alignCB->Style())._0;
+      stretch = inlineAxisAlignment == StyleAlignFlags::STRETCH ||
+                (inlineAxisAlignment == StyleAlignFlags::NORMAL &&
+                 !mayUseAspectRatio);
+    }
+
+    // Apply the preferred aspect ratio for alignments other than *stretch* and
+    // *normal without aspect ratio*.
+    // The spec says all other values should size the items as fit-content, and
+    // the intrinsic size should respect the preferred aspect ratio, so we also
+    // apply aspect ratio for all other values.
+    // https://drafts.csswg.org/css-grid/#grid-item-sizing
+    if (!stretch && mayUseAspectRatio) {
+      // Note: we don't need to handle aspect ratio for inline axis if both
+      // width/height are auto. The default ratio-dependent axis is block axis
+      // in this case, so we can simply get the block size from the non-auto
+      // |styleBSize|.
+      auto bSize = nsLayoutUtils::ComputeBSizeValue(
+          aCBSize.BSize(aWM), boxSizingAdjust.BSize(aWM),
+          styleBSize.AsLengthPercentage());
+      result.ISize(aWM) = aspectRatio.ComputeRatioDependentSize(
+          LogicalAxis::eLogicalAxisInline, aWM, bSize, boxSizingAdjust);
+      aspectRatioUsage = AspectRatioUsage::ToComputeISize;
+    }
+
+    if (stretch || aFlags.contains(ComputeSizeFlag::IClampMarginBoxMinSize)) {
+      auto iSizeToFillCB =
+          std::max(nscoord(0), aCBSize.ISize(aWM) - aBorderPadding.ISize(aWM) -
+                                   aMargin.ISize(aWM));
+      if (stretch || result.ISize(aWM) > iSizeToFillCB) {
+        result.ISize(aWM) = iSizeToFillCB;
+      }
+    }
+  } else if (aspectRatio && !isAutoBSize) {
+    auto bSize = nsLayoutUtils::ComputeBSizeValue(
+        aCBSize.BSize(aWM), boxSizingAdjust.BSize(aWM),
+        styleBSize.AsLengthPercentage());
+    result.ISize(aWM) = aspectRatio.ComputeRatioDependentSize(
+        LogicalAxis::eLogicalAxisInline, aWM, bSize, boxSizingAdjust);
+    aspectRatioUsage = AspectRatioUsage::ToComputeISize;
+  }
+
+  // Calculate and apply transferred min & max size contraints.
+  // https://drafts.csswg.org/css-sizing-4/#aspect-ratio-size-transfers
+  //
+  // Note: The basic principle is that sizing constraints transfer through the
+  // aspect-ratio to the other side to preserve the aspect ratio to the extent
+  // that they can without violating any sizes specified explicitly on that
+  // affected axis.
+  //
+  // FIXME: The spec words may not be correct, so we may have to update this
+  // tentative solution once this spec issue gets resolved. Here, we clamp the
+  // flex base size by the transferred min and max sizes, and don't include
+  // the transferred min & max sizes into its used min & max sizes. So this
+  // lets us match other browsers' current behaviors.
+  // https://github.com/w3c/csswg-drafts/issues/6071
+  //
+  // Note: This may make more sense if we clamp the flex base size in
+  // FlexItem::ResolveFlexBaseSizeFromAspectRatio(). However, the result should
+  // be identical. FlexItem::ResolveFlexBaseSizeFromAspectRatio() only handles
+  // the case of the definite cross size, and the definite cross size is clamped
+  // by the min & max cross sizes below in this function. This means its flex
+  // base size has been clamped by the transferred min & max size already after
+  // generating the flex items. So here we make the code more general for both
+  // definite cross size and indefinite cross size.
+  const bool isDefiniteISize = styleISize.IsLengthPercentage();
+  const auto& minBSizeCoord = stylePos->MinBSize(aWM);
+  const auto& maxBSizeCoord = stylePos->MaxBSize(aWM);
+  const bool isAutoMinBSize =
+      nsLayoutUtils::IsAutoBSize(minBSizeCoord, aCBSize.BSize(aWM));
+  const bool isAutoMaxBSize =
+      nsLayoutUtils::IsAutoBSize(maxBSizeCoord, aCBSize.BSize(aWM));
+  if (aspectRatio && !isDefiniteISize) {
+    const MinMaxSize minMaxBSize{
+        isAutoMinBSize ? 0
+                       : nsLayoutUtils::ComputeBSizeValue(
+                             aCBSize.BSize(aWM), boxSizingAdjust.BSize(aWM),
+                             minBSizeCoord.AsLengthPercentage()),
+        isAutoMaxBSize ? NS_UNCONSTRAINEDSIZE
+                       : nsLayoutUtils::ComputeBSizeValue(
+                             aCBSize.BSize(aWM), boxSizingAdjust.BSize(aWM),
+                             maxBSizeCoord.AsLengthPercentage())};
+    MinMaxSize transferredMinMaxISize = ComputeTransferredMinMaxInlineSize(
+        aWM, aspectRatio, minMaxBSize, boxSizingAdjust);
+
+    result.ISize(aWM) =
+        transferredMinMaxISize.ClampSizeToMinAndMax(result.ISize(aWM));
+  }
+
+  // Flex items ignore their min & max sizing properties in their
+  // flex container's main-axis.  (Those properties get applied later in
+  // the flexbox algorithm.)
+  const bool isFlexItemInlineAxisMainAxis =
+      isFlexItem && flexMainAxis == eLogicalAxisInline;
+  // Grid items that are subgridded in inline-axis also ignore their min & max
+  // sizing properties in that axis.
+  const bool shouldIgnoreMinMaxISize =
+      isFlexItemInlineAxisMainAxis || isSubgriddedInInlineAxis;
+  const auto& maxISizeCoord = stylePos->MaxISize(aWM);
+  nscoord maxISize = NS_UNCONSTRAINEDSIZE;
+  if (!maxISizeCoord.IsNone() && !shouldIgnoreMinMaxISize) {
+    maxISize = ComputeISizeValue(aRenderingContext, aWM, aCBSize,
+                                 boxSizingAdjust, boxSizingToMarginEdgeISize,
+                                 maxISizeCoord, aSizeOverrides, aFlags)
+                   .mISize;
+    result.ISize(aWM) = std::min(maxISize, result.ISize(aWM));
+  }
+
+  const auto& minISizeCoord = stylePos->MinISize(aWM);
+  nscoord minISize;
+  if (!minISizeCoord.IsAuto() && !shouldIgnoreMinMaxISize) {
+    minISize = ComputeISizeValue(aRenderingContext, aWM, aCBSize,
+                                 boxSizingAdjust, boxSizingToMarginEdgeISize,
+                                 minISizeCoord, aSizeOverrides, aFlags)
+                   .mISize;
+  } else if (MOZ_UNLIKELY(
+                 aFlags.contains(ComputeSizeFlag::IApplyAutoMinSize))) {
+    // This implements "Implied Minimum Size of Grid Items".
+    // https://drafts.csswg.org/css-grid/#min-size-auto
+    minISize = std::min(maxISize, GetMinISize(aRenderingContext));
+    if (styleISize.IsLengthPercentage()) {
+      minISize = std::min(minISize, result.ISize(aWM));
+    } else if (aFlags.contains(ComputeSizeFlag::IClampMarginBoxMinSize)) {
+      // "if the grid item spans only grid tracks that have a fixed max track
+      // sizing function, its automatic minimum size in that dimension is
+      // further clamped to less than or equal to the size necessary to fit
+      // its margin box within the resulting grid area (flooring at zero)"
+      // https://drafts.csswg.org/css-grid/#min-size-auto
+      auto maxMinISize =
+          std::max(nscoord(0), aCBSize.ISize(aWM) - aBorderPadding.ISize(aWM) -
+                                   aMargin.ISize(aWM));
+      minISize = std::min(minISize, maxMinISize);
+    }
+  } else if (aspectRatioUsage == AspectRatioUsage::ToComputeISize &&
+             ShouldApplyAutomaticMinimumOnInlineAxis(aWM, disp, stylePos)) {
+    // This means we successfully applied aspect-ratio and now need to check
+    // if we need to apply the implied minimum size:
+    // https://drafts.csswg.org/css-sizing-4/#aspect-ratio-minimum
+    MOZ_ASSERT(!HasReplacedSizing(),
+               "aspect-ratio minimums should not apply to replaced elements");
+    // The inline size computed by aspect-ratio shouldn't less than the content
+    // size.
+    minISize = GetMinISize(aRenderingContext);
+  } else {
+    // Treat "min-width: auto" as 0.
+    // NOTE: Technically, "auto" is supposed to behave like "min-content" on
+    // flex items. However, we don't need to worry about that here, because
+    // flex items' min-sizes are intentionally ignored until the flex
+    // container explicitly considers them during space distribution.
+    minISize = 0;
+  }
+  result.ISize(aWM) = std::max(minISize, result.ISize(aWM));
+
+  // Compute block-axis size
+  // (but not if we have auto bsize  -- then, we'll just stick with the bsize
+  // that we already calculated in the initial ComputeAutoSize() call. However,
+  // if we have a valid preferred aspect ratio, we still have to compute the
+  // block size because aspect ratio affects the intrinsic content size.)
+  const bool isSubgriddedInBlockAxis =
+      isSubgrid && static_cast<nsGridContainerFrame*>(this)->IsRowSubgrid();
+
+  // Per https://drafts.csswg.org/css-grid/#subgrid-box-alignment, if we are
+  // subgridded in the block-axis, ignore our style block-size, and stretch to
+  // fill the CB.
+  const bool shouldComputeBSize = !isAutoBSize && !isSubgriddedInBlockAxis;
+  if (shouldComputeBSize) {
+    result.BSize(aWM) = nsLayoutUtils::ComputeBSizeValue(
+        aCBSize.BSize(aWM), boxSizingAdjust.BSize(aWM),
+        styleBSize.AsLengthPercentage());
+  } else if (MOZ_UNLIKELY(isGridItem) && styleBSize.IsAuto() &&
+             !aFlags.contains(ComputeSizeFlag::IsGridMeasuringReflow) &&
+             !IsTrueOverflowContainer() &&
+             !alignCB->IsMasonry(isOrthogonal ? eLogicalAxisInline
+                                              : eLogicalAxisBlock)) {
+    auto cbSize = aCBSize.BSize(aWM);
+    if (cbSize != NS_UNCONSTRAINEDSIZE) {
+      // 'auto' block-size for grid-level box - fill the CB for 'stretch' /
+      // 'normal' and clamp it to the CB if requested:
+      bool stretch = false;
+      bool mayUseAspectRatio =
+          aspectRatio && result.ISize(aWM) != NS_UNCONSTRAINEDSIZE;
+      if (!StyleMargin()->HasBlockAxisAuto(aWM)) {
+        auto blockAxisAlignment =
+            isOrthogonal ? StylePosition()->UsedJustifySelf(alignCB->Style())._0
+                         : StylePosition()->UsedAlignSelf(alignCB->Style())._0;
+        stretch = blockAxisAlignment == StyleAlignFlags::STRETCH ||
+                  (blockAxisAlignment == StyleAlignFlags::NORMAL &&
+                   !mayUseAspectRatio);
+      }
+
+      // Apply the preferred aspect ratio for alignments other than *stretch*
+      // and *normal without aspect ratio*.
+      // The spec says all other values should size the items as fit-content,
+      // and the intrinsic size should respect the preferred aspect ratio, so
+      // we also apply aspect ratio for all other values.
+      // https://drafts.csswg.org/css-grid/#grid-item-sizing
+      if (!stretch && mayUseAspectRatio) {
+        result.BSize(aWM) = aspectRatio.ComputeRatioDependentSize(
+            LogicalAxis::eLogicalAxisBlock, aWM, result.ISize(aWM),
+            boxSizingAdjust);
+        MOZ_ASSERT(aspectRatioUsage == AspectRatioUsage::None);
+        aspectRatioUsage = AspectRatioUsage::ToComputeBSize;
+      }
+
+      if (stretch || aFlags.contains(ComputeSizeFlag::BClampMarginBoxMinSize)) {
+        auto bSizeToFillCB =
+            std::max(nscoord(0),
+                     cbSize - aBorderPadding.BSize(aWM) - aMargin.BSize(aWM));
+        if (stretch || (result.BSize(aWM) != NS_UNCONSTRAINEDSIZE &&
+                        result.BSize(aWM) > bSizeToFillCB)) {
+          result.BSize(aWM) = bSizeToFillCB;
+        }
+      }
+    }
+  } else if (aspectRatio) {
+    // If both inline and block dimensions are auto, the block axis is the
+    // ratio-dependent axis by default.
+    // If we have a super large inline size, aspect-ratio should still be
+    // applied (so aspectRatioUsage flag is set as expected). That's why we
+    // apply aspect-ratio unconditionally for auto block size here.
+    result.BSize(aWM) = aspectRatio.ComputeRatioDependentSize(
+        LogicalAxis::eLogicalAxisBlock, aWM, result.ISize(aWM),
+        boxSizingAdjust);
+    MOZ_ASSERT(aspectRatioUsage == AspectRatioUsage::None);
+    aspectRatioUsage = AspectRatioUsage::ToComputeBSize;
+  }
+
+  if (result.BSize(aWM) != NS_UNCONSTRAINEDSIZE) {
+    // Flex items ignore their min & max sizing properties in their flex
+    // container's main-axis. (Those properties get applied later in the flexbox
+    // algorithm.)
+    const bool isFlexItemBlockAxisMainAxis =
+        isFlexItem && flexMainAxis == eLogicalAxisBlock;
+    // Grid items that are subgridded in block-axis also ignore their min & max
+    // sizing properties in that axis.
+    const bool shouldIgnoreMinMaxBSize =
+        isFlexItemBlockAxisMainAxis || isSubgriddedInBlockAxis;
+    if (!isAutoMaxBSize && !shouldIgnoreMinMaxBSize) {
+      nscoord maxBSize = nsLayoutUtils::ComputeBSizeValue(
+          aCBSize.BSize(aWM), boxSizingAdjust.BSize(aWM),
+          maxBSizeCoord.AsLengthPercentage());
+      result.BSize(aWM) = std::min(maxBSize, result.BSize(aWM));
+    }
+
+    if (!isAutoMinBSize && !shouldIgnoreMinMaxBSize) {
+      nscoord minBSize = nsLayoutUtils::ComputeBSizeValue(
+          aCBSize.BSize(aWM), boxSizingAdjust.BSize(aWM),
+          minBSizeCoord.AsLengthPercentage());
+      result.BSize(aWM) = std::max(minBSize, result.BSize(aWM));
+    }
+  }
+
+  if (IsThemed(disp)) {
+    nsPresContext* pc = PresContext();
+    const LayoutDeviceIntSize widget = pc->Theme()->GetMinimumWidgetSize(
+        pc, this, disp->EffectiveAppearance());
+
+    // Convert themed widget's physical dimensions to logical coords
+    LogicalSize size(aWM, LayoutDeviceIntSize::ToAppUnits(
+                              widget, pc->AppUnitsPerDevPixel()));
+
+    // GetMinimumWidgetSize() returns border-box; we need content-box.
+    size -= aBorderPadding;
+
+    if (size.BSize(aWM) > result.BSize(aWM)) {
+      result.BSize(aWM) = size.BSize(aWM);
+    }
+    if (size.ISize(aWM) > result.ISize(aWM)) {
+      result.ISize(aWM) = size.ISize(aWM);
+    }
+  }
+
+  result.ISize(aWM) = std::max(0, result.ISize(aWM));
+  result.BSize(aWM) = std::max(0, result.BSize(aWM));
+
+  return {result, aspectRatioUsage};
+}
+
+nsRect nsIFrame::ComputeTightBounds(DrawTarget* aDrawTarget) const {
+  return InkOverflowRect();
+}
+
+/* virtual */
+nsresult nsIFrame::GetPrefWidthTightBounds(gfxContext* aContext, nscoord* aX,
+                                           nscoord* aXMost) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+/* virtual */
+LogicalSize nsIFrame::ComputeAutoSize(
+    gfxContext* aRenderingContext, WritingMode aWM,
+    const mozilla::LogicalSize& aCBSize, nscoord aAvailableISize,
+    const mozilla::LogicalSize& aMargin,
+    const mozilla::LogicalSize& aBorderPadding,
+    const StyleSizeOverrides& aSizeOverrides, ComputeSizeFlags aFlags) {
+  // Use basic shrink-wrapping as a default implementation.
+  LogicalSize result(aWM, 0xdeadbeef, NS_UNCONSTRAINEDSIZE);
+
+  // don't bother setting it if the result won't be used
+  const auto& styleISize = aSizeOverrides.mStyleISize
+                               ? *aSizeOverrides.mStyleISize
+                               : StylePosition()->ISize(aWM);
+  if (styleISize.IsAuto()) {
+    nscoord availBased =
+        aAvailableISize - aMargin.ISize(aWM) - aBorderPadding.ISize(aWM);
+    result.ISize(aWM) = ShrinkISizeToFit(aRenderingContext, availBased, aFlags);
+  }
+  return result;
+}
+
+nscoord nsIFrame::ShrinkISizeToFit(gfxContext* aRenderingContext,
+                                   nscoord aISizeInCB,
+                                   ComputeSizeFlags aFlags) {
+  // If we're a container for font size inflation, then shrink
+  // wrapping inside of us should not apply font size inflation.
+  AutoMaybeDisableFontInflation an(this);
+
+  nscoord result;
+  nscoord minISize = GetMinISize(aRenderingContext);
+  if (minISize > aISizeInCB) {
+    const bool clamp = aFlags.contains(ComputeSizeFlag::IClampMarginBoxMinSize);
+    result = MOZ_UNLIKELY(clamp) ? aISizeInCB : minISize;
+  } else {
+    nscoord prefISize = GetPrefISize(aRenderingContext);
+    if (prefISize > aISizeInCB) {
+      result = aISizeInCB;
+    } else {
+      result = prefISize;
+    }
+  }
+  return result;
+}
+
+Maybe<nscoord> nsIFrame::ComputeInlineSizeFromAspectRatio(
+    WritingMode aWM, const LogicalSize& aCBSize,
+    const LogicalSize& aContentEdgeToBoxSizing,
+    const StyleSizeOverrides& aSizeOverrides, ComputeSizeFlags aFlags) const {
+  // FIXME: Bug 1670151: Use GetAspectRatio() to cover replaced elements (and
+  // then we can drop the check of eSupportsAspectRatio).
+  const AspectRatio aspectRatio =
+      aSizeOverrides.mAspectRatio
+          ? *aSizeOverrides.mAspectRatio
+          : StylePosition()->mAspectRatio.ToLayoutRatio();
+  if (!SupportsAspectRatio() || !aspectRatio) {
+    return Nothing();
+  }
+
+  const StyleSize& styleBSize = aSizeOverrides.mStyleBSize
+                                    ? *aSizeOverrides.mStyleBSize
+                                    : StylePosition()->BSize(aWM);
+  if (nsLayoutUtils::IsAutoBSize(styleBSize, aCBSize.BSize(aWM))) {
+    return Nothing();
+  }
+
+  MOZ_ASSERT(styleBSize.IsLengthPercentage());
+  nscoord bSize = nsLayoutUtils::ComputeBSizeValue(
+      aCBSize.BSize(aWM), aContentEdgeToBoxSizing.BSize(aWM),
+      styleBSize.AsLengthPercentage());
+  return Some(aspectRatio.ComputeRatioDependentSize(
+      LogicalAxis::eLogicalAxisInline, aWM, bSize, aContentEdgeToBoxSizing));
+}
+
+nsIFrame::ISizeComputationResult nsIFrame::ComputeISizeValue(
+    gfxContext* aRenderingContext, const WritingMode aWM,
+    const LogicalSize& aContainingBlockSize,
+    const LogicalSize& aContentEdgeToBoxSizing, nscoord aBoxSizingToMarginEdge,
+    ExtremumLength aSize, Maybe<nscoord> aAvailableISizeOverride,
+    const StyleSizeOverrides& aSizeOverrides, ComputeSizeFlags aFlags) {
+  // If 'this' is a container for font size inflation, then shrink
+  // wrapping inside of it should not apply font size inflation.
+  AutoMaybeDisableFontInflation an(this);
+  // If we have an aspect-ratio and a definite block size, we resolve the
+  // min-content and max-content size by the aspect-ratio and the block size.
+  // https://github.com/w3c/csswg-drafts/issues/5032
+  Maybe<nscoord> intrinsicSizeFromAspectRatio =
+      aSize == ExtremumLength::MozAvailable
+          ? Nothing()
+          : ComputeInlineSizeFromAspectRatio(aWM, aContainingBlockSize,
+                                             aContentEdgeToBoxSizing,
+                                             aSizeOverrides, aFlags);
+  nscoord result;
+  switch (aSize) {
+    case ExtremumLength::MaxContent:
+      result = intrinsicSizeFromAspectRatio ? *intrinsicSizeFromAspectRatio
+                                            : GetPrefISize(aRenderingContext);
+      NS_ASSERTION(result >= 0, "inline-size less than zero");
+      return {result, intrinsicSizeFromAspectRatio
+                          ? AspectRatioUsage::ToComputeISize
+                          : AspectRatioUsage::None};
+    case ExtremumLength::MinContent:
+      result = intrinsicSizeFromAspectRatio ? *intrinsicSizeFromAspectRatio
+                                            : GetMinISize(aRenderingContext);
+      NS_ASSERTION(result >= 0, "inline-size less than zero");
+      if (MOZ_UNLIKELY(
+              aFlags.contains(ComputeSizeFlag::IClampMarginBoxMinSize))) {
+        auto available =
+            aContainingBlockSize.ISize(aWM) -
+            (aBoxSizingToMarginEdge + aContentEdgeToBoxSizing.ISize(aWM));
+        result = std::min(available, result);
+      }
+      return {result, intrinsicSizeFromAspectRatio
+                          ? AspectRatioUsage::ToComputeISize
+                          : AspectRatioUsage::None};
+    case ExtremumLength::FitContentFunction:
+    case ExtremumLength::FitContent: {
+      nscoord pref = NS_UNCONSTRAINEDSIZE;
+      nscoord min = 0;
+      if (intrinsicSizeFromAspectRatio) {
+        // The min-content and max-content size are identical and equal to the
+        // size computed from the block size and the aspect ratio.
+        pref = min = *intrinsicSizeFromAspectRatio;
+      } else {
+        pref = GetPrefISize(aRenderingContext);
+        min = GetMinISize(aRenderingContext);
+      }
+
+      nscoord fill = aAvailableISizeOverride
+                         ? *aAvailableISizeOverride
+                         : aContainingBlockSize.ISize(aWM) -
+                               (aBoxSizingToMarginEdge +
+                                aContentEdgeToBoxSizing.ISize(aWM));
+
+      if (MOZ_UNLIKELY(
+              aFlags.contains(ComputeSizeFlag::IClampMarginBoxMinSize))) {
+        min = std::min(min, fill);
+      }
+      result = std::max(min, std::min(pref, fill));
+      NS_ASSERTION(result >= 0, "inline-size less than zero");
+      return {result};
+    }
+    case ExtremumLength::MozAvailable:
+      return {aContainingBlockSize.ISize(aWM) -
+              (aBoxSizingToMarginEdge + aContentEdgeToBoxSizing.ISize(aWM))};
+  }
+  MOZ_ASSERT_UNREACHABLE("Unknown extremum length?");
+  return {};
+}
+
+nscoord nsIFrame::ComputeISizeValue(const WritingMode aWM,
+                                    const LogicalSize& aContainingBlockSize,
+                                    const LogicalSize& aContentEdgeToBoxSizing,
+                                    const LengthPercentage& aSize) {
+  LAYOUT_WARN_IF_FALSE(
+      aContainingBlockSize.ISize(aWM) != NS_UNCONSTRAINEDSIZE,
+      "have unconstrained inline-size; this should only result from "
+      "very large sizes, not attempts at intrinsic inline-size "
+      "calculation");
+  NS_ASSERTION(aContainingBlockSize.ISize(aWM) >= 0,
+               "inline-size less than zero");
+
+  nscoord result = aSize.Resolve(aContainingBlockSize.ISize(aWM));
+  // The result of a calc() expression might be less than 0; we
+  // should clamp at runtime (below).  (Percentages and coords that
+  // are less than 0 have already been dropped by the parser.)
+  result -= aContentEdgeToBoxSizing.ISize(aWM);
+  return std::max(0, result);
+}
+
+void nsIFrame::DidReflow(nsPresContext* aPresContext,
+                         const ReflowInput* aReflowInput) {
+  NS_FRAME_TRACE(NS_FRAME_TRACE_CALLS, ("nsIFrame::DidReflow"));
+
+  if (IsHiddenByContentVisibilityOfInFlowParentForLayout()) {
+    RemoveStateBits(NS_FRAME_IN_REFLOW);
+    return;
+  }
+
+  SVGObserverUtils::InvalidateDirectRenderingObservers(
+      this, SVGObserverUtils::INVALIDATE_REFLOW);
+
+  RemoveStateBits(NS_FRAME_IN_REFLOW | NS_FRAME_FIRST_REFLOW |
+                  NS_FRAME_IS_DIRTY | NS_FRAME_HAS_DIRTY_CHILDREN);
+
+  // Clear bits that were used in ReflowInput::InitResizeFlags (see
+  // comment there for why we can't clear it there).
+  SetHasBSizeChange(false);
+  SetHasPaddingChange(false);
+
+  // Notify the percent bsize observer if there is a percent bsize.
+  // The observer may be able to initiate another reflow with a computed
+  // bsize. This happens in the case where a table cell has no computed
+  // bsize but can fabricate one when the cell bsize is known.
+  if (aReflowInput && aReflowInput->mPercentBSizeObserver && !GetPrevInFlow()) {
+    const auto& bsize =
+        aReflowInput->mStylePosition->BSize(aReflowInput->GetWritingMode());
+    if (bsize.HasPercent()) {
+      aReflowInput->mPercentBSizeObserver->NotifyPercentBSize(*aReflowInput);
+    }
+  }
+
+  aPresContext->ReflowedFrame();
+}
+
+void nsIFrame::FinishReflowWithAbsoluteFrames(nsPresContext* aPresContext,
+                                              ReflowOutput& aDesiredSize,
+                                              const ReflowInput& aReflowInput,
+                                              nsReflowStatus& aStatus,
+                                              bool aConstrainBSize) {
+  ReflowAbsoluteFrames(aPresContext, aDesiredSize, aReflowInput, aStatus,
+                       aConstrainBSize);
+
+  FinishAndStoreOverflow(&aDesiredSize, aReflowInput.mStyleDisplay);
+}
+
+void nsIFrame::ReflowAbsoluteFrames(nsPresContext* aPresContext,
+                                    ReflowOutput& aDesiredSize,
+                                    const ReflowInput& aReflowInput,
+                                    nsReflowStatus& aStatus,
+                                    bool aConstrainBSize) {
+  if (HasAbsolutelyPositionedChildren()) {
+    nsAbsoluteContainingBlock* absoluteContainer = GetAbsoluteContainingBlock();
+
+    // Let the absolutely positioned container reflow any absolutely positioned
+    // child frames that need to be reflowed
+
+    // The containing block for the abs pos kids is formed by our padding edge.
+    nsMargin usedBorder = GetUsedBorder();
+    nscoord containingBlockWidth =
+        std::max(0, aDesiredSize.Width() - usedBorder.LeftRight());
+    nscoord containingBlockHeight =
+        std::max(0, aDesiredSize.Height() - usedBorder.TopBottom());
+    nsContainerFrame* container = do_QueryFrame(this);
+    NS_ASSERTION(container,
+                 "Abs-pos children only supported on container frames for now");
+
+    nsRect containingBlock(0, 0, containingBlockWidth, containingBlockHeight);
+    AbsPosReflowFlags flags =
+        AbsPosReflowFlags::CBWidthAndHeightChanged;  // XXX could be optimized
+    if (aConstrainBSize) {
+      flags |= AbsPosReflowFlags::ConstrainHeight;
+    }
+    absoluteContainer->Reflow(container, aPresContext, aReflowInput, aStatus,
+                              containingBlock, flags,
+                              &aDesiredSize.mOverflowAreas);
+  }
+}
+
+/* virtual */
+bool nsIFrame::CanContinueTextRun() const {
+  // By default, a frame will *not* allow a text run to be continued
+  // through it.
+  return false;
+}
+
+void nsIFrame::Reflow(nsPresContext* aPresContext, ReflowOutput& aDesiredSize,
+                      const ReflowInput& aReflowInput,
+                      nsReflowStatus& aStatus) {
+  MarkInReflow();
+  DO_GLOBAL_REFLOW_COUNT("nsFrame");
+  MOZ_ASSERT(aStatus.IsEmpty(), "Caller should pass a fresh reflow status!");
+  aDesiredSize.ClearSize();
+}
+
+bool nsIFrame::IsContentDisabled() const {
+  // FIXME(emilio): Doing this via CSS means callers must ensure the style is up
+  // to date, and they don't!
+  if (StyleUI()->UserInput() == StyleUserInput::None) {
+    return true;
+  }
+
+  auto* element = nsGenericHTMLElement::FromNodeOrNull(GetContent());
+  return element && element->IsDisabled();
+}
+
+bool nsIFrame::IsContentRelevant() const {
+  MOZ_ASSERT(StyleDisplay()->ContentVisibility(*this) ==
+             StyleContentVisibility::Auto);
+
+  auto* element = Element::FromNodeOrNull(GetContent());
+  MOZ_ASSERT(element);
+
+  Maybe<ContentRelevancy> relevancy = element->GetContentRelevancy();
+  return relevancy.isSome() && !relevancy->isEmpty();
+}
+
+bool nsIFrame::HidesContent(
+    const EnumSet<IncludeContentVisibility>& aInclude) const {
+  auto effectiveContentVisibility = StyleDisplay()->ContentVisibility(*this);
+  if (aInclude.contains(IncludeContentVisibility::Hidden) &&
+      effectiveContentVisibility == StyleContentVisibility::Hidden) {
+    return true;
+  }
+
+  if (aInclude.contains(IncludeContentVisibility::Auto) &&
+      effectiveContentVisibility == StyleContentVisibility::Auto) {
+    return !IsContentRelevant();
+  }
+
+  return false;
+}
+
+bool nsIFrame::HidesContentForLayout() const {
+  return HidesContent() && !PresShell()->IsForcingLayoutForHiddenContent(this);
+}
+
+bool nsIFrame::IsHiddenByContentVisibilityOfInFlowParentForLayout() const {
+  const auto* parent = GetInFlowParent();
+  // The anonymous children owned by parent are important for properly sizing
+  // their parents.
+  return parent && parent->HidesContentForLayout() &&
+         !(parent->HasAnyStateBits(NS_FRAME_OWNS_ANON_BOXES) &&
+           Style()->IsAnonBox());
+}
+
+nsIFrame* nsIFrame::GetClosestContentVisibilityAncestor(
+    const EnumSet<IncludeContentVisibility>& aInclude) const {
+  if (!StaticPrefs::layout_css_content_visibility_enabled()) {
+    return nullptr;
+  }
+
+  auto* parent = GetInFlowParent();
+  bool isAnonymousBlock = Style()->IsAnonBox() && parent &&
+                          parent->HasAnyStateBits(NS_FRAME_OWNS_ANON_BOXES);
+  for (nsIFrame* cur = parent; cur; cur = cur->GetInFlowParent()) {
+    if (!isAnonymousBlock && cur->HidesContent(aInclude)) {
+      return cur;
+    }
+
+    // Anonymous boxes are not hidden by the content-visibility of their first
+    // non-anonymous ancestor, but can be hidden by ancestors further up the
+    // tree.
+    isAnonymousBlock = false;
+  }
+
+  return nullptr;
+}
+
+bool nsIFrame::IsHiddenByContentVisibilityOnAnyAncestor(
+    const EnumSet<IncludeContentVisibility>& aInclude) const {
+  return !!GetClosestContentVisibilityAncestor(aInclude);
+}
+
+bool nsIFrame::HasSelectionInSubtree() {
+  if (IsSelected()) {
+    return true;
+  }
+
+  RefPtr<nsFrameSelection> frameSelection = GetFrameSelection();
+  if (!frameSelection) {
+    return false;
+  }
+
+  const Selection* selection =
+      frameSelection->GetSelection(SelectionType::eNormal);
+  if (!selection) {
+    return false;
+  }
+
+  for (uint32_t i = 0; i < selection->RangeCount(); i++) {
+    auto* range = selection->GetRangeAt(i);
+    MOZ_ASSERT(range);
+
+    const auto* commonAncestorNode =
+        range->GetRegisteredClosestCommonInclusiveAncestor();
+    if (commonAncestorNode &&
+        commonAncestorNode->IsInclusiveDescendantOf(GetContent())) {
+      return true;
+    }
+  }
+
+  return false;
+}
+
+bool nsIFrame::UpdateIsRelevantContent(
+    const ContentRelevancy& aRelevancyToUpdate) {
+  MOZ_ASSERT(StyleDisplay()->ContentVisibility(*this) ==
+             StyleContentVisibility::Auto);
+
+  auto* element = Element::FromNodeOrNull(GetContent());
+  MOZ_ASSERT(element);
+
+  ContentRelevancy newRelevancy;
+  Maybe<ContentRelevancy> oldRelevancy = element->GetContentRelevancy();
+  if (oldRelevancy.isSome()) {
+    newRelevancy = *oldRelevancy;
+  }
+
+  auto setRelevancyValue = [&](ContentRelevancyReason reason, bool value) {
+    if (value) {
+      newRelevancy += reason;
+    } else {
+      newRelevancy -= reason;
+    }
+  };
+
+  if (!oldRelevancy ||
+      aRelevancyToUpdate.contains(ContentRelevancyReason::Visible)) {
+    Maybe<bool> visible = element->GetVisibleForContentVisibility();
+    if (visible.isSome()) {
+      setRelevancyValue(ContentRelevancyReason::Visible, *visible);
+    }
+  }
+
+  if (!oldRelevancy ||
+      aRelevancyToUpdate.contains(ContentRelevancyReason::FocusInSubtree)) {
+    setRelevancyValue(ContentRelevancyReason::FocusInSubtree,
+                      element->State().HasAtLeastOneOfStates(
+                          ElementState::FOCUS_WITHIN | ElementState::FOCUS));
+  }
+
+  if (!oldRelevancy ||
+      aRelevancyToUpdate.contains(ContentRelevancyReason::Selected)) {
+    setRelevancyValue(ContentRelevancyReason::Selected,
+                      HasSelectionInSubtree());
+  }
+
+  // If the proximity to the viewport has not been determined yet,
+  // and neither the element nor its contents are focused or selected,
+  // we should wait for the determination of the proximity. Otherwise,
+  // there might be a redundant contentvisibilityautostatechange event.
+  // See https://github.com/w3c/csswg-drafts/issues/9803
+  bool isProximityToViewportDetermined =
+      oldRelevancy ? true : element->GetVisibleForContentVisibility().isSome();
+  if (!isProximityToViewportDetermined && newRelevancy.isEmpty()) {
+    return false;
+  }
+
+  bool overallRelevancyChanged =
+      !oldRelevancy || oldRelevancy->isEmpty() != newRelevancy.isEmpty();
+  if (!oldRelevancy || *oldRelevancy != newRelevancy) {
+    element->SetContentRelevancy(newRelevancy);
+  }
+
+  if (!overallRelevancyChanged) {
+    return false;
+  }
+
+  HandleLastRememberedSize();
+  PresContext()->SetNeedsToUpdateHiddenByContentVisibilityForAnimations();
+  PresShell()->FrameNeedsReflow(
+      this, IntrinsicDirty::FrameAncestorsAndDescendants, NS_FRAME_IS_DIRTY);
+  InvalidateFrame();
+
+  ContentVisibilityAutoStateChangeEventInit init;
+  init.mSkipped = newRelevancy.isEmpty();
+  RefPtr<ContentVisibilityAutoStateChangeEvent> event =
+      ContentVisibilityAutoStateChangeEvent::Constructor(
+          element, u"contentvisibilityautostatechange"_ns, init);
+
+  // Per
+  // https://drafts.csswg.org/css-contain/#content-visibility-auto-state-changed
+  // "This event is dispatched by posting a task at the time when the state
+  // change occurs."
+  RefPtr<AsyncEventDispatcher> asyncDispatcher =
+      new AsyncEventDispatcher(element, event.forget());
+  DebugOnly<nsresult> rv = asyncDispatcher->PostDOMEvent();
+  NS_ASSERTION(NS_SUCCEEDED(rv), "AsyncEventDispatcher failed to dispatch");
+  return true;
+}
+
+nsresult nsIFrame::CharacterDataChanged(const CharacterDataChangeInfo&) {
+  MOZ_ASSERT_UNREACHABLE("should only be called for text frames");
+  return NS_OK;
+}
+
+nsresult nsIFrame::AttributeChanged(int32_t aNameSpaceID, nsAtom* aAttribute,
+                                    int32_t aModType) {
+  return NS_OK;
+}
+
+// Flow member functions
+
+nsIFrame* nsIFrame::GetPrevContinuation() const { return nullptr; }
+
+void nsIFrame::SetPrevContinuation(nsIFrame* aPrevContinuation) {
+  MOZ_ASSERT(false, "not splittable");
+}
+
+nsIFrame* nsIFrame::GetNextContinuation() const { return nullptr; }
+
+void nsIFrame::SetNextContinuation(nsIFrame*) {
+  MOZ_ASSERT(false, "not splittable");
+}
+
+nsIFrame* nsIFrame::GetPrevInFlow() const { return nullptr; }
+
+void nsIFrame::SetPrevInFlow(nsIFrame* aPrevInFlow) {
+  MOZ_ASSERT(false, "not splittable");
+}
+
+nsIFrame* nsIFrame::GetNextInFlow() const { return nullptr; }
+
+void nsIFrame::SetNextInFlow(nsIFrame*) { MOZ_ASSERT(false, "not splittable"); }
+
+nsIFrame* nsIFrame::GetTailContinuation() {
+  nsIFrame* frame = this;
+  while (frame->HasAnyStateBits(NS_FRAME_IS_OVERFLOW_CONTAINER)) {
+    frame = frame->GetPrevContinuation();
+    NS_ASSERTION(frame, "first continuation can't be overflow container");
+  }
+  for (nsIFrame* next = frame->GetNextContinuation();
+       next && !next->HasAnyStateBits(NS_FRAME_IS_OVERFLOW_CONTAINER);
+       next = frame->GetNextContinuation()) {
+    frame = next;
+  }
+
+  MOZ_ASSERT(frame, "illegal state in continuation chain.");
+  return frame;
+}
+
+// Associated view object
+void nsIFrame::SetView(nsView* aView) {
+  if (aView) {
+    aView->SetFrame(this);
+
+#ifdef DEBUG
+    LayoutFrameType frameType = Type();
+    NS_ASSERTION(frameType == LayoutFrameType::SubDocument ||
+                     frameType == LayoutFrameType::ListControl ||
+                     frameType == LayoutFrameType::Viewport ||
+                     frameType == LayoutFrameType::MenuPopup,
+                 "Only specific frame types can have an nsView");
+#endif
+
+    // Store the view on the frame.
+    SetViewInternal(aView);
+
+    // Set the frame state bit that says the frame has a view
+    AddStateBits(NS_FRAME_HAS_VIEW);
+
+    // Let all of the ancestors know they have a descendant with a view.
+    for (nsIFrame* f = GetParent();
+         f && !f->HasAnyStateBits(NS_FRAME_HAS_CHILD_WITH_VIEW);
+         f = f->GetParent())
+      f->AddStateBits(NS_FRAME_HAS_CHILD_WITH_VIEW);
+  } else {
+    MOZ_ASSERT_UNREACHABLE("Destroying a view while the frame is alive?");
+    RemoveStateBits(NS_FRAME_HAS_VIEW);
+    SetViewInternal(nullptr);
+  }
+}
+
+// Find the first geometric parent that has a view
+nsIFrame* nsIFrame::GetAncestorWithView() const {
+  for (nsIFrame* f = GetParent(); nullptr != f; f = f->GetParent()) {
+    if (f->HasView()) {
+      return f;
+    }
+  }
+  return nullptr;
+}
+
+template <nsPoint (nsIFrame::*PositionGetter)() const>
+static nsPoint OffsetCalculator(const nsIFrame* aThis, const nsIFrame* aOther) {
+  MOZ_ASSERT(aOther, "Must have frame for destination coordinate system!");
+
+  NS_ASSERTION(aThis->PresContext() == aOther->PresContext(),
+               "GetOffsetTo called on frames in different documents");
+
+  nsPoint offset(0, 0);
+  const nsIFrame* f;
+  for (f = aThis; f != aOther && f; f = f->GetParent()) {
+    offset += (f->*PositionGetter)();
+  }
+
+  if (f != aOther) {
+    // Looks like aOther wasn't an ancestor of |this|.  So now we have
+    // the root-frame-relative position of |this| in |offset|.  Convert back
+    // to the coordinates of aOther
+    while (aOther) {
+      offset -= (aOther->*PositionGetter)();
+      aOther = aOther->GetParent();
+    }
+  }
+
+  return offset;
+}
+
+nsPoint nsIFrame::GetOffsetTo(const nsIFrame* aOther) const {
+  return OffsetCalculator<&nsIFrame::GetPosition>(this, aOther);
+}
+
+nsPoint nsIFrame::GetOffsetToIgnoringScrolling(const nsIFrame* aOther) const {
+  return OffsetCalculator<&nsIFrame::GetPositionIgnoringScrolling>(this,
+                                                                   aOther);
+}
+
+nsPoint nsIFrame::GetOffsetToCrossDoc(const nsIFrame* aOther) const {
+  return GetOffsetToCrossDoc(aOther, PresContext()->AppUnitsPerDevPixel());
+}
+
+nsPoint nsIFrame::GetOffsetToCrossDoc(const nsIFrame* aOther,
+                                      const int32_t aAPD) const {
+  MOZ_ASSERT(aOther, "Must have frame for destination coordinate system!");
+  NS_ASSERTION(PresContext()->GetRootPresContext() ==
+                   aOther->PresContext()->GetRootPresContext(),
+               "trying to get the offset between frames in different document "
+               "hierarchies?");
+  if (PresContext()->GetRootPresContext() !=
+      aOther->PresContext()->GetRootPresContext()) {
+    // crash right away, we are almost certainly going to crash anyway.
+    MOZ_CRASH(
+        "trying to get the offset between frames in different "
+        "document hierarchies?");
+  }
+
+  const nsIFrame* root = nullptr;
+  // offset will hold the final offset
+  // docOffset holds the currently accumulated offset at the current APD, it
+  // will be converted and added to offset when the current APD changes.
+  nsPoint offset(0, 0), docOffset(0, 0);
+  const nsIFrame* f = this;
+  int32_t currAPD = PresContext()->AppUnitsPerDevPixel();
+  while (f && f != aOther) {
+    docOffset += f->GetPosition();
+    nsIFrame* parent = f->GetParent();
+    if (parent) {
+      f = parent;
+    } else {
+      nsPoint newOffset(0, 0);
+      root = f;
+      f = nsLayoutUtils::GetCrossDocParentFrameInProcess(f, &newOffset);
+      int32_t newAPD = f ? f->PresContext()->AppUnitsPerDevPixel() : 0;
+      if (!f || newAPD != currAPD) {
+        // Convert docOffset to the right APD and add it to offset.
+        offset += docOffset.ScaleToOtherAppUnits(currAPD, aAPD);
+        docOffset.x = docOffset.y = 0;
+      }
+      currAPD = newAPD;
+      docOffset += newOffset;
+    }
+  }
+  if (f == aOther) {
+    offset += docOffset.ScaleToOtherAppUnits(currAPD, aAPD);
+  } else {
+    // Looks like aOther wasn't an ancestor of |this|.  So now we have
+    // the root-document-relative position of |this| in |offset|. Subtract the
+    // root-document-relative position of |aOther| from |offset|.
+    // This call won't try to recurse again because root is an ancestor of
+    // aOther.
+    nsPoint negOffset = aOther->GetOffsetToCrossDoc(root, aAPD);
+    offset -= negOffset;
+  }
+
+  return offset;
+}
+
+CSSIntRect nsIFrame::GetScreenRect() const {
+  return CSSIntRect::FromAppUnitsToNearest(GetScreenRectInAppUnits());
+}
+
+nsRect nsIFrame::GetScreenRectInAppUnits() const {
+  nsPresContext* presContext = PresContext();
+  nsIFrame* rootFrame = presContext->PresShell()->GetRootFrame();
+  nsPoint rootScreenPos(0, 0);
+  nsPoint rootFrameOffsetInParent(0, 0);
+  nsIFrame* rootFrameParent = nsLayoutUtils::GetCrossDocParentFrameInProcess(
+      rootFrame, &rootFrameOffsetInParent);
+  if (rootFrameParent) {
+    nsRect parentScreenRectAppUnits =
+        rootFrameParent->GetScreenRectInAppUnits();
+    nsPresContext* parentPresContext = rootFrameParent->PresContext();
+    double parentScale = double(presContext->AppUnitsPerDevPixel()) /
+                         parentPresContext->AppUnitsPerDevPixel();
+    nsPoint rootPt =
+        parentScreenRectAppUnits.TopLeft() + rootFrameOffsetInParent;
+    rootScreenPos.x = NS_round(parentScale * rootPt.x);
+    rootScreenPos.y = NS_round(parentScale * rootPt.y);
+  } else {
+    nsCOMPtr<nsIWidget> rootWidget =
+        presContext->PresShell()->GetViewManager()->GetRootWidget();
+    if (rootWidget) {
+      LayoutDeviceIntPoint rootDevPx = rootWidget->WidgetToScreenOffset();
+      rootScreenPos.x = presContext->DevPixelsToAppUnits(rootDevPx.x);
+      rootScreenPos.y = presContext->DevPixelsToAppUnits(rootDevPx.y);
+    }
+  }
+
+  return nsRect(rootScreenPos + GetOffsetTo(rootFrame), GetSize());
+}
+
+// Returns the offset from this frame to the closest geometric parent that
+// has a view. Also returns the containing view or null in case of error
+void nsIFrame::GetOffsetFromView(nsPoint& aOffset, nsView** aView) const {
+  MOZ_ASSERT(nullptr != aView, "null OUT parameter pointer");
+  nsIFrame* frame = const_cast<nsIFrame*>(this);
+
+  *aView = nullptr;
+  aOffset.MoveTo(0, 0);
+  do {
+    aOffset += frame->GetPosition();
+    frame = frame->GetParent();
+  } while (frame && !frame->HasView());
+
+  if (frame) {
+    *aView = frame->GetView();
+  }
+}
+
+nsIWidget* nsIFrame::GetNearestWidget() const {
+  return GetClosestView()->GetNearestWidget(nullptr);
+}
+
+nsIWidget* nsIFrame::GetNearestWidget(nsPoint& aOffset) const {
+  nsPoint offsetToView;
+  nsPoint offsetToWidget;
+  nsIWidget* widget =
+      GetClosestView(&offsetToView)->GetNearestWidget(&offsetToWidget);
+  aOffset = offsetToView + offsetToWidget;
+  return widget;
+}
+
+Matrix4x4Flagged nsIFrame::GetTransformMatrix(ViewportType aViewportType,
+                                              RelativeTo aStopAtAncestor,
+                                              nsIFrame** aOutAncestor,
+                                              uint32_t aFlags) const {
+  MOZ_ASSERT(aOutAncestor, "Need a place to put the ancestor!");
+
+  /* If we're transformed, we want to hand back the combination
+   * transform/translate matrix that will apply our current transform, then
+   * shift us to our parent.
+   */
+  const bool isTransformed = IsTransformed();
+  const nsIFrame* zoomedContentRoot = nullptr;
+  if (aStopAtAncestor.mViewportType == ViewportType::Visual) {
+    zoomedContentRoot = ViewportUtils::IsZoomedContentRoot(this);
+    if (zoomedContentRoot) {
+      MOZ_ASSERT(aViewportType != ViewportType::Visual);
+    }
+  }
+
+  if (isTransformed || zoomedContentRoot) {
+    Matrix4x4 result;
+    int32_t scaleFactor =
+        ((aFlags & IN_CSS_UNITS) ? AppUnitsPerCSSPixel()
+                                 : PresContext()->AppUnitsPerDevPixel());
+
+    /* Compute the delta to the parent, which we need because we are converting
+     * coordinates to our parent.
+     */
+    if (isTransformed) {
+      NS_ASSERTION(nsLayoutUtils::GetCrossDocParentFrameInProcess(this),
+                   "Cannot transform the viewport frame!");
+
+      result = result * nsDisplayTransform::GetResultingTransformMatrix(
+                            this, nsPoint(0, 0), scaleFactor,
+                            nsDisplayTransform::INCLUDE_PERSPECTIVE |
+                                nsDisplayTransform::OFFSET_BY_ORIGIN);
+    }
+
+    // The offset from a zoomed content root to its parent (e.g. from
+    // a canvas frame to a scroll frame) is in layout coordinates, so
+    // apply it before applying any layout-to-visual transform.
+    *aOutAncestor = nsLayoutUtils::GetCrossDocParentFrameInProcess(this);
+    nsPoint delta = GetOffsetToCrossDoc(*aOutAncestor);
+    /* Combine the raw transform with a translation to our parent. */
+    result.PostTranslate(NSAppUnitsToFloatPixels(delta.x, scaleFactor),
+                         NSAppUnitsToFloatPixels(delta.y, scaleFactor), 0.0f);
+
+    if (zoomedContentRoot) {
+      Matrix4x4 layoutToVisual;
+      ScrollableLayerGuid::ViewID targetScrollId =
+          nsLayoutUtils::FindOrCreateIDFor(zoomedContentRoot->GetContent());
+      if (aFlags & nsIFrame::IN_CSS_UNITS) {
+        layoutToVisual =
+            ViewportUtils::GetVisualToLayoutTransform(targetScrollId)
+                .Inverse()
+                .ToUnknownMatrix();
+      } else {
+        layoutToVisual =
+            ViewportUtils::GetVisualToLayoutTransform<LayoutDevicePixel>(
+                targetScrollId)
+                .Inverse()
+                .ToUnknownMatrix();
+      }
+      result = result * layoutToVisual;
+    }
+
+    return result;
+  }
+
+  *aOutAncestor = nsLayoutUtils::GetCrossDocParentFrameInProcess(this);
+
+  /* Otherwise, we're not transformed.  In that case, we'll walk up the frame
+   * tree until we either hit the root frame or something that may be
+   * transformed.  We'll then change coordinates into that frame, since we're
+   * guaranteed that nothing in-between can be transformed.  First, however,
+   * we have to check to see if we have a parent.  If not, we'll set the
+   * outparam to null (indicating that there's nothing left) and will hand back
+   * the identity matrix.
+   */
+  if (!*aOutAncestor) return Matrix4x4();
+
+  /* Keep iterating while the frame can't possibly be transformed. */
+  const nsIFrame* current = this;
+  auto shouldStopAt = [](const nsIFrame* aCurrent, nsIFrame* aAncestor,
+                         uint32_t aFlags) {
+    return aAncestor->IsTransformed() || nsLayoutUtils::IsPopup(aAncestor) ||
+           ViewportUtils::IsZoomedContentRoot(aAncestor) ||
+           ((aFlags & STOP_AT_STACKING_CONTEXT_AND_DISPLAY_PORT) &&
+            (aAncestor->IsStackingContext() ||
+             DisplayPortUtils::FrameHasDisplayPort(aAncestor, aCurrent)));
+  };
+  while (*aOutAncestor != aStopAtAncestor.mFrame &&
+         !shouldStopAt(current, *aOutAncestor, aFlags)) {
+    /* If no parent, stop iterating.  Otherwise, update the ancestor. */
+    nsIFrame* parent =
+        nsLayoutUtils::GetCrossDocParentFrameInProcess(*aOutAncestor);
+    if (!parent) break;
+
+    current = *aOutAncestor;
+    *aOutAncestor = parent;
+  }
+
+  NS_ASSERTION(*aOutAncestor, "Somehow ended up with a null ancestor...?");
+
+  /* Translate from this frame to our ancestor, if it exists.  That's the
+   * entire transform, so we're done.
+   */
+  nsPoint delta = GetOffsetToCrossDoc(*aOutAncestor);
+  int32_t scaleFactor =
+      ((aFlags & IN_CSS_UNITS) ? AppUnitsPerCSSPixel()
+                               : PresContext()->AppUnitsPerDevPixel());
+  return Matrix4x4::Translation(NSAppUnitsToFloatPixels(delta.x, scaleFactor),
+                                NSAppUnitsToFloatPixels(delta.y, scaleFactor),
+                                0.0f);
+}
+
+static void InvalidateRenderingObservers(nsIFrame* aDisplayRoot,
+                                         nsIFrame* aFrame,
+                                         bool aFrameChanged = true) {
+  MOZ_ASSERT(aDisplayRoot == nsLayoutUtils::GetDisplayRootFrame(aFrame));
+  SVGObserverUtils::InvalidateDirectRenderingObservers(aFrame);
+  nsIFrame* parent = aFrame;
+  while (parent != aDisplayRoot &&
+         (parent = nsLayoutUtils::GetCrossDocParentFrameInProcess(parent)) &&
+         !parent->HasAnyStateBits(NS_FRAME_DESCENDANT_NEEDS_PAINT)) {
+    SVGObserverUtils::InvalidateDirectRenderingObservers(parent);
+  }
+
+  if (!aFrameChanged) {
+    return;
+  }
+
+  aFrame->MarkNeedsDisplayItemRebuild();
+}
+
+static void SchedulePaintInternal(
+    nsIFrame* aDisplayRoot, nsIFrame* aFrame,
+    nsIFrame::PaintType aType = nsIFrame::PAINT_DEFAULT) {
+  MOZ_ASSERT(aDisplayRoot == nsLayoutUtils::GetDisplayRootFrame(aFrame));
+  nsPresContext* pres = aDisplayRoot->PresContext()->GetRootPresContext();
+
+  // No need to schedule a paint for an external document since they aren't
+  // painted directly.
+  if (!pres || (pres->Document() && pres->Document()->IsResourceDoc())) {
+    return;
+  }
+  if (!pres->GetContainerWeak()) {
+    NS_WARNING("Shouldn't call SchedulePaint in a detached pres context");
+    return;
+  }
+
+  pres->PresShell()->ScheduleViewManagerFlush();
+
+  if (aType == nsIFrame::PAINT_DEFAULT) {
+    aDisplayRoot->AddStateBits(NS_FRAME_UPDATE_LAYER_TREE);
+  }
+}
+
+static void InvalidateFrameInternal(nsIFrame* aFrame, bool aHasDisplayItem,
+                                    bool aRebuildDisplayItems) {
+  if (aHasDisplayItem) {
+    aFrame->AddStateBits(NS_FRAME_NEEDS_PAINT);
+  }
+
+  if (aRebuildDisplayItems) {
+    aFrame->MarkNeedsDisplayItemRebuild();
+  }
+  SVGObserverUtils::InvalidateDirectRenderingObservers(aFrame);
+  bool needsSchedulePaint = false;
+  if (nsLayoutUtils::IsPopup(aFrame)) {
+    needsSchedulePaint = true;
+  } else {
+    nsIFrame* parent = nsLayoutUtils::GetCrossDocParentFrameInProcess(aFrame);
+    while (parent &&
+           !parent->HasAnyStateBits(NS_FRAME_DESCENDANT_NEEDS_PAINT)) {
+      if (aHasDisplayItem && !parent->HasAnyStateBits(NS_FRAME_IS_NONDISPLAY)) {
+        parent->AddStateBits(NS_FRAME_DESCENDANT_NEEDS_PAINT);
+      }
+      SVGObserverUtils::InvalidateDirectRenderingObservers(parent);
+
+      // If we're inside a popup, then we need to make sure that we
+      // call schedule paint so that the NS_FRAME_UPDATE_LAYER_TREE
+      // flag gets added to the popup display root frame.
+      if (nsLayoutUtils::IsPopup(parent)) {
+        needsSchedulePaint = true;
+        break;
+      }
+      parent = nsLayoutUtils::GetCrossDocParentFrameInProcess(parent);
+    }
+    if (!parent) {
+      needsSchedulePaint = true;
+    }
+  }
+  if (!aHasDisplayItem) {
+    return;
+  }
+  if (needsSchedulePaint) {
+    nsIFrame* displayRoot = nsLayoutUtils::GetDisplayRootFrame(aFrame);
+    SchedulePaintInternal(displayRoot, aFrame);
+  }
+  if (aFrame->HasAnyStateBits(NS_FRAME_HAS_INVALID_RECT)) {
+    aFrame->RemoveProperty(nsIFrame::InvalidationRect());
+    aFrame->RemoveStateBits(NS_FRAME_HAS_INVALID_RECT);
+  }
+}
+
+void nsIFrame::InvalidateFrameSubtree(bool aRebuildDisplayItems /* = true */) {
+  InvalidateFrame(0, aRebuildDisplayItems);
+
+  if (HasAnyStateBits(NS_FRAME_ALL_DESCENDANTS_NEED_PAINT)) {
+    return;
+  }
+
+  AddStateBits(NS_FRAME_ALL_DESCENDANTS_NEED_PAINT);
+
+  for (const auto& childList : CrossDocChildLists()) {
+    for (nsIFrame* child : childList.mList) {
+      // Don't explicitly rebuild display items for our descendants,
+      // since we should be marked and it implicitly includes all
+      // descendants.
+      child->InvalidateFrameSubtree(false);
+    }
+  }
+}
+
+void nsIFrame::ClearInvalidationStateBits() {
+  if (HasAnyStateBits(NS_FRAME_DESCENDANT_NEEDS_PAINT)) {
+    for (const auto& childList : CrossDocChildLists()) {
+      for (nsIFrame* child : childList.mList) {
+        child->ClearInvalidationStateBits();
+      }
+    }
+  }
+
+  RemoveStateBits(NS_FRAME_NEEDS_PAINT | NS_FRAME_DESCENDANT_NEEDS_PAINT |
+                  NS_FRAME_ALL_DESCENDANTS_NEED_PAINT);
+}
+
+bool HasRetainedDataFor(const nsIFrame* aFrame, uint32_t aDisplayItemKey) {
+  if (RefPtr<WebRenderUserData> data =
+          GetWebRenderUserData<WebRenderFallbackData>(aFrame,
+                                                      aDisplayItemKey)) {
+    return true;
+  }
+
+  return false;
+}
+
+void nsIFrame::InvalidateFrame(uint32_t aDisplayItemKey,
+                               bool aRebuildDisplayItems /* = true */) {
+  bool hasDisplayItem =
+      !aDisplayItemKey || HasRetainedDataFor(this, aDisplayItemKey);
+  InvalidateFrameInternal(this, hasDisplayItem, aRebuildDisplayItems);
+}
+
+void nsIFrame::InvalidateFrameWithRect(const nsRect& aRect,
+                                       uint32_t aDisplayItemKey,
+                                       bool aRebuildDisplayItems /* = true */) {
+  if (aRect.IsEmpty()) {
+    return;
+  }
+  bool hasDisplayItem =
+      !aDisplayItemKey || HasRetainedDataFor(this, aDisplayItemKey);
+  bool alreadyInvalid = false;
+  if (!HasAnyStateBits(NS_FRAME_NEEDS_PAINT)) {
+    InvalidateFrameInternal(this, hasDisplayItem, aRebuildDisplayItems);
+  } else {
+    alreadyInvalid = true;
+  }
+
+  if (!hasDisplayItem) {
+    return;
+  }
+
+  nsRect* rect;
+  if (HasAnyStateBits(NS_FRAME_HAS_INVALID_RECT)) {
+    rect = GetProperty(InvalidationRect());
+    MOZ_ASSERT(rect);
+  } else {
+    if (alreadyInvalid) {
+      return;
+    }
+    rect = new nsRect();
+    AddProperty(InvalidationRect(), rect);
+    AddStateBits(NS_FRAME_HAS_INVALID_RECT);
+  }
+
+  *rect = rect->Union(aRect);
+}
+
+/*static*/
+uint8_t nsIFrame::sLayerIsPrerenderedDataKey;
+
+bool nsIFrame::IsInvalid(nsRect& aRect) {
+  if (!HasAnyStateBits(NS_FRAME_NEEDS_PAINT)) {
+    return false;
+  }
+
+  if (HasAnyStateBits(NS_FRAME_HAS_INVALID_RECT)) {
+    nsRect* rect = GetProperty(InvalidationRect());
+    NS_ASSERTION(
+        rect, "Must have an invalid rect if NS_FRAME_HAS_INVALID_RECT is set!");
+    aRect = *rect;
+  } else {
+    aRect.SetEmpty();
+  }
+  return true;
+}
+
+void nsIFrame::SchedulePaint(PaintType aType, bool aFrameChanged) {
+  if (PresShell()->IsPaintingSuppressed()) {
+    // We can't have any display items yet, and when we unsuppress we will
+    // invalidate the root frame.
+    return;
+  }
+  nsIFrame* displayRoot = nsLayoutUtils::GetDisplayRootFrame(this);
+  InvalidateRenderingObservers(displayRoot, this, aFrameChanged);
+  SchedulePaintInternal(displayRoot, this, aType);
+}
+
+void nsIFrame::SchedulePaintWithoutInvalidatingObservers(PaintType aType) {
+  nsIFrame* displayRoot = nsLayoutUtils::GetDisplayRootFrame(this);
+  SchedulePaintInternal(displayRoot, this, aType);
+}
+
+void nsIFrame::InvalidateLayer(DisplayItemType aDisplayItemKey,
+                               const nsIntRect* aDamageRect,
+                               const nsRect* aFrameDamageRect,
+                               uint32_t aFlags /* = 0 */) {
+  NS_ASSERTION(aDisplayItemKey > DisplayItemType::TYPE_ZERO, "Need a key");
+
+  nsIFrame* displayRoot = nsLayoutUtils::GetDisplayRootFrame(this);
+  InvalidateRenderingObservers(displayRoot, this, false);
+
+  // Check if frame supports WebRender's async update
+  if ((aFlags & UPDATE_IS_ASYNC) &&
+      WebRenderUserData::SupportsAsyncUpdate(this)) {
+    // WebRender does not use layer, then return nullptr.
+    return;
+  }
+
+  if (aFrameDamageRect && aFrameDamageRect->IsEmpty()) {
+    return;
+  }
+
+  // In the bug 930056, dialer app startup but not shown on the
+  // screen because sometimes we don't have any retainned data
+  // for remote type displayitem and thus Repaint event is not
+  // triggered. So, always invalidate in this case.
+  DisplayItemType displayItemKey = aDisplayItemKey;
+  if (aDisplayItemKey == DisplayItemType::TYPE_REMOTE) {
+    displayItemKey = DisplayItemType::TYPE_ZERO;
+  }
+
+  if (aFrameDamageRect) {
+    InvalidateFrameWithRect(*aFrameDamageRect,
+                            static_cast<uint32_t>(displayItemKey));
+  } else {
+    InvalidateFrame(static_cast<uint32_t>(displayItemKey));
+  }
+}
+
+static nsRect ComputeEffectsRect(nsIFrame* aFrame, const nsRect& aOverflowRect,
+                                 const nsSize& aNewSize) {
+  nsRect r = aOverflowRect;
+
+  if (aFrame->HasAnyStateBits(NS_FRAME_SVG_LAYOUT)) {
+    // For SVG frames, we only need to account for filters.
+    // TODO: We could also take account of clipPath and mask to reduce the
+    // ink overflow, but that's not essential.
+    if (aFrame->StyleEffects()->HasFilters()) {
+      SetOrUpdateRectValuedProperty(aFrame, nsIFrame::PreEffectsBBoxProperty(),
+                                    r);
+      r = SVGUtils::GetPostFilterInkOverflowRect(aFrame, aOverflowRect);
+    }
+    return r;
+  }
+
+  // box-shadow
+  r.UnionRect(r, nsLayoutUtils::GetBoxShadowRectForFrame(aFrame, aNewSize));
+
+  // border-image-outset.
+  // We need to include border-image-outset because it can cause the
+  // border image to be drawn beyond the border box.
+
+  // (1) It's important we not check whether there's a border-image
+  //     since the style hint for a change in border image doesn't cause
+  //     reflow, and that's probably more important than optimizing the
+  //     overflow areas for the silly case of border-image-outset without
+  //     border-image
+  // (2) It's important that we not check whether the border-image
+  //     is actually loaded, since that would require us to reflow when
+  //     the image loads.
+  const nsStyleBorder* styleBorder = aFrame->StyleBorder();
+  nsMargin outsetMargin = styleBorder->GetImageOutset();
+
+  if (outsetMargin != nsMargin(0, 0, 0, 0)) {
+    nsRect outsetRect(nsPoint(0, 0), aNewSize);
+    outsetRect.Inflate(outsetMargin);
+    r.UnionRect(r, outsetRect);
+  }
+
+  // Note that we don't remove the outlineInnerRect if a frame loses outline
+  // style. That would require an extra property lookup for every frame,
+  // or a new frame state bit to track whether a property had been stored,
+  // or something like that. It's not worth doing that here. At most it's
+  // only one heap-allocated rect per frame and it will be cleaned up when
+  // the frame dies.
+
+  if (SVGIntegrationUtils::UsingOverflowAffectingEffects(aFrame)) {
+    SetOrUpdateRectValuedProperty(aFrame, nsIFrame::PreEffectsBBoxProperty(),
+                                  r);
+    r = SVGIntegrationUtils::ComputePostEffectsInkOverflowRect(aFrame, r);
+  }
+
+  return r;
+}
+
+void nsIFrame::SetPosition(const nsPoint& aPt) {
+  if (mRect.TopLeft() == aPt) {
+    return;
+  }
+  mRect.MoveTo(aPt);
+  MarkNeedsDisplayItemRebuild();
+}
+
+void nsIFrame::MovePositionBy(const nsPoint& aTranslation) {
+  nsPoint position = GetNormalPosition() + aTranslation;
+
+  const nsMargin* computedOffsets = nullptr;
+  if (IsRelativelyOrStickyPositioned()) {
+    computedOffsets = GetProperty(nsIFrame::ComputedOffsetProperty());
+  }
+  ReflowInput::ApplyRelativePositioning(
+      this, computedOffsets ? *computedOffsets : nsMargin(), &position);
+  SetPosition(position);
+}
+
+nsRect nsIFrame::GetNormalRect() const {
+  // It might be faster to first check
+  // StyleDisplay()->IsRelativelyPositionedStyle().
+  bool hasProperty;
+  nsPoint normalPosition = GetProperty(NormalPositionProperty(), &hasProperty);
+  if (hasProperty) {
+    return nsRect(normalPosition, GetSize());
+  }
+  return GetRect();
+}
+
+nsRect nsIFrame::GetBoundingClientRect() {
+  return nsLayoutUtils::GetAllInFlowRectsUnion(
+      this, nsLayoutUtils::GetContainingBlockForClientRect(this),
+      nsLayoutUtils::RECTS_ACCOUNT_FOR_TRANSFORMS);
+}
+
+nsPoint nsIFrame::GetPositionIgnoringScrolling() const {
+  return GetParent() ? GetParent()->GetPositionOfChildIgnoringScrolling(this)
+                     : GetPosition();
+}
+
+nsRect nsIFrame::GetOverflowRect(OverflowType aType) const {
+  // Note that in some cases the overflow area might not have been
+  // updated (yet) to reflect any outline set on the frame or the area
+  // of child frames. That's OK because any reflow that updates these
+  // areas will invalidate the appropriate area, so any (mis)uses of
+  // this method will be fixed up.
+
+  if (mOverflow.mType == OverflowStorageType::Large) {
+    // there is an overflow rect, and it's not stored as deltas but as
+    // a separately-allocated rect
+    return GetOverflowAreasProperty()->Overflow(aType);
+  }
+
+  if (aType == OverflowType::Ink &&
+      mOverflow.mType != OverflowStorageType::None) {
+    return InkOverflowFromDeltas();
+  }
+
+  return GetRectRelativeToSelf();
+}
+
+OverflowAreas nsIFrame::GetOverflowAreas() const {
+  if (mOverflow.mType == OverflowStorageType::Large) {
+    // there is an overflow rect, and it's not stored as deltas but as
+    // a separately-allocated rect
+    return *GetOverflowAreasProperty();
+  }
+
+  return OverflowAreas(InkOverflowFromDeltas(),
+                       nsRect(nsPoint(0, 0), GetSize()));
+}
+
+OverflowAreas nsIFrame::GetOverflowAreasRelativeToSelf() const {
+  if (IsTransformed()) {
+    if (OverflowAreas* preTransformOverflows =
+            GetProperty(PreTransformOverflowAreasProperty())) {
+      return *preTransformOverflows;
+    }
+  }
+  return GetOverflowAreas();
+}
+
+OverflowAreas nsIFrame::GetOverflowAreasRelativeToParent() const {
+  return GetOverflowAreas() + GetPosition();
+}
+
+OverflowAreas nsIFrame::GetActualAndNormalOverflowAreasRelativeToParent()
+    const {
+  if (MOZ_LIKELY(!IsRelativelyOrStickyPositioned())) {
+    return GetOverflowAreasRelativeToParent();
+  }
+
+  const OverflowAreas overflows = GetOverflowAreas();
+  OverflowAreas actualAndNormalOverflows = overflows + GetPosition();
+  actualAndNormalOverflows.UnionWith(overflows + GetNormalPosition());
+  return actualAndNormalOverflows;
+}
+
+nsRect nsIFrame::ScrollableOverflowRectRelativeToParent() const {
+  return ScrollableOverflowRect() + GetPosition();
+}
+
+nsRect nsIFrame::InkOverflowRectRelativeToParent() const {
+  return InkOverflowRect() + GetPosition();
+}
+
+nsRect nsIFrame::ScrollableOverflowRectRelativeToSelf() const {
+  if (IsTransformed()) {
+    if (OverflowAreas* preTransformOverflows =
+            GetProperty(PreTransformOverflowAreasProperty())) {
+      return preTransformOverflows->ScrollableOverflow();
+    }
+  }
+  return ScrollableOverflowRect();
+}
+
+nsRect nsIFrame::InkOverflowRectRelativeToSelf() const {
+  if (IsTransformed()) {
+    if (OverflowAreas* preTransformOverflows =
+            GetProperty(PreTransformOverflowAreasProperty())) {
+      return preTransformOverflows->InkOverflow();
+    }
+  }
+  return InkOverflowRect();
+}
+
+nsRect nsIFrame::PreEffectsInkOverflowRect() const {
+  nsRect* r = GetProperty(nsIFrame::PreEffectsBBoxProperty());
+  return r ? *r : InkOverflowRectRelativeToSelf();
+}
+
+bool nsIFrame::UpdateOverflow() {
+  MOZ_ASSERT(FrameMaintainsOverflow(),
+             "Non-display SVG do not maintain ink overflow rects");
+
+  nsRect rect(nsPoint(0, 0), GetSize());
+  OverflowAreas overflowAreas(rect, rect);
+
+  if (!ComputeCustomOverflow(overflowAreas)) {
+    // If updating overflow wasn't supported by this frame, then it should
+    // have scheduled any necessary reflows. We can return false to say nothing
+    // changed, and wait for reflow to correct it.
+    return false;
+  }
+
+  UnionChildOverflow(overflowAreas);
+
+  if (FinishAndStoreOverflow(overflowAreas, GetSize())) {
+    if (nsView* view = GetView()) {
+      // Make sure the frame's view is properly sized.
+      nsViewManager* vm = view->GetViewManager();
+      vm->ResizeView(view, overflowAreas.InkOverflow(), true);
+    }
+
+    return true;
+  }
+
+  // Frames that combine their 3d transform with their ancestors
+  // only compute a pre-transform overflow rect, and then contribute
+  // to the normal overflow rect of the preserve-3d root. Always return
+  // true here so that we propagate changes up to the root for final
+  // calculation.
+  return Combines3DTransformWithAncestors();
+}
+
+/* virtual */
+bool nsIFrame::ComputeCustomOverflow(OverflowAreas& aOverflowAreas) {
+  return true;
+}
+
+bool nsIFrame::DoesClipChildrenInBothAxes() const {
+  if (IsScrollContainer()) {
+    return true;
+  }
+  const nsStyleDisplay* display = StyleDisplay();
+  if (display->IsContainPaint() && SupportsContainLayoutAndPaint()) {
+    return true;
+  }
+  return display->mOverflowX == StyleOverflow::Clip &&
+         display->mOverflowY == StyleOverflow::Clip;
+}
+
+/* virtual */
+void nsIFrame::UnionChildOverflow(OverflowAreas& aOverflowAreas) {
+  if (!DoesClipChildrenInBothAxes()) {
+    nsLayoutUtils::UnionChildOverflow(this, aOverflowAreas);
+  }
+}
+
+// Return true if this form control element's preferred size property (but not
+// percentage max size property) contains a percentage value that should be
+// resolved against zero when calculating its min-content contribution in the
+// corresponding axis.
+//
+// For proper replaced elements, the percentage value in both their max size
+// property or preferred size property should be resolved against zero. This is
+// handled in IsPercentageResolvedAgainstZero().
+inline static bool FormControlShrinksForPercentSize(const nsIFrame* aFrame) {
+  if (!aFrame->IsReplaced()) {
+    // Quick test to reject most frames.
+    return false;
+  }
+
+  LayoutFrameType fType = aFrame->Type();
+  if (fType == LayoutFrameType::Meter || fType == LayoutFrameType::Progress ||
+      fType == LayoutFrameType::Range) {
+    // progress, meter and range do have this shrinking behavior
+    // FIXME: Maybe these should be nsIFormControlFrame?
+    return true;
+  }
+
+  if (!static_cast<nsIFormControlFrame*>(do_QueryFrame(aFrame))) {
+    // Not a form control.  This includes fieldsets, which do not
+    // shrink.
+    return false;
+  }
+
+  if (fType == LayoutFrameType::GfxButtonControl ||
+      fType == LayoutFrameType::HTMLButtonControl) {
+    // Buttons don't have this shrinking behavior.  (Note that color
+    // inputs do, even though they inherit from button, so we can't use
+    // do_QueryFrame here.)
+    return false;
+  }
+
+  return true;
+}
+
+bool nsIFrame::IsPercentageResolvedAgainstZero(
+    const StyleSize& aStyleSize, const StyleMaxSize& aStyleMaxSize) const {
+  const bool sizeHasPercent = aStyleSize.HasPercent();
+  return ((sizeHasPercent || aStyleMaxSize.HasPercent()) &&
+          HasReplacedSizing()) ||
+         (sizeHasPercent && FormControlShrinksForPercentSize(this));
+}
+
+// Summary of the Cyclic-Percentage Intrinsic Size Contribution Rules:
+//
+// Element Type         |       Replaced           |        Non-replaced
+// Contribution Type    | min-content  max-content | min-content  max-content
+// ---------------------------------------------------------------------------
+// min size             | zero         zero        | zero         zero
+// max & preferred size | zero         initial     | initial      initial
+//
+// https://drafts.csswg.org/css-sizing-3/#cyclic-percentage-contribution
+bool nsIFrame::IsPercentageResolvedAgainstZero(const LengthPercentage& aSize,
+                                               SizeProperty aProperty) const {
+  // Early return to avoid calling the virtual function, IsFrameOfType().
+  if (aProperty == SizeProperty::MinSize) {
+    return true;
+  }
+
+  const bool hasPercentOnReplaced = aSize.HasPercent() && HasReplacedSizing();
+  if (aProperty == SizeProperty::MaxSize) {
+    return hasPercentOnReplaced;
+  }
+
+  MOZ_ASSERT(aProperty == SizeProperty::Size);
+  return hasPercentOnReplaced ||
+         (aSize.HasPercent() && FormControlShrinksForPercentSize(this));
+}
+
+bool nsIFrame::IsBlockWrapper() const {
+  auto pseudoType = Style()->GetPseudoType();
+  return pseudoType == PseudoStyleType::mozBlockInsideInlineWrapper ||
+         pseudoType == PseudoStyleType::buttonContent ||
+         pseudoType == PseudoStyleType::cellContent ||
+         pseudoType == PseudoStyleType::columnSpanWrapper;
+}
+
+bool nsIFrame::IsBlockFrameOrSubclass() const {
+  const nsBlockFrame* thisAsBlock = do_QueryFrame(this);
+  return !!thisAsBlock;
+}
+
+bool nsIFrame::IsImageFrameOrSubclass() const {
+  const nsImageFrame* asImage = do_QueryFrame(this);
+  return !!asImage;
+}
+
+bool nsIFrame::IsSubgrid() const {
+  return IsGridContainerFrame() &&
+         static_cast<const nsGridContainerFrame*>(this)->IsSubgrid();
+}
+
+static nsIFrame* GetNearestBlockContainer(nsIFrame* frame) {
+  while (!frame->IsBlockContainer()) {
+    frame = frame->GetParent();
+    NS_ASSERTION(
+        frame,
+        "How come we got to the root frame without seeing a containing block?");
+  }
+  return frame;
+}
+
+bool nsIFrame::IsBlockContainer() const {
+  // The block wrappers we use to wrap blocks inside inlines aren't
+  // described in the CSS spec.  We need to make them not be containing
+  // blocks.
+  // Since the parent of such a block is either a normal block or
+  // another such pseudo, this shouldn't cause anything bad to happen.
+  // Also the anonymous blocks inside table cells are not containing blocks.
+  //
+  // If we ever start skipping table row groups from being containing blocks,
+  // you need to remove the StickyScrollContainer hack referencing bug 1421660.
+  return !IsLineParticipant() && !IsBlockWrapper() && !IsSubgrid() &&
+         // Table rows are not containing blocks either
+         !IsTableRowFrame();
+}
+
+nsIFrame* nsIFrame::GetContainingBlock(
+    uint32_t aFlags, const nsStyleDisplay* aStyleDisplay) const {
+  MOZ_ASSERT(aStyleDisplay == StyleDisplay());
+
+  // Keep this in sync with MightBeContainingBlockFor in ReflowInput.cpp.
+
+  if (!GetParent()) {
+    return nullptr;
+  }
+  // MathML frames might have absolute positioning style, but they would
+  // still be in-flow.  So we have to check to make sure that the frame
+  // is really out-of-flow too.
+  nsIFrame* f;
+  if (IsAbsolutelyPositioned(aStyleDisplay)) {
+    f = GetParent();  // the parent is always the containing block
+  } else {
+    f = GetNearestBlockContainer(GetParent());
+  }
+
+  if (aFlags & SKIP_SCROLLED_FRAME && f &&
+      f->Style()->GetPseudoType() == PseudoStyleType::scrolledContent) {
+    f = f->GetParent();
+  }
+  return f;
+}
+
+#ifdef DEBUG_FRAME_DUMP
+
+Maybe<uint32_t> nsIFrame::ContentIndexInContainer(const nsIFrame* aFrame) {
+  if (nsIContent* content = aFrame->GetContent()) {
+    return content->ComputeIndexInParentContent();
+  }
+  return Nothing();
+}
+
+nsAutoCString nsIFrame::ListTag() const {
+  nsAutoString tmp;
+  GetFrameName(tmp);
+
+  nsAutoCString tag;
+  tag += NS_ConvertUTF16toUTF8(tmp);
+  tag += nsPrintfCString("@%p", static_cast<const void*>(this));
+  return tag;
+}
+
+std::string nsIFrame::ConvertToString(const LogicalRect& aRect,
+                                      const WritingMode aWM, ListFlags aFlags) {
+  if (aFlags.contains(ListFlag::DisplayInCSSPixels)) {
+    // Abuse CSSRect to store all LogicalRect's dimensions in CSS pixels.
+    return ToString(mozilla::CSSRect(CSSPixel::FromAppUnits(aRect.IStart(aWM)),
+                                     CSSPixel::FromAppUnits(aRect.BStart(aWM)),
+                                     CSSPixel::FromAppUnits(aRect.ISize(aWM)),
+                                     CSSPixel::FromAppUnits(aRect.BSize(aWM))));
+  }
+  return ToString(aRect);
+}
+
+std::string nsIFrame::ConvertToString(const LogicalSize& aSize,
+                                      const WritingMode aWM, ListFlags aFlags) {
+  if (aFlags.contains(ListFlag::DisplayInCSSPixels)) {
+    // Abuse CSSSize to store all LogicalSize's dimensions in CSS pixels.
+    return ToString(CSSSize(CSSPixel::FromAppUnits(aSize.ISize(aWM)),
+                            CSSPixel::FromAppUnits(aSize.BSize(aWM))));
+  }
+  return ToString(aSize);
+}
+
+// Debugging
+void nsIFrame::ListGeneric(nsACString& aTo, const char* aPrefix,
+                           ListFlags aFlags) const {
+  aTo += aPrefix;
+  aTo += ListTag();
+  if (HasView()) {
+    aTo += nsPrintfCString(" [view=%p]", static_cast<void*>(GetView()));
+  }
+  if (GetParent()) {
+    aTo += nsPrintfCString(" parent=%p", static_cast<void*>(GetParent()));
+  }
+  if (GetNextSibling()) {
+    aTo += nsPrintfCString(" next=%p", static_cast<void*>(GetNextSibling()));
+  }
+  if (GetPrevContinuation()) {
+    bool fluid = GetPrevInFlow() == GetPrevContinuation();
+    aTo += nsPrintfCString(" prev-%s=%p", fluid ? "in-flow" : "continuation",
+                           static_cast<void*>(GetPrevContinuation()));
+  }
+  if (GetNextContinuation()) {
+    bool fluid = GetNextInFlow() == GetNextContinuation();
+    aTo += nsPrintfCString(" next-%s=%p", fluid ? "in-flow" : "continuation",
+                           static_cast<void*>(GetNextContinuation()));
+  }
+  if (const nsAtom* const autoPageValue =
+          GetProperty(AutoPageValueProperty())) {
+    aTo += " AutoPage=";
+    aTo += nsAtomCString(autoPageValue);
+  }
+  if (const nsIFrame::PageValues* const pageValues =
+          GetProperty(PageValuesProperty())) {
+    aTo += " PageValues={";
+    if (pageValues->mStartPageValue) {
+      aTo += nsAtomCString(pageValues->mStartPageValue);
+    } else {
+      aTo += "<null>";
+    }
+    aTo += ", ";
+    if (pageValues->mEndPageValue) {
+      aTo += nsAtomCString(pageValues->mEndPageValue);
+    } else {
+      aTo += "<null>";
+    }
+    aTo += "}";
+  }
+  void* IBsibling = GetProperty(IBSplitSibling());
+  if (IBsibling) {
+    aTo += nsPrintfCString(" IBSplitSibling=%p", IBsibling);
+  }
+  void* IBprevsibling = GetProperty(IBSplitPrevSibling());
+  if (IBprevsibling) {
+    aTo += nsPrintfCString(" IBSplitPrevSibling=%p", IBprevsibling);
+  }
+  if (nsLayoutUtils::FontSizeInflationEnabled(PresContext())) {
+    if (HasAnyStateBits(NS_FRAME_FONT_INFLATION_FLOW_ROOT)) {
+      aTo += nsPrintfCString(" FFR");
+      if (nsFontInflationData* data =
+              nsFontInflationData::FindFontInflationDataFor(this)) {
+        aTo += nsPrintfCString(
+            ",enabled=%s,UIS=%s", data->InflationEnabled() ? "yes" : "no",
+            ConvertToString(data->UsableISize(), aFlags).c_str());
+      }
+    }
+    if (HasAnyStateBits(NS_FRAME_FONT_INFLATION_CONTAINER)) {
+      aTo += nsPrintfCString(" FIC");
+    }
+    aTo += nsPrintfCString(" FI=%f", nsLayoutUtils::FontSizeInflationFor(this));
+  }
+  aTo += nsPrintfCString(" %s", ConvertToString(mRect, aFlags).c_str());
+
+  mozilla::WritingMode wm = GetWritingMode();
+  if (wm.IsVertical() || wm.IsBidiRTL()) {
+    aTo +=
+        nsPrintfCString(" wm=%s logical-size=(%s)", ToString(wm).c_str(),
+                        ConvertToString(GetLogicalSize(), wm, aFlags).c_str());
+  }
+
+  nsIFrame* parent = GetParent();
+  if (parent) {
+    WritingMode pWM = parent->GetWritingMode();
+    if (pWM.IsVertical() || pWM.IsBidiRTL()) {
+      nsSize containerSize = parent->mRect.Size();
+      LogicalRect lr(pWM, mRect, containerSize);
+      aTo += nsPrintfCString(" parent-wm=%s cs=(%s) logical-rect=%s",
+                             ToString(pWM).c_str(),
+                             ConvertToString(containerSize, aFlags).c_str(),
+                             ConvertToString(lr, pWM, aFlags).c_str());
+    }
+  }
+  nsIFrame* f = const_cast<nsIFrame*>(this);
+  if (f->HasOverflowAreas()) {
+    nsRect io = f->InkOverflowRect();
+    if (!io.IsEqualEdges(mRect)) {
+      aTo += nsPrintfCString(" ink-overflow=%s",
+                             ConvertToString(io, aFlags).c_str());
+    }
+    nsRect so = f->ScrollableOverflowRect();
+    if (!so.IsEqualEdges(mRect)) {
+      aTo += nsPrintfCString(" scr-overflow=%s",
+                             ConvertToString(so, aFlags).c_str());
+    }
+  }
+  if (OverflowAreas* preTransformOverflows =
+          f->GetProperty(PreTransformOverflowAreasProperty())) {
+    nsRect io = preTransformOverflows->InkOverflow();
+    if (!io.IsEqualEdges(mRect) &&
+        (!f->HasOverflowAreas() || !io.IsEqualEdges(f->InkOverflowRect()))) {
+      aTo += nsPrintfCString(" pre-transform-ink-overflow=%s",
+                             ConvertToString(io, aFlags).c_str());
+    }
+    nsRect so = preTransformOverflows->ScrollableOverflow();
+    if (!so.IsEqualEdges(mRect) &&
+        (!f->HasOverflowAreas() ||
+         !so.IsEqualEdges(f->ScrollableOverflowRect()))) {
+      aTo += nsPrintfCString(" pre-transform-scr-overflow=%s",
+                             ConvertToString(so, aFlags).c_str());
+    }
+  }
+  bool hasNormalPosition;
+  nsPoint normalPosition = GetNormalPosition(&hasNormalPosition);
+  if (hasNormalPosition) {
+    aTo += nsPrintfCString(" normal-position=%s",
+                           ConvertToString(normalPosition, aFlags).c_str());
+  }
+  if (HasProperty(BidiDataProperty())) {
+    FrameBidiData bidi = GetBidiData();
+    aTo += nsPrintfCString(" bidi(%d,%d,%d)", bidi.baseLevel.Value(),
+                           bidi.embeddingLevel.Value(),
+                           bidi.precedingControl.Value());
+  }
+  if (IsTransformed()) {
+    aTo += nsPrintfCString(" transformed");
+  }
+  if (ChildrenHavePerspective()) {
+    aTo += nsPrintfCString(" perspective");
+  }
+  if (Extend3DContext()) {
+    aTo += nsPrintfCString(" extend-3d");
+  }
+  if (Combines3DTransformWithAncestors()) {
+    aTo += nsPrintfCString(" combines-3d-transform-with-ancestors");
+  }
+  if (mContent) {
+    aTo += nsPrintfCString(" [content=%p]", static_cast<void*>(mContent));
+  }
+  aTo += nsPrintfCString(" [cs=%p", static_cast<void*>(mComputedStyle));
+  if (mComputedStyle) {
+    auto pseudoType = mComputedStyle->GetPseudoType();
+    aTo += ToString(pseudoType).c_str();
+  }
+  aTo += "]";
+
+  auto contentVisibility = StyleDisplay()->ContentVisibility(*this);
+  if (contentVisibility != StyleContentVisibility::Visible) {
+    aTo += nsPrintfCString(" [content-visibility=");
+    if (contentVisibility == StyleContentVisibility::Auto) {
+      aTo += "auto, "_ns;
+    } else if (contentVisibility == StyleContentVisibility::Hidden) {
+      aTo += "hiden, "_ns;
+    }
+
+    if (HidesContent()) {
+      aTo += "HidesContent=hidden"_ns;
+    } else {
+      aTo += "HidesContent=visibile"_ns;
+    }
+    aTo += "]";
+  }
+
+  if (IsFrameModified()) {
+    aTo += nsPrintfCString(" modified");
+  }
+
+  if (HasModifiedDescendants()) {
+    aTo += nsPrintfCString(" has-modified-descendants");
+  }
+}
+
+void nsIFrame::List(FILE* out, const char* aPrefix, ListFlags aFlags) const {
+  nsCString str;
+  ListGeneric(str, aPrefix, aFlags);
+  fprintf_stderr(out, "%s\n", str.get());
+}
+
+void nsIFrame::ListTextRuns(FILE* out) const {
+  nsTHashSet<const void*> seen;
+  ListTextRuns(out, seen);
+}
+
+void nsIFrame::ListTextRuns(FILE* out, nsTHashSet<const void*>& aSeen) const {
+  for (const auto& childList : ChildLists()) {
+    for (const nsIFrame* kid : childList.mList) {
+      kid->ListTextRuns(out, aSeen);
+    }
+  }
+}
+
+void nsIFrame::ListMatchedRules(FILE* out, const char* aPrefix) const {
+  nsTArray<const StyleLockedStyleRule*> rawRuleList;
+  Servo_ComputedValues_GetStyleRuleList(mComputedStyle, &rawRuleList);
+  for (const StyleLockedStyleRule* rawRule : rawRuleList) {
+    nsAutoCString ruleText;
+    Servo_StyleRule_GetCssText(rawRule, &ruleText);
+    fprintf_stderr(out, "%s%s\n", aPrefix, ruleText.get());
+  }
+}
+
+void nsIFrame::ListWithMatchedRules(FILE* out, const char* aPrefix) const {
+  fprintf_stderr(out, "%s%s\n", aPrefix, ListTag().get());
+
+  nsCString rulePrefix;
+  rulePrefix += aPrefix;
+  rulePrefix += "    ";
+  ListMatchedRules(out, rulePrefix.get());
+}
+
+nsresult nsIFrame::GetFrameName(nsAString& aResult) const {
+  return MakeFrameName(u"Frame"_ns, aResult);
+}
+
+nsresult nsIFrame::MakeFrameName(const nsAString& aType,
+                                 nsAString& aResult) const {
+  aResult = aType;
+  if (mContent && !mContent->IsText()) {
+    nsAutoString buf;
+    mContent->NodeInfo()->NameAtom()->ToString(buf);
+    if (nsAtom* id = mContent->GetID()) {
+      buf.AppendLiteral(" id=");
+      buf.Append(nsDependentAtomString(id));
+    }
+    if (IsSubDocumentFrame()) {
+      nsAutoString src;
+      mContent->AsElement()->GetAttr(nsGkAtoms::src, src);
+      buf.AppendLiteral(" src=");
+      buf.Append(src);
+    }
+    aResult.Append('(');
+    aResult.Append(buf);
+    aResult.Append(')');
+  }
+  aResult.Append('(');
+  Maybe<uint32_t> index = ContentIndexInContainer(this);
+  if (index.isSome()) {
+    aResult.AppendInt(*index);
+  } else {
+    aResult.AppendInt(-1);
+  }
+  aResult.Append(')');
+  return NS_OK;
+}
+
+void nsIFrame::DumpFrameTree() const {
+  PresShell()->GetRootFrame()->List(stderr);
+}
+
+void nsIFrame::DumpFrameTreeInCSSPixels() const {
+  PresShell()->GetRootFrame()->List(stderr, "", ListFlag::DisplayInCSSPixels);
+}
+
+void nsIFrame::DumpFrameTreeLimited() const { List(stderr); }
+void nsIFrame::DumpFrameTreeLimitedInCSSPixels() const {
+  List(stderr, "", ListFlag::DisplayInCSSPixels);
+}
+
+#endif
+
+bool nsIFrame::IsVisibleForPainting() const {
+  return StyleVisibility()->IsVisible();
+}
+
+bool nsIFrame::IsVisibleOrCollapsedForPainting() const {
+  return StyleVisibility()->IsVisibleOrCollapsed();
+}
+
+/* virtual */
+bool nsIFrame::IsEmpty() {
+  return IsHiddenByContentVisibilityOfInFlowParentForLayout();
+}
+
+bool nsIFrame::CachedIsEmpty() {
+  MOZ_ASSERT(!HasAnyStateBits(NS_FRAME_IS_DIRTY) ||
+                 IsHiddenByContentVisibilityOfInFlowParentForLayout(),
+             "Must only be called on reflowed lines or those hidden by "
+             "content-visibility.");
+  return IsEmpty();
+}
+
+/* virtual */
+bool nsIFrame::IsSelfEmpty() {
+  return IsHiddenByContentVisibilityOfInFlowParentForLayout();
+}
+
+nsresult nsIFrame::GetSelectionController(nsPresContext* aPresContext,
+                                          nsISelectionController** aSelCon) {
+  if (!aPresContext || !aSelCon) return NS_ERROR_INVALID_ARG;
+
+  nsIFrame* frame = this;
+  while (frame && frame->HasAnyStateBits(NS_FRAME_INDEPENDENT_SELECTION)) {
+    nsITextControlFrame* tcf = do_QueryFrame(frame);
+    if (tcf) {
+      return tcf->GetOwnedSelectionController(aSelCon);
+    }
+    frame = frame->GetParent();
+  }
+
+  *aSelCon = do_AddRef(aPresContext->PresShell()).take();
+  return NS_OK;
+}
+
+already_AddRefed<nsFrameSelection> nsIFrame::GetFrameSelection() {
+  RefPtr<nsFrameSelection> fs =
+      const_cast<nsFrameSelection*>(GetConstFrameSelection());
+  return fs.forget();
+}
+
+const nsFrameSelection* nsIFrame::GetConstFrameSelection() const {
+  nsIFrame* frame = const_cast<nsIFrame*>(this);
+  while (frame && frame->HasAnyStateBits(NS_FRAME_INDEPENDENT_SELECTION)) {
+    nsITextControlFrame* tcf = do_QueryFrame(frame);
+    if (tcf) {
+      return tcf->GetOwnedFrameSelection();
+    }
+    frame = frame->GetParent();
+  }
+
+  return PresShell()->ConstFrameSelection();
+}
+
+bool nsIFrame::IsFrameSelected() const {
+  NS_ASSERTION(!GetContent() || GetContent()->IsMaybeSelected(),
+               "use the public IsSelected() instead");
+  return GetContent()->IsSelected(0, GetContent()->GetChildCount());
+}
+
+nsresult nsIFrame::GetPointFromOffset(int32_t inOffset, nsPoint* outPoint) {
+  MOZ_ASSERT(outPoint != nullptr, "Null parameter");
+  nsRect contentRect = GetContentRectRelativeToSelf();
+  nsPoint pt = contentRect.TopLeft();
+  if (mContent) {
+    nsIContent* newContent = mContent->GetParent();
+    if (newContent) {
+      const int32_t newOffset = newContent->ComputeIndexOf_Deprecated(mContent);
+
+      // Find the direction of the frame from the EmbeddingLevelProperty,
+      // which is the resolved bidi level set in
+      // nsBidiPresUtils::ResolveParagraph (odd levels = right-to-left).
+      // If the embedding level isn't set, just use the CSS direction
+      // property.
+      bool hasBidiData;
+      FrameBidiData bidiData = GetProperty(BidiDataProperty(), &hasBidiData);
+      bool isRTL = hasBidiData
+                       ? bidiData.embeddingLevel.IsRTL()
+                       : StyleVisibility()->mDirection == StyleDirection::Rtl;
+      if ((!isRTL && inOffset > newOffset) ||
+          (isRTL && inOffset <= newOffset)) {
+        pt = contentRect.TopRight();
+      }
+    }
+  }
+  *outPoint = pt;
+  return NS_OK;
+}
+
+nsresult nsIFrame::GetCharacterRectsInRange(int32_t aInOffset, int32_t aLength,
+                                            nsTArray<nsRect>& aOutRect) {
+  /* no text */
+  return NS_ERROR_FAILURE;
+}
+
+nsresult nsIFrame::GetChildFrameContainingOffset(int32_t inContentOffset,
+                                                 bool inHint,
+                                                 int32_t* outFrameContentOffset,
+                                                 nsIFrame** outChildFrame) {
+  MOZ_ASSERT(outChildFrame && outFrameContentOffset, "Null parameter");
+  *outFrameContentOffset = (int32_t)inHint;
+  // the best frame to reflect any given offset would be a visible frame if
+  // possible i.e. we are looking for a valid frame to place the blinking caret
+  nsRect rect = GetRect();
+  if (!rect.width || !rect.height) {
+    // if we have a 0 width or height then lets look for another frame that
+    // possibly has the same content.  If we have no frames in flow then just
+    // let us return 'this' frame
+    nsIFrame* nextFlow = GetNextInFlow();
+    if (nextFlow)
+      return nextFlow->GetChildFrameContainingOffset(
+          inContentOffset, inHint, outFrameContentOffset, outChildFrame);
+  }
+  *outChildFrame = this;
+  return NS_OK;
+}
+
+//
+// What I've pieced together about this routine:
+// Starting with a block frame (from which a line frame can be gotten)
+// and a line number, drill down and get the first/last selectable
+// frame on that line, depending on aPos->mDirection.
+// aOutSideLimit != 0 means ignore aLineStart, instead work from
+// the end (if > 0) or beginning (if < 0).
+//
+static nsresult GetNextPrevLineFromBlockFrame(PeekOffsetStruct* aPos,
+                                              nsIFrame* aBlockFrame,
+                                              int32_t aLineStart,
+                                              int8_t aOutSideLimit) {
+  MOZ_ASSERT(aPos);
+  MOZ_ASSERT(aBlockFrame);
+
+  nsPresContext* pc = aBlockFrame->PresContext();
+
+  // magic numbers: aLineStart will be -1 for end of block, 0 will be start of
+  // block.
+
+  aPos->mResultFrame = nullptr;
+  aPos->mResultContent = nullptr;
+  aPos->mAttach = aPos->mDirection == eDirNext ? CaretAssociationHint::After
+                                               : CaretAssociationHint::Before;
+
+  AutoAssertNoDomMutations guard;
+  nsILineIterator* it = aBlockFrame->GetLineIterator();
+  if (!it) {
+    return NS_ERROR_FAILURE;
+  }
+  int32_t searchingLine = aLineStart;
+  int32_t countLines = it->GetNumLines();
+  if (aOutSideLimit > 0) {  // start at end
+    searchingLine = countLines;
+  } else if (aOutSideLimit < 0) {  // start at beginning
+    searchingLine = -1;            //"next" will be 0
+  } else if ((aPos->mDirection == eDirPrevious && searchingLine == 0) ||
+             (aPos->mDirection == eDirNext &&
+              searchingLine >= (countLines - 1))) {
+    // Not found.
+    return NS_ERROR_FAILURE;
+  }
+  nsIFrame* resultFrame = nullptr;
+  nsIFrame* farStoppingFrame = nullptr;  // we keep searching until we find a
+                                         // "this" frame then we go to next line
+  nsIFrame* nearStoppingFrame = nullptr;  // if we are backing up from edge,
+                                          // stop here
+  nsIFrame* firstFrame;
+  nsIFrame* lastFrame;
+  bool isBeforeFirstFrame, isAfterLastFrame;
+  bool found = false;
+
+  while (!found) {
+    if (aPos->mDirection == eDirPrevious)
+      searchingLine--;
+    else
+      searchingLine++;
+    if ((aPos->mDirection == eDirPrevious && searchingLine < 0) ||
+        (aPos->mDirection == eDirNext && searchingLine >= countLines)) {
+      // we need to jump to new block frame.
+      return NS_ERROR_FAILURE;
+    }
+    auto line = it->GetLine(searchingLine).unwrap();
+    if (!line.mNumFramesOnLine) {
+      continue;
+    }
+    lastFrame = firstFrame = line.mFirstFrameOnLine;
+    for (int32_t lineFrameCount = line.mNumFramesOnLine; lineFrameCount > 1;
+         lineFrameCount--) {
+      lastFrame = lastFrame->GetNextSibling();
+      if (!lastFrame) {
+        NS_ERROR("GetLine promised more frames than could be found");
+        return NS_ERROR_FAILURE;
+      }
+    }
+    nsIFrame::GetLastLeaf(&lastFrame);
+
+    if (aPos->mDirection == eDirNext) {
+      nearStoppingFrame = firstFrame;
+      farStoppingFrame = lastFrame;
+    } else {
+      nearStoppingFrame = lastFrame;
+      farStoppingFrame = firstFrame;
+    }
+    nsPoint offset;
+    nsView* view;  // used for call of get offset from view
+    aBlockFrame->GetOffsetFromView(offset, &view);
+    nsPoint newDesiredPos =
+        aPos->mDesiredCaretPos -
+        offset;  // get desired position into blockframe coords
+    nsresult rv = it->FindFrameAt(searchingLine, newDesiredPos, &resultFrame,
+                                  &isBeforeFirstFrame, &isAfterLastFrame);
+    if (NS_FAILED(rv)) {
+      continue;
+    }
+
+    if (resultFrame) {
+      // check to see if this is ANOTHER blockframe inside the other one if so
+      // then call into its lines
+      if (resultFrame->CanProvideLineIterator()) {
+        aPos->mResultFrame = resultFrame;
+        return NS_OK;
+      }
+      // resultFrame is not a block frame
+      Maybe<nsFrameIterator> frameIterator;
+      frameIterator.emplace(
+          pc, resultFrame, nsFrameIterator::Type::PostOrder,
+          false,  // aVisual
+          aPos->mOptions.contains(PeekOffsetOption::StopAtScroller),
+          false,  // aFollowOOFs
+          false   // aSkipPopupChecks
+      );
+
+      auto FoundValidFrame = [aPos](const nsIFrame::ContentOffsets& aOffsets,
+                                    const nsIFrame* aFrame) {
+        if (!aOffsets.content) {
+          return false;
+        }
+        if (!aFrame->IsSelectable(nullptr)) {
+          return false;
+        }
+        if (aPos->mOptions.contains(PeekOffsetOption::ForceEditableRegion) &&
+            !aOffsets.content->IsEditable()) {
+          return false;
+        }
+        return true;
+      };
+
+      nsIFrame* storeOldResultFrame = resultFrame;
+      while (!found) {
+        nsPoint point;
+        nsRect tempRect = resultFrame->GetRect();
+        nsPoint offset;
+        nsView* view;  // used for call of get offset from view
+        resultFrame->GetOffsetFromView(offset, &view);
+        if (!view) {
+          return NS_ERROR_FAILURE;
+        }
+        if (resultFrame->GetWritingMode().IsVertical()) {
+          point.y = aPos->mDesiredCaretPos.y;
+          point.x = tempRect.width + offset.x;
+        } else {
+          point.y = tempRect.height + offset.y;
+          point.x = aPos->mDesiredCaretPos.x;
+        }
+
+        if (!resultFrame->HasView()) {
+          nsView* view;
+          nsPoint offset;
+          resultFrame->GetOffsetFromView(offset, &view);
+          nsIFrame::ContentOffsets offsets =
+              resultFrame->GetContentOffsetsFromPoint(
+                  point - offset, nsIFrame::IGNORE_NATIVE_ANONYMOUS_SUBTREE);
+          aPos->mResultContent = offsets.content;
+          aPos->mContentOffset = offsets.offset;
+          aPos->mAttach = offsets.associate;
+          if (FoundValidFrame(offsets, resultFrame)) {
+            found = true;
+            break;
+          }
+        }
+
+        if (aPos->mDirection == eDirPrevious &&
+            resultFrame == farStoppingFrame) {
+          break;
+        }
+        if (aPos->mDirection == eDirNext && resultFrame == nearStoppingFrame) {
+          break;
+        }
+        // always try previous on THAT line if that fails go the other way
+        resultFrame = frameIterator->Traverse(/* aForward = */ false);
+        if (!resultFrame) {
+          return NS_ERROR_FAILURE;
+        }
+      }
+
+      if (!found) {
+        resultFrame = storeOldResultFrame;
+        frameIterator.reset();
+        frameIterator.emplace(
+            pc, resultFrame, nsFrameIterator::Type::Leaf,
+            false,  // aVisual
+            aPos->mOptions.contains(PeekOffsetOption::StopAtScroller),
+            false,  // aFollowOOFs
+            false   // aSkipPopupChecks
+        );
+        MOZ_ASSERT(frameIterator);
+      }
+      while (!found) {
+        nsPoint point = aPos->mDesiredCaretPos;
+        nsView* view;
+        nsPoint offset;
+        resultFrame->GetOffsetFromView(offset, &view);
+        nsIFrame::ContentOffsets offsets =
+            resultFrame->GetContentOffsetsFromPoint(
+                point - offset, nsIFrame::IGNORE_NATIVE_ANONYMOUS_SUBTREE);
+        aPos->mResultContent = offsets.content;
+        aPos->mContentOffset = offsets.offset;
+        aPos->mAttach = offsets.associate;
+        if (FoundValidFrame(offsets, resultFrame)) {
+          found = true;
+          aPos->mAttach = resultFrame == farStoppingFrame
+                              ? CaretAssociationHint::Before
+                              : CaretAssociationHint::After;
+          break;
+        }
+        if (aPos->mDirection == eDirPrevious &&
+            (resultFrame == nearStoppingFrame))
+          break;
+        if (aPos->mDirection == eDirNext && (resultFrame == farStoppingFrame))
+          break;
+        // previous didnt work now we try "next"
+        nsIFrame* tempFrame = frameIterator->Traverse(/* aForward = */ true);
+        if (!tempFrame) break;
+        resultFrame = tempFrame;
+      }
+      aPos->mResultFrame = resultFrame;
+    } else {
+      // we need to jump to new block frame.
+      aPos->mAmount = eSelectLine;
+      aPos->mStartOffset = 0;
+      aPos->mAttach = aPos->mDirection == eDirNext
+                          ? CaretAssociationHint::Before
+                          : CaretAssociationHint::After;
+      if (aPos->mDirection == eDirPrevious)
+        aPos->mStartOffset = -1;  // start from end
+      return aBlockFrame->PeekOffset(aPos);
+    }
+  }
+  return NS_OK;
+}
+
+nsIFrame::CaretPosition nsIFrame::GetExtremeCaretPosition(bool aStart) {
+  CaretPosition result;
+
+  FrameTarget targetFrame = DrillDownToSelectionFrame(this, !aStart, 0);
+  FrameContentRange range = GetRangeForFrame(targetFrame.frame);
+  result.mResultContent = range.content;
+  result.mContentOffset = aStart ? range.start : range.end;
+  return result;
+}
+
+// If this is a preformatted text frame, see if it ends with a newline
+static nsContentAndOffset FindLineBreakInText(nsIFrame* aFrame,
+                                              nsDirection aDirection) {
+  nsContentAndOffset result;
+
+  if (aFrame->IsGeneratedContentFrame() ||
+      !aFrame->HasSignificantTerminalNewline()) {
+    return result;
+  }
+
+  int32_t endOffset = aFrame->GetOffsets().second;
+  result.mContent = aFrame->GetContent();
+  result.mOffset = endOffset - (aDirection == eDirPrevious ? 0 : 1);
+  return result;
+}
+
+// Find the first (or last) descendant of the given frame
+// which is either a block-level frame or a BRFrame, or some other kind of break
+// which stops the line.
+static nsContentAndOffset FindLineBreakingFrame(nsIFrame* aFrame,
+                                                nsDirection aDirection) {
+  nsContentAndOffset result;
+
+  if (aFrame->IsGeneratedContentFrame()) {
+    return result;
+  }
+
+  // Treat form controls as inline leaves
+  // XXX we really need a way to determine whether a frame is inline-level
+  if (static_cast<nsIFormControlFrame*>(do_QueryFrame(aFrame))) {
+    return result;
+  }
+
+  // Check the frame itself
+  // Fall through block-in-inline split frames because their mContent is
+  // the content of the inline frames they were created from. The
+  // first/last child of such frames is the real block frame we're
+  // looking for.
+  if ((aFrame->IsBlockOutside() &&
+       !aFrame->HasAnyStateBits(NS_FRAME_PART_OF_IBSPLIT)) ||
+      aFrame->IsBrFrame()) {
+    nsIContent* content = aFrame->GetContent();
+    result.mContent = content->GetParent();
+    // In some cases (bug 310589, bug 370174) we end up here with a null
+    // content. This probably shouldn't ever happen, but since it sometimes
+    // does, we want to avoid crashing here.
+    NS_ASSERTION(result.mContent, "Unexpected orphan content");
+    if (result.mContent) {
+      result.mOffset = result.mContent->ComputeIndexOf_Deprecated(content) +
+                       (aDirection == eDirPrevious ? 1 : 0);
+    }
+    return result;
+  }
+
+  result = FindLineBreakInText(aFrame, aDirection);
+  if (result.mContent) {
+    return result;
+  }
+
+  // Iterate over children and call ourselves recursively
+  if (aDirection == eDirPrevious) {
+    nsIFrame* child = aFrame->PrincipalChildList().LastChild();
+    while (child && !result.mContent) {
+      result = FindLineBreakingFrame(child, aDirection);
+      child = child->GetPrevSibling();
+    }
+  } else {  // eDirNext
+    nsIFrame* child = aFrame->PrincipalChildList().FirstChild();
+    while (child && !result.mContent) {
+      result = FindLineBreakingFrame(child, aDirection);
+      child = child->GetNextSibling();
+    }
+  }
+  return result;
+}
+
+nsresult nsIFrame::PeekOffsetForParagraph(PeekOffsetStruct* aPos) {
+  nsIFrame* frame = this;
+  nsContentAndOffset blockFrameOrBR;
+  blockFrameOrBR.mContent = nullptr;
+  bool reachedLimit = frame->IsBlockOutside() || IsEditingHost(frame);
+
+  auto traverse = [&aPos](nsIFrame* current) {
+    return aPos->mDirection == eDirPrevious ? current->GetPrevSibling()
+                                            : current->GetNextSibling();
+  };
+
+  // Go through containing frames until reaching a block frame.
+  // In each step, search the previous (or next) siblings for the closest
+  // "stop frame" (a block frame or a BRFrame).
+  // If found, set it to be the selection boundary and abort.
+  while (!reachedLimit) {
+    nsIFrame* parent = frame->GetParent();
+    // Treat a frame associated with the root content as if it were a block
+    // frame.
+    if (!frame->mContent || !frame->mContent->GetParent()) {
+      reachedLimit = true;
+      break;
+    }
+
+    if (aPos->mDirection == eDirNext) {
+      // Try to find our own line-break before looking at our siblings.
+      blockFrameOrBR = FindLineBreakInText(frame, eDirNext);
+    }
+
+    nsIFrame* sibling = traverse(frame);
+    while (sibling && !blockFrameOrBR.mContent) {
+      blockFrameOrBR = FindLineBreakingFrame(sibling, aPos->mDirection);
+      sibling = traverse(sibling);
+    }
+    if (blockFrameOrBR.mContent) {
+      aPos->mResultContent = blockFrameOrBR.mContent;
+      aPos->mContentOffset = blockFrameOrBR.mOffset;
+      break;
+    }
+    frame = parent;
+    reachedLimit = frame && (frame->IsBlockOutside() || IsEditingHost(frame));
+  }
+
+  if (reachedLimit) {  // no "stop frame" found
+    aPos->mResultContent = frame->GetContent();
+    if (aPos->mDirection == eDirPrevious) {
+      aPos->mContentOffset = 0;
+    } else if (aPos->mResultContent) {
+      aPos->mContentOffset = aPos->mResultContent->GetChildCount();
+    }
+  }
+  return NS_OK;
+}
+
+// Determine movement direction relative to frame
+static bool IsMovingInFrameDirection(const nsIFrame* frame,
+                                     nsDirection aDirection, bool aVisual) {
+  bool isReverseDirection =
+      aVisual && nsBidiPresUtils::IsReversedDirectionFrame(frame);
+  return aDirection == (isReverseDirection ? eDirPrevious : eDirNext);
+}
+
+// Determines "are we looking for a boundary between whitespace and
+// non-whitespace (in the direction we're moving in)". It is true when moving
+// forward and looking for a beginning of a word, or when moving backwards and
+// looking for an end of a word.
+static bool ShouldWordSelectionEatSpace(const PeekOffsetStruct& aPos) {
+  if (aPos.mWordMovementType != eDefaultBehavior) {
+    // aPos->mWordMovementType possible values:
+    //       eEndWord: eat the space if we're moving backwards
+    //       eStartWord: eat the space if we're moving forwards
+    return (aPos.mWordMovementType == eEndWord) ==
+           (aPos.mDirection == eDirPrevious);
+  }
+  // Use the hidden preference which is based on operating system
+  // behavior. This pref only affects whether moving forward by word
+  // should go to the end of this word or start of the next word. When
+  // going backwards, the start of the word is always used, on every
+  // operating system.
+  return aPos.mDirection == eDirNext &&
+         StaticPrefs::layout_word_select_eat_space_to_next_word();
+}
+
+enum class OffsetIsAtLineEdge : bool { No, Yes };
+
+static void SetPeekResultFromFrame(PeekOffsetStruct& aPos, nsIFrame* aFrame,
+                                   int32_t aOffset,
+                                   OffsetIsAtLineEdge aAtLineEdge) {
+  FrameContentRange range = GetRangeForFrame(aFrame);
+  aPos.mResultFrame = aFrame;
+  aPos.mResultContent = range.content;
+  // Output offset is relative to content, not frame
+  aPos.mContentOffset =
+      aOffset < 0 ? range.end + aOffset + 1 : range.start + aOffset;
+  if (aAtLineEdge == OffsetIsAtLineEdge::Yes) {
+    aPos.mAttach = aPos.mContentOffset == range.start
+                       ? CaretAssociationHint::After
+                       : CaretAssociationHint::Before;
+  }
+}
+
+void nsIFrame::SelectablePeekReport::TransferTo(PeekOffsetStruct& aPos) const {
+  return SetPeekResultFromFrame(aPos, mFrame, mOffset, OffsetIsAtLineEdge::No);
+}
+
+nsIFrame::SelectablePeekReport::SelectablePeekReport(
+    const mozilla::GenericErrorResult<nsresult>&& aErr) {
+  MOZ_ASSERT(NS_FAILED(aErr.operator nsresult()));
+  // Return an empty report
+}
+
+nsresult nsIFrame::PeekOffsetForCharacter(PeekOffsetStruct* aPos,
+                                          int32_t aOffset) {
+  SelectablePeekReport current{this, aOffset};
+
+  nsIFrame::FrameSearchResult peekSearchState = CONTINUE;
+
+  while (peekSearchState != FOUND) {
+    const bool movingInFrameDirection = IsMovingInFrameDirection(
+        current.mFrame, aPos->mDirection,
+        aPos->mOptions.contains(PeekOffsetOption::Visual));
+
+    if (current.mJumpedLine) {
+      // If we jumped lines, it's as if we found a character, but we still need
+      // to eat non-renderable content on the new line.
+      peekSearchState = current.PeekOffsetNoAmount(movingInFrameDirection);
+    } else {
+      PeekOffsetCharacterOptions options;
+      options.mRespectClusters = aPos->mAmount == eSelectCluster;
+      peekSearchState =
+          current.PeekOffsetCharacter(movingInFrameDirection, options);
+    }
+
+    current.mMovedOverNonSelectableText |=
+        peekSearchState == CONTINUE_UNSELECTABLE;
+
+    if (peekSearchState != FOUND) {
+      SelectablePeekReport next = current.mFrame->GetFrameFromDirection(*aPos);
+      if (next.Failed()) {
+        return NS_ERROR_FAILURE;
+      }
+      next.mJumpedLine |= current.mJumpedLine;
+      next.mMovedOverNonSelectableText |= current.mMovedOverNonSelectableText;
+      next.mHasSelectableFrame |= current.mHasSelectableFrame;
+      current = next;
+    }
+
+    // Found frame, but because we moved over non selectable text we want
+    // the offset to be at the frame edge. Note that if we are extending the
+    // selection, this doesn't matter.
+    if (peekSearchState == FOUND && current.mMovedOverNonSelectableText &&
+        (!aPos->mOptions.contains(PeekOffsetOption::Extend) ||
+         current.mHasSelectableFrame)) {
+      auto [start, end] = current.mFrame->GetOffsets();
+      current.mOffset = aPos->mDirection == eDirNext ? 0 : end - start;
+    }
+  }
+
+  // Set outputs
+  current.TransferTo(*aPos);
+  // If we're dealing with a text frame and moving backward positions us at
+  // the end of that line, decrease the offset by one to make sure that
+  // we're placed before the linefeed character on the previous line.
+  if (current.mOffset < 0 && current.mJumpedLine &&
+      aPos->mDirection == eDirPrevious &&
+      current.mFrame->HasSignificantTerminalNewline() &&
+      !current.mIgnoredBrFrame) {
+    --aPos->mContentOffset;
+  }
+  return NS_OK;
+}
+
+nsresult nsIFrame::PeekOffsetForWord(PeekOffsetStruct* aPos, int32_t aOffset) {
+  SelectablePeekReport current{this, aOffset};
+  bool shouldStopAtHardBreak =
+      aPos->mWordMovementType == eDefaultBehavior &&
+      StaticPrefs::layout_word_select_eat_space_to_next_word();
+  bool wordSelectEatSpace = ShouldWordSelectionEatSpace(*aPos);
+
+  PeekWordState state;
+  while (true) {
+    bool movingInFrameDirection = IsMovingInFrameDirection(
+        current.mFrame, aPos->mDirection,
+        aPos->mOptions.contains(PeekOffsetOption::Visual));
+
+    FrameSearchResult searchResult = current.mFrame->PeekOffsetWord(
+        movingInFrameDirection, wordSelectEatSpace,
+        aPos->mOptions.contains(PeekOffsetOption::IsKeyboardSelect),
+        &current.mOffset, &state,
+        !aPos->mOptions.contains(PeekOffsetOption::PreserveSpaces));
+    if (searchResult == FOUND) {
+      break;
+    }
+
+    SelectablePeekReport next = [&]() {
+      PeekOffsetOptions options = aPos->mOptions;
+      if (state.mSawInlineCharacter) {
+        // If we've already found a character, we don't want to stop at
+        // placeholder frame boundary if there is in the word.
+        options += PeekOffsetOption::StopAtPlaceholder;
+      }
+      return current.mFrame->GetFrameFromDirection(aPos->mDirection, options);
+    }();
+    if (next.Failed()) {
+      // If we've crossed the line boundary, check to make sure that we
+      // have not consumed a trailing newline as whitespace if it's
+      // significant.
+      if (next.mJumpedLine && wordSelectEatSpace &&
+          current.mFrame->HasSignificantTerminalNewline() &&
+          current.mFrame->StyleText()->mWhiteSpaceCollapse !=
+              StyleWhiteSpaceCollapse::PreserveBreaks) {
+        current.mOffset -= 1;
+      }
+      break;
+    }
+
+    if ((next.mJumpedLine || next.mFoundPlaceholder) && !wordSelectEatSpace &&
+        state.mSawBeforeType) {
+      // We can't jump lines if we're looking for whitespace following
+      // non-whitespace, and we already encountered non-whitespace.
+      break;
+    }
+
+    if (shouldStopAtHardBreak && next.mJumpedHardBreak) {
+      /**
+       * Prev, always: Jump and stop right there
+       * Next, saw inline: just stop
+       * Next, no inline: Jump and consume whitespaces
+       */
+      if (aPos->mDirection == eDirPrevious) {
+        // Try moving to the previous line if exists
+        current.TransferTo(*aPos);
+        current.mFrame->PeekOffsetForCharacter(aPos, current.mOffset);
+        return NS_OK;
+      }
+      if (state.mSawInlineCharacter || current.mJumpedHardBreak) {
+        if (current.mFrame->HasSignificantTerminalNewline()) {
+          current.mOffset -= 1;
+        }
+        current.TransferTo(*aPos);
+        return NS_OK;
+      }
+      // Mark the state as whitespace and continue
+      state.Update(false, true);
+    }
+
+    if (next.mJumpedLine) {
+      state.mContext.Truncate();
+    }
+    current = next;
+    // Jumping a line is equivalent to encountering whitespace
+    // This affects only when it already met an actual character
+    if (wordSelectEatSpace && next.mJumpedLine) {
+      state.SetSawBeforeType();
+    }
+  }
+
+  // Set outputs
+  current.TransferTo(*aPos);
+  return NS_OK;
+}
+
+static nsIFrame* GetFirstSelectableDescendantWithLineIterator(
+    nsIFrame* aParentFrame, bool aForceEditableRegion) {
+  auto FoundValidFrame = [aForceEditableRegion](const nsIFrame* aFrame) {
+    if (!aFrame->IsSelectable(nullptr)) {
+      return false;
+    }
+    if (aForceEditableRegion && !aFrame->GetContent()->IsEditable()) {
+      return false;
+    }
+    return true;
+  };
+
+  for (nsIFrame* child : aParentFrame->PrincipalChildList()) {
+    // some children may not be selectable, e.g. :before / :after pseudoelements
+    // content with user-select: none, or contenteditable="false"
+    // we need to skip them
+    if (child->CanProvideLineIterator() && FoundValidFrame(child)) {
+      return child;
+    }
+    if (nsIFrame* nested = GetFirstSelectableDescendantWithLineIterator(
+            child, aForceEditableRegion)) {
+      return nested;
+    }
+  }
+  return nullptr;
+}
+
+nsresult nsIFrame::PeekOffsetForLine(PeekOffsetStruct* aPos) {
+  nsIFrame* blockFrame = this;
+  nsresult result = NS_ERROR_FAILURE;
+
+  // outer loop
+  // moving to a next block when no more blocks are available in a subtree
+  AutoAssertNoDomMutations guard;
+  while (NS_FAILED(result)) {
+    auto [newBlock, lineFrame] = blockFrame->GetContainingBlockForLine(
+        aPos->mOptions.contains(PeekOffsetOption::StopAtScroller));
+    if (!newBlock) {
+      return NS_ERROR_FAILURE;
+    }
+    blockFrame = newBlock;
+    nsILineIterator* iter = blockFrame->GetLineIterator();
+    int32_t thisLine = iter->FindLineContaining(lineFrame);
+    if (NS_WARN_IF(thisLine < 0)) {
+      return NS_ERROR_FAILURE;
+    }
+
+    int8_t edgeCase = 0;  // no edge case. This should look at thisLine
+
+    // this part will find a frame or a block frame. If it's a block frame
+    // it will "drill down" to find a viable frame or it will return an
+    // error.
+    nsIFrame* lastFrame = this;
+
+    // inner loop - crawling the frames within a specific block subtree
+    while (true) {
+      result =
+          GetNextPrevLineFromBlockFrame(aPos, blockFrame, thisLine, edgeCase);
+      // we came back to same spot! keep going
+      if (NS_SUCCEEDED(result) &&
+          (!aPos->mResultFrame || aPos->mResultFrame == lastFrame)) {
+        aPos->mResultFrame = nullptr;
+        lastFrame = nullptr;
+        if (aPos->mDirection == eDirPrevious) {
+          thisLine--;
+        } else {
+          thisLine++;
+        }
+        continue;
+      }
+
+      if (NS_FAILED(result)) {
+        break;
+      }
+
+      lastFrame = aPos->mResultFrame;  // set last frame
+      /* SPECIAL CHECK FOR NAVIGATION INTO TABLES
+       * when we hit a frame which doesn't have line iterator, we need to
+       * drill down and find a child with the line iterator to prevent the
+       * crawling process to prematurely finish. Note that this is only sound if
+       * we're guaranteed to not have multiple children implementing
+       * LineIterator.
+       *
+       * So far known cases are:
+       * 1) table wrapper (drill down into table row group)
+       * 2) table cell (drill down into its only anon child)
+       */
+      const bool shouldDrillIntoChildren =
+          aPos->mResultFrame->IsTableWrapperFrame() ||
+          aPos->mResultFrame->IsTableCellFrame();
+
+      if (shouldDrillIntoChildren) {
+        nsIFrame* child = GetFirstSelectableDescendantWithLineIterator(
+            aPos->mResultFrame,
+            aPos->mOptions.contains(PeekOffsetOption::ForceEditableRegion));
+        if (child) {
+          aPos->mResultFrame = child;
+        }
+      }
+
+      if (!aPos->mResultFrame->CanProvideLineIterator()) {
+        // no more selectable content at this level
+        break;
+      }
+
+      if (aPos->mResultFrame == blockFrame) {
+        // Make sure block element is not the same as the one we had before.
+        break;
+      }
+
+      // we've struck another block element with selectable content!
+      if (aPos->mDirection == eDirPrevious) {
+        edgeCase = 1;  // far edge, search from end backwards
+      } else {
+        edgeCase = -1;  // near edge search from beginning onwards
+      }
+      thisLine = 0;  // this line means nothing now.
+      // everything else means something so keep looking "inside" the
+      // block
+      blockFrame = aPos->mResultFrame;
+    }
+  }
+  return result;
+}
+
+nsresult nsIFrame::PeekOffsetForLineEdge(PeekOffsetStruct* aPos) {
+  // Adjusted so that the caret can't get confused when content changes
+  nsIFrame* frame = AdjustFrameForSelectionStyles(this);
+  Element* editingHost = frame->GetContent()->GetEditingHost();
+
+  auto [blockFrame, lineFrame] = frame->GetContainingBlockForLine(
+      aPos->mOptions.contains(PeekOffsetOption::StopAtScroller));
+  if (!blockFrame) {
+    return NS_ERROR_FAILURE;
+  }
+  AutoAssertNoDomMutations guard;
+  nsILineIterator* it = blockFrame->GetLineIterator();
+  int32_t thisLine = it->FindLineContaining(lineFrame);
+  if (thisLine < 0) {
+    return NS_ERROR_FAILURE;
+  }
+
+  nsIFrame* baseFrame = nullptr;
+  bool endOfLine = eSelectEndLine == aPos->mAmount;
+
+  if (aPos->mOptions.contains(PeekOffsetOption::Visual) &&
+      PresContext()->BidiEnabled()) {
+    nsIFrame* firstFrame;
+    bool isReordered;
+    nsIFrame* lastFrame;
+    MOZ_TRY(
+        it->CheckLineOrder(thisLine, &isReordered, &firstFrame, &lastFrame));
+    baseFrame = endOfLine ? lastFrame : firstFrame;
+  } else {
+    auto line = it->GetLine(thisLine).unwrap();
+
+    nsIFrame* frame = line.mFirstFrameOnLine;
+    bool lastFrameWasEditable = false;
+    for (int32_t count = line.mNumFramesOnLine; count;
+         --count, frame = frame->GetNextSibling()) {
+      if (frame->IsGeneratedContentFrame()) {
+        continue;
+      }
+      // When jumping to the end of the line with the "end" key,
+      // try to skip over brFrames
+      if (endOfLine && line.mNumFramesOnLine > 1 && frame->IsBrFrame() &&
+          lastFrameWasEditable == frame->GetContent()->IsEditable()) {
+        continue;
+      }
+      lastFrameWasEditable =
+          frame->GetContent() && frame->GetContent()->IsEditable();
+      baseFrame = frame;
+      if (!endOfLine) {
+        break;
+      }
+    }
+  }
+  if (!baseFrame) {
+    return NS_ERROR_FAILURE;
+  }
+  // Make sure we are not leaving our inline editing host if exists
+  if (editingHost) {
+    if (nsIFrame* frame = editingHost->GetPrimaryFrame()) {
+      if (frame->IsInlineOutside() &&
+          !editingHost->Contains(baseFrame->GetContent())) {
+        baseFrame = frame;
+        if (endOfLine) {
+          baseFrame = baseFrame->LastContinuation();
+        }
+      }
+    }
+  }
+  FrameTarget targetFrame = DrillDownToSelectionFrame(baseFrame, endOfLine, 0);
+  SetPeekResultFromFrame(*aPos, targetFrame.frame, endOfLine ? -1 : 0,
+                         OffsetIsAtLineEdge::Yes);
+  if (endOfLine && targetFrame.frame->HasSignificantTerminalNewline()) {
+    // Do not position the caret after the terminating newline if we're
+    // trying to move to the end of line (see bug 596506)
+    --aPos->mContentOffset;
+  }
+  if (!aPos->mResultContent) {
+    return NS_ERROR_FAILURE;
+  }
+  return NS_OK;
+}
+
+nsresult nsIFrame::PeekOffset(PeekOffsetStruct* aPos) {
+  MOZ_ASSERT(aPos);
+
+  if (NS_WARN_IF(HasAnyStateBits(NS_FRAME_IS_DIRTY))) {
+    // FIXME(Bug 1654362): <caption> currently can remain dirty.
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  // Translate content offset to be relative to frame
+  int32_t offset = aPos->mStartOffset - GetRangeForFrame(this).start;
+
+  switch (aPos->mAmount) {
+    case eSelectCharacter:
+    case eSelectCluster:
+      return PeekOffsetForCharacter(aPos, offset);
+    case eSelectWordNoSpace:
+      // eSelectWordNoSpace means that we should not be eating any whitespace
+      // when moving to the adjacent word.  This means that we should set aPos->
+      // mWordMovementType to eEndWord if we're moving forwards, and to
+      // eStartWord if we're moving backwards.
+      if (aPos->mDirection == eDirPrevious) {
+        aPos->mWordMovementType = eStartWord;
+      } else {
+        aPos->mWordMovementType = eEndWord;
+      }
+      // Intentionally fall through the eSelectWord case.
+      [[fallthrough]];
+    case eSelectWord:
+      return PeekOffsetForWord(aPos, offset);
+    case eSelectLine:
+      return PeekOffsetForLine(aPos);
+    case eSelectBeginLine:
+    case eSelectEndLine:
+      return PeekOffsetForLineEdge(aPos);
+    case eSelectParagraph:
+      return PeekOffsetForParagraph(aPos);
+    default: {
+      NS_ASSERTION(false, "Invalid amount");
+      return NS_ERROR_FAILURE;
+    }
+  }
+}
+
+nsIFrame::FrameSearchResult nsIFrame::PeekOffsetNoAmount(bool aForward,
+                                                         int32_t* aOffset) {
+  NS_ASSERTION(aOffset && *aOffset <= 1, "aOffset out of range");
+  // Sure, we can stop right here.
+  return FOUND;
+}
+
+nsIFrame::FrameSearchResult nsIFrame::PeekOffsetCharacter(
+    bool aForward, int32_t* aOffset, PeekOffsetCharacterOptions aOptions) {
+  NS_ASSERTION(aOffset && *aOffset <= 1, "aOffset out of range");
+  int32_t startOffset = *aOffset;
+  // A negative offset means "end of frame", which in our case means offset 1.
+  if (startOffset < 0) startOffset = 1;
+  if (aForward == (startOffset == 0)) {
+    // We're before the frame and moving forward, or after it and moving
+    // backwards: skip to the other side and we're done.
+    *aOffset = 1 - startOffset;
+    return FOUND;
+  }
+  return CONTINUE;
+}
+
+nsIFrame::FrameSearchResult nsIFrame::PeekOffsetWord(
+    bool aForward, bool aWordSelectEatSpace, bool aIsKeyboardSelect,
+    int32_t* aOffset, PeekWordState* aState, bool /*aTrimSpaces*/) {
+  NS_ASSERTION(aOffset && *aOffset <= 1, "aOffset out of range");
+  int32_t startOffset = *aOffset;
+  // This isn't text, so truncate the context
+  aState->mContext.Truncate();
+  if (startOffset < 0) startOffset = 1;
+  if (aForward == (startOffset == 0)) {
+    // We're before the frame and moving forward, or after it and moving
+    // backwards. If we're looking for non-whitespace, we found it (without
+    // skipping this frame).
+    if (!aState->mAtStart) {
+      if (aState->mLastCharWasPunctuation) {
+        // We're not punctuation, so this is a punctuation boundary.
+        if (BreakWordBetweenPunctuation(aState, aForward, false, false,
+                                        aIsKeyboardSelect))
+          return FOUND;
+      } else {
+        // This is not a punctuation boundary.
+        if (aWordSelectEatSpace && aState->mSawBeforeType) return FOUND;
+      }
+    }
+    // Otherwise skip to the other side and note that we encountered
+    // non-whitespace.
+    *aOffset = 1 - startOffset;
+    aState->Update(false,  // not punctuation
+                   false   // not whitespace
+    );
+    if (!aWordSelectEatSpace) aState->SetSawBeforeType();
+  }
+  return CONTINUE;
+}
+
+// static
+bool nsIFrame::BreakWordBetweenPunctuation(const PeekWordState* aState,
+                                           bool aForward, bool aPunctAfter,
+                                           bool aWhitespaceAfter,
+                                           bool aIsKeyboardSelect) {
+  NS_ASSERTION(aPunctAfter != aState->mLastCharWasPunctuation,
+               "Call this only at punctuation boundaries");
+  if (aState->mLastCharWasWhitespace) {
+    // We always stop between whitespace and punctuation
+    return true;
+  }
+  if (!StaticPrefs::layout_word_select_stop_at_punctuation()) {
+    // When this pref is false, we never stop at a punctuation boundary unless
+    // it's followed by whitespace (in the relevant direction).
+    return aWhitespaceAfter;
+  }
+  if (!aIsKeyboardSelect) {
+    // mouse caret movement (e.g. word selection) always stops at every
+    // punctuation boundary
+    return true;
+  }
+  bool afterPunct = aForward ? aState->mLastCharWasPunctuation : aPunctAfter;
+  if (!afterPunct) {
+    // keyboard caret movement only stops after punctuation (in content order)
+    return false;
+  }
+  // Stop only if we've seen some non-punctuation since the last whitespace;
+  // don't stop after punctuation that follows whitespace.
+  return aState->mSeenNonPunctuationSinceWhitespace;
+}
+
+std::pair<nsIFrame*, nsIFrame*> nsIFrame::GetContainingBlockForLine(
+    bool aLockScroll) const {
+  const nsIFrame* parentFrame = this;
+  const nsIFrame* frame;
+  while (parentFrame) {
+    frame = parentFrame;
+    if (frame->HasAnyStateBits(NS_FRAME_OUT_OF_FLOW)) {
+      // if we are searching for a frame that is not in flow we will not find
+      // it. we must instead look for its placeholder
+      if (frame->HasAnyStateBits(NS_FRAME_IS_OVERFLOW_CONTAINER)) {
+        // abspos continuations don't have placeholders, get the fif
+        frame = frame->FirstInFlow();
+      }
+      frame = frame->GetPlaceholderFrame();
+      if (!frame) {
+        return std::pair(nullptr, nullptr);
+      }
+    }
+    parentFrame = frame->GetParent();
+    if (parentFrame) {
+      if (aLockScroll && parentFrame->IsScrollFrame()) {
+        return std::pair(nullptr, nullptr);
+      }
+      if (parentFrame->CanProvideLineIterator()) {
+        return std::pair(const_cast<nsIFrame*>(parentFrame),
+                         const_cast<nsIFrame*>(frame));
+      }
+    }
+  }
+  return std::pair(nullptr, nullptr);
+}
+
+Result<bool, nsresult> nsIFrame::IsVisuallyAtLineEdge(
+    nsILineIterator* aLineIterator, int32_t aLine, nsDirection aDirection) {
+  auto line = aLineIterator->GetLine(aLine).unwrap();
+
+  const bool lineIsRTL = aLineIterator->IsLineIteratorFlowRTL();
+
+  nsIFrame *firstFrame = nullptr, *lastFrame = nullptr;
+  bool isReordered = false;
+  MOZ_TRY(aLineIterator->CheckLineOrder(aLine, &isReordered, &firstFrame,
+                                        &lastFrame));
+  if (!firstFrame || !lastFrame) {
+    return true;  // XXX: Why true?  We check whether `this` is at the edge...
+  }
+
+  nsIFrame* leftmostFrame = lineIsRTL ? lastFrame : firstFrame;
+  nsIFrame* rightmostFrame = lineIsRTL ? firstFrame : lastFrame;
+  auto FrameIsRTL = [](nsIFrame* aFrame) {
+    return nsBidiPresUtils::FrameDirection(aFrame) ==
+           mozilla::intl::BidiDirection::RTL;
+  };
+  if (!lineIsRTL == (aDirection == eDirPrevious)) {
+    nsIFrame* maybeLeftmostFrame = leftmostFrame;
+    for ([[maybe_unused]] int32_t i : IntegerRange(line.mNumFramesOnLine)) {
+      if (maybeLeftmostFrame == this) {
+        return true;
+      }
+      // If left edge of the line starts with placeholder frames, we can ignore
+      // them and should keep checking the following frames.
+      if (!maybeLeftmostFrame->IsPlaceholderFrame()) {
+        if ((FrameIsRTL(maybeLeftmostFrame) == lineIsRTL) ==
+            (aDirection == eDirPrevious)) {
+          nsIFrame::GetFirstLeaf(&maybeLeftmostFrame);
+        } else {
+          nsIFrame::GetLastLeaf(&maybeLeftmostFrame);
+        }
+        return maybeLeftmostFrame == this;
+      }
+      maybeLeftmostFrame = nsBidiPresUtils::GetFrameToRightOf(
+          maybeLeftmostFrame, line.mFirstFrameOnLine, line.mNumFramesOnLine);
+      if (!maybeLeftmostFrame) {
+        return false;
+      }
+    }
+    return false;
+  }
+
+  nsIFrame* maybeRightmostFrame = rightmostFrame;
+  for ([[maybe_unused]] int32_t i : IntegerRange(line.mNumFramesOnLine)) {
+    if (maybeRightmostFrame == this) {
+      return true;
+    }
+    // If the line ends with placehlder frames, we can ignore them and should
+    // keep checking the preceding frames.
+    if (!maybeRightmostFrame->IsPlaceholderFrame()) {
+      if ((FrameIsRTL(maybeRightmostFrame) == lineIsRTL) ==
+          (aDirection == eDirPrevious)) {
+        nsIFrame::GetFirstLeaf(&maybeRightmostFrame);
+      } else {
+        nsIFrame::GetLastLeaf(&maybeRightmostFrame);
+      }
+      return maybeRightmostFrame == this;
+    }
+    maybeRightmostFrame = nsBidiPresUtils::GetFrameToLeftOf(
+        maybeRightmostFrame, line.mFirstFrameOnLine, line.mNumFramesOnLine);
+    if (!maybeRightmostFrame) {
+      return false;
+    }
+  }
+  return false;
+}
+
+Result<bool, nsresult> nsIFrame::IsLogicallyAtLineEdge(
+    nsILineIterator* aLineIterator, int32_t aLine, nsDirection aDirection) {
+  auto line = aLineIterator->GetLine(aLine).unwrap();
+  if (!line.mNumFramesOnLine) {
+    return false;
+  }
+  MOZ_ASSERT(line.mFirstFrameOnLine);
+
+  if (aDirection == eDirPrevious) {
+    nsIFrame* maybeFirstFrame = line.mFirstFrameOnLine;
+    for ([[maybe_unused]] int32_t i : IntegerRange(line.mNumFramesOnLine)) {
+      if (maybeFirstFrame == this) {
+        return true;
+      }
+      // If the line starts with placeholder frames, we can ignore them and
+      // should keep checking the following frames.
+      if (!maybeFirstFrame->IsPlaceholderFrame()) {
+        nsIFrame::GetFirstLeaf(&maybeFirstFrame);
+        return maybeFirstFrame == this;
+      }
+      maybeFirstFrame = maybeFirstFrame->GetNextSibling();
+      if (!maybeFirstFrame) {
+        return false;
+      }
+    }
+    return false;
+  }
+
+  // eDirNext
+  nsIFrame* maybeLastFrame = line.GetLastFrameOnLine();
+  for ([[maybe_unused]] int32_t i : IntegerRange(line.mNumFramesOnLine)) {
+    if (maybeLastFrame == this) {
+      return true;
+    }
+    // If the line ends with placehlder frames, we can ignore them and should
+    // keep checking the preceding frames.
+    if (!maybeLastFrame->IsPlaceholderFrame()) {
+      nsIFrame::GetLastLeaf(&maybeLastFrame);
+      return maybeLastFrame == this;
+    }
+    maybeLastFrame = maybeLastFrame->GetPrevSibling();
+  }
+  return false;
+}
+
+nsIFrame::SelectablePeekReport nsIFrame::GetFrameFromDirection(
+    nsDirection aDirection, const PeekOffsetOptions& aOptions) {
+  SelectablePeekReport result;
+
+  nsPresContext* presContext = PresContext();
+  const bool needsVisualTraversal =
+      aOptions.contains(PeekOffsetOption::Visual) && presContext->BidiEnabled();
+  const bool followOofs =
+      !aOptions.contains(PeekOffsetOption::StopAtPlaceholder);
+  nsFrameIterator frameIterator(
+      presContext, this, nsFrameIterator::Type::Leaf, needsVisualTraversal,
+      aOptions.contains(PeekOffsetOption::StopAtScroller), followOofs,
+      false  // aSkipPopupChecks
+  );
+
+  // Find the prev/next selectable frame
+  bool selectable = false;
+  nsIFrame* traversedFrame = this;
+  AutoAssertNoDomMutations guard;
+  const nsIContent* const nativeAnonymousSubtreeContent =
+      GetClosestNativeAnonymousSubtreeRoot();
+  while (!selectable) {
+    auto [blockFrame, lineFrame] = traversedFrame->GetContainingBlockForLine(
+        aOptions.contains(PeekOffsetOption::StopAtScroller));
+    if (!blockFrame) {
+      return result;
+    }
+
+    nsILineIterator* it = blockFrame->GetLineIterator();
+    int32_t thisLine = it->FindLineContaining(lineFrame);
+    if (thisLine < 0) {
+      return result;
+    }
+
+    bool atLineEdge;
+    MOZ_TRY_VAR(
+        atLineEdge,
+        needsVisualTraversal
+            ? traversedFrame->IsVisuallyAtLineEdge(it, thisLine, aDirection)
+            : traversedFrame->IsLogicallyAtLineEdge(it, thisLine, aDirection));
+    if (atLineEdge) {
+      result.mJumpedLine = true;
+      if (!aOptions.contains(PeekOffsetOption::JumpLines)) {
+        return result;  // we are done. cannot jump lines
+      }
+      int32_t lineToCheckWrap =
+          aDirection == eDirPrevious ? thisLine - 1 : thisLine;
+      if (lineToCheckWrap < 0 ||
+          !it->GetLine(lineToCheckWrap).unwrap().mIsWrapped) {
+        result.mJumpedHardBreak = true;
+      }
+    }
+
+    traversedFrame = frameIterator.Traverse(aDirection == eDirNext);
+    if (!traversedFrame) {
+      return result;
+    }
+
+    if (aOptions.contains(PeekOffsetOption::StopAtPlaceholder) &&
+        traversedFrame->IsPlaceholderFrame()) {
+      // XXX If the placeholder frame does not have meaningful content, the user
+      // may want to select as a word around the out-of-flow cotent.  However,
+      // non-text frame resets context in nsIFrame::PeekOffsetWord(). Therefore,
+      // next text frame considers the new word starts from its edge. So, it's
+      // not enough to implement such behavior with adding a check here whether
+      // the real frame may change the word with its contents if it were not
+      // out-of-flow.
+      result.mFoundPlaceholder = true;
+      return result;
+    }
+
+    auto IsSelectable =
+        [aOptions, nativeAnonymousSubtreeContent](const nsIFrame* aFrame) {
+          if (!aFrame->IsSelectable(nullptr)) {
+            return false;
+          }
+          // If the new frame is in a native anonymous subtree, we should treat
+          // it as not selectable unless the frame and found frame are in same
+          // subtree.
+          if (aFrame->GetClosestNativeAnonymousSubtreeRoot() !=
+              nativeAnonymousSubtreeContent) {
+            return false;
+          }
+          return !aOptions.contains(PeekOffsetOption::ForceEditableRegion) ||
+                 aFrame->GetContent()->IsEditable();
+        };
+
+    // Skip br frames, but only if we can select something before hitting the
+    // end of the line or a non-selectable region.
+    if (atLineEdge && aDirection == eDirPrevious &&
+        traversedFrame->IsBrFrame()) {
+      for (nsIFrame* current = traversedFrame->GetPrevSibling(); current;
+           current = current->GetPrevSibling()) {
+        if (!current->IsBlockOutside() && IsSelectable(current)) {
+          if (!current->IsBrFrame()) {
+            result.mIgnoredBrFrame = true;
+          }
+          break;
+        }
+      }
+      if (result.mIgnoredBrFrame) {
+        continue;
+      }
+    }
+
+    selectable = IsSelectable(traversedFrame);
+    if (!selectable) {
+      if (traversedFrame->IsSelectable(nullptr)) {
+        result.mHasSelectableFrame = true;
+      }
+      result.mMovedOverNonSelectableText = true;
+    }
+  }  // while (!selectable)
+
+  result.mOffset = (aDirection == eDirNext) ? 0 : -1;
+
+  if (aOptions.contains(PeekOffsetOption::Visual) &&
+      nsBidiPresUtils::IsReversedDirectionFrame(traversedFrame)) {
+    // The new frame is reverse-direction, go to the other end
+    result.mOffset = -1 - result.mOffset;
+  }
+  result.mFrame = traversedFrame;
+  return result;
+}
+
+nsIFrame::SelectablePeekReport nsIFrame::GetFrameFromDirection(
+    const PeekOffsetStruct& aPos) {
+  return GetFrameFromDirection(aPos.mDirection, aPos.mOptions);
+}
+
+nsView* nsIFrame::GetClosestView(nsPoint* aOffset) const {
+  nsPoint offset(0, 0);
+  for (const nsIFrame* f = this; f; f = f->GetParent()) {
+    if (f->HasView()) {
+      if (aOffset) *aOffset = offset;
+      return f->GetView();
+    }
+    offset += f->GetPosition();
+  }
+
+  MOZ_ASSERT_UNREACHABLE("No view on any parent?  How did that happen?");
+  return nullptr;
+}
+
+/* virtual */
+void nsIFrame::ChildIsDirty(nsIFrame* aChild) {
+  MOZ_ASSERT_UNREACHABLE(
+      "should never be called on a frame that doesn't "
+      "inherit from nsContainerFrame");
+}
+
+#ifdef ACCESSIBILITY
+a11y::AccType nsIFrame::AccessibleType() {
+  if (IsTableCaption() && !GetRect().IsEmpty()) {
+    return a11y::eHTMLCaptionType;
+  }
+  return a11y::eNoType;
+}
+#endif
+
+bool nsIFrame::ClearOverflowRects() {
+  if (mOverflow.mType == OverflowStorageType::None) {
+    return false;
+  }
+  if (mOverflow.mType == OverflowStorageType::Large) {
+    RemoveProperty(OverflowAreasProperty());
+  }
+  mOverflow.mType = OverflowStorageType::None;
+  return true;
+}
+
+bool nsIFrame::SetOverflowAreas(const OverflowAreas& aOverflowAreas) {
+  if (mOverflow.mType == OverflowStorageType::Large) {
+    OverflowAreas* overflow = GetOverflowAreasProperty();
+    bool changed = *overflow != aOverflowAreas;
+    *overflow = aOverflowAreas;
+
+    // Don't bother with converting to the deltas form if we already
+    // have a property.
+    return changed;
+  }
+
+  const nsRect& vis = aOverflowAreas.InkOverflow();
+  uint32_t l = -vis.x,                 // left edge: positive delta is leftwards
+      t = -vis.y,                      // top: positive is upwards
+      r = vis.XMost() - mRect.width,   // right: positive is rightwards
+      b = vis.YMost() - mRect.height;  // bottom: positive is downwards
+  if (aOverflowAreas.ScrollableOverflow().IsEqualEdges(
+          nsRect(nsPoint(0, 0), GetSize())) &&
+      l <= InkOverflowDeltas::kMax && t <= InkOverflowDeltas::kMax &&
+      r <= InkOverflowDeltas::kMax && b <= InkOverflowDeltas::kMax &&
+      // we have to check these against zero because we *never* want to
+      // set a frame as having no overflow in this function.  This is
+      // because FinishAndStoreOverflow calls this function prior to
+      // SetRect based on whether the overflow areas match aNewSize.
+      // In the case where the overflow areas exactly match mRect but
+      // do not match aNewSize, we need to store overflow in a property
+      // so that our eventual SetRect/SetSize will know that it has to
+      // reset our overflow areas.
+      (l | t | r | b) != 0) {
+    InkOverflowDeltas oldDeltas = mOverflow.mInkOverflowDeltas;
+    // It's a "small" overflow area so we store the deltas for each edge
+    // directly in the frame, rather than allocating a separate rect.
+    // If they're all zero, that's fine; we're setting things to
+    // no-overflow.
+    mOverflow.mInkOverflowDeltas.mLeft = l;
+    mOverflow.mInkOverflowDeltas.mTop = t;
+    mOverflow.mInkOverflowDeltas.mRight = r;
+    mOverflow.mInkOverflowDeltas.mBottom = b;
+    // There was no scrollable overflow before, and there isn't now.
+    return oldDeltas != mOverflow.mInkOverflowDeltas;
+  } else {
+    bool changed =
+        !aOverflowAreas.ScrollableOverflow().IsEqualEdges(
+            nsRect(nsPoint(0, 0), GetSize())) ||
+        !aOverflowAreas.InkOverflow().IsEqualEdges(InkOverflowFromDeltas());
+
+    // it's a large overflow area that we need to store as a property
+    mOverflow.mType = OverflowStorageType::Large;
+    AddProperty(OverflowAreasProperty(), new OverflowAreas(aOverflowAreas));
+    return changed;
+  }
+}
+
+enum class ApplyTransform : bool { No, Yes };
+
+/**
+ * Compute the outline inner rect (so without outline-width and outline-offset)
+ * of aFrame, maybe iterating over its descendants, in aFrame's coordinate space
+ * or its post-transform coordinate space (depending on aApplyTransform).
+ */
+static nsRect ComputeOutlineInnerRect(
+    nsIFrame* aFrame, ApplyTransform aApplyTransform, bool& aOutValid,
+    const nsSize* aSizeOverride = nullptr,
+    const OverflowAreas* aOverflowOverride = nullptr) {
+  const nsRect bounds(nsPoint(0, 0),
+                      aSizeOverride ? *aSizeOverride : aFrame->GetSize());
+
+  // The SVG container frames besides SVGTextFrame do not maintain
+  // an accurate mRect. It will make the outline be larger than
+  // we expect, we need to make them narrow to their children's outline.
+  // aOutValid is set to false if the returned nsRect is not valid
+  // and should not be included in the outline rectangle.
+  aOutValid = !aFrame->HasAnyStateBits(NS_FRAME_SVG_LAYOUT) ||
+              !aFrame->IsSVGContainerFrame() || aFrame->IsSVGTextFrame();
+
+  nsRect u;
+
+  if (!aFrame->FrameMaintainsOverflow()) {
+    return u;
+  }
+
+  // Start from our border-box, transformed.  See comment below about
+  // transform of children.
+  bool doTransform =
+      aApplyTransform == ApplyTransform::Yes && aFrame->IsTransformed();
+  TransformReferenceBox boundsRefBox(nullptr, bounds);
+  if (doTransform) {
+    u = nsDisplayTransform::TransformRect(bounds, aFrame, boundsRefBox);
+  } else {
+    u = bounds;
+  }
+
+  if (aOutValid && !StaticPrefs::layout_outline_include_overflow()) {
+    return u;
+  }
+
+  // Only iterate through the children if the overflow areas suggest
+  // that we might need to, and if the frame doesn't clip its overflow
+  // anyway.
+  if (aOverflowOverride) {
+    if (!doTransform && bounds.IsEqualEdges(aOverflowOverride->InkOverflow()) &&
+        bounds.IsEqualEdges(aOverflowOverride->ScrollableOverflow())) {
+      return u;
+    }
+  } else {
+    if (!doTransform && bounds.IsEqualEdges(aFrame->InkOverflowRect()) &&
+        bounds.IsEqualEdges(aFrame->ScrollableOverflowRect())) {
+      return u;
+    }
+  }
+  const nsStyleDisplay* disp = aFrame->StyleDisplay();
+  LayoutFrameType fType = aFrame->Type();
+  if (fType == LayoutFrameType::Scroll ||
+      fType == LayoutFrameType::ListControl ||
+      fType == LayoutFrameType::SVGOuterSVG) {
+    return u;
+  }
+
+  auto overflowClipAxes = aFrame->ShouldApplyOverflowClipping(disp);
+  auto overflowClipMargin = aFrame->OverflowClipMargin(overflowClipAxes);
+  if (overflowClipAxes == nsIFrame::PhysicalAxes::Both &&
+      overflowClipMargin == nsSize()) {
+    return u;
+  }
+
+  const nsStyleEffects* effects = aFrame->StyleEffects();
+  Maybe<nsRect> clipPropClipRect =
+      aFrame->GetClipPropClipRect(disp, effects, bounds.Size());
+
+  // Iterate over all children except pop-up, absolutely-positioned,
+  // float, and overflow ones.
+  const FrameChildListIDs skip = {
+      FrameChildListID::Popup, FrameChildListID::Absolute,
+      FrameChildListID::Fixed, FrameChildListID::Float,
+      FrameChildListID::Overflow};
+  for (const auto& [list, listID] : aFrame->ChildLists()) {
+    if (skip.contains(listID)) {
+      continue;
+    }
+
+    for (nsIFrame* child : list) {
+      if (child->IsPlaceholderFrame()) {
+        continue;
+      }
+
+      // Note that passing ApplyTransform::Yes when
+      // child->Combines3DTransformWithAncestors() returns true is incorrect if
+      // our aApplyTransform is No... but the opposite would be as well.
+      // This is because elements within a preserve-3d scene are always
+      // transformed up to the top of the scene.  This means we don't have a
+      // mechanism for getting a transform up to an intermediate point within
+      // the scene.  We choose to over-transform rather than under-transform
+      // because this is consistent with other overflow areas.
+      bool validRect = true;
+      nsRect childRect =
+          ComputeOutlineInnerRect(child, ApplyTransform::Yes, validRect) +
+          child->GetPosition();
+
+      if (!validRect) {
+        continue;
+      }
+
+      if (clipPropClipRect) {
+        // Intersect with the clip before transforming.
+        childRect.IntersectRect(childRect, *clipPropClipRect);
+      }
+
+      // Note that we transform each child separately according to
+      // aFrame's transform, and then union, which gives a different
+      // (smaller) result from unioning and then transforming the
+      // union.  This doesn't match the way we handle overflow areas
+      // with 2-D transforms, though it does match the way we handle
+      // overflow areas in preserve-3d 3-D scenes.
+      if (doTransform && !child->Combines3DTransformWithAncestors()) {
+        childRect =
+            nsDisplayTransform::TransformRect(childRect, aFrame, boundsRefBox);
+      }
+
+      // If a SVGContainer has a non-SVGContainer child, we assign
+      // its child's outline to this SVGContainer directly.
+      if (!aOutValid && validRect) {
+        u = childRect;
+        aOutValid = true;
+      } else {
+        u = u.UnionEdges(childRect);
+      }
+    }
+  }
+
+  if (overflowClipAxes != nsIFrame::PhysicalAxes::None) {
+    OverflowAreas::ApplyOverflowClippingOnRect(u, bounds, overflowClipAxes,
+                                               overflowClipMargin);
+  }
+  return u;
+}
+
+static void ComputeAndIncludeOutlineArea(nsIFrame* aFrame,
+                                         OverflowAreas& aOverflowAreas,
+                                         const nsSize& aNewSize) {
+  const nsStyleOutline* outline = aFrame->StyleOutline();
+  if (!outline->ShouldPaintOutline()) {
+    return;
+  }
+
+  // When the outline property is set on a :-moz-block-inside-inline-wrapper
+  // pseudo-element, it inherited that outline from the inline that was broken
+  // because it contained a block.  In that case, we don't want a really wide
+  // outline if the block inside the inline is narrow, so union the actual
+  // contents of the anonymous blocks.
+  nsIFrame* frameForArea = aFrame;
+  do {
+    PseudoStyleType pseudoType = frameForArea->Style()->GetPseudoType();
+    if (pseudoType != PseudoStyleType::mozBlockInsideInlineWrapper) break;
+    // If we're done, we really want it and all its later siblings.
+    frameForArea = frameForArea->PrincipalChildList().FirstChild();
+    NS_ASSERTION(frameForArea, "anonymous block with no children?");
+  } while (frameForArea);
+
+  // Find the union of the border boxes of all descendants, or in
+  // the block-in-inline case, all descendants we care about.
+  //
+  // Note that the interesting perspective-related cases are taken
+  // care of by the code that handles those issues for overflow
+  // calling FinishAndStoreOverflow again, which in turn calls this
+  // function again.  We still need to deal with preserve-3d a bit.
+  nsRect innerRect;
+  bool validRect = false;
+  if (frameForArea == aFrame) {
+    innerRect = ComputeOutlineInnerRect(aFrame, ApplyTransform::No, validRect,
+                                        &aNewSize, &aOverflowAreas);
+  } else {
+    for (; frameForArea; frameForArea = frameForArea->GetNextSibling()) {
+      nsRect r =
+          ComputeOutlineInnerRect(frameForArea, ApplyTransform::Yes, validRect);
+
+      // Adjust for offsets transforms up to aFrame's pre-transform
+      // (i.e., normal) coordinate space; see comments in
+      // UnionBorderBoxes for some of the subtlety here.
+      for (nsIFrame *f = frameForArea, *parent = f->GetParent();
+           /* see middle of loop */; f = parent, parent = f->GetParent()) {
+        r += f->GetPosition();
+        if (parent == aFrame) {
+          break;
+        }
+        if (parent->IsTransformed() && !f->Combines3DTransformWithAncestors()) {
+          TransformReferenceBox refBox(parent);
+          r = nsDisplayTransform::TransformRect(r, parent, refBox);
+        }
+      }
+
+      innerRect.UnionRect(innerRect, r);
+    }
+  }
+
+  // Keep this code in sync with nsDisplayOutline::GetInnerRect.
+  if (innerRect == aFrame->GetRectRelativeToSelf()) {
+    aFrame->RemoveProperty(nsIFrame::OutlineInnerRectProperty());
+  } else {
+    SetOrUpdateRectValuedProperty(aFrame, nsIFrame::OutlineInnerRectProperty(),
+                                  innerRect);
+  }
+
+  nsRect outerRect(innerRect);
+  outerRect.Inflate(outline->EffectiveOffsetFor(outerRect));
+
+  if (outline->mOutlineStyle.IsAuto()) {
+    nsPresContext* pc = aFrame->PresContext();
+
+    pc->Theme()->GetWidgetOverflow(pc->DeviceContext(), aFrame,
+                                   StyleAppearance::FocusOutline, &outerRect);
+  } else {
+    const nscoord width = outline->GetOutlineWidth();
+    outerRect.Inflate(width);
+  }
+
+  nsRect& vo = aOverflowAreas.InkOverflow();
+  vo = vo.UnionEdges(innerRect.Union(outerRect));
+}
+
+bool nsIFrame::FinishAndStoreOverflow(OverflowAreas& aOverflowAreas,
+                                      nsSize aNewSize, nsSize* aOldSize,
+                                      const nsStyleDisplay* aStyleDisplay) {
+  MOZ_ASSERT(FrameMaintainsOverflow(),
+             "Don't call - overflow rects not maintained on these SVG frames");
+
+  const nsStyleDisplay* disp = StyleDisplayWithOptionalParam(aStyleDisplay);
+  bool hasTransform = IsTransformed();
+
+  nsRect bounds(nsPoint(0, 0), aNewSize);
+  // Store the passed in overflow area if we are a preserve-3d frame or we have
+  // a transform, and it's not just the frame bounds.
+  if (hasTransform || Combines3DTransformWithAncestors()) {
+    if (!aOverflowAreas.InkOverflow().IsEqualEdges(bounds) ||
+        !aOverflowAreas.ScrollableOverflow().IsEqualEdges(bounds)) {
+      OverflowAreas* initial = GetProperty(nsIFrame::InitialOverflowProperty());
+      if (!initial) {
+        AddProperty(nsIFrame::InitialOverflowProperty(),
+                    new OverflowAreas(aOverflowAreas));
+      } else if (initial != &aOverflowAreas) {
+        *initial = aOverflowAreas;
+      }
+    } else {
+      RemoveProperty(nsIFrame::InitialOverflowProperty());
+    }
+#ifdef DEBUG
+    SetProperty(nsIFrame::DebugInitialOverflowPropertyApplied(), true);
+#endif
+  } else {
+#ifdef DEBUG
+    RemoveProperty(nsIFrame::DebugInitialOverflowPropertyApplied());
+#endif
+  }
+
+  nsSize oldSize = mRect.Size();
+  bool sizeChanged = ((aOldSize ? *aOldSize : oldSize) != aNewSize);
+
+  // Our frame size may not have been computed and set yet, but code under
+  // functions such as ComputeEffectsRect (which we're about to call) use the
+  // values that are stored in our frame rect to compute their results.  We
+  // need the results from those functions to be based on the frame size that
+  // we *will* have, so we temporarily set our frame size here before calling
+  // those functions.
+  //
+  // XXX Someone should document here why we revert the frame size before we
+  // return rather than just leaving it set.
+  //
+  // We pass false here to avoid invalidating display items for this temporary
+  // change. We sometimes reflow frames multiple times, with the final size
+  // being the same as the initial. The single call to SetSize after reflow is
+  // done will take care of invalidating display items if the size has actually
+  // changed.
+  SetSize(aNewSize, false);
+
+  const auto overflowClipAxes = ShouldApplyOverflowClipping(disp);
+
+  if (ChildrenHavePerspective(disp) && sizeChanged) {
+    RecomputePerspectiveChildrenOverflow(this);
+
+    if (overflowClipAxes != PhysicalAxes::Both) {
+      aOverflowAreas.SetAllTo(bounds);
+      DebugOnly<bool> ok = ComputeCustomOverflow(aOverflowAreas);
+
+      // ComputeCustomOverflow() should not return false, when
+      // FrameMaintainsOverflow() returns true.
+      MOZ_ASSERT(ok, "FrameMaintainsOverflow() != ComputeCustomOverflow()");
+
+      UnionChildOverflow(aOverflowAreas);
+    }
+  }
+
+  // This is now called FinishAndStoreOverflow() instead of
+  // StoreOverflow() because frame-generic ways of adding overflow
+  // can happen here, e.g. CSS2 outline and native theme.
+  // If the overflow area width or height is nscoord_MAX, then a saturating
+  // union may have encountered an overflow, so the overflow may not contain the
+  // frame border-box. Don't warn in that case.
+  // Don't warn for SVG either, since SVG doesn't need the overflow area
+  // to contain the frame bounds.
+#ifdef DEBUG
+  for (const auto otype : AllOverflowTypes()) {
+    const nsRect& r = aOverflowAreas.Overflow(otype);
+    NS_ASSERTION(aNewSize.width == 0 || aNewSize.height == 0 ||
+                     r.width == nscoord_MAX || r.height == nscoord_MAX ||
+                     HasAnyStateBits(NS_FRAME_SVG_LAYOUT) ||
+                     r.Contains(nsRect(nsPoint(), aNewSize)),
+                 "Computed overflow area must contain frame bounds");
+  }
+#endif
+
+  // Overflow area must always include the frame's top-left and bottom-right,
+  // even if the frame rect is empty (so we can scroll to those positions).
+  const bool shouldIncludeBounds = [&] {
+    if (aNewSize.width == 0 && IsInlineFrame()) {
+      // Pending a real fix for bug 426879, don't do this for inline frames with
+      // zero width.
+      return false;
+    }
+    if (HasAnyStateBits(NS_FRAME_SVG_LAYOUT)) {
+      // Do not do this for SVG either, since it will usually massively increase
+      // the area unnecessarily (except for SVG that applies clipping, since
+      // that's the pre-existing behavior, and breaks pre-rendering otherwise).
+      // FIXME(bug 1770704): This check most likely wants to be removed or check
+      // for specific frame types at least.
+      return overflowClipAxes != PhysicalAxes::None;
+    }
+    return true;
+  }();
+
+  if (shouldIncludeBounds) {
+    for (const auto otype : AllOverflowTypes()) {
+      nsRect& o = aOverflowAreas.Overflow(otype);
+      o = o.UnionEdges(bounds);
+    }
+  }
+
+  // If we clip our children, clear accumulated overflow area in the affected
+  // dimension(s). The children are actually clipped to the padding-box, but
+  // since the overflow area should include the entire border-box, just set it
+  // to the border-box size here.
+  if (overflowClipAxes != PhysicalAxes::None) {
+    aOverflowAreas.ApplyClipping(bounds, overflowClipAxes,
+                                 OverflowClipMargin(overflowClipAxes));
+  }
+
+  ComputeAndIncludeOutlineArea(this, aOverflowAreas, aNewSize);
+
+  // Nothing in here should affect scrollable overflow.
+  aOverflowAreas.InkOverflow() =
+      ComputeEffectsRect(this, aOverflowAreas.InkOverflow(), aNewSize);
+
+  // Absolute position clipping
+  const nsStyleEffects* effects = StyleEffects();
+  Maybe<nsRect> clipPropClipRect = GetClipPropClipRect(disp, effects, aNewSize);
+  if (clipPropClipRect) {
+    for (const auto otype : AllOverflowTypes()) {
+      nsRect& o = aOverflowAreas.Overflow(otype);
+      o.IntersectRect(o, *clipPropClipRect);
+    }
+  }
+
+  /* If we're transformed, transform the overflow rect by the current
+   * transformation. */
+  if (hasTransform) {
+    SetProperty(nsIFrame::PreTransformOverflowAreasProperty(),
+                new OverflowAreas(aOverflowAreas));
+
+    if (Combines3DTransformWithAncestors()) {
+      /* If we're a preserve-3d leaf frame, then our pre-transform overflow
+       * should be correct. Our post-transform overflow is empty though, because
+       * we only contribute to the overflow area of the preserve-3d root frame.
+       * If we're an intermediate frame then the pre-transform overflow should
+       * contain all our non-preserve-3d children, which is what we want. Again
+       * we have no post-transform overflow.
+       */
+      aOverflowAreas.SetAllTo(nsRect());
+    } else {
+      TransformReferenceBox refBox(this);
+      for (const auto otype : AllOverflowTypes()) {
+        nsRect& o = aOverflowAreas.Overflow(otype);
+        o = nsDisplayTransform::TransformRect(o, this, refBox);
+      }
+
+      /* If we're the root of the 3d context, then we want to include the
+       * overflow areas of all the participants. This won't have happened yet as
+       * the code above set their overflow area to empty. Manually collect these
+       * overflow areas now.
+       */
+      if (Extend3DContext(disp, effects)) {
+        ComputePreserve3DChildrenOverflow(aOverflowAreas);
+      }
+    }
+  } else {
+    RemoveProperty(nsIFrame::PreTransformOverflowAreasProperty());
+  }
+
+  /* Revert the size change in case some caller is depending on this. */
+  SetSize(oldSize, false);
+
+  bool anyOverflowChanged;
+  if (aOverflowAreas != OverflowAreas(bounds, bounds)) {
+    anyOverflowChanged = SetOverflowAreas(aOverflowAreas);
+  } else {
+    anyOverflowChanged = ClearOverflowRects();
+  }
+
+  if (anyOverflowChanged) {
+    SVGObserverUtils::InvalidateDirectRenderingObservers(this);
+    if (nsBlockFrame* block = do_QueryFrame(this)) {
+      // NOTE(emilio): we need to use BeforeReflow::Yes, because we want to
+      // invalidate in cases where we _used_ to have an overflow marker and no
+      // longer do.
+      if (TextOverflow::CanHaveOverflowMarkers(
+              block, TextOverflow::BeforeReflow::Yes)) {
+        DiscardDisplayItems(this, [](nsDisplayItem* aItem) {
+          return aItem->GetType() == DisplayItemType::TYPE_TEXT_OVERFLOW;
+        });
+        SchedulePaint(PAINT_DEFAULT);
+      }
+    }
+  }
+  return anyOverflowChanged;
+}
+
+void nsIFrame::RecomputePerspectiveChildrenOverflow(
+    const nsIFrame* aStartFrame) {
+  for (const auto& childList : ChildLists()) {
+    for (nsIFrame* child : childList.mList) {
+      if (!child->FrameMaintainsOverflow()) {
+        continue;  // frame does not maintain overflow rects
+      }
+      if (child->HasPerspective()) {
+        OverflowAreas* overflow =
+            child->GetProperty(nsIFrame::InitialOverflowProperty());
+        nsRect bounds(nsPoint(0, 0), child->GetSize());
+        if (overflow) {
+          OverflowAreas overflowCopy = *overflow;
+          child->FinishAndStoreOverflow(overflowCopy, bounds.Size());
+        } else {
+          OverflowAreas boundsOverflow;
+          boundsOverflow.SetAllTo(bounds);
+          child->FinishAndStoreOverflow(boundsOverflow, bounds.Size());
+        }
+      } else if (child->GetContent() == aStartFrame->GetContent() ||
+                 child->GetClosestFlattenedTreeAncestorPrimaryFrame() ==
+                     aStartFrame) {
+        // If a frame is using perspective, then the size used to compute
+        // perspective-origin is the size of the frame belonging to its parent
+        // style. We must find any descendant frames using our size
+        // (by recursing into frames that have the same containing block)
+        // to update their overflow rects too.
+        child->RecomputePerspectiveChildrenOverflow(aStartFrame);
+      }
+    }
+  }
+}
+
+void nsIFrame::ComputePreserve3DChildrenOverflow(
+    OverflowAreas& aOverflowAreas) {
+  // Find all descendants that participate in the 3d context, and include their
+  // overflow. These descendants have an empty overflow, so won't have been
+  // included in the normal overflow calculation. Any children that don't
+  // participate have normal overflow, so will have been included already.
+
+  nsRect childVisual;
+  nsRect childScrollable;
+  for (const auto& childList : ChildLists()) {
+    for (nsIFrame* child : childList.mList) {
+      // If this child participates in the 3d context, then take the
+      // pre-transform region (which contains all descendants that aren't
+      // participating in the 3d context) and transform it into the 3d context
+      // root coordinate space.
+      if (child->Combines3DTransformWithAncestors()) {
+        OverflowAreas childOverflow = child->GetOverflowAreasRelativeToSelf();
+        TransformReferenceBox refBox(child);
+        for (const auto otype : AllOverflowTypes()) {
+          nsRect& o = childOverflow.Overflow(otype);
+          o = nsDisplayTransform::TransformRect(o, child, refBox);
+        }
+
+        aOverflowAreas.UnionWith(childOverflow);
+
+        // If this child also extends the 3d context, then recurse into it
+        // looking for more participants.
+        if (child->Extend3DContext()) {
+          child->ComputePreserve3DChildrenOverflow(aOverflowAreas);
+        }
+      }
+    }
+  }
+}
+
+bool nsIFrame::ZIndexApplies() const {
+  return StyleDisplay()->IsPositionedStyle() || IsFlexOrGridItem() ||
+         IsMenuPopupFrame();
+}
+
+Maybe<int32_t> nsIFrame::ZIndex() const {
+  if (!ZIndexApplies()) {
+    return Nothing();
+  }
+  const auto& zIndex = StylePosition()->mZIndex;
+  if (zIndex.IsAuto()) {
+    return Nothing();
+  }
+  return Some(zIndex.AsInteger());
+}
+
+bool nsIFrame::IsScrollAnchor(ScrollAnchorContainer** aOutContainer) {
+  if (!mInScrollAnchorChain) {
+    return false;
+  }
+
+  nsIFrame* f = this;
+
+  // FIXME(emilio, bug 1629280): We should find a non-null anchor if we have the
+  // flag set, but bug 1629280 makes it so that we cannot really assert it /
+  // make this just a `while (true)`, and uncomment the below assertion.
+  while (auto* container = ScrollAnchorContainer::FindFor(f)) {
+    // MOZ_ASSERT(f->IsInScrollAnchorChain());
+    if (nsIFrame* anchor = container->AnchorNode()) {
+      if (anchor != this) {
+        return false;
+      }
+      if (aOutContainer) {
+        *aOutContainer = container;
+      }
+      return true;
+    }
+
+    f = container->Frame();
+  }
+
+  return false;
+}
+
+bool nsIFrame::IsInScrollAnchorChain() const { return mInScrollAnchorChain; }
+
+void nsIFrame::SetInScrollAnchorChain(bool aInChain) {
+  mInScrollAnchorChain = aInChain;
+}
+
+uint32_t nsIFrame::GetDepthInFrameTree() const {
+  uint32_t result = 0;
+  for (nsContainerFrame* ancestor = GetParent(); ancestor;
+       ancestor = ancestor->GetParent()) {
+    result++;
+  }
+  return result;
+}
+
+/**
+ * This function takes a frame that is part of a block-in-inline split,
+ * and _if_ that frame is an anonymous block created by an ib split it
+ * returns the block's preceding inline.  This is needed because the
+ * split inline's style is the parent of the anonymous block's style.
+ *
+ * If aFrame is not an anonymous block, null is returned.
+ */
+static nsIFrame* GetIBSplitSiblingForAnonymousBlock(const nsIFrame* aFrame) {
+  MOZ_ASSERT(aFrame, "Must have a non-null frame!");
+  NS_ASSERTION(aFrame->HasAnyStateBits(NS_FRAME_PART_OF_IBSPLIT),
+               "GetIBSplitSibling should only be called on ib-split frames");
+
+  if (aFrame->Style()->GetPseudoType() !=
+      PseudoStyleType::mozBlockInsideInlineWrapper) {
+    // it's not an anonymous block
+    return nullptr;
+  }
+
+  // Find the first continuation of the frame.  (Ugh.  This ends up
+  // being O(N^2) when it is called O(N) times.)
+  aFrame = aFrame->FirstContinuation();
+
+  /*
+   * Now look up the nsGkAtoms::IBSplitPrevSibling
+   * property.
+   */
+  nsIFrame* ibSplitSibling =
+      aFrame->GetProperty(nsIFrame::IBSplitPrevSibling());
+  NS_ASSERTION(ibSplitSibling, "Broken frame tree?");
+  return ibSplitSibling;
+}
+
+/**
+ * Get the parent, corrected for the mangled frame tree resulting from
+ * having a block within an inline.  The result only differs from the
+ * result of |GetParent| when |GetParent| returns an anonymous block
+ * that was created for an element that was 'display: inline' because
+ * that element contained a block.
+ *
+ * Also skip anonymous scrolled-content parents; inherit directly from the
+ * outer scroll frame.
+ *
+ * Also skip NAC parents if the child frame is NAC.
+ */
+static nsIFrame* GetCorrectedParent(const nsIFrame* aFrame) {
+  nsIFrame* parent = aFrame->GetParent();
+  if (!parent) {
+    return nullptr;
+  }
+
+  // For a table caption we want the _inner_ table frame (unless it's anonymous)
+  // as the style parent.
+  if (aFrame->IsTableCaption()) {
+    nsIFrame* innerTable = parent->PrincipalChildList().FirstChild();
+    if (!innerTable->Style()->IsAnonBox()) {
+      return innerTable;
+    }
+  }
+
+  // Table wrappers are always anon boxes; if we're in here for an outer
+  // table, that actually means its the _inner_ table that wants to
+  // know its parent. So get the pseudo of the inner in that case.
+  auto pseudo = aFrame->Style()->GetPseudoType();
+  if (pseudo == PseudoStyleType::tableWrapper) {
+    pseudo =
+        aFrame->PrincipalChildList().FirstChild()->Style()->GetPseudoType();
+  }
+
+  // Prevent a NAC pseudo-element from inheriting from its NAC parent, and
+  // inherit from the NAC generator element instead.
+  if (pseudo != PseudoStyleType::NotPseudo) {
+    MOZ_ASSERT(aFrame->GetContent());
+    Element* element = Element::FromNode(aFrame->GetContent());
+    // Make sure to avoid doing the fixup for non-element-backed pseudos like
+    // ::first-line and such.
+    if (element && !element->IsRootOfNativeAnonymousSubtree() &&
+        element->GetPseudoElementType() == aFrame->Style()->GetPseudoType()) {
+      while (parent->GetContent() &&
+             !parent->GetContent()->IsRootOfNativeAnonymousSubtree()) {
+        parent = parent->GetInFlowParent();
+      }
+      parent = parent->GetInFlowParent();
+    }
+  }
+
+  return nsIFrame::CorrectStyleParentFrame(parent, pseudo);
+}
+
+/* static */
+nsIFrame* nsIFrame::CorrectStyleParentFrame(nsIFrame* aProspectiveParent,
+                                            PseudoStyleType aChildPseudo) {
+  MOZ_ASSERT(aProspectiveParent, "Must have a prospective parent");
+
+  if (aChildPseudo != PseudoStyleType::NotPseudo) {
+    // Non-inheriting anon boxes have no style parent frame at all.
+    if (PseudoStyle::IsNonInheritingAnonBox(aChildPseudo)) {
+      return nullptr;
+    }
+
+    // Other anon boxes are parented to their actual parent already, except
+    // for non-elements.  Those should not be treated as an anon box.
+    if (PseudoStyle::IsAnonBox(aChildPseudo) &&
+        !nsCSSAnonBoxes::IsNonElement(aChildPseudo)) {
+      NS_ASSERTION(aChildPseudo != PseudoStyleType::mozBlockInsideInlineWrapper,
+                   "Should have dealt with kids that have "
+                   "NS_FRAME_PART_OF_IBSPLIT elsewhere");
+      return aProspectiveParent;
+    }
+  }
+
+  // Otherwise, walk up out of all anon boxes.  For placeholder frames, walk out
+  // of all pseudo-elements as well.  Otherwise ReparentComputedStyle could
+  // cause style data to be out of sync with the frame tree.
+  nsIFrame* parent = aProspectiveParent;
+  do {
+    if (parent->HasAnyStateBits(NS_FRAME_PART_OF_IBSPLIT)) {
+      nsIFrame* sibling = GetIBSplitSiblingForAnonymousBlock(parent);
+
+      if (sibling) {
+        // |parent| was a block in an {ib} split; use the inline as
+        // |the style parent.
+        parent = sibling;
+      }
+    }
+
+    if (!parent->Style()->IsPseudoOrAnonBox()) {
+      return parent;
+    }
+
+    if (!parent->Style()->IsAnonBox() && aChildPseudo != PseudoStyleType::MAX) {
+      // nsPlaceholderFrame passes in PseudoStyleType::MAX for
+      // aChildPseudo (even though that's not a valid pseudo-type) just to
+      // trigger this behavior of walking up to the nearest non-pseudo
+      // ancestor.
+      return parent;
+    }
+
+    parent = parent->GetInFlowParent();
+  } while (parent);
+
+  if (aProspectiveParent->Style()->GetPseudoType() ==
+      PseudoStyleType::viewportScroll) {
+    // aProspectiveParent is the scrollframe for a viewport
+    // and the kids are the anonymous scrollbars
+    return aProspectiveParent;
+  }
+
+  // We can get here if the root element is absolutely positioned.
+  // We can't test for this very accurately, but it can only happen
+  // when the prospective parent is a canvas frame.
+  NS_ASSERTION(aProspectiveParent->IsCanvasFrame(),
+               "Should have found a parent before this");
+  return nullptr;
+}
+
+ComputedStyle* nsIFrame::DoGetParentComputedStyle(
+    nsIFrame** aProviderFrame) const {
+  *aProviderFrame = nullptr;
+
+  // Handle display:contents and the root frame, when there's no parent frame
+  // to inherit from.
+  if (MOZ_LIKELY(mContent)) {
+    Element* parentElement = mContent->GetFlattenedTreeParentElement();
+    if (MOZ_LIKELY(parentElement)) {
+      auto pseudo = Style()->GetPseudoType();
+      if (pseudo == PseudoStyleType::NotPseudo || !mContent->IsElement() ||
+          (!PseudoStyle::IsAnonBox(pseudo) &&
+           // Ensure that we don't return the display:contents style
+           // of the parent content for pseudos that have the same content
+           // as their primary frame (like -moz-list-bullets do):
+           IsPrimaryFrame()) ||
+          /* if next is true then it's really a request for the table frame's
+             parent context, see nsTable[Outer]Frame::GetParentComputedStyle. */
+          pseudo == PseudoStyleType::tableWrapper) {
+        // In some edge cases involving display: contents, we may end up here
+        // for something that's pending to be reframed. In this case we return
+        // the wrong style from here (because we've already lost track of it!),
+        // but it's not a big deal as we're going to be reframed anyway.
+        if (MOZ_LIKELY(parentElement->HasServoData()) &&
+            Servo_Element_IsDisplayContents(parentElement)) {
+          RefPtr<ComputedStyle> style =
+              ServoStyleSet::ResolveServoStyle(*parentElement);
+          // NOTE(emilio): we return a weak reference because the element also
+          // holds the style context alive. This is a bit silly (we could've
+          // returned a weak ref directly), but it's probably not worth
+          // optimizing, given this function has just one caller which is rare,
+          // and this path is rare itself.
+          return style;
+        }
+      }
+    } else {
+      if (Style()->GetPseudoType() == PseudoStyleType::NotPseudo) {
+        // We're a frame for the root.  We have no style parent.
+        return nullptr;
+      }
+    }
+  }
+
+  if (!HasAnyStateBits(NS_FRAME_OUT_OF_FLOW)) {
+    /*
+     * If this frame is an anonymous block created when an inline with a block
+     * inside it got split, then the parent style is on its preceding inline. We
+     * can get to it using GetIBSplitSiblingForAnonymousBlock.
+     */
+    if (HasAnyStateBits(NS_FRAME_PART_OF_IBSPLIT)) {
+      nsIFrame* ibSplitSibling = GetIBSplitSiblingForAnonymousBlock(this);
+      if (ibSplitSibling) {
+        return (*aProviderFrame = ibSplitSibling)->Style();
+      }
+    }
+
+    // If this frame is one of the blocks that split an inline, we must
+    // return the "special" inline parent, i.e., the parent that this
+    // frame would have if we didn't mangle the frame structure.
+    *aProviderFrame = GetCorrectedParent(this);
+    return *aProviderFrame ? (*aProviderFrame)->Style() : nullptr;
+  }
+
+  // We're an out-of-flow frame.  For out-of-flow frames, we must
+  // resolve underneath the placeholder's parent.  The placeholder is
+  // reached from the first-in-flow.
+  nsPlaceholderFrame* placeholder = FirstInFlow()->GetPlaceholderFrame();
+  if (!placeholder) {
+    MOZ_ASSERT_UNREACHABLE("no placeholder frame for out-of-flow frame");
+    *aProviderFrame = GetCorrectedParent(this);
+    return *aProviderFrame ? (*aProviderFrame)->Style() : nullptr;
+  }
+  return placeholder->GetParentComputedStyleForOutOfFlow(aProviderFrame);
+}
+
+void nsIFrame::GetLastLeaf(nsIFrame** aFrame) {
+  if (!aFrame || !*aFrame) return;
+  nsIFrame* child = *aFrame;
+  // if we are a block frame then go for the last line of 'this'
+  while (1) {
+    child = child->PrincipalChildList().FirstChild();
+    if (!child) return;  // nothing to do
+    nsIFrame* siblingFrame;
+    nsIContent* content;
+    // ignore anonymous elements, e.g. mozTableAdd* mozTableRemove*
+    // see bug 278197 comment #12 #13 for details
+    while ((siblingFrame = child->GetNextSibling()) &&
+           (content = siblingFrame->GetContent()) &&
+           !content->IsRootOfNativeAnonymousSubtree())
+      child = siblingFrame;
+    *aFrame = child;
+  }
+}
+
+void nsIFrame::GetFirstLeaf(nsIFrame** aFrame) {
+  if (!aFrame || !*aFrame) return;
+  nsIFrame* child = *aFrame;
+  while (1) {
+    child = child->PrincipalChildList().FirstChild();
+    if (!child) return;  // nothing to do
+    *aFrame = child;
+  }
+}
+
+bool nsIFrame::IsFocusableDueToScrollFrame() {
+  if (!IsScrollFrame()) {
+    if (nsFieldSetFrame* fieldset = do_QueryFrame(this)) {
+      // TODO: Do we have similar special-cases like this where we can have
+      // anonymous scrollable boxes hanging off a primary frame?
+      if (nsIFrame* inner = fieldset->GetInner()) {
+        return inner->IsFocusableDueToScrollFrame();
+      }
+    }
+    return false;
+  }
+  if (!mContent->IsHTMLElement()) {
+    return false;
+  }
+  if (mContent->IsRootOfNativeAnonymousSubtree()) {
+    return false;
+  }
+  if (!mContent->GetParent()) {
+    return false;
+  }
+  if (mContent->AsElement()->HasAttr(nsGkAtoms::tabindex)) {
+    return false;
+  }
+  // Elements with scrollable view are focusable with script & tabbable
+  // Otherwise you couldn't scroll them with keyboard, which is an accessibility
+  // issue (e.g. Section 508 rules) However, we don't make them to be focusable
+  // with the mouse, because the extra focus outlines are considered
+  // unnecessarily ugly.  When clicked on, the selection position within the
+  // element will be enough to make them keyboard scrollable.
+  nsIScrollableFrame* scrollFrame = do_QueryFrame(this);
+  if (!scrollFrame) {
+    return false;
+  }
+  if (scrollFrame->IsForTextControlWithNoScrollbars()) {
+    return false;
+  }
+  if (scrollFrame->GetScrollStyles().IsHiddenInBothDirections()) {
+    return false;
+  }
+  if (scrollFrame->GetScrollRange().IsEqualEdges(nsRect(0, 0, 0, 0))) {
+    return false;
+  }
+  return true;
+}
+
+Focusable nsIFrame::IsFocusable(bool aWithMouse, bool aCheckVisibility) {
+  // cannot focus content in print preview mode. Only the root can be focused,
+  // but that's handled elsewhere.
+  if (PresContext()->Type() == nsPresContext::eContext_PrintPreview) {
+    return {};
+  }
+
+  if (!mContent || !mContent->IsElement()) {
+    return {};
+  }
+
+  if (aCheckVisibility && !IsVisibleConsideringAncestors()) {
+    return {};
+  }
+
+  const StyleUserFocus uf = StyleUI()->UserFocus();
+  if (uf == StyleUserFocus::None) {
+    return {};
+  }
+  MOZ_ASSERT(!StyleUI()->IsInert(), "inert implies -moz-user-focus: none");
+
+  const PseudoStyleType pseudo = Style()->GetPseudoType();
+  if (pseudo == PseudoStyleType::anonymousItem) {
+    return {};
+  }
+
+  Focusable focusable;
+  if (auto* xul = nsXULElement::FromNode(mContent)) {
+    // As a legacy special-case, -moz-user-focus controls focusability and
+    // tabability of XUL elements in some circumstances (which default to
+    // -moz-user-focus: ignore).
+    auto focusability = xul->GetXULFocusability(aWithMouse);
+    focusable.mFocusable =
+        focusability.mForcedFocusable.valueOr(uf == StyleUserFocus::Normal);
+    if (focusable) {
+      focusable.mTabIndex = focusability.mForcedTabIndexIfFocusable.valueOr(0);
+    }
+  } else {
+    focusable = mContent->IsFocusableWithoutStyle(aWithMouse);
+  }
+
+  if (focusable) {
+    return focusable;
+  }
+
+  // If we're focusing with the mouse we never focus scroll areas.
+  if (!aWithMouse && IsFocusableDueToScrollFrame()) {
+    return {true, 0};
+  }
+
+  // FIXME(emilio): some callers rely on somewhat broken return values
+  // (focusable = false, but non-negative tab-index) from
+  // IsFocusableWithoutStyle (for image maps in particular).
+  return focusable;
+}
+
+/**
+ * @return true if this text frame ends with a newline character which is
+ * treated as preformatted. It should return false if this is not a text frame.
+ */
+bool nsIFrame::HasSignificantTerminalNewline() const { return false; }
+
+static StyleVerticalAlignKeyword ConvertSVGDominantBaselineToVerticalAlign(
+    StyleDominantBaseline aDominantBaseline) {
+  // Most of these are approximate mappings.
+  switch (aDominantBaseline) {
+    case StyleDominantBaseline::Hanging:
+    case StyleDominantBaseline::TextBeforeEdge:
+      return StyleVerticalAlignKeyword::TextTop;
+    case StyleDominantBaseline::TextAfterEdge:
+    case StyleDominantBaseline::Ideographic:
+      return StyleVerticalAlignKeyword::TextBottom;
+    case StyleDominantBaseline::Central:
+    case StyleDominantBaseline::Middle:
+    case StyleDominantBaseline::Mathematical:
+      return StyleVerticalAlignKeyword::Middle;
+    case StyleDominantBaseline::Auto:
+    case StyleDominantBaseline::Alphabetic:
+      return StyleVerticalAlignKeyword::Baseline;
+    default:
+      MOZ_ASSERT_UNREACHABLE("unexpected aDominantBaseline value");
+      return StyleVerticalAlignKeyword::Baseline;
+  }
+}
+
+Maybe<StyleVerticalAlignKeyword> nsIFrame::VerticalAlignEnum() const {
+  if (IsInSVGTextSubtree()) {
+    StyleDominantBaseline dominantBaseline = StyleSVG()->mDominantBaseline;
+    return Some(ConvertSVGDominantBaselineToVerticalAlign(dominantBaseline));
+  }
+
+  const auto& verticalAlign = StyleDisplay()->mVerticalAlign;
+  if (verticalAlign.IsKeyword()) {
+    return Some(verticalAlign.AsKeyword());
+  }
+
+  return Nothing();
+}
+
+void nsIFrame::UpdateStyleOfChildAnonBox(nsIFrame* aChildFrame,
+                                         ServoRestyleState& aRestyleState) {
+#ifdef DEBUG
+  nsIFrame* parent = aChildFrame->GetInFlowParent();
+  if (aChildFrame->IsTableFrame()) {
+    parent = parent->GetParent();
+  }
+  if (parent->IsLineFrame()) {
+    parent = parent->GetParent();
+  }
+  MOZ_ASSERT(nsLayoutUtils::FirstContinuationOrIBSplitSibling(parent) == this,
+             "This should only be used for children!");
+#endif  // DEBUG
+  MOZ_ASSERT(!GetContent() || !aChildFrame->GetContent() ||
+                 aChildFrame->GetContent() == GetContent(),
+             "What content node is it a frame for?");
+  MOZ_ASSERT(!aChildFrame->GetPrevContinuation(),
+             "Only first continuations should end up here");
+
+  // We could force the caller to pass in the pseudo, since some callers know it
+  // statically...  But this API is a bit nicer.
+  auto pseudo = aChildFrame->Style()->GetPseudoType();
+  MOZ_ASSERT(PseudoStyle::IsAnonBox(pseudo), "Child is not an anon box?");
+  MOZ_ASSERT(!PseudoStyle::IsNonInheritingAnonBox(pseudo),
+             "Why did the caller bother calling us?");
+
+  // Anon boxes inherit from their parent; that's us.
+  RefPtr<ComputedStyle> newContext =
+      aRestyleState.StyleSet().ResolveInheritingAnonymousBoxStyle(pseudo,
+                                                                  Style());
+
+  nsChangeHint childHint =
+      UpdateStyleOfOwnedChildFrame(aChildFrame, newContext, aRestyleState);
+
+  // Now that we've updated the style on aChildFrame, check whether it itself
+  // has anon boxes to deal with.
+  ServoRestyleState childrenState(*aChildFrame, aRestyleState, childHint,
+                                  ServoRestyleState::Type::InFlow);
+  aChildFrame->UpdateStyleOfOwnedAnonBoxes(childrenState);
+
+  // Assuming anon boxes don't have ::backdrop associated with them... if that
+  // ever changes, we'd need to handle that here, like we do in
+  // RestyleManager::ProcessPostTraversal
+
+  // We do need to handle block pseudo-elements here, though.  Especially list
+  // bullets.
+  if (nsBlockFrame* block = do_QueryFrame(aChildFrame)) {
+    block->UpdatePseudoElementStyles(childrenState);
+  }
+}
+
+/* static */
+nsChangeHint nsIFrame::UpdateStyleOfOwnedChildFrame(
+    nsIFrame* aChildFrame, ComputedStyle* aNewComputedStyle,
+    ServoRestyleState& aRestyleState,
+    const Maybe<ComputedStyle*>& aContinuationComputedStyle) {
+  MOZ_ASSERT(!aChildFrame->GetAdditionalComputedStyle(0),
+             "We don't handle additional styles here");
+
+  // Figure out whether we have an actual change.  It's important that we do
+  // this, for several reasons:
+  //
+  // 1) Even if all the child's changes are due to properties it inherits from
+  //    us, it's possible that no one ever asked us for those style structs and
+  //    hence changes to them aren't reflected in the changes handled at all.
+  //
+  // 2) Content can change stylesheets that change the styles of pseudos, and
+  //    extensions can add/remove stylesheets that change the styles of
+  //    anonymous boxes directly.
+  uint32_t equalStructs;  // Not used, actually.
+  nsChangeHint childHint = aChildFrame->Style()->CalcStyleDifference(
+      *aNewComputedStyle, &equalStructs);
+
+  // If aChildFrame is out of flow, then aRestyleState's "changes handled by the
+  // parent" doesn't apply to it, because it may have some other parent in the
+  // frame tree.
+  if (!aChildFrame->HasAnyStateBits(NS_FRAME_OUT_OF_FLOW)) {
+    childHint = NS_RemoveSubsumedHints(
+        childHint, aRestyleState.ChangesHandledFor(aChildFrame));
+  }
+  if (childHint) {
+    if (childHint & nsChangeHint_ReconstructFrame) {
+      // If we generate a reconstruct here, remove any non-reconstruct hints we
+      // may have already generated for this content.
+      aRestyleState.ChangeList().PopChangesForContent(
+          aChildFrame->GetContent());
+    }
+    aRestyleState.ChangeList().AppendChange(
+        aChildFrame, aChildFrame->GetContent(), childHint);
+  }
+
+  aChildFrame->SetComputedStyle(aNewComputedStyle);
+  ComputedStyle* continuationStyle = aContinuationComputedStyle
+                                         ? *aContinuationComputedStyle
+                                         : aNewComputedStyle;
+  for (nsIFrame* kid = aChildFrame->GetNextContinuation(); kid;
+       kid = kid->GetNextContinuation()) {
+    MOZ_ASSERT(!kid->GetAdditionalComputedStyle(0));
+    kid->SetComputedStyle(continuationStyle);
+  }
+
+  return childHint;
+}
+
+/* static */
+void nsIFrame::AddInPopupStateBitToDescendants(nsIFrame* aFrame) {
+  if (!aFrame->HasAnyStateBits(NS_FRAME_IN_POPUP) &&
+      aFrame->TrackingVisibility()) {
+    // Assume all frames in popups are visible.
+    aFrame->IncApproximateVisibleCount();
+  }
+
+  aFrame->AddStateBits(NS_FRAME_IN_POPUP);
+
+  for (const auto& childList : aFrame->CrossDocChildLists()) {
+    for (nsIFrame* child : childList.mList) {
+      AddInPopupStateBitToDescendants(child);
+    }
+  }
+}
+
+/* static */
+void nsIFrame::RemoveInPopupStateBitFromDescendants(nsIFrame* aFrame) {
+  if (!aFrame->HasAnyStateBits(NS_FRAME_IN_POPUP) ||
+      nsLayoutUtils::IsPopup(aFrame)) {
+    return;
+  }
+
+  aFrame->RemoveStateBits(NS_FRAME_IN_POPUP);
+
+  if (aFrame->TrackingVisibility()) {
+    // We assume all frames in popups are visible, so this decrement balances
+    // out the increment in AddInPopupStateBitToDescendants above.
+    aFrame->DecApproximateVisibleCount();
+  }
+  for (const auto& childList : aFrame->CrossDocChildLists()) {
+    for (nsIFrame* child : childList.mList) {
+      RemoveInPopupStateBitFromDescendants(child);
+    }
+  }
+}
+
+void nsIFrame::SetParent(nsContainerFrame* aParent) {
+  // If our parent is a wrapper anon box, our new parent should be too.  We
+  // _can_ change parent if our parent is a wrapper anon box, because some
+  // wrapper anon boxes can have continuations.
+  MOZ_ASSERT_IF(ParentIsWrapperAnonBox(),
+                aParent->Style()->IsInheritingAnonBox());
+
+  // Note that the current mParent may already be destroyed at this point.
+  mParent = aParent;
+  MOZ_DIAGNOSTIC_ASSERT(!mParent || PresShell() == mParent->PresShell());
+
+  if (HasAnyStateBits(NS_FRAME_HAS_VIEW | NS_FRAME_HAS_CHILD_WITH_VIEW)) {
+    for (nsIFrame* f = aParent;
+         f && !f->HasAnyStateBits(NS_FRAME_HAS_CHILD_WITH_VIEW);
+         f = f->GetParent()) {
+      f->AddStateBits(NS_FRAME_HAS_CHILD_WITH_VIEW);
+    }
+  }
+
+  if (HasAnyStateBits(NS_FRAME_CONTAINS_RELATIVE_BSIZE)) {
+    for (nsIFrame* f = aParent; f; f = f->GetParent()) {
+      if (f->HasAnyStateBits(NS_FRAME_CONTAINS_RELATIVE_BSIZE)) {
+        break;
+      }
+      f->AddStateBits(NS_FRAME_CONTAINS_RELATIVE_BSIZE);
+    }
+  }
+
+  if (HasAnyStateBits(NS_FRAME_DESCENDANT_INTRINSIC_ISIZE_DEPENDS_ON_BSIZE)) {
+    for (nsIFrame* f = aParent; f; f = f->GetParent()) {
+      if (f->HasAnyStateBits(
+              NS_FRAME_DESCENDANT_INTRINSIC_ISIZE_DEPENDS_ON_BSIZE)) {
+        break;
+      }
+      f->AddStateBits(NS_FRAME_DESCENDANT_INTRINSIC_ISIZE_DEPENDS_ON_BSIZE);
+    }
+  }
+
+  if (HasInvalidFrameInSubtree()) {
+    for (nsIFrame* f = aParent;
+         f && !f->HasAnyStateBits(NS_FRAME_DESCENDANT_NEEDS_PAINT |
+                                  NS_FRAME_IS_NONDISPLAY);
+         f = nsLayoutUtils::GetCrossDocParentFrameInProcess(f)) {
+      f->AddStateBits(NS_FRAME_DESCENDANT_NEEDS_PAINT);
+    }
+  }
+
+  if (aParent->HasAnyStateBits(NS_FRAME_IN_POPUP)) {
+    AddInPopupStateBitToDescendants(this);
+  } else {
+    RemoveInPopupStateBitFromDescendants(this);
+  }
+
+  // If our new parent only has invalid children, then we just invalidate
+  // ourselves too. This is probably faster than clearing the flag all
+  // the way up the frame tree.
+  if (aParent->HasAnyStateBits(NS_FRAME_ALL_DESCENDANTS_NEED_PAINT)) {
+    InvalidateFrame();
+  } else {
+    SchedulePaint();
+  }
+}
+
+bool nsIFrame::IsStackingContext(const nsStyleDisplay* aStyleDisplay,
+                                 const nsStyleEffects* aStyleEffects) {
+  // Properties that influence the output of this function should be handled in
+  // change_bits_for_longhand as well.
+  if (HasOpacity(aStyleDisplay, aStyleEffects, nullptr)) {
+    return true;
+  }
+  if (IsTransformed()) {
+    return true;
+  }
+  auto willChange = aStyleDisplay->mWillChange.bits;
+  if (aStyleDisplay->IsContainPaint() || aStyleDisplay->IsContainLayout() ||
+      willChange & StyleWillChangeBits::CONTAIN) {
+    if (SupportsContainLayoutAndPaint()) {
+      return true;
+    }
+  }
+  // strictly speaking, 'perspective' doesn't require visual atomicity,
+  // but the spec says it acts like the rest of these
+  if (aStyleDisplay->HasPerspectiveStyle() ||
+      willChange & StyleWillChangeBits::PERSPECTIVE) {
+    if (SupportsCSSTransforms()) {
+      return true;
+    }
+  }
+  if (!StylePosition()->mZIndex.IsAuto() ||
+      willChange & StyleWillChangeBits::Z_INDEX) {
+    if (ZIndexApplies()) {
+      return true;
+    }
+  }
+  return aStyleEffects->mMixBlendMode != StyleBlend::Normal ||
+         SVGIntegrationUtils::UsingEffectsForFrame(this) ||
+         aStyleDisplay->IsPositionForcingStackingContext() ||
+         aStyleDisplay->mIsolation != StyleIsolation::Auto ||
+         willChange & StyleWillChangeBits::STACKING_CONTEXT_UNCONDITIONAL;
+}
+
+bool nsIFrame::IsStackingContext() {
+  return IsStackingContext(StyleDisplay(), StyleEffects());
+}
+
+static bool IsFrameScrolledOutOfView(const nsIFrame* aTarget,
+                                     const nsRect& aTargetRect,
+                                     const nsIFrame* aParent) {
+  // The ancestor frame we are checking if it clips out aTargetRect relative to
+  // aTarget.
+  nsIFrame* clipParent = nullptr;
+
+  // find the first scrollable frame or root frame if we are in a fixed pos
+  // subtree
+  for (nsIFrame* f = const_cast<nsIFrame*>(aParent); f;
+       f = nsLayoutUtils::GetCrossDocParentFrameInProcess(f)) {
+    nsIScrollableFrame* scrollableFrame = do_QueryFrame(f);
+    if (scrollableFrame) {
+      clipParent = f;
+      break;
+    }
+    if (f->StyleDisplay()->mPosition == StylePositionProperty::Fixed &&
+        nsLayoutUtils::IsReallyFixedPos(f)) {
+      clipParent = f->GetParent();
+      break;
+    }
+  }
+
+  if (!clipParent) {
+    // Even if we couldn't find the nearest scrollable frame, it might mean we
+    // are in an out-of-process iframe, try to see if |aTarget| frame is
+    // scrolled out of view in an scrollable frame in a cross-process ancestor
+    // document.
+    return nsLayoutUtils::FrameIsScrolledOutOfViewInCrossProcess(aTarget);
+  }
+
+  nsRect clipRect = clipParent->InkOverflowRectRelativeToSelf();
+  // We consider that the target is scrolled out if the scrollable (or root)
+  // frame is empty.
+  if (clipRect.IsEmpty()) {
+    return true;
+  }
+
+  nsRect transformedRect = nsLayoutUtils::TransformFrameRectToAncestor(
+      aTarget, aTargetRect, clipParent);
+
+  if (transformedRect.IsEmpty()) {
+    // If the transformed rect is empty it represents a line or a point that we
+    // should check is outside the the scrollable rect.
+    if (transformedRect.x > clipRect.XMost() ||
+        transformedRect.y > clipRect.YMost() ||
+        clipRect.x > transformedRect.XMost() ||
+        clipRect.y > transformedRect.YMost()) {
+      return true;
+    }
+  } else if (!transformedRect.Intersects(clipRect)) {
+    return true;
+  }
+
+  nsIFrame* parent = clipParent->GetParent();
+  if (!parent) {
+    return false;
+  }
+
+  return IsFrameScrolledOutOfView(aTarget, aTargetRect, parent);
+}
+
+bool nsIFrame::IsScrolledOutOfView() const {
+  nsRect rect = InkOverflowRectRelativeToSelf();
+  return IsFrameScrolledOutOfView(this, rect, this);
+}
+
+gfx::Matrix nsIFrame::ComputeWidgetTransform() const {
+  const nsStyleUIReset* uiReset = StyleUIReset();
+  if (uiReset->mMozWindowTransform.IsNone()) {
+    return gfx::Matrix();
+  }
+
+  TransformReferenceBox refBox(nullptr, nsRect(nsPoint(), GetSize()));
+
+  nsPresContext* presContext = PresContext();
+  int32_t appUnitsPerDevPixel = presContext->AppUnitsPerDevPixel();
+  gfx::Matrix4x4 matrix = nsStyleTransformMatrix::ReadTransforms(
+      uiReset->mMozWindowTransform, refBox, float(appUnitsPerDevPixel));
+
+  // Apply the -moz-window-transform-origin translation to the matrix.
+  const StyleTransformOrigin& origin = uiReset->mWindowTransformOrigin;
+  Point transformOrigin = nsStyleTransformMatrix::Convert2DPosition(
+      origin.horizontal, origin.vertical, refBox, appUnitsPerDevPixel);
+  matrix.ChangeBasis(Point3D(transformOrigin.x, transformOrigin.y, 0));
+
+  gfx::Matrix result2d;
+  if (!matrix.CanDraw2D(&result2d)) {
+    // FIXME: It would be preferable to reject non-2D transforms at parse time.
+    NS_WARNING(
+        "-moz-window-transform does not describe a 2D transform, "
+        "but only 2d transforms are supported");
+    return gfx::Matrix();
+  }
+
+  return result2d;
+}
+
+void nsIFrame::DoUpdateStyleOfOwnedAnonBoxes(ServoRestyleState& aRestyleState) {
+  // As a special case, we check for {ib}-split block frames here, rather
+  // than have an nsInlineFrame::AppendDirectlyOwnedAnonBoxes implementation
+  // that returns them.
+  //
+  // (If we did handle them in AppendDirectlyOwnedAnonBoxes, we would have to
+  // return *all* of the in-flow {ib}-split block frames, not just the first
+  // one.  For restyling, we really just need the first in flow, and the other
+  // user of the AppendOwnedAnonBoxes API, AllChildIterator, doesn't need to
+  // know about them at all, since these block frames never create NAC.  So we
+  // avoid any unncessary hashtable lookups for the {ib}-split frames by calling
+  // UpdateStyleOfOwnedAnonBoxesForIBSplit directly here.)
+  if (IsInlineFrame()) {
+    if (HasAnyStateBits(NS_FRAME_PART_OF_IBSPLIT)) {
+      static_cast<nsInlineFrame*>(this)->UpdateStyleOfOwnedAnonBoxesForIBSplit(
+          aRestyleState);
+    }
+    return;
+  }
+
+  AutoTArray<OwnedAnonBox, 4> frames;
+  AppendDirectlyOwnedAnonBoxes(frames);
+  for (OwnedAnonBox& box : frames) {
+    if (box.mUpdateStyleFn) {
+      box.mUpdateStyleFn(this, box.mAnonBoxFrame, aRestyleState);
+    } else {
+      UpdateStyleOfChildAnonBox(box.mAnonBoxFrame, aRestyleState);
+    }
+  }
+}
+
+/* virtual */
+void nsIFrame::AppendDirectlyOwnedAnonBoxes(nsTArray<OwnedAnonBox>& aResult) {
+  MOZ_ASSERT(!HasAnyStateBits(NS_FRAME_OWNS_ANON_BOXES));
+  MOZ_ASSERT(false, "Why did this get called?");
+}
+
+void nsIFrame::DoAppendOwnedAnonBoxes(nsTArray<OwnedAnonBox>& aResult) {
+  size_t i = aResult.Length();
+  AppendDirectlyOwnedAnonBoxes(aResult);
+
+  // After appending the directly owned anonymous boxes of this frame to
+  // aResult above, we need to check each of them to see if they own
+  // any anonymous boxes themselves.  Note that we keep progressing
+  // through aResult, looking for additional entries in aResult from these
+  // subsequent AppendDirectlyOwnedAnonBoxes calls.  (Thus we can't
+  // use a ranged for loop here.)
+
+  while (i < aResult.Length()) {
+    nsIFrame* f = aResult[i].mAnonBoxFrame;
+    if (f->HasAnyStateBits(NS_FRAME_OWNS_ANON_BOXES)) {
+      f->AppendDirectlyOwnedAnonBoxes(aResult);
+    }
+    ++i;
+  }
+}
+
+nsIFrame::CaretPosition::CaretPosition() : mContentOffset(0) {}
+
+nsIFrame::CaretPosition::~CaretPosition() = default;
+
+bool nsIFrame::HasCSSAnimations() {
+  auto* collection = AnimationCollection<CSSAnimation>::Get(this);
+  return collection && !collection->mAnimations.IsEmpty();
+}
+
+bool nsIFrame::HasCSSTransitions() {
+  auto* collection = AnimationCollection<CSSTransition>::Get(this);
+  return collection && !collection->mAnimations.IsEmpty();
+}
+
+void nsIFrame::AddSizeOfExcludingThisForTree(nsWindowSizes& aSizes) const {
+  aSizes.mLayoutFramePropertiesSize +=
+      mProperties.SizeOfExcludingThis(aSizes.mState.mMallocSizeOf);
+
+  // We don't do this for Gecko because this stuff is stored in the nsPresArena
+  // and so measured elsewhere.
+  if (!aSizes.mState.HaveSeenPtr(mComputedStyle)) {
+    mComputedStyle->AddSizeOfIncludingThis(aSizes,
+                                           &aSizes.mLayoutComputedValuesNonDom);
+  }
+
+  // And our additional styles.
+  int32_t index = 0;
+  while (auto* extra = GetAdditionalComputedStyle(index++)) {
+    if (!aSizes.mState.HaveSeenPtr(extra)) {
+      extra->AddSizeOfIncludingThis(aSizes,
+                                    &aSizes.mLayoutComputedValuesNonDom);
+    }
+  }
+
+  for (const auto& childList : ChildLists()) {
+    for (const nsIFrame* f : childList.mList) {
+      f->AddSizeOfExcludingThisForTree(aSizes);
+    }
+  }
+}
+
+nsRect nsIFrame::GetCompositorHitTestArea(nsDisplayListBuilder* aBuilder) {
+  nsRect area;
+
+  nsIScrollableFrame* scrollFrame = nsLayoutUtils::GetScrollableFrameFor(this);
+  if (scrollFrame) {
+    // If the frame is content of a scrollframe, then we need to pick up the
+    // area corresponding to the overflow rect as well. Otherwise the parts of
+    // the overflow that are not occupied by descendants get skipped and the
+    // APZ code sends touch events to the content underneath instead.
+    // See https://bugzilla.mozilla.org/show_bug.cgi?id=1127773#c15.
+    area = ScrollableOverflowRect();
+  } else {
+    area = GetRectRelativeToSelf();
+  }
+
+  if (!area.IsEmpty()) {
+    return area + aBuilder->ToReferenceFrame(this);
+  }
+
+  return area;
+}
+
+CompositorHitTestInfo nsIFrame::GetCompositorHitTestInfo(
+    nsDisplayListBuilder* aBuilder) {
+  CompositorHitTestInfo result = CompositorHitTestInvisibleToHit;
+
+  if (aBuilder->IsInsidePointerEventsNoneDoc()) {
+    // Somewhere up the parent document chain is a subdocument with pointer-
+    // events:none set on it.
+    return result;
+  }
+  if (!GetParent()) {
+    MOZ_ASSERT(IsViewportFrame());
+    // Viewport frames are never event targets, other frames, like canvas
+    // frames, are the event targets for any regions viewport frames may cover.
+    return result;
+  }
+  if (Style()->PointerEvents() == StylePointerEvents::None) {
+    return result;
+  }
+  if (!StyleVisibility()->IsVisible()) {
+    return result;
+  }
+
+  // Anything that didn't match the above conditions is visible to hit-testing.
+  result = CompositorHitTestFlags::eVisibleToHitTest;
+  SVGUtils::MaskUsage maskUsage = SVGUtils::DetermineMaskUsage(this, false);
+  if (maskUsage.UsingMaskOrClipPath()) {
+    // If WebRender is enabled, simple clip-paths can be converted into WR
+    // clips that WR knows how to hit-test against, so we don't need to mark
+    // it as an irregular area.
+    if (!maskUsage.IsSimpleClipShape()) {
+      result += CompositorHitTestFlags::eIrregularArea;
+    }
+  }
+
+  if (aBuilder->IsBuildingNonLayerizedScrollbar()) {
+    // Scrollbars may be painted into a layer below the actual layer they will
+    // scroll, and therefore wheel events may be dispatched to the outer frame
+    // instead of the intended scrollframe. To address this, we force a d-t-c
+    // region on scrollbar frames that won't be placed in their own layer. See
+    // bug 1213324 for details.
+    result += CompositorHitTestFlags::eInactiveScrollframe;
+  } else if (aBuilder->GetAncestorHasApzAwareEventHandler()) {
+    result += CompositorHitTestFlags::eApzAwareListeners;
+  } else if (IsRangeFrame()) {
+    // Range frames handle touch events directly without having a touch listener
+    // so we need to let APZ know that this area cares about events.
+    result += CompositorHitTestFlags::eApzAwareListeners;
+  }
+
+  if (aBuilder->IsTouchEventPrefEnabledDoc()) {
+    // Inherit the touch-action flags from the parent, if there is one. We do
+    // this because of how the touch-action on a frame combines the touch-action
+    // from ancestor DOM elements. Refer to the documentation in
+    // TouchActionHelper.cpp for details; this code is meant to be equivalent to
+    // that code, but woven into the top-down recursive display list building
+    // process.
+    CompositorHitTestInfo inheritedTouchAction =
+        aBuilder->GetCompositorHitTestInfo() & CompositorHitTestTouchActionMask;
+
+    nsIFrame* touchActionFrame = this;
+    if (nsIScrollableFrame* scrollFrame =
+            nsLayoutUtils::GetScrollableFrameFor(this)) {
+      ScrollStyles ss = scrollFrame->GetScrollStyles();
+      if (ss.mVertical != StyleOverflow::Hidden ||
+          ss.mHorizontal != StyleOverflow::Hidden) {
+        touchActionFrame = do_QueryFrame(scrollFrame);
+        // On scrollframes, stop inheriting the pan-x and pan-y flags; instead,
+        // reset them back to zero to allow panning on the scrollframe unless we
+        // encounter an element that disables it that's inside the scrollframe.
+        // This is equivalent to the |considerPanning| variable in
+        // TouchActionHelper.cpp, but for a top-down traversal.
+        CompositorHitTestInfo panMask(
+            CompositorHitTestFlags::eTouchActionPanXDisabled,
+            CompositorHitTestFlags::eTouchActionPanYDisabled);
+        inheritedTouchAction -= panMask;
+      }
+    }
+
+    result += inheritedTouchAction;
+
+    const StyleTouchAction touchAction = touchActionFrame->UsedTouchAction();
+    // The CSS allows the syntax auto | none | [pan-x || pan-y] | manipulation
+    // so we can eliminate some combinations of things.
+    if (touchAction == StyleTouchAction::AUTO) {
+      // nothing to do
+    } else if (touchAction & StyleTouchAction::MANIPULATION) {
+      result += CompositorHitTestFlags::eTouchActionAnimatingZoomDisabled;
+    } else {
+      // This path handles the cases none | [pan-x || pan-y || pinch-zoom] so
+      // double-tap is disabled in here.
+      if (!(touchAction & StyleTouchAction::PINCH_ZOOM)) {
+        result += CompositorHitTestFlags::eTouchActionPinchZoomDisabled;
+      }
+
+      result += CompositorHitTestFlags::eTouchActionAnimatingZoomDisabled;
+
+      if (!(touchAction & StyleTouchAction::PAN_X)) {
+        result += CompositorHitTestFlags::eTouchActionPanXDisabled;
+      }
+      if (!(touchAction & StyleTouchAction::PAN_Y)) {
+        result += CompositorHitTestFlags::eTouchActionPanYDisabled;
+      }
+      if (touchAction & StyleTouchAction::NONE) {
+        // all the touch-action disabling flags will already have been set above
+        MOZ_ASSERT(result.contains(CompositorHitTestTouchActionMask));
+      }
+    }
+  }
+
+  const Maybe<ScrollDirection> scrollDirection =
+      aBuilder->GetCurrentScrollbarDirection();
+  if (scrollDirection.isSome()) {
+    if (GetContent()->IsXULElement(nsGkAtoms::thumb)) {
+      const bool thumbGetsLayer = aBuilder->GetCurrentScrollbarTarget() !=
+                                  layers::ScrollableLayerGuid::NULL_SCROLL_ID;
+      if (thumbGetsLayer) {
+        result += CompositorHitTestFlags::eScrollbarThumb;
+      } else {
+        result += CompositorHitTestFlags::eInactiveScrollframe;
+      }
+    }
+
+    if (*scrollDirection == ScrollDirection::eVertical) {
+      result += CompositorHitTestFlags::eScrollbarVertical;
+    }
+
+    // includes the ScrollbarFrame, SliderFrame, anything else that
+    // might be inside the xul:scrollbar
+    result += CompositorHitTestFlags::eScrollbar;
+  }
+
+  return result;
+}
+
+// Returns true if we can guarantee there is no visible descendants.
+static bool HasNoVisibleDescendants(const nsIFrame* aFrame) {
+  for (const auto& childList : aFrame->ChildLists()) {
+    for (nsIFrame* f : childList.mList) {
+      if (nsPlaceholderFrame::GetRealFrameFor(f)
+              ->IsVisibleOrMayHaveVisibleDescendants()) {
+        return false;
+      }
+    }
+  }
+  return true;
+}
+
+nsIScrollableFrame* nsIFrame::GetAsScrollContainer() const {
+  return do_QueryFrame(this);
+}
+
+void nsIFrame::UpdateVisibleDescendantsState() {
+  if (StyleVisibility()->IsVisible()) {
+    // Notify invisible ancestors that a visible descendant exists now.
+    nsIFrame* ancestor;
+    for (ancestor = GetInFlowParent();
+         ancestor && !ancestor->StyleVisibility()->IsVisible();
+         ancestor = ancestor->GetInFlowParent()) {
+      ancestor->mAllDescendantsAreInvisible = false;
+    }
+  } else {
+    mAllDescendantsAreInvisible = HasNoVisibleDescendants(this);
+  }
+}
+
+nsIFrame::PhysicalAxes nsIFrame::ShouldApplyOverflowClipping(
+    const nsStyleDisplay* aDisp) const {
+  MOZ_ASSERT(aDisp == StyleDisplay(), "Wrong display struct");
+
+  // 'contain:paint', which we handle as 'overflow:clip' here. Except for
+  // scrollframes we don't need contain:paint to add any clipping, because
+  // the scrollable frame will already clip overflowing content, and because
+  // 'contain:paint' should prevent all means of escaping that clipping
+  // (e.g. because it forms a fixed-pos containing block).
+  if (aDisp->IsContainPaint() && !IsScrollFrame() &&
+      SupportsContainLayoutAndPaint()) {
+    return PhysicalAxes::Both;
+  }
+
+  // and overflow:hidden that we should interpret as clip
+  if (aDisp->mOverflowX == StyleOverflow::Hidden &&
+      aDisp->mOverflowY == StyleOverflow::Hidden) {
+    // REVIEW: these are the frame types that set up clipping.
+    LayoutFrameType type = Type();
+    switch (type) {
+      case LayoutFrameType::Table:
+      case LayoutFrameType::TableCell:
+      case LayoutFrameType::SVGOuterSVG:
+      case LayoutFrameType::SVGInnerSVG:
+      case LayoutFrameType::SVGSymbol:
+      case LayoutFrameType::SVGForeignObject:
+        return PhysicalAxes::Both;
+      default:
+        if (IsReplacedWithBlock()) {
+          if (type == mozilla::LayoutFrameType::TextInput) {
+            // It has an anonymous scroll frame that handles any overflow.
+            return PhysicalAxes::None;
+          }
+          return PhysicalAxes::Both;
+        }
+    }
+  }
+
+  // clip overflow:clip, except for nsListControlFrame which is
+  // an nsHTMLScrollFrame sub-class.
+  if (MOZ_UNLIKELY((aDisp->mOverflowX == mozilla::StyleOverflow::Clip ||
+                    aDisp->mOverflowY == mozilla::StyleOverflow::Clip) &&
+                   !IsListControlFrame())) {
+    // FIXME: we could use GetViewportScrollStylesOverrideElement() here instead
+    // if that worked correctly in a print context. (see bug 1654667)
+    const auto* element = Element::FromNodeOrNull(GetContent());
+    if (!element ||
+        !PresContext()->ElementWouldPropagateScrollStyles(*element)) {
+      uint8_t axes = uint8_t(PhysicalAxes::None);
+      if (aDisp->mOverflowX == mozilla::StyleOverflow::Clip) {
+        axes |= uint8_t(PhysicalAxes::Horizontal);
+      }
+      if (aDisp->mOverflowY == mozilla::StyleOverflow::Clip) {
+        axes |= uint8_t(PhysicalAxes::Vertical);
+      }
+      return PhysicalAxes(axes);
+    }
+  }
+
+  if (HasAnyStateBits(NS_FRAME_SVG_LAYOUT)) {
+    return PhysicalAxes::None;
+  }
+
+  // If we're paginated and a block, and have NS_BLOCK_CLIP_PAGINATED_OVERFLOW
+  // set, then we want to clip our overflow.
+  bool clip = HasAnyStateBits(NS_BLOCK_CLIP_PAGINATED_OVERFLOW) &&
+              PresContext()->IsPaginated() && IsBlockFrame();
+  return clip ? PhysicalAxes::Both : PhysicalAxes::None;
+}
+
+#ifdef DEBUG
+static void GetTagName(nsIFrame* aFrame, nsIContent* aContent, int aResultSize,
+                       char* aResult) {
+  if (aContent) {
+    snprintf(aResult, aResultSize, "%s@%p",
+             nsAtomCString(aContent->NodeInfo()->NameAtom()).get(), aFrame);
+  } else {
+    snprintf(aResult, aResultSize, "@%p", aFrame);
+  }
+}
+
+void nsIFrame::Trace(const char* aMethod, bool aEnter) {
+  if (NS_FRAME_LOG_TEST(sFrameLogModule, NS_FRAME_TRACE_CALLS)) {
+    char tagbuf[40];
+    GetTagName(this, mContent, sizeof(tagbuf), tagbuf);
+    printf_stderr("%s: %s %s", tagbuf, aEnter ? "enter" : "exit", aMethod);
+  }
+}
+
+void nsIFrame::Trace(const char* aMethod, bool aEnter,
+                     const nsReflowStatus& aStatus) {
+  if (NS_FRAME_LOG_TEST(sFrameLogModule, NS_FRAME_TRACE_CALLS)) {
+    char tagbuf[40];
+    GetTagName(this, mContent, sizeof(tagbuf), tagbuf);
+    printf_stderr("%s: %s %s, status=%scomplete%s", tagbuf,
+                  aEnter ? "enter" : "exit", aMethod,
+                  aStatus.IsIncomplete() ? "not" : "",
+                  (aStatus.NextInFlowNeedsReflow()) ? "+reflow" : "");
+  }
+}
+
+void nsIFrame::TraceMsg(const char* aFormatString, ...) {
+  if (NS_FRAME_LOG_TEST(sFrameLogModule, NS_FRAME_TRACE_CALLS)) {
+    // Format arguments into a buffer
+    char argbuf[200];
+    va_list ap;
+    va_start(ap, aFormatString);
+    VsprintfLiteral(argbuf, aFormatString, ap);
+    va_end(ap);
+
+    char tagbuf[40];
+    GetTagName(this, mContent, sizeof(tagbuf), tagbuf);
+    printf_stderr("%s: %s", tagbuf, argbuf);
+  }
+}
+
+void nsIFrame::VerifyDirtyBitSet(const nsFrameList& aFrameList) {
+  for (nsIFrame* f : aFrameList) {
+    NS_ASSERTION(f->HasAnyStateBits(NS_FRAME_IS_DIRTY), "dirty bit not set");
+  }
+}
+
+// Start Display Reflow
+DR_cookie::DR_cookie(nsPresContext* aPresContext, nsIFrame* aFrame,
+                     const ReflowInput& aReflowInput, ReflowOutput& aMetrics,
+                     nsReflowStatus& aStatus)
+    : mPresContext(aPresContext),
+      mFrame(aFrame),
+      mReflowInput(aReflowInput),
+      mMetrics(aMetrics),
+      mStatus(aStatus) {
+  MOZ_COUNT_CTOR(DR_cookie);
+  mValue = nsIFrame::DisplayReflowEnter(aPresContext, mFrame, mReflowInput);
+}
+
+DR_cookie::~DR_cookie() {
+  MOZ_COUNT_DTOR(DR_cookie);
+  nsIFrame::DisplayReflowExit(mPresContext, mFrame, mMetrics, mStatus, mValue);
+}
+
+DR_layout_cookie::DR_layout_cookie(nsIFrame* aFrame) : mFrame(aFrame) {
+  MOZ_COUNT_CTOR(DR_layout_cookie);
+  mValue = nsIFrame::DisplayLayoutEnter(mFrame);
+}
+
+DR_layout_cookie::~DR_layout_cookie() {
+  MOZ_COUNT_DTOR(DR_layout_cookie);
+  nsIFrame::DisplayLayoutExit(mFrame, mValue);
+}
+
+DR_intrinsic_inline_size_cookie::DR_intrinsic_inline_size_cookie(
+    nsIFrame* aFrame, const char* aType, nscoord& aResult)
+    : mFrame(aFrame), mType(aType), mResult(aResult) {
+  MOZ_COUNT_CTOR(DR_intrinsic_inline_size_cookie);
+  mValue = nsIFrame::DisplayIntrinsicISizeEnter(mFrame, mType);
+}
+
+DR_intrinsic_inline_size_cookie::~DR_intrinsic_inline_size_cookie() {
+  MOZ_COUNT_DTOR(DR_intrinsic_inline_size_cookie);
+  nsIFrame::DisplayIntrinsicISizeExit(mFrame, mType, mResult, mValue);
+}
+
+DR_intrinsic_size_cookie::DR_intrinsic_size_cookie(nsIFrame* aFrame,
+                                                   const char* aType,
+                                                   nsSize& aResult)
+    : mFrame(aFrame), mType(aType), mResult(aResult) {
+  MOZ_COUNT_CTOR(DR_intrinsic_size_cookie);
+  mValue = nsIFrame::DisplayIntrinsicSizeEnter(mFrame, mType);
+}
+
+DR_intrinsic_size_cookie::~DR_intrinsic_size_cookie() {
+  MOZ_COUNT_DTOR(DR_intrinsic_size_cookie);
+  nsIFrame::DisplayIntrinsicSizeExit(mFrame, mType, mResult, mValue);
+}
+
+DR_init_constraints_cookie::DR_init_constraints_cookie(
+    nsIFrame* aFrame, ReflowInput* aState, nscoord aCBWidth, nscoord aCBHeight,
+    const mozilla::Maybe<mozilla::LogicalMargin> aBorder,
+    const mozilla::Maybe<mozilla::LogicalMargin> aPadding)
+    : mFrame(aFrame), mState(aState) {
+  MOZ_COUNT_CTOR(DR_init_constraints_cookie);
+  nsMargin border;
+  if (aBorder) {
+    border = aBorder->GetPhysicalMargin(aFrame->GetWritingMode());
+  }
+  nsMargin padding;
+  if (aPadding) {
+    padding = aPadding->GetPhysicalMargin(aFrame->GetWritingMode());
+  }
+  mValue = ReflowInput::DisplayInitConstraintsEnter(
+      mFrame, mState, aCBWidth, aCBHeight, aBorder ? &border : nullptr,
+      aPadding ? &padding : nullptr);
+}
+
+DR_init_constraints_cookie::~DR_init_constraints_cookie() {
+  MOZ_COUNT_DTOR(DR_init_constraints_cookie);
+  ReflowInput::DisplayInitConstraintsExit(mFrame, mState, mValue);
+}
+
+DR_init_offsets_cookie::DR_init_offsets_cookie(
+    nsIFrame* aFrame, SizeComputationInput* aState, nscoord aPercentBasis,
+    WritingMode aCBWritingMode,
+    const mozilla::Maybe<mozilla::LogicalMargin> aBorder,
+    const mozilla::Maybe<mozilla::LogicalMargin> aPadding)
+    : mFrame(aFrame), mState(aState) {
+  MOZ_COUNT_CTOR(DR_init_offsets_cookie);
+  nsMargin border;
+  if (aBorder) {
+    border = aBorder->GetPhysicalMargin(aFrame->GetWritingMode());
+  }
+  nsMargin padding;
+  if (aPadding) {
+    padding = aPadding->GetPhysicalMargin(aFrame->GetWritingMode());
+  }
+  mValue = SizeComputationInput::DisplayInitOffsetsEnter(
+      mFrame, mState, aPercentBasis, aCBWritingMode,
+      aBorder ? &border : nullptr, aPadding ? &padding : nullptr);
+}
+
+DR_init_offsets_cookie::~DR_init_offsets_cookie() {
+  MOZ_COUNT_DTOR(DR_init_offsets_cookie);
+  SizeComputationInput::DisplayInitOffsetsExit(mFrame, mState, mValue);
+}
+
+struct DR_Rule;
+
+struct DR_FrameTypeInfo {
+  DR_FrameTypeInfo(LayoutFrameType aFrameType, const char* aFrameNameAbbrev,
+                   const char* aFrameName);
+  ~DR_FrameTypeInfo();
+
+  LayoutFrameType mType;
+  char mNameAbbrev[16];
+  char mName[32];
+  nsTArray<DR_Rule*> mRules;
+
+ private:
+  DR_FrameTypeInfo& operator=(const DR_FrameTypeInfo&) = delete;
+};
+
+struct DR_FrameTreeNode;
+struct DR_Rule;
+
+struct DR_State {
+  DR_State();
+  ~DR_State();
+  void Init();
+  void AddFrameTypeInfo(LayoutFrameType aFrameType,
+                        const char* aFrameNameAbbrev, const char* aFrameName);
+  DR_FrameTypeInfo* GetFrameTypeInfo(LayoutFrameType aFrameType);
+  DR_FrameTypeInfo* GetFrameTypeInfo(char* aFrameName);
+  void InitFrameTypeTable();
+  DR_FrameTreeNode* CreateTreeNode(nsIFrame* aFrame,
+                                   const ReflowInput* aReflowInput);
+  void FindMatchingRule(DR_FrameTreeNode& aNode);
+  bool RuleMatches(DR_Rule& aRule, DR_FrameTreeNode& aNode);
+  bool GetToken(FILE* aFile, char* aBuf, size_t aBufSize);
+  DR_Rule* ParseRule(FILE* aFile);
+  void ParseRulesFile();
+  void AddRule(nsTArray<DR_Rule*>& aRules, DR_Rule& aRule);
+  bool IsWhiteSpace(int c);
+  bool GetNumber(char* aBuf, int32_t& aNumber);
+  void PrettyUC(nscoord aSize, char* aBuf, int aBufSize);
+  void PrintMargin(const char* tag, const nsMargin* aMargin);
+  void DisplayFrameTypeInfo(nsIFrame* aFrame, int32_t aIndent);
+  void DeleteTreeNode(DR_FrameTreeNode& aNode);
+
+  bool mInited;
+  bool mActive;
+  int32_t mCount;
+  int32_t mAssert;
+  int32_t mIndent;
+  bool mIndentUndisplayedFrames;
+  bool mDisplayPixelErrors;
+  nsTArray<DR_Rule*> mWildRules;
+  nsTArray<DR_FrameTypeInfo> mFrameTypeTable;
+  // reflow specific state
+  nsTArray<DR_FrameTreeNode*> mFrameTreeLeaves;
+};
+
+static DR_State* DR_state;  // the one and only DR_State
+
+struct DR_RulePart {
+  explicit DR_RulePart(LayoutFrameType aFrameType)
+      : mFrameType(aFrameType), mNext(0) {}
+
+  void Destroy();
+
+  LayoutFrameType mFrameType;
+  DR_RulePart* mNext;
+};
+
+void DR_RulePart::Destroy() {
+  if (mNext) {
+    mNext->Destroy();
+  }
+  delete this;
+}
+
+struct DR_Rule {
+  DR_Rule() : mLength(0), mTarget(nullptr), mDisplay(false) {
+    MOZ_COUNT_CTOR(DR_Rule);
+  }
+  ~DR_Rule() {
+    if (mTarget) mTarget->Destroy();
+    MOZ_COUNT_DTOR(DR_Rule);
+  }
+  void AddPart(LayoutFrameType aFrameType);
+
+  uint32_t mLength;
+  DR_RulePart* mTarget;
+  bool mDisplay;
+};
+
+void DR_Rule::AddPart(LayoutFrameType aFrameType) {
+  DR_RulePart* newPart = new DR_RulePart(aFrameType);
+  newPart->mNext = mTarget;
+  mTarget = newPart;
+  mLength++;
+}
+
+DR_FrameTypeInfo::~DR_FrameTypeInfo() {
+  int32_t numElements;
+  numElements = mRules.Length();
+  for (int32_t i = numElements - 1; i >= 0; i--) {
+    delete mRules.ElementAt(i);
+  }
+}
+
+DR_FrameTypeInfo::DR_FrameTypeInfo(LayoutFrameType aFrameType,
+                                   const char* aFrameNameAbbrev,
+                                   const char* aFrameName) {
+  mType = aFrameType;
+  PL_strncpyz(mNameAbbrev, aFrameNameAbbrev, sizeof(mNameAbbrev));
+  PL_strncpyz(mName, aFrameName, sizeof(mName));
+}
+
+struct DR_FrameTreeNode {
+  DR_FrameTreeNode(nsIFrame* aFrame, DR_FrameTreeNode* aParent)
+      : mFrame(aFrame), mParent(aParent), mDisplay(0), mIndent(0) {
+    MOZ_COUNT_CTOR(DR_FrameTreeNode);
+  }
+
+  MOZ_COUNTED_DTOR(DR_FrameTreeNode)
+
+  nsIFrame* mFrame;
+  DR_FrameTreeNode* mParent;
+  bool mDisplay;
+  uint32_t mIndent;
+};
+
+// DR_State implementation
+
+DR_State::DR_State()
+    : mInited(false),
+      mActive(false),
+      mCount(0),
+      mAssert(-1),
+      mIndent(0),
+      mIndentUndisplayedFrames(false),
+      mDisplayPixelErrors(false) {
+  MOZ_COUNT_CTOR(DR_State);
+}
+
+void DR_State::Init() {
+  char* env = PR_GetEnv("GECKO_DISPLAY_REFLOW_ASSERT");
+  int32_t num;
+  if (env) {
+    if (GetNumber(env, num))
+      mAssert = num;
+    else
+      printf("GECKO_DISPLAY_REFLOW_ASSERT - invalid value = %s", env);
+  }
+
+  env = PR_GetEnv("GECKO_DISPLAY_REFLOW_INDENT_START");
+  if (env) {
+    if (GetNumber(env, num))
+      mIndent = num;
+    else
+      printf("GECKO_DISPLAY_REFLOW_INDENT_START - invalid value = %s", env);
+  }
+
+  env = PR_GetEnv("GECKO_DISPLAY_REFLOW_INDENT_UNDISPLAYED_FRAMES");
+  if (env) {
+    if (GetNumber(env, num))
+      mIndentUndisplayedFrames = num;
+    else
+      printf(
+          "GECKO_DISPLAY_REFLOW_INDENT_UNDISPLAYED_FRAMES - invalid value = %s",
+          env);
+  }
+
+  env = PR_GetEnv("GECKO_DISPLAY_REFLOW_FLAG_PIXEL_ERRORS");
+  if (env) {
+    if (GetNumber(env, num))
+      mDisplayPixelErrors = num;
+    else
+      printf("GECKO_DISPLAY_REFLOW_FLAG_PIXEL_ERRORS - invalid value = %s",
+             env);
+  }
+
+  InitFrameTypeTable();
+  ParseRulesFile();
+  mInited = true;
+}
+
+DR_State::~DR_State() {
+  MOZ_COUNT_DTOR(DR_State);
+  int32_t numElements, i;
+  numElements = mWildRules.Length();
+  for (i = numElements - 1; i >= 0; i--) {
+    delete mWildRules.ElementAt(i);
+  }
+  numElements = mFrameTreeLeaves.Length();
+  for (i = numElements - 1; i >= 0; i--) {
+    delete mFrameTreeLeaves.ElementAt(i);
+  }
+}
+
+bool DR_State::GetNumber(char* aBuf, int32_t& aNumber) {
+  if (sscanf(aBuf, "%d", &aNumber) > 0)
+    return true;
+  else
+    return false;
+}
+
+bool DR_State::IsWhiteSpace(int c) {
+  return (c == ' ') || (c == '\t') || (c == '\n') || (c == '\r');
+}
+
+bool DR_State::GetToken(FILE* aFile, char* aBuf, size_t aBufSize) {
+  bool haveToken = false;
+  aBuf[0] = 0;
+  // get the 1st non whitespace char
+  int c = -1;
+  for (c = getc(aFile); (c > 0) && IsWhiteSpace(c); c = getc(aFile)) {
+  }
+
+  if (c > 0) {
+    haveToken = true;
+    aBuf[0] = c;
+    // get everything up to the next whitespace char
+    size_t cX;
+    for (cX = 1; cX + 1 < aBufSize; cX++) {
+      c = getc(aFile);
+      if (c < 0) {  // EOF
+        ungetc(' ', aFile);
+        break;
+      } else {
+        if (IsWhiteSpace(c)) {
+          break;
+        } else {
+          aBuf[cX] = c;
+        }
+      }
+    }
+    aBuf[cX] = 0;
+  }
+  return haveToken;
+}
+
+DR_Rule* DR_State::ParseRule(FILE* aFile) {
+  char buf[128];
+  int32_t doDisplay;
+  DR_Rule* rule = nullptr;
+  while (GetToken(aFile, buf, sizeof(buf))) {
+    if (GetNumber(buf, doDisplay)) {
+      if (rule) {
+        rule->mDisplay = !!doDisplay;
+        break;
+      } else {
+        printf("unexpected token - %s \n", buf);
+      }
+    } else {
+      if (!rule) {
+        rule = new DR_Rule;
+      }
+      if (strcmp(buf, "*") == 0) {
+        rule->AddPart(LayoutFrameType::None);
+      } else {
+        DR_FrameTypeInfo* info = GetFrameTypeInfo(buf);
+        if (info) {
+          rule->AddPart(info->mType);
+        } else {
+          printf("invalid frame type - %s \n", buf);
+        }
+      }
+    }
+  }
+  return rule;
+}
+
+void DR_State::AddRule(nsTArray<DR_Rule*>& aRules, DR_Rule& aRule) {
+  int32_t numRules = aRules.Length();
+  for (int32_t ruleX = 0; ruleX < numRules; ruleX++) {
+    DR_Rule* rule = aRules.ElementAt(ruleX);
+    NS_ASSERTION(rule, "program error");
+    if (aRule.mLength > rule->mLength) {
+      aRules.InsertElementAt(ruleX, &aRule);
+      return;
+    }
+  }
+  aRules.AppendElement(&aRule);
+}
+
+static Maybe<bool> ShouldLogReflow(const char* processes) {
+  switch (processes[0]) {
+    case 'A':
+    case 'a':
+      return Some(true);
+    case 'P':
+    case 'p':
+      return Some(XRE_IsParentProcess());
+    case 'C':
+    case 'c':
+      return Some(XRE_IsContentProcess());
+    default:
+      return Nothing{};
+  }
+}
+
+void DR_State::ParseRulesFile() {
+  char* processes = PR_GetEnv("GECKO_DISPLAY_REFLOW_PROCESSES");
+  if (processes) {
+    Maybe<bool> enableLog = ShouldLogReflow(processes);
+    if (enableLog.isNothing()) {
+      MOZ_CRASH("GECKO_DISPLAY_REFLOW_PROCESSES: [a]ll [p]arent [c]ontent");
+    } else if (enableLog.value()) {
+      DR_Rule* rule = new DR_Rule;
+      rule->AddPart(LayoutFrameType::None);
+      rule->mDisplay = true;
+      AddRule(mWildRules, *rule);
+      mActive = true;
+    }
+    return;
+  }
+
+  char* path = PR_GetEnv("GECKO_DISPLAY_REFLOW_RULES_FILE");
+  if (path) {
+    FILE* inFile = fopen(path, "r");
+    if (!inFile) {
+      MOZ_CRASH(
+          "Failed to open the specified rules file; Try `--setpref "
+          "security.sandbox.content.level=2` if the sandbox is at cause");
+    }
+    for (DR_Rule* rule = ParseRule(inFile); rule; rule = ParseRule(inFile)) {
+      if (rule->mTarget) {
+        LayoutFrameType fType = rule->mTarget->mFrameType;
+        if (fType != LayoutFrameType::None) {
+          DR_FrameTypeInfo* info = GetFrameTypeInfo(fType);
+          AddRule(info->mRules, *rule);
+        } else {
+          AddRule(mWildRules, *rule);
+        }
+        mActive = true;
+      }
+    }
+
+    fclose(inFile);
+  }
+}
+
+void DR_State::AddFrameTypeInfo(LayoutFrameType aFrameType,
+                                const char* aFrameNameAbbrev,
+                                const char* aFrameName) {
+  mFrameTypeTable.EmplaceBack(aFrameType, aFrameNameAbbrev, aFrameName);
+}
+
+DR_FrameTypeInfo* DR_State::GetFrameTypeInfo(LayoutFrameType aFrameType) {
+  int32_t numEntries = mFrameTypeTable.Length();
+  NS_ASSERTION(numEntries != 0, "empty FrameTypeTable");
+  for (int32_t i = 0; i < numEntries; i++) {
+    DR_FrameTypeInfo& info = mFrameTypeTable.ElementAt(i);
+    if (info.mType == aFrameType) {
+      return &info;
+    }
+  }
+  return &mFrameTypeTable.ElementAt(numEntries -
+                                    1);  // return unknown frame type
+}
+
+DR_FrameTypeInfo* DR_State::GetFrameTypeInfo(char* aFrameName) {
+  int32_t numEntries = mFrameTypeTable.Length();
+  NS_ASSERTION(numEntries != 0, "empty FrameTypeTable");
+  for (int32_t i = 0; i < numEntries; i++) {
+    DR_FrameTypeInfo& info = mFrameTypeTable.ElementAt(i);
+    if ((strcmp(aFrameName, info.mName) == 0) ||
+        (strcmp(aFrameName, info.mNameAbbrev) == 0)) {
+      return &info;
+    }
+  }
+  return &mFrameTypeTable.ElementAt(numEntries -
+                                    1);  // return unknown frame type
+}
+
+void DR_State::InitFrameTypeTable() {
+  AddFrameTypeInfo(LayoutFrameType::Block, "block", "block");
+  AddFrameTypeInfo(LayoutFrameType::Br, "br", "br");
+  AddFrameTypeInfo(LayoutFrameType::ColorControl, "color", "colorControl");
+  AddFrameTypeInfo(LayoutFrameType::GfxButtonControl, "button",
+                   "gfxButtonControl");
+  AddFrameTypeInfo(LayoutFrameType::HTMLButtonControl, "HTMLbutton",
+                   "HTMLButtonControl");
+  AddFrameTypeInfo(LayoutFrameType::HTMLCanvas, "HTMLCanvas", "HTMLCanvas");
+  AddFrameTypeInfo(LayoutFrameType::SubDocument, "subdoc", "subDocument");
+  AddFrameTypeInfo(LayoutFrameType::Image, "img", "image");
+  AddFrameTypeInfo(LayoutFrameType::Inline, "inline", "inline");
+  AddFrameTypeInfo(LayoutFrameType::Letter, "letter", "letter");
+  AddFrameTypeInfo(LayoutFrameType::Line, "line", "line");
+  AddFrameTypeInfo(LayoutFrameType::ListControl, "select", "select");
+  AddFrameTypeInfo(LayoutFrameType::Page, "page", "page");
+  AddFrameTypeInfo(LayoutFrameType::Placeholder, "place", "placeholder");
+  AddFrameTypeInfo(LayoutFrameType::Canvas, "canvas", "canvas");
+  AddFrameTypeInfo(LayoutFrameType::Scroll, "scroll", "scroll");
+  AddFrameTypeInfo(LayoutFrameType::TableCell, "cell", "tableCell");
+  AddFrameTypeInfo(LayoutFrameType::TableCol, "col", "tableCol");
+  AddFrameTypeInfo(LayoutFrameType::TableColGroup, "colG", "tableColGroup");
+  AddFrameTypeInfo(LayoutFrameType::Table, "tbl", "table");
+  AddFrameTypeInfo(LayoutFrameType::TableWrapper, "tblW", "tableWrapper");
+  AddFrameTypeInfo(LayoutFrameType::TableRowGroup, "rowG", "tableRowGroup");
+  AddFrameTypeInfo(LayoutFrameType::TableRow, "row", "tableRow");
+  AddFrameTypeInfo(LayoutFrameType::TextInput, "textCtl", "textInput");
+  AddFrameTypeInfo(LayoutFrameType::Text, "text", "text");
+  AddFrameTypeInfo(LayoutFrameType::Viewport, "VP", "viewport");
+  AddFrameTypeInfo(LayoutFrameType::Slider, "Slider", "Slider");
+  AddFrameTypeInfo(LayoutFrameType::None, "unknown", "unknown");
+}
+
+void DR_State::DisplayFrameTypeInfo(nsIFrame* aFrame, int32_t aIndent) {
+  DR_FrameTypeInfo* frameTypeInfo = GetFrameTypeInfo(aFrame->Type());
+  if (frameTypeInfo) {
+    for (int32_t i = 0; i < aIndent; i++) {
+      printf(" ");
+    }
+    if (!strcmp(frameTypeInfo->mNameAbbrev, "unknown")) {
+      if (aFrame) {
+        nsAutoString name;
+        aFrame->GetFrameName(name);
+        printf("%s %p ", NS_LossyConvertUTF16toASCII(name).get(),
+               (void*)aFrame);
+      } else {
+        printf("%s %p ", frameTypeInfo->mNameAbbrev, (void*)aFrame);
+      }
+    } else {
+      printf("%s %p ", frameTypeInfo->mNameAbbrev, (void*)aFrame);
+    }
+  }
+}
+
+bool DR_State::RuleMatches(DR_Rule& aRule, DR_FrameTreeNode& aNode) {
+  NS_ASSERTION(aRule.mTarget, "program error");
+
+  DR_RulePart* rulePart;
+  DR_FrameTreeNode* parentNode;
+  for (rulePart = aRule.mTarget->mNext, parentNode = aNode.mParent;
+       rulePart && parentNode;
+       rulePart = rulePart->mNext, parentNode = parentNode->mParent) {
+    if (rulePart->mFrameType != LayoutFrameType::None) {
+      if (parentNode->mFrame) {
+        if (rulePart->mFrameType != parentNode->mFrame->Type()) {
+          return false;
+        }
+      } else
+        NS_ASSERTION(false, "program error");
+    }
+    // else wild card match
+  }
+  return true;
+}
+
+void DR_State::FindMatchingRule(DR_FrameTreeNode& aNode) {
+  if (!aNode.mFrame) {
+    NS_ASSERTION(false, "invalid DR_FrameTreeNode \n");
+    return;
+  }
+
+  bool matchingRule = false;
+
+  DR_FrameTypeInfo* info = GetFrameTypeInfo(aNode.mFrame->Type());
+  NS_ASSERTION(info, "program error");
+  int32_t numRules = info->mRules.Length();
+  for (int32_t ruleX = 0; ruleX < numRules; ruleX++) {
+    DR_Rule* rule = info->mRules.ElementAt(ruleX);
+    if (rule && RuleMatches(*rule, aNode)) {
+      aNode.mDisplay = rule->mDisplay;
+      matchingRule = true;
+      break;
+    }
+  }
+  if (!matchingRule) {
+    int32_t numWildRules = mWildRules.Length();
+    for (int32_t ruleX = 0; ruleX < numWildRules; ruleX++) {
+      DR_Rule* rule = mWildRules.ElementAt(ruleX);
+      if (rule && RuleMatches(*rule, aNode)) {
+        aNode.mDisplay = rule->mDisplay;
+        break;
+      }
+    }
+  }
+}
+
+DR_FrameTreeNode* DR_State::CreateTreeNode(nsIFrame* aFrame,
+                                           const ReflowInput* aReflowInput) {
+  // find the frame of the parent reflow input (usually just the parent of
+  // aFrame)
+  nsIFrame* parentFrame;
+  if (aReflowInput) {
+    const ReflowInput* parentRI = aReflowInput->mParentReflowInput;
+    parentFrame = (parentRI) ? parentRI->mFrame : nullptr;
+  } else {
+    parentFrame = aFrame->GetParent();
+  }
+
+  // find the parent tree node leaf
+  DR_FrameTreeNode* parentNode = nullptr;
+
+  DR_FrameTreeNode* lastLeaf = nullptr;
+  if (mFrameTreeLeaves.Length())
+    lastLeaf = mFrameTreeLeaves.ElementAt(mFrameTreeLeaves.Length() - 1);
+  if (lastLeaf) {
+    for (parentNode = lastLeaf;
+         parentNode && (parentNode->mFrame != parentFrame);
+         parentNode = parentNode->mParent) {
+    }
+  }
+  DR_FrameTreeNode* newNode = new DR_FrameTreeNode(aFrame, parentNode);
+  FindMatchingRule(*newNode);
+
+  newNode->mIndent = mIndent;
+  if (newNode->mDisplay || mIndentUndisplayedFrames) {
+    ++mIndent;
+  }
+
+  if (lastLeaf && (lastLeaf == parentNode)) {
+    mFrameTreeLeaves.RemoveLastElement();
+  }
+  mFrameTreeLeaves.AppendElement(newNode);
+  mCount++;
+
+  return newNode;
+}
+
+void DR_State::PrettyUC(nscoord aSize, char* aBuf, int aBufSize) {
+  if (NS_UNCONSTRAINEDSIZE == aSize) {
+    strcpy(aBuf, "UC");
+  } else {
+    if ((nscoord)0xdeadbeefU == aSize) {
+      strcpy(aBuf, "deadbeef");
+    } else {
+      snprintf(aBuf, aBufSize, "%d", aSize);
+    }
+  }
+}
+
+void DR_State::PrintMargin(const char* tag, const nsMargin* aMargin) {
+  if (aMargin) {
+    char t[16], r[16], b[16], l[16];
+    PrettyUC(aMargin->top, t, 16);
+    PrettyUC(aMargin->right, r, 16);
+    PrettyUC(aMargin->bottom, b, 16);
+    PrettyUC(aMargin->left, l, 16);
+    printf(" %s=%s,%s,%s,%s", tag, t, r, b, l);
+  } else {
+    // use %p here for consistency with other null-pointer printouts
+    printf(" %s=%p", tag, (void*)aMargin);
+  }
+}
+
+void DR_State::DeleteTreeNode(DR_FrameTreeNode& aNode) {
+  mFrameTreeLeaves.RemoveElement(&aNode);
+  int32_t numLeaves = mFrameTreeLeaves.Length();
+  if ((0 == numLeaves) ||
+      (aNode.mParent != mFrameTreeLeaves.ElementAt(numLeaves - 1))) {
+    mFrameTreeLeaves.AppendElement(aNode.mParent);
+  }
+
+  if (aNode.mDisplay || mIndentUndisplayedFrames) {
+    --mIndent;
+  }
+  // delete the tree node
+  delete &aNode;
+}
+
+static void CheckPixelError(nscoord aSize, int32_t aPixelToTwips) {
+  if (NS_UNCONSTRAINEDSIZE != aSize) {
+    if ((aSize % aPixelToTwips) > 0) {
+      printf("VALUE %d is not a whole pixel \n", aSize);
+    }
+  }
+}
+
+static void DisplayReflowEnterPrint(nsPresContext* aPresContext,
+                                    nsIFrame* aFrame,
+                                    const ReflowInput& aReflowInput,
+                                    DR_FrameTreeNode& aTreeNode,
+                                    bool aChanged) {
+  if (aTreeNode.mDisplay) {
+    DR_state->DisplayFrameTypeInfo(aFrame, aTreeNode.mIndent);
+
+    char width[16];
+    char height[16];
+
+    DR_state->PrettyUC(aReflowInput.AvailableWidth(), width, 16);
+    DR_state->PrettyUC(aReflowInput.AvailableHeight(), height, 16);
+    printf("Reflow a=%s,%s ", width, height);
+
+    DR_state->PrettyUC(aReflowInput.ComputedWidth(), width, 16);
+    DR_state->PrettyUC(aReflowInput.ComputedHeight(), height, 16);
+    printf("c=%s,%s ", width, height);
+
+    if (aFrame->HasAnyStateBits(NS_FRAME_IS_DIRTY)) printf("dirty ");
+
+    if (aFrame->HasAnyStateBits(NS_FRAME_HAS_DIRTY_CHILDREN))
+      printf("dirty-children ");
+
+    if (aReflowInput.mFlags.mSpecialBSizeReflow) printf("special-bsize ");
+
+    if (aReflowInput.IsHResize()) printf("h-resize ");
+
+    if (aReflowInput.IsVResize()) printf("v-resize ");
+
+    nsIFrame* inFlow = aFrame->GetPrevInFlow();
+    if (inFlow) {
+      printf("pif=%p ", (void*)inFlow);
+    }
+    inFlow = aFrame->GetNextInFlow();
+    if (inFlow) {
+      printf("nif=%p ", (void*)inFlow);
+    }
+    if (aChanged)
+      printf("CHANGED \n");
+    else
+      printf("cnt=%d \n", DR_state->mCount);
+    if (DR_state->mDisplayPixelErrors) {
+      int32_t d2a = aPresContext->AppUnitsPerDevPixel();
+      CheckPixelError(aReflowInput.AvailableWidth(), d2a);
+      CheckPixelError(aReflowInput.AvailableHeight(), d2a);
+      CheckPixelError(aReflowInput.ComputedWidth(), d2a);
+      CheckPixelError(aReflowInput.ComputedHeight(), d2a);
+    }
+  }
+}
+
+void* nsIFrame::DisplayReflowEnter(nsPresContext* aPresContext,
+                                   nsIFrame* aFrame,
+                                   const ReflowInput& aReflowInput) {
+  if (!DR_state->mInited) DR_state->Init();
+  if (!DR_state->mActive) return nullptr;
+
+  NS_ASSERTION(aFrame, "invalid call");
+
+  DR_FrameTreeNode* treeNode = DR_state->CreateTreeNode(aFrame, &aReflowInput);
+  if (treeNode) {
+    DisplayReflowEnterPrint(aPresContext, aFrame, aReflowInput, *treeNode,
+                            false);
+  }
+  return treeNode;
+}
+
+void* nsIFrame::DisplayLayoutEnter(nsIFrame* aFrame) {
+  if (!DR_state->mInited) DR_state->Init();
+  if (!DR_state->mActive) return nullptr;
+
+  NS_ASSERTION(aFrame, "invalid call");
+
+  DR_FrameTreeNode* treeNode = DR_state->CreateTreeNode(aFrame, nullptr);
+  if (treeNode && treeNode->mDisplay) {
+    DR_state->DisplayFrameTypeInfo(aFrame, treeNode->mIndent);
+    printf("XULLayout\n");
+  }
+  return treeNode;
+}
+
+void* nsIFrame::DisplayIntrinsicISizeEnter(nsIFrame* aFrame,
+                                           const char* aType) {
+  if (!DR_state->mInited) DR_state->Init();
+  if (!DR_state->mActive) return nullptr;
+
+  NS_ASSERTION(aFrame, "invalid call");
+
+  DR_FrameTreeNode* treeNode = DR_state->CreateTreeNode(aFrame, nullptr);
+  if (treeNode && treeNode->mDisplay) {
+    DR_state->DisplayFrameTypeInfo(aFrame, treeNode->mIndent);
+    printf("Get%sISize\n", aType);
+  }
+  return treeNode;
+}
+
+void* nsIFrame::DisplayIntrinsicSizeEnter(nsIFrame* aFrame, const char* aType) {
+  if (!DR_state->mInited) DR_state->Init();
+  if (!DR_state->mActive) return nullptr;
+
+  NS_ASSERTION(aFrame, "invalid call");
+
+  DR_FrameTreeNode* treeNode = DR_state->CreateTreeNode(aFrame, nullptr);
+  if (treeNode && treeNode->mDisplay) {
+    DR_state->DisplayFrameTypeInfo(aFrame, treeNode->mIndent);
+    printf("Get%sSize\n", aType);
+  }
+  return treeNode;
+}
+
+void nsIFrame::DisplayReflowExit(nsPresContext* aPresContext, nsIFrame* aFrame,
+                                 ReflowOutput& aMetrics,
+                                 const nsReflowStatus& aStatus,
+                                 void* aFrameTreeNode) {
+  if (!DR_state->mActive) return;
+
+  NS_ASSERTION(aFrame, "DisplayReflowExit - invalid call");
+  if (!aFrameTreeNode) return;
+
+  DR_FrameTreeNode* treeNode = (DR_FrameTreeNode*)aFrameTreeNode;
+  if (treeNode->mDisplay) {
+    DR_state->DisplayFrameTypeInfo(aFrame, treeNode->mIndent);
+
+    char width[16];
+    char height[16];
+    char x[16];
+    char y[16];
+    DR_state->PrettyUC(aMetrics.Width(), width, 16);
+    DR_state->PrettyUC(aMetrics.Height(), height, 16);
+    printf("Reflow d=%s,%s", width, height);
+
+    if (!aStatus.IsEmpty()) {
+      printf(" status=%s", ToString(aStatus).c_str());
+    }
+    if (aFrame->HasOverflowAreas()) {
+      DR_state->PrettyUC(aMetrics.InkOverflow().x, x, 16);
+      DR_state->PrettyUC(aMetrics.InkOverflow().y, y, 16);
+      DR_state->PrettyUC(aMetrics.InkOverflow().width, width, 16);
+      DR_state->PrettyUC(aMetrics.InkOverflow().height, height, 16);
+      printf(" vis-o=(%s,%s) %s x %s", x, y, width, height);
+
+      nsRect storedOverflow = aFrame->InkOverflowRect();
+      DR_state->PrettyUC(storedOverflow.x, x, 16);
+      DR_state->PrettyUC(storedOverflow.y, y, 16);
+      DR_state->PrettyUC(storedOverflow.width, width, 16);
+      DR_state->PrettyUC(storedOverflow.height, height, 16);
+      printf(" vis-sto=(%s,%s) %s x %s", x, y, width, height);
+
+      DR_state->PrettyUC(aMetrics.ScrollableOverflow().x, x, 16);
+      DR_state->PrettyUC(aMetrics.ScrollableOverflow().y, y, 16);
+      DR_state->PrettyUC(aMetrics.ScrollableOverflow().width, width, 16);
+      DR_state->PrettyUC(aMetrics.ScrollableOverflow().height, height, 16);
+      printf(" scr-o=(%s,%s) %s x %s", x, y, width, height);
+
+      storedOverflow = aFrame->ScrollableOverflowRect();
+      DR_state->PrettyUC(storedOverflow.x, x, 16);
+      DR_state->PrettyUC(storedOverflow.y, y, 16);
+      DR_state->PrettyUC(storedOverflow.width, width, 16);
+      DR_state->PrettyUC(storedOverflow.height, height, 16);
+      printf(" scr-sto=(%s,%s) %s x %s", x, y, width, height);
+    }
+    printf("\n");
+    if (DR_state->mDisplayPixelErrors) {
+      int32_t d2a = aPresContext->AppUnitsPerDevPixel();
+      CheckPixelError(aMetrics.Width(), d2a);
+      CheckPixelError(aMetrics.Height(), d2a);
+    }
+  }
+  DR_state->DeleteTreeNode(*treeNode);
+}
+
+void nsIFrame::DisplayLayoutExit(nsIFrame* aFrame, void* aFrameTreeNode) {
+  if (!DR_state->mActive) return;
+
+  NS_ASSERTION(aFrame, "non-null frame required");
+  if (!aFrameTreeNode) return;
+
+  DR_FrameTreeNode* treeNode = (DR_FrameTreeNode*)aFrameTreeNode;
+  if (treeNode->mDisplay) {
+    DR_state->DisplayFrameTypeInfo(aFrame, treeNode->mIndent);
+    nsRect rect = aFrame->GetRect();
+    printf("XULLayout=%d,%d,%d,%d\n", rect.x, rect.y, rect.width, rect.height);
+  }
+  DR_state->DeleteTreeNode(*treeNode);
+}
+
+void nsIFrame::DisplayIntrinsicISizeExit(nsIFrame* aFrame, const char* aType,
+                                         nscoord aResult,
+                                         void* aFrameTreeNode) {
+  if (!DR_state->mActive) return;
+
+  NS_ASSERTION(aFrame, "non-null frame required");
+  if (!aFrameTreeNode) return;
+
+  DR_FrameTreeNode* treeNode = (DR_FrameTreeNode*)aFrameTreeNode;
+  if (treeNode->mDisplay) {
+    DR_state->DisplayFrameTypeInfo(aFrame, treeNode->mIndent);
+    char iSize[16];
+    DR_state->PrettyUC(aResult, iSize, 16);
+    printf("Get%sISize=%s\n", aType, iSize);
+  }
+  DR_state->DeleteTreeNode(*treeNode);
+}
+
+void nsIFrame::DisplayIntrinsicSizeExit(nsIFrame* aFrame, const char* aType,
+                                        nsSize aResult, void* aFrameTreeNode) {
+  if (!DR_state->mActive) return;
+
+  NS_ASSERTION(aFrame, "non-null frame required");
+  if (!aFrameTreeNode) return;
+
+  DR_FrameTreeNode* treeNode = (DR_FrameTreeNode*)aFrameTreeNode;
+  if (treeNode->mDisplay) {
+    DR_state->DisplayFrameTypeInfo(aFrame, treeNode->mIndent);
+
+    char width[16];
+    char height[16];
+    DR_state->PrettyUC(aResult.width, width, 16);
+    DR_state->PrettyUC(aResult.height, height, 16);
+    printf("Get%sSize=%s,%s\n", aType, width, height);
+  }
+  DR_state->DeleteTreeNode(*treeNode);
+}
+
+/* static */
+void nsIFrame::DisplayReflowStartup() { DR_state = new DR_State(); }
+
+/* static */
+void nsIFrame::DisplayReflowShutdown() {
+  delete DR_state;
+  DR_state = nullptr;
+}
+
+void DR_cookie::Change() const {
+  DR_FrameTreeNode* treeNode = (DR_FrameTreeNode*)mValue;
+  if (treeNode && treeNode->mDisplay) {
+    DisplayReflowEnterPrint(mPresContext, mFrame, mReflowInput, *treeNode,
+                            true);
+  }
+}
+
+/* static */
+void* ReflowInput::DisplayInitConstraintsEnter(nsIFrame* aFrame,
+                                               ReflowInput* aState,
+                                               nscoord aContainingBlockWidth,
+                                               nscoord aContainingBlockHeight,
+                                               const nsMargin* aBorder,
+                                               const nsMargin* aPadding) {
+  MOZ_ASSERT(aFrame, "non-null frame required");
+  MOZ_ASSERT(aState, "non-null state required");
+
+  if (!DR_state->mInited) DR_state->Init();
+  if (!DR_state->mActive) return nullptr;
+
+  DR_FrameTreeNode* treeNode = DR_state->CreateTreeNode(aFrame, aState);
+  if (treeNode && treeNode->mDisplay) {
+    DR_state->DisplayFrameTypeInfo(aFrame, treeNode->mIndent);
+
+    printf("InitConstraints parent=%p", (void*)aState->mParentReflowInput);
+
+    char width[16];
+    char height[16];
+
+    DR_state->PrettyUC(aContainingBlockWidth, width, 16);
+    DR_state->PrettyUC(aContainingBlockHeight, height, 16);
+    printf(" cb=%s,%s", width, height);
+
+    DR_state->PrettyUC(aState->AvailableWidth(), width, 16);
+    DR_state->PrettyUC(aState->AvailableHeight(), height, 16);
+    printf(" as=%s,%s", width, height);
+
+    DR_state->PrintMargin("b", aBorder);
+    DR_state->PrintMargin("p", aPadding);
+    putchar('\n');
+  }
+  return treeNode;
+}
+
+/* static */
+void ReflowInput::DisplayInitConstraintsExit(nsIFrame* aFrame,
+                                             ReflowInput* aState,
+                                             void* aValue) {
+  MOZ_ASSERT(aFrame, "non-null frame required");
+  MOZ_ASSERT(aState, "non-null state required");
+
+  if (!DR_state->mActive) return;
+  if (!aValue) return;
+
+  DR_FrameTreeNode* treeNode = (DR_FrameTreeNode*)aValue;
+  if (treeNode->mDisplay) {
+    DR_state->DisplayFrameTypeInfo(aFrame, treeNode->mIndent);
+    char cmiw[16], cw[16], cmxw[16], cmih[16], ch[16], cmxh[16];
+    DR_state->PrettyUC(aState->ComputedMinWidth(), cmiw, 16);
+    DR_state->PrettyUC(aState->ComputedWidth(), cw, 16);
+    DR_state->PrettyUC(aState->ComputedMaxWidth(), cmxw, 16);
+    DR_state->PrettyUC(aState->ComputedMinHeight(), cmih, 16);
+    DR_state->PrettyUC(aState->ComputedHeight(), ch, 16);
+    DR_state->PrettyUC(aState->ComputedMaxHeight(), cmxh, 16);
+    printf("InitConstraints= cw=(%s <= %s <= %s) ch=(%s <= %s <= %s)", cmiw, cw,
+           cmxw, cmih, ch, cmxh);
+    const nsMargin m = aState->ComputedPhysicalOffsets();
+    DR_state->PrintMargin("co", &m);
+    putchar('\n');
+  }
+  DR_state->DeleteTreeNode(*treeNode);
+}
+
+/* static */
+void* SizeComputationInput::DisplayInitOffsetsEnter(
+    nsIFrame* aFrame, SizeComputationInput* aState, nscoord aPercentBasis,
+    WritingMode aCBWritingMode, const nsMargin* aBorder,
+    const nsMargin* aPadding) {
+  MOZ_ASSERT(aFrame, "non-null frame required");
+  MOZ_ASSERT(aState, "non-null state required");
+
+  if (!DR_state->mInited) DR_state->Init();
+  if (!DR_state->mActive) return nullptr;
+
+  // aState is not necessarily a ReflowInput
+  DR_FrameTreeNode* treeNode = DR_state->CreateTreeNode(aFrame, nullptr);
+  if (treeNode && treeNode->mDisplay) {
+    DR_state->DisplayFrameTypeInfo(aFrame, treeNode->mIndent);
+
+    char pctBasisStr[16];
+    DR_state->PrettyUC(aPercentBasis, pctBasisStr, 16);
+    printf("InitOffsets pct_basis=%s", pctBasisStr);
+
+    DR_state->PrintMargin("b", aBorder);
+    DR_state->PrintMargin("p", aPadding);
+    putchar('\n');
+  }
+  return treeNode;
+}
+
+/* static */
+void SizeComputationInput::DisplayInitOffsetsExit(nsIFrame* aFrame,
+                                                  SizeComputationInput* aState,
+                                                  void* aValue) {
+  MOZ_ASSERT(aFrame, "non-null frame required");
+  MOZ_ASSERT(aState, "non-null state required");
+
+  if (!DR_state->mActive) return;
+  if (!aValue) return;
+
+  DR_FrameTreeNode* treeNode = (DR_FrameTreeNode*)aValue;
+  if (treeNode->mDisplay) {
+    DR_state->DisplayFrameTypeInfo(aFrame, treeNode->mIndent);
+    printf("InitOffsets=");
+    const auto m = aState->ComputedPhysicalMargin();
+    DR_state->PrintMargin("m", &m);
+    const auto p = aState->ComputedPhysicalPadding();
+    DR_state->PrintMargin("p", &p);
+    const auto bp = aState->ComputedPhysicalBorderPadding();
+    DR_state->PrintMargin("b+p", &bp);
+    putchar('\n');
+  }
+  DR_state->DeleteTreeNode(*treeNode);
+}
+
+// End Display Reflow
+
+// Validation of SideIsVertical.
+#  define CASE(side, result) \
+    static_assert(SideIsVertical(side) == result, "SideIsVertical is wrong")
+CASE(eSideTop, false);
+CASE(eSideRight, true);
+CASE(eSideBottom, false);
+CASE(eSideLeft, true);
+#  undef CASE
+
+// Validation of HalfCornerIsX.
+#  define CASE(corner, result) \
+    static_assert(HalfCornerIsX(corner) == result, "HalfCornerIsX is wrong")
+CASE(eCornerTopLeftX, true);
+CASE(eCornerTopLeftY, false);
+CASE(eCornerTopRightX, true);
+CASE(eCornerTopRightY, false);
+CASE(eCornerBottomRightX, true);
+CASE(eCornerBottomRightY, false);
+CASE(eCornerBottomLeftX, true);
+CASE(eCornerBottomLeftY, false);
+#  undef CASE
+
+// Validation of HalfToFullCorner.
+#  define CASE(corner, result)                        \
+    static_assert(HalfToFullCorner(corner) == result, \
+                  "HalfToFullCorner is "              \
+                  "wrong")
+CASE(eCornerTopLeftX, eCornerTopLeft);
+CASE(eCornerTopLeftY, eCornerTopLeft);
+CASE(eCornerTopRightX, eCornerTopRight);
+CASE(eCornerTopRightY, eCornerTopRight);
+CASE(eCornerBottomRightX, eCornerBottomRight);
+CASE(eCornerBottomRightY, eCornerBottomRight);
+CASE(eCornerBottomLeftX, eCornerBottomLeft);
+CASE(eCornerBottomLeftY, eCornerBottomLeft);
+#  undef CASE
+
+// Validation of FullToHalfCorner.
+#  define CASE(corner, vert, result)                        \
+    static_assert(FullToHalfCorner(corner, vert) == result, \
+                  "FullToHalfCorner is wrong")
+CASE(eCornerTopLeft, false, eCornerTopLeftX);
+CASE(eCornerTopLeft, true, eCornerTopLeftY);
+CASE(eCornerTopRight, false, eCornerTopRightX);
+CASE(eCornerTopRight, true, eCornerTopRightY);
+CASE(eCornerBottomRight, false, eCornerBottomRightX);
+CASE(eCornerBottomRight, true, eCornerBottomRightY);
+CASE(eCornerBottomLeft, false, eCornerBottomLeftX);
+CASE(eCornerBottomLeft, true, eCornerBottomLeftY);
+#  undef CASE
+
+// Validation of SideToFullCorner.
+#  define CASE(side, second, result)                        \
+    static_assert(SideToFullCorner(side, second) == result, \
+                  "SideToFullCorner is wrong")
+CASE(eSideTop, false, eCornerTopLeft);
+CASE(eSideTop, true, eCornerTopRight);
+
+CASE(eSideRight, false, eCornerTopRight);
+CASE(eSideRight, true, eCornerBottomRight);
+
+CASE(eSideBottom, false, eCornerBottomRight);
+CASE(eSideBottom, true, eCornerBottomLeft);
+
+CASE(eSideLeft, false, eCornerBottomLeft);
+CASE(eSideLeft, true, eCornerTopLeft);
+#  undef CASE
+
+// Validation of SideToHalfCorner.
+#  define CASE(side, second, parallel, result)                        \
+    static_assert(SideToHalfCorner(side, second, parallel) == result, \
+                  "SideToHalfCorner is wrong")
+CASE(eSideTop, false, true, eCornerTopLeftX);
+CASE(eSideTop, false, false, eCornerTopLeftY);
+CASE(eSideTop, true, true, eCornerTopRightX);
+CASE(eSideTop, true, false, eCornerTopRightY);
+
+CASE(eSideRight, false, false, eCornerTopRightX);
+CASE(eSideRight, false, true, eCornerTopRightY);
+CASE(eSideRight, true, false, eCornerBottomRightX);
+CASE(eSideRight, true, true, eCornerBottomRightY);
+
+CASE(eSideBottom, false, true, eCornerBottomRightX);
+CASE(eSideBottom, false, false, eCornerBottomRightY);
+CASE(eSideBottom, true, true, eCornerBottomLeftX);
+CASE(eSideBottom, true, false, eCornerBottomLeftY);
+
+CASE(eSideLeft, false, false, eCornerBottomLeftX);
+CASE(eSideLeft, false, true, eCornerBottomLeftY);
+CASE(eSideLeft, true, false, eCornerTopLeftX);
+CASE(eSideLeft, true, true, eCornerTopLeftY);
+#  undef CASE
+
+#endif