Adding upstream version 1:115.7.0.upstream/1%115.7.0upstream

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

1 files changed, 3079 insertions, 0 deletions

diff --git a/layout/generic/nsContainerFrame.cpp b/layout/generic/nsContainerFrame.cpp
new file mode 100644
index 0000000000..813f6170a9
--- /dev/null
+++ b/layout/generic/nsContainerFrame.cpp
@@ -0,0 +1,3079 @@
+/* -*- 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 #1 for rendering objects that have child lists */
+
+#include "nsContainerFrame.h"
+#include "mozilla/widget/InitData.h"
+#include "nsContainerFrameInlines.h"
+
+#include "mozilla/ComputedStyle.h"
+#include "mozilla/PresShell.h"
+#include "mozilla/dom/HTMLSummaryElement.h"
+#include "mozilla/gfx/2D.h"
+#include "mozilla/gfx/Types.h"
+#include "nsAbsoluteContainingBlock.h"
+#include "nsAttrValue.h"
+#include "nsAttrValueInlines.h"
+#include "nsFlexContainerFrame.h"
+#include "nsFrameSelection.h"
+#include "mozilla/dom/Document.h"
+#include "nsPresContext.h"
+#include "nsRect.h"
+#include "nsPoint.h"
+#include "nsStyleConsts.h"
+#include "nsView.h"
+#include "nsCOMPtr.h"
+#include "nsGkAtoms.h"
+#include "nsViewManager.h"
+#include "nsIWidget.h"
+#include "nsCanvasFrame.h"
+#include "nsCSSRendering.h"
+#include "nsError.h"
+#include "nsDisplayList.h"
+#include "nsIBaseWindow.h"
+#include "nsCSSFrameConstructor.h"
+#include "nsBlockFrame.h"
+#include "nsPlaceholderFrame.h"
+#include "mozilla/AutoRestore.h"
+#include "nsIFrameInlines.h"
+#include "nsPrintfCString.h"
+#include "mozilla/webrender/WebRenderAPI.h"
+#include <algorithm>
+
+using namespace mozilla;
+using namespace mozilla::dom;
+using namespace mozilla::layout;
+
+using mozilla::gfx::ColorPattern;
+using mozilla::gfx::DeviceColor;
+using mozilla::gfx::DrawTarget;
+using mozilla::gfx::Rect;
+using mozilla::gfx::sRGBColor;
+using mozilla::gfx::ToDeviceColor;
+
+nsContainerFrame::~nsContainerFrame() = default;
+
+NS_QUERYFRAME_HEAD(nsContainerFrame)
+  NS_QUERYFRAME_ENTRY(nsContainerFrame)
+NS_QUERYFRAME_TAIL_INHERITING(nsSplittableFrame)
+
+void nsContainerFrame::Init(nsIContent* aContent, nsContainerFrame* aParent,
+                            nsIFrame* aPrevInFlow) {
+  nsSplittableFrame::Init(aContent, aParent, aPrevInFlow);
+  if (aPrevInFlow) {
+    // Make sure we copy bits from our prev-in-flow that will affect
+    // us. A continuation for a container frame needs to know if it
+    // has a child with a view so that we'll properly reposition it.
+    if (aPrevInFlow->HasAnyStateBits(NS_FRAME_HAS_CHILD_WITH_VIEW)) {
+      AddStateBits(NS_FRAME_HAS_CHILD_WITH_VIEW);
+    }
+  }
+}
+
+void nsContainerFrame::SetInitialChildList(ChildListID aListID,
+                                           nsFrameList&& aChildList) {
+#ifdef DEBUG
+  nsIFrame::VerifyDirtyBitSet(aChildList);
+  for (nsIFrame* f : aChildList) {
+    MOZ_ASSERT(f->GetParent() == this, "Unexpected parent");
+  }
+#endif
+  if (aListID == FrameChildListID::Principal) {
+    MOZ_ASSERT(mFrames.IsEmpty(),
+               "unexpected second call to SetInitialChildList");
+    mFrames = std::move(aChildList);
+  } else if (aListID == FrameChildListID::Backdrop) {
+    MOZ_ASSERT(StyleDisplay()->mTopLayer != StyleTopLayer::None,
+               "Only top layer frames should have backdrop");
+    MOZ_ASSERT(HasAnyStateBits(NS_FRAME_OUT_OF_FLOW),
+               "Top layer frames should be out-of-flow");
+    MOZ_ASSERT(!GetProperty(BackdropProperty()),
+               "We shouldn't have setup backdrop frame list before");
+#ifdef DEBUG
+    {
+      nsIFrame* placeholder = aChildList.FirstChild();
+      MOZ_ASSERT(aChildList.OnlyChild(), "Should have only one backdrop");
+      MOZ_ASSERT(placeholder->IsPlaceholderFrame(),
+                 "The frame to be stored should be a placeholder");
+      MOZ_ASSERT(static_cast<nsPlaceholderFrame*>(placeholder)
+                     ->GetOutOfFlowFrame()
+                     ->IsBackdropFrame(),
+                 "The placeholder should points to a backdrop frame");
+    }
+#endif
+    nsFrameList* list = new (PresShell()) nsFrameList(std::move(aChildList));
+    SetProperty(BackdropProperty(), list);
+  } else {
+    MOZ_ASSERT_UNREACHABLE("Unexpected child list");
+  }
+}
+
+void nsContainerFrame::AppendFrames(ChildListID aListID,
+                                    nsFrameList&& aFrameList) {
+  MOZ_ASSERT(aListID == FrameChildListID::Principal ||
+                 aListID == FrameChildListID::NoReflowPrincipal,
+             "unexpected child list");
+
+  if (MOZ_UNLIKELY(aFrameList.IsEmpty())) {
+    return;
+  }
+
+  DrainSelfOverflowList();  // ensure the last frame is in mFrames
+  mFrames.AppendFrames(this, std::move(aFrameList));
+
+  if (aListID != FrameChildListID::NoReflowPrincipal) {
+    PresShell()->FrameNeedsReflow(this, IntrinsicDirty::FrameAndAncestors,
+                                  NS_FRAME_HAS_DIRTY_CHILDREN);
+  }
+}
+
+void nsContainerFrame::InsertFrames(ChildListID aListID, nsIFrame* aPrevFrame,
+                                    const nsLineList::iterator* aPrevFrameLine,
+                                    nsFrameList&& aFrameList) {
+  MOZ_ASSERT(aListID == FrameChildListID::Principal ||
+                 aListID == FrameChildListID::NoReflowPrincipal,
+             "unexpected child list");
+  NS_ASSERTION(!aPrevFrame || aPrevFrame->GetParent() == this,
+               "inserting after sibling frame with different parent");
+
+  if (MOZ_UNLIKELY(aFrameList.IsEmpty())) {
+    return;
+  }
+
+  DrainSelfOverflowList();  // ensure aPrevFrame is in mFrames
+  mFrames.InsertFrames(this, aPrevFrame, std::move(aFrameList));
+
+  if (aListID != FrameChildListID::NoReflowPrincipal) {
+    PresShell()->FrameNeedsReflow(this, IntrinsicDirty::FrameAndAncestors,
+                                  NS_FRAME_HAS_DIRTY_CHILDREN);
+  }
+}
+
+void nsContainerFrame::RemoveFrame(DestroyContext& aContext,
+                                   ChildListID aListID, nsIFrame* aOldFrame) {
+  MOZ_ASSERT(aListID == FrameChildListID::Principal ||
+                 aListID == FrameChildListID::NoReflowPrincipal,
+             "unexpected child list");
+
+  AutoTArray<nsIFrame*, 10> continuations;
+  {
+    nsIFrame* continuation = aOldFrame;
+    while (continuation) {
+      continuations.AppendElement(continuation);
+      continuation = continuation->GetNextContinuation();
+    }
+  }
+
+  mozilla::PresShell* presShell = PresShell();
+  nsContainerFrame* lastParent = nullptr;
+
+  // Loop and destroy aOldFrame and all of its continuations.
+  //
+  // Request a reflow on the parent frames involved unless we were explicitly
+  // told not to (FrameChildListID::NoReflowPrincipal).
+  const bool generateReflowCommand =
+      aListID != FrameChildListID::NoReflowPrincipal;
+  for (nsIFrame* continuation : Reversed(continuations)) {
+    nsContainerFrame* parent = continuation->GetParent();
+
+    // Please note that 'parent' may not actually be where 'continuation' lives.
+    // We really MUST use StealFrame() and nothing else here.
+    // @see nsInlineFrame::StealFrame for details.
+    parent->StealFrame(continuation);
+    continuation->Destroy(aContext);
+    if (generateReflowCommand && parent != lastParent) {
+      presShell->FrameNeedsReflow(parent, IntrinsicDirty::FrameAndAncestors,
+                                  NS_FRAME_HAS_DIRTY_CHILDREN);
+      lastParent = parent;
+    }
+  }
+}
+
+void nsContainerFrame::DestroyAbsoluteFrames(DestroyContext& aContext) {
+  if (IsAbsoluteContainer()) {
+    GetAbsoluteContainingBlock()->DestroyFrames(aContext);
+    MarkAsNotAbsoluteContainingBlock();
+  }
+}
+
+void nsContainerFrame::SafelyDestroyFrameListProp(
+    DestroyContext& aContext, mozilla::PresShell* aPresShell,
+    FrameListPropertyDescriptor aProp) {
+  // Note that the last frame can be removed through another route and thus
+  // delete the property -- that's why we fetch the property again before
+  // removing each frame rather than fetching it once and iterating the list.
+  while (nsFrameList* frameList = GetProperty(aProp)) {
+    nsIFrame* frame = frameList->RemoveFirstChild();
+    if (MOZ_LIKELY(frame)) {
+      frame->Destroy(aContext);
+    } else {
+      Unused << TakeProperty(aProp);
+      frameList->Delete(aPresShell);
+      return;
+    }
+  }
+}
+
+void nsContainerFrame::Destroy(DestroyContext& aContext) {
+  // Prevent event dispatch during destruction.
+  if (HasView()) {
+    GetView()->SetFrame(nullptr);
+  }
+
+  DestroyAbsoluteFrames(aContext);
+
+  // Destroy frames on the principal child list.
+  mFrames.DestroyFrames(aContext);
+
+  // If we have any IB split siblings, clear their references to us.
+  if (HasAnyStateBits(NS_FRAME_PART_OF_IBSPLIT)) {
+    // Delete previous sibling's reference to me.
+    if (nsIFrame* prevSib = GetProperty(nsIFrame::IBSplitPrevSibling())) {
+      NS_WARNING_ASSERTION(
+          this == prevSib->GetProperty(nsIFrame::IBSplitSibling()),
+          "IB sibling chain is inconsistent");
+      prevSib->RemoveProperty(nsIFrame::IBSplitSibling());
+    }
+
+    // Delete next sibling's reference to me.
+    if (nsIFrame* nextSib = GetProperty(nsIFrame::IBSplitSibling())) {
+      NS_WARNING_ASSERTION(
+          this == nextSib->GetProperty(nsIFrame::IBSplitPrevSibling()),
+          "IB sibling chain is inconsistent");
+      nextSib->RemoveProperty(nsIFrame::IBSplitPrevSibling());
+    }
+
+#ifdef DEBUG
+    // This is just so we can assert it's not set in nsIFrame::DestroyFrom.
+    RemoveStateBits(NS_FRAME_PART_OF_IBSPLIT);
+#endif
+  }
+
+  if (MOZ_UNLIKELY(!mProperties.IsEmpty())) {
+    using T = mozilla::FrameProperties::UntypedDescriptor;
+    bool hasO = false, hasOC = false, hasEOC = false, hasBackdrop = false;
+    mProperties.ForEach([&](const T& aProp, uint64_t) {
+      if (aProp == OverflowProperty()) {
+        hasO = true;
+      } else if (aProp == OverflowContainersProperty()) {
+        hasOC = true;
+      } else if (aProp == ExcessOverflowContainersProperty()) {
+        hasEOC = true;
+      } else if (aProp == BackdropProperty()) {
+        hasBackdrop = true;
+      }
+      return true;
+    });
+
+    // Destroy frames on the auxiliary frame lists and delete the lists.
+    nsPresContext* pc = PresContext();
+    mozilla::PresShell* presShell = pc->PresShell();
+    if (hasO) {
+      SafelyDestroyFrameListProp(aContext, presShell, OverflowProperty());
+    }
+
+    MOZ_ASSERT(
+        IsFrameOfType(eCanContainOverflowContainers) || !(hasOC || hasEOC),
+        "this type of frame shouldn't have overflow containers");
+    if (hasOC) {
+      SafelyDestroyFrameListProp(aContext, presShell,
+                                 OverflowContainersProperty());
+    }
+    if (hasEOC) {
+      SafelyDestroyFrameListProp(aContext, presShell,
+                                 ExcessOverflowContainersProperty());
+    }
+
+    MOZ_ASSERT(!GetProperty(BackdropProperty()) ||
+                   StyleDisplay()->mTopLayer != StyleTopLayer::None,
+               "only top layer frame may have backdrop");
+    if (hasBackdrop) {
+      SafelyDestroyFrameListProp(aContext, presShell, BackdropProperty());
+    }
+  }
+
+  nsSplittableFrame::Destroy(aContext);
+}
+
+/////////////////////////////////////////////////////////////////////////////
+// Child frame enumeration
+
+const nsFrameList& nsContainerFrame::GetChildList(ChildListID aListID) const {
+  // We only know about the principal child list, the overflow lists,
+  // and the backdrop list.
+  switch (aListID) {
+    case FrameChildListID::Principal:
+      return mFrames;
+    case FrameChildListID::Overflow: {
+      nsFrameList* list = GetOverflowFrames();
+      return list ? *list : nsFrameList::EmptyList();
+    }
+    case FrameChildListID::OverflowContainers: {
+      nsFrameList* list = GetOverflowContainers();
+      return list ? *list : nsFrameList::EmptyList();
+    }
+    case FrameChildListID::ExcessOverflowContainers: {
+      nsFrameList* list = GetExcessOverflowContainers();
+      return list ? *list : nsFrameList::EmptyList();
+    }
+    case FrameChildListID::Backdrop: {
+      nsFrameList* list = GetProperty(BackdropProperty());
+      return list ? *list : nsFrameList::EmptyList();
+    }
+    default:
+      return nsSplittableFrame::GetChildList(aListID);
+  }
+}
+
+void nsContainerFrame::GetChildLists(nsTArray<ChildList>* aLists) const {
+  mFrames.AppendIfNonempty(aLists, FrameChildListID::Principal);
+
+  using T = mozilla::FrameProperties::UntypedDescriptor;
+  mProperties.ForEach([this, aLists](const T& aProp, uint64_t aValue) {
+    typedef const nsFrameList* L;
+    if (aProp == OverflowProperty()) {
+      reinterpret_cast<L>(aValue)->AppendIfNonempty(aLists,
+                                                    FrameChildListID::Overflow);
+    } else if (aProp == OverflowContainersProperty()) {
+      MOZ_ASSERT(IsFrameOfType(nsIFrame::eCanContainOverflowContainers),
+                 "found unexpected OverflowContainersProperty");
+      Unused << this;  // silence clang -Wunused-lambda-capture in opt builds
+      reinterpret_cast<L>(aValue)->AppendIfNonempty(
+          aLists, FrameChildListID::OverflowContainers);
+    } else if (aProp == ExcessOverflowContainersProperty()) {
+      MOZ_ASSERT(IsFrameOfType(nsIFrame::eCanContainOverflowContainers),
+                 "found unexpected ExcessOverflowContainersProperty");
+      Unused << this;  // silence clang -Wunused-lambda-capture in opt builds
+      reinterpret_cast<L>(aValue)->AppendIfNonempty(
+          aLists, FrameChildListID::ExcessOverflowContainers);
+    } else if (aProp == BackdropProperty()) {
+      reinterpret_cast<L>(aValue)->AppendIfNonempty(aLists,
+                                                    FrameChildListID::Backdrop);
+    }
+    return true;
+  });
+
+  nsSplittableFrame::GetChildLists(aLists);
+}
+
+/////////////////////////////////////////////////////////////////////////////
+// Painting/Events
+
+void nsContainerFrame::BuildDisplayList(nsDisplayListBuilder* aBuilder,
+                                        const nsDisplayListSet& aLists) {
+  DisplayBorderBackgroundOutline(aBuilder, aLists);
+  BuildDisplayListForNonBlockChildren(aBuilder, aLists);
+}
+
+void nsContainerFrame::BuildDisplayListForNonBlockChildren(
+    nsDisplayListBuilder* aBuilder, const nsDisplayListSet& aLists,
+    DisplayChildFlags aFlags) {
+  nsIFrame* kid = mFrames.FirstChild();
+  // Put each child's background directly onto the content list
+  nsDisplayListSet set(aLists, aLists.Content());
+  // The children should be in content order
+  while (kid) {
+    BuildDisplayListForChild(aBuilder, kid, set, aFlags);
+    kid = kid->GetNextSibling();
+  }
+}
+
+class nsDisplaySelectionOverlay : public nsPaintedDisplayItem {
+ public:
+  /**
+   * @param aSelectionValue nsISelectionController::getDisplaySelection.
+   */
+  nsDisplaySelectionOverlay(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                            int16_t aSelectionValue)
+      : nsPaintedDisplayItem(aBuilder, aFrame),
+        mSelectionValue(aSelectionValue) {
+    MOZ_COUNT_CTOR(nsDisplaySelectionOverlay);
+  }
+  MOZ_COUNTED_DTOR_OVERRIDE(nsDisplaySelectionOverlay)
+
+  virtual void Paint(nsDisplayListBuilder* aBuilder, gfxContext* aCtx) override;
+  bool CreateWebRenderCommands(
+      mozilla::wr::DisplayListBuilder& aBuilder,
+      mozilla::wr::IpcResourceUpdateQueue& aResources,
+      const StackingContextHelper& aSc,
+      mozilla::layers::RenderRootStateManager* aManager,
+      nsDisplayListBuilder* aDisplayListBuilder) override;
+  NS_DISPLAY_DECL_NAME("SelectionOverlay", TYPE_SELECTION_OVERLAY)
+ private:
+  DeviceColor ComputeColor() const;
+
+  static DeviceColor ComputeColorFromSelectionStyle(ComputedStyle&);
+  static DeviceColor ApplyTransparencyIfNecessary(nscolor);
+
+  // nsISelectionController::getDisplaySelection.
+  int16_t mSelectionValue;
+};
+
+DeviceColor nsDisplaySelectionOverlay::ApplyTransparencyIfNecessary(
+    nscolor aColor) {
+  // If it has already alpha, leave it like that.
+  if (NS_GET_A(aColor) != 255) {
+    return ToDeviceColor(aColor);
+  }
+
+  // NOTE(emilio): Blink and WebKit do something slightly different here, and
+  // blend the color with white instead, both for overlays and text backgrounds.
+  auto color = sRGBColor::FromABGR(aColor);
+  color.a = 0.5;
+  return ToDeviceColor(color);
+}
+
+DeviceColor nsDisplaySelectionOverlay::ComputeColorFromSelectionStyle(
+    ComputedStyle& aStyle) {
+  return ApplyTransparencyIfNecessary(
+      aStyle.GetVisitedDependentColor(&nsStyleBackground::mBackgroundColor));
+}
+
+DeviceColor nsDisplaySelectionOverlay::ComputeColor() const {
+  LookAndFeel::ColorID colorID;
+  if (RefPtr<ComputedStyle> style =
+          mFrame->ComputeSelectionStyle(mSelectionValue)) {
+    return ComputeColorFromSelectionStyle(*style);
+  }
+  if (mSelectionValue == nsISelectionController::SELECTION_ON) {
+    colorID = LookAndFeel::ColorID::Highlight;
+  } else if (mSelectionValue == nsISelectionController::SELECTION_ATTENTION) {
+    colorID = LookAndFeel::ColorID::TextSelectAttentionBackground;
+  } else {
+    colorID = LookAndFeel::ColorID::TextSelectDisabledBackground;
+  }
+
+  return ApplyTransparencyIfNecessary(
+      LookAndFeel::Color(colorID, mFrame, NS_RGB(255, 255, 255)));
+}
+
+void nsDisplaySelectionOverlay::Paint(nsDisplayListBuilder* aBuilder,
+                                      gfxContext* aCtx) {
+  DrawTarget& aDrawTarget = *aCtx->GetDrawTarget();
+  ColorPattern color(ComputeColor());
+
+  nsIntRect pxRect =
+      GetPaintRect(aBuilder, aCtx)
+          .ToOutsidePixels(mFrame->PresContext()->AppUnitsPerDevPixel());
+  Rect rect(pxRect.x, pxRect.y, pxRect.width, pxRect.height);
+  MaybeSnapToDevicePixels(rect, aDrawTarget, true);
+
+  aDrawTarget.FillRect(rect, color);
+}
+
+bool nsDisplaySelectionOverlay::CreateWebRenderCommands(
+    mozilla::wr::DisplayListBuilder& aBuilder,
+    mozilla::wr::IpcResourceUpdateQueue& aResources,
+    const StackingContextHelper& aSc,
+    mozilla::layers::RenderRootStateManager* aManager,
+    nsDisplayListBuilder* aDisplayListBuilder) {
+  wr::LayoutRect bounds = wr::ToLayoutRect(LayoutDeviceRect::FromAppUnits(
+      nsRect(ToReferenceFrame(), Frame()->GetSize()),
+      mFrame->PresContext()->AppUnitsPerDevPixel()));
+  aBuilder.PushRect(bounds, bounds, !BackfaceIsHidden(), false, false,
+                    wr::ToColorF(ComputeColor()));
+  return true;
+}
+
+void nsContainerFrame::DisplaySelectionOverlay(nsDisplayListBuilder* aBuilder,
+                                               nsDisplayList* aList,
+                                               uint16_t aContentType) {
+  if (!IsSelected() || !IsVisibleForPainting()) {
+    return;
+  }
+
+  int16_t displaySelection = PresShell()->GetSelectionFlags();
+  if (!(displaySelection & aContentType)) {
+    return;
+  }
+
+  const nsFrameSelection* frameSelection = GetConstFrameSelection();
+  int16_t selectionValue = frameSelection->GetDisplaySelection();
+
+  if (selectionValue <= nsISelectionController::SELECTION_HIDDEN) {
+    return;  // selection is hidden or off
+  }
+
+  nsIContent* newContent = mContent->GetParent();
+
+  // check to see if we are anonymous content
+  // XXXbz there has GOT to be a better way of determining this!
+  int32_t offset =
+      newContent ? newContent->ComputeIndexOf_Deprecated(mContent) : 0;
+
+  // look up to see what selection(s) are on this frame
+  UniquePtr<SelectionDetails> details =
+      frameSelection->LookUpSelection(newContent, offset, 1, false);
+  if (!details) {
+    return;
+  }
+
+  bool normal = false;
+  for (SelectionDetails* sd = details.get(); sd; sd = sd->mNext.get()) {
+    if (sd->mSelectionType == SelectionType::eNormal) {
+      normal = true;
+    }
+  }
+
+  if (!normal && aContentType == nsISelectionDisplay::DISPLAY_IMAGES) {
+    // Don't overlay an image if it's not in the primary selection.
+    return;
+  }
+
+  aList->AppendNewToTop<nsDisplaySelectionOverlay>(aBuilder, this,
+                                                   selectionValue);
+}
+
+/* virtual */
+void nsContainerFrame::ChildIsDirty(nsIFrame* aChild) {
+  NS_ASSERTION(aChild->IsSubtreeDirty(), "child isn't actually dirty");
+
+  AddStateBits(NS_FRAME_HAS_DIRTY_CHILDREN);
+}
+
+nsIFrame::FrameSearchResult nsContainerFrame::PeekOffsetNoAmount(
+    bool aForward, int32_t* aOffset) {
+  NS_ASSERTION(aOffset && *aOffset <= 1, "aOffset out of range");
+  // Don't allow the caret to stay in an empty (leaf) container frame.
+  return CONTINUE_EMPTY;
+}
+
+nsIFrame::FrameSearchResult nsContainerFrame::PeekOffsetCharacter(
+    bool aForward, int32_t* aOffset, PeekOffsetCharacterOptions aOptions) {
+  NS_ASSERTION(aOffset && *aOffset <= 1, "aOffset out of range");
+  // Don't allow the caret to stay in an empty (leaf) container frame.
+  return CONTINUE_EMPTY;
+}
+
+/////////////////////////////////////////////////////////////////////////////
+// Helper member functions
+
+/**
+ * Position the view associated with |aKidFrame|, if there is one. A
+ * container frame should call this method after positioning a frame,
+ * but before |Reflow|.
+ */
+void nsContainerFrame::PositionFrameView(nsIFrame* aKidFrame) {
+  nsIFrame* parentFrame = aKidFrame->GetParent();
+  if (!aKidFrame->HasView() || !parentFrame) return;
+
+  nsView* view = aKidFrame->GetView();
+  nsViewManager* vm = view->GetViewManager();
+  nsPoint pt;
+  nsView* ancestorView = parentFrame->GetClosestView(&pt);
+
+  if (ancestorView != view->GetParent()) {
+    NS_ASSERTION(ancestorView == view->GetParent()->GetParent(),
+                 "Allowed only one anonymous view between frames");
+    // parentFrame is responsible for positioning aKidFrame's view
+    // explicitly
+    return;
+  }
+
+  pt += aKidFrame->GetPosition();
+  vm->MoveViewTo(view, pt.x, pt.y);
+}
+
+void nsContainerFrame::ReparentFrameView(nsIFrame* aChildFrame,
+                                         nsIFrame* aOldParentFrame,
+                                         nsIFrame* aNewParentFrame) {
+#ifdef DEBUG
+  MOZ_ASSERT(aChildFrame, "null child frame pointer");
+  MOZ_ASSERT(aOldParentFrame, "null old parent frame pointer");
+  MOZ_ASSERT(aNewParentFrame, "null new parent frame pointer");
+  MOZ_ASSERT(aOldParentFrame != aNewParentFrame,
+             "same old and new parent frame");
+
+  // See if either the old parent frame or the new parent frame have a view
+  while (!aOldParentFrame->HasView() && !aNewParentFrame->HasView()) {
+    // Walk up both the old parent frame and the new parent frame nodes
+    // stopping when we either find a common parent or views for one
+    // or both of the frames.
+    //
+    // This works well in the common case where we push/pull and the old parent
+    // frame and the new parent frame are part of the same flow. They will
+    // typically be the same distance (height wise) from the
+    aOldParentFrame = aOldParentFrame->GetParent();
+    aNewParentFrame = aNewParentFrame->GetParent();
+
+    // We should never walk all the way to the root frame without finding
+    // a view
+    NS_ASSERTION(aOldParentFrame && aNewParentFrame, "didn't find view");
+
+    // See if we reached a common ancestor
+    if (aOldParentFrame == aNewParentFrame) {
+      break;
+    }
+  }
+
+  // See if we found a common parent frame
+  if (aOldParentFrame == aNewParentFrame) {
+    // We found a common parent and there are no views between the old parent
+    // and the common parent or the new parent frame and the common parent.
+    // Because neither the old parent frame nor the new parent frame have views,
+    // then any child views don't need reparenting
+    return;
+  }
+
+  // We found views for one or both of the ancestor frames before we
+  // found a common ancestor.
+  nsView* oldParentView = aOldParentFrame->GetClosestView();
+  nsView* newParentView = aNewParentFrame->GetClosestView();
+
+  // See if the old parent frame and the new parent frame are in the
+  // same view sub-hierarchy. If they are then we don't have to do
+  // anything
+  if (oldParentView != newParentView) {
+    MOZ_ASSERT_UNREACHABLE("can't move frames between views");
+    // They're not so we need to reparent any child views
+    aChildFrame->ReparentFrameViewTo(oldParentView->GetViewManager(),
+                                     newParentView);
+  }
+#endif
+}
+
+void nsContainerFrame::ReparentFrameViewList(const nsFrameList& aChildFrameList,
+                                             nsIFrame* aOldParentFrame,
+                                             nsIFrame* aNewParentFrame) {
+#ifdef DEBUG
+  MOZ_ASSERT(aChildFrameList.NotEmpty(), "empty child frame list");
+  MOZ_ASSERT(aOldParentFrame, "null old parent frame pointer");
+  MOZ_ASSERT(aNewParentFrame, "null new parent frame pointer");
+  MOZ_ASSERT(aOldParentFrame != aNewParentFrame,
+             "same old and new parent frame");
+
+  // See if either the old parent frame or the new parent frame have a view
+  while (!aOldParentFrame->HasView() && !aNewParentFrame->HasView()) {
+    // Walk up both the old parent frame and the new parent frame nodes
+    // stopping when we either find a common parent or views for one
+    // or both of the frames.
+    //
+    // This works well in the common case where we push/pull and the old parent
+    // frame and the new parent frame are part of the same flow. They will
+    // typically be the same distance (height wise) from the
+    aOldParentFrame = aOldParentFrame->GetParent();
+    aNewParentFrame = aNewParentFrame->GetParent();
+
+    // We should never walk all the way to the root frame without finding
+    // a view
+    NS_ASSERTION(aOldParentFrame && aNewParentFrame, "didn't find view");
+
+    // See if we reached a common ancestor
+    if (aOldParentFrame == aNewParentFrame) {
+      break;
+    }
+  }
+
+  // See if we found a common parent frame
+  if (aOldParentFrame == aNewParentFrame) {
+    // We found a common parent and there are no views between the old parent
+    // and the common parent or the new parent frame and the common parent.
+    // Because neither the old parent frame nor the new parent frame have views,
+    // then any child views don't need reparenting
+    return;
+  }
+
+  // We found views for one or both of the ancestor frames before we
+  // found a common ancestor.
+  nsView* oldParentView = aOldParentFrame->GetClosestView();
+  nsView* newParentView = aNewParentFrame->GetClosestView();
+
+  // See if the old parent frame and the new parent frame are in the
+  // same view sub-hierarchy. If they are then we don't have to do
+  // anything
+  if (oldParentView != newParentView) {
+    MOZ_ASSERT_UNREACHABLE("can't move frames between views");
+    nsViewManager* viewManager = oldParentView->GetViewManager();
+
+    // They're not so we need to reparent any child views
+    for (nsIFrame* f : aChildFrameList) {
+      f->ReparentFrameViewTo(viewManager, newParentView);
+    }
+  }
+#endif
+}
+
+void nsContainerFrame::ReparentFrame(nsIFrame* aFrame,
+                                     nsContainerFrame* aOldParent,
+                                     nsContainerFrame* aNewParent) {
+  NS_ASSERTION(aOldParent == aFrame->GetParent(),
+               "Parent not consistent with expectations");
+
+  aFrame->SetParent(aNewParent);
+
+  // When pushing and pulling frames we need to check for whether any
+  // views need to be reparented
+  ReparentFrameView(aFrame, aOldParent, aNewParent);
+}
+
+void nsContainerFrame::ReparentFrames(nsFrameList& aFrameList,
+                                      nsContainerFrame* aOldParent,
+                                      nsContainerFrame* aNewParent) {
+  for (auto* f : aFrameList) {
+    ReparentFrame(f, aOldParent, aNewParent);
+  }
+}
+
+void nsContainerFrame::SetSizeConstraints(nsPresContext* aPresContext,
+                                          nsIWidget* aWidget,
+                                          const nsSize& aMinSize,
+                                          const nsSize& aMaxSize) {
+  LayoutDeviceIntSize devMinSize(
+      aPresContext->AppUnitsToDevPixels(aMinSize.width),
+      aPresContext->AppUnitsToDevPixels(aMinSize.height));
+  LayoutDeviceIntSize devMaxSize(
+      aMaxSize.width == NS_UNCONSTRAINEDSIZE
+          ? NS_MAXSIZE
+          : aPresContext->AppUnitsToDevPixels(aMaxSize.width),
+      aMaxSize.height == NS_UNCONSTRAINEDSIZE
+          ? NS_MAXSIZE
+          : aPresContext->AppUnitsToDevPixels(aMaxSize.height));
+
+  // MinSize has a priority over MaxSize
+  if (devMinSize.width > devMaxSize.width) devMaxSize.width = devMinSize.width;
+  if (devMinSize.height > devMaxSize.height)
+    devMaxSize.height = devMinSize.height;
+
+  nsIWidget* rootWidget = aPresContext->GetNearestWidget();
+  DesktopToLayoutDeviceScale constraintsScale(MOZ_WIDGET_INVALID_SCALE);
+  if (rootWidget) {
+    constraintsScale = rootWidget->GetDesktopToDeviceScale();
+  }
+
+  widget::SizeConstraints constraints(devMinSize, devMaxSize, constraintsScale);
+
+  // The sizes are in inner window sizes, so convert them into outer window
+  // sizes. Use a size of (200, 200) as only the difference between the inner
+  // and outer size is needed.
+  const LayoutDeviceIntSize sizeDiff = aWidget->ClientToWindowSizeDifference();
+  if (constraints.mMinSize.width) {
+    constraints.mMinSize.width += sizeDiff.width;
+  }
+  if (constraints.mMinSize.height) {
+    constraints.mMinSize.height += sizeDiff.height;
+  }
+  if (constraints.mMaxSize.width != NS_MAXSIZE) {
+    constraints.mMaxSize.width += sizeDiff.width;
+  }
+  if (constraints.mMaxSize.height != NS_MAXSIZE) {
+    constraints.mMaxSize.height += sizeDiff.height;
+  }
+
+  aWidget->SetSizeConstraints(constraints);
+}
+
+void nsContainerFrame::SyncFrameViewAfterReflow(nsPresContext* aPresContext,
+                                                nsIFrame* aFrame, nsView* aView,
+                                                const nsRect& aInkOverflowArea,
+                                                ReflowChildFlags aFlags) {
+  if (!aView) {
+    return;
+  }
+
+  // Make sure the view is sized and positioned correctly
+  if (!(aFlags & ReflowChildFlags::NoMoveView)) {
+    PositionFrameView(aFrame);
+  }
+
+  if (!(aFlags & ReflowChildFlags::NoSizeView)) {
+    nsViewManager* vm = aView->GetViewManager();
+
+    vm->ResizeView(aView, aInkOverflowArea, true);
+  }
+}
+
+void nsContainerFrame::DoInlineMinISize(gfxContext* aRenderingContext,
+                                        InlineMinISizeData* aData) {
+  auto handleChildren = [aRenderingContext](auto frame, auto data) {
+    for (nsIFrame* kid : frame->mFrames) {
+      kid->AddInlineMinISize(aRenderingContext, data);
+    }
+  };
+  DoInlineIntrinsicISize(aData, handleChildren);
+}
+
+void nsContainerFrame::DoInlinePrefISize(gfxContext* aRenderingContext,
+                                         InlinePrefISizeData* aData) {
+  auto handleChildren = [aRenderingContext](auto frame, auto data) {
+    for (nsIFrame* kid : frame->mFrames) {
+      kid->AddInlinePrefISize(aRenderingContext, data);
+    }
+  };
+  DoInlineIntrinsicISize(aData, handleChildren);
+  aData->mLineIsEmpty = false;
+}
+
+/* virtual */
+LogicalSize nsContainerFrame::ComputeAutoSize(
+    gfxContext* aRenderingContext, WritingMode aWM, const LogicalSize& aCBSize,
+    nscoord aAvailableISize, const LogicalSize& aMargin,
+    const mozilla::LogicalSize& aBorderPadding,
+    const StyleSizeOverrides& aSizeOverrides, ComputeSizeFlags aFlags) {
+  LogicalSize result(aWM, 0xdeadbeef, NS_UNCONSTRAINEDSIZE);
+  nscoord availBased =
+      aAvailableISize - aMargin.ISize(aWM) - aBorderPadding.ISize(aWM);
+  // replaced elements always shrink-wrap
+  if (aFlags.contains(ComputeSizeFlag::ShrinkWrap) ||
+      IsFrameOfType(eReplaced)) {
+    // Only bother computing our 'auto' ISize if the result will be used.
+    const auto& styleISize = aSizeOverrides.mStyleISize
+                                 ? *aSizeOverrides.mStyleISize
+                                 : StylePosition()->ISize(aWM);
+    if (styleISize.IsAuto()) {
+      result.ISize(aWM) =
+          ShrinkISizeToFit(aRenderingContext, availBased, aFlags);
+    }
+  } else {
+    result.ISize(aWM) = availBased;
+  }
+
+  if (IsTableCaption()) {
+    // If we're a container for font size inflation, then shrink
+    // wrapping inside of us should not apply font size inflation.
+    AutoMaybeDisableFontInflation an(this);
+
+    WritingMode tableWM = GetParent()->GetWritingMode();
+    if (aWM.IsOrthogonalTo(tableWM)) {
+      // For an orthogonal caption on a block-dir side of the table, shrink-wrap
+      // to min-isize.
+      result.ISize(aWM) = GetMinISize(aRenderingContext);
+    } else {
+      // The outer frame constrains our available isize to the isize of
+      // the table.  Grow if our min-isize is bigger than that, but not
+      // larger than the containing block isize.  (It would really be nice
+      // to transmit that information another way, so we could grow up to
+      // the table's available isize, but that's harder.)
+      nscoord min = GetMinISize(aRenderingContext);
+      if (min > aCBSize.ISize(aWM)) {
+        min = aCBSize.ISize(aWM);
+      }
+      if (min > result.ISize(aWM)) {
+        result.ISize(aWM) = min;
+      }
+    }
+  }
+  return result;
+}
+
+void nsContainerFrame::ReflowChild(
+    nsIFrame* aKidFrame, nsPresContext* aPresContext,
+    ReflowOutput& aDesiredSize, const ReflowInput& aReflowInput,
+    const WritingMode& aWM, const LogicalPoint& aPos,
+    const nsSize& aContainerSize, ReflowChildFlags aFlags,
+    nsReflowStatus& aStatus, nsOverflowContinuationTracker* aTracker) {
+  MOZ_ASSERT(aReflowInput.mFrame == aKidFrame, "bad reflow input");
+  if (aWM.IsPhysicalRTL()) {
+    NS_ASSERTION(aContainerSize.width != NS_UNCONSTRAINEDSIZE,
+                 "ReflowChild with unconstrained container width!");
+  }
+  MOZ_ASSERT(aDesiredSize.InkOverflow() == nsRect(0, 0, 0, 0) &&
+                 aDesiredSize.ScrollableOverflow() == nsRect(0, 0, 0, 0),
+             "please reset the overflow areas before calling ReflowChild");
+
+  // Position the child frame and its view if requested.
+  if (ReflowChildFlags::NoMoveFrame !=
+      (aFlags & ReflowChildFlags::NoMoveFrame)) {
+    aKidFrame->SetPosition(aWM, aPos, aContainerSize);
+  }
+
+  if (!(aFlags & ReflowChildFlags::NoMoveView)) {
+    PositionFrameView(aKidFrame);
+    PositionChildViews(aKidFrame);
+  }
+
+  // Reflow the child frame
+  aKidFrame->Reflow(aPresContext, aDesiredSize, aReflowInput, aStatus);
+
+  // If the child frame is complete, delete any next-in-flows,
+  // but only if the NoDeleteNextInFlowChild flag isn't set.
+  if (!aStatus.IsInlineBreakBefore() && aStatus.IsFullyComplete() &&
+      !(aFlags & ReflowChildFlags::NoDeleteNextInFlowChild)) {
+    if (nsIFrame* kidNextInFlow = aKidFrame->GetNextInFlow()) {
+      // Remove all of the childs next-in-flows. Make sure that we ask
+      // the right parent to do the removal (it's possible that the
+      // parent is not this because we are executing pullup code)
+      nsOverflowContinuationTracker::AutoFinish fini(aTracker, aKidFrame);
+      DestroyContext context(PresShell());
+      kidNextInFlow->GetParent()->DeleteNextInFlowChild(context, kidNextInFlow,
+                                                        true);
+    }
+  }
+}
+
+// XXX temporary: hold on to a copy of the old physical version of
+//    ReflowChild so that we can convert callers incrementally.
+void nsContainerFrame::ReflowChild(nsIFrame* aKidFrame,
+                                   nsPresContext* aPresContext,
+                                   ReflowOutput& aDesiredSize,
+                                   const ReflowInput& aReflowInput, nscoord aX,
+                                   nscoord aY, ReflowChildFlags aFlags,
+                                   nsReflowStatus& aStatus,
+                                   nsOverflowContinuationTracker* aTracker) {
+  MOZ_ASSERT(aReflowInput.mFrame == aKidFrame, "bad reflow input");
+
+  // Position the child frame and its view if requested.
+  if (ReflowChildFlags::NoMoveFrame !=
+      (aFlags & ReflowChildFlags::NoMoveFrame)) {
+    aKidFrame->SetPosition(nsPoint(aX, aY));
+  }
+
+  if (!(aFlags & ReflowChildFlags::NoMoveView)) {
+    PositionFrameView(aKidFrame);
+    PositionChildViews(aKidFrame);
+  }
+
+  // Reflow the child frame
+  aKidFrame->Reflow(aPresContext, aDesiredSize, aReflowInput, aStatus);
+
+  // If the child frame is complete, delete any next-in-flows,
+  // but only if the NoDeleteNextInFlowChild flag isn't set.
+  if (aStatus.IsFullyComplete() &&
+      !(aFlags & ReflowChildFlags::NoDeleteNextInFlowChild)) {
+    if (nsIFrame* kidNextInFlow = aKidFrame->GetNextInFlow()) {
+      // Remove all of the childs next-in-flows. Make sure that we ask
+      // the right parent to do the removal (it's possible that the
+      // parent is not this because we are executing pullup code)
+      nsOverflowContinuationTracker::AutoFinish fini(aTracker, aKidFrame);
+      DestroyContext context(PresShell());
+      kidNextInFlow->GetParent()->DeleteNextInFlowChild(context, kidNextInFlow,
+                                                        true);
+    }
+  }
+}
+
+/**
+ * Position the views of |aFrame|'s descendants. A container frame
+ * should call this method if it moves a frame after |Reflow|.
+ */
+void nsContainerFrame::PositionChildViews(nsIFrame* aFrame) {
+  if (!aFrame->HasAnyStateBits(NS_FRAME_HAS_CHILD_WITH_VIEW)) {
+    return;
+  }
+
+  // Recursively walk aFrame's child frames.
+  // Process the additional child lists, but skip the popup list as the view for
+  // popups is managed by the parent.
+  // Currently only nsMenuFrame has a popupList and during layout will adjust
+  // the view manually to position the popup.
+  for (const auto& [list, listID] : aFrame->ChildLists()) {
+    if (listID == FrameChildListID::Popup) {
+      continue;
+    }
+    for (nsIFrame* childFrame : list) {
+      // Position the frame's view (if it has one) otherwise recursively
+      // process its children
+      if (childFrame->HasView()) {
+        PositionFrameView(childFrame);
+      } else {
+        PositionChildViews(childFrame);
+      }
+    }
+  }
+}
+
+/**
+ * De-optimize function to work around a VC2017 15.5+ compiler bug:
+ * https://bugzil.la/1424281#c12
+ */
+#if defined(_MSC_VER) && !defined(__clang__) && defined(_M_AMD64)
+#  pragma optimize("g", off)
+#endif
+void nsContainerFrame::FinishReflowChild(
+    nsIFrame* aKidFrame, nsPresContext* aPresContext,
+    const ReflowOutput& aDesiredSize, const ReflowInput* aReflowInput,
+    const WritingMode& aWM, const LogicalPoint& aPos,
+    const nsSize& aContainerSize, nsIFrame::ReflowChildFlags aFlags) {
+  MOZ_ASSERT(!aReflowInput || aReflowInput->mFrame == aKidFrame);
+  MOZ_ASSERT(aReflowInput || aKidFrame->IsFrameOfType(eMathML) ||
+                 aKidFrame->IsTableCellFrame(),
+             "aReflowInput should be passed in almost all cases");
+
+  if (aWM.IsPhysicalRTL()) {
+    NS_ASSERTION(aContainerSize.width != NS_UNCONSTRAINEDSIZE,
+                 "FinishReflowChild with unconstrained container width!");
+  }
+
+  nsPoint curOrigin = aKidFrame->GetPosition();
+  const LogicalSize convertedSize = aDesiredSize.Size(aWM);
+  LogicalPoint pos(aPos);
+
+  if (aFlags & ReflowChildFlags::ApplyRelativePositioning) {
+    MOZ_ASSERT(aReflowInput, "caller must have passed reflow input");
+    // ApplyRelativePositioning in right-to-left writing modes needs to know
+    // the updated frame width to set the normal position correctly.
+    aKidFrame->SetSize(aWM, convertedSize);
+
+    const LogicalMargin offsets = aReflowInput->ComputedLogicalOffsets(aWM);
+    ReflowInput::ApplyRelativePositioning(aKidFrame, aWM, offsets, &pos,
+                                          aContainerSize);
+  }
+
+  if (ReflowChildFlags::NoMoveFrame !=
+      (aFlags & ReflowChildFlags::NoMoveFrame)) {
+    aKidFrame->SetRect(aWM, LogicalRect(aWM, pos, convertedSize),
+                       aContainerSize);
+  } else {
+    aKidFrame->SetSize(aWM, convertedSize);
+  }
+
+  if (aKidFrame->HasView()) {
+    nsView* view = aKidFrame->GetView();
+    // Make sure the frame's view is properly sized and positioned and has
+    // things like opacity correct
+    SyncFrameViewAfterReflow(aPresContext, aKidFrame, view,
+                             aDesiredSize.InkOverflow(), aFlags);
+  }
+
+  nsPoint newOrigin = aKidFrame->GetPosition();
+  if (!(aFlags & ReflowChildFlags::NoMoveView) && curOrigin != newOrigin) {
+    if (!aKidFrame->HasView()) {
+      // If the frame has moved, then we need to make sure any child views are
+      // correctly positioned
+      PositionChildViews(aKidFrame);
+    }
+  }
+
+  aKidFrame->DidReflow(aPresContext, aReflowInput);
+}
+#if defined(_MSC_VER) && !defined(__clang__) && defined(_M_AMD64)
+#  pragma optimize("", on)
+#endif
+
+// XXX temporary: hold on to a copy of the old physical version of
+//    FinishReflowChild so that we can convert callers incrementally.
+void nsContainerFrame::FinishReflowChild(nsIFrame* aKidFrame,
+                                         nsPresContext* aPresContext,
+                                         const ReflowOutput& aDesiredSize,
+                                         const ReflowInput* aReflowInput,
+                                         nscoord aX, nscoord aY,
+                                         ReflowChildFlags aFlags) {
+  MOZ_ASSERT(!(aFlags & ReflowChildFlags::ApplyRelativePositioning),
+             "only the logical version supports ApplyRelativePositioning "
+             "since ApplyRelativePositioning requires the container size");
+
+  nsPoint curOrigin = aKidFrame->GetPosition();
+  nsPoint pos(aX, aY);
+  nsSize size(aDesiredSize.PhysicalSize());
+
+  if (ReflowChildFlags::NoMoveFrame !=
+      (aFlags & ReflowChildFlags::NoMoveFrame)) {
+    aKidFrame->SetRect(nsRect(pos, size));
+  } else {
+    aKidFrame->SetSize(size);
+  }
+
+  if (aKidFrame->HasView()) {
+    nsView* view = aKidFrame->GetView();
+    // Make sure the frame's view is properly sized and positioned and has
+    // things like opacity correct
+    SyncFrameViewAfterReflow(aPresContext, aKidFrame, view,
+                             aDesiredSize.InkOverflow(), aFlags);
+  }
+
+  if (!(aFlags & ReflowChildFlags::NoMoveView) && curOrigin != pos) {
+    if (!aKidFrame->HasView()) {
+      // If the frame has moved, then we need to make sure any child views are
+      // correctly positioned
+      PositionChildViews(aKidFrame);
+    }
+  }
+
+  aKidFrame->DidReflow(aPresContext, aReflowInput);
+}
+
+void nsContainerFrame::ReflowOverflowContainerChildren(
+    nsPresContext* aPresContext, const ReflowInput& aReflowInput,
+    OverflowAreas& aOverflowRects, ReflowChildFlags aFlags,
+    nsReflowStatus& aStatus, ChildFrameMerger aMergeFunc,
+    Maybe<nsSize> aContainerSize) {
+  MOZ_ASSERT(aPresContext, "null pointer");
+
+  nsFrameList* overflowContainers =
+      DrainExcessOverflowContainersList(aMergeFunc);
+  if (!overflowContainers) {
+    return;  // nothing to reflow
+  }
+
+  nsOverflowContinuationTracker tracker(this, false, false);
+  bool shouldReflowAllKids = aReflowInput.ShouldReflowAllKids();
+
+  for (nsIFrame* frame : *overflowContainers) {
+    if (frame->GetPrevInFlow()->GetParent() != GetPrevInFlow()) {
+      // frame's prevInFlow has moved, skip reflowing this frame;
+      // it will get reflowed once it's been placed
+      if (GetNextInFlow()) {
+        // We report OverflowIncomplete status in this case to avoid our parent
+        // deleting our next-in-flows which might destroy non-empty frames.
+        nsReflowStatus status;
+        status.SetOverflowIncomplete();
+        aStatus.MergeCompletionStatusFrom(status);
+      }
+      continue;
+    }
+
+    auto ScrollableOverflowExceedsAvailableBSize =
+        [this, &aReflowInput](nsIFrame* aFrame) {
+          if (aReflowInput.AvailableBSize() == NS_UNCONSTRAINEDSIZE) {
+            return false;
+          }
+          const auto parentWM = GetWritingMode();
+          const nscoord scrollableOverflowRectBEnd =
+              LogicalRect(parentWM,
+                          aFrame->ScrollableOverflowRectRelativeToParent(),
+                          GetSize())
+                  .BEnd(parentWM);
+          return scrollableOverflowRectBEnd > aReflowInput.AvailableBSize();
+        };
+
+    // If the available block-size has changed, or the existing scrollable
+    // overflow's block-end exceeds it, we need to reflow even if the frame
+    // isn't dirty.
+    if (shouldReflowAllKids || frame->IsSubtreeDirty() ||
+        ScrollableOverflowExceedsAvailableBSize(frame)) {
+      // Get prev-in-flow
+      nsIFrame* prevInFlow = frame->GetPrevInFlow();
+      NS_ASSERTION(prevInFlow,
+                   "overflow container frame must have a prev-in-flow");
+      NS_ASSERTION(
+          frame->HasAnyStateBits(NS_FRAME_IS_OVERFLOW_CONTAINER),
+          "overflow container frame must have overflow container bit set");
+      WritingMode wm = frame->GetWritingMode();
+      nsSize containerSize =
+          aContainerSize ? *aContainerSize
+                         : aReflowInput.AvailableSize(wm).GetPhysicalSize(wm);
+      LogicalRect prevRect = prevInFlow->GetLogicalRect(wm, containerSize);
+
+      // Initialize reflow params
+      LogicalSize availSpace(wm, prevRect.ISize(wm),
+                             aReflowInput.AvailableSize(wm).BSize(wm));
+      ReflowOutput desiredSize(aReflowInput);
+
+      StyleSizeOverrides sizeOverride;
+      if (frame->IsFlexItem()) {
+        // A flex item's size is determined by the flex algorithm, not solely by
+        // its style. Thus, the following overrides are necessary.
+        //
+        // Use the overflow container flex item's prev-in-flow inline-size since
+        // this continuation's inline-size is the same.
+        sizeOverride.mStyleISize.emplace(
+            StyleSize::LengthPercentage(LengthPercentage::FromAppUnits(
+                frame->StylePosition()->mBoxSizing == StyleBoxSizing::Border
+                    ? prevRect.ISize(wm)
+                    : prevInFlow->ContentSize(wm).ISize(wm))));
+
+        // An overflow container's block-size must be 0.
+        sizeOverride.mStyleBSize.emplace(
+            StyleSize::LengthPercentage(LengthPercentage::FromAppUnits(0)));
+      }
+      ReflowInput reflowInput(aPresContext, aReflowInput, frame, availSpace,
+                              Nothing(), {}, sizeOverride);
+
+      LogicalPoint pos(wm, prevRect.IStart(wm), 0);
+      nsReflowStatus frameStatus;
+      ReflowChild(frame, aPresContext, desiredSize, reflowInput, wm, pos,
+                  containerSize, aFlags, frameStatus, &tracker);
+      FinishReflowChild(frame, aPresContext, desiredSize, &reflowInput, wm, pos,
+                        containerSize, aFlags);
+
+      // Handle continuations
+      if (!frameStatus.IsFullyComplete()) {
+        if (frame->HasAnyStateBits(NS_FRAME_OUT_OF_FLOW)) {
+          // Abspos frames can't cause their parent to be incomplete,
+          // only overflow incomplete.
+          frameStatus.SetOverflowIncomplete();
+        } else {
+          NS_ASSERTION(frameStatus.IsComplete(),
+                       "overflow container frames can't be incomplete, only "
+                       "overflow-incomplete");
+        }
+
+        // Acquire a next-in-flow, creating it if necessary
+        nsIFrame* nif = frame->GetNextInFlow();
+        if (!nif) {
+          NS_ASSERTION(frameStatus.NextInFlowNeedsReflow(),
+                       "Someone forgot a NextInFlowNeedsReflow flag");
+          nif = PresShell()->FrameConstructor()->CreateContinuingFrame(frame,
+                                                                       this);
+        } else if (!nif->HasAnyStateBits(NS_FRAME_IS_OVERFLOW_CONTAINER)) {
+          // used to be a normal next-in-flow; steal it from the child list
+          nif->GetParent()->StealFrame(nif);
+        }
+
+        tracker.Insert(nif, frameStatus);
+      }
+      aStatus.MergeCompletionStatusFrom(frameStatus);
+      // At this point it would be nice to assert
+      // !frame->GetOverflowRect().IsEmpty(), but we have some unsplittable
+      // frames that, when taller than availableHeight will push zero-height
+      // content into a next-in-flow.
+    } else {
+      tracker.Skip(frame, aStatus);
+      if (aReflowInput.mFloatManager) {
+        nsBlockFrame::RecoverFloatsFor(frame, *aReflowInput.mFloatManager,
+                                       aReflowInput.GetWritingMode(),
+                                       aReflowInput.ComputedPhysicalSize());
+      }
+    }
+    ConsiderChildOverflow(aOverflowRects, frame);
+  }
+}
+
+void nsContainerFrame::DisplayOverflowContainers(
+    nsDisplayListBuilder* aBuilder, const nsDisplayListSet& aLists) {
+  nsFrameList* overflowconts = GetOverflowContainers();
+  if (overflowconts) {
+    for (nsIFrame* frame : *overflowconts) {
+      BuildDisplayListForChild(aBuilder, frame, aLists);
+    }
+  }
+}
+
+bool nsContainerFrame::TryRemoveFrame(FrameListPropertyDescriptor aProp,
+                                      nsIFrame* aChildToRemove) {
+  nsFrameList* list = GetProperty(aProp);
+  if (list && list->StartRemoveFrame(aChildToRemove)) {
+    // aChildToRemove *may* have been removed from this list.
+    if (list->IsEmpty()) {
+      Unused << TakeProperty(aProp);
+      list->Delete(PresShell());
+    }
+    return true;
+  }
+  return false;
+}
+
+bool nsContainerFrame::MaybeStealOverflowContainerFrame(nsIFrame* aChild) {
+  bool removed = false;
+  if (MOZ_UNLIKELY(aChild->HasAnyStateBits(NS_FRAME_IS_OVERFLOW_CONTAINER))) {
+    // Try removing from the overflow container list.
+    removed = TryRemoveFrame(OverflowContainersProperty(), aChild);
+    if (!removed) {
+      // It might be in the excess overflow container list.
+      removed = TryRemoveFrame(ExcessOverflowContainersProperty(), aChild);
+    }
+  }
+  return removed;
+}
+
+void nsContainerFrame::StealFrame(nsIFrame* aChild) {
+#ifdef DEBUG
+  if (!mFrames.ContainsFrame(aChild)) {
+    nsFrameList* list = GetOverflowFrames();
+    if (!list || !list->ContainsFrame(aChild)) {
+      list = GetOverflowContainers();
+      if (!list || !list->ContainsFrame(aChild)) {
+        list = GetExcessOverflowContainers();
+        MOZ_ASSERT(list && list->ContainsFrame(aChild),
+                   "aChild isn't our child"
+                   " or on a frame list not supported by StealFrame");
+      }
+    }
+  }
+#endif
+
+  if (MaybeStealOverflowContainerFrame(aChild)) {
+    return;
+  }
+
+  // NOTE nsColumnSetFrame and nsCanvasFrame have their overflow containers
+  // on the normal lists so we might get here also if the frame bit
+  // NS_FRAME_IS_OVERFLOW_CONTAINER is set.
+  if (mFrames.StartRemoveFrame(aChild)) {
+    return;
+  }
+
+  // We didn't find the child in our principal child list.
+  // Maybe it's on the overflow list?
+  nsFrameList* frameList = GetOverflowFrames();
+  if (frameList && frameList->ContinueRemoveFrame(aChild)) {
+    if (frameList->IsEmpty()) {
+      DestroyOverflowList();
+    }
+    return;
+  }
+
+  MOZ_ASSERT_UNREACHABLE("StealFrame: can't find aChild");
+}
+
+nsFrameList nsContainerFrame::StealFramesAfter(nsIFrame* aChild) {
+  NS_ASSERTION(
+      !aChild || !aChild->HasAnyStateBits(NS_FRAME_IS_OVERFLOW_CONTAINER),
+      "StealFramesAfter doesn't handle overflow containers");
+  NS_ASSERTION(!IsBlockFrame(), "unexpected call");
+
+  if (!aChild) {
+    return std::move(mFrames);
+  }
+
+  for (nsIFrame* f : mFrames) {
+    if (f == aChild) {
+      return mFrames.TakeFramesAfter(f);
+    }
+  }
+
+  // We didn't find the child in the principal child list.
+  // Maybe it's on the overflow list?
+  if (nsFrameList* overflowFrames = GetOverflowFrames()) {
+    for (nsIFrame* f : *overflowFrames) {
+      if (f == aChild) {
+        return mFrames.TakeFramesAfter(f);
+      }
+    }
+  }
+
+  NS_ERROR("StealFramesAfter: can't find aChild");
+  return nsFrameList();
+}
+
+/*
+ * Create a next-in-flow for aFrame. Will return the newly created
+ * frame <b>if and only if</b> a new frame is created; otherwise
+ * nullptr is returned.
+ */
+nsIFrame* nsContainerFrame::CreateNextInFlow(nsIFrame* aFrame) {
+  MOZ_ASSERT(
+      !IsBlockFrame(),
+      "you should have called nsBlockFrame::CreateContinuationFor instead");
+  MOZ_ASSERT(mFrames.ContainsFrame(aFrame), "expected an in-flow child frame");
+
+  nsIFrame* nextInFlow = aFrame->GetNextInFlow();
+  if (nullptr == nextInFlow) {
+    // Create a continuation frame for the child frame and insert it
+    // into our child list.
+    nextInFlow =
+        PresShell()->FrameConstructor()->CreateContinuingFrame(aFrame, this);
+    mFrames.InsertFrame(nullptr, aFrame, nextInFlow);
+
+    NS_FRAME_LOG(NS_FRAME_TRACE_NEW_FRAMES,
+                 ("nsContainerFrame::CreateNextInFlow: frame=%p nextInFlow=%p",
+                  aFrame, nextInFlow));
+
+    return nextInFlow;
+  }
+  return nullptr;
+}
+
+/**
+ * Remove and delete aNextInFlow and its next-in-flows. Updates the sibling and
+ * flow pointers
+ */
+void nsContainerFrame::DeleteNextInFlowChild(DestroyContext& aContext,
+                                             nsIFrame* aNextInFlow,
+                                             bool aDeletingEmptyFrames) {
+#ifdef DEBUG
+  nsIFrame* prevInFlow = aNextInFlow->GetPrevInFlow();
+#endif
+  MOZ_ASSERT(prevInFlow, "bad prev-in-flow");
+
+  // If the next-in-flow has a next-in-flow then delete it, too (and
+  // delete it first).
+  // Do this in a loop so we don't overflow the stack for frames
+  // with very many next-in-flows
+  nsIFrame* nextNextInFlow = aNextInFlow->GetNextInFlow();
+  if (nextNextInFlow) {
+    AutoTArray<nsIFrame*, 8> frames;
+    for (nsIFrame* f = nextNextInFlow; f; f = f->GetNextInFlow()) {
+      frames.AppendElement(f);
+    }
+    for (nsIFrame* delFrame : Reversed(frames)) {
+      nsContainerFrame* parent = delFrame->GetParent();
+      parent->DeleteNextInFlowChild(aContext, delFrame, aDeletingEmptyFrames);
+    }
+  }
+
+  // Take the next-in-flow out of the parent's child list
+  StealFrame(aNextInFlow);
+
+#ifdef DEBUG
+  if (aDeletingEmptyFrames) {
+    nsLayoutUtils::AssertTreeOnlyEmptyNextInFlows(aNextInFlow);
+  }
+#endif
+
+  // Delete the next-in-flow frame and its descendants. This will also
+  // remove it from its next-in-flow/prev-in-flow chain.
+  aNextInFlow->Destroy(aContext);
+
+  MOZ_ASSERT(!prevInFlow->GetNextInFlow(), "non null next-in-flow");
+}
+
+void nsContainerFrame::PushChildrenToOverflow(nsIFrame* aFromChild,
+                                              nsIFrame* aPrevSibling) {
+  MOZ_ASSERT(aFromChild, "null pointer");
+  MOZ_ASSERT(aPrevSibling, "pushing first child");
+  MOZ_ASSERT(aPrevSibling->GetNextSibling() == aFromChild, "bad prev sibling");
+
+  // Add the frames to our overflow list (let our next in flow drain
+  // our overflow list when it is ready)
+  SetOverflowFrames(mFrames.TakeFramesAfter(aPrevSibling));
+}
+
+void nsContainerFrame::PushChildren(nsIFrame* aFromChild,
+                                    nsIFrame* aPrevSibling) {
+  MOZ_ASSERT(aFromChild, "null pointer");
+  MOZ_ASSERT(aPrevSibling, "pushing first child");
+  MOZ_ASSERT(aPrevSibling->GetNextSibling() == aFromChild, "bad prev sibling");
+
+  // Disconnect aFromChild from its previous sibling
+  nsFrameList tail = mFrames.TakeFramesAfter(aPrevSibling);
+
+  nsContainerFrame* nextInFlow =
+      static_cast<nsContainerFrame*>(GetNextInFlow());
+  if (nextInFlow) {
+    // XXX This is not a very good thing to do. If it gets removed
+    // then remove the copy of this routine that doesn't do this from
+    // nsInlineFrame.
+    // When pushing and pulling frames we need to check for whether any
+    // views need to be reparented.
+    for (nsIFrame* f = aFromChild; f; f = f->GetNextSibling()) {
+      nsContainerFrame::ReparentFrameView(f, this, nextInFlow);
+    }
+    nextInFlow->mFrames.InsertFrames(nextInFlow, nullptr, std::move(tail));
+  } else {
+    // Add the frames to our overflow list
+    SetOverflowFrames(std::move(tail));
+  }
+}
+
+bool nsContainerFrame::PushIncompleteChildren(
+    const FrameHashtable& aPushedItems, const FrameHashtable& aIncompleteItems,
+    const FrameHashtable& aOverflowIncompleteItems) {
+  MOZ_ASSERT(IsFlexOrGridContainer(),
+             "Only Grid / Flex containers can call this!");
+
+  if (aPushedItems.IsEmpty() && aIncompleteItems.IsEmpty() &&
+      aOverflowIncompleteItems.IsEmpty()) {
+    return false;
+  }
+
+  // Iterate the children in normal document order and append them (or a NIF)
+  // to one of the following frame lists according to their status.
+  nsFrameList pushedList;
+  nsFrameList incompleteList;
+  nsFrameList overflowIncompleteList;
+  auto* fc = PresShell()->FrameConstructor();
+  for (nsIFrame* child = PrincipalChildList().FirstChild(); child;) {
+    MOZ_ASSERT((aPushedItems.Contains(child) ? 1 : 0) +
+                       (aIncompleteItems.Contains(child) ? 1 : 0) +
+                       (aOverflowIncompleteItems.Contains(child) ? 1 : 0) <=
+                   1,
+               "child should only be in one of these sets");
+    // Save the next-sibling so we can continue the loop if |child| is moved.
+    nsIFrame* next = child->GetNextSibling();
+    if (aPushedItems.Contains(child)) {
+      MOZ_ASSERT(child->GetParent() == this);
+      StealFrame(child);
+      pushedList.AppendFrame(nullptr, child);
+    } else if (aIncompleteItems.Contains(child)) {
+      nsIFrame* childNIF = child->GetNextInFlow();
+      if (!childNIF) {
+        childNIF = fc->CreateContinuingFrame(child, this);
+        incompleteList.AppendFrame(nullptr, childNIF);
+      } else {
+        auto* parent = childNIF->GetParent();
+        MOZ_ASSERT(parent != this || !mFrames.ContainsFrame(childNIF),
+                   "child's NIF shouldn't be in the same principal list");
+        // If child's existing NIF is an overflow container, convert it to an
+        // actual NIF, since now |child| has non-overflow stuff to give it.
+        // Or, if it's further away then our next-in-flow, then pull it up.
+        if (childNIF->HasAnyStateBits(NS_FRAME_IS_OVERFLOW_CONTAINER) ||
+            (parent != this && parent != GetNextInFlow())) {
+          parent->StealFrame(childNIF);
+          childNIF->RemoveStateBits(NS_FRAME_IS_OVERFLOW_CONTAINER);
+          if (parent == this) {
+            incompleteList.AppendFrame(nullptr, childNIF);
+          } else {
+            // If childNIF already lives on the next fragment, then we
+            // don't need to reparent it, since we know it's destined to end
+            // up there anyway.  Just move it to its parent's overflow list.
+            if (parent == GetNextInFlow()) {
+              nsFrameList toMove(childNIF, childNIF);
+              parent->MergeSortedOverflow(toMove);
+            } else {
+              ReparentFrame(childNIF, parent, this);
+              incompleteList.AppendFrame(nullptr, childNIF);
+            }
+          }
+        }
+      }
+    } else if (aOverflowIncompleteItems.Contains(child)) {
+      nsIFrame* childNIF = child->GetNextInFlow();
+      if (!childNIF) {
+        childNIF = fc->CreateContinuingFrame(child, this);
+        childNIF->AddStateBits(NS_FRAME_IS_OVERFLOW_CONTAINER);
+        overflowIncompleteList.AppendFrame(nullptr, childNIF);
+      } else {
+        DebugOnly<nsContainerFrame*> lastParent = this;
+        auto* nif = static_cast<nsContainerFrame*>(GetNextInFlow());
+        // If child has any non-overflow-container NIFs, convert them to
+        // overflow containers, since that's all |child| needs now.
+        while (childNIF &&
+               !childNIF->HasAnyStateBits(NS_FRAME_IS_OVERFLOW_CONTAINER)) {
+          auto* parent = childNIF->GetParent();
+          parent->StealFrame(childNIF);
+          childNIF->AddStateBits(NS_FRAME_IS_OVERFLOW_CONTAINER);
+          if (parent == this) {
+            overflowIncompleteList.AppendFrame(nullptr, childNIF);
+          } else {
+            if (!nif || parent == nif) {
+              nsFrameList toMove(childNIF, childNIF);
+              parent->MergeSortedExcessOverflowContainers(toMove);
+            } else {
+              ReparentFrame(childNIF, parent, nif);
+              nsFrameList toMove(childNIF, childNIF);
+              nif->MergeSortedExcessOverflowContainers(toMove);
+            }
+            // We only need to reparent the first childNIF (or not at all if
+            // its parent is our NIF).
+            nif = nullptr;
+          }
+          lastParent = parent;
+          childNIF = childNIF->GetNextInFlow();
+        }
+      }
+    }
+    child = next;
+  }
+
+  // Merge the results into our respective overflow child lists.
+  if (!pushedList.IsEmpty()) {
+    MergeSortedOverflow(pushedList);
+  }
+  if (!incompleteList.IsEmpty()) {
+    MergeSortedOverflow(incompleteList);
+  }
+  if (!overflowIncompleteList.IsEmpty()) {
+    // If our next-in-flow already has overflow containers list, merge the
+    // overflowIncompleteList into that list. Otherwise, merge it into our
+    // excess overflow containers list, to be drained by our next-in-flow.
+    auto* nif = static_cast<nsContainerFrame*>(GetNextInFlow());
+    nsFrameList* oc = nif ? nif->GetOverflowContainers() : nullptr;
+    if (oc) {
+      ReparentFrames(overflowIncompleteList, this, nif);
+      MergeSortedFrameLists(*oc, overflowIncompleteList, GetContent());
+    } else {
+      MergeSortedExcessOverflowContainers(overflowIncompleteList);
+    }
+  }
+  return true;
+}
+
+void nsContainerFrame::NormalizeChildLists() {
+  MOZ_ASSERT(IsFlexOrGridContainer(),
+             "Only Flex / Grid containers can call this!");
+
+  // Note: the following description uses grid container as an example. Flex
+  // container is similar.
+  //
+  // First we gather child frames we should include in our reflow/placement,
+  // i.e. overflowed children from our prev-in-flow, and pushed first-in-flow
+  // children (that might now fit). It's important to note that these children
+  // can be in arbitrary order vis-a-vis the current children in our lists.
+  // E.g. grid items in the document order: A, B, C may be placed in the rows
+  // 3, 2, 1.  Assume each row goes in a separate grid container fragment,
+  // and we reflow the second fragment.  Now if C (in fragment 1) overflows,
+  // we can't just prepend it to our mFrames like we usually do because that
+  // would violate the document order invariant that other code depends on.
+  // Similarly if we pull up child A (from fragment 3) we can't just append
+  // that for the same reason.  Instead, we must sort these children into
+  // our child lists.  (The sorting is trivial given that both lists are
+  // already fully sorted individually - it's just a merge.)
+  //
+  // The invariants that we maintain are that each grid container child list
+  // is sorted in the normal document order at all times, but that children
+  // in different grid container continuations may be in arbitrary order.
+
+  const auto didPushItemsBit = IsFlexContainerFrame()
+                                   ? NS_STATE_FLEX_DID_PUSH_ITEMS
+                                   : NS_STATE_GRID_DID_PUSH_ITEMS;
+  const auto hasChildNifBit = IsFlexContainerFrame()
+                                  ? NS_STATE_FLEX_HAS_CHILD_NIFS
+                                  : NS_STATE_GRID_HAS_CHILD_NIFS;
+
+  auto* prevInFlow = static_cast<nsContainerFrame*>(GetPrevInFlow());
+  // Merge overflow frames from our prev-in-flow into our principal child list.
+  if (prevInFlow) {
+    AutoFrameListPtr overflow(PresContext(), prevInFlow->StealOverflowFrames());
+    if (overflow) {
+      ReparentFrames(*overflow, prevInFlow, this);
+      MergeSortedFrameLists(mFrames, *overflow, GetContent());
+
+      // Move trailing next-in-flows into our overflow list.
+      nsFrameList continuations;
+      for (nsIFrame* f = mFrames.FirstChild(); f;) {
+        nsIFrame* next = f->GetNextSibling();
+        nsIFrame* pif = f->GetPrevInFlow();
+        if (pif && pif->GetParent() == this) {
+          mFrames.RemoveFrame(f);
+          continuations.AppendFrame(nullptr, f);
+        }
+        f = next;
+      }
+      MergeSortedOverflow(continuations);
+
+      // Move prev-in-flow's excess overflow containers list into our own
+      // overflow containers list. If we already have an excess overflow
+      // containers list, any child in that list which doesn't have a
+      // prev-in-flow in this frame is also merged into our overflow container
+      // list.
+      nsFrameList* overflowContainers =
+          DrainExcessOverflowContainersList(MergeSortedFrameListsFor);
+
+      // Move trailing OC next-in-flows into our excess overflow containers
+      // list.
+      if (overflowContainers) {
+        nsFrameList moveToEOC;
+        for (nsIFrame* f = overflowContainers->FirstChild(); f;) {
+          nsIFrame* next = f->GetNextSibling();
+          nsIFrame* pif = f->GetPrevInFlow();
+          if (pif && pif->GetParent() == this) {
+            overflowContainers->RemoveFrame(f);
+            moveToEOC.AppendFrame(nullptr, f);
+          }
+          f = next;
+        }
+        if (overflowContainers->IsEmpty()) {
+          DestroyOverflowContainers();
+        }
+        MergeSortedExcessOverflowContainers(moveToEOC);
+      }
+    }
+  }
+
+  // For each item in aItems, pull up its next-in-flow (if any), and reparent it
+  // to our next-in-flow, unless its parent is already ourselves or our
+  // next-in-flow (to avoid leaving a hole there).
+  auto PullItemsNextInFlow = [this](const nsFrameList& aItems) {
+    auto* firstNIF = static_cast<nsContainerFrame*>(GetNextInFlow());
+    if (!firstNIF) {
+      return;
+    }
+    nsFrameList childNIFs;
+    nsFrameList childOCNIFs;
+    for (auto* child : aItems) {
+      if (auto* childNIF = child->GetNextInFlow()) {
+        if (auto* parent = childNIF->GetParent();
+            parent != this && parent != firstNIF) {
+          parent->StealFrame(childNIF);
+          ReparentFrame(childNIF, parent, firstNIF);
+          if (childNIF->HasAnyStateBits(NS_FRAME_IS_OVERFLOW_CONTAINER)) {
+            childOCNIFs.AppendFrame(nullptr, childNIF);
+          } else {
+            childNIFs.AppendFrame(nullptr, childNIF);
+          }
+        }
+      }
+    }
+    // Merge aItems' NIFs into our NIF's respective overflow child lists.
+    firstNIF->MergeSortedOverflow(childNIFs);
+    firstNIF->MergeSortedExcessOverflowContainers(childOCNIFs);
+  };
+
+  // Merge our own overflow frames into our principal child list,
+  // except those that are a next-in-flow for one of our items.
+  DebugOnly<bool> foundOwnPushedChild = false;
+  {
+    nsFrameList* ourOverflow = GetOverflowFrames();
+    if (ourOverflow) {
+      nsFrameList items;
+      for (nsIFrame* f = ourOverflow->FirstChild(); f;) {
+        nsIFrame* next = f->GetNextSibling();
+        nsIFrame* pif = f->GetPrevInFlow();
+        if (!pif || pif->GetParent() != this) {
+          MOZ_ASSERT(f->GetParent() == this);
+          ourOverflow->RemoveFrame(f);
+          items.AppendFrame(nullptr, f);
+          if (!pif) {
+            foundOwnPushedChild = true;
+          }
+        }
+        f = next;
+      }
+
+      if (ourOverflow->IsEmpty()) {
+        DestroyOverflowList();
+        ourOverflow = nullptr;
+      }
+      if (items.NotEmpty()) {
+        PullItemsNextInFlow(items);
+      }
+      MergeSortedFrameLists(mFrames, items, GetContent());
+    }
+  }
+
+  // Push any child next-in-flows in our principal list to OverflowList.
+  if (HasAnyStateBits(hasChildNifBit)) {
+    nsFrameList framesToPush;
+    nsIFrame* firstChild = mFrames.FirstChild();
+    // Note that we potentially modify our mFrames list as we go.
+    for (auto* child = firstChild; child; child = child->GetNextSibling()) {
+      if (auto* childNIF = child->GetNextInFlow()) {
+        if (childNIF->GetParent() == this) {
+          for (auto* c = child->GetNextSibling(); c; c = c->GetNextSibling()) {
+            if (c == childNIF) {
+              // child's next-in-flow is in our principal child list, push it.
+              mFrames.RemoveFrame(childNIF);
+              framesToPush.AppendFrame(nullptr, childNIF);
+              break;
+            }
+          }
+        }
+      }
+    }
+    if (!framesToPush.IsEmpty()) {
+      MergeSortedOverflow(framesToPush);
+    }
+    RemoveStateBits(hasChildNifBit);
+  }
+
+  // Pull up any first-in-flow children we might have pushed.
+  if (HasAnyStateBits(didPushItemsBit)) {
+    RemoveStateBits(didPushItemsBit);
+    nsFrameList items;
+    auto* nif = static_cast<nsContainerFrame*>(GetNextInFlow());
+    DebugOnly<bool> nifNeedPushedItem = false;
+    while (nif) {
+      nsFrameList nifItems;
+      for (nsIFrame* nifChild = nif->PrincipalChildList().FirstChild();
+           nifChild;) {
+        nsIFrame* next = nifChild->GetNextSibling();
+        if (!nifChild->GetPrevInFlow()) {
+          nif->StealFrame(nifChild);
+          ReparentFrame(nifChild, nif, this);
+          nifItems.AppendFrame(nullptr, nifChild);
+          nifNeedPushedItem = false;
+        }
+        nifChild = next;
+      }
+      MergeSortedFrameLists(items, nifItems, GetContent());
+
+      if (!nif->HasAnyStateBits(didPushItemsBit)) {
+        MOZ_ASSERT(!nifNeedPushedItem || mDidPushItemsBitMayLie,
+                   "The state bit stored in didPushItemsBit lied!");
+        break;
+      }
+      nifNeedPushedItem = true;
+
+      for (nsIFrame* nifChild =
+               nif->GetChildList(FrameChildListID::Overflow).FirstChild();
+           nifChild;) {
+        nsIFrame* next = nifChild->GetNextSibling();
+        if (!nifChild->GetPrevInFlow()) {
+          nif->StealFrame(nifChild);
+          ReparentFrame(nifChild, nif, this);
+          nifItems.AppendFrame(nullptr, nifChild);
+          nifNeedPushedItem = false;
+        }
+        nifChild = next;
+      }
+      MergeSortedFrameLists(items, nifItems, GetContent());
+
+      nif->RemoveStateBits(didPushItemsBit);
+      nif = static_cast<nsContainerFrame*>(nif->GetNextInFlow());
+      MOZ_ASSERT(nif || !nifNeedPushedItem || mDidPushItemsBitMayLie,
+                 "The state bit stored in didPushItemsBit lied!");
+    }
+
+    if (!items.IsEmpty()) {
+      PullItemsNextInFlow(items);
+    }
+
+    MOZ_ASSERT(
+        foundOwnPushedChild || !items.IsEmpty() || mDidPushItemsBitMayLie,
+        "The state bit stored in didPushItemsBit lied!");
+    MergeSortedFrameLists(mFrames, items, GetContent());
+  }
+}
+
+void nsContainerFrame::NoteNewChildren(ChildListID aListID,
+                                       const nsFrameList& aFrameList) {
+  MOZ_ASSERT(aListID == FrameChildListID::Principal, "unexpected child list");
+  MOZ_ASSERT(IsFlexOrGridContainer(),
+             "Only Flex / Grid containers can call this!");
+
+  mozilla::PresShell* presShell = PresShell();
+  const auto didPushItemsBit = IsFlexContainerFrame()
+                                   ? NS_STATE_FLEX_DID_PUSH_ITEMS
+                                   : NS_STATE_GRID_DID_PUSH_ITEMS;
+  for (auto* pif = GetPrevInFlow(); pif; pif = pif->GetPrevInFlow()) {
+    pif->AddStateBits(didPushItemsBit);
+    presShell->FrameNeedsReflow(pif, IntrinsicDirty::FrameAndAncestors,
+                                NS_FRAME_IS_DIRTY);
+  }
+}
+
+bool nsContainerFrame::MoveOverflowToChildList() {
+  bool result = false;
+
+  // Check for an overflow list with our prev-in-flow
+  nsContainerFrame* prevInFlow = (nsContainerFrame*)GetPrevInFlow();
+  if (nullptr != prevInFlow) {
+    AutoFrameListPtr prevOverflowFrames(PresContext(),
+                                        prevInFlow->StealOverflowFrames());
+    if (prevOverflowFrames) {
+      // Tables are special; they can have repeated header/footer
+      // frames on mFrames at this point.
+      NS_ASSERTION(mFrames.IsEmpty() || IsTableFrame(), "bad overflow list");
+      // When pushing and pulling frames we need to check for whether any
+      // views need to be reparented.
+      nsContainerFrame::ReparentFrameViewList(*prevOverflowFrames, prevInFlow,
+                                              this);
+      mFrames.AppendFrames(this, std::move(*prevOverflowFrames));
+      result = true;
+    }
+  }
+
+  // It's also possible that we have an overflow list for ourselves.
+  return DrainSelfOverflowList() || result;
+}
+
+void nsContainerFrame::MergeSortedOverflow(nsFrameList& aList) {
+  if (aList.IsEmpty()) {
+    return;
+  }
+  MOZ_ASSERT(
+      !aList.FirstChild()->HasAnyStateBits(NS_FRAME_IS_OVERFLOW_CONTAINER),
+      "this is the wrong list to put this child frame");
+  MOZ_ASSERT(aList.FirstChild()->GetParent() == this);
+  nsFrameList* overflow = GetOverflowFrames();
+  if (overflow) {
+    MergeSortedFrameLists(*overflow, aList, GetContent());
+  } else {
+    SetOverflowFrames(std::move(aList));
+  }
+}
+
+void nsContainerFrame::MergeSortedExcessOverflowContainers(nsFrameList& aList) {
+  if (aList.IsEmpty()) {
+    return;
+  }
+  MOZ_ASSERT(
+      aList.FirstChild()->HasAnyStateBits(NS_FRAME_IS_OVERFLOW_CONTAINER),
+      "this is the wrong list to put this child frame");
+  MOZ_ASSERT(aList.FirstChild()->GetParent() == this);
+  if (nsFrameList* eoc = GetExcessOverflowContainers()) {
+    MergeSortedFrameLists(*eoc, aList, GetContent());
+  } else {
+    SetExcessOverflowContainers(std::move(aList));
+  }
+}
+
+nsIFrame* nsContainerFrame::GetFirstNonAnonBoxInSubtree(nsIFrame* aFrame) {
+  while (aFrame) {
+    // If aFrame isn't an anonymous container, or it's text or such, then it'll
+    // do.
+    if (!aFrame->Style()->IsAnonBox() ||
+        nsCSSAnonBoxes::IsNonElement(aFrame->Style()->GetPseudoType())) {
+      break;
+    }
+
+    // Otherwise, descend to its first child and repeat.
+
+    // SPECIAL CASE: if we're dealing with an anonymous table, then it might
+    // be wrapping something non-anonymous in its caption or col-group lists
+    // (instead of its principal child list), so we have to look there.
+    // (Note: For anonymous tables that have a non-anon cell *and* a non-anon
+    // column, we'll always return the column. This is fine; we're really just
+    // looking for a handle to *anything* with a meaningful content node inside
+    // the table, for use in DOM comparisons to things outside of the table.)
+    if (MOZ_UNLIKELY(aFrame->IsTableWrapperFrame())) {
+      nsIFrame* captionDescendant = GetFirstNonAnonBoxInSubtree(
+          aFrame->GetChildList(FrameChildListID::Caption).FirstChild());
+      if (captionDescendant) {
+        return captionDescendant;
+      }
+    } else if (MOZ_UNLIKELY(aFrame->IsTableFrame())) {
+      nsIFrame* colgroupDescendant = GetFirstNonAnonBoxInSubtree(
+          aFrame->GetChildList(FrameChildListID::ColGroup).FirstChild());
+      if (colgroupDescendant) {
+        return colgroupDescendant;
+      }
+    }
+
+    // USUAL CASE: Descend to the first child in principal list.
+    aFrame = aFrame->PrincipalChildList().FirstChild();
+  }
+  return aFrame;
+}
+
+/**
+ * Is aFrame1 a prev-continuation of aFrame2?
+ */
+static bool IsPrevContinuationOf(nsIFrame* aFrame1, nsIFrame* aFrame2) {
+  nsIFrame* prev = aFrame2;
+  while ((prev = prev->GetPrevContinuation())) {
+    if (prev == aFrame1) {
+      return true;
+    }
+  }
+  return false;
+}
+
+void nsContainerFrame::MergeSortedFrameLists(nsFrameList& aDest,
+                                             nsFrameList& aSrc,
+                                             nsIContent* aCommonAncestor) {
+  // Returns a frame whose DOM node can be used for the purpose of ordering
+  // aFrame among its sibling frames by DOM position. If aFrame is
+  // non-anonymous, this just returns aFrame itself. Otherwise, this returns the
+  // first non-anonymous descendant in aFrame's continuation chain.
+  auto FrameForDOMPositionComparison = [](nsIFrame* aFrame) {
+    if (!aFrame->Style()->IsAnonBox()) {
+      // The usual case.
+      return aFrame;
+    }
+
+    // Walk the continuation chain from the start, and return the first
+    // non-anonymous descendant that we find.
+    for (nsIFrame* f = aFrame->FirstContinuation(); f;
+         f = f->GetNextContinuation()) {
+      if (nsIFrame* nonAnonBox = GetFirstNonAnonBoxInSubtree(f)) {
+        return nonAnonBox;
+      }
+    }
+
+    MOZ_ASSERT_UNREACHABLE(
+        "Why is there no non-anonymous descendants in the continuation chain?");
+    return aFrame;
+  };
+
+  nsIFrame* dest = aDest.FirstChild();
+  for (nsIFrame* src = aSrc.FirstChild(); src;) {
+    if (!dest) {
+      aDest.AppendFrames(nullptr, std::move(aSrc));
+      break;
+    }
+    nsIContent* srcContent = FrameForDOMPositionComparison(src)->GetContent();
+    nsIContent* destContent = FrameForDOMPositionComparison(dest)->GetContent();
+    int32_t result = nsLayoutUtils::CompareTreePosition(srcContent, destContent,
+                                                        aCommonAncestor);
+    if (MOZ_UNLIKELY(result == 0)) {
+      // NOTE: we get here when comparing ::before/::after for the same element.
+      if (MOZ_UNLIKELY(srcContent->IsGeneratedContentContainerForBefore())) {
+        if (MOZ_LIKELY(!destContent->IsGeneratedContentContainerForBefore()) ||
+            ::IsPrevContinuationOf(src, dest)) {
+          result = -1;
+        }
+      } else if (MOZ_UNLIKELY(
+                     srcContent->IsGeneratedContentContainerForAfter())) {
+        if (MOZ_UNLIKELY(destContent->IsGeneratedContentContainerForAfter()) &&
+            ::IsPrevContinuationOf(src, dest)) {
+          result = -1;
+        }
+      } else if (::IsPrevContinuationOf(src, dest)) {
+        result = -1;
+      }
+    }
+    if (result < 0) {
+      // src should come before dest
+      nsIFrame* next = src->GetNextSibling();
+      aSrc.RemoveFrame(src);
+      aDest.InsertFrame(nullptr, dest->GetPrevSibling(), src);
+      src = next;
+    } else {
+      dest = dest->GetNextSibling();
+    }
+  }
+  MOZ_ASSERT(aSrc.IsEmpty());
+}
+
+bool nsContainerFrame::MoveInlineOverflowToChildList(nsIFrame* aLineContainer) {
+  MOZ_ASSERT(aLineContainer,
+             "Must have line container for moving inline overflows");
+
+  bool result = false;
+
+  // Check for an overflow list with our prev-in-flow
+  if (auto prevInFlow = static_cast<nsContainerFrame*>(GetPrevInFlow())) {
+    AutoFrameListPtr prevOverflowFrames(PresContext(),
+                                        prevInFlow->StealOverflowFrames());
+    if (prevOverflowFrames) {
+      // We may need to reparent floats from prev-in-flow to our line
+      // container if the container has prev continuation.
+      if (aLineContainer->GetPrevContinuation()) {
+        ReparentFloatsForInlineChild(aLineContainer,
+                                     prevOverflowFrames->FirstChild(), true);
+      }
+      // When pushing and pulling frames we need to check for whether
+      // any views need to be reparented.
+      nsContainerFrame::ReparentFrameViewList(*prevOverflowFrames, prevInFlow,
+                                              this);
+      // Prepend overflow frames to the list.
+      mFrames.InsertFrames(this, nullptr, std::move(*prevOverflowFrames));
+      result = true;
+    }
+  }
+
+  // It's also possible that we have overflow list for ourselves.
+  return DrainSelfOverflowList() || result;
+}
+
+bool nsContainerFrame::DrainSelfOverflowList() {
+  AutoFrameListPtr overflowFrames(PresContext(), StealOverflowFrames());
+  if (overflowFrames) {
+    mFrames.AppendFrames(nullptr, std::move(*overflowFrames));
+    return true;
+  }
+  return false;
+}
+
+bool nsContainerFrame::DrainAndMergeSelfOverflowList() {
+  MOZ_ASSERT(IsFlexOrGridContainer(),
+             "Only Flex / Grid containers can call this!");
+
+  // Unlike nsContainerFrame::DrainSelfOverflowList, flex or grid containers
+  // need to merge these lists so that the resulting mFrames is in document
+  // content order.
+  // NOTE: nsContainerFrame::AppendFrames/InsertFrames calls this method and
+  // there are also direct calls from the fctor (FindAppendPrevSibling).
+  AutoFrameListPtr overflowFrames(PresContext(), StealOverflowFrames());
+  if (overflowFrames) {
+    MergeSortedFrameLists(mFrames, *overflowFrames, GetContent());
+    // We set a frame bit to push them again in Reflow() to avoid creating
+    // multiple flex / grid items per flex / grid container fragment for the
+    // same content.
+    AddStateBits(IsFlexContainerFrame() ? NS_STATE_FLEX_HAS_CHILD_NIFS
+                                        : NS_STATE_GRID_HAS_CHILD_NIFS);
+    return true;
+  }
+  return false;
+}
+
+nsFrameList* nsContainerFrame::DrainExcessOverflowContainersList(
+    ChildFrameMerger aMergeFunc) {
+  nsFrameList* overflowContainers = GetOverflowContainers();
+
+  // Drain excess overflow containers from our prev-in-flow.
+  if (auto* prev = static_cast<nsContainerFrame*>(GetPrevInFlow())) {
+    AutoFrameListPtr excessFrames(PresContext(),
+                                  prev->StealExcessOverflowContainers());
+    if (excessFrames) {
+      excessFrames->ApplySetParent(this);
+      nsContainerFrame::ReparentFrameViewList(*excessFrames, prev, this);
+      if (overflowContainers) {
+        // The default merge function is AppendFrames, so we use excessFrames as
+        // the destination and then assign the result to overflowContainers.
+        aMergeFunc(*excessFrames, *overflowContainers, this);
+        *overflowContainers = std::move(*excessFrames);
+      } else {
+        overflowContainers = SetOverflowContainers(std::move(*excessFrames));
+      }
+    }
+  }
+
+  // Our own excess overflow containers from a previous reflow can still be
+  // present if our next-in-flow hasn't been reflown yet.  Move any children
+  // from it that don't have a continuation in this frame to the
+  // OverflowContainers list.
+  AutoFrameListPtr selfExcessOCFrames(PresContext(),
+                                      StealExcessOverflowContainers());
+  if (selfExcessOCFrames) {
+    nsFrameList toMove;
+    auto child = selfExcessOCFrames->FirstChild();
+    while (child) {
+      auto next = child->GetNextSibling();
+      MOZ_ASSERT(child->GetPrevInFlow(),
+                 "ExcessOverflowContainers frames must be continuations");
+      if (child->GetPrevInFlow()->GetParent() != this) {
+        selfExcessOCFrames->RemoveFrame(child);
+        toMove.AppendFrame(nullptr, child);
+      }
+      child = next;
+    }
+
+    // If there's any remaining excess overflow containers, put them back.
+    if (selfExcessOCFrames->NotEmpty()) {
+      SetExcessOverflowContainers(std::move(*selfExcessOCFrames));
+    }
+
+    if (toMove.NotEmpty()) {
+      if (overflowContainers) {
+        aMergeFunc(*overflowContainers, toMove, this);
+      } else {
+        overflowContainers = SetOverflowContainers(std::move(toMove));
+      }
+    }
+  }
+
+  return overflowContainers;
+}
+
+nsIFrame* nsContainerFrame::GetNextInFlowChild(
+    ContinuationTraversingState& aState, bool* aIsInOverflow) {
+  nsContainerFrame*& nextInFlow = aState.mNextInFlow;
+  while (nextInFlow) {
+    // See if there is any frame in the container
+    nsIFrame* frame = nextInFlow->mFrames.FirstChild();
+    if (frame) {
+      if (aIsInOverflow) {
+        *aIsInOverflow = false;
+      }
+      return frame;
+    }
+    // No frames in the principal list, try its overflow list
+    nsFrameList* overflowFrames = nextInFlow->GetOverflowFrames();
+    if (overflowFrames) {
+      if (aIsInOverflow) {
+        *aIsInOverflow = true;
+      }
+      return overflowFrames->FirstChild();
+    }
+    nextInFlow = static_cast<nsContainerFrame*>(nextInFlow->GetNextInFlow());
+  }
+  return nullptr;
+}
+
+nsIFrame* nsContainerFrame::PullNextInFlowChild(
+    ContinuationTraversingState& aState) {
+  bool isInOverflow;
+  nsIFrame* frame = GetNextInFlowChild(aState, &isInOverflow);
+  if (frame) {
+    nsContainerFrame* nextInFlow = aState.mNextInFlow;
+    if (isInOverflow) {
+      nsFrameList* overflowFrames = nextInFlow->GetOverflowFrames();
+      overflowFrames->RemoveFirstChild();
+      if (overflowFrames->IsEmpty()) {
+        nextInFlow->DestroyOverflowList();
+      }
+    } else {
+      nextInFlow->mFrames.RemoveFirstChild();
+    }
+
+    // Move the frame to the principal frame list of this container
+    mFrames.AppendFrame(this, frame);
+    // AppendFrame has reparented the frame, we need
+    // to reparent the frame view then.
+    nsContainerFrame::ReparentFrameView(frame, nextInFlow, this);
+  }
+  return frame;
+}
+
+/* static */
+void nsContainerFrame::ReparentFloatsForInlineChild(nsIFrame* aOurLineContainer,
+                                                    nsIFrame* aFrame,
+                                                    bool aReparentSiblings) {
+  // XXXbz this would be better if it took a nsFrameList or a frame
+  // list slice....
+  NS_ASSERTION(aOurLineContainer->GetNextContinuation() ||
+                   aOurLineContainer->GetPrevContinuation(),
+               "Don't call this when we have no continuation, it's a waste");
+  if (!aFrame) {
+    NS_ASSERTION(aReparentSiblings, "Why did we get called?");
+    return;
+  }
+
+  nsBlockFrame* frameBlock = nsLayoutUtils::GetFloatContainingBlock(aFrame);
+  if (!frameBlock || frameBlock == aOurLineContainer) {
+    return;
+  }
+
+  nsBlockFrame* ourBlock = do_QueryFrame(aOurLineContainer);
+  NS_ASSERTION(ourBlock, "Not a block, but broke vertically?");
+
+  while (true) {
+    ourBlock->ReparentFloats(aFrame, frameBlock, false);
+
+    if (!aReparentSiblings) return;
+    nsIFrame* next = aFrame->GetNextSibling();
+    if (!next) return;
+    if (next->GetParent() == aFrame->GetParent()) {
+      aFrame = next;
+      continue;
+    }
+    // This is paranoid and will hardly ever get hit ... but we can't actually
+    // trust that the frames in the sibling chain all have the same parent,
+    // because lazy reparenting may be going on. If we find a different
+    // parent we need to redo our analysis.
+    ReparentFloatsForInlineChild(aOurLineContainer, next, aReparentSiblings);
+    return;
+  }
+}
+
+bool nsContainerFrame::ResolvedOrientationIsVertical() {
+  StyleOrient orient = StyleDisplay()->mOrient;
+  switch (orient) {
+    case StyleOrient::Horizontal:
+      return false;
+    case StyleOrient::Vertical:
+      return true;
+    case StyleOrient::Inline:
+      return GetWritingMode().IsVertical();
+    case StyleOrient::Block:
+      return !GetWritingMode().IsVertical();
+  }
+  MOZ_ASSERT_UNREACHABLE("unexpected -moz-orient value");
+  return false;
+}
+
+LogicalSize nsContainerFrame::ComputeSizeWithIntrinsicDimensions(
+    gfxContext* aRenderingContext, WritingMode aWM,
+    const IntrinsicSize& aIntrinsicSize, const AspectRatio& aAspectRatio,
+    const LogicalSize& aCBSize, const LogicalSize& aMargin,
+    const LogicalSize& aBorderPadding, const StyleSizeOverrides& aSizeOverrides,
+    ComputeSizeFlags aFlags) {
+  const nsStylePosition* stylePos = StylePosition();
+  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 : aAspectRatio;
+
+  auto* parentFrame = GetParent();
+  const bool isGridItem = IsGridItem();
+  const bool isFlexItem =
+      IsFlexItem() && !parentFrame->HasAnyStateBits(
+                          NS_STATE_FLEX_IS_EMULATING_LEGACY_WEBKIT_BOX);
+  // This variable only gets meaningfully set if isFlexItem is true.  It
+  // indicates which axis (in this frame's own WM) corresponds to its
+  // flex container's main axis.
+  LogicalAxis flexMainAxis = eLogicalAxisBlock;
+  if (isFlexItem && nsFlexContainerFrame::IsItemInlineAxisMainAxis(this)) {
+    flexMainAxis = eLogicalAxisInline;
+  }
+
+  // Handle intrinsic sizes and their interaction with
+  // {min-,max-,}{width,height} according to the rules in
+  // https://www.w3.org/TR/CSS22/visudet.html#min-max-widths and
+  // https://drafts.csswg.org/css-sizing-3/#intrinsic-sizes
+
+  // Note: throughout the following section of the function, I avoid
+  // a * (b / c) because of its reduced accuracy relative to a * b / c
+  // or (a * b) / c (which are equivalent).
+
+  const bool isAutoOrMaxContentISize =
+      styleISize.IsAuto() || styleISize.IsMaxContent();
+  const bool isAutoBSize =
+      nsLayoutUtils::IsAutoBSize(styleBSize, aCBSize.BSize(aWM));
+
+  const auto boxSizingAdjust = stylePos->mBoxSizing == StyleBoxSizing::Border
+                                   ? aBorderPadding
+                                   : LogicalSize(aWM);
+  const nscoord boxSizingToMarginEdgeISize = aMargin.ISize(aWM) +
+                                             aBorderPadding.ISize(aWM) -
+                                             boxSizingAdjust.ISize(aWM);
+
+  nscoord iSize, minISize, maxISize, bSize, minBSize, maxBSize;
+  enum class Stretch {
+    // stretch to fill the CB (preserving intrinsic ratio) in the relevant axis
+    StretchPreservingRatio,
+    // stretch to fill the CB in the relevant axis
+    Stretch,
+    // no stretching in the relevant axis
+    NoStretch,
+  };
+  // just to avoid having to type these out everywhere:
+  const auto eStretchPreservingRatio = Stretch::StretchPreservingRatio;
+  const auto eStretch = Stretch::Stretch;
+  const auto eNoStretch = Stretch::NoStretch;
+
+  Stretch stretchI = eNoStretch;  // stretch behavior in the inline axis
+  Stretch stretchB = eNoStretch;  // stretch behavior in the block axis
+
+  const bool isOrthogonal = aWM.IsOrthogonalTo(parentFrame->GetWritingMode());
+  const bool isVertical = aWM.IsVertical();
+  const LogicalSize fallbackIntrinsicSize(aWM, kFallbackIntrinsicSize);
+  const auto& isizeCoord =
+      isVertical ? aIntrinsicSize.height : aIntrinsicSize.width;
+  const bool hasIntrinsicISize = isizeCoord.isSome();
+  nscoord intrinsicISize = std::max(0, isizeCoord.valueOr(0));
+
+  const auto& bsizeCoord =
+      isVertical ? aIntrinsicSize.width : aIntrinsicSize.height;
+  const bool hasIntrinsicBSize = bsizeCoord.isSome();
+  nscoord intrinsicBSize = std::max(0, bsizeCoord.valueOr(0));
+
+  if (!isAutoOrMaxContentISize) {
+    iSize = ComputeISizeValue(aRenderingContext, aWM, aCBSize, boxSizingAdjust,
+                              boxSizingToMarginEdgeISize, styleISize,
+                              aSizeOverrides, aFlags)
+                .mISize;
+  } else if (MOZ_UNLIKELY(isGridItem) &&
+             !parentFrame->IsMasonry(isOrthogonal ? eLogicalAxisBlock
+                                                  : eLogicalAxisInline)) {
+    MOZ_ASSERT(!IsTrueOverflowContainer());
+    // 'auto' inline-size for grid-level box - apply 'stretch' as needed:
+    auto cbSize = aCBSize.ISize(aWM);
+    if (cbSize != NS_UNCONSTRAINEDSIZE) {
+      if (!StyleMargin()->HasInlineAxisAuto(aWM)) {
+        auto inlineAxisAlignment =
+            isOrthogonal ? stylePos->UsedAlignSelf(GetParent()->Style())._0
+                         : stylePos->UsedJustifySelf(GetParent()->Style())._0;
+        if (inlineAxisAlignment == StyleAlignFlags::STRETCH) {
+          stretchI = eStretch;
+        }
+      }
+      if (stretchI != eNoStretch ||
+          aFlags.contains(ComputeSizeFlag::IClampMarginBoxMinSize)) {
+        iSize = std::max(nscoord(0), cbSize - aBorderPadding.ISize(aWM) -
+                                         aMargin.ISize(aWM));
+      }
+    } else {
+      // Reset this flag to avoid applying the clamping below.
+      aFlags -= ComputeSizeFlag::IClampMarginBoxMinSize;
+    }
+  }
+
+  const auto& maxISizeCoord = stylePos->MaxISize(aWM);
+
+  if (!maxISizeCoord.IsNone() &&
+      !(isFlexItem && flexMainAxis == eLogicalAxisInline)) {
+    maxISize = ComputeISizeValue(aRenderingContext, aWM, aCBSize,
+                                 boxSizingAdjust, boxSizingToMarginEdgeISize,
+                                 maxISizeCoord, aSizeOverrides, aFlags)
+                   .mISize;
+  } else {
+    maxISize = nscoord_MAX;
+  }
+
+  // NOTE: 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 auto& minISizeCoord = stylePos->MinISize(aWM);
+
+  if (!minISizeCoord.IsAuto() &&
+      !(isFlexItem && flexMainAxis == eLogicalAxisInline)) {
+    minISize = ComputeISizeValue(aRenderingContext, aWM, aCBSize,
+                                 boxSizingAdjust, boxSizingToMarginEdgeISize,
+                                 minISizeCoord, aSizeOverrides, aFlags)
+                   .mISize;
+  } 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;
+  }
+
+  if (!isAutoBSize) {
+    bSize = nsLayoutUtils::ComputeBSizeValue(aCBSize.BSize(aWM),
+                                             boxSizingAdjust.BSize(aWM),
+                                             styleBSize.AsLengthPercentage());
+  } else if (MOZ_UNLIKELY(isGridItem) &&
+             !parentFrame->IsMasonry(isOrthogonal ? eLogicalAxisInline
+                                                  : eLogicalAxisBlock)) {
+    MOZ_ASSERT(!IsTrueOverflowContainer());
+    // 'auto' block-size for grid-level box - apply 'stretch' as needed:
+    auto cbSize = aCBSize.BSize(aWM);
+    if (cbSize != NS_UNCONSTRAINEDSIZE) {
+      if (!StyleMargin()->HasBlockAxisAuto(aWM)) {
+        auto blockAxisAlignment =
+            !isOrthogonal ? stylePos->UsedAlignSelf(GetParent()->Style())._0
+                          : stylePos->UsedJustifySelf(GetParent()->Style())._0;
+        if (blockAxisAlignment == StyleAlignFlags::STRETCH) {
+          stretchB = eStretch;
+        }
+      }
+      if (stretchB != eNoStretch ||
+          aFlags.contains(ComputeSizeFlag::BClampMarginBoxMinSize)) {
+        bSize = std::max(nscoord(0), cbSize - aBorderPadding.BSize(aWM) -
+                                         aMargin.BSize(aWM));
+      }
+    } else {
+      // Reset this flag to avoid applying the clamping below.
+      aFlags -= ComputeSizeFlag::BClampMarginBoxMinSize;
+    }
+  }
+
+  const auto& maxBSizeCoord = stylePos->MaxBSize(aWM);
+
+  if (!nsLayoutUtils::IsAutoBSize(maxBSizeCoord, aCBSize.BSize(aWM)) &&
+      !(isFlexItem && flexMainAxis == eLogicalAxisBlock)) {
+    maxBSize = nsLayoutUtils::ComputeBSizeValue(
+        aCBSize.BSize(aWM), boxSizingAdjust.BSize(aWM),
+        maxBSizeCoord.AsLengthPercentage());
+  } else {
+    maxBSize = nscoord_MAX;
+  }
+
+  const auto& minBSizeCoord = stylePos->MinBSize(aWM);
+
+  if (!nsLayoutUtils::IsAutoBSize(minBSizeCoord, aCBSize.BSize(aWM)) &&
+      !(isFlexItem && flexMainAxis == eLogicalAxisBlock)) {
+    minBSize = nsLayoutUtils::ComputeBSizeValue(
+        aCBSize.BSize(aWM), boxSizingAdjust.BSize(aWM),
+        minBSizeCoord.AsLengthPercentage());
+  } else {
+    minBSize = 0;
+  }
+
+  NS_ASSERTION(aCBSize.ISize(aWM) != NS_UNCONSTRAINEDSIZE,
+               "Our containing block must not have unconstrained inline-size!");
+
+  // Now calculate the used values for iSize and bSize:
+  if (isAutoOrMaxContentISize) {
+    if (isAutoBSize) {
+      // 'auto' iSize, 'auto' bSize
+
+      // Get tentative values - CSS 2.1 sections 10.3.2 and 10.6.2:
+
+      nscoord tentISize, tentBSize;
+
+      if (hasIntrinsicISize) {
+        tentISize = intrinsicISize;
+      } else if (hasIntrinsicBSize && aspectRatio) {
+        tentISize = aspectRatio.ComputeRatioDependentSize(
+            LogicalAxis::eLogicalAxisInline, aWM, intrinsicBSize,
+            boxSizingAdjust);
+      } else if (aspectRatio) {
+        tentISize =
+            aCBSize.ISize(aWM) - boxSizingToMarginEdgeISize;  // XXX scrollbar?
+        if (tentISize < 0) {
+          tentISize = 0;
+        }
+      } else {
+        tentISize = fallbackIntrinsicSize.ISize(aWM);
+      }
+
+      // If we need to clamp the inline size to fit the CB, we use the 'stretch'
+      // or 'normal' codepath.  We use the ratio-preserving 'normal' codepath
+      // unless we have 'stretch' in the other axis.
+      if (aFlags.contains(ComputeSizeFlag::IClampMarginBoxMinSize) &&
+          stretchI != eStretch && tentISize > iSize) {
+        stretchI = (stretchB == eStretch ? eStretch : eStretchPreservingRatio);
+      }
+
+      if (hasIntrinsicBSize) {
+        tentBSize = intrinsicBSize;
+      } else if (aspectRatio) {
+        tentBSize = aspectRatio.ComputeRatioDependentSize(
+            LogicalAxis::eLogicalAxisBlock, aWM, tentISize, boxSizingAdjust);
+      } else {
+        tentBSize = fallbackIntrinsicSize.BSize(aWM);
+      }
+
+      // (ditto the comment about clamping the inline size above)
+      if (aFlags.contains(ComputeSizeFlag::BClampMarginBoxMinSize) &&
+          stretchB != eStretch && tentBSize > bSize) {
+        stretchB = (stretchI == eStretch ? eStretch : eStretchPreservingRatio);
+      }
+
+      if (stretchI == eStretch) {
+        tentISize = iSize;  // * / 'stretch'
+        if (stretchB == eStretch) {
+          tentBSize = bSize;  // 'stretch' / 'stretch'
+        } else if (stretchB == eStretchPreservingRatio && aspectRatio) {
+          // 'normal' / 'stretch'
+          tentBSize = aspectRatio.ComputeRatioDependentSize(
+              LogicalAxis::eLogicalAxisBlock, aWM, iSize, boxSizingAdjust);
+        }
+      } else if (stretchB == eStretch) {
+        tentBSize = bSize;  // 'stretch' / * (except 'stretch')
+        if (stretchI == eStretchPreservingRatio && aspectRatio) {
+          // 'stretch' / 'normal'
+          tentISize = aspectRatio.ComputeRatioDependentSize(
+              LogicalAxis::eLogicalAxisInline, aWM, bSize, boxSizingAdjust);
+        }
+      } else if (stretchI == eStretchPreservingRatio && aspectRatio) {
+        tentISize = iSize;  // * (except 'stretch') / 'normal'
+        tentBSize = aspectRatio.ComputeRatioDependentSize(
+            LogicalAxis::eLogicalAxisBlock, aWM, iSize, boxSizingAdjust);
+        if (stretchB == eStretchPreservingRatio && tentBSize > bSize) {
+          // Stretch within the CB size with preserved intrinsic ratio.
+          tentBSize = bSize;  // 'normal' / 'normal'
+          tentISize = aspectRatio.ComputeRatioDependentSize(
+              LogicalAxis::eLogicalAxisInline, aWM, bSize, boxSizingAdjust);
+        }
+      } else if (stretchB == eStretchPreservingRatio && aspectRatio) {
+        tentBSize = bSize;  // 'normal' / * (except 'normal' and 'stretch')
+        tentISize = aspectRatio.ComputeRatioDependentSize(
+            LogicalAxis::eLogicalAxisInline, aWM, bSize, boxSizingAdjust);
+      }
+
+      // ComputeAutoSizeWithIntrinsicDimensions preserves the ratio when
+      // applying the min/max-size.  We don't want that when we have 'stretch'
+      // in either axis because tentISize/tentBSize is likely not according to
+      // ratio now.
+      if (aspectRatio && stretchI != eStretch && stretchB != eStretch) {
+        nsSize autoSize = nsLayoutUtils::ComputeAutoSizeWithIntrinsicDimensions(
+            minISize, minBSize, maxISize, maxBSize, tentISize, tentBSize);
+        // The nsSize that ComputeAutoSizeWithIntrinsicDimensions returns will
+        // actually contain logical values if the parameters passed to it were
+        // logical coordinates, so we do NOT perform a physical-to-logical
+        // conversion here, but just assign the fields directly to our result.
+        iSize = autoSize.width;
+        bSize = autoSize.height;
+      } else {
+        // Not honoring an intrinsic ratio: clamp the dimensions independently.
+        iSize = NS_CSS_MINMAX(tentISize, minISize, maxISize);
+        bSize = NS_CSS_MINMAX(tentBSize, minBSize, maxBSize);
+      }
+    } else {
+      // 'auto' iSize, non-'auto' bSize
+      bSize = NS_CSS_MINMAX(bSize, minBSize, maxBSize);
+      if (stretchI != eStretch) {
+        if (aspectRatio) {
+          iSize = aspectRatio.ComputeRatioDependentSize(
+              LogicalAxis::eLogicalAxisInline, aWM, bSize, boxSizingAdjust);
+        } else if (hasIntrinsicISize) {
+          if (!(aFlags.contains(ComputeSizeFlag::IClampMarginBoxMinSize) &&
+                intrinsicISize > iSize)) {
+            iSize = intrinsicISize;
+          }  // else - leave iSize as is to fill the CB
+        } else {
+          iSize = fallbackIntrinsicSize.ISize(aWM);
+        }
+      }  // else - leave iSize as is to fill the CB
+      iSize = NS_CSS_MINMAX(iSize, minISize, maxISize);
+    }
+  } else {
+    if (isAutoBSize) {
+      // non-'auto' iSize, 'auto' bSize
+      iSize = NS_CSS_MINMAX(iSize, minISize, maxISize);
+      if (stretchB != eStretch) {
+        if (aspectRatio) {
+          bSize = aspectRatio.ComputeRatioDependentSize(
+              LogicalAxis::eLogicalAxisBlock, aWM, iSize, boxSizingAdjust);
+        } else if (hasIntrinsicBSize) {
+          if (!(aFlags.contains(ComputeSizeFlag::BClampMarginBoxMinSize) &&
+                intrinsicBSize > bSize)) {
+            bSize = intrinsicBSize;
+          }  // else - leave bSize as is to fill the CB
+        } else {
+          bSize = fallbackIntrinsicSize.BSize(aWM);
+        }
+      }  // else - leave bSize as is to fill the CB
+      bSize = NS_CSS_MINMAX(bSize, minBSize, maxBSize);
+
+    } else {
+      // non-'auto' iSize, non-'auto' bSize
+      iSize = NS_CSS_MINMAX(iSize, minISize, maxISize);
+      bSize = NS_CSS_MINMAX(bSize, minBSize, maxBSize);
+    }
+  }
+
+  return LogicalSize(aWM, iSize, bSize);
+}
+
+nsRect nsContainerFrame::ComputeSimpleTightBounds(
+    DrawTarget* aDrawTarget) const {
+  if (StyleOutline()->ShouldPaintOutline() || StyleBorder()->HasBorder() ||
+      !StyleBackground()->IsTransparent(this) ||
+      StyleDisplay()->HasAppearance()) {
+    // Not necessarily tight, due to clipping, negative
+    // outline-offset, and lots of other issues, but that's OK
+    return InkOverflowRect();
+  }
+
+  nsRect r(0, 0, 0, 0);
+  for (const auto& childLists : ChildLists()) {
+    for (nsIFrame* child : childLists.mList) {
+      r.UnionRect(
+          r, child->ComputeTightBounds(aDrawTarget) + child->GetPosition());
+    }
+  }
+  return r;
+}
+
+void nsContainerFrame::PushDirtyBitToAbsoluteFrames() {
+  if (!HasAnyStateBits(NS_FRAME_IS_DIRTY)) {
+    return;  // No dirty bit to push.
+  }
+  if (!HasAbsolutelyPositionedChildren()) {
+    return;  // No absolute children to push to.
+  }
+  GetAbsoluteContainingBlock()->MarkAllFramesDirty();
+}
+
+// Define the MAX_FRAME_DEPTH to be the ContentSink's MAX_REFLOW_DEPTH plus
+// 4 for the frames above the document's frames:
+//  the Viewport, GFXScroll, ScrollPort, and Canvas
+#define MAX_FRAME_DEPTH (MAX_REFLOW_DEPTH + 4)
+
+bool nsContainerFrame::IsFrameTreeTooDeep(const ReflowInput& aReflowInput,
+                                          ReflowOutput& aMetrics,
+                                          nsReflowStatus& aStatus) {
+  if (aReflowInput.mReflowDepth > MAX_FRAME_DEPTH) {
+    NS_WARNING("frame tree too deep; setting zero size and returning");
+    AddStateBits(NS_FRAME_TOO_DEEP_IN_FRAME_TREE);
+    ClearOverflowRects();
+    aMetrics.ClearSize();
+    aMetrics.SetBlockStartAscent(0);
+    aMetrics.mCarriedOutBEndMargin.Zero();
+    aMetrics.mOverflowAreas.Clear();
+
+    aStatus.Reset();
+    if (GetNextInFlow()) {
+      // Reflow depth might vary between reflows, so we might have
+      // successfully reflowed and split this frame before.  If so, we
+      // shouldn't delete its continuations.
+      aStatus.SetIncomplete();
+    }
+
+    return true;
+  }
+  RemoveStateBits(NS_FRAME_TOO_DEEP_IN_FRAME_TREE);
+  return false;
+}
+
+bool nsContainerFrame::ShouldAvoidBreakInside(
+    const ReflowInput& aReflowInput) const {
+  MOZ_ASSERT(this == aReflowInput.mFrame,
+             "Caller should pass a ReflowInput for this frame!");
+
+  const auto* disp = StyleDisplay();
+  const bool mayAvoidBreak = [&] {
+    switch (disp->mBreakInside) {
+      case StyleBreakWithin::Auto:
+        return false;
+      case StyleBreakWithin::Avoid:
+        return true;
+      case StyleBreakWithin::AvoidPage:
+        return aReflowInput.mBreakType == ReflowInput::BreakType::Page;
+      case StyleBreakWithin::AvoidColumn:
+        return aReflowInput.mBreakType == ReflowInput::BreakType::Column;
+    }
+    MOZ_ASSERT_UNREACHABLE("Unknown break-inside value");
+    return false;
+  }();
+
+  if (!mayAvoidBreak) {
+    return false;
+  }
+  if (aReflowInput.mFlags.mIsTopOfPage) {
+    return false;
+  }
+  if (IsAbsolutelyPositioned(disp)) {
+    return false;
+  }
+  if (GetPrevInFlow()) {
+    return false;
+  }
+  return true;
+}
+
+void nsContainerFrame::ConsiderChildOverflow(OverflowAreas& aOverflowAreas,
+                                             nsIFrame* aChildFrame) {
+  if (StyleDisplay()->IsContainLayout() &&
+      IsFrameOfType(eSupportsContainLayoutAndPaint)) {
+    // If we have layout containment and are not a non-atomic, inline-level
+    // principal box, we should only consider our child's ink overflow,
+    // leaving the scrollable regions of the parent unaffected.
+    // Note: scrollable overflow is a subset of ink overflow,
+    // so this has the same affect as unioning the child's ink and
+    // scrollable overflow with the parent's ink overflow.
+    const OverflowAreas childOverflows(aChildFrame->InkOverflowRect(),
+                                       nsRect());
+    aOverflowAreas.UnionWith(childOverflows + aChildFrame->GetPosition());
+  } else {
+    aOverflowAreas.UnionWith(
+        aChildFrame->GetActualAndNormalOverflowAreasRelativeToParent());
+  }
+}
+
+StyleAlignFlags nsContainerFrame::CSSAlignmentForAbsPosChild(
+    const ReflowInput& aChildRI, LogicalAxis aLogicalAxis) const {
+  MOZ_ASSERT(aChildRI.mFrame->IsAbsolutelyPositioned(),
+             "This method should only be called for abspos children");
+  NS_ERROR(
+      "Child classes that use css box alignment for abspos children "
+      "should provide their own implementation of this method!");
+
+  // In the unexpected/unlikely event that this implementation gets invoked,
+  // just use "start" alignment.
+  return StyleAlignFlags::START;
+}
+
+nsOverflowContinuationTracker::nsOverflowContinuationTracker(
+    nsContainerFrame* aFrame, bool aWalkOOFFrames,
+    bool aSkipOverflowContainerChildren)
+    : mOverflowContList(nullptr),
+      mPrevOverflowCont(nullptr),
+      mSentry(nullptr),
+      mParent(aFrame),
+      mSkipOverflowContainerChildren(aSkipOverflowContainerChildren),
+      mWalkOOFFrames(aWalkOOFFrames) {
+  MOZ_ASSERT(aFrame, "null frame pointer");
+  SetupOverflowContList();
+}
+
+void nsOverflowContinuationTracker::SetupOverflowContList() {
+  MOZ_ASSERT(mParent, "null frame pointer");
+  MOZ_ASSERT(!mOverflowContList, "already have list");
+  nsContainerFrame* nif =
+      static_cast<nsContainerFrame*>(mParent->GetNextInFlow());
+  if (nif) {
+    mOverflowContList = nif->GetOverflowContainers();
+    if (mOverflowContList) {
+      mParent = nif;
+      SetUpListWalker();
+    }
+  }
+  if (!mOverflowContList) {
+    mOverflowContList = mParent->GetExcessOverflowContainers();
+    if (mOverflowContList) {
+      SetUpListWalker();
+    }
+  }
+}
+
+/**
+ * Helper function to walk past overflow continuations whose prev-in-flow
+ * isn't a normal child and to set mSentry and mPrevOverflowCont correctly.
+ */
+void nsOverflowContinuationTracker::SetUpListWalker() {
+  NS_ASSERTION(!mSentry && !mPrevOverflowCont,
+               "forgot to reset mSentry or mPrevOverflowCont");
+  if (mOverflowContList) {
+    nsIFrame* cur = mOverflowContList->FirstChild();
+    if (mSkipOverflowContainerChildren) {
+      while (cur && cur->GetPrevInFlow()->HasAnyStateBits(
+                        NS_FRAME_IS_OVERFLOW_CONTAINER)) {
+        mPrevOverflowCont = cur;
+        cur = cur->GetNextSibling();
+      }
+      while (cur &&
+             (cur->HasAnyStateBits(NS_FRAME_OUT_OF_FLOW) != mWalkOOFFrames)) {
+        mPrevOverflowCont = cur;
+        cur = cur->GetNextSibling();
+      }
+    }
+    if (cur) {
+      mSentry = cur->GetPrevInFlow();
+    }
+  }
+}
+
+/**
+ * Helper function to step forward through the overflow continuations list.
+ * Sets mSentry and mPrevOverflowCont, skipping over OOF or non-OOF frames
+ * as appropriate. May only be called when we have already set up an
+ * mOverflowContList; mOverflowContList cannot be null.
+ */
+void nsOverflowContinuationTracker::StepForward() {
+  MOZ_ASSERT(mOverflowContList, "null list");
+
+  // Step forward
+  if (mPrevOverflowCont) {
+    mPrevOverflowCont = mPrevOverflowCont->GetNextSibling();
+  } else {
+    mPrevOverflowCont = mOverflowContList->FirstChild();
+  }
+
+  // Skip over oof or non-oof frames as appropriate
+  if (mSkipOverflowContainerChildren) {
+    nsIFrame* cur = mPrevOverflowCont->GetNextSibling();
+    while (cur &&
+           (cur->HasAnyStateBits(NS_FRAME_OUT_OF_FLOW) != mWalkOOFFrames)) {
+      mPrevOverflowCont = cur;
+      cur = cur->GetNextSibling();
+    }
+  }
+
+  // Set up the sentry
+  mSentry = (mPrevOverflowCont->GetNextSibling())
+                ? mPrevOverflowCont->GetNextSibling()->GetPrevInFlow()
+                : nullptr;
+}
+
+nsresult nsOverflowContinuationTracker::Insert(nsIFrame* aOverflowCont,
+                                               nsReflowStatus& aReflowStatus) {
+  MOZ_ASSERT(aOverflowCont, "null frame pointer");
+  MOZ_ASSERT(!mSkipOverflowContainerChildren ||
+                 mWalkOOFFrames ==
+                     aOverflowCont->HasAnyStateBits(NS_FRAME_OUT_OF_FLOW),
+             "shouldn't insert frame that doesn't match walker type");
+  MOZ_ASSERT(aOverflowCont->GetPrevInFlow(),
+             "overflow containers must have a prev-in-flow");
+
+  nsresult rv = NS_OK;
+  bool reparented = false;
+  nsPresContext* presContext = aOverflowCont->PresContext();
+  bool addToList = !mSentry || aOverflowCont != mSentry->GetNextInFlow();
+
+  // If we have a list and aOverflowCont is already in it then don't try to
+  // add it again.
+  if (addToList && aOverflowCont->GetParent() == mParent &&
+      aOverflowCont->HasAnyStateBits(NS_FRAME_IS_OVERFLOW_CONTAINER) &&
+      mOverflowContList && mOverflowContList->ContainsFrame(aOverflowCont)) {
+    addToList = false;
+    mPrevOverflowCont = aOverflowCont->GetPrevSibling();
+  }
+
+  if (addToList) {
+    if (aOverflowCont->HasAnyStateBits(NS_FRAME_IS_OVERFLOW_CONTAINER)) {
+      // aOverflowCont is in some other overflow container list,
+      // steal it first
+      NS_ASSERTION(!(mOverflowContList &&
+                     mOverflowContList->ContainsFrame(aOverflowCont)),
+                   "overflow containers out of order");
+      aOverflowCont->GetParent()->StealFrame(aOverflowCont);
+    } else {
+      aOverflowCont->AddStateBits(NS_FRAME_IS_OVERFLOW_CONTAINER);
+    }
+    if (!mOverflowContList) {
+      // Note: We don't use SetExcessOverflowContainers() since it requires
+      // setting a non-empty list. It's OK to manually set an empty list to
+      // ExcessOverflowContainersProperty() because we are going to insert
+      // aOverflowCont to mOverflowContList below, which guarantees an nonempty
+      // list in ExcessOverflowContainersProperty().
+      mOverflowContList = new (presContext->PresShell()) nsFrameList();
+      mParent->SetProperty(nsContainerFrame::ExcessOverflowContainersProperty(),
+                           mOverflowContList);
+      SetUpListWalker();
+    }
+    if (aOverflowCont->GetParent() != mParent) {
+      nsContainerFrame::ReparentFrameView(aOverflowCont,
+                                          aOverflowCont->GetParent(), mParent);
+      reparented = true;
+    }
+
+    // If aOverflowCont has a prev/next-in-flow that might be in
+    // mOverflowContList we need to find it and insert after/before it to
+    // maintain the order amongst next-in-flows in this list.
+    nsIFrame* pif = aOverflowCont->GetPrevInFlow();
+    nsIFrame* nif = aOverflowCont->GetNextInFlow();
+    if ((pif && pif->GetParent() == mParent && pif != mPrevOverflowCont) ||
+        (nif && nif->GetParent() == mParent && mPrevOverflowCont)) {
+      for (nsIFrame* f : *mOverflowContList) {
+        if (f == pif) {
+          mPrevOverflowCont = pif;
+          break;
+        }
+        if (f == nif) {
+          mPrevOverflowCont = f->GetPrevSibling();
+          break;
+        }
+      }
+    }
+
+    mOverflowContList->InsertFrame(mParent, mPrevOverflowCont, aOverflowCont);
+    aReflowStatus.SetNextInFlowNeedsReflow();
+  }
+
+  // If we need to reflow it, mark it dirty
+  if (aReflowStatus.NextInFlowNeedsReflow()) {
+    aOverflowCont->MarkSubtreeDirty();
+  }
+
+  // It's in our list, just step forward
+  StepForward();
+  NS_ASSERTION(mPrevOverflowCont == aOverflowCont ||
+                   (mSkipOverflowContainerChildren &&
+                    mPrevOverflowCont->HasAnyStateBits(NS_FRAME_OUT_OF_FLOW) !=
+                        aOverflowCont->HasAnyStateBits(NS_FRAME_OUT_OF_FLOW)),
+               "OverflowContTracker in unexpected state");
+
+  if (addToList) {
+    // Convert all non-overflow-container next-in-flows of aOverflowCont
+    // into overflow containers and move them to our overflow
+    // tracker. This preserves the invariant that the next-in-flows
+    // of an overflow container are also overflow containers.
+    nsIFrame* f = aOverflowCont->GetNextInFlow();
+    if (f && (!f->HasAnyStateBits(NS_FRAME_IS_OVERFLOW_CONTAINER) ||
+              (!reparented && f->GetParent() == mParent) ||
+              (reparented && f->GetParent() != mParent))) {
+      if (!f->HasAnyStateBits(NS_FRAME_IS_OVERFLOW_CONTAINER)) {
+        f->GetParent()->StealFrame(f);
+      }
+      Insert(f, aReflowStatus);
+    }
+  }
+  return rv;
+}
+
+void nsOverflowContinuationTracker::BeginFinish(nsIFrame* aChild) {
+  MOZ_ASSERT(aChild, "null ptr");
+  MOZ_ASSERT(aChild->GetNextInFlow(),
+             "supposed to call Finish *before* deleting next-in-flow!");
+
+  for (nsIFrame* f = aChild; f; f = f->GetNextInFlow()) {
+    // We'll update these in EndFinish after the next-in-flows are gone.
+    if (f == mPrevOverflowCont) {
+      mSentry = nullptr;
+      mPrevOverflowCont = nullptr;
+      break;
+    }
+    if (f == mSentry) {
+      mSentry = nullptr;
+      break;
+    }
+  }
+}
+
+void nsOverflowContinuationTracker::EndFinish(nsIFrame* aChild) {
+  if (!mOverflowContList) {
+    return;
+  }
+  // Forget mOverflowContList if it was deleted.
+  nsFrameList* eoc = mParent->GetExcessOverflowContainers();
+  if (eoc != mOverflowContList) {
+    nsFrameList* oc = mParent->GetOverflowContainers();
+    if (oc != mOverflowContList) {
+      // mOverflowContList was deleted
+      mPrevOverflowCont = nullptr;
+      mSentry = nullptr;
+      mParent = aChild->GetParent();
+      mOverflowContList = nullptr;
+      SetupOverflowContList();
+      return;
+    }
+  }
+  // The list survived, update mSentry if needed.
+  if (!mSentry) {
+    if (!mPrevOverflowCont) {
+      SetUpListWalker();
+    } else {
+      mozilla::AutoRestore<nsIFrame*> saved(mPrevOverflowCont);
+      // step backward to make StepForward() use our current mPrevOverflowCont
+      mPrevOverflowCont = mPrevOverflowCont->GetPrevSibling();
+      StepForward();
+    }
+  }
+}
+
+/////////////////////////////////////////////////////////////////////////////
+// Debugging
+
+#ifdef DEBUG
+void nsContainerFrame::SanityCheckChildListsBeforeReflow() const {
+  MOZ_ASSERT(IsFlexOrGridContainer(),
+             "Only Flex / Grid containers can call this!");
+
+  const auto didPushItemsBit = IsFlexContainerFrame()
+                                   ? NS_STATE_FLEX_DID_PUSH_ITEMS
+                                   : NS_STATE_GRID_DID_PUSH_ITEMS;
+  ChildListIDs absLists = {FrameChildListID::Absolute, FrameChildListID::Fixed,
+                           FrameChildListID::OverflowContainers,
+                           FrameChildListID::ExcessOverflowContainers};
+  ChildListIDs itemLists = {FrameChildListID::Principal,
+                            FrameChildListID::Overflow};
+  for (const nsIFrame* f = this; f; f = f->GetNextInFlow()) {
+    MOZ_ASSERT(!f->HasAnyStateBits(didPushItemsBit),
+               "At start of reflow, we should've pulled items back from all "
+               "NIFs and cleared the state bit stored in didPushItemsBit in "
+               "the process.");
+    for (const auto& [list, listID] : f->ChildLists()) {
+      if (!itemLists.contains(listID)) {
+        MOZ_ASSERT(
+            absLists.contains(listID) || listID == FrameChildListID::Backdrop,
+            "unexpected non-empty child list");
+        continue;
+      }
+      for (const auto* child : list) {
+        MOZ_ASSERT(f == this || child->GetPrevInFlow(),
+                   "all pushed items must be pulled up before reflow");
+      }
+    }
+  }
+  // If we have a prev-in-flow, each of its children's next-in-flow
+  // should be one of our children or be null.
+  const auto* pif = static_cast<nsContainerFrame*>(GetPrevInFlow());
+  if (pif) {
+    const nsFrameList* oc = GetOverflowContainers();
+    const nsFrameList* eoc = GetExcessOverflowContainers();
+    const nsFrameList* pifEOC = pif->GetExcessOverflowContainers();
+    for (const nsIFrame* child : pif->PrincipalChildList()) {
+      const nsIFrame* childNIF = child->GetNextInFlow();
+      MOZ_ASSERT(!childNIF || mFrames.ContainsFrame(childNIF) ||
+                 (pifEOC && pifEOC->ContainsFrame(childNIF)) ||
+                 (oc && oc->ContainsFrame(childNIF)) ||
+                 (eoc && eoc->ContainsFrame(childNIF)));
+    }
+  }
+}
+
+void nsContainerFrame::SetDidPushItemsBitIfNeeded(ChildListID aListID,
+                                                  nsIFrame* aOldFrame) {
+  MOZ_ASSERT(IsFlexOrGridContainer(),
+             "Only Flex / Grid containers can call this!");
+
+  // Note that FrameChildListID::Principal doesn't mean aOldFrame must be on
+  // that list. It can also be on FrameChildListID::Overflow, in which case it
+  // might be a pushed item, and if it's the only pushed item our DID_PUSH_ITEMS
+  // bit will lie.
+  if (aListID == FrameChildListID::Principal && !aOldFrame->GetPrevInFlow()) {
+    // Since the bit may lie, set the mDidPushItemsBitMayLie value to true for
+    // ourself and for all our prev-in-flows.
+    nsContainerFrame* frameThatMayLie = this;
+    do {
+      frameThatMayLie->mDidPushItemsBitMayLie = true;
+      frameThatMayLie =
+          static_cast<nsContainerFrame*>(frameThatMayLie->GetPrevInFlow());
+    } while (frameThatMayLie);
+  }
+}
+#endif
+
+#ifdef DEBUG_FRAME_DUMP
+void nsContainerFrame::List(FILE* out, const char* aPrefix,
+                            ListFlags aFlags) const {
+  nsCString str;
+  ListGeneric(str, aPrefix, aFlags);
+  ExtraContainerFrameInfo(str);
+
+  // Output the frame name and various fields.
+  fprintf_stderr(out, "%s <\n", str.get());
+
+  const nsCString pfx = nsCString(aPrefix) + "  "_ns;
+
+  // Output principal child list separately since we want to omit its
+  // name and address.
+  for (nsIFrame* kid : PrincipalChildList()) {
+    kid->List(out, pfx.get(), aFlags);
+  }
+
+  // Output rest of the child lists.
+  const ChildListIDs skippedListIDs = {FrameChildListID::Principal};
+  ListChildLists(out, pfx.get(), aFlags, skippedListIDs);
+
+  fprintf_stderr(out, "%s>\n", aPrefix);
+}
+
+void nsContainerFrame::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());
+
+  nsCString childPrefix;
+  childPrefix += aPrefix;
+  childPrefix += "  ";
+
+  for (const auto& childList : ChildLists()) {
+    for (const nsIFrame* kid : childList.mList) {
+      kid->ListWithMatchedRules(out, childPrefix.get());
+    }
+  }
+}
+
+void nsContainerFrame::ListChildLists(FILE* aOut, const char* aPrefix,
+                                      ListFlags aFlags,
+                                      ChildListIDs aSkippedListIDs) const {
+  const nsCString nestedPfx = nsCString(aPrefix) + "  "_ns;
+
+  for (const auto& [list, listID] : ChildLists()) {
+    if (aSkippedListIDs.contains(listID)) {
+      continue;
+    }
+
+    // Use nsPrintfCString so that %p don't output prefix "0x". This is
+    // consistent with nsIFrame::ListTag().
+    const nsPrintfCString str("%s%s@%p <\n", aPrefix, ChildListName(listID),
+                              &GetChildList(listID));
+    fprintf_stderr(aOut, "%s", str.get());
+
+    for (nsIFrame* kid : list) {
+      // Verify the child frame's parent frame pointer is correct.
+      NS_ASSERTION(kid->GetParent() == this, "Bad parent frame pointer!");
+      kid->List(aOut, nestedPfx.get(), aFlags);
+    }
+    fprintf_stderr(aOut, "%s>\n", aPrefix);
+  }
+}
+
+void nsContainerFrame::ExtraContainerFrameInfo(nsACString& aTo) const {
+  (void)aTo;
+}
+
+#endif