Adding upstream version 115.7.0esr.upstream/115.7.0esrupstream

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

1 files changed, 5606 insertions, 0 deletions

diff --git a/layout/generic/nsIFrame.h b/layout/generic/nsIFrame.h
new file mode 100644
index 0000000000..03eea383b1
--- /dev/null
+++ b/layout/generic/nsIFrame.h
@@ -0,0 +1,5606 @@
+/* -*- 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/. */
+
+/* interface for all rendering objects */
+
+#ifndef nsIFrame_h___
+#define nsIFrame_h___
+
+#ifndef MOZILLA_INTERNAL_API
+#error This header/class should only be used within Mozilla code. It should not be used by extensions.
+#endif
+
+#if (defined(XP_WIN) && !defined(HAVE_64BIT_BUILD)) || defined(ANDROID)
+// Blink's magic depth limit from its HTML parser (513) plus as much as fits in
+// the default run-time stack on armv7 Android on Dalvik when using display:
+// block minus a bit just to be sure. The Dalvik default stack crashes at 588.
+// ART can do a few frames more. Using the same number for 32-bit Windows for
+// consistency. Over there, Blink's magic depth of 513 doesn't fit in the
+// default stack of 1 MB, but this magic depth fits when the default is grown by
+// mere 192 KB (tested in 64 KB increments).
+//
+// 32-bit Windows has a different limit compared to 64-bit desktop, because the
+// default stack size affects all threads and consumes address space. Fixing
+// that is bug 1257522.
+//
+// 32-bit Android on ARM already happens to have defaults that are close enough
+// to what makes sense as a temporary measure on Windows, so adjusting the
+// Android stack can be a follow-up. The stack on 64-bit ARM needs adjusting in
+// any case before 64-bit ARM can become tier-1. See bug 1400811.
+//
+// Ideally, we'd get rid of this smaller limit and make 32-bit Windows and
+// Android capable of working with the Linux/Mac/Win64 number below.
+#  define MAX_REFLOW_DEPTH 585
+#else
+// Blink's magic depth limit from its HTML parser times two. Also just about
+// fits within the system default runtime stack limit of 8 MB on 64-bit Mac and
+// Linux with display: table-cell.
+#  define MAX_REFLOW_DEPTH 1026
+#endif
+
+/* nsIFrame is in the process of being deCOMtaminated, i.e., this file is
+   eventually going to be eliminated, and all callers will use nsFrame instead.
+   At the moment we're midway through this process, so you will see inlined
+   functions and member variables in this file.  -dwh */
+
+#include <algorithm>
+#include <stdio.h>
+
+#include "CaretAssociationHint.h"
+#include "FrameProperties.h"
+#include "LayoutConstants.h"
+#include "mozilla/AspectRatio.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/Baseline.h"
+#include "mozilla/EnumSet.h"
+#include "mozilla/EventForwards.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/RelativeTo.h"
+#include "mozilla/Result.h"
+#include "mozilla/SmallPointerArray.h"
+#include "mozilla/ToString.h"
+#include "mozilla/WritingModes.h"
+#include "nsDirection.h"
+#include "nsFrameList.h"
+#include "nsFrameState.h"
+#include "mozilla/ReflowInput.h"
+#include "nsIContent.h"
+#include "nsITheme.h"
+#include "nsQueryFrame.h"
+#include "mozilla/ComputedStyle.h"
+#include "nsStyleStruct.h"
+#include "Visibility.h"
+#include "nsChangeHint.h"
+#include "mozilla/EnumSet.h"
+#include "mozilla/gfx/2D.h"
+#include "mozilla/gfx/CompositorHitTestInfo.h"
+#include "mozilla/gfx/MatrixFwd.h"
+#include "mozilla/intl/BidiEmbeddingLevel.h"
+#include "nsDisplayItemTypes.h"
+#include "nsPresContext.h"
+#include "nsTHashSet.h"
+
+#ifdef ACCESSIBILITY
+#  include "mozilla/a11y/AccTypes.h"
+#endif
+
+/**
+ * New rules of reflow:
+ * 1. you get a WillReflow() followed by a Reflow() followed by a DidReflow() in
+ *    order (no separate pass over the tree)
+ * 2. it's the parent frame's responsibility to size/position the child's view
+ *    (not the child frame's responsibility as it is today) during reflow (and
+ *    before sending the DidReflow() notification)
+ * 3. positioning of child frames (and their views) is done on the way down the
+ *    tree, and sizing of child frames (and their views) on the way back up
+ * 4. if you move a frame (outside of the reflow process, or after reflowing
+ *    it), then you must make sure that its view (or its child frame's views)
+ *    are re-positioned as well. It's reasonable to not position the view until
+ *    after all reflowing the entire line, for example, but the frame should
+ *    still be positioned and sized (and the view sized) during the reflow
+ *    (i.e., before sending the DidReflow() notification)
+ * 5. the view system handles moving of widgets, i.e., it's not our problem
+ */
+
+class nsAtom;
+class nsView;
+class nsFrameSelection;
+class nsIWidget;
+class nsIScrollableFrame;
+class nsISelectionController;
+class nsILineIterator;
+class gfxSkipChars;
+class gfxSkipCharsIterator;
+class gfxContext;
+class nsLineList_iterator;
+class nsAbsoluteContainingBlock;
+class nsContainerFrame;
+class nsPlaceholderFrame;
+class nsStyleChangeList;
+class nsViewManager;
+class nsWindowSizes;
+
+struct CharacterDataChangeInfo;
+
+namespace mozilla {
+
+enum class PeekOffsetOption : uint8_t;
+enum class PseudoStyleType : uint8_t;
+enum class TableSelectionMode : uint32_t;
+
+class nsDisplayItem;
+class nsDisplayList;
+class nsDisplayListBuilder;
+class nsDisplayListSet;
+
+class ServoRestyleState;
+class EffectSet;
+class LazyLogModule;
+class PresShell;
+class WidgetGUIEvent;
+class WidgetMouseEvent;
+
+struct PeekOffsetStruct;
+
+namespace layers {
+class Layer;
+class LayerManager;
+}  // namespace layers
+
+namespace layout {
+class ScrollAnchorContainer;
+}  // namespace layout
+
+}  // namespace mozilla
+
+//----------------------------------------------------------------------
+
+// 1 million CSS pixels less than our max app unit measure.
+// For reflowing with an "infinite" available inline space per [css-sizing].
+// (reflowing with an NS_UNCONSTRAINEDSIZE available inline size isn't allowed
+//  and leads to assertions)
+#define INFINITE_ISIZE_COORD nscoord(NS_MAXSIZE - (1000000 * 60))
+
+//----------------------------------------------------------------------
+
+namespace mozilla {
+
+enum class LayoutFrameType : uint8_t {
+#define FRAME_TYPE(ty_, ...) ty_,
+#include "mozilla/FrameTypeList.h"
+#undef FRAME_TYPE
+};
+
+}  // namespace mozilla
+
+enum nsSelectionAmount {
+  eSelectCharacter = 0,  // a single Unicode character;
+                         // do not use this (prefer Cluster) unless you
+                         // are really sure it's what you want
+  eSelectCluster = 1,    // a grapheme cluster: this is usually the right
+                         // choice for movement or selection by "character"
+                         // as perceived by the user
+  eSelectWord = 2,
+  eSelectWordNoSpace = 3,  // select a "word" without selecting the following
+                           // space, no matter what the default platform
+                           // behavior is
+  eSelectLine = 4,         // previous drawn line in flow.
+  // NOTE that selection code depends on the ordering of the above values,
+  // allowing simple <= tests to check categories of caret movement.
+  // Don't rearrange without checking the usage in nsSelection.cpp!
+
+  eSelectBeginLine = 5,
+  eSelectEndLine = 6,
+  eSelectNoAmount = 7,  // just bounce back current offset.
+  eSelectParagraph = 8  // select a "paragraph"
+};
+
+//----------------------------------------------------------------------
+// Reflow status returned by the Reflow() methods.
+class nsReflowStatus final {
+ public:
+  nsReflowStatus()
+      : mFloatClearType(mozilla::StyleClear::None),
+        mInlineBreak(InlineBreak::None),
+        mCompletion(Completion::FullyComplete),
+        mNextInFlowNeedsReflow(false),
+        mFirstLetterComplete(false) {}
+
+  // Reset all the member variables.
+  void Reset() {
+    mFloatClearType = mozilla::StyleClear::None;
+    mInlineBreak = InlineBreak::None;
+    mCompletion = Completion::FullyComplete;
+    mNextInFlowNeedsReflow = false;
+    mFirstLetterComplete = false;
+  }
+
+  // Return true if all member variables have their default values.
+  bool IsEmpty() const {
+    return (IsFullyComplete() && !IsInlineBreak() && !mNextInFlowNeedsReflow &&
+            !mFirstLetterComplete);
+  }
+
+  // There are three possible completion statuses, represented by
+  // mCompletion.
+  //
+  // Incomplete means the frame does *not* map all its content, and the
+  // parent frame should create a continuing frame.
+  //
+  // OverflowIncomplete means that the frame has an overflow that is not
+  // complete, but its own box is complete. (This happens when the content
+  // overflows a fixed-height box.) The reflower should place and size the
+  // frame and continue its reflow, but it needs to create an overflow
+  // container as a continuation for this frame. See "Overflow containers"
+  // documentation in nsContainerFrame.h for more information.
+  //
+  // FullyComplete means the frame is neither Incomplete nor
+  // OverflowIncomplete. This is the default state for a nsReflowStatus.
+  //
+  enum class Completion : uint8_t {
+    // The order of the enum values is important, which represents the
+    // precedence when merging.
+    FullyComplete,
+    OverflowIncomplete,
+    Incomplete,
+  };
+
+  bool IsIncomplete() const { return mCompletion == Completion::Incomplete; }
+  bool IsOverflowIncomplete() const {
+    return mCompletion == Completion::OverflowIncomplete;
+  }
+  bool IsFullyComplete() const {
+    return mCompletion == Completion::FullyComplete;
+  }
+  // Just for convenience; not a distinct state.
+  bool IsComplete() const { return !IsIncomplete(); }
+
+  void SetIncomplete() { mCompletion = Completion::Incomplete; }
+  void SetOverflowIncomplete() { mCompletion = Completion::OverflowIncomplete; }
+
+  // mNextInFlowNeedsReflow bit flag means that the next-in-flow is dirty,
+  // and also needs to be reflowed. This status only makes sense for a frame
+  // that is not complete, i.e. you wouldn't set mNextInFlowNeedsReflow when
+  // IsComplete() is true.
+  bool NextInFlowNeedsReflow() const { return mNextInFlowNeedsReflow; }
+  void SetNextInFlowNeedsReflow() { mNextInFlowNeedsReflow = true; }
+
+  // Merge the frame completion status bits from aStatus into this.
+  void MergeCompletionStatusFrom(const nsReflowStatus& aStatus) {
+    if (mCompletion < aStatus.mCompletion) {
+      mCompletion = aStatus.mCompletion;
+    }
+
+    // These asserts ensure that the mCompletion merging works as we expect.
+    // (Incomplete beats OverflowIncomplete, which beats FullyComplete.)
+    static_assert(
+        Completion::Incomplete > Completion::OverflowIncomplete &&
+            Completion::OverflowIncomplete > Completion::FullyComplete,
+        "mCompletion merging won't work without this!");
+
+    mNextInFlowNeedsReflow |= aStatus.mNextInFlowNeedsReflow;
+  }
+
+  // There are three possible inline-break statuses, represented by
+  // mInlineBreak.
+  //
+  // "None" means no break is requested.
+  // "Before" means the break should occur before the frame.
+  // "After" means the break should occur after the frame.
+  // (Here, "the frame" is the frame whose reflow results are being reported by
+  // this nsReflowStatus.)
+  //
+  enum class InlineBreak : uint8_t {
+    None,
+    Before,
+    After,
+  };
+
+  bool IsInlineBreak() const { return mInlineBreak != InlineBreak::None; }
+  bool IsInlineBreakBefore() const {
+    return mInlineBreak == InlineBreak::Before;
+  }
+  bool IsInlineBreakAfter() const { return mInlineBreak == InlineBreak::After; }
+  mozilla::StyleClear FloatClearType() const { return mFloatClearType; }
+
+  // Set the inline line-break-before status, and reset other bit flags. Note
+  // that other frame completion status isn't expected to matter after calling
+  // this method.
+  //
+  // Here's one scenario where a child frame would report this status. Suppose
+  // the child has "break-inside:avoid" in its style, and the child (and its
+  // content) won't fit in the available block-size. This child would want to
+  // report this status so that it gets pushed (in its entirety) to the next
+  // column/page where it will hopefully fit.
+  void SetInlineLineBreakBeforeAndReset() {
+    Reset();
+    mFloatClearType = mozilla::StyleClear::None;
+    mInlineBreak = InlineBreak::Before;
+  }
+
+  // Set the inline line-break-after status. The clear type can be changed
+  // via the optional aClearType param.
+  void SetInlineLineBreakAfter(
+      mozilla::StyleClear aClearType = mozilla::StyleClear::None) {
+    mFloatClearType = aClearType;
+    mInlineBreak = InlineBreak::After;
+  }
+
+  // mFirstLetterComplete bit flag means the break was induced by
+  // completion of a first-letter.
+  bool FirstLetterComplete() const { return mFirstLetterComplete; }
+  void SetFirstLetterComplete() { mFirstLetterComplete = true; }
+
+ private:
+  mozilla::StyleClear mFloatClearType;
+  InlineBreak mInlineBreak;
+  Completion mCompletion;
+  bool mNextInFlowNeedsReflow : 1;
+  bool mFirstLetterComplete : 1;
+};
+
+// Convert nsReflowStatus to a human-readable string.
+std::ostream& operator<<(std::ostream& aStream, const nsReflowStatus& aStatus);
+
+namespace mozilla {
+
+// Loosely: https://drafts.csswg.org/css-align-3/#shared-alignment-context
+enum class AlignmentContext {
+  Inline,
+  Table,
+  Flexbox,
+  Grid,
+};
+
+/*
+ * For replaced elements only. Gets the intrinsic dimensions of this element,
+ * which can be specified on a per-axis basis.
+ */
+struct IntrinsicSize {
+  Maybe<nscoord> width;
+  Maybe<nscoord> height;
+
+  IntrinsicSize() = default;
+
+  IntrinsicSize(nscoord aWidth, nscoord aHeight)
+      : width(Some(aWidth)), height(Some(aHeight)) {}
+
+  explicit IntrinsicSize(const nsSize& aSize)
+      : IntrinsicSize(aSize.Width(), aSize.Height()) {}
+
+  Maybe<nsSize> ToSize() const {
+    return width && height ? Some(nsSize(*width, *height)) : Nothing();
+  }
+
+  bool operator==(const IntrinsicSize& rhs) const {
+    return width == rhs.width && height == rhs.height;
+  }
+  bool operator!=(const IntrinsicSize& rhs) const { return !(*this == rhs); }
+};
+
+// Pseudo bidi embedding level indicating nonexistence.
+static const mozilla::intl::BidiEmbeddingLevel kBidiLevelNone =
+    mozilla::intl::BidiEmbeddingLevel(0xff);
+
+struct FrameBidiData {
+  mozilla::intl::BidiEmbeddingLevel baseLevel;
+  mozilla::intl::BidiEmbeddingLevel embeddingLevel;
+  // The embedding level of virtual bidi formatting character before
+  // this frame if any. kBidiLevelNone is used to indicate nonexistence
+  // or unnecessity of such virtual character.
+  mozilla::intl::BidiEmbeddingLevel precedingControl;
+};
+
+}  // namespace mozilla
+
+/// Generic destructor for frame properties. Calls delete.
+template <typename T>
+static void DeleteValue(T* aPropertyValue) {
+  delete aPropertyValue;
+}
+
+/// Generic destructor for frame properties. Calls Release().
+template <typename T>
+static void ReleaseValue(T* aPropertyValue) {
+  aPropertyValue->Release();
+}
+
+//----------------------------------------------------------------------
+
+/**
+ * nsIFrame logging constants. We redefine the nspr
+ * PRLogModuleInfo.level field to be a bitfield.  Each bit controls a
+ * specific type of logging. Each logging operation has associated
+ * inline methods defined below.
+ *
+ * Due to the redefinition of the level field we cannot use MOZ_LOG directly
+ * as that will cause assertions due to invalid log levels.
+ */
+#define NS_FRAME_TRACE_CALLS 0x1
+#define NS_FRAME_TRACE_PUSH_PULL 0x2
+#define NS_FRAME_TRACE_CHILD_REFLOW 0x4
+#define NS_FRAME_TRACE_NEW_FRAMES 0x8
+
+#define NS_FRAME_LOG_TEST(_lm, _bit) \
+  (int(((mozilla::LogModule*)(_lm))->Level()) & (_bit))
+
+#ifdef DEBUG
+#  define NS_FRAME_LOG(_bit, _args)                           \
+    PR_BEGIN_MACRO                                            \
+    if (NS_FRAME_LOG_TEST(nsIFrame::sFrameLogModule, _bit)) { \
+      printf_stderr _args;                                    \
+    }                                                         \
+    PR_END_MACRO
+#else
+#  define NS_FRAME_LOG(_bit, _args)
+#endif
+
+// XXX Need to rework this so that logging is free when it's off
+#ifdef DEBUG
+#  define NS_FRAME_TRACE_IN(_method) Trace(_method, true)
+
+#  define NS_FRAME_TRACE_OUT(_method) Trace(_method, false)
+
+#  define NS_FRAME_TRACE(_bit, _args)                         \
+    PR_BEGIN_MACRO                                            \
+    if (NS_FRAME_LOG_TEST(nsIFrame::sFrameLogModule, _bit)) { \
+      TraceMsg _args;                                         \
+    }                                                         \
+    PR_END_MACRO
+
+#  define NS_FRAME_TRACE_REFLOW_IN(_method) Trace(_method, true)
+
+#  define NS_FRAME_TRACE_REFLOW_OUT(_method, _status) \
+    Trace(_method, false, _status)
+
+#else
+#  define NS_FRAME_TRACE(_bits, _args)
+#  define NS_FRAME_TRACE_IN(_method)
+#  define NS_FRAME_TRACE_OUT(_method)
+#  define NS_FRAME_TRACE_REFLOW_IN(_method)
+#  define NS_FRAME_TRACE_REFLOW_OUT(_method, _status)
+#endif
+
+//----------------------------------------------------------------------
+
+// Frame allocation boilerplate macros. Every subclass of nsFrame must
+// either use NS_{DECL,IMPL}_FRAMEARENA_HELPERS pair for allocating
+// memory correctly, or use NS_DECL_ABSTRACT_FRAME to declare a frame
+// class abstract and stop it from being instantiated. If a frame class
+// without its own operator new and GetFrameId gets instantiated, the
+// per-frame recycler lists in nsPresArena will not work correctly,
+// with potentially catastrophic consequences (not enough memory is
+// allocated for a frame object).
+
+#define NS_DECL_FRAMEARENA_HELPERS(class)                                      \
+  NS_DECL_QUERYFRAME_TARGET(class)                                             \
+  static constexpr nsIFrame::ClassID kClassID = nsIFrame::ClassID::class##_id; \
+  void* operator new(size_t, mozilla::PresShell*) MOZ_MUST_OVERRIDE;           \
+  nsQueryFrame::FrameIID GetFrameId() const override MOZ_MUST_OVERRIDE {       \
+    return nsQueryFrame::class##_id;                                           \
+  }
+
+#define NS_IMPL_FRAMEARENA_HELPERS(class)                             \
+  void* class ::operator new(size_t sz, mozilla::PresShell* aShell) { \
+    return aShell->AllocateFrame(nsQueryFrame::class##_id, sz);       \
+  }
+
+#define NS_DECL_ABSTRACT_FRAME(class)                                         \
+  void* operator new(size_t, mozilla::PresShell*) MOZ_MUST_OVERRIDE = delete; \
+  nsQueryFrame::FrameIID GetFrameId() const override MOZ_MUST_OVERRIDE = 0;
+
+//----------------------------------------------------------------------
+
+namespace mozilla {
+
+// A simple class to group stuff that we need to keep around when tearing down
+// a frame tree.
+//
+// Native anonymous content created by the frames need to get unbound _after_
+// the frame has been destroyed, see bug 1400618.
+//
+// We destroy the anonymous content bottom-up (so, in reverse order), because
+// it's a bit simpler, though we generally don't have that much nested anonymous
+// content (except for scrollbars).
+struct MOZ_RAII FrameDestroyContext {
+  explicit FrameDestroyContext(PresShell* aPs) : mPresShell(aPs) {}
+
+  void AddAnonymousContent(already_AddRefed<nsIContent>&& aContent) {
+    if (RefPtr<nsIContent> content = aContent) {
+      mAnonymousContent.AppendElement(std::move(content));
+    }
+  }
+
+  ~FrameDestroyContext();
+
+ private:
+  PresShell* const mPresShell;
+  AutoTArray<RefPtr<nsIContent>, 100> mAnonymousContent;
+};
+
+}  // namespace mozilla
+
+/**
+ * A frame in the layout model. This interface is supported by all frame
+ * objects.
+ *
+ * Frames can have multiple child lists: the default child list
+ * (referred to as the <i>principal</i> child list, and additional named
+ * child lists. There is an ordering of frames within a child list, but
+ * there is no order defined between frames in different child lists of
+ * the same parent frame.
+ *
+ * Frames are NOT reference counted. Use the Destroy() member function
+ * to destroy a frame. The lifetime of the frame hierarchy is bounded by the
+ * lifetime of the presentation shell which owns the frames.
+ *
+ * nsIFrame is a private Gecko interface. If you are not Gecko then you
+ * should not use it. If you're not in layout, then you won't be able to
+ * link to many of the functions defined here. Too bad.
+ *
+ * If you're not in layout but you must call functions in here, at least
+ * restrict yourself to calling virtual methods, which won't hurt you as badly.
+ */
+class nsIFrame : public nsQueryFrame {
+ public:
+  using AlignmentContext = mozilla::AlignmentContext;
+  using BaselineSharingGroup = mozilla::BaselineSharingGroup;
+  using BaselineExportContext = mozilla::BaselineExportContext;
+  template <typename T>
+  using Maybe = mozilla::Maybe<T>;
+  template <typename T, typename E>
+  using Result = mozilla::Result<T, E>;
+  using Nothing = mozilla::Nothing;
+  using OnNonvisible = mozilla::OnNonvisible;
+  using ReflowInput = mozilla::ReflowInput;
+  using ReflowOutput = mozilla::ReflowOutput;
+  using Visibility = mozilla::Visibility;
+  using LengthPercentage = mozilla::LengthPercentage;
+  using ContentRelevancy = mozilla::ContentRelevancy;
+
+  using nsDisplayItem = mozilla::nsDisplayItem;
+  using nsDisplayList = mozilla::nsDisplayList;
+  using nsDisplayListSet = mozilla::nsDisplayListSet;
+  using nsDisplayListBuilder = mozilla::nsDisplayListBuilder;
+
+  typedef mozilla::ComputedStyle ComputedStyle;
+  typedef mozilla::FrameProperties FrameProperties;
+  typedef mozilla::layers::LayerManager LayerManager;
+  typedef mozilla::gfx::DrawTarget DrawTarget;
+  typedef mozilla::gfx::Matrix Matrix;
+  typedef mozilla::gfx::Matrix4x4 Matrix4x4;
+  typedef mozilla::gfx::Matrix4x4Flagged Matrix4x4Flagged;
+  typedef mozilla::Sides Sides;
+  typedef mozilla::LogicalSides LogicalSides;
+  typedef mozilla::SmallPointerArray<nsDisplayItem> DisplayItemArray;
+
+  typedef nsQueryFrame::ClassID ClassID;
+
+ protected:
+  using ChildList = mozilla::FrameChildList;
+  using ChildListID = mozilla::FrameChildListID;
+  using ChildListIDs = mozilla::FrameChildListIDs;
+
+ public:
+  // nsQueryFrame
+  NS_DECL_QUERYFRAME
+  NS_DECL_QUERYFRAME_TARGET(nsIFrame)
+
+  explicit nsIFrame(ComputedStyle* aStyle, nsPresContext* aPresContext,
+                    ClassID aID)
+      : mRect(),
+        mContent(nullptr),
+        mComputedStyle(aStyle),
+        mPresContext(aPresContext),
+        mParent(nullptr),
+        mNextSibling(nullptr),
+        mPrevSibling(nullptr),
+        mState(NS_FRAME_FIRST_REFLOW | NS_FRAME_IS_DIRTY),
+        mWritingMode(aStyle),
+        mClass(aID),
+        mMayHaveRoundedCorners(false),
+        mHasImageRequest(false),
+        mHasFirstLetterChild(false),
+        mParentIsWrapperAnonBox(false),
+        mIsWrapperBoxNeedingRestyle(false),
+        mReflowRequestedForCharDataChange(false),
+        mForceDescendIntoIfVisible(false),
+        mBuiltDisplayList(false),
+        mFrameIsModified(false),
+        mHasModifiedDescendants(false),
+        mHasOverrideDirtyRegion(false),
+        mMayHaveWillChangeBudget(false),
+#ifdef DEBUG
+        mWasVisitedByAutoFrameConstructionPageName(false),
+#endif
+        mIsPrimaryFrame(false),
+        mMayHaveTransformAnimation(false),
+        mMayHaveOpacityAnimation(false),
+        mAllDescendantsAreInvisible(false),
+        mHasBSizeChange(false),
+        mHasPaddingChange(false),
+        mInScrollAnchorChain(false),
+        mHasColumnSpanSiblings(false),
+        mDescendantMayDependOnItsStaticPosition(false),
+        mShouldGenerateComputedInfo(false) {
+    MOZ_ASSERT(mComputedStyle);
+    MOZ_ASSERT(mPresContext);
+    mozilla::PodZero(&mOverflow);
+    MOZ_COUNT_CTOR(nsIFrame);
+  }
+  explicit nsIFrame(ComputedStyle* aStyle, nsPresContext* aPresContext)
+      : nsIFrame(aStyle, aPresContext, ClassID::nsIFrame_id) {}
+
+  nsPresContext* PresContext() const { return mPresContext; }
+
+  mozilla::PresShell* PresShell() const { return PresContext()->PresShell(); }
+
+  virtual nsQueryFrame::FrameIID GetFrameId() const MOZ_MUST_OVERRIDE {
+    return kFrameIID;
+  }
+
+  /**
+   * Called to initialize the frame. This is called immediately after creating
+   * the frame.
+   *
+   * If the frame is a continuing frame, then aPrevInFlow indicates the previous
+   * frame (the frame that was split).
+   *
+   * Each subclass that need a view should override this method and call
+   * CreateView() after calling its base class Init().
+   *
+   * @param   aContent the content object associated with the frame
+   * @param   aParent the parent frame
+   * @param   aPrevInFlow the prev-in-flow frame
+   */
+  virtual void Init(nsIContent* aContent, nsContainerFrame* aParent,
+                    nsIFrame* aPrevInFlow);
+
+  void* operator new(size_t, mozilla::PresShell*) MOZ_MUST_OVERRIDE;
+
+  using DestroyContext = mozilla::FrameDestroyContext;
+
+  /**
+   * Flags for PeekOffsetCharacter, PeekOffsetNoAmount, PeekOffsetWord return
+   * values.
+   */
+  enum FrameSearchResult {
+    // Peek found a appropriate offset within frame.
+    FOUND = 0x00,
+    // try next frame for offset.
+    CONTINUE = 0x1,
+    // offset not found because the frame was empty of text.
+    CONTINUE_EMPTY = 0x2 | CONTINUE,
+    // offset not found because the frame didn't contain any text that could be
+    // selected.
+    CONTINUE_UNSELECTABLE = 0x4 | CONTINUE,
+  };
+
+  /**
+   * Options for PeekOffsetCharacter().
+   */
+  struct MOZ_STACK_CLASS PeekOffsetCharacterOptions {
+    // Whether to restrict result to valid cursor locations (between grapheme
+    // clusters) - if this is included, maintains "normal" behavior, otherwise,
+    // used for selection by "code unit" (instead of "character")
+    bool mRespectClusters;
+    // Whether to check user-select style value - if this is included, checks
+    // if user-select is all, then, it may return CONTINUE_UNSELECTABLE.
+    bool mIgnoreUserStyleAll;
+
+    PeekOffsetCharacterOptions()
+        : mRespectClusters(true), mIgnoreUserStyleAll(false) {}
+  };
+
+  virtual void Destroy(DestroyContext&);
+
+ protected:
+  /**
+   * Return true if the frame is part of a Selection.
+   * Helper method to implement the public IsSelected() API.
+   */
+  virtual bool IsFrameSelected() const;
+
+  template <class Source>
+  friend class do_QueryFrameHelper;  // to read mClass
+  friend class nsBlockFrame;         // for GetCaretBaseline
+  friend class nsContainerFrame;     // for ReparentFrameViewTo
+
+  virtual ~nsIFrame();
+
+  // Overridden to prevent the global delete from being called, since
+  // the memory came out of an arena instead of the heap.
+  //
+  // Ideally this would be private and undefined, like the normal
+  // operator new.  Unfortunately, the C++ standard requires an
+  // overridden operator delete to be accessible to any subclass that
+  // defines a virtual destructor, so we can only make it protected;
+  // worse, some C++ compilers will synthesize calls to this function
+  // from the "deleting destructors" that they emit in case of
+  // delete-expressions, so it can't even be undefined.
+  void operator delete(void* aPtr, size_t sz);
+
+ private:
+  // Left undefined; nsFrame objects are never allocated from the heap.
+  void* operator new(size_t sz) noexcept(true);
+
+  // Returns true if this frame has any kind of CSS animations.
+  bool HasCSSAnimations();
+
+  // Returns true if this frame has any kind of CSS transitions.
+  bool HasCSSTransitions();
+
+ public:
+  /**
+   * Get the content object associated with this frame. Does not add a
+   * reference.
+   */
+  nsIContent* GetContent() const { return mContent; }
+
+  /**
+   * @brief Get the closest native anonymous subtree root if the content is in a
+   * native anonymous subtree.
+   *
+   * @return The root of native anonymous subtree which the content belongs to.
+   * Otherwise, nullptr.
+   */
+  nsIContent* GetClosestNativeAnonymousSubtreeRoot() const {
+    return mContent ? mContent->GetClosestNativeAnonymousSubtreeRoot()
+                    : nullptr;
+  }
+
+  /**
+   * Get the frame that should be the parent for the frames of child elements
+   * May return nullptr during reflow
+   */
+  virtual nsContainerFrame* GetContentInsertionFrame() { return nullptr; }
+
+  /**
+   * Move any frames on our overflow list to the end of our principal list.
+   * @return true if there were any overflow frames
+   */
+  virtual bool DrainSelfOverflowList() { return false; }
+
+  /**
+   * Get the frame that should be scrolled if the content associated
+   * with this frame is targeted for scrolling. For frames implementing
+   * nsIScrollableFrame this will return the frame itself. For frames
+   * like nsTextControlFrame that contain a scrollframe, will return
+   * that scrollframe.
+   */
+  virtual nsIScrollableFrame* GetScrollTargetFrame() const { return nullptr; }
+
+  /**
+   * Get the offsets of the frame. most will be 0,0
+   *
+   */
+  virtual std::pair<int32_t, int32_t> GetOffsets() const;
+
+  /**
+   * Reset the offsets when splitting frames during Bidi reordering
+   *
+   */
+  virtual void AdjustOffsetsForBidi(int32_t aStart, int32_t aEnd) {}
+
+  /**
+   * Get the style associated with this frame.
+   */
+  ComputedStyle* Style() const { return mComputedStyle; }
+
+  void AssertNewStyleIsSane(ComputedStyle&)
+#ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
+      ;
+#else
+  {
+  }
+#endif
+
+  void SetComputedStyle(ComputedStyle* aStyle) {
+    if (aStyle != mComputedStyle) {
+      AssertNewStyleIsSane(*aStyle);
+      RefPtr<ComputedStyle> oldComputedStyle = std::move(mComputedStyle);
+      mComputedStyle = aStyle;
+      DidSetComputedStyle(oldComputedStyle);
+    }
+  }
+
+  /**
+   * SetComputedStyleWithoutNotification is for changes to the style
+   * context that should suppress style change processing, in other
+   * words, those that aren't really changes.  This generally means only
+   * changes that happen during frame construction.
+   */
+  void SetComputedStyleWithoutNotification(ComputedStyle* aStyle) {
+    if (aStyle != mComputedStyle) {
+      mComputedStyle = aStyle;
+    }
+  }
+
+ protected:
+  // Style post processing hook
+  // Attention: the old style is the one we're forgetting,
+  // and hence possibly completely bogus for GetStyle* purposes.
+  // Use PeekStyleData instead.
+  virtual void DidSetComputedStyle(ComputedStyle* aOldComputedStyle);
+
+ public:
+/**
+ * Define typesafe getter functions for each style struct by
+ * preprocessing the list of style structs.  These functions are the
+ * preferred way to get style data.  The macro creates functions like:
+ *   const nsStyleBorder* StyleBorder();
+ *   const nsStyleColor* StyleColor();
+ *
+ * Callers outside of libxul should use nsIDOMWindow::GetComputedStyle()
+ * instead of these accessors.
+ *
+ * Callers can use Style*WithOptionalParam if they're in a function that
+ * accepts an *optional* pointer the style struct.
+ */
+#define STYLE_STRUCT(name_)                                          \
+  const nsStyle##name_* Style##name_() const MOZ_NONNULL_RETURN {    \
+    NS_ASSERTION(mComputedStyle, "No style found!");                 \
+    return mComputedStyle->Style##name_();                           \
+  }                                                                  \
+  const nsStyle##name_* Style##name_##WithOptionalParam(             \
+      const nsStyle##name_* aStyleStruct) const MOZ_NONNULL_RETURN { \
+    if (aStyleStruct) {                                              \
+      MOZ_ASSERT(aStyleStruct == Style##name_());                    \
+      return aStyleStruct;                                           \
+    }                                                                \
+    return Style##name_();                                           \
+  }
+#include "nsStyleStructList.h"
+#undef STYLE_STRUCT
+
+  /** Also forward GetVisitedDependentColor to the style */
+  template <typename T, typename S>
+  nscolor GetVisitedDependentColor(T S::*aField) {
+    return mComputedStyle->GetVisitedDependentColor(aField);
+  }
+
+  /**
+   * These methods are to access any additional ComputedStyles that
+   * the frame may be holding.
+   *
+   * These are styles that are children of the frame's primary style and are NOT
+   * used as styles for any child frames.
+   *
+   * These contexts also MUST NOT have any child styles whatsoever. If you need
+   * to insert styles into the style tree, then you should create pseudo element
+   * frames to own them.
+   *
+   * The indicies must be consecutive and implementations MUST return null if
+   * asked for an index that is out of range.
+   */
+  virtual ComputedStyle* GetAdditionalComputedStyle(int32_t aIndex) const;
+
+  virtual void SetAdditionalComputedStyle(int32_t aIndex,
+                                          ComputedStyle* aComputedStyle);
+
+  /**
+   * @param aSelectionStatus nsISelectionController::getDisplaySelection.
+   */
+  already_AddRefed<ComputedStyle> ComputeSelectionStyle(
+      int16_t aSelectionStatus) const;
+
+  already_AddRefed<ComputedStyle> ComputeHighlightSelectionStyle(
+      const nsAtom* aHighlightName);
+
+  /**
+   * Accessor functions for geometric parent.
+   */
+  nsContainerFrame* GetParent() const { return mParent; }
+
+  bool CanBeDynamicReflowRoot() const;
+
+  /**
+   * Gets the parent of a frame, using the parent of the placeholder for
+   * out-of-flow frames.
+   */
+  inline nsContainerFrame* GetInFlowParent() const;
+
+  /**
+   * Gets the primary frame of the closest flattened tree ancestor that has a
+   * frame (flattened tree ancestors may not have frames in presence of display:
+   * contents).
+   */
+  inline nsIFrame* GetClosestFlattenedTreeAncestorPrimaryFrame() const;
+
+  /**
+   * Return the placeholder for this frame (which must be out-of-flow).
+   * @note this will only return non-null if |this| is the first-in-flow
+   * although we don't assert that here for legacy reasons.
+   */
+  inline nsPlaceholderFrame* GetPlaceholderFrame() const {
+    MOZ_ASSERT(HasAnyStateBits(NS_FRAME_OUT_OF_FLOW));
+    return GetProperty(PlaceholderFrameProperty());
+  }
+
+  /**
+   * Set this frame's parent to aParent.
+   * If the frame may have moved into or out of a scrollframe's
+   * frame subtree,
+   * StickyScrollContainer::NotifyReparentedFrameAcrossScrollFrameBoundary must
+   * also be called.
+   */
+  void SetParent(nsContainerFrame* aParent);
+
+  /**
+   * The frame's writing-mode, used for logical layout computations.
+   * It's usually the 'writing-mode' computed value, but there are exceptions:
+   *   * inner table frames copy the value from the table frame
+   *     (@see nsTableRowGroupFrame::Init, nsTableRowFrame::Init etc)
+   *   * the root element frame propagates its value to its ancestors.
+   *     The value may obtain from the principal <body> element.
+   *     (@see nsCSSFrameConstructor::ConstructDocElementFrame)
+   *   * the internal anonymous frames of the root element copy their value
+   *     from the parent.
+   *     (@see nsIFrame::Init)
+   *   * a scrolled frame propagates its value to its ancestor scroll frame
+   *     (@see nsHTMLScrollFrame::ReloadChildFrames)
+   */
+  mozilla::WritingMode GetWritingMode() const { return mWritingMode; }
+
+  /**
+   * Construct a writing mode for line layout in this frame.  This is
+   * the writing mode of this frame, except that if this frame is styled with
+   * unicode-bidi:plaintext, we reset the direction to the resolved paragraph
+   * level of the given subframe (typically the first frame on the line),
+   * because the container frame could be split by hard line breaks into
+   * multiple paragraphs with different base direction.
+   * @param aSelfWM the WM of 'this'
+   */
+  mozilla::WritingMode WritingModeForLine(mozilla::WritingMode aSelfWM,
+                                          nsIFrame* aSubFrame) const;
+
+  /**
+   * Bounding rect of the frame.
+   *
+   * For frames that are laid out according to CSS box model rules the values
+   * are in app units, and the origin is relative to the upper-left of the
+   * geometric parent.  The size includes the content area, borders, and
+   * padding.
+   *
+   * Frames that are laid out according to SVG's coordinate space based rules
+   * (frames with the NS_FRAME_SVG_LAYOUT bit set, which *excludes*
+   * SVGOuterSVGFrame) are different.  Many frames of this type do not set or
+   * use mRect, in which case the frame rect is undefined.  The exceptions are:
+   *
+   *   - SVGInnerSVGFrame
+   *   - SVGGeometryFrame (used for <path>, <circle>, etc.)
+   *   - SVGImageFrame
+   *   - SVGForeignObjectFrame
+   *
+   * For these frames the frame rect contains the frame's element's userspace
+   * bounds including fill, stroke and markers, but converted to app units
+   * rather than being in user units (CSS px).  In the SVG code "userspace" is
+   * defined to be the coordinate system for the attributes that define an
+   * element's geometry (such as the 'cx' attribute for <circle>).  For more
+   * precise details see these frames' implementations of the ReflowSVG method
+   * where mRect is set.
+   *
+   * Note: moving or sizing the frame does not affect the view's size or
+   * position.
+   */
+  nsRect GetRect() const { return mRect; }
+  nsPoint GetPosition() const { return mRect.TopLeft(); }
+  nsSize GetSize() const { return mRect.Size(); }
+  nsRect GetRectRelativeToSelf() const {
+    return nsRect(nsPoint(0, 0), mRect.Size());
+  }
+
+  /**
+   * Like the frame's rect (see |GetRect|), which is the border rect,
+   * other rectangles of the frame, in app units, relative to the parent.
+   */
+  nsRect GetPaddingRect() const;
+  nsRect GetPaddingRectRelativeToSelf() const;
+  nsRect GetContentRect() const;
+  nsRect GetContentRectRelativeToSelf() const;
+  nsRect GetMarginRect() const;
+  nsRect GetMarginRectRelativeToSelf() const;
+
+  /**
+   * Dimensions and position in logical coordinates in the frame's writing mode
+   *  or another writing mode
+   */
+  mozilla::LogicalRect GetLogicalRect(const nsSize& aContainerSize) const {
+    return GetLogicalRect(GetWritingMode(), aContainerSize);
+  }
+  mozilla::LogicalPoint GetLogicalPosition(const nsSize& aContainerSize) const {
+    return GetLogicalPosition(GetWritingMode(), aContainerSize);
+  }
+  mozilla::LogicalSize GetLogicalSize() const {
+    return GetLogicalSize(GetWritingMode());
+  }
+  mozilla::LogicalRect GetLogicalRect(mozilla::WritingMode aWritingMode,
+                                      const nsSize& aContainerSize) const {
+    return mozilla::LogicalRect(aWritingMode, GetRect(), aContainerSize);
+  }
+  mozilla::LogicalPoint GetLogicalPosition(mozilla::WritingMode aWritingMode,
+                                           const nsSize& aContainerSize) const {
+    return GetLogicalRect(aWritingMode, aContainerSize).Origin(aWritingMode);
+  }
+  mozilla::LogicalSize GetLogicalSize(mozilla::WritingMode aWritingMode) const {
+    return mozilla::LogicalSize(aWritingMode, GetSize());
+  }
+  nscoord IStart(const nsSize& aContainerSize) const {
+    return IStart(GetWritingMode(), aContainerSize);
+  }
+  nscoord IStart(mozilla::WritingMode aWritingMode,
+                 const nsSize& aContainerSize) const {
+    return GetLogicalPosition(aWritingMode, aContainerSize).I(aWritingMode);
+  }
+  nscoord BStart(const nsSize& aContainerSize) const {
+    return BStart(GetWritingMode(), aContainerSize);
+  }
+  nscoord BStart(mozilla::WritingMode aWritingMode,
+                 const nsSize& aContainerSize) const {
+    return GetLogicalPosition(aWritingMode, aContainerSize).B(aWritingMode);
+  }
+  nscoord ISize() const { return ISize(GetWritingMode()); }
+  nscoord ISize(mozilla::WritingMode aWritingMode) const {
+    return GetLogicalSize(aWritingMode).ISize(aWritingMode);
+  }
+  nscoord BSize() const { return BSize(GetWritingMode()); }
+  nscoord BSize(mozilla::WritingMode aWritingMode) const {
+    return GetLogicalSize(aWritingMode).BSize(aWritingMode);
+  }
+  mozilla::LogicalSize ContentSize() const {
+    return ContentSize(GetWritingMode());
+  }
+  mozilla::LogicalSize ContentSize(mozilla::WritingMode aWritingMode) const {
+    mozilla::WritingMode wm = GetWritingMode();
+    const auto bp = GetLogicalUsedBorderAndPadding(wm)
+                        .ApplySkipSides(GetLogicalSkipSides())
+                        .ConvertTo(aWritingMode, wm);
+    const auto size = GetLogicalSize(aWritingMode);
+    return mozilla::LogicalSize(
+        aWritingMode,
+        std::max(0, size.ISize(aWritingMode) - bp.IStartEnd(aWritingMode)),
+        std::max(0, size.BSize(aWritingMode) - bp.BStartEnd(aWritingMode)));
+  }
+
+  /**
+   * When we change the size of the frame's border-box rect, we may need to
+   * reset the overflow rect if it was previously stored as deltas.
+   * (If it is currently a "large" overflow and could be re-packed as deltas,
+   * we don't bother as the cost of the allocation has already been paid.)
+   * @param aRebuildDisplayItems If true, then adds this frame to the
+   * list of modified frames for display list building if the rect has changed.
+   * Only pass false if you're sure that the relevant display items will be
+   * rebuilt already (possibly by an ancestor being in the modified list), or if
+   * this is a temporary change.
+   */
+  void SetRect(const nsRect& aRect, bool aRebuildDisplayItems = true) {
+    if (aRect == mRect) {
+      return;
+    }
+    if (mOverflow.mType != OverflowStorageType::Large &&
+        mOverflow.mType != OverflowStorageType::None) {
+      mozilla::OverflowAreas overflow = GetOverflowAreas();
+      mRect = aRect;
+      SetOverflowAreas(overflow);
+    } else {
+      mRect = aRect;
+    }
+    if (aRebuildDisplayItems) {
+      MarkNeedsDisplayItemRebuild();
+    }
+  }
+  /**
+   * Set this frame's rect from a logical rect in its own writing direction
+   */
+  void SetRect(const mozilla::LogicalRect& aRect,
+               const nsSize& aContainerSize) {
+    SetRect(GetWritingMode(), aRect, aContainerSize);
+  }
+  /**
+   * Set this frame's rect from a logical rect in a different writing direction
+   * (GetPhysicalRect will assert if the writing mode doesn't match)
+   */
+  void SetRect(mozilla::WritingMode aWritingMode,
+               const mozilla::LogicalRect& aRect,
+               const nsSize& aContainerSize) {
+    SetRect(aRect.GetPhysicalRect(aWritingMode, aContainerSize));
+  }
+
+  /**
+   * Set this frame's size from a logical size in its own writing direction.
+   * This leaves the frame's logical position unchanged, which means its
+   * physical position may change (for right-to-left modes).
+   */
+  void SetSize(const mozilla::LogicalSize& aSize) {
+    SetSize(GetWritingMode(), aSize);
+  }
+  /*
+   * Set this frame's size from a logical size in a different writing direction.
+   * This leaves the frame's logical position in the given mode unchanged,
+   * which means its physical position may change (for right-to-left modes).
+   */
+  void SetSize(mozilla::WritingMode aWritingMode,
+               const mozilla::LogicalSize& aSize) {
+    if (aWritingMode.IsPhysicalRTL()) {
+      nscoord oldWidth = mRect.Width();
+      SetSize(aSize.GetPhysicalSize(aWritingMode));
+      mRect.x -= mRect.Width() - oldWidth;
+    } else {
+      SetSize(aSize.GetPhysicalSize(aWritingMode));
+    }
+  }
+
+  /**
+   * Set this frame's physical size. This leaves the frame's physical position
+   * (topLeft) unchanged.
+   * @param aRebuildDisplayItems If true, then adds this frame to the
+   * list of modified frames for display list building if the size has changed.
+   * Only pass false if you're sure that the relevant display items will be
+   * rebuilt already (possibly by an ancestor being in the modified list), or if
+   * this is a temporary change.
+   */
+  void SetSize(const nsSize& aSize, bool aRebuildDisplayItems = true) {
+    SetRect(nsRect(mRect.TopLeft(), aSize), aRebuildDisplayItems);
+  }
+
+  void SetPosition(const nsPoint& aPt);
+  void SetPosition(mozilla::WritingMode aWritingMode,
+                   const mozilla::LogicalPoint& aPt,
+                   const nsSize& aContainerSize) {
+    // We subtract mRect.Size() from the container size to account for
+    // the fact that logical origins in RTL coordinate systems are at
+    // the top right of the frame instead of the top left.
+    SetPosition(
+        aPt.GetPhysicalPoint(aWritingMode, aContainerSize - mRect.Size()));
+  }
+
+  /**
+   * Move the frame, accounting for relative positioning. Use this when
+   * adjusting the frame's position by a known amount, to properly update its
+   * saved normal position (see GetNormalPosition below).
+   *
+   * This must be used only when moving a frame *after*
+   * ReflowInput::ApplyRelativePositioning is called.  When moving
+   * a frame during the reflow process prior to calling
+   * ReflowInput::ApplyRelativePositioning, the position should
+   * simply be adjusted directly (e.g., using SetPosition()).
+   */
+  void MovePositionBy(const nsPoint& aTranslation);
+
+  /**
+   * As above, using a logical-point delta in a given writing mode.
+   */
+  void MovePositionBy(mozilla::WritingMode aWritingMode,
+                      const mozilla::LogicalPoint& aTranslation) {
+    // The LogicalPoint represents a vector rather than a point within a
+    // rectangular coordinate space, so we use a null containerSize when
+    // converting logical to physical.
+    const nsSize nullContainerSize;
+    MovePositionBy(
+        aTranslation.GetPhysicalPoint(aWritingMode, nullContainerSize));
+  }
+
+  /**
+   * Return frame's rect without relative positioning
+   */
+  nsRect GetNormalRect() const;
+  mozilla::LogicalRect GetLogicalNormalRect(
+      mozilla::WritingMode aWritingMode, const nsSize& aContainerSize) const {
+    return mozilla::LogicalRect(aWritingMode, GetNormalRect(), aContainerSize);
+  }
+
+  /**
+   * Returns frame's rect as required by the GetBoundingClientRect() DOM API.
+   */
+  nsRect GetBoundingClientRect();
+
+  /**
+   * Return frame's position without relative positioning.
+   * If aHasProperty is provided, returns whether the normal position
+   * was stored in a frame property.
+   */
+  inline nsPoint GetNormalPosition(bool* aHasProperty = nullptr) const;
+  inline mozilla::LogicalPoint GetLogicalNormalPosition(
+      mozilla::WritingMode aWritingMode, const nsSize& aContainerSize) const;
+
+  virtual nsPoint GetPositionOfChildIgnoringScrolling(const nsIFrame* aChild) {
+    return aChild->GetPosition();
+  }
+
+  nsPoint GetPositionIgnoringScrolling() const;
+
+#define NS_DECLARE_FRAME_PROPERTY_WITH_DTOR(prop, type, dtor)              \
+  static const mozilla::FramePropertyDescriptor<type>* prop() {            \
+    /* Use of constexpr caused startup crashes with MSVC2015u1 PGO. */     \
+    static const auto descriptor =                                         \
+        mozilla::FramePropertyDescriptor<type>::NewWithDestructor<dtor>(); \
+    return &descriptor;                                                    \
+  }
+
+// Don't use this unless you really know what you're doing!
+#define NS_DECLARE_FRAME_PROPERTY_WITH_FRAME_IN_DTOR(prop, type, dtor) \
+  static const mozilla::FramePropertyDescriptor<type>* prop() {        \
+    /* Use of constexpr caused startup crashes with MSVC2015u1 PGO. */ \
+    static const auto descriptor = mozilla::FramePropertyDescriptor<   \
+        type>::NewWithDestructorWithFrame<dtor>();                     \
+    return &descriptor;                                                \
+  }
+
+#define NS_DECLARE_FRAME_PROPERTY_WITHOUT_DTOR(prop, type)              \
+  static const mozilla::FramePropertyDescriptor<type>* prop() {         \
+    /* Use of constexpr caused startup crashes with MSVC2015u1 PGO. */  \
+    static const auto descriptor =                                      \
+        mozilla::FramePropertyDescriptor<type>::NewWithoutDestructor(); \
+    return &descriptor;                                                 \
+  }
+
+#define NS_DECLARE_FRAME_PROPERTY_DELETABLE(prop, type) \
+  NS_DECLARE_FRAME_PROPERTY_WITH_DTOR(prop, type, DeleteValue)
+
+#define NS_DECLARE_FRAME_PROPERTY_RELEASABLE(prop, type) \
+  NS_DECLARE_FRAME_PROPERTY_WITH_DTOR(prop, type, ReleaseValue)
+
+#define NS_DECLARE_FRAME_PROPERTY_WITH_DTOR_NEVER_CALLED(prop, type) \
+  static void AssertOnDestroyingProperty##prop(type*) {              \
+    MOZ_ASSERT_UNREACHABLE(                                          \
+        "Frame property " #prop                                      \
+        " should never be destroyed by the FrameProperties class");  \
+  }                                                                  \
+  NS_DECLARE_FRAME_PROPERTY_WITH_DTOR(prop, type,                    \
+                                      AssertOnDestroyingProperty##prop)
+
+#define NS_DECLARE_FRAME_PROPERTY_SMALL_VALUE(prop, type) \
+  NS_DECLARE_FRAME_PROPERTY_WITHOUT_DTOR(prop, mozilla::SmallValueHolder<type>)
+
+  NS_DECLARE_FRAME_PROPERTY_WITHOUT_DTOR(IBSplitSibling, nsContainerFrame)
+  NS_DECLARE_FRAME_PROPERTY_WITHOUT_DTOR(IBSplitPrevSibling, nsContainerFrame)
+
+  NS_DECLARE_FRAME_PROPERTY_SMALL_VALUE(NormalPositionProperty, nsPoint)
+  NS_DECLARE_FRAME_PROPERTY_DELETABLE(ComputedOffsetProperty, nsMargin)
+
+  NS_DECLARE_FRAME_PROPERTY_DELETABLE(OutlineInnerRectProperty, nsRect)
+  NS_DECLARE_FRAME_PROPERTY_DELETABLE(PreEffectsBBoxProperty, nsRect)
+  NS_DECLARE_FRAME_PROPERTY_DELETABLE(PreTransformOverflowAreasProperty,
+                                      mozilla::OverflowAreas)
+
+  NS_DECLARE_FRAME_PROPERTY_DELETABLE(OverflowAreasProperty,
+                                      mozilla::OverflowAreas)
+
+  // The initial overflow area passed to FinishAndStoreOverflow. This is only
+  // set on frames that Preserve3D() or HasPerspective() or IsTransformed(), and
+  // when at least one of the overflow areas differs from the frame bound rect.
+  NS_DECLARE_FRAME_PROPERTY_DELETABLE(InitialOverflowProperty,
+                                      mozilla::OverflowAreas)
+
+#ifdef DEBUG
+  // InitialOverflowPropertyDebug is added to the frame to indicate that either
+  // the InitialOverflowProperty has been stored or the InitialOverflowProperty
+  // has been suppressed due to being set to the default value (frame bounds)
+  NS_DECLARE_FRAME_PROPERTY_SMALL_VALUE(DebugInitialOverflowPropertyApplied,
+                                        bool)
+#endif
+
+  NS_DECLARE_FRAME_PROPERTY_DELETABLE(UsedMarginProperty, nsMargin)
+  NS_DECLARE_FRAME_PROPERTY_DELETABLE(UsedPaddingProperty, nsMargin)
+  NS_DECLARE_FRAME_PROPERTY_DELETABLE(UsedBorderProperty, nsMargin)
+
+  // This tracks the start and end page value for a frame.
+  //
+  // https://www.w3.org/TR/css-page-3/#using-named-pages
+  //
+  // This is only tracked during paginated frame construction.
+  // This is used to implement fragmentation based on CSS page names. During
+  // frame construction, we insert page breaks when we begin a new page box and
+  // the previous page box had a different name.
+  struct PageValues {
+    // A value of null indicates that the value is equal to what auto resolves
+    // to for this frame.
+    RefPtr<const nsAtom> mStartPageValue = nullptr;
+    RefPtr<const nsAtom> mEndPageValue = nullptr;
+  };
+  NS_DECLARE_FRAME_PROPERTY_DELETABLE(PageValuesProperty, PageValues)
+
+  const nsAtom* GetStartPageValue() const {
+    if (const PageValues* const values = GetProperty(PageValuesProperty())) {
+      return values->mStartPageValue;
+    }
+    return nullptr;
+  }
+
+  const nsAtom* GetEndPageValue() const {
+    if (const PageValues* const values = GetProperty(PageValuesProperty())) {
+      return values->mEndPageValue;
+    }
+    return nullptr;
+  }
+
+ private:
+  // The value that the CSS page-name "auto" keyword resolves to for children
+  // of this frame.
+  //
+  // A missing value for this property indicates that the auto value is the
+  // empty string, which is the default if no ancestors of a frame specify a
+  // page name. This avoids ever storing this property if the document doesn't
+  // use named pages.
+  //
+  // https://www.w3.org/TR/css-page-3/#using-named-pages
+  //
+  // Ideally this would be a const atom, but that isn't possible with the
+  // Release() call. This isn't too bad, since it's hidden behind constness-
+  // preserving getter/setter.
+  NS_DECLARE_FRAME_PROPERTY_RELEASABLE(AutoPageValueProperty, nsAtom)
+
+ public:
+  // Get the value that the CSS page-name "auto" keyword resolves to for
+  // children of this frame.
+  // This is needed when propagating page-name values up the frame tree.
+  const nsAtom* GetAutoPageValue() const {
+    if (const nsAtom* const atom = GetProperty(AutoPageValueProperty())) {
+      return atom;
+    }
+    return nsGkAtoms::_empty;
+  }
+  void SetAutoPageValue(const nsAtom* aAtom) {
+    MOZ_ASSERT(aAtom, "Atom must not be null");
+    nsAtom* const atom = const_cast<nsAtom*>(aAtom);
+    if (atom != nsGkAtoms::_empty) {
+      SetProperty(AutoPageValueProperty(), do_AddRef(atom).take());
+    }
+  }
+
+  NS_DECLARE_FRAME_PROPERTY_SMALL_VALUE(LineBaselineOffset, nscoord)
+
+  NS_DECLARE_FRAME_PROPERTY_DELETABLE(InvalidationRect, nsRect)
+
+  NS_DECLARE_FRAME_PROPERTY_SMALL_VALUE(RefusedAsyncAnimationProperty, bool)
+
+  NS_DECLARE_FRAME_PROPERTY_SMALL_VALUE(FragStretchBSizeProperty, nscoord)
+
+  // The block-axis margin-box size associated with eBClampMarginBoxMinSize.
+  NS_DECLARE_FRAME_PROPERTY_SMALL_VALUE(BClampMarginBoxMinSizeProperty, nscoord)
+
+  NS_DECLARE_FRAME_PROPERTY_SMALL_VALUE(IBaselinePadProperty, nscoord)
+  NS_DECLARE_FRAME_PROPERTY_SMALL_VALUE(BBaselinePadProperty, nscoord)
+
+  NS_DECLARE_FRAME_PROPERTY_SMALL_VALUE(BidiDataProperty,
+                                        mozilla::FrameBidiData)
+
+  NS_DECLARE_FRAME_PROPERTY_WITHOUT_DTOR(PlaceholderFrameProperty,
+                                         nsPlaceholderFrame)
+
+  NS_DECLARE_FRAME_PROPERTY_RELEASABLE(OffsetPathCache, mozilla::gfx::Path)
+
+  mozilla::FrameBidiData GetBidiData() const {
+    bool exists;
+    mozilla::FrameBidiData bidiData = GetProperty(BidiDataProperty(), &exists);
+    if (!exists) {
+      bidiData.precedingControl = mozilla::kBidiLevelNone;
+    }
+    return bidiData;
+  }
+
+  mozilla::intl::BidiEmbeddingLevel GetBaseLevel() const {
+    return GetBidiData().baseLevel;
+  }
+
+  mozilla::intl::BidiEmbeddingLevel GetEmbeddingLevel() const {
+    return GetBidiData().embeddingLevel;
+  }
+
+  /**
+   * Return the distance between the border edge of the frame and the
+   * margin edge of the frame.  Like GetRect(), returns the dimensions
+   * as of the most recent reflow.
+   *
+   * This doesn't include any margin collapsing that may have occurred.
+   * It also doesn't consider GetSkipSides()/GetLogicalSkipSides(), so
+   * may report nonzero values on sides that are actually skipped for
+   * this fragment.
+   *
+   * It also treats 'auto' margins as zero, and treats any margins that
+   * should have been turned into 'auto' because of overconstraint as
+   * having their original values.
+   */
+  virtual nsMargin GetUsedMargin() const;
+  virtual mozilla::LogicalMargin GetLogicalUsedMargin(
+      mozilla::WritingMode aWritingMode) const {
+    return mozilla::LogicalMargin(aWritingMode, GetUsedMargin());
+  }
+
+  /**
+   * Return the distance between the border edge of the frame (which is
+   * its rect) and the padding edge of the frame. Like GetRect(), returns
+   * the dimensions as of the most recent reflow.
+   *
+   * This doesn't consider GetSkipSides()/GetLogicalSkipSides(), so
+   * may report nonzero values on sides that are actually skipped for
+   * this fragment.
+   *
+   * Note that this differs from StyleBorder()->GetComputedBorder() in
+   * that this describes a region of the frame's box, and
+   * StyleBorder()->GetComputedBorder() describes a border.  They differ
+   * for tables (particularly border-collapse tables) and themed
+   * elements.
+   */
+  virtual nsMargin GetUsedBorder() const;
+  virtual mozilla::LogicalMargin GetLogicalUsedBorder(
+      mozilla::WritingMode aWritingMode) const {
+    return mozilla::LogicalMargin(aWritingMode, GetUsedBorder());
+  }
+
+  /**
+   * Return the distance between the padding edge of the frame and the
+   * content edge of the frame.  Like GetRect(), returns the dimensions
+   * as of the most recent reflow.
+   *
+   * This doesn't consider GetSkipSides()/GetLogicalSkipSides(), so
+   * may report nonzero values on sides that are actually skipped for
+   * this fragment.
+   */
+  virtual nsMargin GetUsedPadding() const;
+  virtual mozilla::LogicalMargin GetLogicalUsedPadding(
+      mozilla::WritingMode aWritingMode) const {
+    return mozilla::LogicalMargin(aWritingMode, GetUsedPadding());
+  }
+
+  nsMargin GetUsedBorderAndPadding() const {
+    return GetUsedBorder() + GetUsedPadding();
+  }
+  mozilla::LogicalMargin GetLogicalUsedBorderAndPadding(
+      mozilla::WritingMode aWritingMode) const {
+    return mozilla::LogicalMargin(aWritingMode, GetUsedBorderAndPadding());
+  }
+
+  /**
+   * The area to paint box-shadows around.  The default is the border rect.
+   * (nsFieldSetFrame overrides this).
+   */
+  virtual nsRect VisualBorderRectRelativeToSelf() const {
+    return nsRect(0, 0, mRect.Width(), mRect.Height());
+  }
+
+  /**
+   * Get the size, in app units, of the border radii. It returns FALSE iff all
+   * returned radii == 0 (so no border radii), TRUE otherwise.
+   * For the aRadii indexes, use the enum HalfCorner constants in gfx/2d/Types.h
+   * If a side is skipped via aSkipSides, its corners are forced to 0.
+   *
+   * All corner radii are then adjusted so they do not require more
+   * space than aBorderArea, according to the algorithm in css3-background.
+   *
+   * aFrameSize is used as the basis for percentage widths and heights.
+   * aBorderArea is used for the adjustment of radii that might be too
+   * large.
+   *
+   * Return whether any radii are nonzero.
+   */
+  static bool ComputeBorderRadii(const mozilla::BorderRadius&,
+                                 const nsSize& aFrameSize,
+                                 const nsSize& aBorderArea, Sides aSkipSides,
+                                 nscoord aRadii[8]);
+
+  /*
+   * Given a set of border radii for one box (e.g., border box), convert
+   * it to the equivalent set of radii for another box (e.g., in to
+   * padding box, out to outline box) by reducing radii or increasing
+   * nonzero radii as appropriate.
+   *
+   * Indices into aRadii are the enum HalfCorner constants in gfx/2d/Types.h
+   *
+   * Note that insetting the radii is lossy, since it can turn nonzero radii
+   * into zero, and re-adjusting does not inflate zero radii.
+   *
+   * Therefore, callers should always adjust directly from the original value
+   * coming from style.
+   */
+  static void AdjustBorderRadii(nscoord aRadii[8], const nsMargin& aOffsets);
+
+  /**
+   * Fill in border radii for this frame.  Return whether any are nonzero.
+   * Indices into aRadii are the enum HalfCorner constants in gfx/2d/Types.h
+   * aSkipSides is a union of SideBits::eLeft/Right/Top/Bottom bits that says
+   * which side(s) to skip.
+   *
+   * Note: GetMarginBoxBorderRadii() and GetShapeBoxBorderRadii() work only
+   * on frames that establish block formatting contexts since they don't
+   * participate in margin-collapsing.
+   */
+  virtual bool GetBorderRadii(const nsSize& aFrameSize,
+                              const nsSize& aBorderArea, Sides aSkipSides,
+                              nscoord aRadii[8]) const;
+  bool GetBorderRadii(nscoord aRadii[8]) const;
+  bool GetMarginBoxBorderRadii(nscoord aRadii[8]) const;
+  bool GetPaddingBoxBorderRadii(nscoord aRadii[8]) const;
+  bool GetContentBoxBorderRadii(nscoord aRadii[8]) const;
+  bool GetBoxBorderRadii(nscoord aRadii[8], const nsMargin& aOffset) const;
+  bool GetShapeBoxBorderRadii(nscoord aRadii[8]) const;
+
+  /**
+   * `GetNaturalBaselineBOffset`, but determines the baseline sharing group
+   * through `GetDefaultBaselineSharingGroup` (If not specified), assuming line
+   * layout context, and never fails, returning a synthesized baseline through
+   * `SynthesizeFallbackBaseline`. Unlike `GetNaturalBaselineBOffset`, Result is
+   * always relative to the block start of the frame.
+   */
+  nscoord GetLogicalBaseline(mozilla::WritingMode aWM) const;
+  /**
+   * Same as the above, but with baseline sharing group & export
+   * context specified.
+   */
+  nscoord GetLogicalBaseline(mozilla::WritingMode aWM,
+                             BaselineSharingGroup aBaselineGroup,
+                             BaselineExportContext aExportContext) const;
+
+  /**
+   * Return true if the frame has a first(last) inline-axis baseline per
+   * CSS Box Alignment.  If so, the returned baseline is the distance from
+   * the relevant block-axis border-box edge (Start for
+   * BaselineSharingGroup::First, end for BaselineSharingGroup::Last), where
+   * a positive value points towards the content-box.
+   * Some frames can export different baselines depending if it's in a line
+   * layout context or any other context (e.g. Flex, grid).
+   * https://drafts.csswg.org/css-align-3/#baseline-export
+   * @note The returned value is only valid when reflow is not needed.
+   * @note You should only call this on frames with a WM that's parallel to aWM.
+   * @note We're approaching `nsLayoutUtils::Get(First|Last)LineBaseline` ==
+   * `GetNaturalBaselineBOffset(aWM, (First|Last), Other)`. Grid relies on
+   * baseline synthesis behaviour in `nsLayoutUtils` implementations (bug
+   * 1609403), which blocks its removal.
+   * @param aWM the writing-mode of the alignment context.
+   * @return the baseline offset, if one exists
+   */
+  virtual Maybe<nscoord> GetNaturalBaselineBOffset(
+      mozilla::WritingMode aWM, BaselineSharingGroup aBaselineGroup,
+      BaselineExportContext aExportContext) const {
+    return Nothing{};
+  }
+
+  struct CaretBlockAxisMetrics {
+    nscoord mOffset = 0;
+    nscoord mExtent = 0;
+  };
+  /**
+   * Get the offset (Block start of the caret) and extent of the caret in this
+   * frame. The returned offset is corrected for vertical & line-inverted
+   * writing modes.
+   */
+  CaretBlockAxisMetrics GetCaretBlockAxisMetrics(mozilla::WritingMode,
+                                                 const nsFontMetrics&) const;
+  // Gets the page-name value to be used for the page that contains this frame
+  // during paginated reflow.
+  const nsAtom* ComputePageValue() const MOZ_NONNULL_RETURN;
+
+  ///////////////////////////////////////////////////////////////////////////////
+  // The public visibility API.
+  ///////////////////////////////////////////////////////////////////////////////
+
+  /// @return true if we're tracking visibility for this frame.
+  bool TrackingVisibility() const {
+    return HasAnyStateBits(NS_FRAME_VISIBILITY_IS_TRACKED);
+  }
+
+  /// @return the visibility state of this frame. See the Visibility enum
+  /// for the possible return values and their meanings.
+  Visibility GetVisibility() const;
+
+  /// Update the visibility state of this frame synchronously.
+  /// XXX(seth): Avoid using this method; we should be relying on the refresh
+  /// driver for visibility updates. This method, which replaces
+  /// nsLayoutUtils::UpdateApproximateFrameVisibility(), exists purely as a
+  /// temporary measure to avoid changing behavior during the transition from
+  /// the old image visibility code.
+  void UpdateVisibilitySynchronously();
+
+  // A frame property which stores the visibility state of this frame. Right
+  // now that consists of an approximate visibility counter represented as a
+  // uint32_t. When the visibility of this frame is not being tracked, this
+  // property is absent.
+  NS_DECLARE_FRAME_PROPERTY_SMALL_VALUE(VisibilityStateProperty, uint32_t);
+
+ protected:
+  /**
+   * Get the position of the baseline on which the caret needs to be placed,
+   * relative to the top of the frame.  This is mostly needed for frames
+   * which return a baseline from GetBaseline which is not useful for
+   * caret positioning.
+   */
+  virtual nscoord GetCaretBaseline() const {
+    return GetLogicalBaseline(GetWritingMode());
+  }
+
+  /**
+   * Subclasses can call this method to enable visibility tracking for this
+   * frame.
+   *
+   * If visibility tracking was previously disabled, this will schedule an
+   * update an asynchronous update of visibility.
+   */
+  void EnableVisibilityTracking();
+
+  /**
+   * Subclasses can call this method to disable visibility tracking for this
+   * frame.
+   *
+   * Note that if visibility tracking was previously enabled, disabling
+   * visibility tracking will cause a synchronous call to OnVisibilityChange().
+   */
+  void DisableVisibilityTracking();
+
+  /**
+   * Called when a frame transitions between visibility states (for example,
+   * from nonvisible to visible, or from visible to nonvisible).
+   *
+   * @param aNewVisibility    The new visibility state.
+   * @param aNonvisibleAction A requested action if the frame has become
+   *                          nonvisible. If Nothing(), no action is
+   *                          requested. If DISCARD_IMAGES is specified, the
+   *                          frame is requested to ask any images it's
+   *                          associated with to discard their surfaces if
+   *                          possible.
+   *
+   * Subclasses which override this method should call their parent class's
+   * implementation.
+   */
+  virtual void OnVisibilityChange(
+      Visibility aNewVisibility,
+      const Maybe<OnNonvisible>& aNonvisibleAction = Nothing());
+
+  /**
+   * Synthesize a baseline for this element. The returned baseline is the
+   * distance from the relevant block-axis border-box edge (Start for
+   * BaselineSharingGroup::First, end for BaselineSharingGroup::Last), where a
+   * positive value points towards the content-box.
+   * @note This always returns a synthesized baseline, even if the element may
+   * have an actual baseline.
+   */
+  virtual nscoord SynthesizeFallbackBaseline(
+      mozilla::WritingMode aWM, BaselineSharingGroup aBaselineGroup) const;
+
+ public:
+  /**
+   * Get the suitable baseline sharing group for this element, assuming line
+   * layout.
+   */
+  virtual BaselineSharingGroup GetDefaultBaselineSharingGroup() const {
+    return BaselineSharingGroup::First;
+  }
+
+  ///////////////////////////////////////////////////////////////////////////////
+  // Internal implementation for the approximate frame visibility API.
+  ///////////////////////////////////////////////////////////////////////////////
+
+  /**
+   * We track the approximate visibility of frames using a counter; if it's
+   * non-zero, then the frame is considered visible. Using a counter allows us
+   * to account for situations where the frame may be visible in more than one
+   * place (for example, via -moz-element), and it simplifies the
+   * implementation of our approximate visibility tracking algorithms.
+   *
+   * @param aNonvisibleAction A requested action if the frame has become
+   *                          nonvisible. If Nothing(), no action is
+   *                          requested. If DISCARD_IMAGES is specified, the
+   *                          frame is requested to ask any images it's
+   *                          associated with to discard their surfaces if
+   *                          possible.
+   */
+  void DecApproximateVisibleCount(
+      const Maybe<OnNonvisible>& aNonvisibleAction = Nothing());
+  void IncApproximateVisibleCount();
+
+  /**
+   * Get the specified child list.
+   *
+   * @param   aListID identifies the requested child list.
+   * @return  the child list.  If the requested list is unsupported by this
+   *          frame type, an empty list will be returned.
+   */
+  virtual const nsFrameList& GetChildList(ChildListID aListID) const;
+  const nsFrameList& PrincipalChildList() const {
+    return GetChildList(mozilla::FrameChildListID::Principal);
+  }
+
+  /**
+   * Sub-classes should override this methods if they want to append their own
+   * child lists into aLists.
+   */
+  virtual void GetChildLists(nsTArray<ChildList>* aLists) const;
+
+  /**
+   * Returns the child lists for this frame.
+   */
+  AutoTArray<ChildList, 4> ChildLists() const {
+    AutoTArray<ChildList, 4> childLists;
+    GetChildLists(&childLists);
+    return childLists;
+  }
+
+  /**
+   * Returns the child lists for this frame, including ones belong to a child
+   * document.
+   */
+  AutoTArray<ChildList, 4> CrossDocChildLists();
+
+  /**
+   * Child frames are linked together in a doubly-linked list
+   */
+  nsIFrame* GetNextSibling() const { return mNextSibling; }
+  void SetNextSibling(nsIFrame* aNextSibling) {
+    NS_ASSERTION(this != aNextSibling,
+                 "Creating a circular frame list, this is very bad.");
+    if (mNextSibling && mNextSibling->GetPrevSibling() == this) {
+      mNextSibling->mPrevSibling = nullptr;
+    }
+    mNextSibling = aNextSibling;
+    if (mNextSibling) {
+      mNextSibling->mPrevSibling = this;
+    }
+  }
+
+  nsIFrame* GetPrevSibling() const { return mPrevSibling; }
+
+  /**
+   * Builds the display lists for the content represented by this frame
+   * and its descendants. The background+borders of this element must
+   * be added first, before any other content.
+   *
+   * This should only be called by methods in nsFrame. Instead of calling this
+   * directly, call either BuildDisplayListForStackingContext or
+   * BuildDisplayListForChild.
+   *
+   * See nsDisplayList.h for more information about display lists.
+   */
+  virtual void BuildDisplayList(nsDisplayListBuilder* aBuilder,
+                                const nsDisplayListSet& aLists) {}
+  /**
+   * Displays the caret onto the given display list builder. The caret is
+   * painted on top of the rest of the display list items.
+   */
+  void DisplayCaret(nsDisplayListBuilder* aBuilder, nsDisplayList* aList);
+
+  /**
+   * Get the preferred caret color at the offset.
+   *
+   * @param aOffset is offset of the content.
+   */
+  virtual nscolor GetCaretColorAt(int32_t aOffset);
+
+  bool IsThemed(nsITheme::Transparency* aTransparencyState = nullptr) const {
+    return IsThemed(StyleDisplay(), aTransparencyState);
+  }
+  bool IsThemed(const nsStyleDisplay* aDisp,
+                nsITheme::Transparency* aTransparencyState = nullptr) const {
+    if (!aDisp->HasAppearance()) {
+      return false;
+    }
+    nsIFrame* mutable_this = const_cast<nsIFrame*>(this);
+    nsPresContext* pc = PresContext();
+    nsITheme* theme = pc->Theme();
+    if (!theme->ThemeSupportsWidget(pc, mutable_this,
+                                    aDisp->EffectiveAppearance())) {
+      return false;
+    }
+    if (aTransparencyState) {
+      *aTransparencyState = theme->GetWidgetTransparency(
+          mutable_this, aDisp->EffectiveAppearance());
+    }
+    return true;
+  }
+
+  /**
+   * Builds a display list for the content represented by this frame,
+   * treating this frame as the root of a stacking context.
+   * Optionally sets aCreatedContainerItem to true if we created a
+   * single container display item for the stacking context, and no
+   * other wrapping items are needed.
+   */
+  void BuildDisplayListForStackingContext(
+      nsDisplayListBuilder* aBuilder, nsDisplayList* aList,
+      bool* aCreatedContainerItem = nullptr);
+
+  enum class DisplayChildFlag {
+    ForcePseudoStackingContext,
+    ForceStackingContext,
+    Inline,
+  };
+  using DisplayChildFlags = mozilla::EnumSet<DisplayChildFlag>;
+
+  /**
+   * Adjusts aDirtyRect for the child's offset, checks that the dirty rect
+   * actually intersects the child (or its descendants), calls BuildDisplayList
+   * on the child if necessary, and puts things in the right lists if the child
+   * is positioned.
+   *
+   * @param aFlags a set of of DisplayChildFlag values that are applicable for
+   * this operation.
+   */
+  void BuildDisplayListForChild(nsDisplayListBuilder* aBuilder,
+                                nsIFrame* aChild,
+                                const nsDisplayListSet& aLists,
+                                DisplayChildFlags aFlags = {});
+
+  void BuildDisplayListForSimpleChild(nsDisplayListBuilder* aBuilder,
+                                      nsIFrame* aChild,
+                                      const nsDisplayListSet& aLists);
+
+  /**
+   * Helper for BuildDisplayListForChild, to implement this special-case for
+   * grid (and flex) items from the spec:
+   *   The painting order of grid items is exactly the same as inline blocks,
+   *   except that [...], and 'z-index' values other than 'auto' create a
+   *   stacking context even if 'position' is 'static' (behaving exactly as if
+   *   'position' were 'relative'). https://drafts.csswg.org/css-grid/#z-order
+   *
+   * Flex items also have the same special-case described in
+   * https://drafts.csswg.org/css-flexbox/#painting
+   */
+  static DisplayChildFlags DisplayFlagsForFlexOrGridItem() {
+    return DisplayChildFlags{DisplayChildFlag::ForcePseudoStackingContext};
+  }
+
+  bool RefusedAsyncAnimation() const {
+    return GetProperty(RefusedAsyncAnimationProperty());
+  }
+
+  /**
+   * Returns true if this frame is transformed (e.g. has CSS, SVG, or custom
+   * transforms) or if its parent is an SVG frame that has children-only
+   * transforms (e.g.  an SVG viewBox attribute) or if its transform-style is
+   * preserve-3d or the frame has transform animations.
+   */
+  bool IsTransformed() const;
+
+  /**
+   * Same as IsTransformed, except that it doesn't take SVG transforms
+   * into account.
+   */
+  bool IsCSSTransformed() const;
+
+  /**
+   * True if this frame has any animation of transform in effect.
+   */
+  bool HasAnimationOfTransform() const;
+
+  /**
+   * True if this frame has any animation of opacity in effect.
+   *
+   * EffectSet is just an optimization.
+   */
+  bool HasAnimationOfOpacity(mozilla::EffectSet* = nullptr) const;
+
+  /**
+   * Returns true if the frame is translucent or the frame has opacity
+   * animations for the purposes of creating a stacking context.
+   *
+   * @param aStyleDisplay:  This function needs style display struct.
+   *
+   * @param aStyleEffects:  This function needs style effects struct.
+   *
+   * @param aEffectSet: This function may need to look up EffectSet property.
+   *   If a caller already have one, pass it in can save property look up
+   *   time; otherwise, just leave it as nullptr.
+   */
+  bool HasOpacity(const nsStyleDisplay* aStyleDisplay,
+                  const nsStyleEffects* aStyleEffects,
+                  mozilla::EffectSet* aEffectSet = nullptr) const {
+    return HasOpacityInternal(1.0f, aStyleDisplay, aStyleEffects, aEffectSet);
+  }
+  /**
+   * Returns true if the frame is translucent for display purposes.
+   *
+   * @param aStyleDisplay:  This function needs style display struct.
+   *
+   * @param aStyleEffects:  This function needs style effects struct.
+   *
+   * @param aEffectSet: This function may need to look up EffectSet property.
+   *   If a caller already have one, pass it in can save property look up
+   *   time; otherwise, just leave it as nullptr.
+   */
+  bool HasVisualOpacity(const nsStyleDisplay* aStyleDisplay,
+                        const nsStyleEffects* aStyleEffects,
+                        mozilla::EffectSet* aEffectSet = nullptr) const {
+    // Treat an opacity value of 0.99 and above as opaque.  This is an
+    // optimization aimed at Web content which use opacity:0.99 as a hint for
+    // creating a stacking context only.
+    return HasOpacityInternal(0.99f, aStyleDisplay, aStyleEffects, aEffectSet);
+  }
+
+  /**
+   * Returns a matrix (in pixels) for the current frame. The matrix should be
+   * relative to the current frame's coordinate space.
+   *
+   * @param aFrame The frame to compute the transform for.
+   * @param aAppUnitsPerPixel The number of app units per graphics unit.
+   */
+  using ComputeTransformFunction = Matrix4x4 (*)(const nsIFrame*,
+                                                 float aAppUnitsPerPixel);
+  /** Returns the transform getter of this frame, if any. */
+  virtual ComputeTransformFunction GetTransformGetter() const {
+    return nullptr;
+  }
+
+  /**
+   * Returns true if this frame is an SVG frame that has SVG transforms applied
+   * to it, or if its parent frame is an SVG frame that has children-only
+   * transforms (e.g. an SVG viewBox attribute).
+   * If aOwnTransforms is non-null and the frame has its own SVG transforms,
+   * aOwnTransforms will be set to these transforms. If aFromParentTransforms
+   * is non-null and the frame has an SVG parent with children-only transforms,
+   * then aFromParentTransforms will be set to these transforms.
+   */
+  virtual bool IsSVGTransformed(Matrix* aOwnTransforms = nullptr,
+                                Matrix* aFromParentTransforms = nullptr) const;
+
+  /**
+   * Returns whether this frame will attempt to extend the 3d transforms of its
+   * children. This requires transform-style: preserve-3d, as well as no
+   * clipping or svg effects.
+   *
+   * @param aStyleDisplay:  If the caller has this->StyleDisplay(), providing
+   *   it here will improve performance.
+   *
+   * @param aStyleEffects:  If the caller has this->StyleEffects(), providing
+   *   it here will improve performance.
+   *
+   * @param aEffectSetForOpacity: This function may need to look up the
+   *   EffectSet for opacity animations on this frame.
+   *   If the caller already has looked up this EffectSet, it may pass it in to
+   *   save an extra property lookup.
+   */
+  bool Extend3DContext(
+      const nsStyleDisplay* aStyleDisplay, const nsStyleEffects* aStyleEffects,
+      mozilla::EffectSet* aEffectSetForOpacity = nullptr) const;
+  bool Extend3DContext(
+      mozilla::EffectSet* aEffectSetForOpacity = nullptr) const {
+    return Extend3DContext(StyleDisplay(), StyleEffects(),
+                           aEffectSetForOpacity);
+  }
+
+  /**
+   * Returns whether this frame has a parent that Extend3DContext() and has
+   * its own transform (or hidden backface) to be combined with the parent's
+   * transform.
+   */
+  bool Combines3DTransformWithAncestors() const;
+
+  /**
+   * Returns whether this frame has a hidden backface and has a parent that
+   * Extend3DContext(). This is useful because in some cases the hidden
+   * backface can safely be ignored if it could not be visible anyway.
+   *
+   */
+  bool In3DContextAndBackfaceIsHidden() const;
+
+  bool IsPreserve3DLeaf(const nsStyleDisplay* aStyleDisplay,
+                        mozilla::EffectSet* aEffectSet = nullptr) const {
+    return Combines3DTransformWithAncestors() &&
+           !Extend3DContext(aStyleDisplay, StyleEffects(), aEffectSet);
+  }
+  bool IsPreserve3DLeaf(mozilla::EffectSet* aEffectSet = nullptr) const {
+    return IsPreserve3DLeaf(StyleDisplay(), aEffectSet);
+  }
+
+  bool HasPerspective() const;
+
+  bool ChildrenHavePerspective(const nsStyleDisplay* aStyleDisplay) const;
+  bool ChildrenHavePerspective() const {
+    return ChildrenHavePerspective(StyleDisplay());
+  }
+
+  /**
+   * Includes the overflow area of all descendants that participate in the
+   * current 3d context into aOverflowAreas.
+   */
+  void ComputePreserve3DChildrenOverflow(
+      mozilla::OverflowAreas& aOverflowAreas);
+
+  void RecomputePerspectiveChildrenOverflow(const nsIFrame* aStartFrame);
+
+  /**
+   * Returns whether z-index applies to this frame.
+   */
+  bool ZIndexApplies() const;
+
+  /**
+   * Returns the computed z-index for this frame, returning Nothing() for
+   * z-index: auto, and for frames that don't support z-index.
+   */
+  Maybe<int32_t> ZIndex() const;
+
+  /**
+   * Returns whether this frame is the anchor of some ancestor scroll frame. As
+   * this frame is moved, the scroll frame will apply adjustments to keep this
+   * scroll frame in the same relative position.
+   *
+   * aOutContainer will optionally be set to the scroll anchor container for
+   * this frame if this frame is an anchor.
+   */
+  bool IsScrollAnchor(
+      mozilla::layout::ScrollAnchorContainer** aOutContainer = nullptr);
+
+  /**
+   * Returns whether this frame is the anchor of some ancestor scroll frame, or
+   * has a descendant which is the scroll anchor.
+   */
+  bool IsInScrollAnchorChain() const;
+  void SetInScrollAnchorChain(bool aInChain);
+
+  /**
+   * Returns the number of ancestors between this and the root of our frame tree
+   */
+  uint32_t GetDepthInFrameTree() const;
+
+  /**
+   * Event handling of GUI events.
+   *
+   * @param aEvent event structure describing the type of event and rge widget
+   * where the event originated. The |point| member of this is in the coordinate
+   * system of the view returned by GetOffsetFromView.
+   *
+   * @param aEventStatus a return value indicating whether the event was
+   * handled and whether default processing should be done
+   *
+   * XXX From a frame's perspective it's unclear what the effect of the event
+   * status is. Does it cause the event to continue propagating through the
+   * frame hierarchy or is it just returned to the widgets?
+   *
+   * @see     WidgetGUIEvent
+   * @see     nsEventStatus
+   */
+  MOZ_CAN_RUN_SCRIPT_BOUNDARY
+  virtual nsresult HandleEvent(nsPresContext* aPresContext,
+                               mozilla::WidgetGUIEvent* aEvent,
+                               nsEventStatus* aEventStatus);
+
+  /**
+   * Search for selectable content at point and attempt to select
+   * based on the start and end selection behaviours.
+   *
+   * @param aPresContext Presentation context
+   * @param aPoint Point at which selection will occur. Coordinates
+   * should be relative to this frame.
+   * @param aBeginAmountType, aEndAmountType Selection behavior, see
+   * nsIFrame for definitions.
+   * @param aSelectFlags Selection flags defined in nsIFrame.h.
+   * @return success or failure at finding suitable content to select.
+   */
+  MOZ_CAN_RUN_SCRIPT nsresult
+  SelectByTypeAtPoint(nsPresContext* aPresContext, const nsPoint& aPoint,
+                      nsSelectionAmount aBeginAmountType,
+                      nsSelectionAmount aEndAmountType, uint32_t aSelectFlags);
+
+  MOZ_CAN_RUN_SCRIPT nsresult PeekBackwardAndForward(
+      nsSelectionAmount aAmountBack, nsSelectionAmount aAmountForward,
+      int32_t aStartPos, bool aJumpLines, uint32_t aSelectFlags);
+
+  enum { SELECT_ACCUMULATE = 0x01 };
+
+ protected:
+  // Fire DOM event. If no aContent argument use frame's mContent.
+  void FireDOMEvent(const nsAString& aDOMEventName,
+                    nsIContent* aContent = nullptr);
+
+  // Selection Methods
+
+  MOZ_CAN_RUN_SCRIPT_BOUNDARY NS_IMETHOD
+  HandlePress(nsPresContext* aPresContext, mozilla::WidgetGUIEvent* aEvent,
+              nsEventStatus* aEventStatus);
+
+  /**
+   * MoveCaretToEventPoint() moves caret at the point of aMouseEvent.
+   *
+   * @param aPresContext        Must not be nullptr.
+   * @param aMouseEvent         Must not be nullptr, the message must be
+   *                            eMouseDown and its button must be primary or
+   *                            middle button.
+   * @param aEventStatus        [out] Must not be nullptr.  This method ignores
+   *                            its initial value, but callees may refer it.
+   */
+  MOZ_CAN_RUN_SCRIPT nsresult MoveCaretToEventPoint(
+      nsPresContext* aPresContext, mozilla::WidgetMouseEvent* aMouseEvent,
+      nsEventStatus* aEventStatus);
+
+  MOZ_CAN_RUN_SCRIPT_BOUNDARY NS_IMETHOD HandleMultiplePress(
+      nsPresContext* aPresContext, mozilla::WidgetGUIEvent* aEvent,
+      nsEventStatus* aEventStatus, bool aControlHeld);
+
+  /**
+   * @param aPresContext must be non-nullptr.
+   * @param aEvent must be non-nullptr.
+   * @param aEventStatus must be non-nullptr.
+   */
+  MOZ_CAN_RUN_SCRIPT
+  NS_IMETHOD HandleDrag(nsPresContext* aPresContext,
+                        mozilla::WidgetGUIEvent* aEvent,
+                        nsEventStatus* aEventStatus);
+
+  MOZ_CAN_RUN_SCRIPT_BOUNDARY NS_IMETHOD
+  HandleRelease(nsPresContext* aPresContext, mozilla::WidgetGUIEvent* aEvent,
+                nsEventStatus* aEventStatus);
+
+  // Test if we are selecting a table object:
+  //  Most table/cell selection requires that Ctrl (Cmd on Mac) key is down
+  //   during a mouse click or drag. Exception is using Shift+click when
+  //   already in "table/cell selection mode" to extend a block selection
+  //  Get the parent content node and offset of the frame
+  //   of the enclosing cell or table (if not inside a cell)
+  //  aTarget tells us what table element to select (currently only cell and
+  //  table supported) (enums for this are defined in nsIFrame.h)
+  nsresult GetDataForTableSelection(const nsFrameSelection* aFrameSelection,
+                                    mozilla::PresShell* aPresShell,
+                                    mozilla::WidgetMouseEvent* aMouseEvent,
+                                    nsIContent** aParentContent,
+                                    int32_t* aContentOffset,
+                                    mozilla::TableSelectionMode* aTarget);
+
+  /**
+   * @return see nsISelectionController.idl's `getDisplaySelection`.
+   */
+  int16_t DetermineDisplaySelection();
+
+ public:
+  virtual nsresult GetContentForEvent(const mozilla::WidgetEvent* aEvent,
+                                      nsIContent** aContent);
+
+  // This structure keeps track of the content node and offsets associated with
+  // a point; there is a primary and a secondary offset associated with any
+  // point.  The primary and secondary offsets differ when the point is over a
+  // non-text object.  The primary offset is the expected position of the
+  // cursor calculated from a point; the secondary offset, when it is different,
+  // indicates that the point is in the boundaries of some selectable object.
+  // Note that the primary offset can be after the secondary offset; for places
+  // that need the beginning and end of the object, the StartOffset and
+  // EndOffset helpers can be used.
+  struct MOZ_STACK_CLASS ContentOffsets {
+    ContentOffsets()
+        : offset(0),
+          secondaryOffset(0),
+          associate(mozilla::CARET_ASSOCIATE_BEFORE) {}
+    bool IsNull() { return !content; }
+    // Helpers for places that need the ends of the offsets and expect them in
+    // numerical order, as opposed to wanting the primary and secondary offsets
+    int32_t StartOffset() { return std::min(offset, secondaryOffset); }
+    int32_t EndOffset() { return std::max(offset, secondaryOffset); }
+
+    nsCOMPtr<nsIContent> content;
+    int32_t offset;
+    int32_t secondaryOffset;
+    // This value indicates whether the associated content is before or after
+    // the offset; the most visible use is to allow the caret to know which line
+    // to display on.
+    mozilla::CaretAssociationHint associate;
+  };
+  enum {
+    IGNORE_SELECTION_STYLE = 0x01,
+    // Treat visibility:hidden frames as non-selectable
+    SKIP_HIDDEN = 0x02
+  };
+  /**
+   * This function calculates the content offsets for selection relative to
+   * a point.  Note that this should generally only be callled on the event
+   * frame associated with an event because this function does not account
+   * for frame lists other than the primary one.
+   * @param aPoint point relative to this frame
+   */
+  ContentOffsets GetContentOffsetsFromPoint(const nsPoint& aPoint,
+                                            uint32_t aFlags = 0);
+
+  virtual ContentOffsets GetContentOffsetsFromPointExternal(
+      const nsPoint& aPoint, uint32_t aFlags = 0) {
+    return GetContentOffsetsFromPoint(aPoint, aFlags);
+  }
+
+  // Helper for GetContentAndOffsetsFromPoint; calculation of content offsets
+  // in this function assumes there is no child frame that can be targeted.
+  virtual ContentOffsets CalcContentOffsetsFromFramePoint(
+      const nsPoint& aPoint);
+
+  /**
+   * Ensure that `this` gets notifed when `aImage`s underlying image request
+   * loads or animates.
+   *
+   * This in practice is only needed for the canvas frame and table cell
+   * backgrounds, which are the only cases that should paint a background that
+   * isn't its own. The canvas paints the background from the root element or
+   * body, and the table cell paints the background for its row.
+   *
+   * For regular frames, this is done in DidSetComputedStyle.
+   *
+   * NOTE: It's unclear if we even actually _need_ this for the second case, as
+   * invalidating the row should invalidate all the cells. For the canvas case
+   * this is definitely needed as it paints the background from somewhere "down"
+   * in the frame tree.
+   *
+   * Returns whether the image was in fact associated with the frame.
+   */
+  [[nodiscard]] bool AssociateImage(const mozilla::StyleImage&);
+
+  /**
+   * This needs to be called if the above caller returned true, once the above
+   * caller doesn't care about getting notified anymore.
+   */
+  void DisassociateImage(const mozilla::StyleImage&);
+
+  mozilla::StyleImageRendering UsedImageRendering() const;
+  mozilla::StyleTouchAction UsedTouchAction() const;
+
+  enum class AllowCustomCursorImage {
+    No,
+    Yes,
+  };
+
+  /**
+   * This structure holds information about a cursor. AllowCustomCursorImage
+   * is `No`, then no cursor image should be loaded from the style specified on
+   * `mStyle`, or the frame's style.
+   *
+   * The `mStyle` member is used for `<area>` elements.
+   */
+  struct MOZ_STACK_CLASS Cursor {
+    mozilla::StyleCursorKind mCursor = mozilla::StyleCursorKind::Auto;
+    AllowCustomCursorImage mAllowCustomCursor = AllowCustomCursorImage::Yes;
+    RefPtr<mozilla::ComputedStyle> mStyle;
+  };
+
+  /**
+   * Get the cursor for a given frame.
+   */
+  virtual Maybe<Cursor> GetCursor(const nsPoint&);
+
+  /**
+   * Get a point (in the frame's coordinate space) given an offset into
+   * the content. This point should be on the baseline of text with
+   * the correct horizontal offset
+   */
+  virtual nsresult GetPointFromOffset(int32_t inOffset, nsPoint* outPoint);
+
+  /**
+   * Get a list of character rects in a given range.
+   * This is similar version of GetPointFromOffset.
+   */
+  virtual nsresult GetCharacterRectsInRange(int32_t aInOffset, int32_t aLength,
+                                            nsTArray<nsRect>& aRects);
+
+  /**
+   * Get the child frame of this frame which contains the given
+   * content offset. outChildFrame may be this frame, or nullptr on return.
+   * outContentOffset returns the content offset relative to the start
+   * of the returned node. You can also pass a hint which tells the method
+   * to stick to the end of the first found frame or the beginning of the
+   * next in case the offset falls on a boundary.
+   */
+  virtual nsresult GetChildFrameContainingOffset(
+      int32_t inContentOffset,
+      bool inHint,  // false stick left
+      int32_t* outFrameContentOffset, nsIFrame** outChildFrame);
+
+  /**
+   * Get the current frame-state value for this frame. aResult is
+   * filled in with the state bits.
+   */
+  nsFrameState GetStateBits() const { return mState; }
+
+  /**
+   * Update the current frame-state value for this frame.
+   */
+  void AddStateBits(nsFrameState aBits) { mState |= aBits; }
+  void RemoveStateBits(nsFrameState aBits) { mState &= ~aBits; }
+  void AddOrRemoveStateBits(nsFrameState aBits, bool aVal) {
+    aVal ? AddStateBits(aBits) : RemoveStateBits(aBits);
+  }
+
+  /**
+   * Checks if the current frame-state includes all of the listed bits
+   */
+  bool HasAllStateBits(nsFrameState aBits) const {
+    return (mState & aBits) == aBits;
+  }
+
+  /**
+   * Checks if the current frame-state includes any of the listed bits
+   */
+  bool HasAnyStateBits(nsFrameState aBits) const { return mState & aBits; }
+
+ private:
+  /**
+   * Called when this frame becomes primary for mContent.
+   */
+  void InitPrimaryFrame();
+
+ public:
+  /**
+   * Return true if this frame is the primary frame for mContent.
+   */
+  bool IsPrimaryFrame() const { return mIsPrimaryFrame; }
+
+  void SetIsPrimaryFrame(bool aIsPrimary) {
+    mIsPrimaryFrame = aIsPrimary;
+    if (aIsPrimary) {
+      InitPrimaryFrame();
+    }
+  }
+
+  bool IsPrimaryFrameOfRootOrBodyElement() const;
+
+  /**
+   * @return true if this frame is used as a fieldset's rendered legend.
+   */
+  bool IsRenderedLegend() const;
+
+  /**
+   * This call is invoked on the primary frame for a character data content
+   * node, when it is changed in the content tree.
+   */
+  virtual nsresult CharacterDataChanged(const CharacterDataChangeInfo&);
+
+  /**
+   * This call is invoked when the value of a content objects's attribute
+   * is changed.
+   * The first frame that maps that content is asked to deal
+   * with the change by doing whatever is appropriate.
+   *
+   * @param aNameSpaceID the namespace of the attribute
+   * @param aAttribute the atom name of the attribute
+   * @param aModType Whether or not the attribute was added, changed, or
+   * removed. The constants are defined in MutationEvent.webidl.
+   */
+  virtual nsresult AttributeChanged(int32_t aNameSpaceID, nsAtom* aAttribute,
+                                    int32_t aModType);
+
+  /**
+   * When the element states of mContent change, this method is invoked on the
+   * primary frame of that element.
+   *
+   * @param aStates the changed states
+   */
+  virtual void ElementStateChanged(mozilla::dom::ElementState aStates);
+
+  /**
+   * Continuation member functions
+   */
+  virtual nsIFrame* GetPrevContinuation() const;
+  virtual void SetPrevContinuation(nsIFrame*);
+  virtual nsIFrame* GetNextContinuation() const;
+  virtual void SetNextContinuation(nsIFrame*);
+  virtual nsIFrame* FirstContinuation() const {
+    return const_cast<nsIFrame*>(this);
+  }
+  virtual nsIFrame* LastContinuation() const {
+    return const_cast<nsIFrame*>(this);
+  }
+
+  /**
+   * GetTailContinuation gets the last non-overflow-container continuation
+   * in the continuation chain, i.e. where the next sibling element
+   * should attach).
+   */
+  nsIFrame* GetTailContinuation();
+
+  /**
+   * Flow member functions
+   */
+  virtual nsIFrame* GetPrevInFlow() const;
+  virtual void SetPrevInFlow(nsIFrame*);
+
+  virtual nsIFrame* GetNextInFlow() const;
+  virtual void SetNextInFlow(nsIFrame*);
+
+  /**
+   * Return the first frame in our current flow.
+   */
+  virtual nsIFrame* FirstInFlow() const { return const_cast<nsIFrame*>(this); }
+
+  /**
+   * Return the last frame in our current flow.
+   */
+  virtual nsIFrame* LastInFlow() const { return const_cast<nsIFrame*>(this); }
+
+  /**
+   * Note: "width" in the names and comments on the following methods
+   * means inline-size, which could be height in vertical layout
+   */
+
+  /**
+   * Mark any stored intrinsic width information as dirty (requiring
+   * re-calculation).  Note that this should generally not be called
+   * directly; PresShell::FrameNeedsReflow() will call it instead.
+   */
+  virtual void MarkIntrinsicISizesDirty();
+
+ public:
+  /**
+   * Make this frame and all descendants dirty (if not already).
+   * Exceptions: TableColGroupFrame children.
+   */
+  void MarkSubtreeDirty();
+
+  /**
+   * Get the min-content intrinsic inline size of the frame.  This must be
+   * less than or equal to the max-content intrinsic inline size.
+   *
+   * This is *not* affected by the CSS 'min-width', 'width', and
+   * 'max-width' properties on this frame, but it is affected by the
+   * values of those properties on this frame's descendants.  (It may be
+   * called during computation of the values of those properties, so it
+   * cannot depend on any values in the nsStylePosition for this frame.)
+   *
+   * The value returned should **NOT** include the space required for
+   * padding and border.
+   *
+   * Note that many frames will cache the result of this function call
+   * unless MarkIntrinsicISizesDirty is called.
+   *
+   * It is not acceptable for a frame to mark itself dirty when this
+   * method is called.
+   *
+   * This method must not return a negative value.
+   */
+  virtual nscoord GetMinISize(gfxContext* aRenderingContext);
+
+  /**
+   * Get the max-content intrinsic inline size of the frame.  This must be
+   * greater than or equal to the min-content intrinsic inline size.
+   *
+   * Otherwise, all the comments for |GetMinISize| above apply.
+   */
+  virtual nscoord GetPrefISize(gfxContext* aRenderingContext);
+
+  /**
+   * |InlineIntrinsicISize| represents the intrinsic width information
+   * in inline layout.  Code that determines the intrinsic width of a
+   * region of inline layout accumulates the result into this structure.
+   * This pattern is needed because we need to maintain state
+   * information about whitespace (for both collapsing and trimming).
+   */
+  struct InlineIntrinsicISizeData {
+    InlineIntrinsicISizeData()
+        : mLine(nullptr),
+          mLineContainer(nullptr),
+          mPrevLines(0),
+          mCurrentLine(0),
+          mTrailingWhitespace(0),
+          mSkipWhitespace(true) {}
+
+    // The line. This may be null if the inlines are not associated with
+    // a block or if we just don't know the line.
+    const nsLineList_iterator* mLine;
+
+    // The line container. Private, to ensure we always use SetLineContainer
+    // to update it.
+    //
+    // Note that nsContainerFrame::DoInlineIntrinsicISize will clear the
+    // |mLine| and |mLineContainer| fields when following a next-in-flow link,
+    // so we must not assume these can always be dereferenced.
+   private:
+    nsIFrame* mLineContainer;
+
+    // Setter and getter for the lineContainer field:
+   public:
+    void SetLineContainer(nsIFrame* aLineContainer) {
+      mLineContainer = aLineContainer;
+    }
+    nsIFrame* LineContainer() const { return mLineContainer; }
+
+    // The maximum intrinsic width for all previous lines.
+    nscoord mPrevLines;
+
+    // The maximum intrinsic width for the current line.  At a line
+    // break (mandatory for preferred width; allowed for minimum width),
+    // the caller should call |Break()|.
+    nscoord mCurrentLine;
+
+    // This contains the width of the trimmable whitespace at the end of
+    // |mCurrentLine|; it is zero if there is no such whitespace.
+    nscoord mTrailingWhitespace;
+
+    // True if initial collapsable whitespace should be skipped.  This
+    // should be true at the beginning of a block, after hard breaks
+    // and when the last text ended with whitespace.
+    bool mSkipWhitespace;
+
+    // Floats encountered in the lines.
+    class FloatInfo {
+     public:
+      FloatInfo(const nsIFrame* aFrame, nscoord aWidth)
+          : mFrame(aFrame), mWidth(aWidth) {}
+      const nsIFrame* Frame() const { return mFrame; }
+      nscoord Width() const { return mWidth; }
+
+     private:
+      const nsIFrame* mFrame;
+      nscoord mWidth;
+    };
+
+    nsTArray<FloatInfo> mFloats;
+  };
+
+  struct InlineMinISizeData : public InlineIntrinsicISizeData {
+    InlineMinISizeData() : mAtStartOfLine(true) {}
+
+    // The default implementation for nsIFrame::AddInlineMinISize.
+    void DefaultAddInlineMinISize(nsIFrame* aFrame, nscoord aISize,
+                                  bool aAllowBreak = true);
+
+    // We need to distinguish forced and optional breaks for cases where the
+    // current line total is negative.  When it is, we need to ignore
+    // optional breaks to prevent min-width from ending up bigger than
+    // pref-width.
+    void ForceBreak();
+
+    // If the break here is actually taken, aHyphenWidth must be added to the
+    // width of the current line.
+    void OptionallyBreak(nscoord aHyphenWidth = 0);
+
+    // Whether we're currently at the start of the line.  If we are, we
+    // can't break (for example, between the text-indent and the first
+    // word).
+    bool mAtStartOfLine;
+  };
+
+  struct InlinePrefISizeData : public InlineIntrinsicISizeData {
+    InlinePrefISizeData() : mLineIsEmpty(true) {}
+
+    /**
+     * Finish the current line and start a new line.
+     *
+     * @param aClearType controls whether isize of floats are considered
+     * and what floats are kept for the next line:
+     *  * |None| skips handling floats, which means no floats are
+     *    removed, and isizes of floats are not considered either.
+     *  * |Both| takes floats into consideration when computing isize
+     *    of the current line, and removes all floats after that.
+     *  * |Left| and |Right| do the same as |Both| except that they only
+     *    remove floats on the given side, and any floats on the other
+     *    side that are prior to a float on the given side that has a
+     *    'clear' property that clears them.
+     */
+    void ForceBreak(mozilla::StyleClear aClearType = mozilla::StyleClear::Both);
+
+    // The default implementation for nsIFrame::AddInlinePrefISize.
+    void DefaultAddInlinePrefISize(nscoord aISize);
+
+    // True if the current line contains nothing other than placeholders.
+    bool mLineIsEmpty;
+  };
+
+  /**
+   * Add the intrinsic minimum width of a frame in a way suitable for
+   * use in inline layout to an |InlineIntrinsicISizeData| object that
+   * represents the intrinsic width information of all the previous
+   * frames in the inline layout region.
+   *
+   * All *allowed* breakpoints within the frame determine what counts as
+   * a line for the |InlineIntrinsicISizeData|.  This means that
+   * |aData->mTrailingWhitespace| will always be zero (unlike for
+   * AddInlinePrefISize).
+   *
+   * All the comments for |GetMinISize| apply, except that this function
+   * is responsible for adding padding, border, and margin and for
+   * considering the effects of 'width', 'min-width', and 'max-width'.
+   *
+   * This may be called on any frame.  Frames that do not participate in
+   * line breaking can inherit the default implementation on nsFrame,
+   * which calls |GetMinISize|.
+   */
+  virtual void AddInlineMinISize(gfxContext* aRenderingContext,
+                                 InlineMinISizeData* aData);
+
+  /**
+   * Add the intrinsic preferred width of a frame in a way suitable for
+   * use in inline layout to an |InlineIntrinsicISizeData| object that
+   * represents the intrinsic width information of all the previous
+   * frames in the inline layout region.
+   *
+   * All the comments for |AddInlineMinISize| and |GetPrefISize| apply,
+   * except that this fills in an |InlineIntrinsicISizeData| structure
+   * based on using all *mandatory* breakpoints within the frame.
+   */
+  virtual void AddInlinePrefISize(gfxContext* aRenderingContext,
+                                  InlinePrefISizeData* aData);
+
+  /**
+   * Intrinsic size of a frame in a single axis.
+   *
+   * This can represent either isize or bsize.
+   */
+  struct IntrinsicSizeOffsetData {
+    nscoord padding = 0;
+    nscoord border = 0;
+    nscoord margin = 0;
+    nscoord BorderPadding() const { return border + padding; };
+  };
+
+  /**
+   * Return the isize components of padding, border, and margin
+   * that contribute to the intrinsic width that applies to the parent.
+   * @param aPercentageBasis the percentage basis to use for padding/margin -
+   *   i.e. the Containing Block's inline-size
+   */
+  virtual IntrinsicSizeOffsetData IntrinsicISizeOffsets(
+      nscoord aPercentageBasis = NS_UNCONSTRAINEDSIZE);
+
+  /**
+   * Return the bsize components of padding, border, and margin
+   * that contribute to the intrinsic width that applies to the parent.
+   * @param aPercentageBasis the percentage basis to use for padding/margin -
+   *   i.e. the Containing Block's inline-size
+   */
+  IntrinsicSizeOffsetData IntrinsicBSizeOffsets(
+      nscoord aPercentageBasis = NS_UNCONSTRAINEDSIZE);
+
+  virtual mozilla::IntrinsicSize GetIntrinsicSize();
+
+  /**
+   * Get the preferred aspect ratio of this frame, or a default-constructed
+   * AspectRatio if it has none.
+   *
+   * https://drafts.csswg.org/css-sizing-4/#preferred-aspect-ratio
+   */
+  mozilla::AspectRatio GetAspectRatio() const;
+
+  /**
+   * Get the intrinsic aspect ratio of this frame, or a default-constructed
+   * AspectRatio if it has no intrinsic ratio.
+   *
+   * The intrinsic ratio is the ratio of the width/height of a box with an
+   * intrinsic size or the intrinsic aspect ratio of a scalable vector image
+   * without an intrinsic size. A frame class implementing a replaced element
+   * should override this method if it has a intrinsic ratio.
+   */
+  virtual mozilla::AspectRatio GetIntrinsicRatio() const;
+
+  /**
+   * Compute the size that a frame will occupy.  Called while
+   * constructing the ReflowInput to be used to Reflow the frame,
+   * in order to fill its mComputedWidth and mComputedHeight member
+   * variables.
+   *
+   * Note that the reason that border and padding need to be passed
+   * separately is so that the 'box-sizing' property can be handled.
+   * Thus aMargin includes absolute positioning offsets as well.
+   *
+   * @param aWM  The writing mode to use for the returned size (need not match
+   *             this frame's writing mode). This is also the writing mode of
+   *             the passed-in LogicalSize parameters.
+   * @param aCBSize  The size of the element's containing block.  (Well,
+   *                 the BSize() component isn't really.)
+   * @param aAvailableISize  The available inline-size for 'auto' inline-size.
+   *                         This is usually the same as aCBSize.ISize(),
+   *                         but differs in cases such as block
+   *                         formatting context roots next to floats, or
+   *                         in some cases of float reflow in quirks
+   *                         mode.
+   * @param aMargin  The sum of the inline / block margins ***AND***
+   *                 absolute positioning offsets (inset-block and
+   *                 inset-inline) of the frame, including actual values
+   *                 resulting from percentages and from the
+   *                 "hypothetical box" for absolute positioning, but
+   *                 not including actual values resulting from 'auto'
+   *                 margins or ignored 'auto' values in absolute
+   *                 positioning.
+   * @param aBorderPadding  The sum of the frame's inline / block border-widths
+   *                        and padding (including actual values resulting from
+   *                        percentage padding values).
+   * @param aSizeOverride Optional override values for size properties, which
+   *                      this function will use internally instead of the
+   *                      actual property values.
+   * @param aFlags   Flags to further customize behavior (definitions in
+   *                 LayoutConstants.h).
+   *
+   * The return value includes the computed LogicalSize and AspectRatioUsage
+   * which indicates whether the inline/block size is affected by aspect-ratio
+   * or not. The BSize() of the returned LogicalSize may be
+   * NS_UNCONSTRAINEDSIZE, but the ISize() must not be. We need AspectRatioUsage
+   * during reflow because the final size may be affected by the content size
+   * after applying aspect-ratio.
+   * https://drafts.csswg.org/css-sizing-4/#aspect-ratio-minimum
+   *
+   */
+  enum class AspectRatioUsage : uint8_t {
+    None,
+    ToComputeISize,
+    ToComputeBSize,
+  };
+  struct SizeComputationResult {
+    mozilla::LogicalSize mLogicalSize;
+    AspectRatioUsage mAspectRatioUsage = AspectRatioUsage::None;
+  };
+  virtual SizeComputationResult ComputeSize(
+      gfxContext* aRenderingContext, mozilla::WritingMode aWM,
+      const mozilla::LogicalSize& aCBSize, nscoord aAvailableISize,
+      const mozilla::LogicalSize& aMargin,
+      const mozilla::LogicalSize& aBorderPadding,
+      const mozilla::StyleSizeOverrides& aSizeOverrides,
+      mozilla::ComputeSizeFlags aFlags);
+
+ protected:
+  /**
+   * A helper, used by |nsIFrame::ComputeSize| (for frames that need to
+   * override only this part of ComputeSize), that computes the size
+   * that should be returned when inline-size, block-size, and
+   * [min|max]-[inline-size|block-size] are all 'auto' or equivalent.
+   *
+   * In general, frames that can accept any computed inline-size/block-size
+   * should override only ComputeAutoSize, and frames that cannot do so need to
+   * override ComputeSize to enforce their inline-size/block-size invariants.
+   *
+   * Implementations may optimize by returning a garbage inline-size if
+   * StylePosition()->ISize() is not 'auto' (or inline-size override in
+   * aSizeOverrides is not 'auto' if provided), and likewise for BSize(), since
+   * in such cases the result is guaranteed to be unused.
+   *
+   * Most of the frame are not expected to check the aSizeOverrides parameter
+   * apart from checking the inline size override for 'auto' if they want to
+   * optimize and return garbage inline-size.
+   */
+  virtual mozilla::LogicalSize ComputeAutoSize(
+      gfxContext* aRenderingContext, mozilla::WritingMode aWM,
+      const mozilla::LogicalSize& aCBSize, nscoord aAvailableISize,
+      const mozilla::LogicalSize& aMargin,
+      const mozilla::LogicalSize& aBorderPadding,
+      const mozilla::StyleSizeOverrides& aSizeOverrides,
+      mozilla::ComputeSizeFlags aFlags);
+
+  /**
+   * Utility function for ComputeAutoSize implementations.  Return
+   * max(GetMinISize(), min(aISizeInCB, GetPrefISize()))
+   */
+  nscoord ShrinkISizeToFit(gfxContext* aRenderingContext, nscoord aISizeInCB,
+                           mozilla::ComputeSizeFlags aFlags);
+
+ public:
+  /**
+   * Compute a tight bounding rectangle for the frame. This is a rectangle
+   * that encloses the pixels that are actually drawn. We're allowed to be
+   * conservative and currently we don't try very hard. The rectangle is
+   * in appunits and relative to the origin of this frame.
+   *
+   * This probably only needs to include frame bounds, glyph bounds, and
+   * text decorations, but today it sometimes includes other things that
+   * contribute to ink overflow.
+   *
+   * @param aDrawTarget a draw target that can be used if we need
+   * to do measurement
+   */
+  virtual nsRect ComputeTightBounds(DrawTarget* aDrawTarget) const;
+
+  /**
+   * This function is similar to GetPrefISize and ComputeTightBounds: it
+   * computes the left and right coordinates of a preferred tight bounding
+   * rectangle for the frame. This is a rectangle that would enclose the pixels
+   * that are drawn if we lay out the element without taking any optional line
+   * breaks. The rectangle is in appunits and relative to the origin of this
+   * frame. Currently, this function is only implemented for nsBlockFrame and
+   * nsTextFrame and is used to determine intrinsic widths of MathML token
+   * elements.
+
+   * @param aContext a rendering context that can be used if we need
+   * to do measurement
+   * @param aX      computed left coordinate of the tight bounding rectangle
+   * @param aXMost  computed intrinsic width of the tight bounding rectangle
+   *
+   */
+  virtual nsresult GetPrefWidthTightBounds(gfxContext* aContext, nscoord* aX,
+                                           nscoord* aXMost);
+
+  /**
+   * The frame is given an available size and asked for its desired
+   * size.  This is the frame's opportunity to reflow its children.
+   *
+   * If the frame has the NS_FRAME_IS_DIRTY bit set then it is
+   * responsible for completely reflowing itself and all of its
+   * descendants.
+   *
+   * Otherwise, if the frame has the NS_FRAME_HAS_DIRTY_CHILDREN bit
+   * set, then it is responsible for reflowing at least those
+   * children that have NS_FRAME_HAS_DIRTY_CHILDREN or NS_FRAME_IS_DIRTY
+   * set.
+   *
+   * If a difference in available size from the previous reflow causes
+   * the frame's size to change, it should reflow descendants as needed.
+   *
+   * Calculates the size of this frame after reflowing (calling Reflow on, and
+   * updating the size and position of) its children, as necessary.  The
+   * calculated size is returned to the caller via the ReflowOutput
+   * outparam.  (The caller is responsible for setting the actual size and
+   * position of this frame.)
+   *
+   * A frame's children must _all_ be reflowed if the frame is dirty (the
+   * NS_FRAME_IS_DIRTY bit is set on it).  Otherwise, individual children
+   * must be reflowed if they are dirty or have the NS_FRAME_HAS_DIRTY_CHILDREN
+   * bit set on them.  Otherwise, whether children need to be reflowed depends
+   * on the frame's type (it's up to individual Reflow methods), and on what
+   * has changed.  For example, a change in the width of the frame may require
+   * all of its children to be reflowed (even those without dirty bits set on
+   * them), whereas a change in its height might not.
+   * (ReflowInput::ShouldReflowAllKids may be helpful in deciding whether
+   * to reflow all the children, but for some frame types it might result in
+   * over-reflow.)
+   *
+   * Note: if it's only the overflow rect(s) of a frame that need to be
+   * updated, then UpdateOverflow should be called instead of Reflow.
+   *
+   * @param aReflowOutput <i>out</i> parameter where you should return the
+   *          desired size and ascent/descent info. You should include any
+   *          space you want for border/padding in the desired size you return.
+   *
+   *          It's okay to return a desired size that exceeds the avail
+   *          size if that's the smallest you can be, i.e. it's your
+   *          minimum size.
+   *
+   *          For an incremental reflow you are responsible for invalidating
+   *          any area within your frame that needs repainting (including
+   *          borders). If your new desired size is different than your current
+   *          size, then your parent frame is responsible for making sure that
+   *          the difference between the two rects is repainted
+   *
+   * @param aReflowInput information about your reflow including the reason
+   *          for the reflow and the available space in which to lay out. Each
+   *          dimension of the available space can either be constrained or
+   *          unconstrained (a value of NS_UNCONSTRAINEDSIZE).
+   *
+   *          Note that the available space can be negative. In this case you
+   *          still must return an accurate desired size. If you're a container
+   *          you must <b>always</b> reflow at least one frame regardless of the
+   *          available space
+   *
+   * @param aStatus a return value indicating whether the frame is complete
+   *          and whether the next-in-flow is dirty and needs to be reflowed
+   */
+  virtual void Reflow(nsPresContext* aPresContext, ReflowOutput& aReflowOutput,
+                      const ReflowInput& aReflowInput, nsReflowStatus& aStatus);
+
+  // Option flags for ReflowChild(), FinishReflowChild(), and
+  // SyncFrameViewAfterReflow().
+  enum class ReflowChildFlags : uint32_t {
+    Default = 0,
+
+    // Don't position the frame's view. Set this if you don't want to
+    // automatically sync the frame and view.
+    NoMoveView = 1 << 0,
+
+    // Don't move the frame. Also implies NoMoveView.
+    NoMoveFrame = (1 << 1) | NoMoveView,
+
+    // Don't size the frame's view.
+    NoSizeView = 1 << 2,
+
+    // Only applies to ReflowChild; if true, don't delete the next-in-flow, even
+    // if the reflow is fully complete.
+    NoDeleteNextInFlowChild = 1 << 3,
+
+    // Only applies to FinishReflowChild.  Tell it to call
+    // ApplyRelativePositioning.
+    ApplyRelativePositioning = 1 << 4,
+  };
+
+  /**
+   * Post-reflow hook. After a frame is reflowed this method will be called
+   * informing the frame that this reflow process is complete, and telling the
+   * frame the status returned by the Reflow member function.
+   *
+   * This call may be invoked many times, while NS_FRAME_IN_REFLOW is set,
+   * before it is finally called once with a NS_FRAME_REFLOW_COMPLETE value.
+   * When called with a NS_FRAME_REFLOW_COMPLETE value the NS_FRAME_IN_REFLOW
+   * bit in the frame state will be cleared.
+   *
+   * XXX This doesn't make sense. If the frame is reflowed but not complete,
+   * then the status should have IsIncomplete() equal to true.
+   * XXX Don't we want the semantics to dictate that we only call this once for
+   * a given reflow?
+   */
+  virtual void DidReflow(nsPresContext* aPresContext,
+                         const ReflowInput* aReflowInput);
+
+  void FinishReflowWithAbsoluteFrames(nsPresContext* aPresContext,
+                                      ReflowOutput& aDesiredSize,
+                                      const ReflowInput& aReflowInput,
+                                      nsReflowStatus& aStatus,
+                                      bool aConstrainBSize = true);
+
+  /**
+   * Updates the overflow areas of the frame. This can be called if an
+   * overflow area of the frame's children has changed without reflowing.
+   * @return true if either of the overflow areas for this frame have changed.
+   */
+  bool UpdateOverflow();
+
+  /**
+   * Computes any overflow area created by the frame itself (outside of the
+   * frame bounds) and includes it into aOverflowAreas.
+   *
+   * Returns false if updating overflow isn't supported for this frame.
+   * If the frame requires a reflow instead, then it is responsible
+   * for scheduling one.
+   */
+  virtual bool ComputeCustomOverflow(mozilla::OverflowAreas& aOverflowAreas);
+
+  /**
+   * Computes any overflow area created by children of this frame and
+   * includes it into aOverflowAreas.
+   */
+  virtual void UnionChildOverflow(mozilla::OverflowAreas& aOverflowAreas);
+
+  // Returns the applicable overflow-clip-margin values.
+  using PhysicalAxes = mozilla::PhysicalAxes;
+
+  nsSize OverflowClipMargin(PhysicalAxes aClipAxes) const;
+  // Returns the axes on which this frame should apply overflow clipping.
+  PhysicalAxes ShouldApplyOverflowClipping(const nsStyleDisplay* aDisp) const;
+
+  /**
+   * Helper method used by block reflow to identify runs of text so
+   * that proper word-breaking can be done.
+   *
+   * @return
+   *    true if we can continue a "text run" through the frame. A
+   *    text run is text that should be treated contiguously for line
+   *    and word breaking.
+   */
+  virtual bool CanContinueTextRun() const;
+
+  /**
+   * Computes an approximation of the rendered text of the frame and its
+   * continuations. Returns nothing for non-text frames.
+   * The appended text will often not contain all the whitespace from source,
+   * depending on CSS white-space processing.
+   * if aEndOffset goes past end, use the text up to the string's end.
+   * Call this on the primary frame for a text node.
+   * aStartOffset and aEndOffset can be content offsets or offsets in the
+   * rendered text, depending on aOffsetType.
+   * Returns a string, as well as offsets identifying the start of the text
+   * within the rendered text for the whole node, and within the text content
+   * of the node.
+   */
+  struct RenderedText {
+    nsAutoString mString;
+    uint32_t mOffsetWithinNodeRenderedText;
+    int32_t mOffsetWithinNodeText;
+    RenderedText()
+        : mOffsetWithinNodeRenderedText(0), mOffsetWithinNodeText(0) {}
+  };
+  enum class TextOffsetType {
+    // Passed-in start and end offsets are within the content text.
+    OffsetsInContentText,
+    // Passed-in start and end offsets are within the rendered text.
+    OffsetsInRenderedText,
+  };
+  enum class TrailingWhitespace {
+    Trim,
+    // Spaces preceding a caret at the end of a line should not be trimmed
+    DontTrim,
+  };
+  virtual RenderedText GetRenderedText(
+      uint32_t aStartOffset = 0, uint32_t aEndOffset = UINT32_MAX,
+      TextOffsetType aOffsetType = TextOffsetType::OffsetsInContentText,
+      TrailingWhitespace aTrimTrailingWhitespace = TrailingWhitespace::Trim) {
+    return RenderedText();
+  }
+
+  /**
+   * Returns true if the frame contains any non-collapsed characters.
+   * This method is only available for text frames, and it will return false
+   * for all other frame types.
+   */
+  virtual bool HasAnyNoncollapsedCharacters() { return false; }
+
+  /**
+   * Returns true if events of the given type targeted at this frame
+   * should only be dispatched to the system group.
+   */
+  virtual bool OnlySystemGroupDispatch(mozilla::EventMessage aMessage) const {
+    return false;
+  }
+
+  //
+  // Accessor functions to an associated view object:
+  //
+  bool HasView() const { return !!(mState & NS_FRAME_HAS_VIEW); }
+
+  // Returns true iff this frame's computed block-size property is one of the
+  // intrinsic-sizing keywords.
+  bool HasIntrinsicKeywordForBSize() const {
+    const auto& bSize = StylePosition()->BSize(GetWritingMode());
+    return bSize.IsFitContent() || bSize.IsMinContent() ||
+           bSize.IsMaxContent() || bSize.IsFitContentFunction();
+  }
+  /**
+   * Helper method to create a view for a frame.  Only used by a few sub-classes
+   * that need a view.
+   */
+  void CreateView();
+
+ protected:
+  virtual nsView* GetViewInternal() const {
+    MOZ_ASSERT_UNREACHABLE("method should have been overridden by subclass");
+    return nullptr;
+  }
+  virtual void SetViewInternal(nsView* aView) {
+    MOZ_ASSERT_UNREACHABLE("method should have been overridden by subclass");
+  }
+
+ public:
+  nsView* GetView() const {
+    if (MOZ_LIKELY(!HasView())) {
+      return nullptr;
+    }
+    nsView* view = GetViewInternal();
+    MOZ_ASSERT(view, "GetViewInternal() should agree with HasView()");
+    return view;
+  }
+  void SetView(nsView* aView);
+
+  /**
+   * Find the closest view (on |this| or an ancestor).
+   * If aOffset is non-null, it will be set to the offset of |this|
+   * from the returned view.
+   */
+  nsView* GetClosestView(nsPoint* aOffset = nullptr) const;
+
+  /**
+   * Find the closest ancestor (excluding |this| !) that has a view
+   */
+  nsIFrame* GetAncestorWithView() const;
+
+  /**
+   * Sets the view's attributes from the frame style.
+   * Call this for nsChangeHint_SyncFrameView style changes or when the view
+   * has just been created.
+   * @param aView the frame's view or use GetView() if nullptr is given
+   */
+  void SyncFrameViewProperties(nsView* aView = nullptr);
+
+  /**
+   * Get the offset between the coordinate systems of |this| and aOther.
+   * Adding the return value to a point in the coordinate system of |this|
+   * will transform the point to the coordinate system of aOther.
+   *
+   * aOther must be non-null.
+   *
+   * This function is fastest when aOther is an ancestor of |this|.
+   *
+   * This function _DOES NOT_ work across document boundaries.
+   * Use this function only when |this| and aOther are in the same document.
+   *
+   * NOTE: this actually returns the offset from aOther to |this|, but
+   * that offset is added to transform _coordinates_ from |this| to
+   * aOther.
+   */
+  nsPoint GetOffsetTo(const nsIFrame* aOther) const;
+
+  /**
+   * Just like GetOffsetTo, but treats all scrollframes as scrolled to
+   * their origin.
+   */
+  nsPoint GetOffsetToIgnoringScrolling(const nsIFrame* aOther) const;
+
+  /**
+   * Get the offset between the coordinate systems of |this| and aOther
+   * expressed in appunits per dev pixel of |this|' document. Adding the return
+   * value to a point that is relative to the origin of |this| will make the
+   * point relative to the origin of aOther but in the appunits per dev pixel
+   * ratio of |this|.
+   *
+   * aOther must be non-null.
+   *
+   * This function is fastest when aOther is an ancestor of |this|.
+   *
+   * This function works across document boundaries.
+   *
+   * Because this function may cross document boundaries that have different
+   * app units per dev pixel ratios it needs to be used very carefully.
+   *
+   * NOTE: this actually returns the offset from aOther to |this|, but
+   * that offset is added to transform _coordinates_ from |this| to
+   * aOther.
+   */
+  nsPoint GetOffsetToCrossDoc(const nsIFrame* aOther) const;
+
+  /**
+   * Like GetOffsetToCrossDoc, but the caller can specify which appunits
+   * to return the result in.
+   */
+  nsPoint GetOffsetToCrossDoc(const nsIFrame* aOther, const int32_t aAPD) const;
+
+  /**
+   * Get the rect of the frame relative to the top-left corner of the
+   * screen in CSS pixels.
+   * @return the CSS pixel rect of the frame relative to the top-left
+   *         corner of the screen.
+   */
+  mozilla::CSSIntRect GetScreenRect() const;
+
+  /**
+   * Get the screen rect of the frame in app units.
+   * @return the app unit rect of the frame in screen coordinates.
+   */
+  nsRect GetScreenRectInAppUnits() const;
+
+  /**
+   * Returns the offset from this frame to the closest geometric parent that
+   * has a view. Also returns the containing view or null in case of error
+   */
+  void GetOffsetFromView(nsPoint& aOffset, nsView** aView) const;
+
+  /**
+   * Returns the nearest widget containing this frame. If this frame has a
+   * view and the view has a widget, then this frame's widget is
+   * returned, otherwise this frame's geometric parent is checked
+   * recursively upwards.
+   */
+  nsIWidget* GetNearestWidget() const;
+
+  /**
+   * Whether the frame is a subgrid right now.
+   */
+  bool IsSubgrid() const;
+
+  /**
+   * Same as GetNearestWidget() above but uses an outparam to return the offset
+   * of this frame to the returned widget expressed in appunits of |this| (the
+   * widget might be in a different document with a different zoom).
+   */
+  nsIWidget* GetNearestWidget(nsPoint& aOffset) const;
+
+  /**
+   * Whether the content for this frame is disabled, used for event handling.
+   */
+  bool IsContentDisabled() const;
+
+  enum class IncludeContentVisibility {
+    Auto,
+    Hidden,
+  };
+
+  constexpr static mozilla::EnumSet<IncludeContentVisibility>
+  IncludeAllContentVisibility() {
+    return {IncludeContentVisibility::Auto, IncludeContentVisibility::Hidden};
+  }
+
+  /**
+   * Returns true if this frame's `content-visibility: auto` element is
+   * considered relevant content.
+   */
+  bool IsContentRelevant() const;
+
+  /**
+   * Whether this frame hides its contents via the `content-visibility`
+   * property.
+   * @param aInclude specifies what kind of `content-visibility` to include.
+   */
+  bool HidesContent(const mozilla::EnumSet<IncludeContentVisibility>& =
+                        IncludeAllContentVisibility()) const;
+
+  /**
+   * Whether this frame hides its contents via the `content-visibility`
+   * property, while doing layout. This might be true when `HidesContent()` is
+   * true in the case that hidden content is being forced to lay out by position
+   * or size queries from script.
+   */
+  bool HidesContentForLayout() const;
+
+  /**
+   * Returns true if this frame is entirely hidden due the `content-visibility`
+   * property on an ancestor.
+   * @param aInclude specifies what kind of `content-visibility` to include.
+   */
+  bool IsHiddenByContentVisibilityOnAnyAncestor(
+      const mozilla::EnumSet<IncludeContentVisibility>& =
+          IncludeAllContentVisibility()) const;
+
+  /**
+   * Returns true is this frame is hidden by its first unskipped in flow
+   * ancestor due to `content-visibility`.
+   */
+  bool IsHiddenByContentVisibilityOfInFlowParentForLayout() const;
+
+  /**
+   * Whether or not this frame's content is a descendant of a top layer element
+   * used to determine if this frame is relevant content for
+   * `content-visibility: auto`.
+   */
+  bool IsDescendantOfTopLayerElement() const;
+
+  /**
+   * Returns true if this frame has a SelectionType::eNormal type selection in
+   * somewhere in its subtree of frames. This is used to determine content
+   * relevancy for `content-visibility: auto`.
+   */
+  bool HasSelectionInSubtree();
+
+  /**
+   * Update the whether or not this frame is considered relevant content for the
+   * purposes of `content-visibility: auto` according to the rules specified in
+   * https://drafts.csswg.org/css-contain-2/#relevant-to-the-user.
+   */
+  void UpdateIsRelevantContent(const ContentRelevancy& aRelevancyToUpdate);
+
+  /**
+   * Get the "type" of the frame.
+   *
+   * @see mozilla::LayoutFrameType
+   */
+  mozilla::LayoutFrameType Type() const {
+    MOZ_ASSERT(uint8_t(mClass) < mozilla::ArrayLength(sLayoutFrameTypes));
+    return sLayoutFrameTypes[uint8_t(mClass)];
+  }
+
+#ifdef __GNUC__
+#  pragma GCC diagnostic push
+#  pragma GCC diagnostic ignored "-Wtype-limits"
+#endif
+#ifdef __clang__
+#  pragma clang diagnostic push
+#  pragma clang diagnostic ignored "-Wunknown-pragmas"
+#  pragma clang diagnostic ignored "-Wtautological-unsigned-zero-compare"
+#endif
+
+#define FRAME_TYPE(name_, first_class_, last_class_)                 \
+  bool Is##name_##Frame() const {                                    \
+    return uint8_t(mClass) >= uint8_t(ClassID::first_class_##_id) && \
+           uint8_t(mClass) <= uint8_t(ClassID::last_class_##_id);    \
+  }
+#include "mozilla/FrameTypeList.h"
+#undef FRAME_TYPE
+
+#ifdef __GNUC__
+#  pragma GCC diagnostic pop
+#endif
+#ifdef __clang__
+#  pragma clang diagnostic pop
+#endif
+
+  /**
+   * Returns a transformation matrix that converts points in this frame's
+   * coordinate space to points in some ancestor frame's coordinate space.
+   * The frame decides which ancestor it will use as a reference point.
+   * If this frame has no ancestor, aOutAncestor will be set to null.
+   *
+   * @param aViewportType specifies whether the starting point is layout
+   *   or visual coordinates
+   * @param aStopAtAncestor don't look further than aStopAtAncestor. If null,
+   *   all ancestors (including across documents) will be traversed.
+   * @param aOutAncestor [out] The ancestor frame the frame has chosen.  If
+   *   this frame has no ancestor, *aOutAncestor will be set to null. If
+   * this frame is not a root frame, then *aOutAncestor will be in the same
+   * document as this frame. If this frame IsTransformed(), then *aOutAncestor
+   * will be the parent frame (if not preserve-3d) or the nearest
+   * non-transformed ancestor (if preserve-3d).
+   * @return A Matrix4x4 that converts points in the coordinate space
+   *   RelativeTo{this, aViewportType} into points in aOutAncestor's
+   *   coordinate space.
+   */
+  enum {
+    IN_CSS_UNITS = 1 << 0,
+    STOP_AT_STACKING_CONTEXT_AND_DISPLAY_PORT = 1 << 1
+  };
+  Matrix4x4Flagged GetTransformMatrix(mozilla::ViewportType aViewportType,
+                                      mozilla::RelativeTo aStopAtAncestor,
+                                      nsIFrame** aOutAncestor,
+                                      uint32_t aFlags = 0) const;
+
+  /**
+   * Bit-flags to pass to IsFrameOfType()
+   */
+  enum {
+    eMathML = 1 << 0,
+    eSVG = 1 << 1,
+    eSVGContainer = 1 << 2,
+    eBidiInlineContainer = 1 << 3,
+    // the frame is for a replaced element, such as an image
+    eReplaced = 1 << 4,
+    // Frame that contains a block but looks like a replaced element
+    // from the outside
+    eReplacedContainsBlock = 1 << 5,
+    // A frame that participates in inline reflow, i.e., one that
+    // requires ReflowInput::mLineLayout.
+    eLineParticipant = 1 << 6,
+    eCanContainOverflowContainers = 1 << 7,
+    eTablePart = 1 << 8,
+    eSupportsCSSTransforms = 1 << 9,
+
+    // A replaced element that has replaced-element sizing
+    // characteristics (i.e., like images or iframes), as opposed to
+    // inline-block sizing characteristics (like form controls).
+    eReplacedSizing = 1 << 10,
+
+    // Does this frame class support 'contain: layout' and
+    // 'contain:paint' (supporting one is equivalent to supporting the
+    // other).
+    eSupportsContainLayoutAndPaint = 1 << 11,
+
+    // Does this frame class support `aspect-ratio` property.
+    eSupportsAspectRatio = 1 << 12,
+
+    // These are to allow nsIFrame::Init to assert that IsFrameOfType
+    // implementations all call the base class method.  They are only
+    // meaningful in DEBUG builds.
+    eDEBUGAllFrames = 1 << 30,
+    eDEBUGNoFrames = 1 << 31
+  };
+
+  /**
+   * API for doing a quick check if a frame is of a given
+   * type. Returns true if the frame matches ALL flags passed in.
+   *
+   * Implementations should always override with inline virtual
+   * functions that call the base class's IsFrameOfType method.
+   */
+  virtual bool IsFrameOfType(uint32_t aFlags) const {
+    return !(aFlags & ~(
+#ifdef DEBUG
+                          nsIFrame::eDEBUGAllFrames |
+#endif
+                          nsIFrame::eSupportsCSSTransforms |
+                          nsIFrame::eSupportsContainLayoutAndPaint |
+                          nsIFrame::eSupportsAspectRatio));
+  }
+
+  /**
+   * Return true if this frame's preferred size property or max size property
+   * contains a percentage value that should be resolved against zero when
+   * calculating its min-content contribution in the corresponding axis.
+   *
+   * This is a special case for webcompat required by CSS Sizing 3 §5.2.1c
+   * https://drafts.csswg.org/css-sizing-3/#replaced-percentage-min-contribution,
+   * and applies only to some replaced elements and form control elements. See
+   * CSS Sizing 3 §5.2.2 for the list of elements this rule applies to.
+   * https://drafts.csswg.org/css-sizing-3/#min-content-zero
+   *
+   * Bug 1463700: some callers may not match the spec by resolving the entire
+   * preferred size property or max size property against zero.
+   */
+  bool IsPercentageResolvedAgainstZero(
+      const mozilla::StyleSize& aStyleSize,
+      const mozilla::StyleMaxSize& aStyleMaxSize) const;
+
+  // Type of preferred size/min size/max size.
+  enum class SizeProperty { Size, MinSize, MaxSize };
+  /**
+   * This is simliar to the above method but accepts LengthPercentage. Return
+   * true if the frame's preferred size property or max size property contains
+   * a percentage value that should be resolved against zero. For min size, it
+   * always returns true.
+   */
+  bool IsPercentageResolvedAgainstZero(const mozilla::LengthPercentage& aSize,
+                                       SizeProperty aProperty) const;
+
+  /**
+   * Returns true if the frame is a block wrapper.
+   */
+  bool IsBlockWrapper() const;
+
+  /**
+   * Returns true if the frame is an instance of nsBlockFrame or one of its
+   * subclasses.
+   */
+  bool IsBlockFrameOrSubclass() const;
+
+  /**
+   * Returns true if the frame is an instance of nsImageFrame or one of its
+   * subclasses.
+   */
+  bool IsImageFrameOrSubclass() const;
+
+  /**
+   * Get this frame's CSS containing block.
+   *
+   * The algorithm is defined in
+   * http://www.w3.org/TR/CSS2/visudet.html#containing-block-details.
+   *
+   * NOTE: This is guaranteed to return a non-null pointer when invoked on any
+   * frame other than the root frame.
+   *
+   * Requires SKIP_SCROLLED_FRAME to get behaviour matching the spec, otherwise
+   * it can return anonymous inner scrolled frames. Bug 1204044 is filed for
+   * investigating whether any of the callers actually require the default
+   * behaviour.
+   */
+  enum {
+    // If the containing block is an anonymous scrolled frame, then skip over
+    // this and return the outer scroll frame.
+    SKIP_SCROLLED_FRAME = 0x01
+  };
+  nsIFrame* GetContainingBlock(uint32_t aFlags,
+                               const nsStyleDisplay* aStyleDisplay) const;
+  nsIFrame* GetContainingBlock(uint32_t aFlags = 0) const {
+    return GetContainingBlock(aFlags, StyleDisplay());
+  }
+
+  /**
+   * If this frame can be a block container, i.e. whether it can serve as a
+   * containing block for its descendants. See also GetNearestBlockContainer()
+   * and GetContainingBlock().
+   */
+  bool IsBlockContainer() const;
+
+  /**
+   * Is this frame a containing block for floating elements?
+   * Note that very few frames are, so default to false.
+   */
+  virtual bool IsFloatContainingBlock() const { return false; }
+
+  /**
+   * Is this a leaf frame?  Frames that want the frame constructor to be able
+   * to construct kids for them should return false, all others should return
+   * true.  Note that returning true here does not mean that the frame _can't_
+   * have kids.  It could still have kids created via
+   * nsIAnonymousContentCreator.  Returning true indicates that "normal"
+   * (non-anonymous, CSS generated content, etc) children should not be
+   * constructed.
+   */
+  bool IsLeaf() const {
+    MOZ_ASSERT(uint8_t(mClass) < mozilla::ArrayLength(sFrameClassBits));
+    FrameClassBits bits = sFrameClassBits[uint8_t(mClass)];
+    if (MOZ_UNLIKELY(bits & eFrameClassBitsDynamicLeaf)) {
+      return IsLeafDynamic();
+    }
+    return bits & eFrameClassBitsLeaf;
+  }
+
+  virtual bool IsLeafDynamic() const { return false; }
+
+  /**
+   * Marks all display items created by this frame as needing a repaint,
+   * and calls SchedulePaint() if requested and one is not already pending.
+   *
+   * This includes all display items created by this frame, including
+   * container types.
+   *
+   * @param aDisplayItemKey If specified, only issues an invalidate
+   * if this frame painted a display item of that type during the
+   * previous paint. SVG rendering observers are always notified.
+   * @param aRebuildDisplayItems If true, then adds this frame to the
+   * list of modified frames for display list building. Only pass false
+   * if you're sure that the relevant display items will be rebuilt
+   * already (possibly by an ancestor being in the modified list).
+   */
+  virtual void InvalidateFrame(uint32_t aDisplayItemKey = 0,
+                               bool aRebuildDisplayItems = true);
+
+  /**
+   * Same as InvalidateFrame(), but only mark a fixed rect as needing
+   * repainting.
+   *
+   * @param aRect The rect to invalidate, relative to the TopLeft of the
+   * frame's border box.
+   * @param aDisplayItemKey If specified, only issues an invalidate
+   * if this frame painted a display item of that type during the
+   * previous paint. SVG rendering observers are always notified.
+   * @param aRebuildDisplayItems If true, then adds this frame to the
+   * list of modified frames for display list building. Only pass false
+   * if you're sure that the relevant display items will be rebuilt
+   * already (possibly by an ancestor being in the modified list).
+   */
+  virtual void InvalidateFrameWithRect(const nsRect& aRect,
+                                       uint32_t aDisplayItemKey = 0,
+                                       bool aRebuildDisplayItems = true);
+
+  /**
+   * Calls InvalidateFrame() on all frames descendant frames (including
+   * this one).
+   *
+   * This function doesn't walk through placeholder frames to invalidate
+   * the out-of-flow frames.
+   *
+   * @param aRebuildDisplayItems If true, then adds this frame to the
+   * list of modified frames for display list building. Only pass false
+   * if you're sure that the relevant display items will be rebuilt
+   * already (possibly by an ancestor being in the modified list).
+   */
+  void InvalidateFrameSubtree(bool aRebuildDisplayItems = true);
+
+  /**
+   * Called when a frame is about to be removed and needs to be invalidated.
+   * Normally does nothing since DLBI handles removed frames.
+   */
+  virtual void InvalidateFrameForRemoval() {}
+
+  /**
+   * When HasUserData(frame->LayerIsPrerenderedDataKey()), then the
+   * entire overflow area of this frame has been rendered in its
+   * layer(s).
+   */
+  static void* LayerIsPrerenderedDataKey() {
+    return &sLayerIsPrerenderedDataKey;
+  }
+  static uint8_t sLayerIsPrerenderedDataKey;
+
+  /**
+   * Checks if a frame has had InvalidateFrame() called on it since the
+   * last paint.
+   *
+   * If true, then the invalid rect is returned in aRect, with an
+   * empty rect meaning all pixels drawn by this frame should be
+   * invalidated.
+   * If false, aRect is left unchanged.
+   */
+  bool IsInvalid(nsRect& aRect);
+
+  /**
+   * Check if any frame within the frame subtree (including this frame)
+   * returns true for IsInvalid().
+   */
+  bool HasInvalidFrameInSubtree() {
+    return HasAnyStateBits(NS_FRAME_NEEDS_PAINT |
+                           NS_FRAME_DESCENDANT_NEEDS_PAINT);
+  }
+
+  /**
+   * Removes the invalid state from the current frame and all
+   * descendant frames.
+   */
+  void ClearInvalidationStateBits();
+
+  /**
+   * Ensures that the refresh driver is running, and schedules a view
+   * manager flush on the next tick.
+   *
+   * The view manager flush will update the layer tree, repaint any
+   * invalid areas in the layer tree and schedule a layer tree
+   * composite operation to display the layer tree.
+   *
+   * In general it is not necessary for frames to call this when they change.
+   * For example, changes that result in a reflow will have this called for
+   * them by PresContext::DoReflow when the reflow begins. Style changes that
+   * do not trigger a reflow should have this called for them by
+   * DoApplyRenderingChangeToTree.
+   *
+   * @param aType PAINT_COMPOSITE_ONLY : No changes have been made
+   * that require a layer tree update, so only schedule a layer
+   * tree composite.
+   */
+  enum PaintType { PAINT_DEFAULT = 0, PAINT_COMPOSITE_ONLY };
+  void SchedulePaint(PaintType aType = PAINT_DEFAULT,
+                     bool aFrameChanged = true);
+
+  // Similar to SchedulePaint() but without calling
+  // InvalidateRenderingObservers() for SVG.
+  void SchedulePaintWithoutInvalidatingObservers(
+      PaintType aType = PAINT_DEFAULT);
+
+  /**
+   * Checks if the layer tree includes a dedicated layer for this
+   * frame/display item key pair, and invalidates at least aDamageRect
+   * area within that layer.
+   *
+   * If no layer is found, calls InvalidateFrame() instead.
+   *
+   * @param aDamageRect Area of the layer to invalidate.
+   * @param aFrameDamageRect If no layer is found, the area of the frame to
+   *                         invalidate. If null, the entire frame will be
+   *                         invalidated.
+   * @param aDisplayItemKey Display item type.
+   * @param aFlags UPDATE_IS_ASYNC : Will skip the invalidation
+   * if the found layer is being composited by a remote
+   * compositor.
+   * @return Layer, if found, nullptr otherwise.
+   */
+  enum { UPDATE_IS_ASYNC = 1 << 0 };
+  void InvalidateLayer(DisplayItemType aDisplayItemKey,
+                       const nsIntRect* aDamageRect = nullptr,
+                       const nsRect* aFrameDamageRect = nullptr,
+                       uint32_t aFlags = 0);
+
+  void MarkNeedsDisplayItemRebuild();
+
+  /**
+   * Returns a rect that encompasses everything that might be painted by
+   * this frame.  This includes this frame, all its descendant frames, this
+   * frame's outline, and descendant frames' outline, but does not include
+   * areas clipped out by the CSS "overflow" and "clip" properties.
+   *
+   * HasOverflowAreas() (below) will return true when this overflow
+   * rect has been explicitly set, even if it matches mRect.
+   * XXX Note: because of a space optimization using the formula above,
+   * during reflow this function does not give accurate data if
+   * FinishAndStoreOverflow has been called but mRect hasn't yet been
+   * updated yet.  FIXME: This actually isn't true, but it should be.
+   *
+   * The ink overflow rect should NEVER be used for things that
+   * affect layout.  The scrollable overflow rect is permitted to affect
+   * layout.
+   *
+   * @return the rect relative to this frame's origin, but after
+   * CSS transforms have been applied (i.e. not really this frame's coordinate
+   * system, and may not contain the frame's border-box, e.g. if there
+   * is a CSS transform scaling it down)
+   */
+  nsRect InkOverflowRect() const {
+    return GetOverflowRect(mozilla::OverflowType::Ink);
+  }
+
+  /**
+   * Returns a rect that encompasses the area of this frame that the
+   * user should be able to scroll to reach.  This is similar to
+   * InkOverflowRect, but does not include outline or shadows, and
+   * may in the future include more margins than ink overflow does.
+   * It does not include areas clipped out by the CSS "overflow" and
+   * "clip" properties.
+   *
+   * HasOverflowAreas() (below) will return true when this overflow
+   * rect has been explicitly set, even if it matches mRect.
+   * XXX Note: because of a space optimization using the formula above,
+   * during reflow this function does not give accurate data if
+   * FinishAndStoreOverflow has been called but mRect hasn't yet been
+   * updated yet.
+   *
+   * @return the rect relative to this frame's origin, but after
+   * CSS transforms have been applied (i.e. not really this frame's coordinate
+   * system, and may not contain the frame's border-box, e.g. if there
+   * is a CSS transform scaling it down)
+   */
+  nsRect ScrollableOverflowRect() const {
+    return GetOverflowRect(mozilla::OverflowType::Scrollable);
+  }
+
+  mozilla::OverflowAreas GetOverflowAreas() const;
+
+  /**
+   * Same as GetOverflowAreas, except in this frame's coordinate
+   * system (before transforms are applied).
+   *
+   * @return the overflow areas relative to this frame, before any CSS
+   * transforms have been applied, i.e. in this frame's coordinate system
+   */
+  mozilla::OverflowAreas GetOverflowAreasRelativeToSelf() const;
+
+  /**
+   * Same as GetOverflowAreas, except relative to the parent frame.
+   *
+   * @return the overflow area relative to the parent frame, in the parent
+   * frame's coordinate system
+   */
+  mozilla::OverflowAreas GetOverflowAreasRelativeToParent() const;
+
+  /**
+   * Same as GetOverflowAreasRelativeToParent(), except that it also unions in
+   * the normal position overflow area if this frame is relatively or sticky
+   * positioned.
+   *
+   * @return the overflow area relative to the parent frame, in the parent
+   * frame's coordinate system
+   */
+  mozilla::OverflowAreas GetActualAndNormalOverflowAreasRelativeToParent()
+      const;
+
+  /**
+   * Same as ScrollableOverflowRect, except relative to the parent
+   * frame.
+   *
+   * @return the rect relative to the parent frame, in the parent frame's
+   * coordinate system
+   */
+  nsRect ScrollableOverflowRectRelativeToParent() const;
+
+  /**
+   * Same as ScrollableOverflowRect, except in this frame's coordinate
+   * system (before transforms are applied).
+   *
+   * @return the rect relative to this frame, before any CSS transforms have
+   * been applied, i.e. in this frame's coordinate system
+   */
+  nsRect ScrollableOverflowRectRelativeToSelf() const;
+
+  /**
+   * Like InkOverflowRect, except in this frame's
+   * coordinate system (before transforms are applied).
+   *
+   * @return the rect relative to this frame, before any CSS transforms have
+   * been applied, i.e. in this frame's coordinate system
+   */
+  nsRect InkOverflowRectRelativeToSelf() const;
+
+  /**
+   * Same as InkOverflowRect, except relative to the parent
+   * frame.
+   *
+   * @return the rect relative to the parent frame, in the parent frame's
+   * coordinate system
+   */
+  nsRect InkOverflowRectRelativeToParent() const;
+
+  /**
+   * Returns this frame's ink overflow rect as it would be before taking
+   * account of SVG effects or transforms. The rect returned is relative to
+   * this frame.
+   */
+  nsRect PreEffectsInkOverflowRect() const;
+
+  /**
+   * Store the overflow area in the frame's mOverflow.mInkOverflowDeltas
+   * fields or as a frame property in OverflowAreasProperty() so that it can
+   * be retrieved later without reflowing the frame. Returns true if either of
+   * the overflow areas changed.
+   */
+  bool FinishAndStoreOverflow(mozilla::OverflowAreas& aOverflowAreas,
+                              nsSize aNewSize, nsSize* aOldSize = nullptr,
+                              const nsStyleDisplay* aStyleDisplay = nullptr);
+
+  bool FinishAndStoreOverflow(ReflowOutput* aMetrics,
+                              const nsStyleDisplay* aStyleDisplay = nullptr) {
+    return FinishAndStoreOverflow(aMetrics->mOverflowAreas,
+                                  nsSize(aMetrics->Width(), aMetrics->Height()),
+                                  nullptr, aStyleDisplay);
+  }
+
+  /**
+   * Returns whether the frame has an overflow rect that is different from
+   * its border-box.
+   */
+  bool HasOverflowAreas() const {
+    return mOverflow.mType != OverflowStorageType::None;
+  }
+
+  /**
+   * Removes any stored overflow rects (visual and scrollable) from the frame.
+   * Returns true if the overflow changed.
+   */
+  bool ClearOverflowRects();
+
+  /**
+   * Determine whether borders, padding, margins etc should NOT be applied
+   * on certain sides of the frame.
+   * @see mozilla::Sides in gfx/2d/BaseMargin.h
+   * @see mozilla::LogicalSides in layout/generic/WritingModes.h
+   *
+   * @note (See also bug 743402, comment 11) GetSkipSides() checks to see
+   *       if this frame has a previous or next continuation to determine
+   *       if a side should be skipped.
+   *       So this only works after the entire frame tree has been reflowed.
+   *       During reflow, if this frame can be split in the block axis, you
+   *       should use nsSplittableFrame::PreReflowBlockLevelLogicalSkipSides().
+   */
+  Sides GetSkipSides() const;
+  virtual LogicalSides GetLogicalSkipSides() const {
+    return LogicalSides(mWritingMode);
+  }
+
+  /**
+   * @returns true if this frame is selected.
+   */
+  bool IsSelected() const {
+    return (GetContent() && GetContent()->IsMaybeSelected()) ? IsFrameSelected()
+                                                             : false;
+  }
+
+  /**
+   * Shouldn't be called if this is a `nsTextFrame`. Call the
+   * `nsTextFrame::SelectionStateChanged` overload instead.
+   */
+  void SelectionStateChanged() {
+    MOZ_ASSERT(!IsTextFrame());
+    InvalidateFrameSubtree();  // TODO: should this deal with continuations?
+  }
+
+  /**
+   * Called to discover where this frame, or a parent frame has user-select
+   * style applied, which affects that way that it is selected.
+   *
+   * @param aSelectStyle out param. Returns the type of selection style found
+   * (using values defined in nsStyleConsts.h).
+   *
+   * @return Whether the frame can be selected (i.e. is not affected by
+   * user-select: none)
+   */
+  bool IsSelectable(mozilla::StyleUserSelect* aSelectStyle) const;
+
+  /**
+   * Returns whether this frame should have the content-block-size of a line,
+   * even if empty.
+   */
+  bool ShouldHaveLineIfEmpty() const;
+
+  /**
+   * Called to retrieve the SelectionController associated with the frame.
+   *
+   * @param aSelCon will contain the selection controller associated with
+   * the frame.
+   */
+  nsresult GetSelectionController(nsPresContext* aPresContext,
+                                  nsISelectionController** aSelCon);
+
+  /**
+   * Call to get nsFrameSelection for this frame.
+   */
+  already_AddRefed<nsFrameSelection> GetFrameSelection();
+
+  /**
+   * GetConstFrameSelection returns an object which methods are safe to use for
+   * example in nsIFrame code.
+   */
+  const nsFrameSelection* GetConstFrameSelection() const;
+
+  /**
+   * called to find the previous/next character, word, or line. Returns the
+   * actual nsIFrame and the frame offset. THIS DOES NOT CHANGE SELECTION STATE.
+   * Uses frame's begin selection state to start. If no selection on this frame
+   * will return NS_ERROR_FAILURE.
+   *
+   * @param aPos is defined in nsFrameSelection
+   */
+  virtual nsresult PeekOffset(mozilla::PeekOffsetStruct* aPos);
+
+ private:
+  nsresult PeekOffsetForCharacter(mozilla::PeekOffsetStruct* aPos,
+                                  int32_t aOffset);
+  nsresult PeekOffsetForWord(mozilla::PeekOffsetStruct* aPos, int32_t aOffset);
+  nsresult PeekOffsetForLine(mozilla::PeekOffsetStruct* aPos);
+  nsresult PeekOffsetForLineEdge(mozilla::PeekOffsetStruct* aPos);
+
+  /**
+   * Search for the first paragraph boundary before or after the given position
+   * @param  aPos See description in nsFrameSelection.h. The following fields
+   *              are used by this method:
+   *              Input: mDirection
+   *              Output: mResultContent, mContentOffset
+   */
+  nsresult PeekOffsetForParagraph(mozilla::PeekOffsetStruct* aPos);
+
+ public:
+  // given a frame five me the first/last leaf available
+  // XXX Robert O'Callahan wants to move these elsewhere
+  static void GetLastLeaf(nsIFrame** aFrame);
+  static void GetFirstLeaf(nsIFrame** aFrame);
+
+  struct SelectablePeekReport {
+    /** the previous/next selectable leaf frame */
+    nsIFrame* mFrame = nullptr;
+    /**
+     * 0 indicates that we arrived at the beginning of the output frame; -1
+     * indicates that we arrived at its end.
+     */
+    int32_t mOffset = 0;
+    /** whether the input frame and the returned frame are on different lines */
+    bool mJumpedLine = false;
+    /** whether we met a hard break between the input and the returned frame */
+    bool mJumpedHardBreak = false;
+    /** whether we jumped over a non-selectable frame during the search */
+    bool mMovedOverNonSelectableText = false;
+    /** whether we met selectable text frame that isn't editable during the
+     *  search */
+    bool mHasSelectableFrame = false;
+    /** whether we ignored a br frame */
+    bool mIgnoredBrFrame = false;
+
+    FrameSearchResult PeekOffsetNoAmount(bool aForward) {
+      return mFrame->PeekOffsetNoAmount(aForward, &mOffset);
+    }
+    FrameSearchResult PeekOffsetCharacter(bool aForward,
+                                          PeekOffsetCharacterOptions aOptions) {
+      return mFrame->PeekOffsetCharacter(aForward, &mOffset, aOptions);
+    };
+
+    /** Transfers frame and offset info for PeekOffset() result */
+    void TransferTo(mozilla::PeekOffsetStruct& aPos) const;
+    bool Failed() { return !mFrame; }
+
+    explicit SelectablePeekReport(nsIFrame* aFrame = nullptr,
+                                  int32_t aOffset = 0)
+        : mFrame(aFrame), mOffset(aOffset) {}
+    MOZ_IMPLICIT SelectablePeekReport(
+        const mozilla::GenericErrorResult<nsresult>&& aErr);
+  };
+
+  /**
+   * Called to find the previous/next non-anonymous selectable leaf frame.
+   *
+   * @param aDirection the direction to move in (eDirPrevious or eDirNext)
+   * @param aOptions the other options which is same as
+   * PeekOffsetStruct::mOptions.
+   * FIXME: Due to the include hell, we cannot use the alias, PeekOffsetOptions
+   * is not available in this header file.
+   */
+  SelectablePeekReport GetFrameFromDirection(
+      nsDirection aDirection,
+      const mozilla::EnumSet<mozilla::PeekOffsetOption>& aOptions);
+  SelectablePeekReport GetFrameFromDirection(
+      const mozilla::PeekOffsetStruct& aPos);
+
+  /**
+   * Return:
+   * (1) the containing block frame for a line; i.e. the frame which
+   * supports a line iterator, or null if none can be found; and
+   * (2) the frame to use to get a line number, which will be direct child of
+   * the returned containing block.
+   * @param aLockScroll true to avoid breaking outside scrollframes.
+   */
+  std::pair<nsIFrame*, nsIFrame*> GetContainingBlockForLine(
+      bool aLockScroll) const;
+
+ private:
+  Result<bool, nsresult> IsVisuallyAtLineEdge(nsILineIterator* aLineIterator,
+                                              int32_t aLine,
+                                              nsDirection aDirection);
+  Result<bool, nsresult> IsLogicallyAtLineEdge(nsILineIterator* aLineIterator,
+                                               int32_t aLine,
+                                               nsDirection aDirection);
+
+ public:
+  /**
+   * Called to tell a frame that one of its child frames is dirty (i.e.,
+   * has the NS_FRAME_IS_DIRTY *or* NS_FRAME_HAS_DIRTY_CHILDREN bit
+   * set).  This should always set the NS_FRAME_HAS_DIRTY_CHILDREN on
+   * the frame, and may do other work.
+   */
+  virtual void ChildIsDirty(nsIFrame* aChild);
+
+  /**
+   * Called to retrieve this frame's accessible.
+   * If this frame implements Accessibility return a valid accessible
+   * If not return NS_ERROR_NOT_IMPLEMENTED.
+   * Note: LocalAccessible must be refcountable. Do not implement directly on
+   * your frame Use a mediatior of some kind.
+   */
+#ifdef ACCESSIBILITY
+  virtual mozilla::a11y::AccType AccessibleType();
+#endif
+
+  /**
+   * Get the frame whose style should be the parent of this frame's style (i.e.,
+   * provide the parent style).
+   *
+   * This frame must either be an ancestor of this frame or a child.  If
+   * this returns a child frame, then the child frame must be sure to
+   * return a grandparent or higher!  Furthermore, if a child frame is
+   * returned it must have the same GetContent() as this frame.
+   *
+   * @param aProviderFrame (out) the frame associated with the returned value
+   *     or nullptr if the style is for display:contents content.
+   * @return The style that should be the parent of this frame's style. Null is
+   *         permitted, and means that this frame's style should be the root of
+   *         the style tree.
+   */
+  virtual ComputedStyle* GetParentComputedStyle(
+      nsIFrame** aProviderFrame) const {
+    return DoGetParentComputedStyle(aProviderFrame);
+  }
+
+  /**
+   * Do the work for getting the parent ComputedStyle frame so that
+   * other frame's |GetParentComputedStyle| methods can call this
+   * method on *another* frame.  (This function handles out-of-flow
+   * frames by using the frame manager's placeholder map and it also
+   * handles block-within-inline and generated content wrappers.)
+   *
+   * @param aProviderFrame (out) the frame associated with the returned value
+   *   or null if the ComputedStyle is for display:contents content.
+   * @return The ComputedStyle that should be the parent of this frame's
+   *   ComputedStyle.  Null is permitted, and means that this frame's
+   *   ComputedStyle should be the root of the ComputedStyle tree.
+   */
+  ComputedStyle* DoGetParentComputedStyle(nsIFrame** aProviderFrame) const;
+
+  /**
+   * Adjust the given parent frame to the right ComputedStyle parent frame for
+   * the child, given the pseudo-type of the prospective child.  This handles
+   * things like walking out of table pseudos and so forth.
+   *
+   * @param aProspectiveParent what GetParent() on the child returns.
+   *                           Must not be null.
+   * @param aChildPseudo the child's pseudo type, if any.
+   */
+  static nsIFrame* CorrectStyleParentFrame(
+      nsIFrame* aProspectiveParent, mozilla::PseudoStyleType aChildPseudo);
+
+  /**
+   * Called by RestyleManager to update the style of anonymous boxes
+   * directly associated with this frame.
+   *
+   * The passed-in ServoRestyleState can be used to create new ComputedStyles as
+   * needed, as well as posting changes to the change list.
+   *
+   * It's guaranteed to already have a change in it for this frame and this
+   * frame's content.
+   *
+   * This function will be called after this frame's style has already been
+   * updated.  This function will only be called on frames which have the
+   * NS_FRAME_OWNS_ANON_BOXES bit set.
+   */
+  void UpdateStyleOfOwnedAnonBoxes(mozilla::ServoRestyleState& aRestyleState) {
+    if (HasAnyStateBits(NS_FRAME_OWNS_ANON_BOXES)) {
+      DoUpdateStyleOfOwnedAnonBoxes(aRestyleState);
+    }
+  }
+
+  mozilla::ContainSizeAxes GetContainSizeAxes() const {
+    return StyleDisplay()->GetContainSizeAxes(*this);
+  }
+
+  Maybe<nscoord> ContainIntrinsicBSize(nscoord aNoneValue = 0) const {
+    return GetContainSizeAxes().ContainIntrinsicBSize(*this, aNoneValue);
+  }
+
+  Maybe<nscoord> ContainIntrinsicISize(nscoord aNoneValue = 0) const {
+    return GetContainSizeAxes().ContainIntrinsicISize(*this, aNoneValue);
+  }
+
+ protected:
+  // This does the actual work of UpdateStyleOfOwnedAnonBoxes.  It calls
+  // AppendDirectlyOwnedAnonBoxes to find all of the anonymous boxes
+  // owned by this frame, and then updates styles on each of them.
+  void DoUpdateStyleOfOwnedAnonBoxes(mozilla::ServoRestyleState& aRestyleState);
+
+  // A helper for DoUpdateStyleOfOwnedAnonBoxes for the specific case
+  // of the owned anon box being a child of this frame.
+  void UpdateStyleOfChildAnonBox(nsIFrame* aChildFrame,
+                                 mozilla::ServoRestyleState& aRestyleState);
+
+  // Allow ServoRestyleState to call UpdateStyleOfChildAnonBox.
+  friend class mozilla::ServoRestyleState;
+
+ public:
+  // A helper both for UpdateStyleOfChildAnonBox, and to update frame-backed
+  // pseudo-elements in RestyleManager.
+  //
+  // This gets a ComputedStyle that will be the new style for `aChildFrame`, and
+  // takes care of updating it, calling CalcStyleDifference, and adding to the
+  // change list as appropriate.
+  //
+  // If aContinuationComputedStyle is not Nothing, it should be used for
+  // continuations instead of aNewComputedStyle.  In either case, changehints
+  // are only computed based on aNewComputedStyle.
+  //
+  // Returns the generated change hint for the frame.
+  static nsChangeHint UpdateStyleOfOwnedChildFrame(
+      nsIFrame* aChildFrame, ComputedStyle* aNewComputedStyle,
+      mozilla::ServoRestyleState& aRestyleState,
+      const Maybe<ComputedStyle*>& aContinuationComputedStyle = Nothing());
+
+  struct OwnedAnonBox {
+    typedef void (*UpdateStyleFn)(nsIFrame* aOwningFrame, nsIFrame* aAnonBox,
+                                  mozilla::ServoRestyleState& aRestyleState);
+
+    explicit OwnedAnonBox(nsIFrame* aAnonBoxFrame,
+                          UpdateStyleFn aUpdateStyleFn = nullptr)
+        : mAnonBoxFrame(aAnonBoxFrame), mUpdateStyleFn(aUpdateStyleFn) {}
+
+    nsIFrame* mAnonBoxFrame;
+    UpdateStyleFn mUpdateStyleFn;
+  };
+
+  /**
+   * Appends information about all of the anonymous boxes owned by this frame,
+   * including other anonymous boxes owned by those which this frame owns
+   * directly.
+   */
+  void AppendOwnedAnonBoxes(nsTArray<OwnedAnonBox>& aResult) {
+    if (HasAnyStateBits(NS_FRAME_OWNS_ANON_BOXES)) {
+      if (IsInlineFrame()) {
+        // See comment in nsIFrame::DoUpdateStyleOfOwnedAnonBoxes for why
+        // we skip nsInlineFrames.
+        return;
+      }
+      DoAppendOwnedAnonBoxes(aResult);
+    }
+  }
+
+ protected:
+  // This does the actual work of AppendOwnedAnonBoxes.
+  void DoAppendOwnedAnonBoxes(nsTArray<OwnedAnonBox>& aResult);
+
+ public:
+  /**
+   * Hook subclasses can override to return their owned anonymous boxes.
+   *
+   * This function only appends anonymous boxes that are directly owned by
+   * this frame, i.e. direct children or (for certain frames) a wrapper
+   * parent, unlike AppendOwnedAnonBoxes, which will append all anonymous
+   * boxes transitively owned by this frame.
+   */
+  virtual void AppendDirectlyOwnedAnonBoxes(nsTArray<OwnedAnonBox>& aResult);
+
+  /**
+   * Determines whether a frame is visible for painting;
+   * taking into account whether it is painting a selection or printing.
+   */
+  bool IsVisibleForPainting() const;
+  /**
+   * Determines whether a frame is visible for painting or collapsed;
+   * taking into account whether it is painting a selection or printing,
+   */
+  bool IsVisibleOrCollapsedForPainting() const;
+
+  /**
+   * Determines if this frame is a stacking context.
+   */
+  bool IsStackingContext(const nsStyleDisplay*, const nsStyleEffects*);
+  bool IsStackingContext();
+
+  // Whether we should paint backgrounds or not.
+  struct ShouldPaintBackground {
+    bool mColor = false;
+    bool mImage = false;
+  };
+  ShouldPaintBackground ComputeShouldPaintBackground() const;
+
+  /**
+   * Determine whether the frame is logically empty, which is roughly
+   * whether the layout would be the same whether or not the frame is
+   * present.  Placeholder frames should return true.  Block frames
+   * should be considered empty whenever margins collapse through them,
+   * even though those margins are relevant.  Text frames containing
+   * only whitespace that does not contribute to the height of the line
+   * should return true.
+   */
+  virtual bool IsEmpty();
+  /**
+   * Return the same as IsEmpty(). This may only be called after the frame
+   * has been reflowed and before any further style or content changes.
+   */
+  virtual bool CachedIsEmpty();
+  /**
+   * Determine whether the frame is logically empty, assuming that all
+   * its children are empty.
+   */
+  virtual bool IsSelfEmpty();
+
+  /**
+   * IsGeneratedContentFrame returns whether a frame corresponds to
+   * generated content
+   *
+   * @return whether the frame correspods to generated content
+   */
+  bool IsGeneratedContentFrame() const {
+    return HasAnyStateBits(NS_FRAME_GENERATED_CONTENT);
+  }
+
+  /**
+   * IsPseudoFrame returns whether a frame is a pseudo frame (eg an
+   * anonymous table-row frame created for a CSS table-cell without an
+   * enclosing table-row.
+   *
+   * @param aParentContent the content node corresponding to the parent frame
+   * @return whether the frame is a pseudo frame
+   */
+  bool IsPseudoFrame(const nsIContent* aParentContent) {
+    return mContent == aParentContent;
+  }
+
+  /**
+   * Support for reading and writing properties on the frame.
+   * These call through to the frame's FrameProperties object, if it
+   * exists, but avoid creating it if no property is ever set.
+   */
+  template <typename T>
+  FrameProperties::PropertyType<T> GetProperty(
+      FrameProperties::Descriptor<T> aProperty,
+      bool* aFoundResult = nullptr) const {
+    return mProperties.Get(aProperty, aFoundResult);
+  }
+
+  template <typename T>
+  bool HasProperty(FrameProperties::Descriptor<T> aProperty) const {
+    return mProperties.Has(aProperty);
+  }
+
+  /**
+   * Add a property, or update an existing property for the given descriptor.
+   *
+   * Note: This function asserts if updating an existing nsFrameList property.
+   */
+  template <typename T>
+  void SetProperty(FrameProperties::Descriptor<T> aProperty,
+                   FrameProperties::PropertyType<T> aValue) {
+    if constexpr (std::is_same_v<T, nsFrameList>) {
+      MOZ_ASSERT(aValue, "Shouldn't set nullptr to a nsFrameList property!");
+      MOZ_ASSERT(!HasProperty(aProperty),
+                 "Shouldn't update an existing nsFrameList property!");
+    }
+    mProperties.Set(aProperty, aValue, this);
+  }
+
+  // Unconditionally add a property; use ONLY if the descriptor is known
+  // to NOT already be present.
+  template <typename T>
+  void AddProperty(FrameProperties::Descriptor<T> aProperty,
+                   FrameProperties::PropertyType<T> aValue) {
+    mProperties.Add(aProperty, aValue);
+  }
+
+  /**
+   * Remove a property and return its value without destroying it. May return
+   * nullptr.
+   *
+   * Note: The caller is responsible for handling the life cycle of the returned
+   * value.
+   */
+  template <typename T>
+  [[nodiscard]] FrameProperties::PropertyType<T> TakeProperty(
+      FrameProperties::Descriptor<T> aProperty, bool* aFoundResult = nullptr) {
+    return mProperties.Take(aProperty, aFoundResult);
+  }
+
+  template <typename T>
+  void RemoveProperty(FrameProperties::Descriptor<T> aProperty) {
+    mProperties.Remove(aProperty, this);
+  }
+
+  void RemoveAllProperties() { mProperties.RemoveAll(this); }
+
+  // nsIFrames themselves are in the nsPresArena, and so are not measured here.
+  // Instead, this measures heap-allocated things hanging off the nsIFrame, and
+  // likewise for its descendants.
+  virtual void AddSizeOfExcludingThisForTree(nsWindowSizes& aWindowSizes) const;
+
+  /**
+   * Return true if and only if this frame obeys visibility:hidden.
+   * if it does not, then nsContainerFrame will hide its view even though
+   * this means children can't be made visible again.
+   */
+  virtual bool SupportsVisibilityHidden() { return true; }
+
+  /**
+   * Returns the clip rect set via the 'clip' property, if the 'clip' property
+   * applies to this frame; otherwise returns Nothing(). The 'clip' property
+   * applies to HTML frames if they are absolutely positioned. The 'clip'
+   * property applies to SVG frames regardless of the value of the 'position'
+   * property.
+   *
+   * The coordinates of the returned rectangle are relative to this frame's
+   * origin.
+   */
+  Maybe<nsRect> GetClipPropClipRect(const nsStyleDisplay* aDisp,
+                                    const nsStyleEffects* aEffects,
+                                    const nsSize& aSize) const;
+
+  struct Focusable {
+    bool mFocusable = false;
+    // The computed tab index:
+    //         < 0 if not tabbable
+    //         == 0 if in normal tab order
+    //         > 0 can be tabbed to in the order specified by this value
+    int32_t mTabIndex = -1;
+
+    explicit operator bool() const { return mFocusable; }
+  };
+
+  /**
+   * Check if this frame is focusable and in the current tab order.
+   * Tabbable is indicated by a nonnegative tabindex & is a subset of focusable.
+   * For example, only the selected radio button in a group is in the
+   * tab order, unless the radio group has no selection in which case
+   * all of the visible, non-disabled radio buttons in the group are
+   * in the tab order. On the other hand, all of the visible, non-disabled
+   * radio buttons are always focusable via clicking or script.
+   * Also, depending on the pref accessibility.tabfocus some widgets may be
+   * focusable but removed from the tab order. This is the default on
+   * Mac OS X, where fewer items are focusable.
+   * @param  [in, optional] aWithMouse, is this focus query for mouse clicking
+   * @param  [in, optional] aCheckVisibility, whether to treat an invisible
+   *   frame as not focusable
+   * @return whether the frame is focusable via mouse, kbd or script.
+   */
+  [[nodiscard]] Focusable IsFocusable(bool aWithMouse = false,
+                                      bool aCheckVisibility = true);
+
+ protected:
+  // Helper for IsFocusable.
+  bool IsFocusableDueToScrollFrame();
+
+  /**
+   * Returns true if this box clips its children, e.g., if this box is an
+   * scrollbox or has overflow: clip in both axes.
+   */
+  bool DoesClipChildrenInBothAxes() const;
+
+  /**
+   * NOTE: aStatus is assumed to be already-initialized. The reflow statuses of
+   * any reflowed absolute children will be merged into aStatus; aside from
+   * that, this method won't modify aStatus.
+   */
+  void ReflowAbsoluteFrames(nsPresContext* aPresContext,
+                            ReflowOutput& aDesiredSize,
+                            const ReflowInput& aReflowInput,
+                            nsReflowStatus& aStatus,
+                            bool aConstrainBSize = true);
+
+ private:
+  Maybe<nscoord> ComputeInlineSizeFromAspectRatio(
+      mozilla::WritingMode aWM, const mozilla::LogicalSize& aCBSize,
+      const mozilla::LogicalSize& aContentEdgeToBoxSizing,
+      const mozilla::StyleSizeOverrides& aSizeOverrides,
+      mozilla::ComputeSizeFlags aFlags) const;
+
+ public:
+  /**
+   * @return true if this text frame ends with a newline character.  It
+   * should return false if this is not a text frame.
+   */
+  virtual bool HasSignificantTerminalNewline() const;
+
+  struct CaretPosition {
+    CaretPosition();
+    ~CaretPosition();
+
+    nsCOMPtr<nsIContent> mResultContent;
+    int32_t mContentOffset;
+  };
+
+  /**
+   * gets the first or last possible caret position within the frame
+   *
+   * @param  [in] aStart
+   *         true  for getting the first possible caret position
+   *         false for getting the last possible caret position
+   * @return The caret position in a CaretPosition.
+   *         the returned value is a 'best effort' in case errors
+   *         are encountered rummaging through the frame.
+   */
+  CaretPosition GetExtremeCaretPosition(bool aStart);
+
+  /**
+   * Query whether this frame supports getting a line iterator.
+   * @return true if a line iterator is supported.
+   */
+  virtual bool CanProvideLineIterator() const { return false; }
+
+  /**
+   * Get a line iterator for this frame, if supported.
+   *
+   * @return nullptr if no line iterator is supported.
+   * @note dispose the line iterator using nsILineIterator::DisposeLineIterator
+   */
+  virtual nsILineIterator* GetLineIterator() { return nullptr; }
+
+  /**
+   * If this frame is a next-in-flow, and its prev-in-flow has something on its
+   * overflow list, pull those frames into the child list of this one.
+   */
+  virtual void PullOverflowsFromPrevInFlow() {}
+
+  /**
+   * Accessors for the absolute containing block.
+   */
+  bool IsAbsoluteContainer() const {
+    return !!(mState & NS_FRAME_HAS_ABSPOS_CHILDREN);
+  }
+  bool HasAbsolutelyPositionedChildren() const;
+  nsAbsoluteContainingBlock* GetAbsoluteContainingBlock() const;
+  void MarkAsAbsoluteContainingBlock();
+  void MarkAsNotAbsoluteContainingBlock();
+  // Child frame types override this function to select their own child list
+  // name
+  virtual mozilla::FrameChildListID GetAbsoluteListID() const {
+    return mozilla::FrameChildListID::Absolute;
+  }
+
+  // Checks if we (or any of our descendants) have NS_FRAME_PAINTED_THEBES set,
+  // and clears this bit if so.
+  bool CheckAndClearPaintedState();
+
+  // Checks if we (or any of our descendents) have mBuiltDisplayList set, and
+  // clears this bit if so.
+  bool CheckAndClearDisplayListState();
+
+  // CSS visibility just doesn't cut it because it doesn't inherit through
+  // documents. Also if this frame is in a hidden card of a deck then it isn't
+  // visible either and that isn't expressed using CSS visibility. Also if it
+  // is in a hidden view (there are a few cases left and they are hopefully
+  // going away soon).
+  // If the VISIBILITY_CROSS_CHROME_CONTENT_BOUNDARY flag is passed then we
+  // ignore the chrome/content boundary, otherwise we stop looking when we
+  // reach it.
+  enum { VISIBILITY_CROSS_CHROME_CONTENT_BOUNDARY = 0x01 };
+  bool IsVisibleConsideringAncestors(uint32_t aFlags = 0) const;
+
+  struct FrameWithDistance {
+    nsIFrame* mFrame;
+    nscoord mXDistance;
+    nscoord mYDistance;
+  };
+
+  /**
+   * Finds a frame that is closer to a specified point than a current
+   * distance.  Distance is measured as for text selection -- a closer x
+   * distance beats a closer y distance.
+   *
+   * Normally, this function will only check the distance between this
+   * frame's rectangle and the specified point.  SVGTextFrame overrides
+   * this so that it can manage all of its descendant frames and take
+   * into account any SVG text layout.
+   *
+   * If aPoint is closer to this frame's rectangle than aCurrentBestFrame
+   * indicates, then aCurrentBestFrame is updated with the distance between
+   * aPoint and this frame's rectangle, and with a pointer to this frame.
+   * If aPoint is not closer, then aCurrentBestFrame is left unchanged.
+   *
+   * @param aPoint The point to check for its distance to this frame.
+   * @param aCurrentBestFrame Pointer to a struct that will be updated with
+   *   a pointer to this frame and its distance to aPoint, if this frame
+   *   is indeed closer than the current distance in aCurrentBestFrame.
+   */
+  virtual void FindCloserFrameForSelection(
+      const nsPoint& aPoint, FrameWithDistance* aCurrentBestFrame);
+
+  /**
+   * Is this a flex item? (i.e. a non-abs-pos child of a flex container)
+   */
+  inline bool IsFlexItem() const;
+  /**
+   * Is this a grid item? (i.e. a non-abs-pos child of a grid container)
+   */
+  inline bool IsGridItem() const;
+  /**
+   * Is this a flex or grid item? (i.e. a non-abs-pos child of a flex/grid
+   * container)
+   */
+  inline bool IsFlexOrGridItem() const;
+  inline bool IsFlexOrGridContainer() const;
+
+  /**
+   * Return true if this frame has masonry layout in aAxis.
+   * @note only valid to call on nsGridContainerFrames
+   */
+  inline bool IsMasonry(mozilla::LogicalAxis aAxis) const;
+
+  /**
+   * @return true if this frame is used as a table caption.
+   */
+  inline bool IsTableCaption() const;
+
+  inline bool IsBlockOutside() const;
+  inline bool IsInlineOutside() const;
+  inline mozilla::StyleDisplay GetDisplay() const;
+  inline bool IsFloating() const;
+  inline bool IsAbsPosContainingBlock() const;
+  inline bool IsFixedPosContainingBlock() const;
+  inline bool IsRelativelyOrStickyPositioned() const;
+
+  // Note: In general, you'd want to call IsRelativelyOrStickyPositioned()
+  // unless you want to deal with "position:relative" and "position:sticky"
+  // differently.
+  inline bool IsRelativelyPositioned() const;
+  inline bool IsStickyPositioned() const;
+
+  inline bool IsAbsolutelyPositioned(
+      const nsStyleDisplay* aStyleDisplay = nullptr) const;
+  inline bool IsTrueOverflowContainer() const;
+
+  // Does this frame have "column-span: all" style.
+  //
+  // Note this only checks computed style, but not testing whether the
+  // containing block formatting context was established by a multicol. Callers
+  // need to use IsColumnSpanInMulticolSubtree() to check whether multi-column
+  // effects apply or not.
+  inline bool IsColumnSpan() const;
+
+  // Like IsColumnSpan(), but this also checks whether the frame has a
+  // multi-column ancestor or not.
+  inline bool IsColumnSpanInMulticolSubtree() const;
+
+  /**
+   * Returns the vertical-align value to be used for layout, if it is one
+   * of the enumerated values.  If this is an SVG text frame, it returns a value
+   * that corresponds to the value of dominant-baseline.  If the
+   * vertical-align property has length or percentage value, this returns
+   * Nothing().
+   */
+  Maybe<mozilla::StyleVerticalAlignKeyword> VerticalAlignEnum() const;
+
+  /**
+   * Adds the NS_FRAME_IN_POPUP state bit to aFrame, and
+   * all descendant frames (including cross-doc ones).
+   */
+  static void AddInPopupStateBitToDescendants(nsIFrame* aFrame);
+  /**
+   * Removes the NS_FRAME_IN_POPUP state bit from aFrame and
+   * all descendant frames (including cross-doc ones), unless
+   * the frame is a popup itself.
+   */
+  static void RemoveInPopupStateBitFromDescendants(nsIFrame* aFrame);
+
+  /**
+   * Return true if aFrame is in an {ib} split and is NOT one of the
+   * continuations of the first inline in it.
+   */
+  bool FrameIsNonFirstInIBSplit() const {
+    return HasAnyStateBits(NS_FRAME_PART_OF_IBSPLIT) &&
+           FirstContinuation()->GetProperty(nsIFrame::IBSplitPrevSibling());
+  }
+
+  /**
+   * Return true if aFrame is in an {ib} split and is NOT one of the
+   * continuations of the last inline in it.
+   */
+  bool FrameIsNonLastInIBSplit() const {
+    return HasAnyStateBits(NS_FRAME_PART_OF_IBSPLIT) &&
+           FirstContinuation()->GetProperty(nsIFrame::IBSplitSibling());
+  }
+
+  /**
+   * Return whether this is a frame whose width is used when computing
+   * the font size inflation of its descendants.
+   */
+  bool IsContainerForFontSizeInflation() const {
+    return HasAnyStateBits(NS_FRAME_FONT_INFLATION_CONTAINER);
+  }
+
+  /**
+   * Return whether this frame or any of its children is dirty.
+   */
+  bool IsSubtreeDirty() const {
+    return HasAnyStateBits(NS_FRAME_IS_DIRTY | NS_FRAME_HAS_DIRTY_CHILDREN);
+  }
+
+  /**
+   * Returns true if the frame is an SVGTextFrame or one of its descendants.
+   */
+  bool IsInSVGTextSubtree() const {
+    return HasAnyStateBits(NS_FRAME_IS_SVG_TEXT);
+  }
+
+  /**
+   * Return whether this frame keeps track of overflow areas. (Frames for
+   * non-display SVG elements -- e.g. <clipPath> -- do not maintain overflow
+   * areas, because they're never painted.)
+   */
+  bool FrameMaintainsOverflow() const {
+    return !HasAllStateBits(NS_FRAME_SVG_LAYOUT | NS_FRAME_IS_NONDISPLAY) &&
+           !(IsSVGOuterSVGFrame() && HasAnyStateBits(NS_FRAME_IS_NONDISPLAY));
+  }
+
+  /*
+   * @param aStyleDisplay:  If the caller has this->StyleDisplay(), providing
+   *   it here will improve performance.
+   */
+  bool BackfaceIsHidden(const nsStyleDisplay* aStyleDisplay) const {
+    MOZ_ASSERT(aStyleDisplay == StyleDisplay());
+    return aStyleDisplay->BackfaceIsHidden();
+  }
+  bool BackfaceIsHidden() const { return StyleDisplay()->BackfaceIsHidden(); }
+
+  /**
+   * Returns true if the frame is scrolled out of view.
+   */
+  bool IsScrolledOutOfView() const;
+
+  /**
+   * Computes a 2D matrix from the -moz-window-transform and
+   * -moz-window-transform-origin properties on aFrame.
+   * Values that don't result in a 2D matrix will be ignored and an identity
+   * matrix will be returned instead.
+   */
+  Matrix ComputeWidgetTransform() const;
+
+  /**
+   * @return true iff this frame has one or more associated image requests.
+   * @see mozilla::css::ImageLoader.
+   */
+  bool HasImageRequest() const { return mHasImageRequest; }
+
+  /**
+   * Update this frame's image request state.
+   */
+  void SetHasImageRequest(bool aHasRequest) { mHasImageRequest = aHasRequest; }
+
+  /**
+   * Whether this frame has a first-letter child.  If it does, the frame is
+   * actually an nsContainerFrame and the first-letter frame can be gotten by
+   * walking up to the nearest ancestor blockframe and getting its first
+   * continuation's nsContainerFrame::FirstLetterProperty() property.  This will
+   * only return true for the first continuation of the first-letter's parent.
+   */
+  bool HasFirstLetterChild() const { return mHasFirstLetterChild; }
+
+  /**
+   * Whether this frame's parent is a wrapper anonymous box.  See documentation
+   * for mParentIsWrapperAnonBox.
+   */
+  bool ParentIsWrapperAnonBox() const { return mParentIsWrapperAnonBox; }
+  void SetParentIsWrapperAnonBox() { mParentIsWrapperAnonBox = true; }
+
+  /**
+   * Whether this is a wrapper anonymous box needing a restyle.
+   */
+  bool IsWrapperAnonBoxNeedingRestyle() const {
+    return mIsWrapperBoxNeedingRestyle;
+  }
+  void SetIsWrapperAnonBoxNeedingRestyle(bool aNeedsRestyle) {
+    mIsWrapperBoxNeedingRestyle = aNeedsRestyle;
+  }
+
+  bool MayHaveTransformAnimation() const { return mMayHaveTransformAnimation; }
+  void SetMayHaveTransformAnimation() {
+    AddStateBits(NS_FRAME_MAY_BE_TRANSFORMED);
+    mMayHaveTransformAnimation = true;
+  }
+  bool MayHaveOpacityAnimation() const { return mMayHaveOpacityAnimation; }
+  void SetMayHaveOpacityAnimation() { mMayHaveOpacityAnimation = true; }
+
+  // Returns true if this frame is visible or may have visible descendants.
+  // Note: This function is accurate only on primary frames, because
+  // mAllDescendantsAreInvisible is not updated on continuations.
+  bool IsVisibleOrMayHaveVisibleDescendants() const {
+    return !mAllDescendantsAreInvisible || StyleVisibility()->IsVisible();
+  }
+  // Update mAllDescendantsAreInvisible flag for this frame and ancestors.
+  void UpdateVisibleDescendantsState();
+
+  void UpdateAnimationVisibility();
+
+  /**
+   * If this returns true, the frame it's called on should get the
+   * NS_FRAME_HAS_DIRTY_CHILDREN bit set on it by the caller; either directly
+   * if it's already in reflow, or via calling FrameNeedsReflow() to schedule a
+   * reflow.
+   */
+  virtual bool RenumberFrameAndDescendants(int32_t* aOrdinal, int32_t aDepth,
+                                           int32_t aIncrement,
+                                           bool aForCounting) {
+    return false;
+  }
+
+  enum class ExtremumLength {
+    MinContent,
+    MaxContent,
+    MozAvailable,
+    FitContent,
+    FitContentFunction,
+  };
+
+  template <typename SizeOrMaxSize>
+  static Maybe<ExtremumLength> ToExtremumLength(const SizeOrMaxSize& aSize) {
+    switch (aSize.tag) {
+      case SizeOrMaxSize::Tag::MinContent:
+        return mozilla::Some(ExtremumLength::MinContent);
+      case SizeOrMaxSize::Tag::MaxContent:
+        return mozilla::Some(ExtremumLength::MaxContent);
+      case SizeOrMaxSize::Tag::MozAvailable:
+        return mozilla::Some(ExtremumLength::MozAvailable);
+      case SizeOrMaxSize::Tag::FitContent:
+        return mozilla::Some(ExtremumLength::FitContent);
+      case SizeOrMaxSize::Tag::FitContentFunction:
+        return mozilla::Some(ExtremumLength::FitContentFunction);
+      default:
+        return mozilla::Nothing();
+    }
+  }
+
+  /**
+   * Helper function - computes the content-box inline size for aSize, which is
+   * a more complex version to resolve a StyleExtremumLength.
+   * @param aAvailableISizeOverride If this has a value, it is used as the
+   *                                available inline-size instead of
+   *                                aContainingBlockSize.ISize(aWM) when
+   *                                resolving fit-content.
+   */
+  struct ISizeComputationResult {
+    nscoord mISize = 0;
+    AspectRatioUsage mAspectRatioUsage = AspectRatioUsage::None;
+  };
+  ISizeComputationResult ComputeISizeValue(
+      gfxContext* aRenderingContext, const mozilla::WritingMode aWM,
+      const mozilla::LogicalSize& aContainingBlockSize,
+      const mozilla::LogicalSize& aContentEdgeToBoxSizing,
+      nscoord aBoxSizingToMarginEdge, ExtremumLength aSize,
+      Maybe<nscoord> aAvailableISizeOverride,
+      const mozilla::StyleSizeOverrides& aSizeOverrides,
+      mozilla::ComputeSizeFlags aFlags);
+
+  /**
+   * Helper function - computes the content-box inline size for aSize, which is
+   * a simpler version to resolve a LengthPercentage.
+   */
+  nscoord ComputeISizeValue(const mozilla::WritingMode aWM,
+                            const mozilla::LogicalSize& aContainingBlockSize,
+                            const mozilla::LogicalSize& aContentEdgeToBoxSizing,
+                            const LengthPercentage& aSize);
+
+  template <typename SizeOrMaxSize>
+  ISizeComputationResult ComputeISizeValue(
+      gfxContext* aRenderingContext, const mozilla::WritingMode aWM,
+      const mozilla::LogicalSize& aContainingBlockSize,
+      const mozilla::LogicalSize& aContentEdgeToBoxSizing,
+      nscoord aBoxSizingToMarginEdge, const SizeOrMaxSize& aSize,
+      const mozilla::StyleSizeOverrides& aSizeOverrides = {},
+      mozilla::ComputeSizeFlags aFlags = {}) {
+    if (aSize.IsLengthPercentage()) {
+      return {ComputeISizeValue(aWM, aContainingBlockSize,
+                                aContentEdgeToBoxSizing,
+                                aSize.AsLengthPercentage())};
+    }
+    auto length = ToExtremumLength(aSize);
+    MOZ_ASSERT(length, "This doesn't handle none / auto");
+    Maybe<nscoord> availbleISizeOverride;
+    if (aSize.IsFitContentFunction()) {
+      availbleISizeOverride.emplace(aSize.AsFitContentFunction().Resolve(
+          aContainingBlockSize.ISize(aWM)));
+    }
+    return ComputeISizeValue(aRenderingContext, aWM, aContainingBlockSize,
+                             aContentEdgeToBoxSizing, aBoxSizingToMarginEdge,
+                             length.valueOr(ExtremumLength::MinContent),
+                             availbleISizeOverride, aSizeOverrides, aFlags);
+  }
+
+  DisplayItemArray& DisplayItems() { return mDisplayItems; }
+  const DisplayItemArray& DisplayItems() const { return mDisplayItems; }
+
+  void AddDisplayItem(nsDisplayItem* aItem);
+  bool RemoveDisplayItem(nsDisplayItem* aItem);
+  void RemoveDisplayItemDataForDeletion();
+  bool HasDisplayItems();
+  bool HasDisplayItem(nsDisplayItem* aItem);
+  bool HasDisplayItem(uint32_t aKey);
+
+  static void PrintDisplayList(nsDisplayListBuilder* aBuilder,
+                               const nsDisplayList& aList,
+                               bool aDumpHtml = false);
+  static void PrintDisplayList(nsDisplayListBuilder* aBuilder,
+                               const nsDisplayList& aList,
+                               std::stringstream& aStream,
+                               bool aDumpHtml = false);
+  static void PrintDisplayItem(nsDisplayListBuilder* aBuilder,
+                               nsDisplayItem* aItem, std::stringstream& aStream,
+                               uint32_t aIndent = 0, bool aDumpSublist = false,
+                               bool aDumpHtml = false);
+#ifdef MOZ_DUMP_PAINTING
+  static void PrintDisplayListSet(nsDisplayListBuilder* aBuilder,
+                                  const nsDisplayListSet& aSet,
+                                  std::stringstream& aStream,
+                                  bool aDumpHtml = false);
+#endif
+
+  /**
+   * Adds display items for standard CSS background if necessary.
+   * Does not check IsVisibleForPainting.
+   * @return whether a themed background item was created.
+   */
+  bool DisplayBackgroundUnconditional(nsDisplayListBuilder* aBuilder,
+                                      const nsDisplayListSet& aLists);
+  /**
+   * Adds display items for standard CSS borders, background and outline for
+   * for this frame, as necessary. Checks IsVisibleForPainting and won't
+   * display anything if the frame is not visible.
+   */
+  void DisplayBorderBackgroundOutline(nsDisplayListBuilder* aBuilder,
+                                      const nsDisplayListSet& aLists);
+  /**
+   * Add a display item for the CSS outline. Does not check visibility.
+   */
+  void DisplayOutlineUnconditional(nsDisplayListBuilder* aBuilder,
+                                   const nsDisplayListSet& aLists);
+  /**
+   * Add a display item for the CSS outline, after calling
+   * IsVisibleForPainting to confirm we are visible.
+   */
+  void DisplayOutline(nsDisplayListBuilder* aBuilder,
+                      const nsDisplayListSet& aLists);
+
+  /**
+   * Add a display item for CSS inset box shadows. Does not check visibility.
+   */
+  void DisplayInsetBoxShadowUnconditional(nsDisplayListBuilder* aBuilder,
+                                          nsDisplayList* aList);
+
+  /**
+   * Add a display item for CSS inset box shadow, after calling
+   * IsVisibleForPainting to confirm we are visible.
+   */
+  void DisplayInsetBoxShadow(nsDisplayListBuilder* aBuilder,
+                             nsDisplayList* aList);
+
+  /**
+   * Add a display item for CSS outset box shadows. Does not check visibility.
+   */
+  void DisplayOutsetBoxShadowUnconditional(nsDisplayListBuilder* aBuilder,
+                                           nsDisplayList* aList);
+
+  /**
+   * Add a display item for CSS outset box shadow, after calling
+   * IsVisibleForPainting to confirm we are visible.
+   */
+  void DisplayOutsetBoxShadow(nsDisplayListBuilder* aBuilder,
+                              nsDisplayList* aList);
+
+  bool ForceDescendIntoIfVisible() const { return mForceDescendIntoIfVisible; }
+  void SetForceDescendIntoIfVisible(bool aForce) {
+    mForceDescendIntoIfVisible = aForce;
+  }
+
+  bool BuiltDisplayList() const { return mBuiltDisplayList; }
+  void SetBuiltDisplayList(const bool aBuilt) { mBuiltDisplayList = aBuilt; }
+
+  bool IsFrameModified() const { return mFrameIsModified; }
+  void SetFrameIsModified(const bool aFrameIsModified) {
+    mFrameIsModified = aFrameIsModified;
+  }
+
+  bool HasModifiedDescendants() const { return mHasModifiedDescendants; }
+  void SetHasModifiedDescendants(const bool aHasModifiedDescendants) {
+    mHasModifiedDescendants = aHasModifiedDescendants;
+  }
+
+  bool HasOverrideDirtyRegion() const { return mHasOverrideDirtyRegion; }
+  void SetHasOverrideDirtyRegion(const bool aHasDirtyRegion) {
+    mHasOverrideDirtyRegion = aHasDirtyRegion;
+  }
+
+  bool MayHaveWillChangeBudget() const { return mMayHaveWillChangeBudget; }
+  void SetMayHaveWillChangeBudget(const bool aHasBudget) {
+    mMayHaveWillChangeBudget = aHasBudget;
+  }
+
+  bool HasBSizeChange() const { return mHasBSizeChange; }
+  void SetHasBSizeChange(const bool aHasBSizeChange) {
+    mHasBSizeChange = aHasBSizeChange;
+  }
+
+  bool HasPaddingChange() const { return mHasPaddingChange; }
+  void SetHasPaddingChange(const bool aHasPaddingChange) {
+    mHasPaddingChange = aHasPaddingChange;
+  }
+
+  bool HasColumnSpanSiblings() const { return mHasColumnSpanSiblings; }
+  void SetHasColumnSpanSiblings(bool aHasColumnSpanSiblings) {
+    mHasColumnSpanSiblings = aHasColumnSpanSiblings;
+  }
+
+  bool DescendantMayDependOnItsStaticPosition() const {
+    return mDescendantMayDependOnItsStaticPosition;
+  }
+  void SetDescendantMayDependOnItsStaticPosition(bool aValue) {
+    mDescendantMayDependOnItsStaticPosition = aValue;
+  }
+
+  bool ShouldGenerateComputedInfo() const {
+    return mShouldGenerateComputedInfo;
+  }
+  void SetShouldGenerateComputedInfo(bool aValue) {
+    mShouldGenerateComputedInfo = aValue;
+  }
+
+  /**
+   * Returns the hit test area of the frame.
+   */
+  nsRect GetCompositorHitTestArea(nsDisplayListBuilder* aBuilder);
+
+  /**
+   * Returns the set of flags indicating the properties of the frame that the
+   * compositor might care about for hit-testing purposes. Note that this
+   * function must be called during Gecko display list construction time (i.e
+   * while the frame tree is being traversed) because that is when the display
+   * list builder has the necessary state set up correctly.
+   */
+  mozilla::gfx::CompositorHitTestInfo GetCompositorHitTestInfo(
+      nsDisplayListBuilder* aBuilder);
+
+  /**
+   * Copies aWM to mWritingMode on 'this' and all its ancestors.
+   */
+  inline void PropagateWritingModeToSelfAndAncestors(mozilla::WritingMode aWM);
+
+  /**
+   * Observes or unobserves the element with an internal ResizeObserver,
+   * depending on whether it needs to update its last remembered size.
+   * Also removes a previously stored last remembered size if the element
+   * can no longer have it.
+   * @see {@link https://drafts.csswg.org/css-sizing-4/#last-remembered}
+   */
+  void HandleLastRememberedSize();
+
+ protected:
+  /**
+   * Reparent this frame's view if it has one.
+   */
+  void ReparentFrameViewTo(nsViewManager* aViewManager, nsView* aNewParentView);
+
+  // Members
+  nsRect mRect;
+  nsCOMPtr<nsIContent> mContent;
+  RefPtr<ComputedStyle> mComputedStyle;
+
+ private:
+  nsPresContext* const mPresContext;
+  nsContainerFrame* mParent;
+  nsIFrame* mNextSibling;  // doubly-linked list of frames
+  nsIFrame* mPrevSibling;  // Do not touch outside SetNextSibling!
+
+  DisplayItemArray mDisplayItems;
+
+  void MarkAbsoluteFramesForDisplayList(nsDisplayListBuilder* aBuilder);
+
+ protected:
+  void MarkInReflow() {
+#ifdef DEBUG_dbaron_off
+    // bug 81268
+    NS_ASSERTION(!(mState & NS_FRAME_IN_REFLOW), "frame is already in reflow");
+#endif
+    AddStateBits(NS_FRAME_IN_REFLOW);
+  }
+
+ private:
+  nsFrameState mState;
+
+ protected:
+  /**
+   * List of properties attached to the frame.
+   */
+  FrameProperties mProperties;
+
+  // When there is no scrollable overflow area, and the ink overflow area only
+  // slightly larger than mRect, the ink overflow area may be stored a set of
+  // four 1-byte deltas from the edges of mRect rather than allocating a whole
+  // separate rectangle property. If all four deltas are zero, this means that
+  // no overflow area has actually been set (this is the initial state of
+  // newly-created frames).
+  //
+  // Note that these are unsigned values, all measured "outwards" from the edges
+  // of mRect, so mLeft and mTop are reversed from our normal coordinate system.
+  struct InkOverflowDeltas {
+    // The maximum delta value we can store in any of the four edges.
+    static constexpr uint8_t kMax = 0xfe;
+
+    uint8_t mLeft;
+    uint8_t mTop;
+    uint8_t mRight;
+    uint8_t mBottom;
+    bool operator==(const InkOverflowDeltas& aOther) const {
+      return mLeft == aOther.mLeft && mTop == aOther.mTop &&
+             mRight == aOther.mRight && mBottom == aOther.mBottom;
+    }
+    bool operator!=(const InkOverflowDeltas& aOther) const {
+      return !(*this == aOther);
+    }
+  };
+  enum class OverflowStorageType : uint32_t {
+    // No overflow area; code relies on this being an all-zero value.
+    None = 0x00000000u,
+
+    // Ink overflow is too large to stored in InkOverflowDeltas.
+    Large = 0x000000ffu,
+  };
+  // If mOverflow.mType is OverflowStorageType::Large, then the delta values are
+  // not meaningful and the overflow area is stored in OverflowAreasProperty()
+  // instead.
+  union {
+    OverflowStorageType mType;
+    InkOverflowDeltas mInkOverflowDeltas;
+  } mOverflow;
+
+  /** @see GetWritingMode() */
+  mozilla::WritingMode mWritingMode;
+
+  /** The ClassID of the concrete class of this instance. */
+  ClassID mClass;  // 1 byte
+
+  bool mMayHaveRoundedCorners : 1;
+
+  /**
+   * True iff this frame has one or more associated image requests.
+   * @see mozilla::css::ImageLoader.
+   */
+  bool mHasImageRequest : 1;
+
+  /**
+   * True if this frame has a continuation that has a first-letter frame, or its
+   * placeholder, as a child.  In that case this frame has a blockframe ancestor
+   * that has the first-letter frame hanging off it in the
+   * nsContainerFrame::FirstLetterProperty() property.
+   */
+  bool mHasFirstLetterChild : 1;
+
+  /**
+   * True if this frame's parent is a wrapper anonymous box (e.g. a table
+   * anonymous box as specified at
+   * <https://www.w3.org/TR/CSS21/tables.html#anonymous-boxes>).
+   *
+   * We could compute this information directly when we need it, but it wouldn't
+   * be all that cheap, and since this information is immutable for the lifetime
+   * of the frame we might as well cache it.
+   *
+   * Note that our parent may itself have mParentIsWrapperAnonBox set to true.
+   */
+  bool mParentIsWrapperAnonBox : 1;
+
+  /**
+   * True if this is a wrapper anonymous box needing a restyle.  This is used to
+   * track, during stylo post-traversal, whether we've already recomputed the
+   * style of this anonymous box, if we end up seeing it twice.
+   */
+  bool mIsWrapperBoxNeedingRestyle : 1;
+
+  /**
+   * This bit is used in nsTextFrame::CharacterDataChanged() as an optimization
+   * to skip redundant reflow-requests when the character data changes multiple
+   * times between reflows. If this flag is set, then it implies that the
+   * NS_FRAME_IS_DIRTY state bit is also set (and that intrinsic sizes have
+   * been marked as dirty on our ancestor chain).
+   *
+   * XXXdholbert This bit is *only* used on nsTextFrame, but it lives here on
+   * nsIFrame simply because this is where we've got unused state bits
+   * available in a gap. If bits become more scarce, we should perhaps consider
+   * expanding the range of frame-specific state bits in nsFrameStateBits.h and
+   * moving this to be one of those (e.g. by swapping one of the adjacent
+   * general-purpose bits to take the place of this bool:1 here, so we can grow
+   * that range of frame-specific bits by 1).
+   */
+  bool mReflowRequestedForCharDataChange : 1;
+
+  /**
+   * This bit is used during BuildDisplayList to mark frames that need to
+   * have display items rebuilt. We will descend into them if they are
+   * currently visible, even if they don't intersect the dirty area.
+   */
+  bool mForceDescendIntoIfVisible : 1;
+
+  /**
+   * True if we have built display items for this frame since
+   * the last call to CheckAndClearDisplayListState, false
+   * otherwise. Used for the reftest harness to verify minimal
+   * display list building.
+   */
+  bool mBuiltDisplayList : 1;
+
+  /**
+   * True if the frame has been marked modified by
+   * |MarkNeedsDisplayItemRebuild()|, usually due to a style change or reflow.
+   */
+  bool mFrameIsModified : 1;
+
+  /**
+   * True if the frame has modified descendants. Set before display list
+   * preprocessing and only used during partial display list builds.
+   */
+  bool mHasModifiedDescendants : 1;
+
+  /**
+   * Used by merging based retained display lists to restrict the dirty area
+   * during partial display list builds.
+   */
+  bool mHasOverrideDirtyRegion : 1;
+
+  /**
+   * True if frame has will-change, and currently has display
+   * items consuming some of the will-change budget.
+   */
+  bool mMayHaveWillChangeBudget : 1;
+
+#ifdef DEBUG
+ public:
+  /**
+   * True if this frame has already been been visited by
+   * nsCSSFrameConstructor::AutoFrameConstructionPageName.
+   *
+   * This is used to assert that we have visited each frame only once, and is
+   * not useful otherwise.
+   */
+  bool mWasVisitedByAutoFrameConstructionPageName : 1;
+#endif
+
+ private:
+  /**
+   * True if this is the primary frame for mContent.
+   */
+  bool mIsPrimaryFrame : 1;
+
+  bool mMayHaveTransformAnimation : 1;
+  bool mMayHaveOpacityAnimation : 1;
+
+  /**
+   * True if we are certain that all descendants are not visible.
+   *
+   * This flag is conservative in that it might sometimes be false even if, in
+   * fact, all descendants are invisible.
+   * For example; an element is visibility:visible and has a visibility:hidden
+   * child. This flag is stil false in such case.
+   */
+  bool mAllDescendantsAreInvisible : 1;
+
+  bool mHasBSizeChange : 1;
+
+  /**
+   * True if the frame seems to be in the process of being reflowed with a
+   * different amount of inline-axis padding as compared to its most recent
+   * reflow. This flag's purpose is to detect cases where the frame's
+   * inline-axis content-box-size has changed, without any style change or any
+   * change to the border-box size, so that we can mark/invalidate things
+   * appropriately in ReflowInput::InitResizeFlags().
+   *
+   * This flag is set in SizeComputationResult::InitOffsets() and cleared in
+   * nsIFrame::DidReflow().
+   */
+  bool mHasPaddingChange : 1;
+
+  /**
+   * True if we are or contain the scroll anchor for a scrollable frame.
+   */
+  bool mInScrollAnchorChain : 1;
+
+  /**
+   * Suppose a frame was split into multiple parts to separate parts containing
+   * column-spans from parts not containing column-spans. This bit is set on all
+   * continuations *not* containing column-spans except for the those after the
+   * last column-span/non-column-span boundary (i.e., the bit really means it
+   * has a *later* sibling across a split). Note that the last part is always
+   * created to containing no columns-spans even if it has no children. See
+   * nsCSSFrameConstructor::CreateColumnSpanSiblings() for the implementation.
+   *
+   * If the frame having this bit set is removed, we need to reframe the
+   * multi-column container.
+   */
+  bool mHasColumnSpanSiblings : 1;
+
+  /**
+   * True if we may have any descendant whose positioning may depend on its
+   * static position (and thus which we need to recompute the position for if we
+   * move).
+   */
+  bool mDescendantMayDependOnItsStaticPosition : 1;
+
+  /**
+   * True if the next reflow of this frame should generate computed info
+   * metrics. These are used by devtools to reveal details of the layout
+   * process.
+   */
+  bool mShouldGenerateComputedInfo : 1;
+
+ protected:
+  // Helpers
+  /**
+   * Can we stop inside this frame when we're skipping non-rendered whitespace?
+   *
+   * @param aForward [in] Are we moving forward (or backward) in content order.
+   *
+   * @param aOffset [in/out] At what offset into the frame to start looking.
+   * at offset was reached (whether or not we found a place to stop).
+   *
+   * @return
+   *   * STOP: An appropriate offset was found within this frame,
+   *     and is given by aOffset.
+   *   * CONTINUE: Not found within this frame, need to try the next frame.
+   *     See enum FrameSearchResult for more details.
+   */
+  virtual FrameSearchResult PeekOffsetNoAmount(bool aForward, int32_t* aOffset);
+
+  /**
+   * Search the frame for the next character
+   *
+   * @param aForward [in] Are we moving forward (or backward) in content order.
+   *
+   * @param aOffset [in/out] At what offset into the frame to start looking.
+   * on output - what offset was reached (whether or not we found a place to
+   * stop).
+   *
+   * @param aOptions [in] Options, see the comment in PeekOffsetCharacterOptions
+   * for the detail.
+   *
+   * @return
+   *   * STOP: An appropriate offset was found within this frame, and is given
+   *     by aOffset.
+   *   * CONTINUE: Not found within this frame, need to try the next frame. See
+   *     enum FrameSearchResult for more details.
+   */
+  virtual FrameSearchResult PeekOffsetCharacter(
+      bool aForward, int32_t* aOffset,
+      PeekOffsetCharacterOptions aOptions = PeekOffsetCharacterOptions());
+  static_assert(sizeof(PeekOffsetCharacterOptions) <= sizeof(intptr_t),
+                "aOptions should be changed to const reference");
+
+  struct PeekWordState {
+    // true when we're still at the start of the search, i.e., we can't return
+    // this point as a valid offset!
+    bool mAtStart;
+    // true when we've encountered at least one character of the type before the
+    // boundary we're looking for:
+    // 1. If we're moving forward and eating whitepace, looking for a word
+    //    beginning (i.e. a boundary between whitespace and non-whitespace),
+    //    then mSawBeforeType==true means "we already saw some whitespace".
+    // 2. Otherwise, looking for a word beginning (i.e. a boundary between
+    //    non-whitespace and whitespace), then mSawBeforeType==true means "we
+    //    already saw some non-whitespace".
+    bool mSawBeforeType;
+    // true when we've encountered at least one non-newline character
+    bool mSawInlineCharacter;
+    // true when the last character encountered was punctuation
+    bool mLastCharWasPunctuation;
+    // true when the last character encountered was whitespace
+    bool mLastCharWasWhitespace;
+    // true when we've seen non-punctuation since the last whitespace
+    bool mSeenNonPunctuationSinceWhitespace;
+    // text that's *before* the current frame when aForward is true, *after*
+    // the current frame when aForward is false. Only includes the text
+    // on the current line.
+    nsAutoString mContext;
+
+    PeekWordState()
+        : mAtStart(true),
+          mSawBeforeType(false),
+          mSawInlineCharacter(false),
+          mLastCharWasPunctuation(false),
+          mLastCharWasWhitespace(false),
+          mSeenNonPunctuationSinceWhitespace(false) {}
+    void SetSawBeforeType() { mSawBeforeType = true; }
+    void SetSawInlineCharacter() { mSawInlineCharacter = true; }
+    void Update(bool aAfterPunctuation, bool aAfterWhitespace) {
+      mLastCharWasPunctuation = aAfterPunctuation;
+      mLastCharWasWhitespace = aAfterWhitespace;
+      if (aAfterWhitespace) {
+        mSeenNonPunctuationSinceWhitespace = false;
+      } else if (!aAfterPunctuation) {
+        mSeenNonPunctuationSinceWhitespace = true;
+      }
+      mAtStart = false;
+    }
+  };
+
+  /**
+   * Search the frame for the next word boundary
+   * @param  aForward [in] Are we moving forward (or backward) in content order.
+   * @param  aWordSelectEatSpace [in] true: look for non-whitespace following
+   *         whitespace (in the direction of movement).
+   *         false: look for whitespace following non-whitespace (in the
+   *         direction  of movement).
+   * @param  aIsKeyboardSelect [in] Was the action initiated by a keyboard
+   * operation? If true, punctuation immediately following a word is considered
+   * part of that word. Otherwise, a sequence of punctuation is always
+   * considered as a word on its own.
+   * @param  aOffset [in/out] At what offset into the frame to start looking.
+   *         on output - what offset was reached (whether or not we found a
+   * place to stop).
+   * @param  aState [in/out] the state that is carried from frame to frame
+   */
+  virtual FrameSearchResult PeekOffsetWord(
+      bool aForward, bool aWordSelectEatSpace, bool aIsKeyboardSelect,
+      int32_t* aOffset, PeekWordState* aState, bool aTrimSpaces);
+
+ protected:
+  /**
+   * Check whether we should break at a boundary between punctuation and
+   * non-punctuation. Only call it at a punctuation boundary
+   * (i.e. exactly one of the previous and next characters are punctuation).
+   * @param aForward true if we're moving forward in content order
+   * @param aPunctAfter true if the next character is punctuation
+   * @param aWhitespaceAfter true if the next character is whitespace
+   */
+  static bool BreakWordBetweenPunctuation(const PeekWordState* aState,
+                                          bool aForward, bool aPunctAfter,
+                                          bool aWhitespaceAfter,
+                                          bool aIsKeyboardSelect);
+
+ private:
+  nsRect GetOverflowRect(mozilla::OverflowType aType) const;
+
+  // Get a pointer to the overflow areas property attached to the frame.
+  mozilla::OverflowAreas* GetOverflowAreasProperty() const {
+    MOZ_ASSERT(mOverflow.mType == OverflowStorageType::Large);
+    mozilla::OverflowAreas* overflow = GetProperty(OverflowAreasProperty());
+    MOZ_ASSERT(overflow);
+    return overflow;
+  }
+
+  nsRect InkOverflowFromDeltas() const {
+    MOZ_ASSERT(mOverflow.mType != OverflowStorageType::Large,
+               "should not be called when overflow is in a property");
+    // Calculate the rect using deltas from the frame's border rect.
+    // Note that the mOverflow.mInkOverflowDeltas fields are unsigned, but we
+    // will often need to return negative values for the left and top, so take
+    // care to cast away the unsigned-ness.
+    return nsRect(-(int32_t)mOverflow.mInkOverflowDeltas.mLeft,
+                  -(int32_t)mOverflow.mInkOverflowDeltas.mTop,
+                  mRect.Width() + mOverflow.mInkOverflowDeltas.mRight +
+                      mOverflow.mInkOverflowDeltas.mLeft,
+                  mRect.Height() + mOverflow.mInkOverflowDeltas.mBottom +
+                      mOverflow.mInkOverflowDeltas.mTop);
+  }
+
+  /**
+   * Set the OverflowArea rect, storing it as deltas or a separate rect
+   * depending on its size in relation to the primary frame rect.
+   *
+   * @return true if any overflow changed.
+   */
+  bool SetOverflowAreas(const mozilla::OverflowAreas& aOverflowAreas);
+
+  bool HasOpacityInternal(float aThreshold, const nsStyleDisplay* aStyleDisplay,
+                          const nsStyleEffects* aStyleEffects,
+                          mozilla::EffectSet* aEffectSet = nullptr) const;
+
+  // Maps mClass to LayoutFrameType.
+  static const mozilla::LayoutFrameType sLayoutFrameTypes[
+#define FRAME_ID(...) 1 +
+#define ABSTRACT_FRAME_ID(...)
+#include "mozilla/FrameIdList.h"
+#undef FRAME_ID
+#undef ABSTRACT_FRAME_ID
+      0];
+
+  enum FrameClassBits {
+    eFrameClassBitsNone = 0x0,
+    eFrameClassBitsLeaf = 0x1,
+    eFrameClassBitsDynamicLeaf = 0x2,
+  };
+  // Maps mClass to IsLeaf() flags.
+  static const FrameClassBits sFrameClassBits[
+#define FRAME_ID(...) 1 +
+#define ABSTRACT_FRAME_ID(...)
+#include "mozilla/FrameIdList.h"
+#undef FRAME_ID
+#undef ABSTRACT_FRAME_ID
+      0];
+
+#ifdef DEBUG_FRAME_DUMP
+ public:
+  static void IndentBy(FILE* out, int32_t aIndent) {
+    while (--aIndent >= 0) fputs("  ", out);
+  }
+  void ListTag(FILE* out) const { fputs(ListTag().get(), out); }
+  nsAutoCString ListTag() const;
+
+  enum class ListFlag{TraverseSubdocumentFrames, DisplayInCSSPixels};
+  using ListFlags = mozilla::EnumSet<ListFlag>;
+
+  template <typename T>
+  static std::string ConvertToString(const T& aValue, ListFlags aFlags) {
+    // This method can convert all physical types in app units to CSS pixels.
+    return aFlags.contains(ListFlag::DisplayInCSSPixels)
+               ? mozilla::ToString(mozilla::CSSPixel::FromAppUnits(aValue))
+               : mozilla::ToString(aValue);
+  }
+  static std::string ConvertToString(const mozilla::LogicalRect& aRect,
+                                     const mozilla::WritingMode aWM,
+                                     ListFlags aFlags);
+  static std::string ConvertToString(const mozilla::LogicalSize& aSize,
+                                     const mozilla::WritingMode aWM,
+                                     ListFlags aFlags);
+
+  void ListGeneric(nsACString& aTo, const char* aPrefix = "",
+                   ListFlags aFlags = ListFlags()) const;
+  virtual void List(FILE* out = stderr, const char* aPrefix = "",
+                    ListFlags aFlags = ListFlags()) const;
+
+  void ListTextRuns(FILE* out = stderr) const;
+  virtual void ListTextRuns(FILE* out, nsTHashSet<const void*>& aSeen) const;
+
+  virtual void ListWithMatchedRules(FILE* out = stderr,
+                                    const char* aPrefix = "") const;
+  void ListMatchedRules(FILE* out, const char* aPrefix) const;
+
+  /**
+   * Dump the frame tree beginning from the root frame.
+   */
+  void DumpFrameTree() const;
+  void DumpFrameTreeInCSSPixels() const;
+
+  /**
+   * Dump the frame tree beginning from ourselves.
+   */
+  void DumpFrameTreeLimited() const;
+  void DumpFrameTreeLimitedInCSSPixels() const;
+
+  /**
+   * Get a printable from of the name of the frame type.
+   * XXX This should be eliminated and we use GetType() instead...
+   */
+  virtual nsresult GetFrameName(nsAString& aResult) const;
+  nsresult MakeFrameName(const nsAString& aType, nsAString& aResult) const;
+  // Helper function to return the index in parent of the frame's content
+  // object. Returns Nothing on error or if the frame doesn't have a content
+  // object
+  static mozilla::Maybe<uint32_t> ContentIndexInContainer(
+      const nsIFrame* aFrame);
+#endif
+
+#ifdef DEBUG
+  /**
+   * Tracing method that writes a method enter/exit routine to the
+   * nspr log using the nsIFrame log module. The tracing is only
+   * done when the NS_FRAME_TRACE_CALLS bit is set in the log module's
+   * level field.
+   */
+  void Trace(const char* aMethod, bool aEnter);
+  void Trace(const char* aMethod, bool aEnter, const nsReflowStatus& aStatus);
+  void TraceMsg(const char* aFormatString, ...) MOZ_FORMAT_PRINTF(2, 3);
+
+  // Helper function that verifies that each frame in the list has the
+  // NS_FRAME_IS_DIRTY bit set
+  static void VerifyDirtyBitSet(const nsFrameList& aFrameList);
+
+  // Display Reflow Debugging
+  static void* DisplayReflowEnter(nsPresContext* aPresContext, nsIFrame* aFrame,
+                                  const ReflowInput& aReflowInput);
+  static void* DisplayLayoutEnter(nsIFrame* aFrame);
+  static void* DisplayIntrinsicISizeEnter(nsIFrame* aFrame, const char* aType);
+  static void* DisplayIntrinsicSizeEnter(nsIFrame* aFrame, const char* aType);
+  static void DisplayReflowExit(nsPresContext* aPresContext, nsIFrame* aFrame,
+                                ReflowOutput& aMetrics,
+                                const nsReflowStatus& aStatus,
+                                void* aFrameTreeNode);
+  static void DisplayLayoutExit(nsIFrame* aFrame, void* aFrameTreeNode);
+  static void DisplayIntrinsicISizeExit(nsIFrame* aFrame, const char* aType,
+                                        nscoord aResult, void* aFrameTreeNode);
+  static void DisplayIntrinsicSizeExit(nsIFrame* aFrame, const char* aType,
+                                       nsSize aResult, void* aFrameTreeNode);
+
+  static void DisplayReflowStartup();
+  static void DisplayReflowShutdown();
+
+  static mozilla::LazyLogModule sFrameLogModule;
+#endif
+};
+
+MOZ_MAKE_ENUM_CLASS_BITWISE_OPERATORS(nsIFrame::ReflowChildFlags)
+
+//----------------------------------------------------------------------
+
+/**
+ * AutoWeakFrame can be used to keep a reference to a nsIFrame in a safe way.
+ * Whenever an nsIFrame object is deleted, the AutoWeakFrames pointing
+ * to it will be cleared.  AutoWeakFrame is for variables on the stack or
+ * in static storage only, there is also a WeakFrame below for heap uses.
+ *
+ * Create AutoWeakFrame object when it is sure that nsIFrame object
+ * is alive and after some operations which may destroy the nsIFrame
+ * (for example any DOM modifications) use IsAlive() or GetFrame() methods to
+ * check whether it is safe to continue to use the nsIFrame object.
+ *
+ * @note The usage of this class should be kept to a minimum.
+ */
+class WeakFrame;
+class MOZ_NONHEAP_CLASS AutoWeakFrame {
+ public:
+  explicit AutoWeakFrame() : mPrev(nullptr), mFrame(nullptr) {}
+
+  AutoWeakFrame(const AutoWeakFrame& aOther) : mPrev(nullptr), mFrame(nullptr) {
+    Init(aOther.GetFrame());
+  }
+
+  MOZ_IMPLICIT AutoWeakFrame(const WeakFrame& aOther);
+
+  MOZ_IMPLICIT AutoWeakFrame(nsIFrame* aFrame)
+      : mPrev(nullptr), mFrame(nullptr) {
+    Init(aFrame);
+  }
+
+  AutoWeakFrame& operator=(AutoWeakFrame& aOther) {
+    Init(aOther.GetFrame());
+    return *this;
+  }
+
+  AutoWeakFrame& operator=(nsIFrame* aFrame) {
+    Init(aFrame);
+    return *this;
+  }
+
+  nsIFrame* operator->() { return mFrame; }
+
+  operator nsIFrame*() { return mFrame; }
+
+  void Clear(mozilla::PresShell* aPresShell);
+
+  bool IsAlive() const { return !!mFrame; }
+
+  nsIFrame* GetFrame() const { return mFrame; }
+
+  AutoWeakFrame* GetPreviousWeakFrame() { return mPrev; }
+
+  void SetPreviousWeakFrame(AutoWeakFrame* aPrev) { mPrev = aPrev; }
+
+  ~AutoWeakFrame();
+
+ private:
+  // Not available for the heap!
+  void* operator new(size_t) = delete;
+  void* operator new[](size_t) = delete;
+  void operator delete(void*) = delete;
+  void operator delete[](void*) = delete;
+
+  void Init(nsIFrame* aFrame);
+
+  AutoWeakFrame* mPrev;
+  nsIFrame* mFrame;
+};
+
+// Use nsIFrame's fast-path to avoid QueryFrame:
+inline do_QueryFrameHelper<nsIFrame> do_QueryFrame(AutoWeakFrame& s) {
+  return do_QueryFrameHelper<nsIFrame>(s.GetFrame());
+}
+
+/**
+ * @see AutoWeakFrame
+ */
+class MOZ_HEAP_CLASS WeakFrame {
+ public:
+  WeakFrame() : mFrame(nullptr) {}
+
+  WeakFrame(const WeakFrame& aOther) : mFrame(nullptr) {
+    Init(aOther.GetFrame());
+  }
+
+  MOZ_IMPLICIT WeakFrame(const AutoWeakFrame& aOther) : mFrame(nullptr) {
+    Init(aOther.GetFrame());
+  }
+
+  MOZ_IMPLICIT WeakFrame(nsIFrame* aFrame) : mFrame(nullptr) { Init(aFrame); }
+
+  ~WeakFrame() {
+    Clear(mFrame ? mFrame->PresContext()->GetPresShell() : nullptr);
+  }
+
+  WeakFrame& operator=(WeakFrame& aOther) {
+    Init(aOther.GetFrame());
+    return *this;
+  }
+
+  WeakFrame& operator=(nsIFrame* aFrame) {
+    Init(aFrame);
+    return *this;
+  }
+
+  nsIFrame* operator->() { return mFrame; }
+  operator nsIFrame*() { return mFrame; }
+
+  void Clear(mozilla::PresShell* aPresShell);
+
+  bool IsAlive() const { return !!mFrame; }
+  nsIFrame* GetFrame() const { return mFrame; }
+
+ private:
+  void Init(nsIFrame* aFrame);
+
+  nsIFrame* mFrame;
+};
+
+// Use nsIFrame's fast-path to avoid QueryFrame:
+inline do_QueryFrameHelper<nsIFrame> do_QueryFrame(WeakFrame& s) {
+  return do_QueryFrameHelper<nsIFrame>(s.GetFrame());
+}
+
+inline bool nsFrameList::ContinueRemoveFrame(nsIFrame* aFrame) {
+  MOZ_ASSERT(!aFrame->GetPrevSibling() || !aFrame->GetNextSibling(),
+             "Forgot to call StartRemoveFrame?");
+  if (aFrame == mLastChild) {
+    MOZ_ASSERT(!aFrame->GetNextSibling(), "broken frame list");
+    nsIFrame* prevSibling = aFrame->GetPrevSibling();
+    if (!prevSibling) {
+      MOZ_ASSERT(aFrame == mFirstChild, "broken frame list");
+      mFirstChild = mLastChild = nullptr;
+      return true;
+    }
+    MOZ_ASSERT(prevSibling->GetNextSibling() == aFrame, "Broken frame linkage");
+    prevSibling->SetNextSibling(nullptr);
+    mLastChild = prevSibling;
+    return true;
+  }
+  if (aFrame == mFirstChild) {
+    MOZ_ASSERT(!aFrame->GetPrevSibling(), "broken frame list");
+    mFirstChild = aFrame->GetNextSibling();
+    aFrame->SetNextSibling(nullptr);
+    MOZ_ASSERT(mFirstChild, "broken frame list");
+    return true;
+  }
+  return false;
+}
+
+inline bool nsFrameList::StartRemoveFrame(nsIFrame* aFrame) {
+  if (aFrame->GetPrevSibling() && aFrame->GetNextSibling()) {
+    UnhookFrameFromSiblings(aFrame);
+    return true;
+  }
+  return ContinueRemoveFrame(aFrame);
+}
+
+// Operators of nsFrameList::Iterator
+// ---------------------------------------------------
+
+inline nsIFrame* nsFrameList::ForwardFrameTraversal::Next(nsIFrame* aFrame) {
+  MOZ_ASSERT(aFrame);
+  return aFrame->GetNextSibling();
+}
+inline nsIFrame* nsFrameList::ForwardFrameTraversal::Prev(nsIFrame* aFrame) {
+  MOZ_ASSERT(aFrame);
+  return aFrame->GetPrevSibling();
+}
+
+inline nsIFrame* nsFrameList::BackwardFrameTraversal::Next(nsIFrame* aFrame) {
+  MOZ_ASSERT(aFrame);
+  return aFrame->GetPrevSibling();
+}
+inline nsIFrame* nsFrameList::BackwardFrameTraversal::Prev(nsIFrame* aFrame) {
+  MOZ_ASSERT(aFrame);
+  return aFrame->GetNextSibling();
+}
+
+#endif /* nsIFrame_h___ */