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

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

1 files changed, 1570 insertions, 0 deletions

diff --git a/layout/generic/nsLineBox.h b/layout/generic/nsLineBox.h
new file mode 100644
index 0000000000..f11c582678
--- /dev/null
+++ b/layout/generic/nsLineBox.h
@@ -0,0 +1,1570 @@
+/* -*- 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/. */
+
+/* representation of one line within a block frame, a CSS line box */
+
+#ifndef nsLineBox_h___
+#define nsLineBox_h___
+
+#include "mozilla/Attributes.h"
+#include "mozilla/Likely.h"
+#include "nsILineIterator.h"
+#include "nsIFrame.h"
+#include "nsStyleConsts.h"
+#include "nsTHashSet.h"
+
+#include <algorithm>
+
+class nsLineBox;
+class nsWindowSizes;
+
+namespace mozilla {
+class PresShell;
+}  // namespace mozilla
+
+/**
+ * Function to create a line box and initialize it with a single frame.
+ * The allocation is infallible.
+ * If the frame was moved from another line then you're responsible
+ * for notifying that line using NoteFrameRemoved().  Alternatively,
+ * it's better to use the next function that does that for you in an
+ * optimal way.
+ */
+nsLineBox* NS_NewLineBox(mozilla::PresShell* aPresShell, nsIFrame* aFrame,
+                         bool aIsBlock);
+/**
+ * Function to create a line box and initialize it with aCount frames
+ * that are currently on aFromLine.  The allocation is infallible.
+ */
+nsLineBox* NS_NewLineBox(mozilla::PresShell* aPresShell, nsLineBox* aFromLine,
+                         nsIFrame* aFrame, int32_t aCount);
+
+class nsLineList;
+
+// don't use the following names outside of this file.  Instead, use
+// nsLineList::iterator, etc.  These are just here to allow them to
+// be specified as parameters to methods of nsLineBox.
+class nsLineList_iterator;
+class nsLineList_const_iterator;
+class nsLineList_reverse_iterator;
+class nsLineList_const_reverse_iterator;
+
+/**
+ * Users must have the class that is to be part of the list inherit
+ * from nsLineLink.  If they want to be efficient, it should be the
+ * first base class.  (This was originally nsCLink in a templatized
+ * nsCList, but it's still useful separately.)
+ */
+
+class nsLineLink {
+ public:
+  friend class nsLineList;
+  friend class nsLineList_iterator;
+  friend class nsLineList_reverse_iterator;
+  friend class nsLineList_const_iterator;
+  friend class nsLineList_const_reverse_iterator;
+
+ private:
+  nsLineLink* _mNext;  // or head
+  nsLineLink* _mPrev;  // or tail
+};
+
+/**
+ * The nsLineBox class represents a horizontal line of frames. It contains
+ * enough state to support incremental reflow of the frames, event handling
+ * for the frames, and rendering of the frames.
+ */
+class nsLineBox final : public nsLineLink {
+ private:
+  nsLineBox(nsIFrame* aFrame, int32_t aCount, bool aIsBlock);
+  ~nsLineBox();
+
+  // Infallible overloaded new operator. Uses an arena (which comes from the
+  // presShell) to perform the allocation.
+  void* operator new(size_t sz, mozilla::PresShell* aPresShell);
+  void operator delete(void* aPtr, size_t sz) = delete;
+
+ public:
+  // Use these functions to allocate and destroy line boxes
+  friend nsLineBox* NS_NewLineBox(mozilla::PresShell* aPresShell,
+                                  nsIFrame* aFrame, bool aIsBlock);
+  friend nsLineBox* NS_NewLineBox(mozilla::PresShell* aPresShell,
+                                  nsLineBox* aFromLine, nsIFrame* aFrame,
+                                  int32_t aCount);
+  void Destroy(mozilla::PresShell* aPresShell);
+
+  // mBlock bit
+  bool IsBlock() const { return mFlags.mBlock; }
+  bool IsInline() const { return !mFlags.mBlock; }
+
+  // mDirty bit
+  void MarkDirty() { mFlags.mDirty = 1; }
+  void ClearDirty() { mFlags.mDirty = 0; }
+  bool IsDirty() const { return mFlags.mDirty; }
+
+  // mPreviousMarginDirty bit
+  void MarkPreviousMarginDirty() { mFlags.mPreviousMarginDirty = 1; }
+  void ClearPreviousMarginDirty() { mFlags.mPreviousMarginDirty = 0; }
+  bool IsPreviousMarginDirty() const { return mFlags.mPreviousMarginDirty; }
+
+  // mHasClearance bit
+  void SetHasClearance() { mFlags.mHasClearance = 1; }
+  void ClearHasClearance() { mFlags.mHasClearance = 0; }
+  bool HasClearance() const { return mFlags.mHasClearance; }
+
+  // mImpactedByFloat bit
+  void SetLineIsImpactedByFloat(bool aValue) {
+    mFlags.mImpactedByFloat = aValue;
+  }
+  bool IsImpactedByFloat() const { return mFlags.mImpactedByFloat; }
+
+  // mLineWrapped bit
+  void SetLineWrapped(bool aOn) { mFlags.mLineWrapped = aOn; }
+  bool IsLineWrapped() const { return mFlags.mLineWrapped; }
+
+  // mInvalidateTextRuns bit
+  void SetInvalidateTextRuns(bool aOn) { mFlags.mInvalidateTextRuns = aOn; }
+  bool GetInvalidateTextRuns() const { return mFlags.mInvalidateTextRuns; }
+
+  // mResizeReflowOptimizationDisabled bit
+  void DisableResizeReflowOptimization() {
+    mFlags.mResizeReflowOptimizationDisabled = true;
+  }
+  void EnableResizeReflowOptimization() {
+    mFlags.mResizeReflowOptimizationDisabled = false;
+  }
+  bool ResizeReflowOptimizationDisabled() const {
+    return mFlags.mResizeReflowOptimizationDisabled;
+  }
+
+  // mHasMarker bit
+  void SetHasMarker() {
+    mFlags.mHasMarker = true;
+    InvalidateCachedIsEmpty();
+  }
+  void ClearHasMarker() {
+    mFlags.mHasMarker = false;
+    InvalidateCachedIsEmpty();
+  }
+  bool HasMarker() const { return mFlags.mHasMarker; }
+
+  // mHadFloatPushed bit
+  void SetHadFloatPushed() { mFlags.mHadFloatPushed = true; }
+  void ClearHadFloatPushed() { mFlags.mHadFloatPushed = false; }
+  bool HadFloatPushed() const { return mFlags.mHadFloatPushed; }
+
+  // mHasLineClampEllipsis bit
+  void SetHasLineClampEllipsis() { mFlags.mHasLineClampEllipsis = true; }
+  void ClearHasLineClampEllipsis() { mFlags.mHasLineClampEllipsis = false; }
+  bool HasLineClampEllipsis() const { return mFlags.mHasLineClampEllipsis; }
+
+  // mMovedFragments bit
+  void SetMovedFragments() { mFlags.mMovedFragments = true; }
+  void ClearMovedFragments() { mFlags.mMovedFragments = false; }
+  bool MovedFragments() const { return mFlags.mMovedFragments; }
+
+ private:
+  // Add a hash table for fast lookup when the line has more frames than this.
+  static const uint32_t kMinChildCountForHashtable = 200;
+
+  /**
+   * Take ownership of aFromLine's hash table and remove the frames that
+   * stay on aFromLine from it, i.e. aFromLineNewCount frames starting with
+   * mFirstChild.  This method is used to optimize moving a large number
+   * of frames from one line to the next.
+   */
+  void StealHashTableFrom(nsLineBox* aFromLine, uint32_t aFromLineNewCount);
+
+  /**
+   * Does the equivalent of this->NoteFrameAdded and aFromLine->NoteFrameRemoved
+   * for each frame on this line, but in a optimized way.
+   */
+  void NoteFramesMovedFrom(nsLineBox* aFromLine);
+
+  void SwitchToHashtable() {
+    MOZ_ASSERT(!mFlags.mHasHashedFrames);
+    uint32_t count = GetChildCount();
+    mFlags.mHasHashedFrames = 1;
+    uint32_t minLength =
+        std::max(kMinChildCountForHashtable,
+                 uint32_t(PLDHashTable::kDefaultInitialLength));
+    mFrames = new nsTHashSet<nsIFrame*>(std::max(count, minLength));
+    for (nsIFrame* f = mFirstChild; count-- > 0; f = f->GetNextSibling()) {
+      mFrames->Insert(f);
+    }
+  }
+  void SwitchToCounter() {
+    MOZ_ASSERT(mFlags.mHasHashedFrames);
+    uint32_t count = GetChildCount();
+    delete mFrames;
+    mFlags.mHasHashedFrames = 0;
+    mChildCount = count;
+  }
+
+ public:
+  int32_t GetChildCount() const {
+    return MOZ_UNLIKELY(mFlags.mHasHashedFrames) ? mFrames->Count()
+                                                 : mChildCount;
+  }
+
+  /**
+   * Register that aFrame is now on this line.
+   */
+  void NoteFrameAdded(nsIFrame* aFrame) {
+    if (MOZ_UNLIKELY(mFlags.mHasHashedFrames)) {
+      mFrames->Insert(aFrame);
+    } else {
+      if (++mChildCount >= kMinChildCountForHashtable) {
+        SwitchToHashtable();
+      }
+    }
+  }
+
+  /**
+   * Register that aFrame is not on this line anymore.
+   */
+  void NoteFrameRemoved(nsIFrame* aFrame) {
+    MOZ_ASSERT(GetChildCount() > 0);
+    if (MOZ_UNLIKELY(mFlags.mHasHashedFrames)) {
+      mFrames->Remove(aFrame);
+      if (mFrames->Count() < kMinChildCountForHashtable) {
+        SwitchToCounter();
+      }
+    } else {
+      --mChildCount;
+    }
+  }
+
+  // mHasForcedLineBreak bit & mFloatClearType value
+  // Break information is applied *before* the line if the line is a block,
+  // or *after* the line if the line is an inline.
+  bool HasForcedLineBreak() const { return mFlags.mHasForcedLineBreak; }
+  void ClearForcedLineBreak() {
+    mFlags.mHasForcedLineBreak = false;
+    mFlags.mFloatClearType = mozilla::StyleClear::None;
+  }
+
+  bool HasForcedLineBreakBefore() const {
+    return IsBlock() && HasForcedLineBreak();
+  }
+  void SetForcedLineBreakBefore(mozilla::StyleClear aClearType) {
+    MOZ_ASSERT(IsBlock(), "Only blocks have break-before");
+    MOZ_ASSERT(aClearType != mozilla::StyleClear::None,
+               "Only StyleClear:Left/Right/Both are allowed before a line");
+    mFlags.mHasForcedLineBreak = true;
+    mFlags.mFloatClearType = aClearType;
+  }
+  mozilla::StyleClear FloatClearTypeBefore() const {
+    return IsBlock() ? FloatClearType() : mozilla::StyleClear::None;
+  }
+
+  bool HasForcedLineBreakAfter() const {
+    return IsInline() && HasForcedLineBreak();
+  }
+  void SetForcedLineBreakAfter(mozilla::StyleClear aClearType) {
+    MOZ_ASSERT(IsInline(), "Only inlines have break-after");
+    mFlags.mHasForcedLineBreak = true;
+    mFlags.mFloatClearType = aClearType;
+  }
+  bool HasFloatClearTypeAfter() const {
+    return IsInline() && FloatClearType() != mozilla::StyleClear::None;
+  }
+  mozilla::StyleClear FloatClearTypeAfter() const {
+    return IsInline() ? FloatClearType() : mozilla::StyleClear::None;
+  }
+
+  // mCarriedOutBEndMargin value
+  nsCollapsingMargin GetCarriedOutBEndMargin() const;
+  // Returns true if the margin changed
+  bool SetCarriedOutBEndMargin(nsCollapsingMargin aValue);
+
+  // mFloats
+  bool HasFloats() const {
+    return (IsInline() && mInlineData) && !mInlineData->mFloats.IsEmpty();
+  }
+  const nsTArray<nsIFrame*>& Floats() const {
+    MOZ_ASSERT(HasFloats());
+    return mInlineData->mFloats;
+  }
+  // Append aFloats to mFloat. aFloats will be empty.
+  void AppendFloats(nsTArray<nsIFrame*>&& aFloats);
+  void ClearFloats();
+  bool RemoveFloat(nsIFrame* aFrame);
+
+  // The ink overflow area should never be used for things that affect layout.
+  // The scrollable overflow area are permitted to affect layout for handling of
+  // overflow and scrollbars.
+  void SetOverflowAreas(const mozilla::OverflowAreas& aOverflowAreas);
+  mozilla::LogicalRect GetOverflowArea(mozilla::OverflowType aType,
+                                       mozilla::WritingMode aWM,
+                                       const nsSize& aContainerSize) {
+    return mozilla::LogicalRect(aWM, GetOverflowArea(aType), aContainerSize);
+  }
+  nsRect GetOverflowArea(mozilla::OverflowType aType) const {
+    return mData ? mData->mOverflowAreas.Overflow(aType) : GetPhysicalBounds();
+  }
+  mozilla::OverflowAreas GetOverflowAreas() const {
+    if (mData) {
+      return mData->mOverflowAreas;
+    }
+    nsRect bounds = GetPhysicalBounds();
+    return mozilla::OverflowAreas(bounds, bounds);
+  }
+  nsRect InkOverflowRect() const {
+    return GetOverflowArea(mozilla::OverflowType::Ink);
+  }
+  nsRect ScrollableOverflowRect() {
+    return GetOverflowArea(mozilla::OverflowType::Scrollable);
+  }
+
+  void SlideBy(nscoord aDBCoord, const nsSize& aContainerSize) {
+    NS_ASSERTION(
+        aContainerSize == mContainerSize || mContainerSize == nsSize(-1, -1),
+        "container size doesn't match");
+    mContainerSize = aContainerSize;
+    mBounds.BStart(mWritingMode) += aDBCoord;
+    if (mData) {
+      // Use a null containerSize to convert vector from logical to physical.
+      const nsSize nullContainerSize;
+      nsPoint physicalDelta =
+          mozilla::LogicalPoint(mWritingMode, 0, aDBCoord)
+              .GetPhysicalPoint(mWritingMode, nullContainerSize);
+      for (const auto otype : mozilla::AllOverflowTypes()) {
+        mData->mOverflowAreas.Overflow(otype) += physicalDelta;
+      }
+    }
+  }
+
+  // Container-size for the line is changing (and therefore if writing mode
+  // was vertical-rl, the line will move physically; this is like SlideBy,
+  // but it is the container size instead of the line's own logical coord
+  // that is changing.
+  nsSize UpdateContainerSize(const nsSize aNewContainerSize) {
+    NS_ASSERTION(mContainerSize != nsSize(-1, -1), "container size not set");
+    nsSize delta = mContainerSize - aNewContainerSize;
+    mContainerSize = aNewContainerSize;
+    // this has a physical-coordinate effect only in vertical-rl mode
+    if (mWritingMode.IsVerticalRL() && mData) {
+      nsPoint physicalDelta(-delta.width, 0);
+      for (const auto otype : mozilla::AllOverflowTypes()) {
+        mData->mOverflowAreas.Overflow(otype) += physicalDelta;
+      }
+    }
+    return delta;
+  }
+
+  void IndentBy(nscoord aDICoord, const nsSize& aContainerSize) {
+    NS_ASSERTION(
+        aContainerSize == mContainerSize || mContainerSize == nsSize(-1, -1),
+        "container size doesn't match");
+    mContainerSize = aContainerSize;
+    mBounds.IStart(mWritingMode) += aDICoord;
+  }
+
+  void ExpandBy(nscoord aDISize, const nsSize& aContainerSize) {
+    NS_ASSERTION(
+        aContainerSize == mContainerSize || mContainerSize == nsSize(-1, -1),
+        "container size doesn't match");
+    mContainerSize = aContainerSize;
+    mBounds.ISize(mWritingMode) += aDISize;
+  }
+
+  /**
+   * The logical ascent (distance from block-start to baseline) of the
+   * linebox is the logical ascent of the anonymous inline box (for
+   * which we don't actually create a frame) that wraps all the
+   * consecutive inline children of a block.
+   *
+   * This is currently unused for block lines.
+   */
+  nscoord GetLogicalAscent() const { return mAscent; }
+  void SetLogicalAscent(nscoord aAscent) { mAscent = aAscent; }
+
+  nscoord BStart() const { return mBounds.BStart(mWritingMode); }
+  nscoord BSize() const { return mBounds.BSize(mWritingMode); }
+  nscoord BEnd() const { return mBounds.BEnd(mWritingMode); }
+  nscoord IStart() const { return mBounds.IStart(mWritingMode); }
+  nscoord ISize() const { return mBounds.ISize(mWritingMode); }
+  nscoord IEnd() const { return mBounds.IEnd(mWritingMode); }
+  void SetBoundsEmpty() {
+    mBounds.IStart(mWritingMode) = 0;
+    mBounds.ISize(mWritingMode) = 0;
+    mBounds.BStart(mWritingMode) = 0;
+    mBounds.BSize(mWritingMode) = 0;
+  }
+
+  using DestroyContext = nsIFrame::DestroyContext;
+  static void DeleteLineList(nsPresContext* aPresContext, nsLineList& aLines,
+                             nsFrameList* aFrames, DestroyContext&);
+
+  // search from end to beginning of [aBegin, aEnd)
+  // Returns true if it found the line and false if not.
+  // Moves aEnd as it searches so that aEnd points to the resulting line.
+  // aLastFrameBeforeEnd is the last frame before aEnd (so if aEnd is
+  // the end of the line list, it's just the last frame in the frame
+  // list).
+  static bool RFindLineContaining(nsIFrame* aFrame,
+                                  const nsLineList_iterator& aBegin,
+                                  nsLineList_iterator& aEnd,
+                                  nsIFrame* aLastFrameBeforeEnd,
+                                  int32_t* aFrameIndexInLine);
+
+#ifdef DEBUG_FRAME_DUMP
+  static const char* StyleClearToString(mozilla::StyleClear aClearType);
+
+  void List(FILE* out, int32_t aIndent,
+            nsIFrame::ListFlags aFlags = nsIFrame::ListFlags()) const;
+  void List(FILE* out = stderr, const char* aPrefix = "",
+            nsIFrame::ListFlags aFlags = nsIFrame::ListFlags()) const;
+  nsIFrame* LastChild() const;
+#endif
+
+  void AddSizeOfExcludingThis(nsWindowSizes& aSizes) const;
+
+  // Find the index of aFrame within the line, starting search at the start.
+  int32_t IndexOf(nsIFrame* aFrame) const;
+
+  // Find the index of aFrame within the line, starting search at the end.
+  // (Produces the same result as IndexOf, but with different performance
+  // characteristics.)  The caller must provide the last frame in the line.
+  int32_t RIndexOf(nsIFrame* aFrame, nsIFrame* aLastFrameInLine) const;
+
+  bool Contains(nsIFrame* aFrame) const {
+    return MOZ_UNLIKELY(mFlags.mHasHashedFrames) ? mFrames->Contains(aFrame)
+                                                 : IndexOf(aFrame) >= 0;
+  }
+
+  // whether the line box is "logically" empty (just like nsIFrame::IsEmpty)
+  bool IsEmpty() const;
+
+  // Call this only while in Reflow() for the block the line belongs
+  // to, only between reflowing the line (or sliding it, if we skip
+  // reflowing it) and the end of reflowing the block.
+  bool CachedIsEmpty();
+
+  void InvalidateCachedIsEmpty() { mFlags.mEmptyCacheValid = false; }
+
+  // For debugging purposes
+  bool IsValidCachedIsEmpty() { return mFlags.mEmptyCacheValid; }
+
+#ifdef DEBUG
+  static int32_t GetCtorCount();
+#endif
+
+  nsIFrame* mFirstChild;
+
+  mozilla::WritingMode mWritingMode;
+
+  // Physical size. Use only for physical <-> logical coordinate conversion.
+  nsSize mContainerSize;
+
+ private:
+  mozilla::LogicalRect mBounds;
+
+ public:
+  const mozilla::LogicalRect& GetBounds() { return mBounds; }
+  nsRect GetPhysicalBounds() const {
+    if (mBounds.IsAllZero()) {
+      return nsRect(0, 0, 0, 0);
+    }
+
+    NS_ASSERTION(mContainerSize != nsSize(-1, -1),
+                 "mContainerSize not initialized");
+    return mBounds.GetPhysicalRect(mWritingMode, mContainerSize);
+  }
+  void SetBounds(mozilla::WritingMode aWritingMode, nscoord aIStart,
+                 nscoord aBStart, nscoord aISize, nscoord aBSize,
+                 const nsSize& aContainerSize) {
+    mWritingMode = aWritingMode;
+    mContainerSize = aContainerSize;
+    mBounds =
+        mozilla::LogicalRect(aWritingMode, aIStart, aBStart, aISize, aBSize);
+  }
+
+  // mFlags.mHasHashedFrames says which one to use
+  union {
+    nsTHashSet<nsIFrame*>* mFrames;
+    uint32_t mChildCount;
+  };
+
+  struct FlagBits {
+    bool mDirty : 1;
+    bool mPreviousMarginDirty : 1;
+    bool mHasClearance : 1;
+    bool mBlock : 1;
+    bool mImpactedByFloat : 1;
+    bool mLineWrapped : 1;
+    bool mInvalidateTextRuns : 1;
+    // default 0 = means that the opt potentially applies to this line.
+    // 1 = never skip reflowing this line for a resize reflow
+    bool mResizeReflowOptimizationDisabled : 1;
+    bool mEmptyCacheValid : 1;
+    bool mEmptyCacheState : 1;
+    // mHasMarker indicates that this is an inline line whose block's
+    // ::marker is adjacent to this line and non-empty.
+    bool mHasMarker : 1;
+    // Indicates that this line *may* have a placeholder for a float
+    // that was pushed to a later column or page.
+    bool mHadFloatPushed : 1;
+    bool mHasHashedFrames : 1;
+    // Indicates that this line is the one identified by an ancestor block
+    // with -webkit-line-clamp on its legacy flex container, and that subsequent
+    // lines under that block are "clamped" away, and therefore we need to
+    // render a 'text-overflow: ellipsis'-like marker in this line.  At most one
+    // line in the set of lines found by LineClampLineIterator for a given
+    // block will have this flag set.
+    bool mHasLineClampEllipsis : 1;
+    // Has this line moved to a different fragment of the block since
+    // the last time it was reflowed?
+    bool mMovedFragments : 1;
+    // mHasForcedLineBreak indicates that this line has either a break-before or
+    // a break-after.
+    bool mHasForcedLineBreak : 1;
+    // mFloatClearType indicates that there's a float clearance before or after
+    // this line.
+    mozilla::StyleClear mFloatClearType;
+  };
+
+  struct ExtraData {
+    explicit ExtraData(const nsRect& aBounds)
+        : mOverflowAreas(aBounds, aBounds) {}
+    mozilla::OverflowAreas mOverflowAreas;
+  };
+
+  struct ExtraBlockData : public ExtraData {
+    explicit ExtraBlockData(const nsRect& aBounds)
+        : ExtraData(aBounds), mCarriedOutBEndMargin() {}
+    nsCollapsingMargin mCarriedOutBEndMargin;
+  };
+
+  struct ExtraInlineData : public ExtraData {
+    explicit ExtraInlineData(const nsRect& aBounds)
+        : ExtraData(aBounds),
+          mFloatEdgeIStart(nscoord_MIN),
+          mFloatEdgeIEnd(nscoord_MIN) {}
+    nscoord mFloatEdgeIStart;
+    nscoord mFloatEdgeIEnd;
+    nsTArray<nsIFrame*> mFloats;
+  };
+
+  bool GetFloatEdges(nscoord* aStart, nscoord* aEnd) const {
+    MOZ_ASSERT(IsInline(), "block line can't have float edges");
+    if (mInlineData && mInlineData->mFloatEdgeIStart != nscoord_MIN) {
+      *aStart = mInlineData->mFloatEdgeIStart;
+      *aEnd = mInlineData->mFloatEdgeIEnd;
+      return true;
+    }
+    return false;
+  }
+  void SetFloatEdges(nscoord aStart, nscoord aEnd);
+  void ClearFloatEdges();
+
+ protected:
+  nscoord mAscent;  // see |SetAscent| / |GetAscent|
+  static_assert(sizeof(FlagBits) <= sizeof(uint32_t),
+                "size of FlagBits should not be larger than size of uint32_t");
+  union {
+    uint32_t mAllFlags;
+    FlagBits mFlags;
+  };
+
+  mozilla::StyleClear FloatClearType() const { return mFlags.mFloatClearType; };
+
+  union {
+    ExtraData* mData;
+    ExtraBlockData* mBlockData;
+    ExtraInlineData* mInlineData;
+  };
+
+  void Cleanup();
+  void MaybeFreeData();
+};
+
+/**
+ * A linked list type where the items in the list must inherit from
+ * a link type to fuse allocations.
+ *
+ * API heavily based on the |list| class in the C++ standard.
+ */
+
+class nsLineList_iterator {
+ public:
+  friend class nsLineList;
+  friend class nsLineList_reverse_iterator;
+  friend class nsLineList_const_iterator;
+  friend class nsLineList_const_reverse_iterator;
+
+  typedef nsLineList_iterator iterator_self_type;
+  typedef nsLineList_reverse_iterator iterator_reverse_type;
+
+  typedef nsLineBox& reference;
+  typedef const nsLineBox& const_reference;
+
+  typedef nsLineBox* pointer;
+  typedef const nsLineBox* const_pointer;
+
+  typedef uint32_t size_type;
+  typedef int32_t difference_type;
+
+  typedef nsLineLink link_type;
+
+#ifdef DEBUG
+  nsLineList_iterator() : mListLink(nullptr) {
+    memset(&mCurrent, 0xcd, sizeof(mCurrent));
+  }
+#else
+  // Auto generated default constructor OK.
+#endif
+  // Auto generated copy-constructor OK.
+
+  inline iterator_self_type& operator=(const iterator_self_type& aOther);
+  inline iterator_self_type& operator=(const iterator_reverse_type& aOther);
+
+  iterator_self_type& operator++() {
+    mCurrent = mCurrent->_mNext;
+    return *this;
+  }
+
+  iterator_self_type operator++(int) {
+    iterator_self_type rv(*this);
+    mCurrent = mCurrent->_mNext;
+    return rv;
+  }
+
+  iterator_self_type& operator--() {
+    mCurrent = mCurrent->_mPrev;
+    return *this;
+  }
+
+  iterator_self_type operator--(int) {
+    iterator_self_type rv(*this);
+    mCurrent = mCurrent->_mPrev;
+    return rv;
+  }
+
+  reference operator*() {
+    MOZ_ASSERT(mListLink);
+    MOZ_ASSERT(mCurrent != mListLink, "running past end");
+    return *static_cast<pointer>(mCurrent);
+  }
+
+  pointer operator->() {
+    MOZ_ASSERT(mListLink);
+    MOZ_ASSERT(mCurrent != mListLink, "running past end");
+    return static_cast<pointer>(mCurrent);
+  }
+
+  pointer get() {
+    MOZ_ASSERT(mListLink);
+    MOZ_ASSERT(mCurrent != mListLink, "running past end");
+    return static_cast<pointer>(mCurrent);
+  }
+
+  operator pointer() {
+    MOZ_ASSERT(mListLink);
+    MOZ_ASSERT(mCurrent != mListLink, "running past end");
+    return static_cast<pointer>(mCurrent);
+  }
+
+  const_reference operator*() const {
+    MOZ_ASSERT(mListLink);
+    MOZ_ASSERT(mCurrent != mListLink, "running past end");
+    return *static_cast<const_pointer>(mCurrent);
+  }
+
+  const_pointer operator->() const {
+    MOZ_ASSERT(mListLink);
+    MOZ_ASSERT(mCurrent != mListLink, "running past end");
+    return static_cast<const_pointer>(mCurrent);
+  }
+
+#ifndef __MWERKS__
+  operator const_pointer() const {
+    MOZ_ASSERT(mListLink);
+    MOZ_ASSERT(mCurrent != mListLink, "running past end");
+    return static_cast<const_pointer>(mCurrent);
+  }
+#endif /* !__MWERKS__ */
+
+  iterator_self_type next() {
+    iterator_self_type copy(*this);
+    return ++copy;
+  }
+
+  const iterator_self_type next() const {
+    iterator_self_type copy(*this);
+    return ++copy;
+  }
+
+  iterator_self_type prev() {
+    iterator_self_type copy(*this);
+    return --copy;
+  }
+
+  const iterator_self_type prev() const {
+    iterator_self_type copy(*this);
+    return --copy;
+  }
+
+  bool operator==(const iterator_self_type& aOther) const {
+    MOZ_ASSERT(mListLink);
+    MOZ_ASSERT(mListLink == aOther.mListLink,
+               "comparing iterators over different lists");
+    return mCurrent == aOther.mCurrent;
+  }
+  bool operator!=(const iterator_self_type& aOther) const {
+    MOZ_ASSERT(mListLink);
+    MOZ_ASSERT(mListLink == aOther.mListLink,
+               "comparing iterators over different lists");
+    return mCurrent != aOther.mCurrent;
+  }
+
+#ifdef DEBUG
+  bool IsInSameList(const iterator_self_type& aOther) const {
+    return mListLink == aOther.mListLink;
+  }
+#endif
+
+ private:
+  link_type* mCurrent;
+#ifdef DEBUG
+  link_type* mListLink;  // the list's link, i.e., the end
+#endif
+};
+
+class nsLineList_reverse_iterator {
+ public:
+  friend class nsLineList;
+  friend class nsLineList_iterator;
+  friend class nsLineList_const_iterator;
+  friend class nsLineList_const_reverse_iterator;
+
+  typedef nsLineList_reverse_iterator iterator_self_type;
+  typedef nsLineList_iterator iterator_reverse_type;
+
+  typedef nsLineBox& reference;
+  typedef const nsLineBox& const_reference;
+
+  typedef nsLineBox* pointer;
+  typedef const nsLineBox* const_pointer;
+
+  typedef uint32_t size_type;
+  typedef int32_t difference_type;
+
+  typedef nsLineLink link_type;
+
+#ifdef DEBUG
+  nsLineList_reverse_iterator() : mListLink(nullptr) {
+    memset(&mCurrent, 0xcd, sizeof(mCurrent));
+  }
+#else
+  // Auto generated default constructor OK.
+#endif
+  // Auto generated copy-constructor OK.
+
+  inline iterator_self_type& operator=(const iterator_reverse_type& aOther);
+  inline iterator_self_type& operator=(const iterator_self_type& aOther);
+
+  iterator_self_type& operator++() {
+    mCurrent = mCurrent->_mPrev;
+    return *this;
+  }
+
+  iterator_self_type operator++(int) {
+    iterator_self_type rv(*this);
+    mCurrent = mCurrent->_mPrev;
+    return rv;
+  }
+
+  iterator_self_type& operator--() {
+    mCurrent = mCurrent->_mNext;
+    return *this;
+  }
+
+  iterator_self_type operator--(int) {
+    iterator_self_type rv(*this);
+    mCurrent = mCurrent->_mNext;
+    return rv;
+  }
+
+  reference operator*() {
+    MOZ_ASSERT(mListLink);
+    MOZ_ASSERT(mCurrent != mListLink, "running past end");
+    return *static_cast<pointer>(mCurrent);
+  }
+
+  pointer operator->() {
+    MOZ_ASSERT(mListLink);
+    MOZ_ASSERT(mCurrent != mListLink, "running past end");
+    return static_cast<pointer>(mCurrent);
+  }
+
+  pointer get() {
+    MOZ_ASSERT(mListLink);
+    MOZ_ASSERT(mCurrent != mListLink, "running past end");
+    return static_cast<pointer>(mCurrent);
+  }
+
+  operator pointer() {
+    MOZ_ASSERT(mListLink);
+    MOZ_ASSERT(mCurrent != mListLink, "running past end");
+    return static_cast<pointer>(mCurrent);
+  }
+
+  const_reference operator*() const {
+    MOZ_ASSERT(mListLink);
+    MOZ_ASSERT(mCurrent != mListLink, "running past end");
+    return *static_cast<const_pointer>(mCurrent);
+  }
+
+  const_pointer operator->() const {
+    MOZ_ASSERT(mListLink);
+    MOZ_ASSERT(mCurrent != mListLink, "running past end");
+    return static_cast<const_pointer>(mCurrent);
+  }
+
+#ifndef __MWERKS__
+  operator const_pointer() const {
+    MOZ_ASSERT(mListLink);
+    MOZ_ASSERT(mCurrent != mListLink, "running past end");
+    return static_cast<const_pointer>(mCurrent);
+  }
+#endif /* !__MWERKS__ */
+
+  bool operator==(const iterator_self_type& aOther) const {
+    MOZ_ASSERT(mListLink);
+    NS_ASSERTION(mListLink == aOther.mListLink,
+                 "comparing iterators over different lists");
+    return mCurrent == aOther.mCurrent;
+  }
+  bool operator!=(const iterator_self_type& aOther) const {
+    MOZ_ASSERT(mListLink);
+    NS_ASSERTION(mListLink == aOther.mListLink,
+                 "comparing iterators over different lists");
+    return mCurrent != aOther.mCurrent;
+  }
+
+#ifdef DEBUG
+  bool IsInSameList(const iterator_self_type& aOther) const {
+    return mListLink == aOther.mListLink;
+  }
+#endif
+
+ private:
+  link_type* mCurrent;
+#ifdef DEBUG
+  link_type* mListLink;  // the list's link, i.e., the end
+#endif
+};
+
+class nsLineList_const_iterator {
+ public:
+  friend class nsLineList;
+  friend class nsLineList_iterator;
+  friend class nsLineList_reverse_iterator;
+  friend class nsLineList_const_reverse_iterator;
+
+  typedef nsLineList_const_iterator iterator_self_type;
+  typedef nsLineList_const_reverse_iterator iterator_reverse_type;
+  typedef nsLineList_iterator iterator_nonconst_type;
+  typedef nsLineList_reverse_iterator iterator_nonconst_reverse_type;
+
+  typedef nsLineBox& reference;
+  typedef const nsLineBox& const_reference;
+
+  typedef nsLineBox* pointer;
+  typedef const nsLineBox* const_pointer;
+
+  typedef uint32_t size_type;
+  typedef int32_t difference_type;
+
+  typedef nsLineLink link_type;
+
+#ifdef DEBUG
+  nsLineList_const_iterator() : mListLink(nullptr) {
+    memset(&mCurrent, 0xcd, sizeof(mCurrent));
+  }
+#else
+  // Auto generated default constructor OK.
+#endif
+  // Auto generated copy-constructor OK.
+
+  inline iterator_self_type& operator=(const iterator_nonconst_type& aOther);
+  inline iterator_self_type& operator=(
+      const iterator_nonconst_reverse_type& aOther);
+  inline iterator_self_type& operator=(const iterator_self_type& aOther);
+  inline iterator_self_type& operator=(const iterator_reverse_type& aOther);
+
+  iterator_self_type& operator++() {
+    mCurrent = mCurrent->_mNext;
+    return *this;
+  }
+
+  iterator_self_type operator++(int) {
+    iterator_self_type rv(*this);
+    mCurrent = mCurrent->_mNext;
+    return rv;
+  }
+
+  iterator_self_type& operator--() {
+    mCurrent = mCurrent->_mPrev;
+    return *this;
+  }
+
+  iterator_self_type operator--(int) {
+    iterator_self_type rv(*this);
+    mCurrent = mCurrent->_mPrev;
+    return rv;
+  }
+
+  const_reference operator*() const {
+    MOZ_ASSERT(mListLink);
+    MOZ_ASSERT(mCurrent != mListLink, "running past end");
+    return *static_cast<const_pointer>(mCurrent);
+  }
+
+  const_pointer operator->() const {
+    MOZ_ASSERT(mListLink);
+    MOZ_ASSERT(mCurrent != mListLink, "running past end");
+    return static_cast<const_pointer>(mCurrent);
+  }
+
+  const_pointer get() const {
+    MOZ_ASSERT(mListLink);
+    MOZ_ASSERT(mCurrent != mListLink, "running past end");
+    return static_cast<const_pointer>(mCurrent);
+  }
+
+#ifndef __MWERKS__
+  operator const_pointer() const {
+    MOZ_ASSERT(mListLink);
+    MOZ_ASSERT(mCurrent != mListLink, "running past end");
+    return static_cast<const_pointer>(mCurrent);
+  }
+#endif /* !__MWERKS__ */
+
+  const iterator_self_type next() const {
+    iterator_self_type copy(*this);
+    return ++copy;
+  }
+
+  const iterator_self_type prev() const {
+    iterator_self_type copy(*this);
+    return --copy;
+  }
+
+  bool operator==(const iterator_self_type& aOther) const {
+    MOZ_ASSERT(mListLink);
+    NS_ASSERTION(mListLink == aOther.mListLink,
+                 "comparing iterators over different lists");
+    return mCurrent == aOther.mCurrent;
+  }
+  bool operator!=(const iterator_self_type& aOther) const {
+    MOZ_ASSERT(mListLink);
+    NS_ASSERTION(mListLink == aOther.mListLink,
+                 "comparing iterators over different lists");
+    return mCurrent != aOther.mCurrent;
+  }
+
+#ifdef DEBUG
+  bool IsInSameList(const iterator_self_type& aOther) const {
+    return mListLink == aOther.mListLink;
+  }
+#endif
+
+ private:
+  const link_type* mCurrent;
+#ifdef DEBUG
+  const link_type* mListLink;  // the list's link, i.e., the end
+#endif
+};
+
+class nsLineList_const_reverse_iterator {
+ public:
+  friend class nsLineList;
+  friend class nsLineList_iterator;
+  friend class nsLineList_reverse_iterator;
+  friend class nsLineList_const_iterator;
+
+  typedef nsLineList_const_reverse_iterator iterator_self_type;
+  typedef nsLineList_const_iterator iterator_reverse_type;
+  typedef nsLineList_iterator iterator_nonconst_reverse_type;
+  typedef nsLineList_reverse_iterator iterator_nonconst_type;
+
+  typedef nsLineBox& reference;
+  typedef const nsLineBox& const_reference;
+
+  typedef nsLineBox* pointer;
+  typedef const nsLineBox* const_pointer;
+
+  typedef uint32_t size_type;
+  typedef int32_t difference_type;
+
+  typedef nsLineLink link_type;
+
+#ifdef DEBUG
+  nsLineList_const_reverse_iterator() : mListLink(nullptr) {
+    memset(&mCurrent, 0xcd, sizeof(mCurrent));
+  }
+#else
+  // Auto generated default constructor OK.
+#endif
+  // Auto generated copy-constructor OK.
+
+  inline iterator_self_type& operator=(const iterator_nonconst_type& aOther);
+  inline iterator_self_type& operator=(
+      const iterator_nonconst_reverse_type& aOther);
+  inline iterator_self_type& operator=(const iterator_self_type& aOther);
+  inline iterator_self_type& operator=(const iterator_reverse_type& aOther);
+
+  iterator_self_type& operator++() {
+    mCurrent = mCurrent->_mPrev;
+    return *this;
+  }
+
+  iterator_self_type operator++(int) {
+    iterator_self_type rv(*this);
+    mCurrent = mCurrent->_mPrev;
+    return rv;
+  }
+
+  iterator_self_type& operator--() {
+    mCurrent = mCurrent->_mNext;
+    return *this;
+  }
+
+  iterator_self_type operator--(int) {
+    iterator_self_type rv(*this);
+    mCurrent = mCurrent->_mNext;
+    return rv;
+  }
+
+  const_reference operator*() const {
+    MOZ_ASSERT(mListLink);
+    MOZ_ASSERT(mCurrent != mListLink, "running past end");
+    return *static_cast<const_pointer>(mCurrent);
+  }
+
+  const_pointer operator->() const {
+    MOZ_ASSERT(mListLink);
+    MOZ_ASSERT(mCurrent != mListLink, "running past end");
+    return static_cast<const_pointer>(mCurrent);
+  }
+
+  const_pointer get() const {
+    MOZ_ASSERT(mListLink);
+    MOZ_ASSERT(mCurrent != mListLink, "running past end");
+    return static_cast<const_pointer>(mCurrent);
+  }
+
+#ifndef __MWERKS__
+  operator const_pointer() const {
+    MOZ_ASSERT(mListLink);
+    MOZ_ASSERT(mCurrent != mListLink, "running past end");
+    return static_cast<const_pointer>(mCurrent);
+  }
+#endif /* !__MWERKS__ */
+
+  bool operator==(const iterator_self_type& aOther) const {
+    MOZ_ASSERT(mListLink);
+    NS_ASSERTION(mListLink == aOther.mListLink,
+                 "comparing iterators over different lists");
+    return mCurrent == aOther.mCurrent;
+  }
+  bool operator!=(const iterator_self_type& aOther) const {
+    MOZ_ASSERT(mListLink);
+    NS_ASSERTION(mListLink == aOther.mListLink,
+                 "comparing iterators over different lists");
+    return mCurrent != aOther.mCurrent;
+  }
+
+#ifdef DEBUG
+  bool IsInSameList(const iterator_self_type& aOther) const {
+    return mListLink == aOther.mListLink;
+  }
+#endif
+
+  // private:
+  const link_type* mCurrent;
+#ifdef DEBUG
+  const link_type* mListLink;  // the list's link, i.e., the end
+#endif
+};
+
+class nsLineList {
+ public:
+  friend class nsLineList_iterator;
+  friend class nsLineList_reverse_iterator;
+  friend class nsLineList_const_iterator;
+  friend class nsLineList_const_reverse_iterator;
+
+  typedef uint32_t size_type;
+  typedef int32_t difference_type;
+
+  typedef nsLineLink link_type;
+
+ private:
+  link_type mLink;
+
+ public:
+  typedef nsLineList self_type;
+
+  typedef nsLineBox& reference;
+  typedef const nsLineBox& const_reference;
+
+  typedef nsLineBox* pointer;
+  typedef const nsLineBox* const_pointer;
+
+  typedef nsLineList_iterator iterator;
+  typedef nsLineList_reverse_iterator reverse_iterator;
+  typedef nsLineList_const_iterator const_iterator;
+  typedef nsLineList_const_reverse_iterator const_reverse_iterator;
+
+  nsLineList() {
+    MOZ_COUNT_CTOR(nsLineList);
+    clear();
+  }
+
+  MOZ_COUNTED_DTOR(nsLineList)
+
+  const_iterator begin() const {
+    const_iterator rv;
+    rv.mCurrent = mLink._mNext;
+#ifdef DEBUG
+    rv.mListLink = &mLink;
+#endif
+    return rv;
+  }
+
+  iterator begin() {
+    iterator rv;
+    rv.mCurrent = mLink._mNext;
+#ifdef DEBUG
+    rv.mListLink = &mLink;
+#endif
+    return rv;
+  }
+
+  iterator begin(nsLineBox* aLine) {
+    iterator rv;
+    rv.mCurrent = aLine;
+#ifdef DEBUG
+    rv.mListLink = &mLink;
+#endif
+    return rv;
+  }
+
+  const_iterator end() const {
+    const_iterator rv;
+    rv.mCurrent = &mLink;
+#ifdef DEBUG
+    rv.mListLink = &mLink;
+#endif
+    return rv;
+  }
+
+  iterator end() {
+    iterator rv;
+    rv.mCurrent = &mLink;
+#ifdef DEBUG
+    rv.mListLink = &mLink;
+#endif
+    return rv;
+  }
+
+  const_reverse_iterator rbegin() const {
+    const_reverse_iterator rv;
+    rv.mCurrent = mLink._mPrev;
+#ifdef DEBUG
+    rv.mListLink = &mLink;
+#endif
+    return rv;
+  }
+
+  reverse_iterator rbegin() {
+    reverse_iterator rv;
+    rv.mCurrent = mLink._mPrev;
+#ifdef DEBUG
+    rv.mListLink = &mLink;
+#endif
+    return rv;
+  }
+
+  reverse_iterator rbegin(nsLineBox* aLine) {
+    reverse_iterator rv;
+    rv.mCurrent = aLine;
+#ifdef DEBUG
+    rv.mListLink = &mLink;
+#endif
+    return rv;
+  }
+
+  const_reverse_iterator rend() const {
+    const_reverse_iterator rv;
+    rv.mCurrent = &mLink;
+#ifdef DEBUG
+    rv.mListLink = &mLink;
+#endif
+    return rv;
+  }
+
+  reverse_iterator rend() {
+    reverse_iterator rv;
+    rv.mCurrent = &mLink;
+#ifdef DEBUG
+    rv.mListLink = &mLink;
+#endif
+    return rv;
+  }
+
+  bool empty() const { return mLink._mNext == &mLink; }
+
+  // NOTE: O(N).
+  size_type size() const {
+    size_type count = 0;
+    for (const link_type* cur = mLink._mNext; cur != &mLink;
+         cur = cur->_mNext) {
+      ++count;
+    }
+    return count;
+  }
+
+  pointer front() {
+    NS_ASSERTION(!empty(), "no element to return");
+    return static_cast<pointer>(mLink._mNext);
+  }
+
+  const_pointer front() const {
+    NS_ASSERTION(!empty(), "no element to return");
+    return static_cast<const_pointer>(mLink._mNext);
+  }
+
+  pointer back() {
+    NS_ASSERTION(!empty(), "no element to return");
+    return static_cast<pointer>(mLink._mPrev);
+  }
+
+  const_pointer back() const {
+    NS_ASSERTION(!empty(), "no element to return");
+    return static_cast<const_pointer>(mLink._mPrev);
+  }
+
+  void push_front(pointer aNew) {
+    aNew->_mNext = mLink._mNext;
+    mLink._mNext->_mPrev = aNew;
+    aNew->_mPrev = &mLink;
+    mLink._mNext = aNew;
+  }
+
+  void pop_front()
+  // NOTE: leaves dangling next/prev pointers
+  {
+    NS_ASSERTION(!empty(), "no element to pop");
+    link_type* newFirst = mLink._mNext->_mNext;
+    newFirst->_mPrev = &mLink;
+    // mLink._mNext->_mNext = nullptr;
+    // mLink._mNext->_mPrev = nullptr;
+    mLink._mNext = newFirst;
+  }
+
+  void push_back(pointer aNew) {
+    aNew->_mPrev = mLink._mPrev;
+    mLink._mPrev->_mNext = aNew;
+    aNew->_mNext = &mLink;
+    mLink._mPrev = aNew;
+  }
+
+  void pop_back()
+  // NOTE: leaves dangling next/prev pointers
+  {
+    NS_ASSERTION(!empty(), "no element to pop");
+    link_type* newLast = mLink._mPrev->_mPrev;
+    newLast->_mNext = &mLink;
+    // mLink._mPrev->_mPrev = nullptr;
+    // mLink._mPrev->_mNext = nullptr;
+    mLink._mPrev = newLast;
+  }
+
+  // inserts x before position
+  iterator before_insert(iterator position, pointer x) {
+    // use |mCurrent| to prevent DEBUG_PASS_END assertions
+    x->_mPrev = position.mCurrent->_mPrev;
+    x->_mNext = position.mCurrent;
+    position.mCurrent->_mPrev->_mNext = x;
+    position.mCurrent->_mPrev = x;
+    return --position;
+  }
+
+  // inserts x after position
+  iterator after_insert(iterator position, pointer x) {
+    // use |mCurrent| to prevent DEBUG_PASS_END assertions
+    x->_mNext = position.mCurrent->_mNext;
+    x->_mPrev = position.mCurrent;
+    position.mCurrent->_mNext->_mPrev = x;
+    position.mCurrent->_mNext = x;
+    return ++position;
+  }
+
+  // returns iterator pointing to after the element
+  iterator erase(iterator position)
+  // NOTE: leaves dangling next/prev pointers
+  {
+    position->_mPrev->_mNext = position->_mNext;
+    position->_mNext->_mPrev = position->_mPrev;
+    return ++position;
+  }
+
+  void swap(self_type& y) {
+    link_type tmp(y.mLink);
+    y.mLink = mLink;
+    mLink = tmp;
+
+    if (!empty()) {
+      mLink._mNext->_mPrev = &mLink;
+      mLink._mPrev->_mNext = &mLink;
+    }
+
+    if (!y.empty()) {
+      y.mLink._mNext->_mPrev = &y.mLink;
+      y.mLink._mPrev->_mNext = &y.mLink;
+    }
+  }
+
+  void clear()
+  // NOTE:  leaves dangling next/prev pointers
+  {
+    mLink._mNext = &mLink;
+    mLink._mPrev = &mLink;
+  }
+
+  // inserts the conts of x before position and makes x empty
+  void splice(iterator position, self_type& x) {
+    // use |mCurrent| to prevent DEBUG_PASS_END assertions
+    position.mCurrent->_mPrev->_mNext = x.mLink._mNext;
+    x.mLink._mNext->_mPrev = position.mCurrent->_mPrev;
+    x.mLink._mPrev->_mNext = position.mCurrent;
+    position.mCurrent->_mPrev = x.mLink._mPrev;
+    x.clear();
+  }
+
+  // Inserts element *i from list x before position and removes
+  // it from x.
+  void splice(iterator position, self_type& x, iterator i) {
+    NS_ASSERTION(!x.empty(), "Can't insert from empty list.");
+    NS_ASSERTION(position != i && position.mCurrent != i->_mNext,
+                 "We don't check for this case.");
+
+    // remove from |x|
+    i->_mPrev->_mNext = i->_mNext;
+    i->_mNext->_mPrev = i->_mPrev;
+
+    // use |mCurrent| to prevent DEBUG_PASS_END assertions
+    // link into |this|, before-side
+    i->_mPrev = position.mCurrent->_mPrev;
+    position.mCurrent->_mPrev->_mNext = i.get();
+
+    // link into |this|, after-side
+    i->_mNext = position.mCurrent;
+    position.mCurrent->_mPrev = i.get();
+  }
+
+  // Inserts elements in [|first|, |last|), which are in |x|,
+  // into |this| before |position| and removes them from |x|.
+  void splice(iterator position, self_type& x, iterator first, iterator last) {
+    NS_ASSERTION(!x.empty(), "Can't insert from empty list.");
+
+    if (first == last) return;
+
+    --last;  // so we now want to move [first, last]
+    // remove from |x|
+    first->_mPrev->_mNext = last->_mNext;
+    last->_mNext->_mPrev = first->_mPrev;
+
+    // use |mCurrent| to prevent DEBUG_PASS_END assertions
+    // link into |this|, before-side
+    first->_mPrev = position.mCurrent->_mPrev;
+    position.mCurrent->_mPrev->_mNext = first.get();
+
+    // link into |this|, after-side
+    last->_mNext = position.mCurrent;
+    position.mCurrent->_mPrev = last.get();
+  }
+};
+
+// Many of these implementations of operator= don't work yet.  I don't
+// know why.
+
+#ifdef DEBUG
+
+// NOTE: ASSIGN_FROM is meant to be used *only* as the entire body
+// of a function and therefore lacks PR_{BEGIN,END}_MACRO
+#  define ASSIGN_FROM(other_)     \
+    mCurrent = other_.mCurrent;   \
+    mListLink = other_.mListLink; \
+    return *this;
+
+#else /* !NS_LINELIST_DEBUG_PASS_END */
+
+#  define ASSIGN_FROM(other_)   \
+    mCurrent = other_.mCurrent; \
+    return *this;
+
+#endif /* !NS_LINELIST_DEBUG_PASS_END */
+
+inline nsLineList_iterator& nsLineList_iterator::operator=(
+    const nsLineList_iterator& aOther) = default;
+
+inline nsLineList_iterator& nsLineList_iterator::operator=(
+    const nsLineList_reverse_iterator& aOther) {
+  ASSIGN_FROM(aOther)
+}
+
+inline nsLineList_reverse_iterator& nsLineList_reverse_iterator::operator=(
+    const nsLineList_iterator& aOther) {
+  ASSIGN_FROM(aOther)
+}
+
+inline nsLineList_reverse_iterator& nsLineList_reverse_iterator::operator=(
+    const nsLineList_reverse_iterator& aOther) = default;
+
+inline nsLineList_const_iterator& nsLineList_const_iterator::operator=(
+    const nsLineList_iterator& aOther) {
+  ASSIGN_FROM(aOther)
+}
+
+inline nsLineList_const_iterator& nsLineList_const_iterator::operator=(
+    const nsLineList_reverse_iterator& aOther) {
+  ASSIGN_FROM(aOther)
+}
+
+inline nsLineList_const_iterator& nsLineList_const_iterator::operator=(
+    const nsLineList_const_iterator& aOther) = default;
+
+inline nsLineList_const_iterator& nsLineList_const_iterator::operator=(
+    const nsLineList_const_reverse_iterator& aOther) {
+  ASSIGN_FROM(aOther)
+}
+
+inline nsLineList_const_reverse_iterator&
+nsLineList_const_reverse_iterator::operator=(
+    const nsLineList_iterator& aOther) {
+  ASSIGN_FROM(aOther)
+}
+
+inline nsLineList_const_reverse_iterator&
+nsLineList_const_reverse_iterator::operator=(
+    const nsLineList_reverse_iterator& aOther) {
+  ASSIGN_FROM(aOther)
+}
+
+inline nsLineList_const_reverse_iterator&
+nsLineList_const_reverse_iterator::operator=(
+    const nsLineList_const_iterator& aOther) {
+  ASSIGN_FROM(aOther)
+}
+
+inline nsLineList_const_reverse_iterator&
+nsLineList_const_reverse_iterator::operator=(
+    const nsLineList_const_reverse_iterator& aOther) = default;
+
+//----------------------------------------------------------------------
+
+class nsLineIterator final : public nsILineIterator {
+ public:
+  nsLineIterator(const nsLineList& aLines, bool aRightToLeft)
+      : mLines(aLines), mRightToLeft(aRightToLeft) {
+    mIter = mLines.begin();
+    if (mIter != mLines.end()) {
+      mIndex = 0;
+    }
+  }
+
+  int32_t GetNumLines() const final {
+    if (mNumLines < 0) {
+      mNumLines = int32_t(mLines.size());  // This is O(N) in number of lines!
+    }
+    return mNumLines;
+  }
+
+  bool IsLineIteratorFlowRTL() final { return mRightToLeft; }
+
+  // Note that this updates the iterator's current position!
+  mozilla::Result<LineInfo, nsresult> GetLine(int32_t aLineNumber) final;
+
+  int32_t FindLineContaining(nsIFrame* aFrame, int32_t aStartLine = 0) final;
+
+  NS_IMETHOD FindFrameAt(int32_t aLineNumber, nsPoint aPos,
+                         nsIFrame** aFrameFound, bool* aPosIsBeforeFirstFrame,
+                         bool* aPosIsAfterLastFrame) final;
+
+  NS_IMETHOD CheckLineOrder(int32_t aLine, bool* aIsReordered,
+                            nsIFrame** aFirstVisual,
+                            nsIFrame** aLastVisual) final;
+
+ private:
+  nsLineIterator() = delete;
+  nsLineIterator(const nsLineIterator& aOther) = delete;
+
+  const nsLineBox* GetNextLine() {
+    MOZ_ASSERT(mIter != mLines.end(), "Already at end!");
+    ++mIndex;
+    ++mIter;
+    if (mIter == mLines.end()) {
+      MOZ_ASSERT(mNumLines < 0 || mNumLines == mIndex);
+      mNumLines = mIndex;
+      return nullptr;
+    }
+    return mIter.get();
+  }
+
+  // Note that this updates the iterator's current position to the given line.
+  const nsLineBox* GetLineAt(int32_t aIndex) {
+    MOZ_ASSERT(mIndex >= 0);
+    if (aIndex < 0 || (mNumLines >= 0 && aIndex >= mNumLines)) {
+      return nullptr;
+    }
+    // Check if we should start counting lines from mIndex, or reset to the
+    // start or end of the list and count from there (if the requested index is
+    // closer to an end than to the current position).
+    if (aIndex < mIndex / 2) {
+      // Reset to the beginning and search from there.
+      mIter = mLines.begin();
+      mIndex = 0;
+    } else if (mNumLines > 0 && aIndex > (mNumLines + mIndex) / 2) {
+      // Jump to the end and search back from there.
+      mIter = mLines.end();
+      --mIter;
+      mIndex = mNumLines - 1;
+    }
+    while (mIndex > aIndex) {
+      // This cannot run past the start of the list, because we checked that
+      // aIndex is non-negative.
+      --mIter;
+      --mIndex;
+    }
+    while (mIndex < aIndex) {
+      // Here we have to check for reaching the end, as aIndex could be out of
+      // range (if mNumLines was not initialized, so we couldn't range-check
+      // aIndex on entry).
+      if (mIter == mLines.end()) {
+        MOZ_ASSERT(mNumLines < 0 || mNumLines == mIndex);
+        mNumLines = mIndex;
+        return nullptr;
+      }
+      ++mIter;
+      ++mIndex;
+    }
+    return mIter.get();
+  }
+
+  const nsLineList& mLines;
+  nsLineList_const_iterator mIter;
+  int32_t mIndex = -1;
+  mutable int32_t mNumLines = -1;
+  const bool mRightToLeft;
+};
+
+#endif /* nsLineBox_h___ */