Adding upstream version 124.0.1.upstream/124.0.1

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

1 files changed, 8626 insertions, 0 deletions

diff --git a/layout/generic/nsBlockFrame.cpp b/layout/generic/nsBlockFrame.cpp
new file mode 100644
index 0000000000..54976ecc47
--- /dev/null
+++ b/layout/generic/nsBlockFrame.cpp
@@ -0,0 +1,8626 @@
+/* -*- 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/. */
+
+/*
+ * rendering object for CSS display:block, inline-block, and list-item
+ * boxes, also used for various anonymous boxes
+ */
+
+#include "nsBlockFrame.h"
+
+#include "gfxContext.h"
+
+#include "mozilla/AppUnits.h"
+#include "mozilla/Baseline.h"
+#include "mozilla/ComputedStyle.h"
+#include "mozilla/DebugOnly.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/PresShell.h"
+#include "mozilla/StaticPrefs_browser.h"
+#include "mozilla/StaticPrefs_layout.h"
+#include "mozilla/ToString.h"
+#include "mozilla/UniquePtr.h"
+
+#include "nsCRT.h"
+#include "nsCOMPtr.h"
+#include "nsCSSRendering.h"
+#include "nsAbsoluteContainingBlock.h"
+#include "nsBlockReflowContext.h"
+#include "BlockReflowState.h"
+#include "nsFontMetrics.h"
+#include "nsGenericHTMLElement.h"
+#include "nsLineBox.h"
+#include "nsLineLayout.h"
+#include "nsPlaceholderFrame.h"
+#include "nsStyleConsts.h"
+#include "nsFrameManager.h"
+#include "nsPresContext.h"
+#include "nsPresContextInlines.h"
+#include "nsHTMLParts.h"
+#include "nsGkAtoms.h"
+#include "nsAttrValueInlines.h"
+#include "mozilla/Sprintf.h"
+#include "nsFloatManager.h"
+#include "prenv.h"
+#include "nsError.h"
+#include "nsIScrollableFrame.h"
+#include <algorithm>
+#include "nsLayoutUtils.h"
+#include "nsDisplayList.h"
+#include "nsCSSAnonBoxes.h"
+#include "nsCSSFrameConstructor.h"
+#include "TextOverflow.h"
+#include "nsIFrameInlines.h"
+#include "CounterStyleManager.h"
+#include "mozilla/dom/HTMLDetailsElement.h"
+#include "mozilla/dom/HTMLSummaryElement.h"
+#include "mozilla/dom/Selection.h"
+#include "mozilla/PresShell.h"
+#include "mozilla/RestyleManager.h"
+#include "mozilla/ServoStyleSet.h"
+#include "mozilla/Telemetry.h"
+#include "nsFlexContainerFrame.h"
+#include "nsFileControlFrame.h"
+#include "nsMathMLContainerFrame.h"
+#include "nsSelectsAreaFrame.h"
+
+#include "nsBidiPresUtils.h"
+
+#include <inttypes.h>
+
+static const int MIN_LINES_NEEDING_CURSOR = 20;
+
+using namespace mozilla;
+using namespace mozilla::css;
+using namespace mozilla::dom;
+using namespace mozilla::layout;
+using AbsPosReflowFlags = nsAbsoluteContainingBlock::AbsPosReflowFlags;
+using ClearFloatsResult = BlockReflowState::ClearFloatsResult;
+using ShapeType = nsFloatManager::ShapeType;
+
+static void MarkAllDescendantLinesDirty(nsBlockFrame* aBlock) {
+  for (auto& line : aBlock->Lines()) {
+    if (line.IsBlock()) {
+      nsBlockFrame* bf = do_QueryFrame(line.mFirstChild);
+      if (bf) {
+        MarkAllDescendantLinesDirty(bf);
+      }
+    }
+    line.MarkDirty();
+  }
+}
+
+static void MarkSameFloatManagerLinesDirty(nsBlockFrame* aBlock) {
+  nsBlockFrame* blockWithFloatMgr = aBlock;
+  while (!blockWithFloatMgr->HasAnyStateBits(NS_BLOCK_BFC_STATE_BITS)) {
+    nsBlockFrame* bf = do_QueryFrame(blockWithFloatMgr->GetParent());
+    if (!bf) {
+      break;
+    }
+    blockWithFloatMgr = bf;
+  }
+
+  // Mark every line at and below the line where the float was
+  // dirty, and mark their lines dirty too. We could probably do
+  // something more efficient --- e.g., just dirty the lines that intersect
+  // the float vertically.
+  MarkAllDescendantLinesDirty(blockWithFloatMgr);
+}
+
+/**
+ * Returns true if aFrame is a block that has one or more float children.
+ */
+static bool BlockHasAnyFloats(nsIFrame* aFrame) {
+  nsBlockFrame* block = do_QueryFrame(aFrame);
+  if (!block) {
+    return false;
+  }
+  if (block->GetChildList(FrameChildListID::Float).FirstChild()) {
+    return true;
+  }
+
+  for (const auto& line : block->Lines()) {
+    if (line.IsBlock() && BlockHasAnyFloats(line.mFirstChild)) {
+      return true;
+    }
+  }
+  return false;
+}
+
+/**
+ * Determines whether the given frame is visible or has
+ * visible children that participate in the same line. Frames
+ * that are not line participants do not have their
+ * children checked.
+ */
+static bool FrameHasVisibleInlineContent(nsIFrame* aFrame) {
+  MOZ_ASSERT(aFrame, "Frame argument cannot be null");
+
+  if (aFrame->StyleVisibility()->IsVisible()) {
+    return true;
+  }
+
+  if (aFrame->IsLineParticipant()) {
+    for (nsIFrame* kid : aFrame->PrincipalChildList()) {
+      if (kid->StyleVisibility()->IsVisible() ||
+          FrameHasVisibleInlineContent(kid)) {
+        return true;
+      }
+    }
+  }
+  return false;
+}
+
+/**
+ * Determines whether any of the frames descended from the
+ * given line have inline content with 'visibility: visible'.
+ * This function calls FrameHasVisibleInlineContent to process
+ * each frame in the line's child list.
+ */
+static bool LineHasVisibleInlineContent(nsLineBox* aLine) {
+  nsIFrame* kid = aLine->mFirstChild;
+  int32_t n = aLine->GetChildCount();
+  while (n-- > 0) {
+    if (FrameHasVisibleInlineContent(kid)) {
+      return true;
+    }
+
+    kid = kid->GetNextSibling();
+  }
+
+  return false;
+}
+
+/**
+ * Iterates through the frame's in-flow children and
+ * unions the ink overflow of all text frames which
+ * participate in the line aFrame belongs to.
+ * If a child of aFrame is not a text frame,
+ * we recurse with the child as the aFrame argument.
+ * If aFrame isn't a line participant, we skip it entirely
+ * and return an empty rect.
+ * The resulting nsRect is offset relative to the parent of aFrame.
+ */
+static nsRect GetFrameTextArea(nsIFrame* aFrame,
+                               nsDisplayListBuilder* aBuilder) {
+  nsRect textArea;
+  if (const nsTextFrame* textFrame = do_QueryFrame(aFrame)) {
+    if (!textFrame->IsEntirelyWhitespace()) {
+      textArea = aFrame->InkOverflowRect();
+    }
+  } else if (aFrame->IsLineParticipant()) {
+    for (nsIFrame* kid : aFrame->PrincipalChildList()) {
+      nsRect kidTextArea = GetFrameTextArea(kid, aBuilder);
+      textArea.OrWith(kidTextArea);
+    }
+  }
+  // add aFrame's position to keep textArea relative to aFrame's parent
+  return textArea + aFrame->GetPosition();
+}
+
+/**
+ * Iterates through the line's children and
+ * unions the ink overflow of all text frames.
+ * GetFrameTextArea unions and returns the ink overflow
+ * from all line-participating text frames within the given child.
+ * The nsRect returned from GetLineTextArea is offset
+ * relative to the given line.
+ */
+static nsRect GetLineTextArea(nsLineBox* aLine,
+                              nsDisplayListBuilder* aBuilder) {
+  nsRect textArea;
+  nsIFrame* kid = aLine->mFirstChild;
+  int32_t n = aLine->GetChildCount();
+  while (n-- > 0) {
+    nsRect kidTextArea = GetFrameTextArea(kid, aBuilder);
+    textArea.OrWith(kidTextArea);
+    kid = kid->GetNextSibling();
+  }
+
+  return textArea;
+}
+
+/**
+ * Starting with aFrame, iterates upward through parent frames and checks for
+ * non-transparent background colors. If one is found, we use that as our
+ * backplate color. Otheriwse, we use the default background color from
+ * our high contrast theme.
+ */
+static nscolor GetBackplateColor(nsIFrame* aFrame) {
+  nsPresContext* pc = aFrame->PresContext();
+  nscolor currentBackgroundColor = NS_TRANSPARENT;
+  for (nsIFrame* frame = aFrame; frame; frame = frame->GetParent()) {
+    // NOTE(emilio): We assume themed frames (frame->IsThemed()) have correct
+    // background-color information so as to compute the right backplate color.
+    //
+    // This holds because HTML widgets with author-specified backgrounds or
+    // borders disable theming. So as long as the UA-specified background colors
+    // match the actual theme (which they should because we always use system
+    // colors with the non-native theme, and native system colors should also
+    // match the native theme), then we're alright and we should compute an
+    // appropriate backplate color.
+    const auto* style = frame->Style();
+    if (style->StyleBackground()->IsTransparent(style)) {
+      continue;
+    }
+    bool drawImage = false, drawColor = false;
+    nscolor backgroundColor = nsCSSRendering::DetermineBackgroundColor(
+        pc, style, frame, drawImage, drawColor);
+    if (!drawColor && !drawImage) {
+      continue;
+    }
+    if (NS_GET_A(backgroundColor) == 0) {
+      // Even if there's a background image, if there's no background color we
+      // keep going up the frame tree, see bug 1723938.
+      continue;
+    }
+    if (NS_GET_A(currentBackgroundColor) == 0) {
+      // Try to avoid somewhat expensive math in the common case.
+      currentBackgroundColor = backgroundColor;
+    } else {
+      currentBackgroundColor =
+          NS_ComposeColors(backgroundColor, currentBackgroundColor);
+    }
+    if (NS_GET_A(currentBackgroundColor) == 0xff) {
+      // If fully opaque, we're done, otherwise keep going up blending with our
+      // background.
+      return currentBackgroundColor;
+    }
+  }
+  nscolor backgroundColor = aFrame->PresContext()->DefaultBackgroundColor();
+  if (NS_GET_A(currentBackgroundColor) == 0) {
+    return backgroundColor;
+  }
+  return NS_ComposeColors(backgroundColor, currentBackgroundColor);
+}
+
+#ifdef DEBUG
+#  include "nsBlockDebugFlags.h"
+
+bool nsBlockFrame::gLamePaintMetrics;
+bool nsBlockFrame::gLameReflowMetrics;
+bool nsBlockFrame::gNoisy;
+bool nsBlockFrame::gNoisyDamageRepair;
+bool nsBlockFrame::gNoisyIntrinsic;
+bool nsBlockFrame::gNoisyReflow;
+bool nsBlockFrame::gReallyNoisyReflow;
+bool nsBlockFrame::gNoisyFloatManager;
+bool nsBlockFrame::gVerifyLines;
+bool nsBlockFrame::gDisableResizeOpt;
+
+int32_t nsBlockFrame::gNoiseIndent;
+
+struct BlockDebugFlags {
+  const char* name;
+  bool* on;
+};
+
+static const BlockDebugFlags gFlags[] = {
+    {"reflow", &nsBlockFrame::gNoisyReflow},
+    {"really-noisy-reflow", &nsBlockFrame::gReallyNoisyReflow},
+    {"intrinsic", &nsBlockFrame::gNoisyIntrinsic},
+    {"float-manager", &nsBlockFrame::gNoisyFloatManager},
+    {"verify-lines", &nsBlockFrame::gVerifyLines},
+    {"damage-repair", &nsBlockFrame::gNoisyDamageRepair},
+    {"lame-paint-metrics", &nsBlockFrame::gLamePaintMetrics},
+    {"lame-reflow-metrics", &nsBlockFrame::gLameReflowMetrics},
+    {"disable-resize-opt", &nsBlockFrame::gDisableResizeOpt},
+};
+#  define NUM_DEBUG_FLAGS (sizeof(gFlags) / sizeof(gFlags[0]))
+
+static void ShowDebugFlags() {
+  printf("Here are the available GECKO_BLOCK_DEBUG_FLAGS:\n");
+  const BlockDebugFlags* bdf = gFlags;
+  const BlockDebugFlags* end = gFlags + NUM_DEBUG_FLAGS;
+  for (; bdf < end; bdf++) {
+    printf("  %s\n", bdf->name);
+  }
+  printf("Note: GECKO_BLOCK_DEBUG_FLAGS is a comma separated list of flag\n");
+  printf("names (no whitespace)\n");
+}
+
+void nsBlockFrame::InitDebugFlags() {
+  static bool firstTime = true;
+  if (firstTime) {
+    firstTime = false;
+    char* flags = PR_GetEnv("GECKO_BLOCK_DEBUG_FLAGS");
+    if (flags) {
+      bool error = false;
+      for (;;) {
+        char* cm = strchr(flags, ',');
+        if (cm) {
+          *cm = '\0';
+        }
+
+        bool found = false;
+        const BlockDebugFlags* bdf = gFlags;
+        const BlockDebugFlags* end = gFlags + NUM_DEBUG_FLAGS;
+        for (; bdf < end; bdf++) {
+          if (nsCRT::strcasecmp(bdf->name, flags) == 0) {
+            *(bdf->on) = true;
+            printf("nsBlockFrame: setting %s debug flag on\n", bdf->name);
+            gNoisy = true;
+            found = true;
+            break;
+          }
+        }
+        if (!found) {
+          error = true;
+        }
+
+        if (!cm) {
+          break;
+        }
+        *cm = ',';
+        flags = cm + 1;
+      }
+      if (error) {
+        ShowDebugFlags();
+      }
+    }
+  }
+}
+
+#endif
+
+//----------------------------------------------------------------------
+
+// Debugging support code
+
+#ifdef DEBUG
+const char* nsBlockFrame::kReflowCommandType[] = {
+    "ContentChanged", "StyleChanged", "ReflowDirty", "Timeout", "UserDefined",
+};
+
+const char* nsBlockFrame::LineReflowStatusToString(
+    LineReflowStatus aLineReflowStatus) const {
+  switch (aLineReflowStatus) {
+    case LineReflowStatus::OK:
+      return "LINE_REFLOW_OK";
+    case LineReflowStatus::Stop:
+      return "LINE_REFLOW_STOP";
+    case LineReflowStatus::RedoNoPull:
+      return "LINE_REFLOW_REDO_NO_PULL";
+    case LineReflowStatus::RedoMoreFloats:
+      return "LINE_REFLOW_REDO_MORE_FLOATS";
+    case LineReflowStatus::RedoNextBand:
+      return "LINE_REFLOW_REDO_NEXT_BAND";
+    case LineReflowStatus::Truncated:
+      return "LINE_REFLOW_TRUNCATED";
+  }
+  return "unknown";
+}
+
+#endif
+
+#ifdef REFLOW_STATUS_COVERAGE
+static void RecordReflowStatus(bool aChildIsBlock,
+                               const nsReflowStatus& aFrameReflowStatus) {
+  static uint32_t record[2];
+
+  // 0: child-is-block
+  // 1: child-is-inline
+  int index = 0;
+  if (!aChildIsBlock) {
+    index |= 1;
+  }
+
+  // Compute new status
+  uint32_t newS = record[index];
+  if (aFrameReflowStatus.IsInlineBreak()) {
+    if (aFrameReflowStatus.IsInlineBreakBefore()) {
+      newS |= 1;
+    } else if (aFrameReflowStatus.IsIncomplete()) {
+      newS |= 2;
+    } else {
+      newS |= 4;
+    }
+  } else if (aFrameReflowStatus.IsIncomplete()) {
+    newS |= 8;
+  } else {
+    newS |= 16;
+  }
+
+  // Log updates to the status that yield different values
+  if (record[index] != newS) {
+    record[index] = newS;
+    printf("record(%d): %02x %02x\n", index, record[0], record[1]);
+  }
+}
+#endif
+
+NS_DECLARE_FRAME_PROPERTY_WITH_DTOR_NEVER_CALLED(OverflowLinesProperty,
+                                                 nsBlockFrame::FrameLines)
+NS_DECLARE_FRAME_PROPERTY_FRAMELIST(OverflowOutOfFlowsProperty)
+NS_DECLARE_FRAME_PROPERTY_FRAMELIST(PushedFloatProperty)
+NS_DECLARE_FRAME_PROPERTY_FRAMELIST(OutsideMarkerProperty)
+NS_DECLARE_FRAME_PROPERTY_WITHOUT_DTOR(InsideMarkerProperty, nsIFrame)
+NS_DECLARE_FRAME_PROPERTY_SMALL_VALUE(BlockEndEdgeOfChildrenProperty, nscoord)
+
+//----------------------------------------------------------------------
+
+nsBlockFrame* NS_NewBlockFrame(PresShell* aPresShell, ComputedStyle* aStyle) {
+  return new (aPresShell) nsBlockFrame(aStyle, aPresShell->GetPresContext());
+}
+
+nsBlockFrame* NS_NewBlockFormattingContext(PresShell* aPresShell,
+                                           ComputedStyle* aComputedStyle) {
+  nsBlockFrame* blockFrame = NS_NewBlockFrame(aPresShell, aComputedStyle);
+  blockFrame->AddStateBits(NS_BLOCK_STATIC_BFC);
+  return blockFrame;
+}
+
+NS_IMPL_FRAMEARENA_HELPERS(nsBlockFrame)
+
+nsBlockFrame::~nsBlockFrame() = default;
+
+void nsBlockFrame::AddSizeOfExcludingThisForTree(
+    nsWindowSizes& aWindowSizes) const {
+  nsContainerFrame::AddSizeOfExcludingThisForTree(aWindowSizes);
+
+  // Add the size of any nsLineBox::mFrames hashtables we might have:
+  for (const auto& line : Lines()) {
+    line.AddSizeOfExcludingThis(aWindowSizes);
+  }
+  const FrameLines* overflowLines = GetOverflowLines();
+  if (overflowLines) {
+    ConstLineIterator line = overflowLines->mLines.begin(),
+                      line_end = overflowLines->mLines.end();
+    for (; line != line_end; ++line) {
+      line->AddSizeOfExcludingThis(aWindowSizes);
+    }
+  }
+}
+
+void nsBlockFrame::Destroy(DestroyContext& aContext) {
+  ClearLineCursors();
+  DestroyAbsoluteFrames(aContext);
+  mFloats.DestroyFrames(aContext);
+  nsPresContext* presContext = PresContext();
+  mozilla::PresShell* presShell = presContext->PresShell();
+  nsLineBox::DeleteLineList(presContext, mLines, &mFrames, aContext);
+
+  if (HasPushedFloats()) {
+    SafelyDestroyFrameListProp(aContext, presShell, PushedFloatProperty());
+    RemoveStateBits(NS_BLOCK_HAS_PUSHED_FLOATS);
+  }
+
+  // destroy overflow lines now
+  FrameLines* overflowLines = RemoveOverflowLines();
+  if (overflowLines) {
+    nsLineBox::DeleteLineList(presContext, overflowLines->mLines,
+                              &overflowLines->mFrames, aContext);
+    delete overflowLines;
+  }
+
+  if (HasAnyStateBits(NS_BLOCK_HAS_OVERFLOW_OUT_OF_FLOWS)) {
+    SafelyDestroyFrameListProp(aContext, presShell,
+                               OverflowOutOfFlowsProperty());
+    RemoveStateBits(NS_BLOCK_HAS_OVERFLOW_OUT_OF_FLOWS);
+  }
+
+  if (HasOutsideMarker()) {
+    SafelyDestroyFrameListProp(aContext, presShell, OutsideMarkerProperty());
+    RemoveStateBits(NS_BLOCK_FRAME_HAS_OUTSIDE_MARKER);
+  }
+
+  nsContainerFrame::Destroy(aContext);
+}
+
+/* virtual */
+nsILineIterator* nsBlockFrame::GetLineIterator() {
+  nsLineIterator* iter = GetProperty(LineIteratorProperty());
+  if (!iter) {
+    const nsStyleVisibility* visibility = StyleVisibility();
+    iter = new nsLineIterator(mLines,
+                              visibility->mDirection == StyleDirection::Rtl);
+    SetProperty(LineIteratorProperty(), iter);
+  }
+  return iter;
+}
+
+NS_QUERYFRAME_HEAD(nsBlockFrame)
+  NS_QUERYFRAME_ENTRY(nsBlockFrame)
+NS_QUERYFRAME_TAIL_INHERITING(nsContainerFrame)
+
+#ifdef DEBUG_FRAME_DUMP
+void nsBlockFrame::List(FILE* out, const char* aPrefix,
+                        ListFlags aFlags) const {
+  nsCString str;
+  ListGeneric(str, aPrefix, aFlags);
+
+  fprintf_stderr(out, "%s <\n", str.get());
+
+  nsCString pfx(aPrefix);
+  pfx += "  ";
+
+  // Output the lines
+  if (!mLines.empty()) {
+    ConstLineIterator line = LinesBegin(), line_end = LinesEnd();
+    for (; line != line_end; ++line) {
+      line->List(out, pfx.get(), aFlags);
+    }
+  }
+
+  // Output the overflow lines.
+  const FrameLines* overflowLines = GetOverflowLines();
+  if (overflowLines && !overflowLines->mLines.empty()) {
+    fprintf_stderr(out, "%sOverflow-lines %p/%p <\n", pfx.get(), overflowLines,
+                   &overflowLines->mFrames);
+    nsCString nestedPfx(pfx);
+    nestedPfx += "  ";
+    ConstLineIterator line = overflowLines->mLines.begin(),
+                      line_end = overflowLines->mLines.end();
+    for (; line != line_end; ++line) {
+      line->List(out, nestedPfx.get(), aFlags);
+    }
+    fprintf_stderr(out, "%s>\n", pfx.get());
+  }
+
+  // skip the principal list - we printed the lines above
+  // skip the overflow list - we printed the overflow lines above
+  ChildListIDs skip = {FrameChildListID::Principal, FrameChildListID::Overflow};
+  ListChildLists(out, pfx.get(), aFlags, skip);
+
+  fprintf_stderr(out, "%s>\n", aPrefix);
+}
+
+nsresult nsBlockFrame::GetFrameName(nsAString& aResult) const {
+  return MakeFrameName(u"Block"_ns, aResult);
+}
+#endif
+
+void nsBlockFrame::InvalidateFrame(uint32_t aDisplayItemKey,
+                                   bool aRebuildDisplayItems) {
+  if (IsInSVGTextSubtree()) {
+    NS_ASSERTION(GetParent()->IsSVGTextFrame(),
+                 "unexpected block frame in SVG text");
+    GetParent()->InvalidateFrame();
+    return;
+  }
+  nsContainerFrame::InvalidateFrame(aDisplayItemKey, aRebuildDisplayItems);
+}
+
+void nsBlockFrame::InvalidateFrameWithRect(const nsRect& aRect,
+                                           uint32_t aDisplayItemKey,
+                                           bool aRebuildDisplayItems) {
+  if (IsInSVGTextSubtree()) {
+    NS_ASSERTION(GetParent()->IsSVGTextFrame(),
+                 "unexpected block frame in SVG text");
+    GetParent()->InvalidateFrame();
+    return;
+  }
+  nsContainerFrame::InvalidateFrameWithRect(aRect, aDisplayItemKey,
+                                            aRebuildDisplayItems);
+}
+
+nscoord nsBlockFrame::SynthesizeFallbackBaseline(
+    WritingMode aWM, BaselineSharingGroup aBaselineGroup) const {
+  return Baseline::SynthesizeBOffsetFromMarginBox(this, aWM, aBaselineGroup);
+}
+
+template <typename LineIteratorType>
+Maybe<nscoord> nsBlockFrame::GetBaselineBOffset(
+    LineIteratorType aStart, LineIteratorType aEnd, WritingMode aWM,
+    BaselineSharingGroup aBaselineGroup,
+    BaselineExportContext aExportContext) const {
+  MOZ_ASSERT((std::is_same_v<LineIteratorType, ConstLineIterator> &&
+              aBaselineGroup == BaselineSharingGroup::First) ||
+                 (std::is_same_v<LineIteratorType, ConstReverseLineIterator> &&
+                  aBaselineGroup == BaselineSharingGroup::Last),
+             "Iterator direction must match baseline sharing group.");
+  for (auto line = aStart; line != aEnd; ++line) {
+    if (!line->IsBlock()) {
+      // XXX Is this the right test?  We have some bogus empty lines
+      // floating around, but IsEmpty is perhaps too weak.
+      if (line->BSize() != 0 || !line->IsEmpty()) {
+        const auto ascent = line->BStart() + line->GetLogicalAscent();
+        if (aBaselineGroup == BaselineSharingGroup::Last) {
+          return Some(BSize(aWM) - ascent);
+        }
+        return Some(ascent);
+      }
+      continue;
+    }
+    nsIFrame* kid = line->mFirstChild;
+    if (aWM.IsOrthogonalTo(kid->GetWritingMode())) {
+      continue;
+    }
+    if (aExportContext == BaselineExportContext::LineLayout &&
+        kid->IsTableWrapperFrame()) {
+      // `<table>` in inline-block context does not export any baseline.
+      continue;
+    }
+    const auto kidBaselineGroup =
+        aExportContext == BaselineExportContext::LineLayout
+            ? kid->GetDefaultBaselineSharingGroup()
+            : aBaselineGroup;
+    const auto kidBaseline =
+        kid->GetNaturalBaselineBOffset(aWM, kidBaselineGroup, aExportContext);
+    if (!kidBaseline) {
+      continue;
+    }
+    auto result = *kidBaseline;
+    if (kidBaselineGroup == BaselineSharingGroup::Last) {
+      result = kid->BSize(aWM) - result;
+    }
+    // Ignore relative positioning for baseline calculations.
+    const nsSize& sz = line->mContainerSize;
+    result += kid->GetLogicalNormalPosition(aWM, sz).B(aWM);
+    if (aBaselineGroup == BaselineSharingGroup::Last) {
+      return Some(BSize(aWM) - result);
+    }
+    return Some(result);
+  }
+  return Nothing{};
+}
+
+Maybe<nscoord> nsBlockFrame::GetNaturalBaselineBOffset(
+    WritingMode aWM, BaselineSharingGroup aBaselineGroup,
+    BaselineExportContext aExportContext) const {
+  if (StyleDisplay()->IsContainLayout()) {
+    return Nothing{};
+  }
+
+  if (aBaselineGroup == BaselineSharingGroup::First) {
+    return GetBaselineBOffset(LinesBegin(), LinesEnd(), aWM, aBaselineGroup,
+                              aExportContext);
+  }
+
+  return GetBaselineBOffset(LinesRBegin(), LinesREnd(), aWM, aBaselineGroup,
+                            aExportContext);
+}
+
+nscoord nsBlockFrame::GetCaretBaseline() const {
+  nsRect contentRect = GetContentRect();
+  nsMargin bp = GetUsedBorderAndPadding();
+
+  if (!mLines.empty()) {
+    ConstLineIterator line = LinesBegin();
+    if (!line->IsEmpty()) {
+      if (line->IsBlock()) {
+        return bp.top + line->mFirstChild->GetCaretBaseline();
+      }
+      return line->BStart() + line->GetLogicalAscent();
+    }
+  }
+
+  float inflation = nsLayoutUtils::FontSizeInflationFor(this);
+  RefPtr<nsFontMetrics> fm =
+      nsLayoutUtils::GetFontMetricsForFrame(this, inflation);
+  nscoord lineHeight = ReflowInput::CalcLineHeight(
+      *Style(), PresContext(), GetContent(), contentRect.height, inflation);
+  const WritingMode wm = GetWritingMode();
+  return nsLayoutUtils::GetCenteredFontBaseline(fm, lineHeight,
+                                                wm.IsLineInverted()) +
+         bp.top;
+}
+
+/////////////////////////////////////////////////////////////////////////////
+// Child frame enumeration
+
+const nsFrameList& nsBlockFrame::GetChildList(ChildListID aListID) const {
+  switch (aListID) {
+    case FrameChildListID::Principal:
+      return mFrames;
+    case FrameChildListID::Overflow: {
+      FrameLines* overflowLines = GetOverflowLines();
+      return overflowLines ? overflowLines->mFrames : nsFrameList::EmptyList();
+    }
+    case FrameChildListID::Float:
+      return mFloats;
+    case FrameChildListID::OverflowOutOfFlow: {
+      const nsFrameList* list = GetOverflowOutOfFlows();
+      return list ? *list : nsFrameList::EmptyList();
+    }
+    case FrameChildListID::PushedFloats: {
+      const nsFrameList* list = GetPushedFloats();
+      return list ? *list : nsFrameList::EmptyList();
+    }
+    case FrameChildListID::Bullet: {
+      const nsFrameList* list = GetOutsideMarkerList();
+      return list ? *list : nsFrameList::EmptyList();
+    }
+    default:
+      return nsContainerFrame::GetChildList(aListID);
+  }
+}
+
+void nsBlockFrame::GetChildLists(nsTArray<ChildList>* aLists) const {
+  nsContainerFrame::GetChildLists(aLists);
+  FrameLines* overflowLines = GetOverflowLines();
+  if (overflowLines) {
+    overflowLines->mFrames.AppendIfNonempty(aLists, FrameChildListID::Overflow);
+  }
+  const nsFrameList* list = GetOverflowOutOfFlows();
+  if (list) {
+    list->AppendIfNonempty(aLists, FrameChildListID::OverflowOutOfFlow);
+  }
+  mFloats.AppendIfNonempty(aLists, FrameChildListID::Float);
+  list = GetOutsideMarkerList();
+  if (list) {
+    list->AppendIfNonempty(aLists, FrameChildListID::Bullet);
+  }
+  list = GetPushedFloats();
+  if (list) {
+    list->AppendIfNonempty(aLists, FrameChildListID::PushedFloats);
+  }
+}
+
+/* virtual */
+bool nsBlockFrame::IsFloatContainingBlock() const { return true; }
+
+/**
+ * Remove the first line from aFromLines and adjust the associated frame list
+ * aFromFrames accordingly.  The removed line is assigned to *aOutLine and
+ * a frame list with its frames is assigned to *aOutFrames, i.e. the frames
+ * that were extracted from the head of aFromFrames.
+ * aFromLines must contain at least one line, the line may be empty.
+ * @return true if aFromLines becomes empty
+ */
+static bool RemoveFirstLine(nsLineList& aFromLines, nsFrameList& aFromFrames,
+                            nsLineBox** aOutLine, nsFrameList* aOutFrames) {
+  nsLineList_iterator removedLine = aFromLines.begin();
+  *aOutLine = removedLine;
+  nsLineList_iterator next = aFromLines.erase(removedLine);
+  bool isLastLine = next == aFromLines.end();
+  nsIFrame* firstFrameInNextLine = isLastLine ? nullptr : next->mFirstChild;
+  *aOutFrames = aFromFrames.TakeFramesBefore(firstFrameInNextLine);
+  return isLastLine;
+}
+
+//////////////////////////////////////////////////////////////////////
+// Reflow methods
+
+/* virtual */
+void nsBlockFrame::MarkIntrinsicISizesDirty() {
+  nsBlockFrame* dirtyBlock = static_cast<nsBlockFrame*>(FirstContinuation());
+  dirtyBlock->mCachedMinISize = NS_INTRINSIC_ISIZE_UNKNOWN;
+  dirtyBlock->mCachedPrefISize = NS_INTRINSIC_ISIZE_UNKNOWN;
+  if (!HasAnyStateBits(NS_BLOCK_NEEDS_BIDI_RESOLUTION)) {
+    for (nsIFrame* frame = dirtyBlock; frame;
+         frame = frame->GetNextContinuation()) {
+      frame->AddStateBits(NS_BLOCK_NEEDS_BIDI_RESOLUTION);
+    }
+  }
+
+  nsContainerFrame::MarkIntrinsicISizesDirty();
+}
+
+void nsBlockFrame::CheckIntrinsicCacheAgainstShrinkWrapState() {
+  nsPresContext* presContext = PresContext();
+  if (!nsLayoutUtils::FontSizeInflationEnabled(presContext)) {
+    return;
+  }
+  bool inflationEnabled = !presContext->mInflationDisabledForShrinkWrap;
+  if (inflationEnabled != HasAnyStateBits(NS_BLOCK_FRAME_INTRINSICS_INFLATED)) {
+    mCachedMinISize = NS_INTRINSIC_ISIZE_UNKNOWN;
+    mCachedPrefISize = NS_INTRINSIC_ISIZE_UNKNOWN;
+    if (inflationEnabled) {
+      AddStateBits(NS_BLOCK_FRAME_INTRINSICS_INFLATED);
+    } else {
+      RemoveStateBits(NS_BLOCK_FRAME_INTRINSICS_INFLATED);
+    }
+  }
+}
+
+// Whether this line is indented by the text-indent amount.
+bool nsBlockFrame::TextIndentAppliesTo(const LineIterator& aLine) const {
+  const auto& textIndent = StyleText()->mTextIndent;
+
+  bool isFirstLineOrAfterHardBreak = [&] {
+    if (aLine != LinesBegin()) {
+      // If not the first line of the block, but 'each-line' is in effect,
+      // check if the previous line was not wrapped.
+      return textIndent.each_line && !aLine.prev()->IsLineWrapped();
+    }
+    if (nsBlockFrame* prevBlock = do_QueryFrame(GetPrevInFlow())) {
+      // There's a prev-in-flow, so this only counts as a first-line if
+      // 'each-line' and the prev-in-flow's last line was not wrapped.
+      return textIndent.each_line &&
+             (prevBlock->Lines().empty() ||
+              !prevBlock->LinesEnd().prev()->IsLineWrapped());
+    }
+    return true;
+  }();
+
+  // The 'hanging' option inverts which lines are/aren't indented.
+  return isFirstLineOrAfterHardBreak != textIndent.hanging;
+}
+
+/* virtual */
+nscoord nsBlockFrame::GetMinISize(gfxContext* aRenderingContext) {
+  nsIFrame* firstInFlow = FirstContinuation();
+  if (firstInFlow != this) {
+    return firstInFlow->GetMinISize(aRenderingContext);
+  }
+
+  DISPLAY_MIN_INLINE_SIZE(this, mCachedMinISize);
+
+  CheckIntrinsicCacheAgainstShrinkWrapState();
+
+  if (mCachedMinISize != NS_INTRINSIC_ISIZE_UNKNOWN) {
+    return mCachedMinISize;
+  }
+
+  if (Maybe<nscoord> containISize = ContainIntrinsicISize()) {
+    mCachedMinISize = *containISize;
+    return mCachedMinISize;
+  }
+
+#ifdef DEBUG
+  if (gNoisyIntrinsic) {
+    IndentBy(stdout, gNoiseIndent);
+    ListTag(stdout);
+    printf(": GetMinISize\n");
+  }
+  AutoNoisyIndenter indenter(gNoisyIntrinsic);
+#endif
+
+  for (nsBlockFrame* curFrame = this; curFrame;
+       curFrame = static_cast<nsBlockFrame*>(curFrame->GetNextContinuation())) {
+    curFrame->LazyMarkLinesDirty();
+  }
+
+  if (HasAnyStateBits(NS_BLOCK_NEEDS_BIDI_RESOLUTION) &&
+      PresContext()->BidiEnabled()) {
+    ResolveBidi();
+  }
+
+  const bool whiteSpaceCanWrap = StyleText()->WhiteSpaceCanWrapStyle();
+  InlineMinISizeData data;
+  for (nsBlockFrame* curFrame = this; curFrame;
+       curFrame = static_cast<nsBlockFrame*>(curFrame->GetNextContinuation())) {
+    for (LineIterator line = curFrame->LinesBegin(),
+                      line_end = curFrame->LinesEnd();
+         line != line_end; ++line) {
+#ifdef DEBUG
+      if (gNoisyIntrinsic) {
+        IndentBy(stdout, gNoiseIndent);
+        printf("line (%s%s)\n", line->IsBlock() ? "block" : "inline",
+               line->IsEmpty() ? ", empty" : "");
+      }
+      AutoNoisyIndenter lineindent(gNoisyIntrinsic);
+#endif
+      if (line->IsBlock()) {
+        data.ForceBreak();
+        data.mCurrentLine = nsLayoutUtils::IntrinsicForContainer(
+            aRenderingContext, line->mFirstChild, IntrinsicISizeType::MinISize);
+        data.ForceBreak();
+      } else {
+        if (!curFrame->GetPrevContinuation() && TextIndentAppliesTo(line)) {
+          data.mCurrentLine += StyleText()->mTextIndent.length.Resolve(0);
+        }
+        data.mLine = &line;
+        data.SetLineContainer(curFrame);
+        nsIFrame* kid = line->mFirstChild;
+        for (int32_t i = 0, i_end = line->GetChildCount(); i != i_end;
+             ++i, kid = kid->GetNextSibling()) {
+          kid->AddInlineMinISize(aRenderingContext, &data);
+          if (whiteSpaceCanWrap && data.mTrailingWhitespace) {
+            data.OptionallyBreak();
+          }
+        }
+      }
+#ifdef DEBUG
+      if (gNoisyIntrinsic) {
+        IndentBy(stdout, gNoiseIndent);
+        printf("min: [prevLines=%d currentLine=%d]\n", data.mPrevLines,
+               data.mCurrentLine);
+      }
+#endif
+    }
+  }
+  data.ForceBreak();
+
+  mCachedMinISize = data.mPrevLines;
+  return mCachedMinISize;
+}
+
+/* virtual */
+nscoord nsBlockFrame::GetPrefISize(gfxContext* aRenderingContext) {
+  nsIFrame* firstInFlow = FirstContinuation();
+  if (firstInFlow != this) {
+    return firstInFlow->GetPrefISize(aRenderingContext);
+  }
+
+  DISPLAY_PREF_INLINE_SIZE(this, mCachedPrefISize);
+
+  CheckIntrinsicCacheAgainstShrinkWrapState();
+
+  if (mCachedPrefISize != NS_INTRINSIC_ISIZE_UNKNOWN) {
+    return mCachedPrefISize;
+  }
+
+  if (Maybe<nscoord> containISize = ContainIntrinsicISize()) {
+    mCachedPrefISize = *containISize;
+    return mCachedPrefISize;
+  }
+
+#ifdef DEBUG
+  if (gNoisyIntrinsic) {
+    IndentBy(stdout, gNoiseIndent);
+    ListTag(stdout);
+    printf(": GetPrefISize\n");
+  }
+  AutoNoisyIndenter indenter(gNoisyIntrinsic);
+#endif
+
+  for (nsBlockFrame* curFrame = this; curFrame;
+       curFrame = static_cast<nsBlockFrame*>(curFrame->GetNextContinuation())) {
+    curFrame->LazyMarkLinesDirty();
+  }
+
+  if (HasAnyStateBits(NS_BLOCK_NEEDS_BIDI_RESOLUTION) &&
+      PresContext()->BidiEnabled()) {
+    ResolveBidi();
+  }
+  InlinePrefISizeData data;
+  for (nsBlockFrame* curFrame = this; curFrame;
+       curFrame = static_cast<nsBlockFrame*>(curFrame->GetNextContinuation())) {
+    for (LineIterator line = curFrame->LinesBegin(),
+                      line_end = curFrame->LinesEnd();
+         line != line_end; ++line) {
+#ifdef DEBUG
+      if (gNoisyIntrinsic) {
+        IndentBy(stdout, gNoiseIndent);
+        printf("line (%s%s)\n", line->IsBlock() ? "block" : "inline",
+               line->IsEmpty() ? ", empty" : "");
+      }
+      AutoNoisyIndenter lineindent(gNoisyIntrinsic);
+#endif
+      if (line->IsBlock()) {
+        StyleClear clearType;
+        if (!data.mLineIsEmpty || BlockCanIntersectFloats(line->mFirstChild)) {
+          clearType = StyleClear::Both;
+        } else {
+          clearType = line->mFirstChild->StyleDisplay()->mClear;
+        }
+        data.ForceBreak(clearType);
+        data.mCurrentLine = nsLayoutUtils::IntrinsicForContainer(
+            aRenderingContext, line->mFirstChild,
+            IntrinsicISizeType::PrefISize);
+        data.ForceBreak();
+      } else {
+        if (!curFrame->GetPrevContinuation() && TextIndentAppliesTo(line)) {
+          nscoord indent = StyleText()->mTextIndent.length.Resolve(0);
+          data.mCurrentLine += indent;
+          // XXXmats should the test below be indent > 0?
+          if (indent != nscoord(0)) {
+            data.mLineIsEmpty = false;
+          }
+        }
+        data.mLine = &line;
+        data.SetLineContainer(curFrame);
+        nsIFrame* kid = line->mFirstChild;
+        for (int32_t i = 0, i_end = line->GetChildCount(); i != i_end;
+             ++i, kid = kid->GetNextSibling()) {
+          kid->AddInlinePrefISize(aRenderingContext, &data);
+        }
+      }
+#ifdef DEBUG
+      if (gNoisyIntrinsic) {
+        IndentBy(stdout, gNoiseIndent);
+        printf("pref: [prevLines=%d currentLine=%d]\n", data.mPrevLines,
+               data.mCurrentLine);
+      }
+#endif
+    }
+  }
+  data.ForceBreak();
+
+  mCachedPrefISize = data.mPrevLines;
+  return mCachedPrefISize;
+}
+
+nsRect nsBlockFrame::ComputeTightBounds(DrawTarget* aDrawTarget) const {
+  // be conservative
+  if (Style()->HasTextDecorationLines()) {
+    return InkOverflowRect();
+  }
+  return ComputeSimpleTightBounds(aDrawTarget);
+}
+
+/* virtual */
+nsresult nsBlockFrame::GetPrefWidthTightBounds(gfxContext* aRenderingContext,
+                                               nscoord* aX, nscoord* aXMost) {
+  nsIFrame* firstInFlow = FirstContinuation();
+  if (firstInFlow != this) {
+    return firstInFlow->GetPrefWidthTightBounds(aRenderingContext, aX, aXMost);
+  }
+
+  *aX = 0;
+  *aXMost = 0;
+
+  nsresult rv;
+  InlinePrefISizeData data;
+  for (nsBlockFrame* curFrame = this; curFrame;
+       curFrame = static_cast<nsBlockFrame*>(curFrame->GetNextContinuation())) {
+    for (LineIterator line = curFrame->LinesBegin(),
+                      line_end = curFrame->LinesEnd();
+         line != line_end; ++line) {
+      nscoord childX, childXMost;
+      if (line->IsBlock()) {
+        data.ForceBreak();
+        rv = line->mFirstChild->GetPrefWidthTightBounds(aRenderingContext,
+                                                        &childX, &childXMost);
+        NS_ENSURE_SUCCESS(rv, rv);
+        *aX = std::min(*aX, childX);
+        *aXMost = std::max(*aXMost, childXMost);
+      } else {
+        if (!curFrame->GetPrevContinuation() && TextIndentAppliesTo(line)) {
+          data.mCurrentLine += StyleText()->mTextIndent.length.Resolve(0);
+        }
+        data.mLine = &line;
+        data.SetLineContainer(curFrame);
+        nsIFrame* kid = line->mFirstChild;
+        for (int32_t i = 0, i_end = line->GetChildCount(); i != i_end;
+             ++i, kid = kid->GetNextSibling()) {
+          rv = kid->GetPrefWidthTightBounds(aRenderingContext, &childX,
+                                            &childXMost);
+          NS_ENSURE_SUCCESS(rv, rv);
+          *aX = std::min(*aX, data.mCurrentLine + childX);
+          *aXMost = std::max(*aXMost, data.mCurrentLine + childXMost);
+          kid->AddInlinePrefISize(aRenderingContext, &data);
+        }
+      }
+    }
+  }
+  data.ForceBreak();
+
+  return NS_OK;
+}
+
+/**
+ * Return whether aNewAvailableSpace is smaller *on either side*
+ * (inline-start or inline-end) than aOldAvailableSpace, so that we know
+ * if we need to redo layout on an line, replaced block, or block
+ * formatting context, because its height (which we used to compute
+ * aNewAvailableSpace) caused it to intersect additional floats.
+ */
+static bool AvailableSpaceShrunk(WritingMode aWM,
+                                 const LogicalRect& aOldAvailableSpace,
+                                 const LogicalRect& aNewAvailableSpace,
+                                 bool aCanGrow /* debug-only */) {
+  if (aNewAvailableSpace.ISize(aWM) == 0) {
+    // Positions are not significant if the inline size is zero.
+    return aOldAvailableSpace.ISize(aWM) != 0;
+  }
+  if (aCanGrow) {
+    NS_ASSERTION(
+        aNewAvailableSpace.IStart(aWM) <= aOldAvailableSpace.IStart(aWM) ||
+            aNewAvailableSpace.IEnd(aWM) <= aOldAvailableSpace.IEnd(aWM),
+        "available space should not shrink on the start side and "
+        "grow on the end side");
+    NS_ASSERTION(
+        aNewAvailableSpace.IStart(aWM) >= aOldAvailableSpace.IStart(aWM) ||
+            aNewAvailableSpace.IEnd(aWM) >= aOldAvailableSpace.IEnd(aWM),
+        "available space should not grow on the start side and "
+        "shrink on the end side");
+  } else {
+    NS_ASSERTION(
+        aOldAvailableSpace.IStart(aWM) <= aNewAvailableSpace.IStart(aWM) &&
+            aOldAvailableSpace.IEnd(aWM) >= aNewAvailableSpace.IEnd(aWM),
+        "available space should never grow");
+  }
+  // Have we shrunk on either side?
+  return aNewAvailableSpace.IStart(aWM) > aOldAvailableSpace.IStart(aWM) ||
+         aNewAvailableSpace.IEnd(aWM) < aOldAvailableSpace.IEnd(aWM);
+}
+
+static LogicalSize CalculateContainingBlockSizeForAbsolutes(
+    WritingMode aWM, const ReflowInput& aReflowInput, LogicalSize aFrameSize) {
+  // The issue here is that for a 'height' of 'auto' the reflow input
+  // code won't know how to calculate the containing block height
+  // because it's calculated bottom up. So we use our own computed
+  // size as the dimensions.
+  nsIFrame* frame = aReflowInput.mFrame;
+
+  LogicalSize cbSize(aFrameSize);
+  // Containing block is relative to the padding edge
+  const LogicalMargin border = aReflowInput.ComputedLogicalBorder(aWM);
+  cbSize.ISize(aWM) -= border.IStartEnd(aWM);
+  cbSize.BSize(aWM) -= border.BStartEnd(aWM);
+
+  if (frame->GetParent()->GetContent() != frame->GetContent() ||
+      frame->GetParent()->IsCanvasFrame()) {
+    return cbSize;
+  }
+
+  // We are a wrapped frame for the content (and the wrapper is not the
+  // canvas frame, whose size is not meaningful here).
+  // Use the container's dimensions, if they have been precomputed.
+  // XXX This is a hack! We really should be waiting until the outermost
+  // frame is fully reflowed and using the resulting dimensions, even
+  // if they're intrinsic.
+  // In fact we should be attaching absolute children to the outermost
+  // frame and not always sticking them in block frames.
+
+  // First, find the reflow input for the outermost frame for this content.
+  const ReflowInput* lastRI = &aReflowInput;
+  DebugOnly<const ReflowInput*> lastButOneRI = &aReflowInput;
+  while (lastRI->mParentReflowInput &&
+         lastRI->mParentReflowInput->mFrame->GetContent() ==
+             frame->GetContent()) {
+    lastButOneRI = lastRI;
+    lastRI = lastRI->mParentReflowInput;
+  }
+
+  if (lastRI == &aReflowInput) {
+    return cbSize;
+  }
+
+  // For scroll containers, we can just use cbSize (which is the padding-box
+  // size of the scrolled-content frame).
+  if (nsIScrollableFrame* scrollFrame = do_QueryFrame(lastRI->mFrame)) {
+    // Assert that we're not missing any frames between the abspos containing
+    // block and the scroll container.
+    // the parent.
+    Unused << scrollFrame;
+    MOZ_ASSERT(lastButOneRI == &aReflowInput);
+    return cbSize;
+  }
+
+  // Same for fieldsets, where the inner anonymous frame has the correct padding
+  // area with the legend taken into account.
+  if (lastRI->mFrame->IsFieldSetFrame()) {
+    return cbSize;
+  }
+
+  // We found a reflow input for the outermost wrapping frame, so use
+  // its computed metrics if available, converted to our writing mode
+  const LogicalSize lastRISize = lastRI->ComputedSize(aWM);
+  const LogicalMargin lastRIPadding = lastRI->ComputedLogicalPadding(aWM);
+  if (lastRISize.ISize(aWM) != NS_UNCONSTRAINEDSIZE) {
+    cbSize.ISize(aWM) =
+        std::max(0, lastRISize.ISize(aWM) + lastRIPadding.IStartEnd(aWM));
+  }
+  if (lastRISize.BSize(aWM) != NS_UNCONSTRAINEDSIZE) {
+    cbSize.BSize(aWM) =
+        std::max(0, lastRISize.BSize(aWM) + lastRIPadding.BStartEnd(aWM));
+  }
+
+  return cbSize;
+}
+
+/**
+ * Returns aFrame if it is a non-BFC block frame, and null otherwise.
+ *
+ * This is used to determine whether to recurse into aFrame when applying
+ * -webkit-line-clamp.
+ */
+static const nsBlockFrame* GetAsLineClampDescendant(const nsIFrame* aFrame) {
+  if (const nsBlockFrame* block = do_QueryFrame(aFrame)) {
+    if (!block->HasAnyStateBits(NS_BLOCK_BFC_STATE_BITS)) {
+      return block;
+    }
+  }
+  return nullptr;
+}
+
+static nsBlockFrame* GetAsLineClampDescendant(nsIFrame* aFrame) {
+  return const_cast<nsBlockFrame*>(
+      GetAsLineClampDescendant(const_cast<const nsIFrame*>(aFrame)));
+}
+
+static bool IsLineClampRoot(const nsBlockFrame* aFrame) {
+  if (!aFrame->StyleDisplay()->mWebkitLineClamp) {
+    return false;
+  }
+
+  if (!aFrame->HasAnyStateBits(NS_BLOCK_BFC_STATE_BITS)) {
+    return false;
+  }
+
+  if (StaticPrefs::layout_css_webkit_line_clamp_block_enabled()) {
+    return true;
+  }
+
+  // For now, -webkit-box is the only thing allowed to be a line-clamp root.
+  // Ideally we'd just make this work everywhere, but for now we're carrying
+  // this forward as a limitation on the legacy -webkit-line-clamp feature,
+  // since relaxing this limitation might create webcompat trouble.
+  auto origDisplay = [&] {
+    if (aFrame->Style()->GetPseudoType() == PseudoStyleType::scrolledContent) {
+      // If we're the anonymous block inside the scroll frame, we need to look
+      // at the original display of our parent frame.
+      MOZ_ASSERT(aFrame->GetParent());
+      const auto& parentDisp = *aFrame->GetParent()->StyleDisplay();
+      MOZ_ASSERT(parentDisp.mWebkitLineClamp ==
+                     aFrame->StyleDisplay()->mWebkitLineClamp,
+                 ":-moz-scrolled-content should inherit -webkit-line-clamp, "
+                 "via rule in UA stylesheet");
+      return parentDisp.mOriginalDisplay;
+    }
+    return aFrame->StyleDisplay()->mOriginalDisplay;
+  }();
+  return origDisplay.Inside() == StyleDisplayInside::WebkitBox;
+}
+
+bool nsBlockFrame::IsInLineClampContext() const {
+  if (IsLineClampRoot(this)) {
+    return true;
+  }
+  const nsBlockFrame* cur = this;
+  while (GetAsLineClampDescendant(cur)) {
+    cur = do_QueryFrame(cur->GetParent());
+    if (!cur) {
+      return false;
+    }
+    if (IsLineClampRoot(cur)) {
+      return true;
+    }
+  }
+  return false;
+}
+
+/**
+ * Iterator over all descendant inline line boxes, except for those that are
+ * under an independent formatting context.
+ */
+class MOZ_RAII LineClampLineIterator {
+ public:
+  explicit LineClampLineIterator(nsBlockFrame* aFrame)
+      : mCur(aFrame->LinesBegin()),
+        mEnd(aFrame->LinesEnd()),
+        mCurrentFrame(mCur == mEnd ? nullptr : aFrame) {
+    if (mCur != mEnd && !mCur->IsInline()) {
+      Advance();
+    }
+  }
+
+  nsLineBox* GetCurrentLine() { return mCurrentFrame ? mCur.get() : nullptr; }
+  nsBlockFrame* GetCurrentFrame() { return mCurrentFrame; }
+
+  // Advances the iterator to the next line line.
+  //
+  // Next() shouldn't be called once the iterator is at the end, which can be
+  // checked for by GetCurrentLine() or GetCurrentFrame() returning null.
+  void Next() {
+    MOZ_ASSERT(mCur != mEnd && mCurrentFrame,
+               "Don't call Next() when the iterator is at the end");
+    ++mCur;
+    Advance();
+  }
+
+ private:
+  void Advance() {
+    for (;;) {
+      if (mCur == mEnd) {
+        // Reached the end of the current block.  Pop the parent off the
+        // stack; if there isn't one, then we've reached the end.
+        if (mStack.IsEmpty()) {
+          mCurrentFrame = nullptr;
+          break;
+        }
+        auto entry = mStack.PopLastElement();
+        mCurrentFrame = entry.first;
+        mCur = entry.second;
+        mEnd = mCurrentFrame->LinesEnd();
+      } else if (mCur->IsBlock()) {
+        if (nsBlockFrame* child = GetAsLineClampDescendant(mCur->mFirstChild)) {
+          nsBlockFrame::LineIterator next = mCur;
+          ++next;
+          mStack.AppendElement(std::make_pair(mCurrentFrame, next));
+          mCur = child->LinesBegin();
+          mEnd = child->LinesEnd();
+          mCurrentFrame = child;
+        } else {
+          // Some kind of frame we shouldn't descend into.
+          ++mCur;
+        }
+      } else {
+        MOZ_ASSERT(mCur->IsInline());
+        break;
+      }
+    }
+  }
+
+  // The current line within the current block.
+  //
+  // When this is equal to mEnd, the iterator is at its end, and mCurrentFrame
+  // is set to null.
+  nsBlockFrame::LineIterator mCur;
+
+  // The iterator end for the current block.
+  nsBlockFrame::LineIterator mEnd;
+
+  // The current block.
+  nsBlockFrame* mCurrentFrame;
+
+  // Stack of mCurrentFrame and mEnd values that we push and pop as we enter and
+  // exist blocks.
+  AutoTArray<std::pair<nsBlockFrame*, nsBlockFrame::LineIterator>, 8> mStack;
+};
+
+static bool ClearLineClampEllipsis(nsBlockFrame* aFrame) {
+  if (!aFrame->HasAnyStateBits(NS_BLOCK_HAS_LINE_CLAMP_ELLIPSIS)) {
+    for (nsIFrame* f : aFrame->PrincipalChildList()) {
+      if (nsBlockFrame* child = GetAsLineClampDescendant(f)) {
+        if (ClearLineClampEllipsis(child)) {
+          return true;
+        }
+      }
+    }
+    return false;
+  }
+
+  aFrame->RemoveStateBits(NS_BLOCK_HAS_LINE_CLAMP_ELLIPSIS);
+
+  for (auto& line : aFrame->Lines()) {
+    if (line.HasLineClampEllipsis()) {
+      line.ClearHasLineClampEllipsis();
+      return true;
+    }
+  }
+
+  // We didn't find a line with the ellipsis; it must have been deleted already.
+  return true;
+}
+
+void nsBlockFrame::ClearLineClampEllipsis() { ::ClearLineClampEllipsis(this); }
+
+void nsBlockFrame::Reflow(nsPresContext* aPresContext, ReflowOutput& aMetrics,
+                          const ReflowInput& aReflowInput,
+                          nsReflowStatus& aStatus) {
+  if (IsHiddenByContentVisibilityOfInFlowParentForLayout()) {
+    FinishAndStoreOverflow(&aMetrics, aReflowInput.mStyleDisplay);
+    return;
+  }
+
+  MarkInReflow();
+  DO_GLOBAL_REFLOW_COUNT("nsBlockFrame");
+  DISPLAY_REFLOW(aPresContext, this, aReflowInput, aMetrics, aStatus);
+  MOZ_ASSERT(aStatus.IsEmpty(), "Caller should pass a fresh reflow status!");
+
+#ifdef DEBUG
+  if (gNoisyReflow) {
+    IndentBy(stdout, gNoiseIndent);
+    ListTag(stdout);
+    printf(": begin reflow availSize=%d,%d computedSize=%d,%d\n",
+           aReflowInput.AvailableISize(), aReflowInput.AvailableBSize(),
+           aReflowInput.ComputedISize(), aReflowInput.ComputedBSize());
+  }
+  AutoNoisyIndenter indent(gNoisy);
+  PRTime start = 0;  // Initialize these variablies to silence the compiler.
+  int32_t ctc = 0;   // We only use these if they are set (gLameReflowMetrics).
+  if (gLameReflowMetrics) {
+    start = PR_Now();
+    ctc = nsLineBox::GetCtorCount();
+  }
+#endif
+
+  // ColumnSetWrapper's children depend on ColumnSetWrapper's block-size or
+  // max-block-size because both affect the children's available block-size.
+  if (IsColumnSetWrapperFrame()) {
+    AddStateBits(NS_FRAME_CONTAINS_RELATIVE_BSIZE);
+  }
+
+  Maybe<nscoord> restoreReflowInputAvailBSize;
+  auto MaybeRestore = MakeScopeExit([&] {
+    if (MOZ_UNLIKELY(restoreReflowInputAvailBSize)) {
+      const_cast<ReflowInput&>(aReflowInput)
+          .SetAvailableBSize(*restoreReflowInputAvailBSize);
+    }
+  });
+
+  WritingMode wm = aReflowInput.GetWritingMode();
+  const nscoord consumedBSize = CalcAndCacheConsumedBSize();
+  const nscoord effectiveContentBoxBSize =
+      GetEffectiveComputedBSize(aReflowInput, consumedBSize);
+  // If we have non-auto block size, we're clipping our kids and we fit,
+  // make sure our kids fit too.
+  const PhysicalAxes physicalBlockAxis =
+      wm.IsVertical() ? PhysicalAxes::Horizontal : PhysicalAxes::Vertical;
+  if (aReflowInput.AvailableBSize() != NS_UNCONSTRAINEDSIZE &&
+      aReflowInput.ComputedBSize() != NS_UNCONSTRAINEDSIZE &&
+      (ShouldApplyOverflowClipping(aReflowInput.mStyleDisplay) &
+       physicalBlockAxis)) {
+    LogicalMargin blockDirExtras =
+        aReflowInput.ComputedLogicalBorderPadding(wm);
+    if (GetLogicalSkipSides().BStart()) {
+      blockDirExtras.BStart(wm) = 0;
+    } else {
+      // Block-end margin never causes us to create continuations, so we
+      // don't need to worry about whether it fits in its entirety.
+      blockDirExtras.BStart(wm) +=
+          aReflowInput.ComputedLogicalMargin(wm).BStart(wm);
+    }
+
+    if (effectiveContentBoxBSize + blockDirExtras.BStartEnd(wm) <=
+        aReflowInput.AvailableBSize()) {
+      restoreReflowInputAvailBSize.emplace(aReflowInput.AvailableBSize());
+      const_cast<ReflowInput&>(aReflowInput)
+          .SetAvailableBSize(NS_UNCONSTRAINEDSIZE);
+    }
+  }
+
+  if (IsFrameTreeTooDeep(aReflowInput, aMetrics, aStatus)) {
+    return;
+  }
+
+  // OK, some lines may be reflowed. Blow away any saved line cursor
+  // because we may invalidate the nondecreasing
+  // overflowArea.InkOverflow().y/yMost invariant, and we may even
+  // delete the line with the line cursor.
+  ClearLineCursors();
+
+  // See comment below about oldSize. Use *only* for the
+  // abs-pos-containing-block-size-change optimization!
+  nsSize oldSize = GetSize();
+
+  // Should we create a float manager?
+  nsAutoFloatManager autoFloatManager(const_cast<ReflowInput&>(aReflowInput));
+
+  // XXXldb If we start storing the float manager in the frame rather
+  // than keeping it around only during reflow then we should create it
+  // only when there are actually floats to manage.  Otherwise things
+  // like tables will gain significant bloat.
+  bool needFloatManager = nsBlockFrame::BlockNeedsFloatManager(this);
+  if (needFloatManager) {
+    autoFloatManager.CreateFloatManager(aPresContext);
+  }
+
+  if (HasAnyStateBits(NS_BLOCK_NEEDS_BIDI_RESOLUTION) &&
+      PresContext()->BidiEnabled()) {
+    static_cast<nsBlockFrame*>(FirstContinuation())->ResolveBidi();
+  }
+
+  // Whether to apply text-wrap: balance behavior.
+  bool tryBalance =
+      StyleText()->mTextWrapStyle == StyleTextWrapStyle::Balance &&
+      !GetPrevContinuation();
+
+  // Struct used to hold the "target" number of lines or clamp position to
+  // maintain when doing text-wrap: balance.
+  struct BalanceTarget {
+    // If line-clamp is in effect, mContent and mOffset indicate the starting
+    // position of the first line after the clamp limit. If line-clamp is not
+    // in use, mContent is null and mOffset is the total number of lines that
+    // the block must contain.
+    nsIContent* mContent = nullptr;
+    int32_t mOffset = -1;
+
+    bool operator==(const BalanceTarget& aOther) const {
+      return mContent == aOther.mContent && mOffset == aOther.mOffset;
+    }
+    bool operator!=(const BalanceTarget& aOther) const {
+      return !(*this == aOther);
+    }
+  };
+
+  BalanceTarget balanceTarget;
+
+  // Helpers for text-wrap: balance implementation:
+
+  // Count the number of lines in the mLines list, but return -1 (to suppress
+  // balancing) instead if the count is going to exceed aLimit, or if we
+  // encounter a block.
+  auto countLinesUpTo = [&](int32_t aLimit) -> int32_t {
+    int32_t n = 0;
+    for (auto iter = mLines.begin(); iter != mLines.end(); ++iter) {
+      if (++n > aLimit || iter->IsBlock()) {
+        return -1;
+      }
+    }
+    return n;
+  };
+
+  // Return a BalanceTarget record representing the position at which line-clamp
+  // will take effect for the current line list. Only to be used when there are
+  // enough lines that the clamp will apply.
+  auto getClampPosition = [&](uint32_t aClampCount) -> BalanceTarget {
+    MOZ_ASSERT(aClampCount < mLines.size());
+    auto iter = mLines.begin();
+    for (uint32_t i = 0; i < aClampCount; i++) {
+      ++iter;
+    }
+    nsIFrame* firstChild = iter->mFirstChild;
+    if (!firstChild) {
+      return BalanceTarget{};
+    }
+    nsIContent* content = firstChild->GetContent();
+    if (!content) {
+      return BalanceTarget{};
+    }
+    int32_t offset = 0;
+    if (firstChild->IsTextFrame()) {
+      auto* textFrame = static_cast<nsTextFrame*>(firstChild);
+      offset = textFrame->GetContentOffset();
+    }
+    return BalanceTarget{content, offset};
+  };
+
+  // "balancing" is implemented by shortening the effective inline-size of the
+  // lines, so that content will tend to be pushed down to fill later lines of
+  // the block. `balanceInset` is the current amount of "inset" to apply, and
+  // `balanceStep` is the increment to adjust it by for the next iteration.
+  nscoord balanceStep = 0;
+
+  // text-wrap: balance loop, executed only once if balancing is not required.
+  nsReflowStatus reflowStatus;
+  TrialReflowState trialState(consumedBSize, effectiveContentBoxBSize,
+                              needFloatManager);
+  while (true) {
+    // Save the initial floatManager state for repeated trial reflows.
+    // We'll restore (and re-save) the initial state each time we repeat the
+    // reflow.
+    nsFloatManager::SavedState floatManagerState;
+    aReflowInput.mFloatManager->PushState(&floatManagerState);
+
+    aMetrics = ReflowOutput(aMetrics.GetWritingMode());
+    reflowStatus =
+        TrialReflow(aPresContext, aMetrics, aReflowInput, trialState);
+
+    // Do we need to start a `text-wrap: balance` iteration?
+    if (tryBalance) {
+      tryBalance = false;
+      // Don't try to balance an incomplete block, or if we had to use an
+      // overflow-wrap break position in the initial reflow.
+      if (!reflowStatus.IsFullyComplete() || trialState.mUsedOverflowWrap) {
+        break;
+      }
+      balanceTarget.mOffset =
+          countLinesUpTo(StaticPrefs::layout_css_text_wrap_balance_limit());
+      if (balanceTarget.mOffset < 2) {
+        // If there are less than 2 lines, or the number exceeds the limit,
+        // no balancing is needed; just break from the balance loop.
+        break;
+      }
+      // Initialize the amount of inset to try, and the iteration step size.
+      balanceStep = aReflowInput.ComputedISize() / balanceTarget.mOffset;
+      trialState.ResetForBalance(balanceStep);
+      balanceStep /= 2;
+
+      // If -webkit-line-clamp is in effect, then we need to maintain the
+      // content location at which clamping occurs, rather than the total
+      // number of lines in the block.
+      if (StaticPrefs::layout_css_text_wrap_balance_after_clamp_enabled() &&
+          IsLineClampRoot(this)) {
+        uint32_t lineClampCount = aReflowInput.mStyleDisplay->mWebkitLineClamp;
+        if (uint32_t(balanceTarget.mOffset) > lineClampCount) {
+          auto t = getClampPosition(lineClampCount);
+          if (t.mContent) {
+            balanceTarget = t;
+          }
+        }
+      }
+
+      // Restore initial floatManager state for a new trial with updated inset.
+      aReflowInput.mFloatManager->PopState(&floatManagerState);
+      continue;
+    }
+
+    // Helper to determine whether the current trial succeeded (i.e. was able
+    // to fit the content into the expected number of lines).
+    auto trialSucceeded = [&]() -> bool {
+      if (!reflowStatus.IsFullyComplete() || trialState.mUsedOverflowWrap) {
+        return false;
+      }
+      if (balanceTarget.mContent) {
+        auto t = getClampPosition(aReflowInput.mStyleDisplay->mWebkitLineClamp);
+        return t == balanceTarget;
+      }
+      int32_t numLines =
+          countLinesUpTo(StaticPrefs::layout_css_text_wrap_balance_limit());
+      return numLines == balanceTarget.mOffset;
+    };
+
+    // If we're in the process of a balance operation, check whether we've
+    // inset by too much and either increase or reduce the inset for the next
+    // iteration.
+    if (balanceStep > 0) {
+      if (trialSucceeded()) {
+        trialState.ResetForBalance(balanceStep);
+      } else {
+        trialState.ResetForBalance(-balanceStep);
+      }
+      balanceStep /= 2;
+
+      aReflowInput.mFloatManager->PopState(&floatManagerState);
+      continue;
+    }
+
+    // If we were attempting to balance, check whether the final iteration was
+    // successful, and if not, back up by one step.
+    if (balanceTarget.mOffset >= 0) {
+      if (!trialState.mInset || trialSucceeded()) {
+        break;
+      }
+      trialState.ResetForBalance(-1);
+
+      aReflowInput.mFloatManager->PopState(&floatManagerState);
+      continue;
+    }
+
+    // If we reach here, no balancing was required, so just exit; we don't
+    // reset (pop) the floatManager state because this is the reflow we're
+    // going to keep. So the saved state is just dropped.
+    break;
+  }  // End of text-wrap: balance retry loop
+
+  // If the block direction is right-to-left, we need to update the bounds of
+  // lines that were placed relative to mContainerSize during reflow, as
+  // we typically do not know the true container size until we've reflowed all
+  // its children. So we use a dummy mContainerSize during reflow (see
+  // BlockReflowState's constructor) and then fix up the positions of the
+  // lines here, once the final block size is known.
+  //
+  // Note that writing-mode:vertical-rl is the only case where the block
+  // logical direction progresses in a negative physical direction, and
+  // therefore block-dir coordinate conversion depends on knowing the width
+  // of the coordinate space in order to translate between the logical and
+  // physical origins.
+  if (aReflowInput.GetWritingMode().IsVerticalRL()) {
+    nsSize containerSize = aMetrics.PhysicalSize();
+    nscoord deltaX = containerSize.width - trialState.mContainerWidth;
+    if (deltaX != 0) {
+      // We compute our lines and markers' overflow areas later in
+      // ComputeOverflowAreas(), so we don't need to adjust their overflow areas
+      // here.
+      const nsPoint physicalDelta(deltaX, 0);
+      for (auto& line : Lines()) {
+        UpdateLineContainerSize(&line, containerSize);
+      }
+      trialState.mFcBounds.Clear();
+      for (nsIFrame* f : mFloats) {
+        f->MovePositionBy(physicalDelta);
+        ConsiderChildOverflow(trialState.mFcBounds, f);
+      }
+      nsFrameList* markerList = GetOutsideMarkerList();
+      if (markerList) {
+        for (nsIFrame* f : *markerList) {
+          f->MovePositionBy(physicalDelta);
+        }
+      }
+      if (nsFrameList* overflowContainers = GetOverflowContainers()) {
+        trialState.mOcBounds.Clear();
+        for (nsIFrame* f : *overflowContainers) {
+          f->MovePositionBy(physicalDelta);
+          ConsiderChildOverflow(trialState.mOcBounds, f);
+        }
+      }
+    }
+  }
+
+  aMetrics.SetOverflowAreasToDesiredBounds();
+  ComputeOverflowAreas(aMetrics.mOverflowAreas,
+                       trialState.mBlockEndEdgeOfChildren,
+                       aReflowInput.mStyleDisplay);
+  // Factor overflow container child bounds into the overflow area
+  aMetrics.mOverflowAreas.UnionWith(trialState.mOcBounds);
+  // Factor pushed float child bounds into the overflow area
+  aMetrics.mOverflowAreas.UnionWith(trialState.mFcBounds);
+
+  // Let the absolutely positioned container reflow any absolutely positioned
+  // child frames that need to be reflowed, e.g., elements with a percentage
+  // based width/height
+  // We want to do this under either of two conditions:
+  //  1. If we didn't do the incremental reflow above.
+  //  2. If our size changed.
+  // Even though it's the padding edge that's the containing block, we
+  // can use our rect (the border edge) since if the border style
+  // changed, the reflow would have been targeted at us so we'd satisfy
+  // condition 1.
+  // XXX checking oldSize is bogus, there are various reasons we might have
+  // reflowed but our size might not have been changed to what we
+  // asked for (e.g., we ended up being pushed to a new page)
+  // When WillReflowAgainForClearance is true, we will reflow again without
+  // resetting the size. Because of this, we must not reflow our abs-pos
+  // children in that situation --- what we think is our "new size" will not be
+  // our real new size. This also happens to be more efficient.
+  WritingMode parentWM = aMetrics.GetWritingMode();
+  if (HasAbsolutelyPositionedChildren()) {
+    nsAbsoluteContainingBlock* absoluteContainer = GetAbsoluteContainingBlock();
+    bool haveInterrupt = aPresContext->HasPendingInterrupt();
+    if (aReflowInput.WillReflowAgainForClearance() || haveInterrupt) {
+      // Make sure that when we reflow again we'll actually reflow all the abs
+      // pos frames that might conceivably depend on our size (or all of them,
+      // if we're dirty right now and interrupted; in that case we also need
+      // to mark them all with NS_FRAME_IS_DIRTY).  Sadly, we can't do much
+      // better than that, because we don't really know what our size will be,
+      // and it might in fact not change on the followup reflow!
+      if (haveInterrupt && HasAnyStateBits(NS_FRAME_IS_DIRTY)) {
+        absoluteContainer->MarkAllFramesDirty();
+      } else {
+        absoluteContainer->MarkSizeDependentFramesDirty();
+      }
+      if (haveInterrupt) {
+        // We're not going to reflow absolute frames; make sure to account for
+        // their existing overflow areas, which is usually a side effect of this
+        // reflow.
+        //
+        // TODO(emilio): nsAbsoluteContainingBlock::Reflow already checks for
+        // interrupt, can we just rely on it and unconditionally take the else
+        // branch below? That's a bit more subtle / risky, since I don't see
+        // what would reflow them in that case if they depended on our size.
+        for (nsIFrame* kid = absoluteContainer->GetChildList().FirstChild();
+             kid; kid = kid->GetNextSibling()) {
+          ConsiderChildOverflow(aMetrics.mOverflowAreas, kid);
+        }
+      }
+    } else {
+      LogicalSize containingBlockSize =
+          CalculateContainingBlockSizeForAbsolutes(parentWM, aReflowInput,
+                                                   aMetrics.Size(parentWM));
+
+      // Mark frames that depend on changes we just made to this frame as dirty:
+      // Now we can assume that the padding edge hasn't moved.
+      // We need to reflow the absolutes if one of them depends on
+      // its placeholder position, or the containing block size in a
+      // direction in which the containing block size might have
+      // changed.
+
+      // XXX "width" and "height" in this block will become ISize and BSize
+      // when nsAbsoluteContainingBlock is logicalized
+      bool cbWidthChanged = aMetrics.Width() != oldSize.width;
+      bool isRoot = !GetContent()->GetParent();
+      // If isRoot and we have auto height, then we are the initial
+      // containing block and the containing block height is the
+      // viewport height, which can't change during incremental
+      // reflow.
+      bool cbHeightChanged =
+          !(isRoot && NS_UNCONSTRAINEDSIZE == aReflowInput.ComputedHeight()) &&
+          aMetrics.Height() != oldSize.height;
+
+      nsRect containingBlock(nsPoint(0, 0),
+                             containingBlockSize.GetPhysicalSize(parentWM));
+      AbsPosReflowFlags flags = AbsPosReflowFlags::ConstrainHeight;
+      if (cbWidthChanged) {
+        flags |= AbsPosReflowFlags::CBWidthChanged;
+      }
+      if (cbHeightChanged) {
+        flags |= AbsPosReflowFlags::CBHeightChanged;
+      }
+      // Setup the line cursor here to optimize line searching for
+      // calculating hypothetical position of absolutely-positioned
+      // frames.
+      SetupLineCursorForQuery();
+      absoluteContainer->Reflow(this, aPresContext, aReflowInput, reflowStatus,
+                                containingBlock, flags,
+                                &aMetrics.mOverflowAreas);
+    }
+  }
+
+  FinishAndStoreOverflow(&aMetrics, aReflowInput.mStyleDisplay);
+
+  aStatus = reflowStatus;
+
+#ifdef DEBUG
+  // Between when we drain pushed floats and when we complete reflow,
+  // we're allowed to have multiple continuations of the same float on
+  // our floats list, since a first-in-flow might get pushed to a later
+  // continuation of its containing block.  But it's not permitted
+  // outside that time.
+  nsLayoutUtils::AssertNoDuplicateContinuations(this, mFloats);
+
+  if (gNoisyReflow) {
+    IndentBy(stdout, gNoiseIndent);
+    ListTag(stdout);
+    printf(": status=%s metrics=%d,%d carriedMargin=%d",
+           ToString(aStatus).c_str(), aMetrics.ISize(parentWM),
+           aMetrics.BSize(parentWM), aMetrics.mCarriedOutBEndMargin.get());
+    if (HasOverflowAreas()) {
+      printf(" overflow-vis={%d,%d,%d,%d}", aMetrics.InkOverflow().x,
+             aMetrics.InkOverflow().y, aMetrics.InkOverflow().width,
+             aMetrics.InkOverflow().height);
+      printf(" overflow-scr={%d,%d,%d,%d}", aMetrics.ScrollableOverflow().x,
+             aMetrics.ScrollableOverflow().y,
+             aMetrics.ScrollableOverflow().width,
+             aMetrics.ScrollableOverflow().height);
+    }
+    printf("\n");
+  }
+
+  if (gLameReflowMetrics) {
+    PRTime end = PR_Now();
+
+    int32_t ectc = nsLineBox::GetCtorCount();
+    int32_t numLines = mLines.size();
+    if (!numLines) {
+      numLines = 1;
+    }
+    PRTime delta, perLineDelta, lines;
+    lines = int64_t(numLines);
+    delta = end - start;
+    perLineDelta = delta / lines;
+
+    ListTag(stdout);
+    char buf[400];
+    SprintfLiteral(buf,
+                   ": %" PRId64 " elapsed (%" PRId64
+                   " per line) (%d lines; %d new lines)",
+                   delta, perLineDelta, numLines, ectc - ctc);
+    printf("%s\n", buf);
+  }
+#endif
+}
+
+nsReflowStatus nsBlockFrame::TrialReflow(nsPresContext* aPresContext,
+                                         ReflowOutput& aMetrics,
+                                         const ReflowInput& aReflowInput,
+                                         TrialReflowState& aTrialState) {
+#ifdef DEBUG
+  // Between when we drain pushed floats and when we complete reflow,
+  // we're allowed to have multiple continuations of the same float on
+  // our floats list, since a first-in-flow might get pushed to a later
+  // continuation of its containing block.  But it's not permitted
+  // outside that time.
+  nsLayoutUtils::AssertNoDuplicateContinuations(this, mFloats);
+#endif
+
+  // ALWAYS drain overflow. We never want to leave the previnflow's
+  // overflow lines hanging around; block reflow depends on the
+  // overflow line lists being cleared out between reflow passes.
+  DrainOverflowLines();
+
+  bool blockStartMarginRoot, blockEndMarginRoot;
+  IsMarginRoot(&blockStartMarginRoot, &blockEndMarginRoot);
+
+  BlockReflowState state(aReflowInput, aPresContext, this, blockStartMarginRoot,
+                         blockEndMarginRoot, aTrialState.mNeedFloatManager,
+                         aTrialState.mConsumedBSize,
+                         aTrialState.mEffectiveContentBoxBSize,
+                         aTrialState.mInset);
+
+  // Handle paginated overflow (see nsContainerFrame.h)
+  nsReflowStatus ocStatus;
+  if (GetPrevInFlow()) {
+    ReflowOverflowContainerChildren(
+        aPresContext, aReflowInput, aTrialState.mOcBounds,
+        ReflowChildFlags::Default, ocStatus, DefaultChildFrameMerge,
+        Some(state.ContainerSize()));
+  }
+
+  // Now that we're done cleaning up our overflow container lists, we can
+  // give |state| its nsOverflowContinuationTracker.
+  nsOverflowContinuationTracker tracker(this, false);
+  state.mOverflowTracker = &tracker;
+
+  // Drain & handle pushed floats
+  DrainPushedFloats();
+  ReflowPushedFloats(state, aTrialState.mFcBounds);
+
+  // If we're not dirty (which means we'll mark everything dirty later)
+  // and our inline-size has changed, mark the lines dirty that we need to
+  // mark dirty for a resize reflow.
+  if (!HasAnyStateBits(NS_FRAME_IS_DIRTY) && aReflowInput.IsIResize()) {
+    PrepareResizeReflow(state);
+  }
+
+  // The same for percentage text-indent, except conditioned on the
+  // parent resizing.
+  if (!HasAnyStateBits(NS_FRAME_IS_DIRTY) && aReflowInput.mCBReflowInput &&
+      aReflowInput.mCBReflowInput->IsIResize() &&
+      StyleText()->mTextIndent.length.HasPercent() && !mLines.empty()) {
+    mLines.front()->MarkDirty();
+  }
+
+  // For text-wrap:balance trials, we need to reflow all the lines even if
+  // they're not all "dirty".
+  if (aTrialState.mBalancing) {
+    MarkAllDescendantLinesDirty(this);
+  } else {
+    LazyMarkLinesDirty();
+  }
+
+  // Now reflow...
+  aTrialState.mUsedOverflowWrap = ReflowDirtyLines(state);
+
+  // If we have a next-in-flow, and that next-in-flow has pushed floats from
+  // this frame from a previous iteration of reflow, then we should not return
+  // a status with IsFullyComplete() equals to true, since we actually have
+  // overflow, it's just already been handled.
+
+  // NOTE: This really shouldn't happen, since we _should_ pull back our floats
+  // and reflow them, but just in case it does, this is a safety precaution so
+  // we don't end up with a placeholder pointing to frames that have already
+  // been deleted as part of removing our next-in-flow.
+  if (state.mReflowStatus.IsFullyComplete()) {
+    nsBlockFrame* nif = static_cast<nsBlockFrame*>(GetNextInFlow());
+    while (nif) {
+      if (nif->HasPushedFloatsFromPrevContinuation()) {
+        if (nif->HasAnyStateBits(NS_FRAME_IS_OVERFLOW_CONTAINER)) {
+          state.mReflowStatus.SetOverflowIncomplete();
+        } else {
+          state.mReflowStatus.SetIncomplete();
+        }
+        break;
+      }
+
+      nif = static_cast<nsBlockFrame*>(nif->GetNextInFlow());
+    }
+  }
+
+  state.mReflowStatus.MergeCompletionStatusFrom(ocStatus);
+
+  // If we end in a BR with clear and affected floats continue,
+  // we need to continue, too.
+  if (NS_UNCONSTRAINEDSIZE != aReflowInput.AvailableBSize() &&
+      state.mReflowStatus.IsComplete() &&
+      state.FloatManager()->ClearContinues(FindTrailingClear())) {
+    state.mReflowStatus.SetIncomplete();
+  }
+
+  if (!state.mReflowStatus.IsFullyComplete()) {
+    if (HasOverflowLines() || HasPushedFloats()) {
+      state.mReflowStatus.SetNextInFlowNeedsReflow();
+    }
+
+#ifdef DEBUG_kipp
+    ListTag(stdout);
+    printf(": block is not fully complete\n");
+#endif
+  }
+
+  // Place the ::marker's frame if it is placed next to a block child.
+  //
+  // According to the CSS2 spec, section 12.6.1, the ::marker's box
+  // participates in the height calculation of the list-item box's
+  // first line box.
+  //
+  // There are exactly two places a ::marker can be placed: near the
+  // first or second line. It's only placed on the second line in a
+  // rare case: an empty first line followed by a second line that
+  // contains a block (example: <LI>\n<P>... ). This is where
+  // the second case can happen.
+  if (HasOutsideMarker() && !mLines.empty() &&
+      (mLines.front()->IsBlock() ||
+       (0 == mLines.front()->BSize() && mLines.front() != mLines.back() &&
+        mLines.begin().next()->IsBlock()))) {
+    // Reflow the ::marker's frame.
+    ReflowOutput reflowOutput(aReflowInput);
+    // XXX Use the entire line when we fix bug 25888.
+    nsLayoutUtils::LinePosition position;
+    WritingMode wm = aReflowInput.GetWritingMode();
+    bool havePosition =
+        nsLayoutUtils::GetFirstLinePosition(wm, this, &position);
+    nscoord lineBStart =
+        havePosition ? position.mBStart
+                     : aReflowInput.ComputedLogicalBorderPadding(wm).BStart(wm);
+    nsIFrame* marker = GetOutsideMarker();
+    ReflowOutsideMarker(marker, state, reflowOutput, lineBStart);
+    NS_ASSERTION(!MarkerIsEmpty() || reflowOutput.BSize(wm) == 0,
+                 "empty ::marker frame took up space");
+
+    if (havePosition && !MarkerIsEmpty()) {
+      // We have some lines to align the ::marker with.
+
+      // Doing the alignment using the baseline will also cater for
+      // ::markers that are placed next to a child block (bug 92896)
+
+      // Tall ::markers won't look particularly nice here...
+      LogicalRect bbox =
+          marker->GetLogicalRect(wm, reflowOutput.PhysicalSize());
+      const auto baselineGroup = BaselineSharingGroup::First;
+      Maybe<nscoord> result;
+      if (MOZ_LIKELY(!wm.IsOrthogonalTo(marker->GetWritingMode()))) {
+        result = marker->GetNaturalBaselineBOffset(
+            wm, baselineGroup, BaselineExportContext::LineLayout);
+      }
+      const auto markerBaseline = result.valueOrFrom([bbox, wm, marker]() {
+        return bbox.BSize(wm) + marker->GetLogicalUsedMargin(wm).BEnd(wm);
+      });
+      bbox.BStart(wm) = position.mBaseline - markerBaseline;
+      marker->SetRect(wm, bbox, reflowOutput.PhysicalSize());
+    }
+    // Otherwise just leave the ::marker where it is, up against our
+    // block-start padding.
+  }
+
+  // Clear any existing -webkit-line-clamp ellipsis.
+  if (aReflowInput.mStyleDisplay->mWebkitLineClamp) {
+    ClearLineClampEllipsis();
+  }
+
+  CheckFloats(state);
+
+  // Compute our final size (for this trial layout)
+  aTrialState.mBlockEndEdgeOfChildren =
+      ComputeFinalSize(aReflowInput, state, aMetrics);
+  aTrialState.mContainerWidth = state.ContainerSize().width;
+
+  return state.mReflowStatus;
+}
+
+bool nsBlockFrame::CheckForCollapsedBEndMarginFromClearanceLine() {
+  for (auto& line : Reversed(Lines())) {
+    if (0 != line.BSize() || !line.CachedIsEmpty()) {
+      return false;
+    }
+    if (line.HasClearance()) {
+      return true;
+    }
+  }
+  return false;
+}
+
+static nsLineBox* FindLineClampTarget(nsBlockFrame*& aFrame,
+                                      StyleLineClamp aLineNumber) {
+  MOZ_ASSERT(aLineNumber > 0);
+  MOZ_ASSERT(!aFrame->HasAnyStateBits(NS_BLOCK_HAS_LINE_CLAMP_ELLIPSIS),
+             "Should have been removed earlier in nsBlockReflow::Reflow");
+
+  nsLineBox* target = nullptr;
+  nsBlockFrame* targetFrame = nullptr;
+  bool foundFollowingLine = false;
+
+  LineClampLineIterator iter(aFrame);
+
+  while (nsLineBox* line = iter.GetCurrentLine()) {
+    MOZ_ASSERT(!line->HasLineClampEllipsis(),
+               "Should have been removed earlier in nsBlockFrame::Reflow");
+    MOZ_ASSERT(!iter.GetCurrentFrame()->HasAnyStateBits(
+                   NS_BLOCK_HAS_LINE_CLAMP_ELLIPSIS),
+               "Should have been removed earlier in nsBlockReflow::Reflow");
+
+    // Don't count a line that only has collapsible white space (as might exist
+    // after calling e.g. getBoxQuads).
+    if (line->IsEmpty()) {
+      iter.Next();
+      continue;
+    }
+
+    if (aLineNumber == 0) {
+      // We already previously found our target line, and now we have
+      // confirmed that there is another line after it.
+      foundFollowingLine = true;
+      break;
+    }
+
+    if (--aLineNumber == 0) {
+      // This is our target line.  Continue looping to confirm that we
+      // have another line after us.
+      target = line;
+      targetFrame = iter.GetCurrentFrame();
+    }
+
+    iter.Next();
+  }
+
+  if (!foundFollowingLine) {
+    aFrame = nullptr;
+    return nullptr;
+  }
+
+  MOZ_ASSERT(target);
+  MOZ_ASSERT(targetFrame);
+
+  aFrame = targetFrame;
+  return target;
+}
+
+static nscoord ApplyLineClamp(const ReflowInput& aReflowInput,
+                              nsBlockFrame* aFrame,
+                              nscoord aContentBlockEndEdge) {
+  if (!IsLineClampRoot(aFrame)) {
+    return aContentBlockEndEdge;
+  }
+  auto lineClamp = aReflowInput.mStyleDisplay->mWebkitLineClamp;
+  nsBlockFrame* frame = aFrame;
+  nsLineBox* line = FindLineClampTarget(frame, lineClamp);
+  if (!line) {
+    // The number of lines did not exceed the -webkit-line-clamp value.
+    return aContentBlockEndEdge;
+  }
+
+  // Mark the line as having an ellipsis so that TextOverflow will render it.
+  line->SetHasLineClampEllipsis();
+  frame->AddStateBits(NS_BLOCK_HAS_LINE_CLAMP_ELLIPSIS);
+
+  // Translate the b-end edge of the line up to aFrame's space.
+  nscoord edge = line->BEnd();
+  for (nsIFrame* f = frame; f != aFrame; f = f->GetParent()) {
+    edge +=
+        f->GetLogicalPosition(f->GetParent()->GetSize()).B(f->GetWritingMode());
+  }
+
+  return edge;
+}
+
+nscoord nsBlockFrame::ComputeFinalSize(const ReflowInput& aReflowInput,
+                                       BlockReflowState& aState,
+                                       ReflowOutput& aMetrics) {
+  WritingMode wm = aState.mReflowInput.GetWritingMode();
+  const LogicalMargin& borderPadding = aState.BorderPadding();
+#ifdef NOISY_FINAL_SIZE
+  ListTag(stdout);
+  printf(": mBCoord=%d mIsBEndMarginRoot=%s mPrevBEndMargin=%d bp=%d,%d\n",
+         aState.mBCoord, aState.mFlags.mIsBEndMarginRoot ? "yes" : "no",
+         aState.mPrevBEndMargin.get(), borderPadding.BStart(wm),
+         borderPadding.BEnd(wm));
+#endif
+
+  // Compute final inline size
+  LogicalSize finalSize(wm);
+  finalSize.ISize(wm) =
+      NSCoordSaturatingAdd(NSCoordSaturatingAdd(borderPadding.IStart(wm),
+                                                aReflowInput.ComputedISize()),
+                           borderPadding.IEnd(wm));
+
+  // Return block-end margin information
+  // rbs says he hit this assertion occasionally (see bug 86947), so
+  // just set the margin to zero and we'll figure out why later
+  // NS_ASSERTION(aMetrics.mCarriedOutBEndMargin.IsZero(),
+  //             "someone else set the margin");
+  nscoord nonCarriedOutBDirMargin = 0;
+  if (!aState.mFlags.mIsBEndMarginRoot) {
+    // Apply rule from CSS 2.1 section 8.3.1. If we have some empty
+    // line with clearance and a non-zero block-start margin and all
+    // subsequent lines are empty, then we do not allow our children's
+    // carried out block-end margin to be carried out of us and collapse
+    // with our own block-end margin.
+    if (CheckForCollapsedBEndMarginFromClearanceLine()) {
+      // Convert the children's carried out margin to something that
+      // we will include in our height
+      nonCarriedOutBDirMargin = aState.mPrevBEndMargin.get();
+      aState.mPrevBEndMargin.Zero();
+    }
+    aMetrics.mCarriedOutBEndMargin = aState.mPrevBEndMargin;
+  } else {
+    aMetrics.mCarriedOutBEndMargin.Zero();
+  }
+
+  nscoord blockEndEdgeOfChildren = aState.mBCoord + nonCarriedOutBDirMargin;
+  // Shrink wrap our height around our contents.
+  if (aState.mFlags.mIsBEndMarginRoot ||
+      NS_UNCONSTRAINEDSIZE != aReflowInput.ComputedBSize()) {
+    // When we are a block-end-margin root make sure that our last
+    // child's block-end margin is fully applied. We also do this when
+    // we have a computed height, since in that case the carried out
+    // margin is not going to be applied anywhere, so we should note it
+    // here to be included in the overflow area.
+    // Apply the margin only if there's space for it.
+    if (blockEndEdgeOfChildren < aState.mReflowInput.AvailableBSize()) {
+      // Truncate block-end margin if it doesn't fit to our available BSize.
+      blockEndEdgeOfChildren =
+          std::min(blockEndEdgeOfChildren + aState.mPrevBEndMargin.get(),
+                   aState.mReflowInput.AvailableBSize());
+    }
+  }
+  if (aState.mFlags.mBlockNeedsFloatManager) {
+    // Include the float manager's state to properly account for the
+    // block-end margin of any floated elements; e.g., inside a table cell.
+    //
+    // Note: The block coordinate returned by ClearFloats is always greater than
+    // or equal to blockEndEdgeOfChildren.
+    std::tie(blockEndEdgeOfChildren, std::ignore) =
+        aState.ClearFloats(blockEndEdgeOfChildren, StyleClear::Both);
+  }
+
+  if (NS_UNCONSTRAINEDSIZE != aReflowInput.ComputedBSize()) {
+    // Note: We don't use blockEndEdgeOfChildren because it includes the
+    // previous margin.
+    const nscoord contentBSizeWithBStartBP =
+        aState.mBCoord + nonCarriedOutBDirMargin;
+
+    // We don't care about ApplyLineClamp's return value (the line-clamped
+    // content BSize) in this explicit-BSize codepath, but we do still need to
+    // call ApplyLineClamp for ellipsis markers to be placed as-needed.
+    ApplyLineClamp(aState.mReflowInput, this, contentBSizeWithBStartBP);
+
+    finalSize.BSize(wm) = ComputeFinalBSize(aState, contentBSizeWithBStartBP);
+
+    // If the content block-size is larger than the effective computed
+    // block-size, we extend the block-size to contain all the content.
+    // https://drafts.csswg.org/css-sizing-4/#aspect-ratio-minimum
+    if (aReflowInput.ShouldApplyAutomaticMinimumOnBlockAxis()) {
+      // Note: finalSize.BSize(wm) is the border-box size, so we compare it with
+      // the content's block-size plus our border and padding..
+      finalSize.BSize(wm) =
+          std::max(finalSize.BSize(wm),
+                   contentBSizeWithBStartBP + borderPadding.BEnd(wm));
+    }
+
+    // Don't carry out a block-end margin when our BSize is fixed.
+    //
+    // Note: this also includes the case that aReflowInput.ComputedBSize() is
+    // calculated from aspect-ratio. i.e. Don't carry out block margin-end if it
+    // is replaced by the block size from aspect-ratio and inline size.
+    aMetrics.mCarriedOutBEndMargin.Zero();
+  } else {
+    Maybe<nscoord> containBSize = ContainIntrinsicBSize(
+        IsComboboxControlFrame() ? NS_UNCONSTRAINEDSIZE : 0);
+    if (containBSize && *containBSize != NS_UNCONSTRAINEDSIZE) {
+      // If we're size-containing in block axis and we don't have a specified
+      // block size, then our final size should actually be computed from only
+      // our border, padding and contain-intrinsic-block-size, ignoring the
+      // actual contents. Hence this case is a simplified version of the case
+      // below.
+      //
+      // NOTE: We exempt the nsComboboxControlFrame subclass from taking this
+      // special case when it has 'contain-intrinsic-block-size: none', because
+      // comboboxes implicitly honors the size-containment behavior on its
+      // nsComboboxDisplayFrame child (which it shrinkwraps) rather than on the
+      // nsComboboxControlFrame. (Moreover, the DisplayFrame child doesn't even
+      // need any special content-size-ignoring behavior in its reflow method,
+      // because that method just resolves "auto" BSize values to one
+      // line-height rather than by measuring its contents' BSize.)
+      nscoord contentBSize = *containBSize;
+      nscoord autoBSize =
+          aReflowInput.ApplyMinMaxBSize(contentBSize, aState.mConsumedBSize);
+      aMetrics.mCarriedOutBEndMargin.Zero();
+      autoBSize += borderPadding.BStartEnd(wm);
+      finalSize.BSize(wm) = autoBSize;
+    } else if (aState.mReflowStatus.IsInlineBreakBefore()) {
+      // Our parent is expected to push this frame to the next page/column so
+      // what size we set here doesn't really matter.
+      finalSize.BSize(wm) = aReflowInput.AvailableBSize();
+    } else if (aState.mReflowStatus.IsComplete()) {
+      const nscoord lineClampedContentBlockEndEdge =
+          ApplyLineClamp(aReflowInput, this, blockEndEdgeOfChildren);
+
+      const nscoord bpBStart = borderPadding.BStart(wm);
+      const nscoord contentBSize = blockEndEdgeOfChildren - bpBStart;
+      const nscoord lineClampedContentBSize =
+          lineClampedContentBlockEndEdge - bpBStart;
+
+      const nscoord autoBSize = aReflowInput.ApplyMinMaxBSize(
+          lineClampedContentBSize, aState.mConsumedBSize);
+      if (autoBSize != contentBSize) {
+        // Our min-block-size, max-block-size, or -webkit-line-clamp value made
+        // our bsize change.  Don't carry out our kids' block-end margins.
+        aMetrics.mCarriedOutBEndMargin.Zero();
+      }
+      nscoord bSize = autoBSize + borderPadding.BStartEnd(wm);
+      if (MOZ_UNLIKELY(autoBSize > contentBSize &&
+                       bSize > aReflowInput.AvailableBSize() &&
+                       aReflowInput.AvailableBSize() != NS_UNCONSTRAINEDSIZE)) {
+        // Applying `min-size` made us overflow our available size.
+        // Clamp it and report that we're Incomplete, or BreakBefore if we have
+        // 'break-inside: avoid' that is applicable.
+        bSize = aReflowInput.AvailableBSize();
+        if (ShouldAvoidBreakInside(aReflowInput)) {
+          aState.mReflowStatus.SetInlineLineBreakBeforeAndReset();
+        } else {
+          aState.mReflowStatus.SetIncomplete();
+        }
+      }
+      finalSize.BSize(wm) = bSize;
+    } else {
+      NS_ASSERTION(
+          aReflowInput.AvailableBSize() != NS_UNCONSTRAINEDSIZE,
+          "Shouldn't be incomplete if availableBSize is UNCONSTRAINED.");
+      nscoord bSize = std::max(aState.mBCoord, aReflowInput.AvailableBSize());
+      if (aReflowInput.AvailableBSize() == NS_UNCONSTRAINEDSIZE) {
+        // This should never happen, but it does. See bug 414255
+        bSize = aState.mBCoord;
+      }
+      const nscoord maxBSize = aReflowInput.ComputedMaxBSize();
+      if (maxBSize != NS_UNCONSTRAINEDSIZE &&
+          aState.mConsumedBSize + bSize - borderPadding.BStart(wm) > maxBSize) {
+        // Compute this fragment's block-size, with the max-block-size
+        // constraint taken into consideration.
+        const nscoord clampedBSizeWithoutEndBP =
+            std::max(0, maxBSize - aState.mConsumedBSize) +
+            borderPadding.BStart(wm);
+        const nscoord clampedBSize =
+            clampedBSizeWithoutEndBP + borderPadding.BEnd(wm);
+        if (clampedBSize <= aReflowInput.AvailableBSize()) {
+          // We actually fit after applying `max-size` so we should be
+          // Overflow-Incomplete instead.
+          bSize = clampedBSize;
+          aState.mReflowStatus.SetOverflowIncomplete();
+        } else {
+          // We cannot fit after applying `max-size` with our block-end BP, so
+          // we should draw it in our next continuation.
+          bSize = clampedBSizeWithoutEndBP;
+        }
+      }
+      finalSize.BSize(wm) = bSize;
+    }
+  }
+
+  if (IsTrueOverflowContainer()) {
+    if (aState.mReflowStatus.IsIncomplete()) {
+      // Overflow containers can only be overflow complete.
+      // Note that auto height overflow containers have no normal children
+      NS_ASSERTION(finalSize.BSize(wm) == 0,
+                   "overflow containers must be zero-block-size");
+      aState.mReflowStatus.SetOverflowIncomplete();
+    }
+  } else if (aReflowInput.AvailableBSize() != NS_UNCONSTRAINEDSIZE &&
+             !aState.mReflowStatus.IsInlineBreakBefore() &&
+             aState.mReflowStatus.IsComplete()) {
+    // Currently only used for grid items, but could be used in other contexts.
+    // The FragStretchBSizeProperty is our expected non-fragmented block-size
+    // we should stretch to (for align-self:stretch etc).  In some fragmentation
+    // cases though, the last fragment (this frame since we're complete), needs
+    // to have extra size applied because earlier fragments consumed too much of
+    // our computed size due to overflowing their containing block.  (E.g. this
+    // ensures we fill the last row when a multi-row grid item is fragmented).
+    bool found;
+    nscoord bSize = GetProperty(FragStretchBSizeProperty(), &found);
+    if (found) {
+      finalSize.BSize(wm) = std::max(bSize, finalSize.BSize(wm));
+    }
+  }
+
+  // Clamp the content size to fit within the margin-box clamp size, if any.
+  if (MOZ_UNLIKELY(aReflowInput.mComputeSizeFlags.contains(
+          ComputeSizeFlag::BClampMarginBoxMinSize)) &&
+      aState.mReflowStatus.IsComplete()) {
+    bool found;
+    nscoord cbSize = GetProperty(BClampMarginBoxMinSizeProperty(), &found);
+    if (found) {
+      auto marginBoxBSize =
+          finalSize.BSize(wm) +
+          aReflowInput.ComputedLogicalMargin(wm).BStartEnd(wm);
+      auto overflow = marginBoxBSize - cbSize;
+      if (overflow > 0) {
+        auto contentBSize = finalSize.BSize(wm) - borderPadding.BStartEnd(wm);
+        auto newContentBSize = std::max(nscoord(0), contentBSize - overflow);
+        // XXXmats deal with percentages better somehow?
+        finalSize.BSize(wm) -= contentBSize - newContentBSize;
+      }
+    }
+  }
+
+  // Screen out negative block sizes --- can happen due to integer overflows :-(
+  finalSize.BSize(wm) = std::max(0, finalSize.BSize(wm));
+
+  if (blockEndEdgeOfChildren != finalSize.BSize(wm) - borderPadding.BEnd(wm)) {
+    SetProperty(BlockEndEdgeOfChildrenProperty(), blockEndEdgeOfChildren);
+  } else {
+    RemoveProperty(BlockEndEdgeOfChildrenProperty());
+  }
+
+  aMetrics.SetSize(wm, finalSize);
+
+#ifdef DEBUG_blocks
+  if ((ABSURD_SIZE(aMetrics.Width()) || ABSURD_SIZE(aMetrics.Height())) &&
+      !GetParent()->IsAbsurdSizeAssertSuppressed()) {
+    ListTag(stdout);
+    printf(": WARNING: desired:%d,%d\n", aMetrics.Width(), aMetrics.Height());
+  }
+#endif
+
+  return blockEndEdgeOfChildren;
+}
+
+void nsBlockFrame::ConsiderBlockEndEdgeOfChildren(
+    OverflowAreas& aOverflowAreas, nscoord aBEndEdgeOfChildren,
+    const nsStyleDisplay* aDisplay) const {
+  const auto wm = GetWritingMode();
+
+  // Factor in the block-end edge of the children.  Child frames will be added
+  // to the overflow area as we iterate through the lines, but their margins
+  // won't, so we need to account for block-end margins here.
+  // REVIEW: For now, we do this for both visual and scrollable area,
+  // although when we make scrollable overflow area not be a subset of
+  // visual, we can change this.
+
+  if (Style()->GetPseudoType() == PseudoStyleType::scrolledContent) {
+    // If we are a scrolled inner frame, add our block-end padding to our
+    // children's block-end edge.
+    //
+    // Note: aBEndEdgeOfChildren already includes our own block-start padding
+    // because it is relative to our block-start edge of our border-box, which
+    // is the same as our padding-box here.
+    MOZ_ASSERT(GetLogicalUsedBorderAndPadding(wm) == GetLogicalUsedPadding(wm),
+               "A scrolled inner frame shouldn't have any border!");
+    aBEndEdgeOfChildren += GetLogicalUsedPadding(wm).BEnd(wm);
+  }
+
+  // XXX Currently, overflow areas are stored as physical rects, so we have
+  // to handle writing modes explicitly here. If we change overflow rects
+  // to be stored logically, this can be simplified again.
+  if (wm.IsVertical()) {
+    if (wm.IsVerticalLR()) {
+      for (const auto otype : AllOverflowTypes()) {
+        if (!(aDisplay->IsContainLayout() &&
+              otype == OverflowType::Scrollable)) {
+          // Layout containment should force all overflow to be ink (visual)
+          // overflow, so if we're layout-contained, we only add our children's
+          // block-end edge to the ink (visual) overflow -- not to the
+          // scrollable overflow.
+          nsRect& o = aOverflowAreas.Overflow(otype);
+          o.width = std::max(o.XMost(), aBEndEdgeOfChildren) - o.x;
+        }
+      }
+    } else {
+      for (const auto otype : AllOverflowTypes()) {
+        if (!(aDisplay->IsContainLayout() &&
+              otype == OverflowType::Scrollable)) {
+          nsRect& o = aOverflowAreas.Overflow(otype);
+          nscoord xmost = o.XMost();
+          o.x = std::min(o.x, xmost - aBEndEdgeOfChildren);
+          o.width = xmost - o.x;
+        }
+      }
+    }
+  } else {
+    for (const auto otype : AllOverflowTypes()) {
+      if (!(aDisplay->IsContainLayout() && otype == OverflowType::Scrollable)) {
+        nsRect& o = aOverflowAreas.Overflow(otype);
+        o.height = std::max(o.YMost(), aBEndEdgeOfChildren) - o.y;
+      }
+    }
+  }
+}
+
+void nsBlockFrame::ComputeOverflowAreas(OverflowAreas& aOverflowAreas,
+                                        nscoord aBEndEdgeOfChildren,
+                                        const nsStyleDisplay* aDisplay) const {
+  // XXX_perf: This can be done incrementally.  It is currently one of
+  // the things that makes incremental reflow O(N^2).
+  auto overflowClipAxes = ShouldApplyOverflowClipping(aDisplay);
+  auto overflowClipMargin = OverflowClipMargin(overflowClipAxes);
+  if (overflowClipAxes == PhysicalAxes::Both &&
+      overflowClipMargin == nsSize()) {
+    return;
+  }
+
+  // We rely here on our caller having called SetOverflowAreasToDesiredBounds().
+  nsRect frameBounds = aOverflowAreas.ScrollableOverflow();
+
+  for (const auto& line : Lines()) {
+    if (aDisplay->IsContainLayout()) {
+      // If we have layout containment, we should only consider our child's
+      // ink overflow, leaving the scrollable regions of the parent
+      // unaffected.
+      // Note: scrollable overflow is a subset of ink overflow,
+      // so this has the same affect as unioning the child's visual and
+      // scrollable overflow with its parent's ink overflow.
+      nsRect childVisualRect = line.InkOverflowRect();
+      OverflowAreas childVisualArea = OverflowAreas(childVisualRect, nsRect());
+      aOverflowAreas.UnionWith(childVisualArea);
+    } else {
+      aOverflowAreas.UnionWith(line.GetOverflowAreas());
+    }
+  }
+
+  // Factor an outside ::marker in; normally the ::marker will be factored
+  // into the line-box's overflow areas. However, if the line is a block
+  // line then it won't; if there are no lines, it won't. So just
+  // factor it in anyway (it can't hurt if it was already done).
+  // XXXldb Can we just fix GetOverflowArea instead?
+  if (nsIFrame* outsideMarker = GetOutsideMarker()) {
+    aOverflowAreas.UnionAllWith(outsideMarker->GetRect());
+  }
+
+  ConsiderBlockEndEdgeOfChildren(aOverflowAreas, aBEndEdgeOfChildren, aDisplay);
+
+  if (overflowClipAxes != PhysicalAxes::None) {
+    aOverflowAreas.ApplyClipping(frameBounds, overflowClipAxes,
+                                 overflowClipMargin);
+  }
+
+#ifdef NOISY_OVERFLOW_AREAS
+  printf("%s: InkOverflowArea=%s, ScrollableOverflowArea=%s\n", ListTag().get(),
+         ToString(aOverflowAreas.InkOverflow()).c_str(),
+         ToString(aOverflowAreas.ScrollableOverflow()).c_str());
+#endif
+}
+
+void nsBlockFrame::UnionChildOverflow(OverflowAreas& aOverflowAreas) {
+  // We need to update the overflow areas of lines manually, as they
+  // get cached and re-used otherwise. Lines aren't exposed as normal
+  // frame children, so calling UnionChildOverflow alone will end up
+  // using the old cached values.
+  for (auto& line : Lines()) {
+    nsRect bounds = line.GetPhysicalBounds();
+    OverflowAreas lineAreas(bounds, bounds);
+
+    int32_t n = line.GetChildCount();
+    for (nsIFrame* lineFrame = line.mFirstChild; n > 0;
+         lineFrame = lineFrame->GetNextSibling(), --n) {
+      ConsiderChildOverflow(lineAreas, lineFrame);
+    }
+
+    // Consider the overflow areas of the floats attached to the line as well
+    if (line.HasFloats()) {
+      for (nsIFrame* f : line.Floats()) {
+        ConsiderChildOverflow(lineAreas, f);
+      }
+    }
+
+    line.SetOverflowAreas(lineAreas);
+    aOverflowAreas.UnionWith(lineAreas);
+  }
+
+  // Union with child frames, skipping the principal and float lists
+  // since we already handled those using the line boxes.
+  nsLayoutUtils::UnionChildOverflow(
+      this, aOverflowAreas,
+      {FrameChildListID::Principal, FrameChildListID::Float});
+}
+
+bool nsBlockFrame::ComputeCustomOverflow(OverflowAreas& aOverflowAreas) {
+  bool found;
+  nscoord blockEndEdgeOfChildren =
+      GetProperty(BlockEndEdgeOfChildrenProperty(), &found);
+  if (found) {
+    ConsiderBlockEndEdgeOfChildren(aOverflowAreas, blockEndEdgeOfChildren,
+                                   StyleDisplay());
+  }
+
+  // Line cursor invariants depend on the overflow areas of the lines, so
+  // we must clear the line cursor since those areas may have changed.
+  ClearLineCursors();
+  return nsContainerFrame::ComputeCustomOverflow(aOverflowAreas);
+}
+
+void nsBlockFrame::LazyMarkLinesDirty() {
+  if (HasAnyStateBits(NS_BLOCK_LOOK_FOR_DIRTY_FRAMES)) {
+    for (LineIterator line = LinesBegin(), line_end = LinesEnd();
+         line != line_end; ++line) {
+      int32_t n = line->GetChildCount();
+      for (nsIFrame* lineFrame = line->mFirstChild; n > 0;
+           lineFrame = lineFrame->GetNextSibling(), --n) {
+        if (lineFrame->IsSubtreeDirty()) {
+          // NOTE:  MarkLineDirty does more than just marking the line dirty.
+          MarkLineDirty(line, &mLines);
+          break;
+        }
+      }
+    }
+    RemoveStateBits(NS_BLOCK_LOOK_FOR_DIRTY_FRAMES);
+  }
+}
+
+void nsBlockFrame::MarkLineDirty(LineIterator aLine,
+                                 const nsLineList* aLineList) {
+  // Mark aLine dirty
+  aLine->MarkDirty();
+  aLine->SetInvalidateTextRuns(true);
+#ifdef DEBUG
+  if (gNoisyReflow) {
+    IndentBy(stdout, gNoiseIndent);
+    ListTag(stdout);
+    printf(": mark line %p dirty\n", static_cast<void*>(aLine.get()));
+  }
+#endif
+
+  // Mark previous line dirty if it's an inline line so that it can
+  // maybe pullup something from the line just affected.
+  // XXX We don't need to do this if aPrevLine ends in a break-after...
+  if (aLine != aLineList->front() && aLine->IsInline() &&
+      aLine.prev()->IsInline()) {
+    aLine.prev()->MarkDirty();
+    aLine.prev()->SetInvalidateTextRuns(true);
+#ifdef DEBUG
+    if (gNoisyReflow) {
+      IndentBy(stdout, gNoiseIndent);
+      ListTag(stdout);
+      printf(": mark prev-line %p dirty\n",
+             static_cast<void*>(aLine.prev().get()));
+    }
+#endif
+  }
+}
+
+/**
+ * Test whether lines are certain to be aligned left so that we can make
+ * resizing optimizations
+ */
+static inline bool IsAlignedLeft(StyleTextAlign aAlignment,
+                                 StyleDirection aDirection,
+                                 StyleUnicodeBidi aUnicodeBidi,
+                                 nsIFrame* aFrame) {
+  return aFrame->IsInSVGTextSubtree() || StyleTextAlign::Left == aAlignment ||
+         (((StyleTextAlign::Start == aAlignment &&
+            StyleDirection::Ltr == aDirection) ||
+           (StyleTextAlign::End == aAlignment &&
+            StyleDirection::Rtl == aDirection)) &&
+          aUnicodeBidi != StyleUnicodeBidi::Plaintext);
+}
+
+void nsBlockFrame::PrepareResizeReflow(BlockReflowState& aState) {
+  // See if we can try and avoid marking all the lines as dirty
+  // FIXME(emilio): This should be writing-mode aware, I guess.
+  bool tryAndSkipLines =
+      // The left content-edge must be a constant distance from the left
+      // border-edge.
+      !StylePadding()->mPadding.Get(eSideLeft).HasPercent();
+
+#ifdef DEBUG
+  if (gDisableResizeOpt) {
+    tryAndSkipLines = false;
+  }
+  if (gNoisyReflow) {
+    if (!tryAndSkipLines) {
+      IndentBy(stdout, gNoiseIndent);
+      ListTag(stdout);
+      printf(": marking all lines dirty: availISize=%d\n",
+             aState.mReflowInput.AvailableISize());
+    }
+  }
+#endif
+
+  if (tryAndSkipLines) {
+    WritingMode wm = aState.mReflowInput.GetWritingMode();
+    nscoord newAvailISize =
+        aState.mReflowInput.ComputedLogicalBorderPadding(wm).IStart(wm) +
+        aState.mReflowInput.ComputedISize();
+
+#ifdef DEBUG
+    if (gNoisyReflow) {
+      IndentBy(stdout, gNoiseIndent);
+      ListTag(stdout);
+      printf(": trying to avoid marking all lines dirty\n");
+    }
+#endif
+
+    for (LineIterator line = LinesBegin(), line_end = LinesEnd();
+         line != line_end; ++line) {
+      // We let child blocks make their own decisions the same
+      // way we are here.
+      bool isLastLine = line == mLines.back() && !GetNextInFlow();
+      if (line->IsBlock() || line->HasFloats() ||
+          (!isLastLine && !line->HasForcedLineBreakAfter()) ||
+          ((isLastLine || !line->IsLineWrapped())) ||
+          line->ResizeReflowOptimizationDisabled() ||
+          line->IsImpactedByFloat() || (line->IEnd() > newAvailISize)) {
+        line->MarkDirty();
+      }
+
+#ifdef REALLY_NOISY_REFLOW
+      if (!line->IsBlock()) {
+        printf("PrepareResizeReflow thinks line %p is %simpacted by floats\n",
+               line.get(), line->IsImpactedByFloat() ? "" : "not ");
+      }
+#endif
+#ifdef DEBUG
+      if (gNoisyReflow && !line->IsDirty()) {
+        IndentBy(stdout, gNoiseIndent + 1);
+        printf(
+            "skipped: line=%p next=%p %s %s%s%s clearTypeBefore/After=%s/%s "
+            "xmost=%d\n",
+            static_cast<void*>(line.get()),
+            static_cast<void*>(
+                (line.next() != LinesEnd() ? line.next().get() : nullptr)),
+            line->IsBlock() ? "block" : "inline",
+            line->HasForcedLineBreakAfter() ? "has-break-after " : "",
+            line->HasFloats() ? "has-floats " : "",
+            line->IsImpactedByFloat() ? "impacted " : "",
+            line->StyleClearToString(line->FloatClearTypeBefore()),
+            line->StyleClearToString(line->FloatClearTypeAfter()),
+            line->IEnd());
+      }
+#endif
+    }
+  } else {
+    // Mark everything dirty
+    for (auto& line : Lines()) {
+      line.MarkDirty();
+    }
+  }
+}
+
+//----------------------------------------
+
+/**
+ * Propagate reflow "damage" from from earlier lines to the current
+ * line.  The reflow damage comes from the following sources:
+ *  1. The regions of float damage remembered during reflow.
+ *  2. The combination of nonzero |aDeltaBCoord| and any impact by a
+ *     float, either the previous reflow or now.
+ *
+ * When entering this function, |aLine| is still at its old position and
+ * |aDeltaBCoord| indicates how much it will later be slid (assuming it
+ * doesn't get marked dirty and reflowed entirely).
+ */
+void nsBlockFrame::PropagateFloatDamage(BlockReflowState& aState,
+                                        nsLineBox* aLine,
+                                        nscoord aDeltaBCoord) {
+  nsFloatManager* floatManager = aState.FloatManager();
+  NS_ASSERTION(
+      (aState.mReflowInput.mParentReflowInput &&
+       aState.mReflowInput.mParentReflowInput->mFloatManager == floatManager) ||
+          aState.mReflowInput.mBlockDelta == 0,
+      "Bad block delta passed in");
+
+  // Check to see if there are any floats; if there aren't, there can't
+  // be any float damage
+  if (!floatManager->HasAnyFloats()) {
+    return;
+  }
+
+  // Check the damage region recorded in the float damage.
+  if (floatManager->HasFloatDamage()) {
+    // Need to check mBounds *and* mCombinedArea to find intersections
+    // with aLine's floats
+    nscoord lineBCoordBefore = aLine->BStart() + aDeltaBCoord;
+    nscoord lineBCoordAfter = lineBCoordBefore + aLine->BSize();
+    // Scrollable overflow should be sufficient for things that affect
+    // layout.
+    WritingMode wm = aState.mReflowInput.GetWritingMode();
+    nsSize containerSize = aState.ContainerSize();
+    LogicalRect overflow =
+        aLine->GetOverflowArea(OverflowType::Scrollable, wm, containerSize);
+    nscoord lineBCoordCombinedBefore = overflow.BStart(wm) + aDeltaBCoord;
+    nscoord lineBCoordCombinedAfter =
+        lineBCoordCombinedBefore + overflow.BSize(wm);
+
+    bool isDirty =
+        floatManager->IntersectsDamage(lineBCoordBefore, lineBCoordAfter) ||
+        floatManager->IntersectsDamage(lineBCoordCombinedBefore,
+                                       lineBCoordCombinedAfter);
+    if (isDirty) {
+      aLine->MarkDirty();
+      return;
+    }
+  }
+
+  // Check if the line is moving relative to the float manager
+  if (aDeltaBCoord + aState.mReflowInput.mBlockDelta != 0) {
+    if (aLine->IsBlock()) {
+      // Unconditionally reflow sliding blocks; we only really need to reflow
+      // if there's a float impacting this block, but the current float manager
+      // makes it difficult to check that.  Therefore, we let the child block
+      // decide what it needs to reflow.
+      aLine->MarkDirty();
+    } else {
+      bool wasImpactedByFloat = aLine->IsImpactedByFloat();
+      nsFlowAreaRect floatAvailableSpace =
+          aState.GetFloatAvailableSpaceForBSize(aLine->BStart() + aDeltaBCoord,
+                                                aLine->BSize(), nullptr);
+
+#ifdef REALLY_NOISY_REFLOW
+      printf("nsBlockFrame::PropagateFloatDamage %p was = %d, is=%d\n", this,
+             wasImpactedByFloat, floatAvailableSpace.HasFloats());
+#endif
+
+      // Mark the line dirty if it was or is affected by a float
+      // We actually only really need to reflow if the amount of impact
+      // changes, but that's not straightforward to check
+      if (wasImpactedByFloat || floatAvailableSpace.HasFloats()) {
+        aLine->MarkDirty();
+      }
+    }
+  }
+}
+
+static bool LineHasClear(nsLineBox* aLine) {
+  return aLine->IsBlock()
+             ? (aLine->HasForcedLineBreakBefore() ||
+                aLine->mFirstChild->HasAnyStateBits(
+                    NS_BLOCK_HAS_CLEAR_CHILDREN) ||
+                !nsBlockFrame::BlockCanIntersectFloats(aLine->mFirstChild))
+             : aLine->HasFloatClearTypeAfter();
+}
+
+/**
+ * Reparent a whole list of floats from aOldParent to this block.  The
+ * floats might be taken from aOldParent's overflow list. They will be
+ * removed from the list. They end up appended to our mFloats list.
+ */
+void nsBlockFrame::ReparentFloats(nsIFrame* aFirstFrame,
+                                  nsBlockFrame* aOldParent,
+                                  bool aReparentSiblings) {
+  nsFrameList list;
+  aOldParent->CollectFloats(aFirstFrame, list, aReparentSiblings);
+  if (list.NotEmpty()) {
+    for (nsIFrame* f : list) {
+      MOZ_ASSERT(!f->HasAnyStateBits(NS_FRAME_IS_PUSHED_FLOAT),
+                 "CollectFloats should've removed that bit");
+      ReparentFrame(f, aOldParent, this);
+    }
+    mFloats.AppendFrames(nullptr, std::move(list));
+  }
+}
+
+static void DumpLine(const BlockReflowState& aState, nsLineBox* aLine,
+                     nscoord aDeltaBCoord, int32_t aDeltaIndent) {
+#ifdef DEBUG
+  if (nsBlockFrame::gNoisyReflow) {
+    nsRect ovis(aLine->InkOverflowRect());
+    nsRect oscr(aLine->ScrollableOverflowRect());
+    nsBlockFrame::IndentBy(stdout, nsBlockFrame::gNoiseIndent + aDeltaIndent);
+    printf(
+        "line=%p mBCoord=%d dirty=%s oldBounds={%d,%d,%d,%d} "
+        "oldoverflow-vis={%d,%d,%d,%d} oldoverflow-scr={%d,%d,%d,%d} "
+        "deltaBCoord=%d mPrevBEndMargin=%d childCount=%d\n",
+        static_cast<void*>(aLine), aState.mBCoord,
+        aLine->IsDirty() ? "yes" : "no", aLine->IStart(), aLine->BStart(),
+        aLine->ISize(), aLine->BSize(), ovis.x, ovis.y, ovis.width, ovis.height,
+        oscr.x, oscr.y, oscr.width, oscr.height, aDeltaBCoord,
+        aState.mPrevBEndMargin.get(), aLine->GetChildCount());
+  }
+#endif
+}
+
+static bool LinesAreEmpty(const nsLineList& aList) {
+  for (const auto& line : aList) {
+    if (!line.IsEmpty()) {
+      return false;
+    }
+  }
+  return true;
+}
+
+bool nsBlockFrame::ReflowDirtyLines(BlockReflowState& aState) {
+  bool keepGoing = true;
+  bool repositionViews = false;  // should we really need this?
+  bool foundAnyClears = aState.mTrailingClearFromPIF != StyleClear::None;
+  bool willReflowAgain = false;
+  bool usedOverflowWrap = false;
+
+#ifdef DEBUG
+  if (gNoisyReflow) {
+    IndentBy(stdout, gNoiseIndent);
+    ListTag(stdout);
+    printf(": reflowing dirty lines");
+    printf(" computedISize=%d\n", aState.mReflowInput.ComputedISize());
+  }
+  AutoNoisyIndenter indent(gNoisyReflow);
+#endif
+
+  bool selfDirty = HasAnyStateBits(NS_FRAME_IS_DIRTY) ||
+                   (aState.mReflowInput.IsBResize() &&
+                    HasAnyStateBits(NS_FRAME_CONTAINS_RELATIVE_BSIZE));
+
+  // Reflow our last line if our availableBSize has increased
+  // so that we (and our last child) pull up content as necessary
+  if (aState.mReflowInput.AvailableBSize() != NS_UNCONSTRAINEDSIZE &&
+      GetNextInFlow() &&
+      aState.mReflowInput.AvailableBSize() >
+          GetLogicalSize().BSize(aState.mReflowInput.GetWritingMode())) {
+    LineIterator lastLine = LinesEnd();
+    if (lastLine != LinesBegin()) {
+      --lastLine;
+      lastLine->MarkDirty();
+    }
+  }
+  // the amount by which we will slide the current line if it is not
+  // dirty
+  nscoord deltaBCoord = 0;
+
+  // whether we did NOT reflow the previous line and thus we need to
+  // recompute the carried out margin before the line if we want to
+  // reflow it or if its previous margin is dirty
+  bool needToRecoverState = false;
+  // Float continuations were reflowed in ReflowPushedFloats
+  bool reflowedFloat =
+      mFloats.NotEmpty() &&
+      mFloats.FirstChild()->HasAnyStateBits(NS_FRAME_IS_PUSHED_FLOAT);
+  bool lastLineMovedUp = false;
+  // We save up information about BR-clearance here
+  StyleClear inlineFloatClearType = aState.mTrailingClearFromPIF;
+
+  LineIterator line = LinesBegin(), line_end = LinesEnd();
+
+  // Determine if children of this frame could have breaks between them for
+  // page names.
+  //
+  // We need to check for paginated layout, the named-page pref, and if the
+  // available block-size is constrained.
+  //
+  // Note that we need to check for paginated layout as named-pages are only
+  // used during paginated reflow. We need to additionally check for
+  // unconstrained block-size to avoid introducing fragmentation breaks during
+  // "measuring" reflows within an overall paginated reflow, and to avoid
+  // fragmentation in monolithic containers like 'inline-block'.
+  //
+  // Because we can only break for named pages using Class A breakpoints, we
+  // also need to check that the block flow direction of the containing frame
+  // of these items (which is this block) is parallel to that of this page.
+  // See: https://www.w3.org/TR/css-break-3/#btw-blocks
+  const nsPresContext* const presCtx = aState.mPresContext;
+  const bool canBreakForPageNames =
+      aState.mReflowInput.mFlags.mCanHaveClassABreakpoints &&
+      aState.mReflowInput.AvailableBSize() != NS_UNCONSTRAINEDSIZE &&
+      presCtx->GetPresShell()->GetRootFrame()->GetWritingMode().IsVertical() ==
+          GetWritingMode().IsVertical();
+
+  // ReflowInput.mFlags.mCanHaveClassABreakpoints should respect the named
+  // pages pref and presCtx->IsPaginated, so we did not explicitly check these
+  // above when setting canBreakForPageNames.
+  if (canBreakForPageNames) {
+    MOZ_ASSERT(presCtx->IsPaginated(),
+               "canBreakForPageNames should not be set during non-paginated "
+               "reflow");
+  }
+
+  // Reflow the lines that are already ours
+  for (; line != line_end; ++line, aState.AdvanceToNextLine()) {
+    DumpLine(aState, line, deltaBCoord, 0);
+#ifdef DEBUG
+    AutoNoisyIndenter indent2(gNoisyReflow);
+#endif
+
+    if (selfDirty) {
+      line->MarkDirty();
+    }
+
+    // This really sucks, but we have to look inside any blocks that have clear
+    // elements inside them.
+    // XXX what can we do smarter here?
+    if (!line->IsDirty() && line->IsBlock() &&
+        line->mFirstChild->HasAnyStateBits(NS_BLOCK_HAS_CLEAR_CHILDREN)) {
+      line->MarkDirty();
+    }
+
+    nsIFrame* floatAvoidingBlock = nullptr;
+    if (line->IsBlock() &&
+        !nsBlockFrame::BlockCanIntersectFloats(line->mFirstChild)) {
+      floatAvoidingBlock = line->mFirstChild;
+    }
+
+    // We have to reflow the line if it's a block whose clearance
+    // might have changed, so detect that.
+    if (!line->IsDirty() &&
+        (line->HasForcedLineBreakBefore() || floatAvoidingBlock)) {
+      nscoord curBCoord = aState.mBCoord;
+      // See where we would be after applying any clearance due to
+      // BRs.
+      if (inlineFloatClearType != StyleClear::None) {
+        std::tie(curBCoord, std::ignore) =
+            aState.ClearFloats(curBCoord, inlineFloatClearType);
+      }
+
+      auto [newBCoord, result] = aState.ClearFloats(
+          curBCoord, line->FloatClearTypeBefore(), floatAvoidingBlock);
+
+      if (line->HasClearance()) {
+        // Reflow the line if it might not have clearance anymore.
+        if (result == ClearFloatsResult::BCoordNoChange
+            // aState.mBCoord is the clearance point which should be the
+            // block-start border-edge of the block frame. If sliding the
+            // block by deltaBCoord isn't going to put it in the predicted
+            // position, then we'd better reflow the line.
+            || newBCoord != line->BStart() + deltaBCoord) {
+          line->MarkDirty();
+        }
+      } else {
+        // Reflow the line if the line might have clearance now.
+        if (result != ClearFloatsResult::BCoordNoChange) {
+          line->MarkDirty();
+        }
+      }
+    }
+
+    // We might have to reflow a line that is after a clearing BR.
+    if (inlineFloatClearType != StyleClear::None) {
+      std::tie(aState.mBCoord, std::ignore) =
+          aState.ClearFloats(aState.mBCoord, inlineFloatClearType);
+      if (aState.mBCoord != line->BStart() + deltaBCoord) {
+        // SlideLine is not going to put the line where the clearance
+        // put it. Reflow the line to be sure.
+        line->MarkDirty();
+      }
+      inlineFloatClearType = StyleClear::None;
+    }
+
+    bool previousMarginWasDirty = line->IsPreviousMarginDirty();
+    if (previousMarginWasDirty) {
+      // If the previous margin is dirty, reflow the current line
+      line->MarkDirty();
+      line->ClearPreviousMarginDirty();
+    } else if (aState.ContentBSize() != NS_UNCONSTRAINEDSIZE) {
+      const nscoord scrollableOverflowBEnd =
+          LogicalRect(line->mWritingMode, line->ScrollableOverflowRect(),
+                      line->mContainerSize)
+              .BEnd(line->mWritingMode);
+      if (scrollableOverflowBEnd + deltaBCoord > aState.ContentBEnd()) {
+        // Lines that aren't dirty but get slid past our available block-size
+        // constraint must be reflowed.
+        line->MarkDirty();
+      }
+    }
+
+    if (!line->IsDirty()) {
+      const bool isPaginated =
+          // Last column can be reflowed unconstrained during column balancing.
+          // Hence the additional NS_FRAME_HAS_MULTI_COLUMN_ANCESTOR bit check
+          // as a fail-safe fallback.
+          aState.mReflowInput.AvailableBSize() != NS_UNCONSTRAINEDSIZE ||
+          HasAnyStateBits(NS_FRAME_HAS_MULTI_COLUMN_ANCESTOR) ||
+          // Table can also be reflowed unconstrained during printing.
+          aState.mPresContext->IsPaginated();
+      if (isPaginated) {
+        // We are in a paginated context, i.e. in columns or pages.
+        const bool mayContainFloats =
+            line->IsBlock() || line->HasFloats() || line->HadFloatPushed();
+        if (mayContainFloats) {
+          // The following if-else conditions check whether this line -- which
+          // might have floats in its subtree, or has floats as direct children,
+          // or had floats pushed -- needs to be reflowed.
+          if (deltaBCoord != 0 || aState.mReflowInput.IsBResize()) {
+            // The distance to the block-end edge might have changed. Reflow the
+            // line both because the breakpoints within its floats may have
+            // changed and because we might have to push/pull the floats in
+            // their entirety.
+            line->MarkDirty();
+          } else if (HasPushedFloats()) {
+            // We had pushed floats which haven't been drained by our
+            // next-in-flow, which means our parent is currently reflowing us
+            // again due to clearance without creating a next-in-flow for us.
+            // Reflow the line to redo the floats split logic to correctly set
+            // our reflow status.
+            line->MarkDirty();
+          } else if (aState.mReflowInput.mFlags.mMustReflowPlaceholders) {
+            // Reflow the line (that may containing a float's placeholder frame)
+            // if our parent tells us to do so.
+            line->MarkDirty();
+          } else if (aState.mReflowInput.mFlags.mMovedBlockFragments) {
+            // Our parent's line containing us moved to a different fragment.
+            // Reflow the line because the decision about whether the float fits
+            // may be different in a different fragment.
+            line->MarkDirty();
+          }
+        }
+      }
+    }
+
+    if (!line->IsDirty()) {
+      // See if there's any reflow damage that requires that we mark the
+      // line dirty.
+      PropagateFloatDamage(aState, line, deltaBCoord);
+    }
+
+    // If the container size has changed, reset mContainerSize. If the
+    // line's writing mode is not ltr, or if the line is not left-aligned, also
+    // mark the line dirty.
+    if (aState.ContainerSize() != line->mContainerSize) {
+      line->mContainerSize = aState.ContainerSize();
+
+      const bool isLastLine = line == mLines.back() && !GetNextInFlow();
+      const auto align = isLastLine ? StyleText()->TextAlignForLastLine()
+                                    : StyleText()->mTextAlign;
+      if (line->mWritingMode.IsVertical() || line->mWritingMode.IsBidiRTL() ||
+          !IsAlignedLeft(align, StyleVisibility()->mDirection,
+                         StyleTextReset()->mUnicodeBidi, this)) {
+        line->MarkDirty();
+      }
+    }
+
+    // Check for a page break caused by CSS named pages.
+    //
+    // We should break for named pages when two frames meet at a class A
+    // breakpoint, where the first frame has a different end page value to the
+    // second frame's start page value. canBreakForPageNames is true iff
+    // children of this frame can form class A breakpoints, and that we are not
+    // in a measurement reflow or in a monolithic container such as
+    // 'inline-block'.
+    //
+    // We specifically do not want to cause a page-break for named pages when
+    // we are at the top of a page. This would otherwise happen when the
+    // previous sibling is an nsPageBreakFrame, or all previous siblings on the
+    // current page are zero-height. The latter may not be per-spec, but is
+    // compatible with Chrome's implementation of named pages.
+    const nsAtom* nextPageName = nullptr;
+    bool shouldBreakForPageName = false;
+    if (canBreakForPageNames && (!aState.mReflowInput.mFlags.mIsTopOfPage ||
+                                 !aState.IsAdjacentWithBStart())) {
+      const nsIFrame* const frame = line->mFirstChild;
+      if (!frame->IsPlaceholderFrame() && !frame->IsPageBreakFrame()) {
+        nextPageName = frame->GetStartPageValue();
+        // Walk back to the last frame that isn't a placeholder.
+        const nsIFrame* prevFrame = frame->GetPrevSibling();
+        while (prevFrame && prevFrame->IsPlaceholderFrame()) {
+          prevFrame = prevFrame->GetPrevSibling();
+        }
+        if (prevFrame && prevFrame->GetEndPageValue() != nextPageName) {
+          shouldBreakForPageName = true;
+          line->MarkDirty();
+        }
+      }
+    }
+
+    if (needToRecoverState && line->IsDirty()) {
+      // We need to reconstruct the block-end margin only if we didn't
+      // reflow the previous line and we do need to reflow (or repair
+      // the block-start position of) the next line.
+      aState.ReconstructMarginBefore(line);
+    }
+
+    bool reflowedPrevLine = !needToRecoverState;
+    if (needToRecoverState) {
+      needToRecoverState = false;
+
+      // Update aState.mPrevChild as if we had reflowed all of the frames in
+      // this line.
+      if (line->IsDirty()) {
+        NS_ASSERTION(
+            line->mFirstChild->GetPrevSibling() == line.prev()->LastChild(),
+            "unexpected line frames");
+        aState.mPrevChild = line->mFirstChild->GetPrevSibling();
+      }
+    }
+
+    // Now repair the line and update |aState.mBCoord| by calling
+    // |ReflowLine| or |SlideLine|.
+    // If we're going to reflow everything again, then no need to reflow
+    // the dirty line ... unless the line has floats, in which case we'd
+    // better reflow it now to refresh its float cache, which may contain
+    // dangling frame pointers! Ugh! This reflow of the line may be
+    // incorrect because we skipped reflowing previous lines (e.g., floats
+    // may be placed incorrectly), but that's OK because we'll mark the
+    // line dirty below under "if (aState.mReflowInput.mDiscoveredClearance..."
+    if (line->IsDirty() && (line->HasFloats() || !willReflowAgain)) {
+      lastLineMovedUp = true;
+
+      bool maybeReflowingForFirstTime =
+          line->IStart() == 0 && line->BStart() == 0 && line->ISize() == 0 &&
+          line->BSize() == 0;
+
+      // Compute the dirty lines "before" BEnd, after factoring in
+      // the running deltaBCoord value - the running value is implicit in
+      // aState.mBCoord.
+      nscoord oldB = line->BStart();
+      nscoord oldBMost = line->BEnd();
+
+      NS_ASSERTION(!willReflowAgain || !line->IsBlock(),
+                   "Don't reflow blocks while willReflowAgain is true, reflow "
+                   "of block abs-pos children depends on this");
+
+      if (shouldBreakForPageName) {
+        // Immediately fragment for page-name. It is possible we could break
+        // out of the loop right here, but this should make it more similar to
+        // what happens when reflow causes fragmentation.
+        PushTruncatedLine(aState, line, &keepGoing);
+        PresShell()->FrameConstructor()->SetNextPageContentFramePageName(
+            nextPageName ? nextPageName : GetAutoPageValue());
+      } else {
+        // Reflow the dirty line. If it's an incremental reflow, then force
+        // it to invalidate the dirty area if necessary
+        usedOverflowWrap |= ReflowLine(aState, line, &keepGoing);
+      }
+
+      if (aState.mReflowInput.WillReflowAgainForClearance()) {
+        line->MarkDirty();
+        willReflowAgain = true;
+        // Note that once we've entered this state, every line that gets here
+        // (e.g. because it has floats) gets marked dirty and reflowed again.
+        // in the next pass. This is important, see above.
+      }
+
+      if (line->HasFloats()) {
+        reflowedFloat = true;
+      }
+
+      if (!keepGoing) {
+        DumpLine(aState, line, deltaBCoord, -1);
+        if (0 == line->GetChildCount()) {
+          DeleteLine(aState, line, line_end);
+        }
+        break;
+      }
+
+      // Test to see whether the margin that should be carried out
+      // to the next line (NL) might have changed. In ReflowBlockFrame
+      // we call nextLine->MarkPreviousMarginDirty if the block's
+      // actual carried-out block-end margin changed. So here we only
+      // need to worry about the following effects:
+      // 1) the line was just created, and it might now be blocking
+      // a carried-out block-end margin from previous lines that
+      // used to reach NL from reaching NL
+      // 2) the line used to be empty, and is now not empty,
+      // thus blocking a carried-out block-end margin from previous lines
+      // that used to reach NL from reaching NL
+      // 3) the line wasn't empty, but now is, so a carried-out
+      // block-end margin from previous lines that didn't used to reach NL
+      // now does
+      // 4) the line might have changed in a way that affects NL's
+      // ShouldApplyBStartMargin decision. The three things that matter
+      // are the line's emptiness, its adjacency to the block-start edge of the
+      // block, and whether it has clearance (the latter only matters if the
+      // block was and is adjacent to the block-start and empty).
+      //
+      // If the line is empty now, we can't reliably tell if the line was empty
+      // before, so we just assume it was and do
+      // nextLine->MarkPreviousMarginDirty. This means the checks in 4) are
+      // redundant; if the line is empty now we don't need to check 4), but if
+      // the line is not empty now and we're sure it wasn't empty before, any
+      // adjacency and clearance changes are irrelevant to the result of
+      // nextLine->ShouldApplyBStartMargin.
+      if (line.next() != LinesEnd()) {
+        bool maybeWasEmpty = oldB == line.next()->BStart();
+        bool isEmpty = line->CachedIsEmpty();
+        if (maybeReflowingForFirstTime /*1*/ ||
+            (isEmpty || maybeWasEmpty) /*2/3/4*/) {
+          line.next()->MarkPreviousMarginDirty();
+          // since it's marked dirty, nobody will care about |deltaBCoord|
+        }
+      }
+
+      // If the line was just reflowed for the first time, then its
+      // old mBounds cannot be trusted so this deltaBCoord computation is
+      // bogus. But that's OK because we just did
+      // MarkPreviousMarginDirty on the next line which will force it
+      // to be reflowed, so this computation of deltaBCoord will not be
+      // used.
+      deltaBCoord = line->BEnd() - oldBMost;
+
+      // Now do an interrupt check. We want to do this only in the case when we
+      // actually reflow the line, so that if we get back in here we'll get
+      // further on the reflow before interrupting.
+      aState.mPresContext->CheckForInterrupt(this);
+    } else {
+      aState.mOverflowTracker->Skip(line->mFirstChild, aState.mReflowStatus);
+      // Nop except for blocks (we don't create overflow container
+      // continuations for any inlines atm), so only checking mFirstChild
+      // is enough
+
+      lastLineMovedUp = deltaBCoord < 0;
+
+      if (deltaBCoord != 0) {
+        SlideLine(aState, line, deltaBCoord);
+      } else {
+        repositionViews = true;
+      }
+
+      NS_ASSERTION(!line->IsDirty() || !line->HasFloats(),
+                   "Possibly stale float cache here!");
+      if (willReflowAgain && line->IsBlock()) {
+        // If we're going to reflow everything again, and this line is a block,
+        // then there is no need to recover float state. The line may contain
+        // other lines with floats, but in that case RecoverStateFrom would only
+        // add floats to the float manager. We don't need to do that because
+        // everything's going to get reflowed again "for real". Calling
+        // RecoverStateFrom in this situation could be lethal because the
+        // block's descendant lines may have float caches containing dangling
+        // frame pointers. Ugh!
+        // If this line is inline, then we need to recover its state now
+        // to make sure that we don't forget to move its floats by deltaBCoord.
+      } else {
+        // XXX EVIL O(N^2) EVIL
+        aState.RecoverStateFrom(line, deltaBCoord);
+      }
+
+      // Keep mBCoord up to date in case we're propagating reflow damage
+      // and also because our final height may depend on it. If the
+      // line is inlines, then only update mBCoord if the line is not
+      // empty, because that's what PlaceLine does. (Empty blocks may
+      // want to update mBCoord, e.g. if they have clearance.)
+      if (line->IsBlock() || !line->CachedIsEmpty()) {
+        aState.mBCoord = line->BEnd();
+      }
+
+      needToRecoverState = true;
+
+      if (reflowedPrevLine && !line->IsBlock() &&
+          aState.mPresContext->HasPendingInterrupt()) {
+        // Need to make sure to pull overflows from any prev-in-flows
+        for (nsIFrame* inlineKid = line->mFirstChild; inlineKid;
+             inlineKid = inlineKid->PrincipalChildList().FirstChild()) {
+          inlineKid->PullOverflowsFromPrevInFlow();
+        }
+      }
+    }
+
+    // Record if we need to clear floats before reflowing the next
+    // line. Note that inlineFloatClearType will be handled and
+    // cleared before the next line is processed, so there is no
+    // need to combine break types here.
+    if (line->HasFloatClearTypeAfter()) {
+      inlineFloatClearType = line->FloatClearTypeAfter();
+    }
+
+    if (LineHasClear(line.get())) {
+      foundAnyClears = true;
+    }
+
+    DumpLine(aState, line, deltaBCoord, -1);
+
+    if (aState.mPresContext->HasPendingInterrupt()) {
+      willReflowAgain = true;
+      // Another option here might be to leave |line| clean if
+      // !HasPendingInterrupt() before the CheckForInterrupt() call, since in
+      // that case the line really did reflow as it should have.  Not sure
+      // whether that would be safe, so doing this for now instead.  Also not
+      // sure whether we really want to mark all lines dirty after an
+      // interrupt, but until we get better at propagating float damage we
+      // really do need to do it this way; see comments inside MarkLineDirty.
+      MarkLineDirtyForInterrupt(line);
+    }
+  }
+
+  // Handle BR-clearance from the last line of the block
+  if (inlineFloatClearType != StyleClear::None) {
+    std::tie(aState.mBCoord, std::ignore) =
+        aState.ClearFloats(aState.mBCoord, inlineFloatClearType);
+  }
+
+  if (needToRecoverState) {
+    // Is this expensive?
+    aState.ReconstructMarginBefore(line);
+
+    // Update aState.mPrevChild as if we had reflowed all of the frames in
+    // the last line.
+    NS_ASSERTION(line == line_end || line->mFirstChild->GetPrevSibling() ==
+                                         line.prev()->LastChild(),
+                 "unexpected line frames");
+    aState.mPrevChild = line == line_end ? mFrames.LastChild()
+                                         : line->mFirstChild->GetPrevSibling();
+  }
+
+  // Should we really have to do this?
+  if (repositionViews) {
+    nsContainerFrame::PlaceFrameView(this);
+  }
+
+  // We can skip trying to pull up the next line if our height is constrained
+  // (so we can report being incomplete) and there is no next in flow or we
+  // were told not to or we know it will be futile, i.e.,
+  // -- the next in flow is not changing
+  // -- and we cannot have added more space for its first line to be
+  // pulled up into,
+  // -- it's an incremental reflow of a descendant
+  // -- and we didn't reflow any floats (so the available space
+  // didn't change)
+  // -- my chain of next-in-flows either has no first line, or its first
+  // line isn't dirty.
+  bool heightConstrained =
+      aState.mReflowInput.AvailableBSize() != NS_UNCONSTRAINEDSIZE;
+  bool skipPull = willReflowAgain && heightConstrained;
+  if (!skipPull && heightConstrained && aState.mNextInFlow &&
+      (aState.mReflowInput.mFlags.mNextInFlowUntouched && !lastLineMovedUp &&
+       !HasAnyStateBits(NS_FRAME_IS_DIRTY) && !reflowedFloat)) {
+    // We'll place lineIter at the last line of this block, so that
+    // nsBlockInFlowLineIterator::Next() will take us to the first
+    // line of my next-in-flow-chain.  (But first, check that I
+    // have any lines -- if I don't, just bail out of this
+    // optimization.)
+    LineIterator lineIter = this->LinesEnd();
+    if (lineIter != this->LinesBegin()) {
+      lineIter--;  // I have lines; step back from dummy iterator to last line.
+      nsBlockInFlowLineIterator bifLineIter(this, lineIter);
+
+      // Check for next-in-flow-chain's first line.
+      // (First, see if there is such a line, and second, see if it's clean)
+      if (!bifLineIter.Next() || !bifLineIter.GetLine()->IsDirty()) {
+        skipPull = true;
+      }
+    }
+  }
+
+  if (skipPull && aState.mNextInFlow) {
+    NS_ASSERTION(heightConstrained, "Height should be constrained here\n");
+    if (aState.mNextInFlow->IsTrueOverflowContainer()) {
+      aState.mReflowStatus.SetOverflowIncomplete();
+    } else {
+      aState.mReflowStatus.SetIncomplete();
+    }
+  }
+
+  if (!skipPull && aState.mNextInFlow) {
+    // Pull data from a next-in-flow if there's still room for more
+    // content here.
+    while (keepGoing && aState.mNextInFlow) {
+      // Grab first line from our next-in-flow
+      nsBlockFrame* nextInFlow = aState.mNextInFlow;
+      nsLineBox* pulledLine;
+      nsFrameList pulledFrames;
+      if (!nextInFlow->mLines.empty()) {
+        RemoveFirstLine(nextInFlow->mLines, nextInFlow->mFrames, &pulledLine,
+                        &pulledFrames);
+      } else {
+        // Grab an overflow line if there are any
+        FrameLines* overflowLines = nextInFlow->GetOverflowLines();
+        if (!overflowLines) {
+          aState.mNextInFlow =
+              static_cast<nsBlockFrame*>(nextInFlow->GetNextInFlow());
+          continue;
+        }
+        bool last =
+            RemoveFirstLine(overflowLines->mLines, overflowLines->mFrames,
+                            &pulledLine, &pulledFrames);
+        if (last) {
+          nextInFlow->DestroyOverflowLines();
+        }
+      }
+
+      if (pulledFrames.IsEmpty()) {
+        // The line is empty. Try the next one.
+        NS_ASSERTION(
+            pulledLine->GetChildCount() == 0 && !pulledLine->mFirstChild,
+            "bad empty line");
+        nextInFlow->FreeLineBox(pulledLine);
+        continue;
+      }
+
+      if (nextInFlow->MaybeHasLineCursor()) {
+        if (pulledLine == nextInFlow->GetLineCursorForDisplay()) {
+          nextInFlow->ClearLineCursorForDisplay();
+        }
+        if (pulledLine == nextInFlow->GetLineCursorForQuery()) {
+          nextInFlow->ClearLineCursorForQuery();
+        }
+      }
+      ReparentFrames(pulledFrames, nextInFlow, this);
+      pulledLine->SetMovedFragments();
+
+      NS_ASSERTION(pulledFrames.LastChild() == pulledLine->LastChild(),
+                   "Unexpected last frame");
+      NS_ASSERTION(aState.mPrevChild || mLines.empty(),
+                   "should have a prevchild here");
+      NS_ASSERTION(aState.mPrevChild == mFrames.LastChild(),
+                   "Incorrect aState.mPrevChild before inserting line at end");
+
+      // Shift pulledLine's frames into our mFrames list.
+      mFrames.AppendFrames(nullptr, std::move(pulledFrames));
+
+      // Add line to our line list, and set its last child as our new prev-child
+      line = mLines.before_insert(LinesEnd(), pulledLine);
+      aState.mPrevChild = mFrames.LastChild();
+
+      // Reparent floats whose placeholders are in the line.
+      ReparentFloats(pulledLine->mFirstChild, nextInFlow, true);
+
+      DumpLine(aState, pulledLine, deltaBCoord, 0);
+#ifdef DEBUG
+      AutoNoisyIndenter indent2(gNoisyReflow);
+#endif
+
+      if (aState.mPresContext->HasPendingInterrupt()) {
+        MarkLineDirtyForInterrupt(line);
+      } else {
+        // Now reflow it and any lines that it makes during it's reflow
+        // (we have to loop here because reflowing the line may cause a new
+        // line to be created; see SplitLine's callers for examples of
+        // when this happens).
+        while (line != LinesEnd()) {
+          usedOverflowWrap |= ReflowLine(aState, line, &keepGoing);
+
+          if (aState.mReflowInput.WillReflowAgainForClearance()) {
+            line->MarkDirty();
+            keepGoing = false;
+            aState.mReflowStatus.SetIncomplete();
+            break;
+          }
+
+          DumpLine(aState, line, deltaBCoord, -1);
+          if (!keepGoing) {
+            if (0 == line->GetChildCount()) {
+              DeleteLine(aState, line, line_end);
+            }
+            break;
+          }
+
+          if (LineHasClear(line.get())) {
+            foundAnyClears = true;
+          }
+
+          if (aState.mPresContext->CheckForInterrupt(this)) {
+            MarkLineDirtyForInterrupt(line);
+            break;
+          }
+
+          // If this is an inline frame then its time to stop
+          ++line;
+          aState.AdvanceToNextLine();
+        }
+      }
+    }
+
+    if (aState.mReflowStatus.IsIncomplete()) {
+      aState.mReflowStatus.SetNextInFlowNeedsReflow();
+    }  // XXXfr shouldn't set this flag when nextinflow has no lines
+  }
+
+  // Handle an odd-ball case: a list-item with no lines
+  if (mLines.empty() && HasOutsideMarker()) {
+    ReflowOutput metrics(aState.mReflowInput);
+    nsIFrame* marker = GetOutsideMarker();
+    WritingMode wm = aState.mReflowInput.GetWritingMode();
+    ReflowOutsideMarker(
+        marker, aState, metrics,
+        aState.mReflowInput.ComputedPhysicalBorderPadding().top);
+    NS_ASSERTION(!MarkerIsEmpty() || metrics.BSize(wm) == 0,
+                 "empty ::marker frame took up space");
+
+    if (!MarkerIsEmpty()) {
+      // There are no lines so we have to fake up some y motion so that
+      // we end up with *some* height.
+      // (Note: if we're layout-contained, we have to be sure to leave our
+      // ReflowOutput's BlockStartAscent() (i.e. the baseline) untouched,
+      // because layout-contained frames have no baseline.)
+      if (!aState.mReflowInput.mStyleDisplay->IsContainLayout() &&
+          metrics.BlockStartAscent() == ReflowOutput::ASK_FOR_BASELINE) {
+        nscoord ascent;
+        WritingMode wm = aState.mReflowInput.GetWritingMode();
+        if (nsLayoutUtils::GetFirstLineBaseline(wm, marker, &ascent)) {
+          metrics.SetBlockStartAscent(ascent);
+        } else {
+          metrics.SetBlockStartAscent(metrics.BSize(wm));
+        }
+      }
+
+      RefPtr<nsFontMetrics> fm =
+          nsLayoutUtils::GetInflatedFontMetricsForFrame(this);
+
+      nscoord minAscent = nsLayoutUtils::GetCenteredFontBaseline(
+          fm, aState.mMinLineHeight, wm.IsLineInverted());
+      nscoord minDescent = aState.mMinLineHeight - minAscent;
+
+      aState.mBCoord +=
+          std::max(minAscent, metrics.BlockStartAscent()) +
+          std::max(minDescent, metrics.BSize(wm) - metrics.BlockStartAscent());
+
+      nscoord offset = minAscent - metrics.BlockStartAscent();
+      if (offset > 0) {
+        marker->SetRect(marker->GetRect() + nsPoint(0, offset));
+      }
+    }
+  }
+
+  if (LinesAreEmpty(mLines) && ShouldHaveLineIfEmpty()) {
+    aState.mBCoord += aState.mMinLineHeight;
+  }
+
+  if (foundAnyClears) {
+    AddStateBits(NS_BLOCK_HAS_CLEAR_CHILDREN);
+  } else {
+    RemoveStateBits(NS_BLOCK_HAS_CLEAR_CHILDREN);
+  }
+
+#ifdef DEBUG
+  VerifyLines(true);
+  VerifyOverflowSituation();
+  if (gNoisyReflow) {
+    IndentBy(stdout, gNoiseIndent - 1);
+    ListTag(stdout);
+    printf(": done reflowing dirty lines (status=%s)\n",
+           ToString(aState.mReflowStatus).c_str());
+  }
+#endif
+
+  return usedOverflowWrap;
+}
+
+void nsBlockFrame::MarkLineDirtyForInterrupt(nsLineBox* aLine) {
+  aLine->MarkDirty();
+
+  // Just checking NS_FRAME_IS_DIRTY is ok, because we've already
+  // marked the lines that need to be marked dirty based on our
+  // vertical resize stuff.  So we'll definitely reflow all those kids;
+  // the only question is how they should behave.
+  if (HasAnyStateBits(NS_FRAME_IS_DIRTY)) {
+    // Mark all our child frames dirty so we make sure to reflow them
+    // later.
+    int32_t n = aLine->GetChildCount();
+    for (nsIFrame* f = aLine->mFirstChild; n > 0;
+         f = f->GetNextSibling(), --n) {
+      f->MarkSubtreeDirty();
+    }
+    // And mark all the floats whose reflows we might be skipping dirty too.
+    if (aLine->HasFloats()) {
+      for (nsIFrame* f : aLine->Floats()) {
+        f->MarkSubtreeDirty();
+      }
+    }
+  } else {
+    // Dirty all the descendant lines of block kids to handle float damage,
+    // since our nsFloatManager will go away by the next time we're reflowing.
+    // XXXbz Can we do something more like what PropagateFloatDamage does?
+    // Would need to sort out the exact business with mBlockDelta for that....
+    // This marks way too much dirty.  If we ever make this better, revisit
+    // which lines we mark dirty in the interrupt case in ReflowDirtyLines.
+    nsBlockFrame* bf = do_QueryFrame(aLine->mFirstChild);
+    if (bf) {
+      MarkAllDescendantLinesDirty(bf);
+    }
+  }
+}
+
+void nsBlockFrame::DeleteLine(BlockReflowState& aState,
+                              nsLineList::iterator aLine,
+                              nsLineList::iterator aLineEnd) {
+  MOZ_ASSERT(0 == aLine->GetChildCount(), "can't delete !empty line");
+  if (0 == aLine->GetChildCount()) {
+    NS_ASSERTION(aState.mCurrentLine == aLine,
+                 "using function more generally than designed, "
+                 "but perhaps OK now");
+    nsLineBox* line = aLine;
+    aLine = mLines.erase(aLine);
+    FreeLineBox(line);
+    // Mark the previous margin of the next line dirty since we need to
+    // recompute its top position.
+    if (aLine != aLineEnd) {
+      aLine->MarkPreviousMarginDirty();
+    }
+  }
+}
+
+/**
+ * Reflow a line. The line will either contain a single block frame
+ * or contain 1 or more inline frames. aKeepReflowGoing indicates
+ * whether or not the caller should continue to reflow more lines.
+ * Returns true if the reflow used an overflow-wrap breakpoint.
+ */
+bool nsBlockFrame::ReflowLine(BlockReflowState& aState, LineIterator aLine,
+                              bool* aKeepReflowGoing) {
+  MOZ_ASSERT(aLine->GetChildCount(), "reflowing empty line");
+
+  // Setup the line-layout for the new line
+  aState.mCurrentLine = aLine;
+  aLine->ClearDirty();
+  aLine->InvalidateCachedIsEmpty();
+  aLine->ClearHadFloatPushed();
+
+  // If this line contains a single block that is hidden by `content-visibility`
+  // don't reflow the line. If this line contains inlines and the first one is
+  // hidden by `content-visibility`, all of them are, so avoid reflow in that
+  // case as well.
+  // For frames that own anonymous children, even the first child is hidden by
+  // `content-visibility`, there could be some anonymous children need reflow,
+  // so we don't skip reflow this line.
+  nsIFrame* firstChild = aLine->mFirstChild;
+  if (firstChild->IsHiddenByContentVisibilityOfInFlowParentForLayout() &&
+      !HasAnyStateBits(NS_FRAME_OWNS_ANON_BOXES)) {
+    return false;
+  }
+
+  // Now that we know what kind of line we have, reflow it
+  bool usedOverflowWrap = false;
+  if (aLine->IsBlock()) {
+    ReflowBlockFrame(aState, aLine, aKeepReflowGoing);
+  } else {
+    aLine->SetLineWrapped(false);
+    usedOverflowWrap = ReflowInlineFrames(aState, aLine, aKeepReflowGoing);
+
+    // Store the line's float edges for overflow marker analysis if needed.
+    aLine->ClearFloatEdges();
+    if (aState.mFlags.mCanHaveOverflowMarkers) {
+      WritingMode wm = aLine->mWritingMode;
+      nsFlowAreaRect r = aState.GetFloatAvailableSpaceForBSize(
+          aLine->BStart(), aLine->BSize(), nullptr);
+      if (r.HasFloats()) {
+        LogicalRect so = aLine->GetOverflowArea(OverflowType::Scrollable, wm,
+                                                aLine->mContainerSize);
+        nscoord s = r.mRect.IStart(wm);
+        nscoord e = r.mRect.IEnd(wm);
+        if (so.IEnd(wm) > e || so.IStart(wm) < s) {
+          // This line is overlapping a float - store the edges marking the area
+          // between the floats for text-overflow analysis.
+          aLine->SetFloatEdges(s, e);
+        }
+      }
+    }
+  }
+
+  aLine->ClearMovedFragments();
+
+  return usedOverflowWrap;
+}
+
+nsIFrame* nsBlockFrame::PullFrame(BlockReflowState& aState,
+                                  LineIterator aLine) {
+  // First check our remaining lines.
+  if (LinesEnd() != aLine.next()) {
+    return PullFrameFrom(aLine, this, aLine.next());
+  }
+
+  NS_ASSERTION(
+      !GetOverflowLines(),
+      "Our overflow lines should have been removed at the start of reflow");
+
+  // Try each next-in-flow.
+  nsBlockFrame* nextInFlow = aState.mNextInFlow;
+  while (nextInFlow) {
+    if (nextInFlow->mLines.empty()) {
+      nextInFlow->DrainSelfOverflowList();
+    }
+    if (!nextInFlow->mLines.empty()) {
+      return PullFrameFrom(aLine, nextInFlow, nextInFlow->mLines.begin());
+    }
+    nextInFlow = static_cast<nsBlockFrame*>(nextInFlow->GetNextInFlow());
+    aState.mNextInFlow = nextInFlow;
+  }
+
+  return nullptr;
+}
+
+nsIFrame* nsBlockFrame::PullFrameFrom(nsLineBox* aLine,
+                                      nsBlockFrame* aFromContainer,
+                                      nsLineList::iterator aFromLine) {
+  nsLineBox* fromLine = aFromLine;
+  MOZ_ASSERT(fromLine, "bad line to pull from");
+  MOZ_ASSERT(fromLine->GetChildCount(), "empty line");
+  MOZ_ASSERT(aLine->GetChildCount(), "empty line");
+  MOZ_ASSERT(!HasProperty(LineIteratorProperty()),
+             "Shouldn't have line iterators mid-reflow");
+
+  NS_ASSERTION(fromLine->IsBlock() == fromLine->mFirstChild->IsBlockOutside(),
+               "Disagreement about whether it's a block or not");
+
+  if (fromLine->IsBlock()) {
+    // If our line is not empty and the child in aFromLine is a block
+    // then we cannot pull up the frame into this line. In this case
+    // we stop pulling.
+    return nullptr;
+  }
+  // Take frame from fromLine
+  nsIFrame* frame = fromLine->mFirstChild;
+  nsIFrame* newFirstChild = frame->GetNextSibling();
+
+  if (aFromContainer != this) {
+    // The frame is being pulled from a next-in-flow; therefore we need to add
+    // it to our sibling list.
+    MOZ_ASSERT(aLine == mLines.back());
+    MOZ_ASSERT(aFromLine == aFromContainer->mLines.begin(),
+               "should only pull from first line");
+    aFromContainer->mFrames.RemoveFrame(frame);
+
+    // When pushing and pulling frames we need to check for whether any
+    // views need to be reparented.
+    ReparentFrame(frame, aFromContainer, this);
+    mFrames.AppendFrame(nullptr, frame);
+
+    // The frame might have (or contain) floats that need to be brought
+    // over too. (pass 'false' since there are no siblings to check)
+    ReparentFloats(frame, aFromContainer, false);
+  } else {
+    MOZ_ASSERT(aLine == aFromLine.prev());
+  }
+
+  aLine->NoteFrameAdded(frame);
+  fromLine->NoteFrameRemoved(frame);
+
+  if (fromLine->GetChildCount() > 0) {
+    // Mark line dirty now that we pulled a child
+    fromLine->MarkDirty();
+    fromLine->mFirstChild = newFirstChild;
+  } else {
+    // Free up the fromLine now that it's empty.
+    // Its bounds might need to be redrawn, though.
+    if (aFromLine.next() != aFromContainer->mLines.end()) {
+      aFromLine.next()->MarkPreviousMarginDirty();
+    }
+    aFromContainer->mLines.erase(aFromLine);
+    // aFromLine is now invalid
+    aFromContainer->FreeLineBox(fromLine);
+  }
+
+#ifdef DEBUG
+  VerifyLines(true);
+  VerifyOverflowSituation();
+#endif
+
+  return frame;
+}
+
+void nsBlockFrame::SlideLine(BlockReflowState& aState, nsLineBox* aLine,
+                             nscoord aDeltaBCoord) {
+  MOZ_ASSERT(aDeltaBCoord != 0, "why slide a line nowhere?");
+
+  // Adjust line state
+  aLine->SlideBy(aDeltaBCoord, aState.ContainerSize());
+
+  // Adjust the frames in the line
+  MoveChildFramesOfLine(aLine, aDeltaBCoord);
+}
+
+void nsBlockFrame::UpdateLineContainerSize(nsLineBox* aLine,
+                                           const nsSize& aNewContainerSize) {
+  if (aNewContainerSize == aLine->mContainerSize) {
+    return;
+  }
+
+  // Adjust line state
+  nsSize sizeDelta = aLine->UpdateContainerSize(aNewContainerSize);
+
+  // Changing container width only matters if writing mode is vertical-rl
+  if (GetWritingMode().IsVerticalRL()) {
+    MoveChildFramesOfLine(aLine, sizeDelta.width);
+  }
+}
+
+void nsBlockFrame::MoveChildFramesOfLine(nsLineBox* aLine,
+                                         nscoord aDeltaBCoord) {
+  // Adjust the frames in the line
+  nsIFrame* kid = aLine->mFirstChild;
+  if (!kid) {
+    return;
+  }
+
+  WritingMode wm = GetWritingMode();
+  LogicalPoint translation(wm, 0, aDeltaBCoord);
+
+  if (aLine->IsBlock()) {
+    if (aDeltaBCoord) {
+      kid->MovePositionBy(wm, translation);
+    }
+
+    // Make sure the frame's view and any child views are updated
+    nsContainerFrame::PlaceFrameView(kid);
+  } else {
+    // Adjust the block-dir coordinate of the frames in the line.
+    // Note: we need to re-position views even if aDeltaBCoord is 0, because
+    // one of our parent frames may have moved and so the view's position
+    // relative to its parent may have changed.
+    int32_t n = aLine->GetChildCount();
+    while (--n >= 0) {
+      if (aDeltaBCoord) {
+        kid->MovePositionBy(wm, translation);
+      }
+      // Make sure the frame's view and any child views are updated
+      nsContainerFrame::PlaceFrameView(kid);
+      kid = kid->GetNextSibling();
+    }
+  }
+}
+
+static inline bool IsNonAutoNonZeroBSize(const StyleSize& aCoord) {
+  // The "extremum length" values (see ExtremumLength) were originally aimed at
+  // inline-size (or width, as it was before logicalization). For now, let them
+  // return false here, so we treat them like 'auto' pending a real
+  // implementation. (See bug 1126420.)
+  //
+  // FIXME (bug 567039, bug 527285) This isn't correct for the 'fill' value,
+  // which should more likely (but not necessarily, depending on the available
+  // space) be returning true.
+  if (aCoord.BehavesLikeInitialValueOnBlockAxis()) {
+    return false;
+  }
+  MOZ_ASSERT(aCoord.IsLengthPercentage());
+  // If we evaluate the length/percent/calc at a percentage basis of
+  // both nscoord_MAX and 0, and it's zero both ways, then it's a zero
+  // length, percent, or combination thereof.  Test > 0 so we clamp
+  // negative calc() results to 0.
+  return aCoord.AsLengthPercentage().Resolve(nscoord_MAX) > 0 ||
+         aCoord.AsLengthPercentage().Resolve(0) > 0;
+}
+
+/* virtual */
+bool nsBlockFrame::IsSelfEmpty() {
+  if (IsHiddenByContentVisibilityOfInFlowParentForLayout()) {
+    return true;
+  }
+
+  // Blocks which are margin-roots (including inline-blocks) cannot be treated
+  // as empty for margin-collapsing and other purposes. They're more like
+  // replaced elements.
+  if (HasAnyStateBits(NS_BLOCK_BFC_STATE_BITS)) {
+    return false;
+  }
+
+  WritingMode wm = GetWritingMode();
+  const nsStylePosition* position = StylePosition();
+
+  if (IsNonAutoNonZeroBSize(position->MinBSize(wm)) ||
+      IsNonAutoNonZeroBSize(position->BSize(wm))) {
+    return false;
+  }
+
+  // FIXME: Bug 1646100 - Take intrinsic size into account.
+  // FIXME: Handle the case that both inline and block sizes are auto.
+  // https://github.com/w3c/csswg-drafts/issues/5060.
+  // Note: block-size could be zero or auto/intrinsic keywords here.
+  if (position->BSize(wm).BehavesLikeInitialValueOnBlockAxis() &&
+      position->mAspectRatio.HasFiniteRatio()) {
+    return false;
+  }
+
+  const nsStyleBorder* border = StyleBorder();
+  const nsStylePadding* padding = StylePadding();
+
+  if (border->GetComputedBorderWidth(wm.PhysicalSide(eLogicalSideBStart)) !=
+          0 ||
+      border->GetComputedBorderWidth(wm.PhysicalSide(eLogicalSideBEnd)) != 0 ||
+      !nsLayoutUtils::IsPaddingZero(padding->mPadding.GetBStart(wm)) ||
+      !nsLayoutUtils::IsPaddingZero(padding->mPadding.GetBEnd(wm))) {
+    return false;
+  }
+
+  if (HasOutsideMarker() && !MarkerIsEmpty()) {
+    return false;
+  }
+
+  return true;
+}
+
+bool nsBlockFrame::CachedIsEmpty() {
+  if (!IsSelfEmpty()) {
+    return false;
+  }
+  for (auto& line : mLines) {
+    if (!line.CachedIsEmpty()) {
+      return false;
+    }
+  }
+  return true;
+}
+
+bool nsBlockFrame::IsEmpty() {
+  if (!IsSelfEmpty()) {
+    return false;
+  }
+
+  return LinesAreEmpty(mLines);
+}
+
+bool nsBlockFrame::ShouldApplyBStartMargin(BlockReflowState& aState,
+                                           nsLineBox* aLine) {
+  if (aLine->mFirstChild->IsPageBreakFrame()) {
+    // A page break frame consumes margins adjacent to it.
+    // https://drafts.csswg.org/css-break/#break-margins
+    return false;
+  }
+
+  if (aState.mFlags.mShouldApplyBStartMargin) {
+    // Apply short-circuit check to avoid searching the line list
+    return true;
+  }
+
+  if (!aState.IsAdjacentWithBStart()) {
+    // If we aren't at the start block-coordinate then something of non-zero
+    // height must have been placed. Therefore the childs block-start margin
+    // applies.
+    aState.mFlags.mShouldApplyBStartMargin = true;
+    return true;
+  }
+
+  // Determine if this line is "essentially" the first line
+  LineIterator line = LinesBegin();
+  if (aState.mFlags.mHasLineAdjacentToTop) {
+    line = aState.mLineAdjacentToTop;
+  }
+  while (line != aLine) {
+    if (!line->CachedIsEmpty() || line->HasClearance()) {
+      // A line which precedes aLine is non-empty, or has clearance,
+      // so therefore the block-start margin applies.
+      aState.mFlags.mShouldApplyBStartMargin = true;
+      return true;
+    }
+    // No need to apply the block-start margin if the line has floats.  We
+    // should collapse anyway (bug 44419)
+    ++line;
+    aState.mFlags.mHasLineAdjacentToTop = true;
+    aState.mLineAdjacentToTop = line;
+  }
+
+  // The line being reflowed is "essentially" the first line in the
+  // block. Therefore its block-start margin will be collapsed by the
+  // generational collapsing logic with its parent (us).
+  return false;
+}
+
+void nsBlockFrame::ReflowBlockFrame(BlockReflowState& aState,
+                                    LineIterator aLine,
+                                    bool* aKeepReflowGoing) {
+  MOZ_ASSERT(*aKeepReflowGoing, "bad caller");
+
+  nsIFrame* frame = aLine->mFirstChild;
+  if (!frame) {
+    NS_ASSERTION(false, "program error - unexpected empty line");
+    return;
+  }
+
+  // If the previous frame was a page-break-frame, then preemptively push this
+  // frame to the next page.
+  // This is primarily important for the placeholders for abspos frames, which
+  // measure as zero height and then would be placed on this page.
+  if (aState.ContentBSize() != NS_UNCONSTRAINEDSIZE) {
+    const nsIFrame* const prev = frame->GetPrevSibling();
+    if (prev && prev->IsPageBreakFrame()) {
+      PushTruncatedLine(aState, aLine, aKeepReflowGoing);
+      return;
+    }
+  }
+
+  // Prepare the block reflow engine
+  nsBlockReflowContext brc(aState.mPresContext, aState.mReflowInput);
+
+  StyleClear clearType = frame->StyleDisplay()->mClear;
+  if (aState.mTrailingClearFromPIF != StyleClear::None) {
+    clearType = nsLayoutUtils::CombineClearType(clearType,
+                                                aState.mTrailingClearFromPIF);
+    aState.mTrailingClearFromPIF = StyleClear::None;
+  }
+
+  // Clear past floats before the block if the clear style is not none
+  aLine->ClearForcedLineBreak();
+  if (clearType != StyleClear::None) {
+    aLine->SetForcedLineBreakBefore(clearType);
+  }
+
+  // See if we should apply the block-start margin. If the block frame being
+  // reflowed is a continuation, then we don't apply its block-start margin
+  // because it's not significant. Otherwise, dig deeper.
+  bool applyBStartMargin =
+      !frame->GetPrevContinuation() && ShouldApplyBStartMargin(aState, aLine);
+  if (applyBStartMargin) {
+    // The HasClearance setting is only valid if ShouldApplyBStartMargin
+    // returned false (in which case the block-start margin-root set our
+    // clearance flag). Otherwise clear it now. We'll set it later on
+    // ourselves if necessary.
+    aLine->ClearHasClearance();
+  }
+  bool treatWithClearance = aLine->HasClearance();
+
+  bool mightClearFloats = clearType != StyleClear::None;
+  nsIFrame* floatAvoidingBlock = nullptr;
+  if (!nsBlockFrame::BlockCanIntersectFloats(frame)) {
+    mightClearFloats = true;
+    floatAvoidingBlock = frame;
+  }
+
+  // If our block-start margin was counted as part of some parent's block-start
+  // margin collapse, and we are being speculatively reflowed assuming this
+  // frame DID NOT need clearance, then we need to check that
+  // assumption.
+  if (!treatWithClearance && !applyBStartMargin && mightClearFloats &&
+      aState.mReflowInput.mDiscoveredClearance) {
+    nscoord curBCoord = aState.mBCoord + aState.mPrevBEndMargin.get();
+    if (auto [clearBCoord, result] =
+            aState.ClearFloats(curBCoord, clearType, floatAvoidingBlock);
+        result != ClearFloatsResult::BCoordNoChange) {
+      Unused << clearBCoord;
+
+      // Only record the first frame that requires clearance
+      if (!*aState.mReflowInput.mDiscoveredClearance) {
+        *aState.mReflowInput.mDiscoveredClearance = frame;
+      }
+      aState.mPrevChild = frame;
+      // Exactly what we do now is flexible since we'll definitely be
+      // reflowed.
+      return;
+    }
+  }
+  if (treatWithClearance) {
+    applyBStartMargin = true;
+  }
+
+  nsIFrame* clearanceFrame = nullptr;
+  const nscoord startingBCoord = aState.mBCoord;
+  const nsCollapsingMargin incomingMargin = aState.mPrevBEndMargin;
+  nscoord clearance;
+  // Save the original position of the frame so that we can reposition
+  // its view as needed.
+  nsPoint originalPosition = frame->GetPosition();
+  while (true) {
+    clearance = 0;
+    nscoord bStartMargin = 0;
+    bool mayNeedRetry = false;
+    bool clearedFloats = false;
+    bool clearedPushedOrSplitFloat = false;
+    if (applyBStartMargin) {
+      // Precompute the blocks block-start margin value so that we can get the
+      // correct available space (there might be a float that's
+      // already been placed below the aState.mPrevBEndMargin
+
+      // Setup a reflowInput to get the style computed block-start margin
+      // value. We'll use a reason of `resize' so that we don't fudge
+      // any incremental reflow input.
+
+      // The availSpace here is irrelevant to our needs - all we want
+      // out if this setup is the block-start margin value which doesn't depend
+      // on the childs available space.
+      // XXX building a complete ReflowInput just to get the block-start
+      // margin seems like a waste. And we do this for almost every block!
+      WritingMode wm = frame->GetWritingMode();
+      LogicalSize availSpace = aState.ContentSize(wm);
+      ReflowInput reflowInput(aState.mPresContext, aState.mReflowInput, frame,
+                              availSpace);
+
+      if (treatWithClearance) {
+        aState.mBCoord += aState.mPrevBEndMargin.get();
+        aState.mPrevBEndMargin.Zero();
+      }
+
+      // Now compute the collapsed margin-block-start value into
+      // aState.mPrevBEndMargin, assuming that all child margins
+      // collapse down to clearanceFrame.
+      brc.ComputeCollapsedBStartMargin(reflowInput, &aState.mPrevBEndMargin,
+                                       clearanceFrame, &mayNeedRetry);
+
+      // XXX optimization; we could check the collapsing children to see if they
+      // are sure to require clearance, and so avoid retrying them
+
+      if (clearanceFrame) {
+        // Don't allow retries on the second pass. The clearance decisions for
+        // the blocks whose block-start margins collapse with ours are now
+        // fixed.
+        mayNeedRetry = false;
+      }
+
+      if (!treatWithClearance && !clearanceFrame && mightClearFloats) {
+        // We don't know if we need clearance and this is the first,
+        // optimistic pass.  So determine whether *this block* needs
+        // clearance. Note that we do not allow the decision for whether
+        // this block has clearance to change on the second pass; that
+        // decision is only allowed to be made under the optimistic
+        // first pass.
+        nscoord curBCoord = aState.mBCoord + aState.mPrevBEndMargin.get();
+        if (auto [clearBCoord, result] =
+                aState.ClearFloats(curBCoord, clearType, floatAvoidingBlock);
+            result != ClearFloatsResult::BCoordNoChange) {
+          Unused << clearBCoord;
+
+          // Looks like we need clearance and we didn't know about it already.
+          // So recompute collapsed margin
+          treatWithClearance = true;
+          // Remember this decision, needed for incremental reflow
+          aLine->SetHasClearance();
+
+          // Apply incoming margins
+          aState.mBCoord += aState.mPrevBEndMargin.get();
+          aState.mPrevBEndMargin.Zero();
+
+          // Compute the collapsed margin again, ignoring the incoming margin
+          // this time
+          mayNeedRetry = false;
+          brc.ComputeCollapsedBStartMargin(reflowInput, &aState.mPrevBEndMargin,
+                                           clearanceFrame, &mayNeedRetry);
+        }
+      }
+
+      // Temporarily advance the running block-direction value so that the
+      // GetFloatAvailableSpace method will return the right available space.
+      // This undone as soon as the horizontal margins are computed.
+      bStartMargin = aState.mPrevBEndMargin.get();
+
+      if (treatWithClearance) {
+        nscoord currentBCoord = aState.mBCoord;
+        // advance mBCoord to the clear position.
+        auto [clearBCoord, result] =
+            aState.ClearFloats(aState.mBCoord, clearType, floatAvoidingBlock);
+        aState.mBCoord = clearBCoord;
+
+        clearedFloats = result != ClearFloatsResult::BCoordNoChange;
+        clearedPushedOrSplitFloat =
+            result == ClearFloatsResult::FloatsPushedOrSplit;
+
+        // Compute clearance. It's the amount we need to add to the block-start
+        // border-edge of the frame, after applying collapsed margins
+        // from the frame and its children, to get it to line up with
+        // the block-end of the floats. The former is
+        // currentBCoord + bStartMargin, the latter is the current
+        // aState.mBCoord.
+        // Note that negative clearance is possible
+        clearance = aState.mBCoord - (currentBCoord + bStartMargin);
+
+        // Add clearance to our block-start margin while we compute available
+        // space for the frame
+        bStartMargin += clearance;
+
+        // Note that aState.mBCoord should stay where it is: at the block-start
+        // border-edge of the frame
+      } else {
+        // Advance aState.mBCoord to the block-start border-edge of the frame.
+        aState.mBCoord += bStartMargin;
+      }
+    }
+
+    aLine->SetLineIsImpactedByFloat(false);
+
+    // Here aState.mBCoord is the block-start border-edge of the block.
+    // Compute the available space for the block
+    nsFlowAreaRect floatAvailableSpace = aState.GetFloatAvailableSpace();
+    WritingMode wm = aState.mReflowInput.GetWritingMode();
+    LogicalRect availSpace = aState.ComputeBlockAvailSpace(
+        frame, floatAvailableSpace, (floatAvoidingBlock));
+
+    // The check for
+    //   (!aState.mReflowInput.mFlags.mIsTopOfPage || clearedFloats)
+    // is to some degree out of paranoia:  if we reliably eat up block-start
+    // margins at the top of the page as we ought to, it wouldn't be
+    // needed.
+    if ((!aState.mReflowInput.mFlags.mIsTopOfPage || clearedFloats) &&
+        (availSpace.BSize(wm) < 0 || clearedPushedOrSplitFloat)) {
+      // We know already that this child block won't fit on this
+      // page/column due to the block-start margin or the clearance.  So we
+      // need to get out of here now.  (If we don't, most blocks will handle
+      // things fine, and report break-before, but zero-height blocks
+      // won't, and will thus make their parent overly-large and force
+      // *it* to be pushed in its entirety.)
+      aState.mBCoord = startingBCoord;
+      aState.mPrevBEndMargin = incomingMargin;
+      if (ShouldAvoidBreakInside(aState.mReflowInput)) {
+        SetBreakBeforeStatusBeforeLine(aState, aLine, aKeepReflowGoing);
+      } else {
+        PushTruncatedLine(aState, aLine, aKeepReflowGoing);
+      }
+      return;
+    }
+
+    // Now put the block-dir coordinate back to the start of the
+    // block-start-margin + clearance.
+    aState.mBCoord -= bStartMargin;
+    availSpace.BStart(wm) -= bStartMargin;
+    if (NS_UNCONSTRAINEDSIZE != availSpace.BSize(wm)) {
+      availSpace.BSize(wm) += bStartMargin;
+    }
+
+    // Construct the reflow input for the block.
+    Maybe<ReflowInput> childReflowInput;
+    Maybe<LogicalSize> cbSize;
+    LogicalSize availSize = availSpace.Size(wm);
+    bool columnSetWrapperHasNoBSizeLeft = false;
+    if (Style()->GetPseudoType() == PseudoStyleType::columnContent) {
+      // Calculate the multicol containing block's block size so that the
+      // children with percentage block size get correct percentage basis.
+      const ReflowInput* cbReflowInput =
+          aState.mReflowInput.mParentReflowInput->mCBReflowInput;
+      MOZ_ASSERT(cbReflowInput->mFrame->StyleColumn()->IsColumnContainerStyle(),
+                 "Get unexpected reflow input of multicol containing block!");
+
+      // Use column-width as the containing block's inline-size, i.e. the column
+      // content's computed inline-size.
+      cbSize.emplace(LogicalSize(wm, aState.mReflowInput.ComputedISize(),
+                                 cbReflowInput->ComputedBSize())
+                         .ConvertTo(frame->GetWritingMode(), wm));
+
+      // If a ColumnSetWrapper is in a balancing column content, it may be
+      // pushed or pulled back and forth between column contents. Always add
+      // NS_FRAME_HAS_DIRTY_CHILDREN bit to it so that its ColumnSet children
+      // can have a chance to reflow under current block size constraint.
+      if (aState.mReflowInput.mFlags.mIsColumnBalancing &&
+          frame->IsColumnSetWrapperFrame()) {
+        frame->AddStateBits(NS_FRAME_HAS_DIRTY_CHILDREN);
+      }
+    } else if (IsColumnSetWrapperFrame()) {
+      // If we are reflowing our ColumnSet children, we want to apply our block
+      // size constraint to the available block size when constructing reflow
+      // input for ColumnSet so that ColumnSet can use it to compute its max
+      // column block size.
+      if (frame->IsColumnSetFrame()) {
+        nscoord contentBSize = aState.mReflowInput.ComputedBSize();
+        if (aState.mReflowInput.ComputedMaxBSize() != NS_UNCONSTRAINEDSIZE) {
+          contentBSize =
+              std::min(contentBSize, aState.mReflowInput.ComputedMaxBSize());
+        }
+        if (contentBSize != NS_UNCONSTRAINEDSIZE) {
+          // To get the remaining content block-size, subtract the content
+          // block-size consumed by our previous continuations.
+          contentBSize -= aState.mConsumedBSize;
+
+          // ColumnSet is not the outermost frame in the column container, so it
+          // cannot have any margin. We don't need to consider any margin that
+          // can be generated by "box-decoration-break: clone" as we do in
+          // BlockReflowState::ComputeBlockAvailSpace().
+          const nscoord availContentBSize = std::max(
+              0, contentBSize - (aState.mBCoord - aState.ContentBStart()));
+          if (availSize.BSize(wm) >= availContentBSize) {
+            availSize.BSize(wm) = availContentBSize;
+            columnSetWrapperHasNoBSizeLeft = true;
+          }
+        }
+      }
+    }
+
+    childReflowInput.emplace(aState.mPresContext, aState.mReflowInput, frame,
+                             availSize.ConvertTo(frame->GetWritingMode(), wm),
+                             cbSize);
+
+    childReflowInput->mFlags.mColumnSetWrapperHasNoBSizeLeft =
+        columnSetWrapperHasNoBSizeLeft;
+
+    if (aLine->MovedFragments()) {
+      // We only need to set this the first reflow, since if we reflow
+      // again (and replace childReflowInput) we'll be reflowing it
+      // again in the same fragment as the previous time.
+      childReflowInput->mFlags.mMovedBlockFragments = true;
+    }
+
+    nsFloatManager::SavedState floatManagerState;
+    nsReflowStatus frameReflowStatus;
+    do {
+      if (floatAvailableSpace.HasFloats()) {
+        // Set if floatAvailableSpace.HasFloats() is true for any
+        // iteration of the loop.
+        aLine->SetLineIsImpactedByFloat(true);
+      }
+
+      // We might need to store into mDiscoveredClearance later if it's
+      // currently null; we want to overwrite any writes that
+      // brc.ReflowBlock() below does, so we need to remember now
+      // whether it's empty.
+      const bool shouldStoreClearance =
+          aState.mReflowInput.mDiscoveredClearance &&
+          !*aState.mReflowInput.mDiscoveredClearance;
+
+      // Reflow the block into the available space
+      if (mayNeedRetry || floatAvoidingBlock) {
+        aState.FloatManager()->PushState(&floatManagerState);
+      }
+
+      if (mayNeedRetry) {
+        childReflowInput->mDiscoveredClearance = &clearanceFrame;
+      } else if (!applyBStartMargin) {
+        childReflowInput->mDiscoveredClearance =
+            aState.mReflowInput.mDiscoveredClearance;
+      }
+
+      frameReflowStatus.Reset();
+      brc.ReflowBlock(availSpace, applyBStartMargin, aState.mPrevBEndMargin,
+                      clearance, aLine.get(), *childReflowInput,
+                      frameReflowStatus, aState);
+
+      if (frameReflowStatus.IsInlineBreakBefore()) {
+        // No need to retry this loop if there is a break opportunity before the
+        // child block.
+        break;
+      }
+
+      // Now the block has a height.  Using that height, get the
+      // available space again and call ComputeBlockAvailSpace again.
+      // If ComputeBlockAvailSpace gives a different result, we need to
+      // reflow again.
+      if (!floatAvoidingBlock) {
+        break;
+      }
+
+      LogicalRect oldFloatAvailableSpaceRect(floatAvailableSpace.mRect);
+      floatAvailableSpace = aState.GetFloatAvailableSpaceForBSize(
+          aState.mBCoord + bStartMargin, brc.GetMetrics().BSize(wm),
+          &floatManagerState);
+      NS_ASSERTION(floatAvailableSpace.mRect.BStart(wm) ==
+                       oldFloatAvailableSpaceRect.BStart(wm),
+                   "yikes");
+      // Restore the height to the position of the next band.
+      floatAvailableSpace.mRect.BSize(wm) =
+          oldFloatAvailableSpaceRect.BSize(wm);
+      // Determine whether the available space shrunk on either side,
+      // because (the first time round) we now know the block's height,
+      // and it may intersect additional floats, or (on later
+      // iterations) because narrowing the width relative to the
+      // previous time may cause the block to become taller.  Note that
+      // since we're reflowing the block, narrowing the width might also
+      // make it shorter, so we must pass aCanGrow as true.
+      if (!AvailableSpaceShrunk(wm, oldFloatAvailableSpaceRect,
+                                floatAvailableSpace.mRect, true)) {
+        // The size and position we chose before are fine (i.e., they
+        // don't cause intersecting with floats that requires a change
+        // in size or position), so we're done.
+        break;
+      }
+
+      bool advanced = false;
+      if (!aState.FloatAvoidingBlockFitsInAvailSpace(floatAvoidingBlock,
+                                                     floatAvailableSpace)) {
+        // Advance to the next band.
+        nscoord newBCoord = aState.mBCoord;
+        if (aState.AdvanceToNextBand(floatAvailableSpace.mRect, &newBCoord)) {
+          advanced = true;
+        }
+        // ClearFloats might be able to advance us further once we're there.
+        std::tie(aState.mBCoord, std::ignore) =
+            aState.ClearFloats(newBCoord, StyleClear::None, floatAvoidingBlock);
+
+        // Start over with a new available space rect at the new height.
+        floatAvailableSpace = aState.GetFloatAvailableSpaceWithState(
+            aState.mBCoord, ShapeType::ShapeOutside, &floatManagerState);
+      }
+
+      const LogicalRect oldAvailSpace = availSpace;
+      availSpace = aState.ComputeBlockAvailSpace(frame, floatAvailableSpace,
+                                                 (floatAvoidingBlock));
+
+      if (!advanced && availSpace.IsEqualEdges(oldAvailSpace)) {
+        break;
+      }
+
+      // We need another reflow.
+      aState.FloatManager()->PopState(&floatManagerState);
+
+      if (!treatWithClearance && !applyBStartMargin &&
+          aState.mReflowInput.mDiscoveredClearance) {
+        // We set shouldStoreClearance above to record only the first
+        // frame that requires clearance.
+        if (shouldStoreClearance) {
+          *aState.mReflowInput.mDiscoveredClearance = frame;
+        }
+        aState.mPrevChild = frame;
+        // Exactly what we do now is flexible since we'll definitely be
+        // reflowed.
+        return;
+      }
+
+      if (advanced) {
+        // We're pushing down the border-box, so we don't apply margin anymore.
+        // This should never cause us to move up since the call to
+        // GetFloatAvailableSpaceForBSize above included the margin.
+        applyBStartMargin = false;
+        bStartMargin = 0;
+        treatWithClearance = true;  // avoid hitting test above
+        clearance = 0;
+      }
+
+      childReflowInput.reset();
+      childReflowInput.emplace(
+          aState.mPresContext, aState.mReflowInput, frame,
+          availSpace.Size(wm).ConvertTo(frame->GetWritingMode(), wm));
+    } while (true);
+
+    if (mayNeedRetry && clearanceFrame) {
+      // Found a clearance frame, so we need to reflow |frame| a second time.
+      // Restore the states and start over again.
+      aState.FloatManager()->PopState(&floatManagerState);
+      aState.mBCoord = startingBCoord;
+      aState.mPrevBEndMargin = incomingMargin;
+      continue;
+    }
+
+    aState.mPrevChild = frame;
+
+    if (childReflowInput->WillReflowAgainForClearance()) {
+      // If an ancestor of ours is going to reflow for clearance, we
+      // need to avoid calling PlaceBlock, because it unsets dirty bits
+      // on the child block (both itself, and through its call to
+      // nsIFrame::DidReflow), and those dirty bits imply dirtiness for
+      // all of the child block, including the lines it didn't reflow.
+      NS_ASSERTION(originalPosition == frame->GetPosition(),
+                   "we need to call PositionChildViews");
+      return;
+    }
+
+#if defined(REFLOW_STATUS_COVERAGE)
+    RecordReflowStatus(true, frameReflowStatus);
+#endif
+
+    if (frameReflowStatus.IsInlineBreakBefore()) {
+      // None of the child block fits.
+      if (ShouldAvoidBreakInside(aState.mReflowInput)) {
+        SetBreakBeforeStatusBeforeLine(aState, aLine, aKeepReflowGoing);
+      } else {
+        PushTruncatedLine(aState, aLine, aKeepReflowGoing);
+      }
+    } else {
+      // Note: line-break-after a block is a nop
+
+      // Try to place the child block.
+      // Don't force the block to fit if we have positive clearance, because
+      // pushing it to the next page would give it more room.
+      // Don't force the block to fit if it's impacted by a float. If it is,
+      // then pushing it to the next page would give it more room. Note that
+      // isImpacted doesn't include impact from the block's own floats.
+      bool forceFit = aState.IsAdjacentWithBStart() && clearance <= 0 &&
+                      !floatAvailableSpace.HasFloats();
+      nsCollapsingMargin collapsedBEndMargin;
+      OverflowAreas overflowAreas;
+      *aKeepReflowGoing =
+          brc.PlaceBlock(*childReflowInput, forceFit, aLine.get(),
+                         collapsedBEndMargin, overflowAreas, frameReflowStatus);
+      if (!frameReflowStatus.IsFullyComplete() &&
+          ShouldAvoidBreakInside(aState.mReflowInput)) {
+        *aKeepReflowGoing = false;
+        aLine->MarkDirty();
+      }
+
+      if (aLine->SetCarriedOutBEndMargin(collapsedBEndMargin)) {
+        LineIterator nextLine = aLine;
+        ++nextLine;
+        if (nextLine != LinesEnd()) {
+          nextLine->MarkPreviousMarginDirty();
+        }
+      }
+
+      aLine->SetOverflowAreas(overflowAreas);
+      if (*aKeepReflowGoing) {
+        // Some of the child block fit
+
+        // Advance to new Y position
+        nscoord newBCoord = aLine->BEnd();
+        aState.mBCoord = newBCoord;
+
+        // Continue the block frame now if it didn't completely fit in
+        // the available space.
+        if (!frameReflowStatus.IsFullyComplete()) {
+          bool madeContinuation = CreateContinuationFor(aState, nullptr, frame);
+
+          nsIFrame* nextFrame = frame->GetNextInFlow();
+          NS_ASSERTION(nextFrame,
+                       "We're supposed to have a next-in-flow by now");
+
+          if (frameReflowStatus.IsIncomplete()) {
+            // If nextFrame used to be an overflow container, make it a normal
+            // block
+            if (!madeContinuation &&
+                nextFrame->HasAnyStateBits(NS_FRAME_IS_OVERFLOW_CONTAINER)) {
+              nsOverflowContinuationTracker::AutoFinish fini(
+                  aState.mOverflowTracker, frame);
+              nsContainerFrame* parent = nextFrame->GetParent();
+              parent->StealFrame(nextFrame);
+              if (parent != this) {
+                ReparentFrame(nextFrame, parent, this);
+              }
+              mFrames.InsertFrame(nullptr, frame, nextFrame);
+              madeContinuation = true;  // needs to be added to mLines
+              nextFrame->RemoveStateBits(NS_FRAME_IS_OVERFLOW_CONTAINER);
+              frameReflowStatus.SetNextInFlowNeedsReflow();
+            }
+
+            // Push continuation to a new line, but only if we actually made
+            // one.
+            if (madeContinuation) {
+              nsLineBox* line = NewLineBox(nextFrame, true);
+              mLines.after_insert(aLine, line);
+            }
+
+            PushTruncatedLine(aState, aLine.next(), aKeepReflowGoing);
+
+            // If we need to reflow the continuation of the block child,
+            // then we'd better reflow our continuation
+            if (frameReflowStatus.NextInFlowNeedsReflow()) {
+              aState.mReflowStatus.SetNextInFlowNeedsReflow();
+              // We also need to make that continuation's line dirty so
+              // it gets reflowed when we reflow our next in flow. The
+              // nif's line must always be either a line of the nif's
+              // parent block (only if we didn't make a continuation) or
+              // else one of our own overflow lines. In the latter case
+              // the line is already marked dirty, so just handle the
+              // first case.
+              if (!madeContinuation) {
+                nsBlockFrame* nifBlock = do_QueryFrame(nextFrame->GetParent());
+                NS_ASSERTION(
+                    nifBlock,
+                    "A block's child's next in flow's parent must be a block!");
+                for (auto& line : nifBlock->Lines()) {
+                  if (line.Contains(nextFrame)) {
+                    line.MarkDirty();
+                    break;
+                  }
+                }
+              }
+            }
+
+            // The block-end margin for a block is only applied on the last
+            // flow block. Since we just continued the child block frame,
+            // we know that line->mFirstChild is not the last flow block
+            // therefore zero out the running margin value.
+#ifdef NOISY_BLOCK_DIR_MARGINS
+            ListTag(stdout);
+            printf(": reflow incomplete, frame=");
+            frame->ListTag(stdout);
+            printf(" prevBEndMargin=%d, setting to zero\n",
+                   aState.mPrevBEndMargin.get());
+#endif
+            aState.mPrevBEndMargin.Zero();
+          } else {  // frame is complete but its overflow is not complete
+            // Disconnect the next-in-flow and put it in our overflow tracker
+            if (!madeContinuation &&
+                !nextFrame->HasAnyStateBits(NS_FRAME_IS_OVERFLOW_CONTAINER)) {
+              // It already exists, but as a normal next-in-flow, so we need
+              // to dig it out of the child lists.
+              nextFrame->GetParent()->StealFrame(nextFrame);
+            } else if (madeContinuation) {
+              mFrames.RemoveFrame(nextFrame);
+            }
+
+            // Put it in our overflow list
+            aState.mOverflowTracker->Insert(nextFrame, frameReflowStatus);
+            aState.mReflowStatus.MergeCompletionStatusFrom(frameReflowStatus);
+
+#ifdef NOISY_BLOCK_DIR_MARGINS
+            ListTag(stdout);
+            printf(": reflow complete but overflow incomplete for ");
+            frame->ListTag(stdout);
+            printf(" prevBEndMargin=%d collapsedBEndMargin=%d\n",
+                   aState.mPrevBEndMargin.get(), collapsedBEndMargin.get());
+#endif
+            aState.mPrevBEndMargin = collapsedBEndMargin;
+          }
+        } else {  // frame is fully complete
+#ifdef NOISY_BLOCK_DIR_MARGINS
+          ListTag(stdout);
+          printf(": reflow complete for ");
+          frame->ListTag(stdout);
+          printf(" prevBEndMargin=%d collapsedBEndMargin=%d\n",
+                 aState.mPrevBEndMargin.get(), collapsedBEndMargin.get());
+#endif
+          aState.mPrevBEndMargin = collapsedBEndMargin;
+        }
+#ifdef NOISY_BLOCK_DIR_MARGINS
+        ListTag(stdout);
+        printf(": frame=");
+        frame->ListTag(stdout);
+        printf(" carriedOutBEndMargin=%d collapsedBEndMargin=%d => %d\n",
+               brc.GetCarriedOutBEndMargin().get(), collapsedBEndMargin.get(),
+               aState.mPrevBEndMargin.get());
+#endif
+      } else {
+        if (!frameReflowStatus.IsFullyComplete()) {
+          // The frame reported an incomplete status, but then it also didn't
+          // fit.  This means we need to reflow it again so that it can
+          // (again) report the incomplete status.
+          frame->AddStateBits(NS_FRAME_HAS_DIRTY_CHILDREN);
+        }
+
+        if ((aLine == mLines.front() && !GetPrevInFlow()) ||
+            ShouldAvoidBreakInside(aState.mReflowInput)) {
+          // If it's our very first line *or* we're not at the top of the page
+          // and we have page-break-inside:avoid, then we need to be pushed to
+          // our parent's next-in-flow.
+          SetBreakBeforeStatusBeforeLine(aState, aLine, aKeepReflowGoing);
+        } else {
+          // Push the line that didn't fit and any lines that follow it
+          // to our next-in-flow.
+          PushTruncatedLine(aState, aLine, aKeepReflowGoing);
+        }
+      }
+    }
+    break;  // out of the reflow retry loop
+  }
+
+  // Now that we've got its final position all figured out, position any child
+  // views it may have.  Note that the case when frame has a view got handled
+  // by FinishReflowChild, but that function didn't have the coordinates needed
+  // to correctly decide whether to reposition child views.
+  if (originalPosition != frame->GetPosition() && !frame->HasView()) {
+    nsContainerFrame::PositionChildViews(frame);
+  }
+
+#ifdef DEBUG
+  VerifyLines(true);
+#endif
+}
+
+// Returns true if an overflow-wrap break was used.
+bool nsBlockFrame::ReflowInlineFrames(BlockReflowState& aState,
+                                      LineIterator aLine,
+                                      bool* aKeepReflowGoing) {
+  *aKeepReflowGoing = true;
+  bool usedOverflowWrap = false;
+
+  aLine->SetLineIsImpactedByFloat(false);
+
+  // Setup initial coordinate system for reflowing the inline frames
+  // into. Apply a previous block frame's block-end margin first.
+  if (ShouldApplyBStartMargin(aState, aLine)) {
+    aState.mBCoord += aState.mPrevBEndMargin.get();
+  }
+  nsFlowAreaRect floatAvailableSpace = aState.GetFloatAvailableSpace();
+
+  LineReflowStatus lineReflowStatus;
+  do {
+    nscoord availableSpaceBSize = 0;
+    aState.mLineBSize.reset();
+    do {
+      bool allowPullUp = true;
+      nsIFrame* forceBreakInFrame = nullptr;
+      int32_t forceBreakOffset = -1;
+      gfxBreakPriority forceBreakPriority = gfxBreakPriority::eNoBreak;
+      do {
+        nsFloatManager::SavedState floatManagerState;
+        aState.FloatManager()->PushState(&floatManagerState);
+
+        // Once upon a time we allocated the first 30 nsLineLayout objects
+        // on the stack, and then we switched to the heap.  At that time
+        // these objects were large (1100 bytes on a 32 bit system).
+        // Then the nsLineLayout object was shrunk to 156 bytes by
+        // removing some internal buffers.  Given that it is so much
+        // smaller, the complexity of 2 different ways of allocating
+        // no longer makes sense.  Now we always allocate on the stack.
+        nsLineLayout lineLayout(aState.mPresContext, aState.FloatManager(),
+                                aState.mReflowInput, &aLine, nullptr);
+        lineLayout.Init(&aState, aState.mMinLineHeight, aState.mLineNumber);
+        if (forceBreakInFrame) {
+          lineLayout.ForceBreakAtPosition(forceBreakInFrame, forceBreakOffset);
+        }
+        DoReflowInlineFrames(aState, lineLayout, aLine, floatAvailableSpace,
+                             availableSpaceBSize, &floatManagerState,
+                             aKeepReflowGoing, &lineReflowStatus, allowPullUp);
+        usedOverflowWrap = lineLayout.EndLineReflow();
+
+        if (LineReflowStatus::RedoNoPull == lineReflowStatus ||
+            LineReflowStatus::RedoMoreFloats == lineReflowStatus ||
+            LineReflowStatus::RedoNextBand == lineReflowStatus) {
+          if (lineLayout.NeedsBackup()) {
+            NS_ASSERTION(!forceBreakInFrame,
+                         "Backing up twice; this should never be necessary");
+            // If there is no saved break position, then this will set
+            // set forceBreakInFrame to null and we won't back up, which is
+            // correct.
+            forceBreakInFrame = lineLayout.GetLastOptionalBreakPosition(
+                &forceBreakOffset, &forceBreakPriority);
+          } else {
+            forceBreakInFrame = nullptr;
+          }
+          // restore the float manager state
+          aState.FloatManager()->PopState(&floatManagerState);
+          // Clear out float lists
+          aState.mCurrentLineFloats.Clear();
+          aState.mBelowCurrentLineFloats.Clear();
+          aState.mNoWrapFloats.Clear();
+        }
+
+        // Don't allow pullup on a subsequent LineReflowStatus::RedoNoPull pass
+        allowPullUp = false;
+      } while (LineReflowStatus::RedoNoPull == lineReflowStatus);
+    } while (LineReflowStatus::RedoMoreFloats == lineReflowStatus);
+  } while (LineReflowStatus::RedoNextBand == lineReflowStatus);
+
+  return usedOverflowWrap;
+}
+
+void nsBlockFrame::SetBreakBeforeStatusBeforeLine(BlockReflowState& aState,
+                                                  LineIterator aLine,
+                                                  bool* aKeepReflowGoing) {
+  aState.mReflowStatus.SetInlineLineBreakBeforeAndReset();
+  // Reflow the line again when we reflow at our new position.
+  aLine->MarkDirty();
+  *aKeepReflowGoing = false;
+}
+
+void nsBlockFrame::PushTruncatedLine(BlockReflowState& aState,
+                                     LineIterator aLine,
+                                     bool* aKeepReflowGoing) {
+  PushLines(aState, aLine.prev());
+  *aKeepReflowGoing = false;
+  aState.mReflowStatus.SetIncomplete();
+}
+
+void nsBlockFrame::DoReflowInlineFrames(
+    BlockReflowState& aState, nsLineLayout& aLineLayout, LineIterator aLine,
+    nsFlowAreaRect& aFloatAvailableSpace, nscoord& aAvailableSpaceBSize,
+    nsFloatManager::SavedState* aFloatStateBeforeLine, bool* aKeepReflowGoing,
+    LineReflowStatus* aLineReflowStatus, bool aAllowPullUp) {
+  // Forget all of the floats on the line
+  aLine->ClearFloats();
+  aState.mFloatOverflowAreas.Clear();
+
+  // We need to set this flag on the line if any of our reflow passes
+  // are impacted by floats.
+  if (aFloatAvailableSpace.HasFloats()) {
+    aLine->SetLineIsImpactedByFloat(true);
+  }
+#ifdef REALLY_NOISY_REFLOW
+  printf("nsBlockFrame::DoReflowInlineFrames %p impacted = %d\n", this,
+         aFloatAvailableSpace.HasFloats());
+#endif
+
+  WritingMode outerWM = aState.mReflowInput.GetWritingMode();
+  WritingMode lineWM = WritingModeForLine(outerWM, aLine->mFirstChild);
+  LogicalRect lineRect = aFloatAvailableSpace.mRect.ConvertTo(
+      lineWM, outerWM, aState.ContainerSize());
+
+  nscoord iStart = lineRect.IStart(lineWM);
+  nscoord availISize = lineRect.ISize(lineWM);
+  nscoord availBSize;
+  if (aState.mReflowInput.AvailableBSize() == NS_UNCONSTRAINEDSIZE) {
+    availBSize = NS_UNCONSTRAINEDSIZE;
+  } else {
+    /* XXX get the height right! */
+    availBSize = lineRect.BSize(lineWM);
+  }
+
+  // Make sure to enable resize optimization before we call BeginLineReflow
+  // because it might get disabled there
+  aLine->EnableResizeReflowOptimization();
+
+  aLineLayout.BeginLineReflow(
+      iStart, aState.mBCoord, availISize, availBSize,
+      aFloatAvailableSpace.HasFloats(), false, /*XXX isTopOfPage*/
+      lineWM, aState.mContainerSize, aState.mInsetForBalance);
+
+  aState.mFlags.mIsLineLayoutEmpty = false;
+
+  // XXX Unfortunately we need to know this before reflowing the first
+  // inline frame in the line. FIX ME.
+  if (0 == aLineLayout.GetLineNumber() &&
+      HasAllStateBits(NS_BLOCK_HAS_FIRST_LETTER_CHILD |
+                      NS_BLOCK_HAS_FIRST_LETTER_STYLE)) {
+    aLineLayout.SetFirstLetterStyleOK(true);
+  }
+  NS_ASSERTION(!(HasAnyStateBits(NS_BLOCK_HAS_FIRST_LETTER_CHILD) &&
+                 GetPrevContinuation()),
+               "first letter child bit should only be on first continuation");
+
+  // Reflow the frames that are already on the line first
+  LineReflowStatus lineReflowStatus = LineReflowStatus::OK;
+  int32_t i;
+  nsIFrame* frame = aLine->mFirstChild;
+
+  if (aFloatAvailableSpace.HasFloats()) {
+    // There is a soft break opportunity at the start of the line, because
+    // we can always move this line down below float(s).
+    if (aLineLayout.NotifyOptionalBreakPosition(
+            frame, 0, true, gfxBreakPriority::eNormalBreak)) {
+      lineReflowStatus = LineReflowStatus::RedoNextBand;
+    }
+  }
+
+  // need to repeatedly call GetChildCount here, because the child
+  // count can change during the loop!
+  for (i = 0;
+       LineReflowStatus::OK == lineReflowStatus && i < aLine->GetChildCount();
+       i++, frame = frame->GetNextSibling()) {
+    ReflowInlineFrame(aState, aLineLayout, aLine, frame, &lineReflowStatus);
+    if (LineReflowStatus::OK != lineReflowStatus) {
+      // It is possible that one or more of next lines are empty
+      // (because of DeleteNextInFlowChild). If so, delete them now
+      // in case we are finished.
+      ++aLine;
+      while ((aLine != LinesEnd()) && (0 == aLine->GetChildCount())) {
+        // XXX Is this still necessary now that DeleteNextInFlowChild
+        // uses DoRemoveFrame?
+        nsLineBox* toremove = aLine;
+        aLine = mLines.erase(aLine);
+        NS_ASSERTION(nullptr == toremove->mFirstChild, "bad empty line");
+        FreeLineBox(toremove);
+      }
+      --aLine;
+
+      NS_ASSERTION(lineReflowStatus != LineReflowStatus::Truncated,
+                   "ReflowInlineFrame should never determine that a line "
+                   "needs to go to the next page/column");
+    }
+  }
+
+  // Don't pull up new frames into lines with continuation placeholders
+  if (aAllowPullUp) {
+    // Pull frames and reflow them until we can't
+    while (LineReflowStatus::OK == lineReflowStatus) {
+      frame = PullFrame(aState, aLine);
+      if (!frame) {
+        break;
+      }
+
+      while (LineReflowStatus::OK == lineReflowStatus) {
+        int32_t oldCount = aLine->GetChildCount();
+        ReflowInlineFrame(aState, aLineLayout, aLine, frame, &lineReflowStatus);
+        if (aLine->GetChildCount() != oldCount) {
+          // We just created a continuation for aFrame AND its going
+          // to end up on this line (e.g. :first-letter
+          // situation). Therefore we have to loop here before trying
+          // to pull another frame.
+          frame = frame->GetNextSibling();
+        } else {
+          break;
+        }
+      }
+    }
+  }
+
+  aState.mFlags.mIsLineLayoutEmpty = aLineLayout.LineIsEmpty();
+
+  // We only need to backup if the line isn't going to be reflowed again anyway
+  bool needsBackup = aLineLayout.NeedsBackup() &&
+                     (lineReflowStatus == LineReflowStatus::Stop ||
+                      lineReflowStatus == LineReflowStatus::OK);
+  if (needsBackup && aLineLayout.HaveForcedBreakPosition()) {
+    NS_WARNING(
+        "We shouldn't be backing up more than once! "
+        "Someone must have set a break opportunity beyond the available width, "
+        "even though there were better break opportunities before it");
+    needsBackup = false;
+  }
+  if (needsBackup) {
+    // We need to try backing up to before a text run
+    // XXX It's possible, in fact not unusual, for the break opportunity to
+    // already be the end of the line. We should detect that and optimize to not
+    // re-do the line.
+    if (aLineLayout.HasOptionalBreakPosition()) {
+      // We can back up!
+      lineReflowStatus = LineReflowStatus::RedoNoPull;
+    }
+  } else {
+    // In case we reflow this line again, remember that we don't
+    // need to force any breaking
+    aLineLayout.ClearOptionalBreakPosition();
+  }
+
+  if (LineReflowStatus::RedoNextBand == lineReflowStatus) {
+    // This happens only when we have a line that is impacted by
+    // floats and the first element in the line doesn't fit with
+    // the floats.
+    //
+    // If there's block space available, we either try to reflow the line
+    // past the current band (if it's non-zero and the band definitely won't
+    // widen around a shape-outside), otherwise we try one pixel down. If
+    // there's no block space available, we push the line to the next
+    // page/column.
+    NS_ASSERTION(
+        NS_UNCONSTRAINEDSIZE != aFloatAvailableSpace.mRect.BSize(outerWM),
+        "unconstrained block size on totally empty line");
+
+    // See the analogous code for blocks in BlockReflowState::ClearFloats.
+    nscoord bandBSize = aFloatAvailableSpace.mRect.BSize(outerWM);
+    if (bandBSize > 0 ||
+        NS_UNCONSTRAINEDSIZE == aState.mReflowInput.AvailableBSize()) {
+      NS_ASSERTION(bandBSize == 0 || aFloatAvailableSpace.HasFloats(),
+                   "redo line on totally empty line with non-empty band...");
+      // We should never hit this case if we've placed floats on the
+      // line; if we have, then the GetFloatAvailableSpace call is wrong
+      // and needs to happen after the caller pops the float manager
+      // state.
+      aState.FloatManager()->AssertStateMatches(aFloatStateBeforeLine);
+
+      if (!aFloatAvailableSpace.MayWiden() && bandBSize > 0) {
+        // Move it down far enough to clear the current band.
+        aState.mBCoord += bandBSize;
+      } else {
+        // Move it down by one dev pixel.
+        aState.mBCoord += aState.mPresContext->DevPixelsToAppUnits(1);
+      }
+
+      aFloatAvailableSpace = aState.GetFloatAvailableSpace();
+    } else {
+      // There's nowhere to retry placing the line, so we want to push
+      // it to the next page/column where its contents can fit not
+      // next to a float.
+      lineReflowStatus = LineReflowStatus::Truncated;
+      PushTruncatedLine(aState, aLine, aKeepReflowGoing);
+    }
+
+    // XXX: a small optimization can be done here when paginating:
+    // if the new Y coordinate is past the end of the block then
+    // push the line and return now instead of later on after we are
+    // past the float.
+  } else if (LineReflowStatus::Truncated != lineReflowStatus &&
+             LineReflowStatus::RedoNoPull != lineReflowStatus) {
+    // If we are propagating out a break-before status then there is
+    // no point in placing the line.
+    if (!aState.mReflowStatus.IsInlineBreakBefore()) {
+      if (!PlaceLine(aState, aLineLayout, aLine, aFloatStateBeforeLine,
+                     aFloatAvailableSpace, aAvailableSpaceBSize,
+                     aKeepReflowGoing)) {
+        lineReflowStatus = LineReflowStatus::RedoMoreFloats;
+        // PlaceLine already called GetFloatAvailableSpaceForBSize or its
+        // variant for us.
+      }
+    }
+  }
+#ifdef DEBUG
+  if (gNoisyReflow) {
+    printf("Line reflow status = %s\n",
+           LineReflowStatusToString(lineReflowStatus));
+  }
+#endif
+
+  if (aLineLayout.GetDirtyNextLine()) {
+    // aLine may have been pushed to the overflow lines.
+    FrameLines* overflowLines = GetOverflowLines();
+    // We can't just compare iterators front() to aLine here, since they may be
+    // in different lists.
+    bool pushedToOverflowLines =
+        overflowLines && overflowLines->mLines.front() == aLine.get();
+    if (pushedToOverflowLines) {
+      // aLine is stale, it's associated with the main line list but it should
+      // be associated with the overflow line list now
+      aLine = overflowLines->mLines.begin();
+    }
+    nsBlockInFlowLineIterator iter(this, aLine, pushedToOverflowLines);
+    if (iter.Next() && iter.GetLine()->IsInline()) {
+      iter.GetLine()->MarkDirty();
+      if (iter.GetContainer() != this) {
+        aState.mReflowStatus.SetNextInFlowNeedsReflow();
+      }
+    }
+  }
+
+  *aLineReflowStatus = lineReflowStatus;
+}
+
+/**
+ * Reflow an inline frame. The reflow status is mapped from the frames
+ * reflow status to the lines reflow status (not to our reflow status).
+ * The line reflow status is simple: true means keep placing frames
+ * on the line; false means don't (the line is done). If the line
+ * has some sort of breaking affect then aLine's break-type will be set
+ * to something other than StyleClear::None.
+ */
+void nsBlockFrame::ReflowInlineFrame(BlockReflowState& aState,
+                                     nsLineLayout& aLineLayout,
+                                     LineIterator aLine, nsIFrame* aFrame,
+                                     LineReflowStatus* aLineReflowStatus) {
+  MOZ_ASSERT(aFrame);
+  *aLineReflowStatus = LineReflowStatus::OK;
+
+#ifdef NOISY_FIRST_LETTER
+  ListTag(stdout);
+  printf(": reflowing ");
+  aFrame->ListTag(stdout);
+  printf(" reflowingFirstLetter=%s\n",
+         aLineLayout.GetFirstLetterStyleOK() ? "on" : "off");
+#endif
+
+  if (aFrame->IsPlaceholderFrame()) {
+    auto ph = static_cast<nsPlaceholderFrame*>(aFrame);
+    ph->ForgetLineIsEmptySoFar();
+  }
+
+  // Reflow the inline frame
+  nsReflowStatus frameReflowStatus;
+  bool pushedFrame;
+  aLineLayout.ReflowFrame(aFrame, frameReflowStatus, nullptr, pushedFrame);
+
+  if (frameReflowStatus.NextInFlowNeedsReflow()) {
+    aLineLayout.SetDirtyNextLine();
+  }
+
+#ifdef REALLY_NOISY_REFLOW
+  aFrame->ListTag(stdout);
+  printf(": status=%s\n", ToString(frameReflowStatus).c_str());
+#endif
+
+#if defined(REFLOW_STATUS_COVERAGE)
+  RecordReflowStatus(false, frameReflowStatus);
+#endif
+
+  // Send post-reflow notification
+  aState.mPrevChild = aFrame;
+
+  /* XXX
+     This is where we need to add logic to handle some odd behavior.
+     For one thing, we should usually place at least one thing next
+     to a left float, even when that float takes up all the width on a line.
+     see bug 22496
+  */
+
+  // Process the child frames reflow status. There are 5 cases:
+  // complete, not-complete, break-before, break-after-complete,
+  // break-after-not-complete. There are two situations: we are a
+  // block or we are an inline. This makes a total of 10 cases
+  // (fortunately, there is some overlap).
+  aLine->ClearForcedLineBreak();
+  if (frameReflowStatus.IsInlineBreak() ||
+      aState.mTrailingClearFromPIF != StyleClear::None) {
+    // Always abort the line reflow (because a line break is the
+    // minimal amount of break we do).
+    *aLineReflowStatus = LineReflowStatus::Stop;
+
+    // XXX what should aLine's break-type be set to in all these cases?
+    if (frameReflowStatus.IsInlineBreakBefore()) {
+      // Break-before cases.
+      if (aFrame == aLine->mFirstChild) {
+        // If we break before the first frame on the line then we must
+        // be trying to place content where there's no room (e.g. on a
+        // line with wide floats). Inform the caller to reflow the
+        // line after skipping past a float.
+        *aLineReflowStatus = LineReflowStatus::RedoNextBand;
+      } else {
+        // It's not the first child on this line so go ahead and split
+        // the line. We will see the frame again on the next-line.
+        SplitLine(aState, aLineLayout, aLine, aFrame, aLineReflowStatus);
+
+        // If we're splitting the line because the frame didn't fit and it
+        // was pushed, then mark the line as having word wrapped. We need to
+        // know that if we're shrink wrapping our width
+        if (pushedFrame) {
+          aLine->SetLineWrapped(true);
+        }
+      }
+    } else {
+      MOZ_ASSERT(frameReflowStatus.IsInlineBreakAfter() ||
+                     aState.mTrailingClearFromPIF != StyleClear::None,
+                 "We should've handled inline break-before in the if-branch!");
+
+      // If a float split and its prev-in-flow was followed by a <BR>, then
+      // combine the <BR>'s float clear type with the inline's float clear type
+      // (the inline will be the very next frame after the split float).
+      StyleClear clearType = frameReflowStatus.FloatClearType();
+      if (aState.mTrailingClearFromPIF != StyleClear::None) {
+        clearType = nsLayoutUtils::CombineClearType(
+            clearType, aState.mTrailingClearFromPIF);
+        aState.mTrailingClearFromPIF = StyleClear::None;
+      }
+      // Break-after cases
+      if (clearType != StyleClear::None || aLineLayout.GetLineEndsInBR()) {
+        aLine->SetForcedLineBreakAfter(clearType);
+      }
+      if (frameReflowStatus.IsComplete()) {
+        // Split line, but after the frame just reflowed
+        SplitLine(aState, aLineLayout, aLine, aFrame->GetNextSibling(),
+                  aLineReflowStatus);
+
+        if (frameReflowStatus.IsInlineBreakAfter() &&
+            !aLineLayout.GetLineEndsInBR()) {
+          aLineLayout.SetDirtyNextLine();
+        }
+      }
+    }
+  }
+
+  if (!frameReflowStatus.IsFullyComplete()) {
+    // Create a continuation for the incomplete frame. Note that the
+    // frame may already have a continuation.
+    CreateContinuationFor(aState, aLine, aFrame);
+
+    // Remember that the line has wrapped
+    if (!aLineLayout.GetLineEndsInBR()) {
+      aLine->SetLineWrapped(true);
+    }
+
+    // If we just ended a first-letter frame or reflowed a placeholder then
+    // don't split the line and don't stop the line reflow...
+    // But if we are going to stop anyways we'd better split the line.
+    if ((!frameReflowStatus.FirstLetterComplete() &&
+         !aFrame->IsPlaceholderFrame()) ||
+        *aLineReflowStatus == LineReflowStatus::Stop) {
+      // Split line after the current frame
+      *aLineReflowStatus = LineReflowStatus::Stop;
+      SplitLine(aState, aLineLayout, aLine, aFrame->GetNextSibling(),
+                aLineReflowStatus);
+    }
+  }
+}
+
+bool nsBlockFrame::CreateContinuationFor(BlockReflowState& aState,
+                                         nsLineBox* aLine, nsIFrame* aFrame) {
+  nsIFrame* newFrame = nullptr;
+
+  if (!aFrame->GetNextInFlow()) {
+    newFrame =
+        PresShell()->FrameConstructor()->CreateContinuingFrame(aFrame, this);
+
+    mFrames.InsertFrame(nullptr, aFrame, newFrame);
+
+    if (aLine) {
+      aLine->NoteFrameAdded(newFrame);
+    }
+  }
+#ifdef DEBUG
+  VerifyLines(false);
+#endif
+  return !!newFrame;
+}
+
+void nsBlockFrame::SplitFloat(BlockReflowState& aState, nsIFrame* aFloat,
+                              const nsReflowStatus& aFloatStatus) {
+  MOZ_ASSERT(!aFloatStatus.IsFullyComplete(),
+             "why split the frame if it's fully complete?");
+  MOZ_ASSERT(aState.mBlock == this);
+
+  nsIFrame* nextInFlow = aFloat->GetNextInFlow();
+  if (nextInFlow) {
+    nsContainerFrame* oldParent = nextInFlow->GetParent();
+    oldParent->StealFrame(nextInFlow);
+    if (oldParent != this) {
+      ReparentFrame(nextInFlow, oldParent, this);
+    }
+    if (!aFloatStatus.IsOverflowIncomplete()) {
+      nextInFlow->RemoveStateBits(NS_FRAME_IS_OVERFLOW_CONTAINER);
+    }
+  } else {
+    nextInFlow =
+        PresShell()->FrameConstructor()->CreateContinuingFrame(aFloat, this);
+  }
+  if (aFloatStatus.IsOverflowIncomplete()) {
+    nextInFlow->AddStateBits(NS_FRAME_IS_OVERFLOW_CONTAINER);
+  }
+
+  StyleFloat floatStyle = aFloat->StyleDisplay()->mFloat;
+  if (floatStyle == StyleFloat::Left) {
+    aState.FloatManager()->SetSplitLeftFloatAcrossBreak();
+  } else {
+    MOZ_ASSERT(floatStyle == StyleFloat::Right, "Unexpected float side!");
+    aState.FloatManager()->SetSplitRightFloatAcrossBreak();
+  }
+
+  aState.AppendPushedFloatChain(nextInFlow);
+  if (MOZ_LIKELY(!HasAnyStateBits(NS_BLOCK_BFC_STATE_BITS)) ||
+      MOZ_UNLIKELY(IsTrueOverflowContainer())) {
+    aState.mReflowStatus.SetOverflowIncomplete();
+  } else {
+    aState.mReflowStatus.SetIncomplete();
+  }
+}
+
+static bool CheckPlaceholderInLine(nsIFrame* aBlock, nsLineBox* aLine,
+                                   nsIFrame* aFloat) {
+  if (!aFloat) {
+    return true;
+  }
+  NS_ASSERTION(!aFloat->GetPrevContinuation(),
+               "float in a line should never be a continuation");
+  NS_ASSERTION(!aFloat->HasAnyStateBits(NS_FRAME_IS_PUSHED_FLOAT),
+               "float in a line should never be a pushed float");
+  nsIFrame* ph = aFloat->FirstInFlow()->GetPlaceholderFrame();
+  for (nsIFrame* f = ph; f; f = f->GetParent()) {
+    if (f->GetParent() == aBlock) {
+      return aLine->Contains(f);
+    }
+  }
+  NS_ASSERTION(false, "aBlock is not an ancestor of aFrame!");
+  return true;
+}
+
+void nsBlockFrame::SplitLine(BlockReflowState& aState,
+                             nsLineLayout& aLineLayout, LineIterator aLine,
+                             nsIFrame* aFrame,
+                             LineReflowStatus* aLineReflowStatus) {
+  MOZ_ASSERT(aLine->IsInline(), "illegal SplitLine on block line");
+
+  int32_t pushCount =
+      aLine->GetChildCount() - aLineLayout.GetCurrentSpanCount();
+  MOZ_ASSERT(pushCount >= 0, "bad push count");
+
+#ifdef DEBUG
+  if (gNoisyReflow) {
+    nsIFrame::IndentBy(stdout, gNoiseIndent);
+    printf("split line: from line=%p pushCount=%d aFrame=",
+           static_cast<void*>(aLine.get()), pushCount);
+    if (aFrame) {
+      aFrame->ListTag(stdout);
+    } else {
+      printf("(null)");
+    }
+    printf("\n");
+    if (gReallyNoisyReflow) {
+      aLine->List(stdout, gNoiseIndent + 1);
+    }
+  }
+#endif
+
+  if (0 != pushCount) {
+    MOZ_ASSERT(aLine->GetChildCount() > pushCount, "bad push");
+    MOZ_ASSERT(nullptr != aFrame, "whoops");
+#ifdef DEBUG
+    {
+      nsIFrame* f = aFrame;
+      int32_t count = pushCount;
+      while (f && count > 0) {
+        f = f->GetNextSibling();
+        --count;
+      }
+      NS_ASSERTION(count == 0, "Not enough frames to push");
+    }
+#endif
+
+    // Put frames being split out into their own line
+    nsLineBox* newLine = NewLineBox(aLine, aFrame, pushCount);
+    mLines.after_insert(aLine, newLine);
+#ifdef DEBUG
+    if (gReallyNoisyReflow) {
+      newLine->List(stdout, gNoiseIndent + 1);
+    }
+#endif
+
+    // Let line layout know that some frames are no longer part of its
+    // state.
+    aLineLayout.SplitLineTo(aLine->GetChildCount());
+
+    // If floats have been placed whose placeholders have been pushed to the new
+    // line, we need to reflow the old line again. We don't want to look at the
+    // frames in the new line, because as a large paragraph is laid out the
+    // we'd get O(N^2) performance. So instead we just check that the last
+    // float and the last below-current-line float are still in aLine.
+    if (!CheckPlaceholderInLine(
+            this, aLine,
+            aLine->HasFloats() ? aLine->Floats().LastElement() : nullptr) ||
+        !CheckPlaceholderInLine(
+            this, aLine,
+            aState.mBelowCurrentLineFloats.SafeLastElement(nullptr))) {
+      *aLineReflowStatus = LineReflowStatus::RedoNoPull;
+    }
+
+#ifdef DEBUG
+    VerifyLines(true);
+#endif
+  }
+}
+
+bool nsBlockFrame::IsLastLine(BlockReflowState& aState, LineIterator aLine) {
+  while (++aLine != LinesEnd()) {
+    // There is another line
+    if (0 != aLine->GetChildCount()) {
+      // If the next line is a block line then this line is the last in a
+      // group of inline lines.
+      return aLine->IsBlock();
+    }
+    // The next line is empty, try the next one
+  }
+
+  // Try our next-in-flows lines to answer the question
+  nsBlockFrame* nextInFlow = (nsBlockFrame*)GetNextInFlow();
+  while (nullptr != nextInFlow) {
+    for (const auto& line : nextInFlow->Lines()) {
+      if (0 != line.GetChildCount()) {
+        return line.IsBlock();
+      }
+    }
+    nextInFlow = (nsBlockFrame*)nextInFlow->GetNextInFlow();
+  }
+
+  // This is the last line - so don't allow justification
+  return true;
+}
+
+bool nsBlockFrame::PlaceLine(BlockReflowState& aState,
+                             nsLineLayout& aLineLayout, LineIterator aLine,
+                             nsFloatManager::SavedState* aFloatStateBeforeLine,
+                             nsFlowAreaRect& aFlowArea,
+                             nscoord& aAvailableSpaceBSize,
+                             bool* aKeepReflowGoing) {
+  // Try to position the floats in a nowrap context.
+  aLineLayout.FlushNoWrapFloats();
+
+  // Trim extra white-space from the line before placing the frames
+  aLineLayout.TrimTrailingWhiteSpace();
+
+  // Vertically align the frames on this line.
+  //
+  // According to the CSS2 spec, section 12.6.1, the "marker" box
+  // participates in the height calculation of the list-item box's
+  // first line box.
+  //
+  // There are exactly two places a ::marker can be placed: near the
+  // first or second line. It's only placed on the second line in a
+  // rare case: when the first line is empty.
+  WritingMode wm = aState.mReflowInput.GetWritingMode();
+  bool addedMarker = false;
+  if (HasOutsideMarker() &&
+      ((aLine == mLines.front() &&
+        (!aLineLayout.IsZeroBSize() || (aLine == mLines.back()))) ||
+       (mLines.front() != mLines.back() && 0 == mLines.front()->BSize() &&
+        aLine == mLines.begin().next()))) {
+    ReflowOutput metrics(aState.mReflowInput);
+    nsIFrame* marker = GetOutsideMarker();
+    ReflowOutsideMarker(marker, aState, metrics, aState.mBCoord);
+    NS_ASSERTION(!MarkerIsEmpty() || metrics.BSize(wm) == 0,
+                 "empty ::marker frame took up space");
+    aLineLayout.AddMarkerFrame(marker, metrics);
+    addedMarker = true;
+  }
+  aLineLayout.VerticalAlignLine();
+
+  // We want to consider the floats in the current line when determining
+  // whether the float available space is shrunk. If mLineBSize doesn't
+  // exist, we are in the first pass trying to place the line. Calling
+  // GetFloatAvailableSpace() like we did in BlockReflowState::AddFloat()
+  // for UpdateBand().
+
+  // floatAvailableSpaceWithOldLineBSize is the float available space with
+  // the old BSize, but including the floats that were added in this line.
+  LogicalRect floatAvailableSpaceWithOldLineBSize =
+      aState.mLineBSize.isNothing()
+          ? aState.GetFloatAvailableSpace(aLine->BStart()).mRect
+          : aState
+                .GetFloatAvailableSpaceForBSize(
+                    aLine->BStart(), aState.mLineBSize.value(), nullptr)
+                .mRect;
+
+  // As we redo for floats, we can't reduce the amount of BSize we're
+  // checking.
+  aAvailableSpaceBSize = std::max(aAvailableSpaceBSize, aLine->BSize());
+  LogicalRect floatAvailableSpaceWithLineBSize =
+      aState
+          .GetFloatAvailableSpaceForBSize(aLine->BStart(), aAvailableSpaceBSize,
+                                          nullptr)
+          .mRect;
+
+  // If the available space between the floats is smaller now that we
+  // know the BSize, return false (and cause another pass with
+  // LineReflowStatus::RedoMoreFloats).  We ensure aAvailableSpaceBSize
+  // never decreases, which means that we can't reduce the set of floats
+  // we intersect, which means that the available space cannot grow.
+  if (AvailableSpaceShrunk(wm, floatAvailableSpaceWithOldLineBSize,
+                           floatAvailableSpaceWithLineBSize, false)) {
+    // Prepare data for redoing the line.
+    aState.mLineBSize = Some(aLine->BSize());
+
+    // Since we want to redo the line, we update aFlowArea by using the
+    // aFloatStateBeforeLine, which is the float manager's state before the
+    // line is placed.
+    LogicalRect oldFloatAvailableSpace(aFlowArea.mRect);
+    aFlowArea = aState.GetFloatAvailableSpaceForBSize(
+        aLine->BStart(), aAvailableSpaceBSize, aFloatStateBeforeLine);
+
+    NS_ASSERTION(
+        aFlowArea.mRect.BStart(wm) == oldFloatAvailableSpace.BStart(wm),
+        "yikes");
+    // Restore the BSize to the position of the next band.
+    aFlowArea.mRect.BSize(wm) = oldFloatAvailableSpace.BSize(wm);
+
+    // Enforce both IStart() and IEnd() never move outwards to prevent
+    // infinite grow-shrink loops.
+    const nscoord iStartDiff =
+        aFlowArea.mRect.IStart(wm) - oldFloatAvailableSpace.IStart(wm);
+    const nscoord iEndDiff =
+        aFlowArea.mRect.IEnd(wm) - oldFloatAvailableSpace.IEnd(wm);
+    if (iStartDiff < 0) {
+      aFlowArea.mRect.IStart(wm) -= iStartDiff;
+      aFlowArea.mRect.ISize(wm) += iStartDiff;
+    }
+    if (iEndDiff > 0) {
+      aFlowArea.mRect.ISize(wm) -= iEndDiff;
+    }
+
+    return false;
+  }
+
+#ifdef DEBUG
+  if (!GetParent()->IsAbsurdSizeAssertSuppressed()) {
+    static nscoord lastHeight = 0;
+    if (ABSURD_SIZE(aLine->BStart())) {
+      lastHeight = aLine->BStart();
+      if (abs(aLine->BStart() - lastHeight) > ABSURD_COORD / 10) {
+        nsIFrame::ListTag(stdout);
+        printf(": line=%p y=%d line.bounds.height=%d\n",
+               static_cast<void*>(aLine.get()), aLine->BStart(),
+               aLine->BSize());
+      }
+    } else {
+      lastHeight = 0;
+    }
+  }
+#endif
+
+  // Only block frames horizontally align their children because
+  // inline frames "shrink-wrap" around their children (therefore
+  // there is no extra horizontal space).
+  const nsStyleText* styleText = StyleText();
+
+  /**
+   * We don't care checking for IsLastLine properly if we don't care (if it
+   * can't change the used text-align value for the line).
+   *
+   * In other words, isLastLine really means isLastLineAndWeCare.
+   */
+  const bool isLastLine =
+      !IsInSVGTextSubtree() &&
+      styleText->TextAlignForLastLine() != styleText->mTextAlign &&
+      (aLineLayout.GetLineEndsInBR() || IsLastLine(aState, aLine));
+
+  aLineLayout.TextAlignLine(aLine, isLastLine);
+
+  // From here on, pfd->mBounds rectangles are incorrect because bidi
+  // might have moved frames around!
+  OverflowAreas overflowAreas;
+  aLineLayout.RelativePositionFrames(overflowAreas);
+  aLine->SetOverflowAreas(overflowAreas);
+  if (addedMarker) {
+    aLineLayout.RemoveMarkerFrame(GetOutsideMarker());
+  }
+
+  // Inline lines do not have margins themselves; however they are
+  // impacted by prior block margins. If this line ends up having some
+  // height then we zero out the previous block-end margin value that was
+  // already applied to the line's starting Y coordinate. Otherwise we
+  // leave it be so that the previous blocks block-end margin can be
+  // collapsed with a block that follows.
+  nscoord newBCoord;
+
+  if (!aLine->CachedIsEmpty()) {
+    // This line has some height. Therefore the application of the
+    // previous-bottom-margin should stick.
+    aState.mPrevBEndMargin.Zero();
+    newBCoord = aLine->BEnd();
+  } else {
+    // Don't let the previous-bottom-margin value affect the newBCoord
+    // coordinate (it was applied in ReflowInlineFrames speculatively)
+    // since the line is empty.
+    // We already called |ShouldApplyBStartMargin|, and if we applied it
+    // then mShouldApplyBStartMargin is set.
+    nscoord dy = aState.mFlags.mShouldApplyBStartMargin
+                     ? -aState.mPrevBEndMargin.get()
+                     : 0;
+    newBCoord = aState.mBCoord + dy;
+  }
+
+  if (!aState.mReflowStatus.IsFullyComplete() &&
+      ShouldAvoidBreakInside(aState.mReflowInput)) {
+    aLine->AppendFloats(std::move(aState.mCurrentLineFloats));
+    SetBreakBeforeStatusBeforeLine(aState, aLine, aKeepReflowGoing);
+    return true;
+  }
+
+  // See if the line fit (our first line always does).
+  if (mLines.front() != aLine &&
+      aState.ContentBSize() != NS_UNCONSTRAINEDSIZE &&
+      newBCoord > aState.ContentBEnd()) {
+    NS_ASSERTION(aState.mCurrentLine == aLine, "oops");
+    if (ShouldAvoidBreakInside(aState.mReflowInput)) {
+      // All our content doesn't fit, start on the next page.
+      SetBreakBeforeStatusBeforeLine(aState, aLine, aKeepReflowGoing);
+    } else {
+      // Push aLine and all of its children and anything else that
+      // follows to our next-in-flow.
+      PushTruncatedLine(aState, aLine, aKeepReflowGoing);
+    }
+    return true;
+  }
+
+  // Note that any early return before this update of aState.mBCoord
+  // must either (a) return false or (b) set aKeepReflowGoing to false.
+  // Otherwise we'll keep reflowing later lines at an incorrect
+  // position, and we might not come back and clean up the damage later.
+  aState.mBCoord = newBCoord;
+
+  // Add the already placed current-line floats to the line
+  aLine->AppendFloats(std::move(aState.mCurrentLineFloats));
+
+  // Any below current line floats to place?
+  if (!aState.mBelowCurrentLineFloats.IsEmpty()) {
+    // Reflow the below-current-line floats, which places on the line's
+    // float list.
+    aState.PlaceBelowCurrentLineFloats(aLine);
+  }
+
+  // When a line has floats, factor them into the overflow areas computations.
+  if (aLine->HasFloats()) {
+    // Union the float overflow areas (stored in aState) and the value computed
+    // by the line layout code.
+    OverflowAreas lineOverflowAreas = aState.mFloatOverflowAreas;
+    lineOverflowAreas.UnionWith(aLine->GetOverflowAreas());
+    aLine->SetOverflowAreas(lineOverflowAreas);
+
+#ifdef NOISY_OVERFLOW_AREAS
+    printf("%s: Line %p, InkOverflowRect=%s, ScrollableOverflowRect=%s\n",
+           ListTag().get(), aLine.get(),
+           ToString(aLine->InkOverflowRect()).c_str(),
+           ToString(aLine->ScrollableOverflowRect()).c_str());
+#endif
+  }
+
+  // Apply break-after clearing if necessary
+  // This must stay in sync with |ReflowDirtyLines|.
+  if (aLine->HasFloatClearTypeAfter()) {
+    std::tie(aState.mBCoord, std::ignore) =
+        aState.ClearFloats(aState.mBCoord, aLine->FloatClearTypeAfter());
+  }
+  return true;
+}
+
+void nsBlockFrame::PushLines(BlockReflowState& aState,
+                             nsLineList::iterator aLineBefore) {
+  // NOTE: aLineBefore is always a normal line, not an overflow line.
+  // The following expression will assert otherwise.
+  DebugOnly<bool> check = aLineBefore == mLines.begin();
+
+  nsLineList::iterator overBegin(aLineBefore.next());
+
+  // PushTruncatedPlaceholderLine sometimes pushes the first line.  Ugh.
+  bool firstLine = overBegin == LinesBegin();
+
+  if (overBegin != LinesEnd()) {
+    // Remove floats in the lines from mFloats
+    nsFrameList floats;
+    CollectFloats(overBegin->mFirstChild, floats, true);
+
+    if (floats.NotEmpty()) {
+#ifdef DEBUG
+      for (nsIFrame* f : floats) {
+        MOZ_ASSERT(!f->HasAnyStateBits(NS_FRAME_IS_PUSHED_FLOAT),
+                   "CollectFloats should've removed that bit");
+      }
+#endif
+      // Push the floats onto the front of the overflow out-of-flows list
+      nsAutoOOFFrameList oofs(this);
+      oofs.mList.InsertFrames(nullptr, nullptr, std::move(floats));
+    }
+
+    // overflow lines can already exist in some cases, in particular,
+    // when shrinkwrapping and we discover that the shrinkwap causes
+    // the height of some child block to grow which creates additional
+    // overflowing content. In such cases we must prepend the new
+    // overflow to the existing overflow.
+    FrameLines* overflowLines = RemoveOverflowLines();
+    if (!overflowLines) {
+      // XXXldb use presshell arena!
+      overflowLines = new FrameLines();
+    }
+    if (overflowLines) {
+      nsIFrame* lineBeforeLastFrame;
+      if (firstLine) {
+        lineBeforeLastFrame = nullptr;  // removes all frames
+      } else {
+        nsIFrame* f = overBegin->mFirstChild;
+        lineBeforeLastFrame = f ? f->GetPrevSibling() : mFrames.LastChild();
+        NS_ASSERTION(!f || lineBeforeLastFrame == aLineBefore->LastChild(),
+                     "unexpected line frames");
+      }
+      nsFrameList pushedFrames = mFrames.TakeFramesAfter(lineBeforeLastFrame);
+      overflowLines->mFrames.InsertFrames(nullptr, nullptr,
+                                          std::move(pushedFrames));
+
+      overflowLines->mLines.splice(overflowLines->mLines.begin(), mLines,
+                                   overBegin, LinesEnd());
+      NS_ASSERTION(!overflowLines->mLines.empty(), "should not be empty");
+      // this takes ownership but it won't delete it immediately so we
+      // can keep using it.
+      SetOverflowLines(overflowLines);
+
+      // Mark all the overflow lines dirty so that they get reflowed when
+      // they are pulled up by our next-in-flow.
+
+      // XXXldb Can this get called O(N) times making the whole thing O(N^2)?
+      for (LineIterator line = overflowLines->mLines.begin(),
+                        line_end = overflowLines->mLines.end();
+           line != line_end; ++line) {
+        line->MarkDirty();
+        line->MarkPreviousMarginDirty();
+        line->SetMovedFragments();
+        line->SetBoundsEmpty();
+        if (line->HasFloats()) {
+          line->ClearFloats();
+        }
+      }
+    }
+  }
+
+#ifdef DEBUG
+  VerifyOverflowSituation();
+#endif
+}
+
+// The overflowLines property is stored as a pointer to a line list,
+// which must be deleted.  However, the following functions all maintain
+// the invariant that the property is never set if the list is empty.
+
+bool nsBlockFrame::DrainOverflowLines() {
+#ifdef DEBUG
+  VerifyOverflowSituation();
+#endif
+
+  // Steal the prev-in-flow's overflow lines and prepend them.
+  bool didFindOverflow = false;
+  nsBlockFrame* prevBlock = static_cast<nsBlockFrame*>(GetPrevInFlow());
+  if (prevBlock) {
+    prevBlock->ClearLineCursors();
+    FrameLines* overflowLines = prevBlock->RemoveOverflowLines();
+    if (overflowLines) {
+      // Make all the frames on the overflow line list mine.
+      ReparentFrames(overflowLines->mFrames, prevBlock, this);
+
+      // Collect overflow containers from our OverflowContainers list that are
+      // continuations from the frames we picked up from our prev-in-flow, then
+      // prepend those to ExcessOverflowContainers to ensure the continuations
+      // are ordered.
+      if (GetOverflowContainers()) {
+        nsFrameList ocContinuations;
+        for (auto* f : overflowLines->mFrames) {
+          auto* cont = f;
+          bool done = false;
+          while (!done && (cont = cont->GetNextContinuation()) &&
+                 cont->GetParent() == this) {
+            bool onlyChild = !cont->GetPrevSibling() && !cont->GetNextSibling();
+            if (cont->HasAnyStateBits(NS_FRAME_IS_OVERFLOW_CONTAINER) &&
+                TryRemoveFrame(OverflowContainersProperty(), cont)) {
+              ocContinuations.AppendFrame(nullptr, cont);
+              done = onlyChild;
+              continue;
+            }
+            break;
+          }
+          if (done) {
+            break;
+          }
+        }
+        if (!ocContinuations.IsEmpty()) {
+          if (nsFrameList* eoc = GetExcessOverflowContainers()) {
+            eoc->InsertFrames(nullptr, nullptr, std::move(ocContinuations));
+          } else {
+            SetExcessOverflowContainers(std::move(ocContinuations));
+          }
+        }
+      }
+
+      // Make the overflow out-of-flow frames mine too.
+      nsAutoOOFFrameList oofs(prevBlock);
+      if (oofs.mList.NotEmpty()) {
+        // In case we own any next-in-flows of any of the drained frames, then
+        // move those to the PushedFloat list.
+        nsFrameList pushedFloats;
+        for (nsIFrame* f : oofs.mList) {
+          nsIFrame* nif = f->GetNextInFlow();
+          for (; nif && nif->GetParent() == this; nif = nif->GetNextInFlow()) {
+            MOZ_ASSERT(nif->HasAnyStateBits(NS_FRAME_IS_PUSHED_FLOAT));
+            RemoveFloat(nif);
+            pushedFloats.AppendFrame(nullptr, nif);
+          }
+        }
+        ReparentFrames(oofs.mList, prevBlock, this);
+        mFloats.InsertFrames(nullptr, nullptr, std::move(oofs.mList));
+        if (!pushedFloats.IsEmpty()) {
+          nsFrameList* pf = EnsurePushedFloats();
+          pf->InsertFrames(nullptr, nullptr, std::move(pushedFloats));
+        }
+      }
+
+      if (!mLines.empty()) {
+        // Remember to recompute the margins on the first line. This will
+        // also recompute the correct deltaBCoord if necessary.
+        mLines.front()->MarkPreviousMarginDirty();
+      }
+      // The overflow lines have already been marked dirty and their previous
+      // margins marked dirty also.
+
+      // Prepend the overflow frames/lines to our principal list.
+      mFrames.InsertFrames(nullptr, nullptr, std::move(overflowLines->mFrames));
+      mLines.splice(mLines.begin(), overflowLines->mLines);
+      NS_ASSERTION(overflowLines->mLines.empty(), "splice should empty list");
+      delete overflowLines;
+      didFindOverflow = true;
+    }
+  }
+
+  // Now append our own overflow lines.
+  return DrainSelfOverflowList() || didFindOverflow;
+}
+
+bool nsBlockFrame::DrainSelfOverflowList() {
+  UniquePtr<FrameLines> ourOverflowLines(RemoveOverflowLines());
+  if (!ourOverflowLines) {
+    return false;
+  }
+
+  // No need to reparent frames in our own overflow lines/oofs, because they're
+  // already ours. But we should put overflow floats back in mFloats.
+  // (explicit scope to remove the OOF list before VerifyOverflowSituation)
+  {
+    nsAutoOOFFrameList oofs(this);
+    if (oofs.mList.NotEmpty()) {
+#ifdef DEBUG
+      for (nsIFrame* f : oofs.mList) {
+        MOZ_ASSERT(!f->HasAnyStateBits(NS_FRAME_IS_PUSHED_FLOAT),
+                   "CollectFloats should've removed that bit");
+      }
+#endif
+      // The overflow floats go after our regular floats.
+      mFloats.AppendFrames(nullptr, std::move(oofs).mList);
+    }
+  }
+  if (!ourOverflowLines->mLines.empty()) {
+    mFrames.AppendFrames(nullptr, std::move(ourOverflowLines->mFrames));
+    mLines.splice(mLines.end(), ourOverflowLines->mLines);
+  }
+
+#ifdef DEBUG
+  VerifyOverflowSituation();
+#endif
+  return true;
+}
+
+/**
+ * Pushed floats are floats whose placeholders are in a previous
+ * continuation.  They might themselves be next-continuations of a float
+ * that partially fit in an earlier continuation, or they might be the
+ * first continuation of a float that couldn't be placed at all.
+ *
+ * Pushed floats live permanently at the beginning of a block's float
+ * list, where they must live *before* any floats whose placeholders are
+ * in that block.
+ *
+ * Temporarily, during reflow, they also live on the pushed floats list,
+ * which only holds them between (a) when one continuation pushes them to
+ * its pushed floats list because they don't fit and (b) when the next
+ * continuation pulls them onto the beginning of its float list.
+ *
+ * DrainPushedFloats sets up pushed floats the way we need them at the
+ * start of reflow; they are then reflowed by ReflowPushedFloats (which
+ * might push some of them on).  Floats with placeholders in this block
+ * are reflowed by (BlockReflowState/nsLineLayout)::AddFloat, which
+ * also maintains these invariants.
+ *
+ * DrainSelfPushedFloats moves any pushed floats from this block's own
+ * PushedFloats list back into mFloats.  DrainPushedFloats additionally
+ * moves frames from its prev-in-flow's PushedFloats list into mFloats.
+ */
+void nsBlockFrame::DrainSelfPushedFloats() {
+  // If we're getting reflowed multiple times without our
+  // next-continuation being reflowed, we might need to pull back floats
+  // that we just put in the list to be pushed to our next-in-flow.
+  // We don't want to pull back any next-in-flows of floats on our own
+  // float list, and we only need to pull back first-in-flows whose
+  // placeholders were in earlier blocks (since first-in-flows whose
+  // placeholders are in this block will get pulled appropriately by
+  // AddFloat, and will then be more likely to be in the correct order).
+  mozilla::PresShell* presShell = PresShell();
+  nsFrameList* ourPushedFloats = GetPushedFloats();
+  if (ourPushedFloats) {
+    // When we pull back floats, we want to put them with the pushed
+    // floats, which must live at the start of our float list, but we
+    // want them at the end of those pushed floats.
+    // FIXME: This isn't quite right!  What if they're all pushed floats?
+    nsIFrame* insertionPrevSibling = nullptr; /* beginning of list */
+    for (nsIFrame* f = mFloats.FirstChild();
+         f && f->HasAnyStateBits(NS_FRAME_IS_PUSHED_FLOAT);
+         f = f->GetNextSibling()) {
+      insertionPrevSibling = f;
+    }
+
+    nsIFrame* f = ourPushedFloats->LastChild();
+    while (f) {
+      nsIFrame* prevSibling = f->GetPrevSibling();
+
+      nsPlaceholderFrame* placeholder = f->GetPlaceholderFrame();
+      nsIFrame* floatOriginalParent =
+          presShell->FrameConstructor()->GetFloatContainingBlock(placeholder);
+      if (floatOriginalParent != this) {
+        // This is a first continuation that was pushed from one of our
+        // previous continuations.  Take it out of the pushed floats
+        // list and put it in our floats list, before any of our
+        // floats, but after other pushed floats.
+        ourPushedFloats->RemoveFrame(f);
+        mFloats.InsertFrame(nullptr, insertionPrevSibling, f);
+      }
+
+      f = prevSibling;
+    }
+
+    if (ourPushedFloats->IsEmpty()) {
+      RemovePushedFloats()->Delete(presShell);
+    }
+  }
+}
+
+void nsBlockFrame::DrainPushedFloats() {
+  DrainSelfPushedFloats();
+
+  // After our prev-in-flow has completed reflow, it may have a pushed
+  // floats list, containing floats that we need to own.  Take these.
+  nsBlockFrame* prevBlock = static_cast<nsBlockFrame*>(GetPrevInFlow());
+  if (prevBlock) {
+    AutoFrameListPtr list(PresContext(), prevBlock->RemovePushedFloats());
+    if (list && list->NotEmpty()) {
+      mFloats.InsertFrames(this, nullptr, std::move(*list));
+    }
+  }
+}
+
+nsBlockFrame::FrameLines* nsBlockFrame::GetOverflowLines() const {
+  if (!HasOverflowLines()) {
+    return nullptr;
+  }
+  FrameLines* prop = GetProperty(OverflowLinesProperty());
+  NS_ASSERTION(
+      prop && !prop->mLines.empty() &&
+              prop->mLines.front()->GetChildCount() == 0
+          ? prop->mFrames.IsEmpty()
+          : prop->mLines.front()->mFirstChild == prop->mFrames.FirstChild(),
+      "value should always be stored and non-empty when state set");
+  return prop;
+}
+
+nsBlockFrame::FrameLines* nsBlockFrame::RemoveOverflowLines() {
+  if (!HasOverflowLines()) {
+    return nullptr;
+  }
+  FrameLines* prop = TakeProperty(OverflowLinesProperty());
+  NS_ASSERTION(
+      prop && !prop->mLines.empty() &&
+              prop->mLines.front()->GetChildCount() == 0
+          ? prop->mFrames.IsEmpty()
+          : prop->mLines.front()->mFirstChild == prop->mFrames.FirstChild(),
+      "value should always be stored and non-empty when state set");
+  RemoveStateBits(NS_BLOCK_HAS_OVERFLOW_LINES);
+  return prop;
+}
+
+void nsBlockFrame::DestroyOverflowLines() {
+  NS_ASSERTION(HasOverflowLines(), "huh?");
+  FrameLines* prop = TakeProperty(OverflowLinesProperty());
+  NS_ASSERTION(prop && prop->mLines.empty(),
+               "value should always be stored but empty when destroying");
+  RemoveStateBits(NS_BLOCK_HAS_OVERFLOW_LINES);
+  delete prop;
+}
+
+// This takes ownership of aOverflowLines.
+// XXX We should allocate overflowLines from presShell arena!
+void nsBlockFrame::SetOverflowLines(FrameLines* aOverflowLines) {
+  NS_ASSERTION(aOverflowLines, "null lines");
+  NS_ASSERTION(!aOverflowLines->mLines.empty(), "empty lines");
+  NS_ASSERTION(aOverflowLines->mLines.front()->mFirstChild ==
+                   aOverflowLines->mFrames.FirstChild(),
+               "invalid overflow lines / frames");
+  NS_ASSERTION(!HasAnyStateBits(NS_BLOCK_HAS_OVERFLOW_LINES),
+               "Overwriting existing overflow lines");
+
+  // Verify that we won't overwrite an existing overflow list
+  NS_ASSERTION(!GetProperty(OverflowLinesProperty()), "existing overflow list");
+  SetProperty(OverflowLinesProperty(), aOverflowLines);
+  AddStateBits(NS_BLOCK_HAS_OVERFLOW_LINES);
+}
+
+nsFrameList* nsBlockFrame::GetOverflowOutOfFlows() const {
+  if (!HasAnyStateBits(NS_BLOCK_HAS_OVERFLOW_OUT_OF_FLOWS)) {
+    return nullptr;
+  }
+  nsFrameList* result = GetProperty(OverflowOutOfFlowsProperty());
+  NS_ASSERTION(result, "value should always be non-empty when state set");
+  return result;
+}
+
+void nsBlockFrame::SetOverflowOutOfFlows(nsFrameList&& aList,
+                                         nsFrameList* aPropValue) {
+  MOZ_ASSERT(
+      HasAnyStateBits(NS_BLOCK_HAS_OVERFLOW_OUT_OF_FLOWS) == !!aPropValue,
+      "state does not match value");
+
+  if (aList.IsEmpty()) {
+    if (!HasAnyStateBits(NS_BLOCK_HAS_OVERFLOW_OUT_OF_FLOWS)) {
+      return;
+    }
+    nsFrameList* list = TakeProperty(OverflowOutOfFlowsProperty());
+    NS_ASSERTION(aPropValue == list, "prop value mismatch");
+    list->Clear();
+    list->Delete(PresShell());
+    RemoveStateBits(NS_BLOCK_HAS_OVERFLOW_OUT_OF_FLOWS);
+  } else if (HasAnyStateBits(NS_BLOCK_HAS_OVERFLOW_OUT_OF_FLOWS)) {
+    NS_ASSERTION(aPropValue == GetProperty(OverflowOutOfFlowsProperty()),
+                 "prop value mismatch");
+    *aPropValue = std::move(aList);
+  } else {
+    SetProperty(OverflowOutOfFlowsProperty(),
+                new (PresShell()) nsFrameList(std::move(aList)));
+    AddStateBits(NS_BLOCK_HAS_OVERFLOW_OUT_OF_FLOWS);
+  }
+}
+
+nsIFrame* nsBlockFrame::GetInsideMarker() const {
+  if (!HasInsideMarker()) {
+    return nullptr;
+  }
+  NS_ASSERTION(!HasOutsideMarker(), "invalid marker state");
+  nsIFrame* frame = GetProperty(InsideMarkerProperty());
+  NS_ASSERTION(frame, "bogus inside ::marker frame");
+  return frame;
+}
+
+nsIFrame* nsBlockFrame::GetOutsideMarker() const {
+  nsFrameList* list = GetOutsideMarkerList();
+  return list ? list->FirstChild() : nullptr;
+}
+
+nsFrameList* nsBlockFrame::GetOutsideMarkerList() const {
+  if (!HasOutsideMarker()) {
+    return nullptr;
+  }
+  NS_ASSERTION(!HasInsideMarker(), "invalid marker state");
+  nsFrameList* list = GetProperty(OutsideMarkerProperty());
+  NS_ASSERTION(list && list->GetLength() == 1, "bogus outside ::marker list");
+  return list;
+}
+
+nsFrameList* nsBlockFrame::GetPushedFloats() const {
+  if (!HasPushedFloats()) {
+    return nullptr;
+  }
+  nsFrameList* result = GetProperty(PushedFloatProperty());
+  NS_ASSERTION(result, "value should always be non-empty when state set");
+  return result;
+}
+
+nsFrameList* nsBlockFrame::EnsurePushedFloats() {
+  nsFrameList* result = GetPushedFloats();
+  if (result) {
+    return result;
+  }
+
+  result = new (PresShell()) nsFrameList;
+  SetProperty(PushedFloatProperty(), result);
+  AddStateBits(NS_BLOCK_HAS_PUSHED_FLOATS);
+
+  return result;
+}
+
+nsFrameList* nsBlockFrame::RemovePushedFloats() {
+  if (!HasPushedFloats()) {
+    return nullptr;
+  }
+  nsFrameList* result = TakeProperty(PushedFloatProperty());
+  RemoveStateBits(NS_BLOCK_HAS_PUSHED_FLOATS);
+  NS_ASSERTION(result, "value should always be non-empty when state set");
+  return result;
+}
+
+//////////////////////////////////////////////////////////////////////
+// Frame list manipulation routines
+
+void nsBlockFrame::AppendFrames(ChildListID aListID, nsFrameList&& aFrameList) {
+  if (aFrameList.IsEmpty()) {
+    return;
+  }
+  if (aListID != FrameChildListID::Principal) {
+    if (FrameChildListID::Float == aListID) {
+      DrainSelfPushedFloats();  // ensure the last frame is in mFloats
+      mFloats.AppendFrames(nullptr, std::move(aFrameList));
+      return;
+    }
+    MOZ_ASSERT(FrameChildListID::NoReflowPrincipal == aListID,
+               "unexpected child list");
+  }
+
+  // Find the proper last-child for where the append should go
+  nsIFrame* lastKid = mFrames.LastChild();
+  NS_ASSERTION(
+      (mLines.empty() ? nullptr : mLines.back()->LastChild()) == lastKid,
+      "out-of-sync mLines / mFrames");
+
+#ifdef NOISY_REFLOW_REASON
+  ListTag(stdout);
+  printf(": append ");
+  for (nsIFrame* frame : aFrameList) {
+    frame->ListTag(stdout);
+  }
+  if (lastKid) {
+    printf(" after ");
+    lastKid->ListTag(stdout);
+  }
+  printf("\n");
+#endif
+
+  if (IsInSVGTextSubtree()) {
+    MOZ_ASSERT(GetParent()->IsSVGTextFrame(),
+               "unexpected block frame in SVG text");
+    // Workaround for bug 1399425 in case this bit has been removed from the
+    // SVGTextFrame just before the parser adds more descendant nodes.
+    GetParent()->AddStateBits(NS_STATE_SVG_TEXT_CORRESPONDENCE_DIRTY);
+  }
+
+  AddFrames(std::move(aFrameList), lastKid, nullptr);
+  if (aListID != FrameChildListID::NoReflowPrincipal) {
+    PresShell()->FrameNeedsReflow(
+        this, IntrinsicDirty::FrameAndAncestors,
+        NS_FRAME_HAS_DIRTY_CHILDREN);  // XXX sufficient?
+  }
+}
+
+void nsBlockFrame::InsertFrames(ChildListID aListID, nsIFrame* aPrevFrame,
+                                const nsLineList::iterator* aPrevFrameLine,
+                                nsFrameList&& aFrameList) {
+  NS_ASSERTION(!aPrevFrame || aPrevFrame->GetParent() == this,
+               "inserting after sibling frame with different parent");
+
+  if (aListID != FrameChildListID::Principal) {
+    if (FrameChildListID::Float == aListID) {
+      DrainSelfPushedFloats();  // ensure aPrevFrame is in mFloats
+      mFloats.InsertFrames(this, aPrevFrame, std::move(aFrameList));
+      return;
+    }
+    MOZ_ASSERT(FrameChildListID::NoReflowPrincipal == aListID,
+               "unexpected child list");
+  }
+
+#ifdef NOISY_REFLOW_REASON
+  ListTag(stdout);
+  printf(": insert ");
+  for (nsIFrame* frame : aFrameList) {
+    frame->ListTag(stdout);
+  }
+  if (aPrevFrame) {
+    printf(" after ");
+    aPrevFrame->ListTag(stdout);
+  }
+  printf("\n");
+#endif
+
+  AddFrames(std::move(aFrameList), aPrevFrame, aPrevFrameLine);
+  if (aListID != FrameChildListID::NoReflowPrincipal) {
+    PresShell()->FrameNeedsReflow(
+        this, IntrinsicDirty::FrameAndAncestors,
+        NS_FRAME_HAS_DIRTY_CHILDREN);  // XXX sufficient?
+  }
+}
+
+void nsBlockFrame::RemoveFrame(DestroyContext& aContext, ChildListID aListID,
+                               nsIFrame* aOldFrame) {
+#ifdef NOISY_REFLOW_REASON
+  ListTag(stdout);
+  printf(": remove ");
+  aOldFrame->ListTag(stdout);
+  printf("\n");
+#endif
+
+  if (aListID == FrameChildListID::Principal) {
+    bool hasFloats = BlockHasAnyFloats(aOldFrame);
+    DoRemoveFrame(aContext, aOldFrame, REMOVE_FIXED_CONTINUATIONS);
+    if (hasFloats) {
+      MarkSameFloatManagerLinesDirty(this);
+    }
+  } else if (FrameChildListID::Float == aListID) {
+    // Make sure to mark affected lines dirty for the float frame
+    // we are removing; this way is a bit messy, but so is the rest of the code.
+    // See bug 390762.
+    NS_ASSERTION(!aOldFrame->GetPrevContinuation(),
+                 "RemoveFrame should not be called on pushed floats.");
+    for (nsIFrame* f = aOldFrame;
+         f && !f->HasAnyStateBits(NS_FRAME_IS_OVERFLOW_CONTAINER);
+         f = f->GetNextContinuation()) {
+      MarkSameFloatManagerLinesDirty(
+          static_cast<nsBlockFrame*>(f->GetParent()));
+    }
+    DoRemoveOutOfFlowFrame(aContext, aOldFrame);
+  } else if (FrameChildListID::NoReflowPrincipal == aListID) {
+    // Skip the call to |FrameNeedsReflow| below by returning now.
+    DoRemoveFrame(aContext, aOldFrame, REMOVE_FIXED_CONTINUATIONS);
+    return;
+  } else {
+    MOZ_CRASH("unexpected child list");
+  }
+
+  PresShell()->FrameNeedsReflow(
+      this, IntrinsicDirty::FrameAndAncestors,
+      NS_FRAME_HAS_DIRTY_CHILDREN);  // XXX sufficient?
+}
+
+static bool ShouldPutNextSiblingOnNewLine(nsIFrame* aLastFrame) {
+  LayoutFrameType type = aLastFrame->Type();
+  if (type == LayoutFrameType::Br) {
+    return true;
+  }
+  // XXX the TEXT_OFFSETS_NEED_FIXING check is a wallpaper for bug 822910.
+  if (type == LayoutFrameType::Text &&
+      !aLastFrame->HasAnyStateBits(TEXT_OFFSETS_NEED_FIXING)) {
+    return aLastFrame->HasSignificantTerminalNewline();
+  }
+  return false;
+}
+
+void nsBlockFrame::AddFrames(nsFrameList&& aFrameList, nsIFrame* aPrevSibling,
+                             const nsLineList::iterator* aPrevSiblingLine) {
+  // Clear our line cursor, since our lines may change.
+  ClearLineCursors();
+
+  if (aFrameList.IsEmpty()) {
+    return;
+  }
+
+  // Attempt to find the line that contains the previous sibling
+  nsLineList* lineList = &mLines;
+  nsFrameList* frames = &mFrames;
+  nsLineList::iterator prevSibLine;
+  int32_t prevSiblingIndex;
+  if (aPrevSiblingLine) {
+    MOZ_ASSERT(aPrevSibling);
+    prevSibLine = *aPrevSiblingLine;
+    FrameLines* overflowLines = GetOverflowLines();
+    MOZ_ASSERT(prevSibLine.IsInSameList(mLines.begin()) ||
+                   (overflowLines &&
+                    prevSibLine.IsInSameList(overflowLines->mLines.begin())),
+               "must be one of our line lists");
+    if (overflowLines) {
+      // We need to find out which list it's actually in.  Assume that
+      // *if* we have overflow lines, that our primary lines aren't
+      // huge, but our overflow lines might be.
+      nsLineList::iterator line = mLines.begin(), lineEnd = mLines.end();
+      while (line != lineEnd) {
+        if (line == prevSibLine) {
+          break;
+        }
+        ++line;
+      }
+      if (line == lineEnd) {
+        // By elimination, the line must be in our overflow lines.
+        lineList = &overflowLines->mLines;
+        frames = &overflowLines->mFrames;
+      }
+    }
+
+    nsLineList::iterator nextLine = prevSibLine.next();
+    nsIFrame* lastFrameInLine = nextLine == lineList->end()
+                                    ? frames->LastChild()
+                                    : nextLine->mFirstChild->GetPrevSibling();
+    prevSiblingIndex = prevSibLine->RIndexOf(aPrevSibling, lastFrameInLine);
+    MOZ_ASSERT(prevSiblingIndex >= 0,
+               "aPrevSibling must be in aPrevSiblingLine");
+  } else {
+    prevSibLine = lineList->end();
+    prevSiblingIndex = -1;
+    if (aPrevSibling) {
+      // XXX_perf This is technically O(N^2) in some cases, but by using
+      // RFind instead of Find, we make it O(N) in the most common case,
+      // which is appending content.
+
+      // Find the line that contains the previous sibling
+      if (!nsLineBox::RFindLineContaining(aPrevSibling, lineList->begin(),
+                                          prevSibLine, mFrames.LastChild(),
+                                          &prevSiblingIndex)) {
+        // Not in mLines - try overflow lines.
+        FrameLines* overflowLines = GetOverflowLines();
+        bool found = false;
+        if (overflowLines) {
+          prevSibLine = overflowLines->mLines.end();
+          prevSiblingIndex = -1;
+          found = nsLineBox::RFindLineContaining(
+              aPrevSibling, overflowLines->mLines.begin(), prevSibLine,
+              overflowLines->mFrames.LastChild(), &prevSiblingIndex);
+        }
+        if (MOZ_LIKELY(found)) {
+          lineList = &overflowLines->mLines;
+          frames = &overflowLines->mFrames;
+        } else {
+          // Note: defensive code! RFindLineContaining must not return
+          // false in this case, so if it does...
+          MOZ_ASSERT_UNREACHABLE("prev sibling not in line list");
+          aPrevSibling = nullptr;
+          prevSibLine = lineList->end();
+        }
+      }
+    }
+  }
+
+  // Find the frame following aPrevSibling so that we can join up the
+  // two lists of frames.
+  if (aPrevSibling) {
+    // Split line containing aPrevSibling in two if the insertion
+    // point is somewhere in the middle of the line.
+    int32_t rem = prevSibLine->GetChildCount() - prevSiblingIndex - 1;
+    if (rem) {
+      // Split the line in two where the frame(s) are being inserted.
+      nsLineBox* line =
+          NewLineBox(prevSibLine, aPrevSibling->GetNextSibling(), rem);
+      lineList->after_insert(prevSibLine, line);
+      // Mark prevSibLine dirty and as needing textrun invalidation, since
+      // we may be breaking up text in the line. Its previous line may also
+      // need to be invalidated because it may be able to pull some text up.
+      MarkLineDirty(prevSibLine, lineList);
+      // The new line will also need its textruns recomputed because of the
+      // frame changes.
+      line->MarkDirty();
+      line->SetInvalidateTextRuns(true);
+    }
+  } else if (!lineList->empty()) {
+    lineList->front()->MarkDirty();
+    lineList->front()->SetInvalidateTextRuns(true);
+  }
+  const nsFrameList::Slice& newFrames =
+      frames->InsertFrames(nullptr, aPrevSibling, std::move(aFrameList));
+
+  // Walk through the new frames being added and update the line data
+  // structures to fit.
+  for (nsIFrame* newFrame : newFrames) {
+    NS_ASSERTION(!aPrevSibling || aPrevSibling->GetNextSibling() == newFrame,
+                 "Unexpected aPrevSibling");
+    NS_ASSERTION(
+        !newFrame->IsPlaceholderFrame() ||
+            (!newFrame->IsAbsolutelyPositioned() && !newFrame->IsFloating()),
+        "Placeholders should not float or be positioned");
+
+    bool isBlock = newFrame->IsBlockOutside();
+
+    // If the frame is a block frame, or if there is no previous line or if the
+    // previous line is a block line we need to make a new line.  We also make
+    // a new line, as an optimization, in the two cases we know we'll need it:
+    // if the previous line ended with a <br>, or if it has significant
+    // whitespace and ended in a newline.
+    if (isBlock || prevSibLine == lineList->end() || prevSibLine->IsBlock() ||
+        (aPrevSibling && ShouldPutNextSiblingOnNewLine(aPrevSibling))) {
+      // Create a new line for the frame and add its line to the line
+      // list.
+      nsLineBox* line = NewLineBox(newFrame, isBlock);
+      if (prevSibLine != lineList->end()) {
+        // Append new line after prevSibLine
+        lineList->after_insert(prevSibLine, line);
+        ++prevSibLine;
+      } else {
+        // New line is going before the other lines
+        lineList->push_front(line);
+        prevSibLine = lineList->begin();
+      }
+    } else {
+      prevSibLine->NoteFrameAdded(newFrame);
+      // We're adding inline content to prevSibLine, so we need to mark it
+      // dirty, ensure its textruns are recomputed, and possibly do the same
+      // to its previous line since that line may be able to pull content up.
+      MarkLineDirty(prevSibLine, lineList);
+    }
+
+    aPrevSibling = newFrame;
+  }
+
+#ifdef DEBUG
+  MOZ_ASSERT(aFrameList.IsEmpty());
+  VerifyLines(true);
+#endif
+}
+
+nsContainerFrame* nsBlockFrame::GetRubyContentPseudoFrame() {
+  auto* firstChild = PrincipalChildList().FirstChild();
+  if (firstChild && firstChild->IsRubyFrame() &&
+      firstChild->Style()->GetPseudoType() ==
+          mozilla::PseudoStyleType::blockRubyContent) {
+    return static_cast<nsContainerFrame*>(firstChild);
+  }
+  return nullptr;
+}
+
+nsContainerFrame* nsBlockFrame::GetContentInsertionFrame() {
+  // 'display:block ruby' use the inner (Ruby) frame for insertions.
+  if (auto* rubyContentPseudoFrame = GetRubyContentPseudoFrame()) {
+    return rubyContentPseudoFrame;
+  }
+  return this;
+}
+
+void nsBlockFrame::AppendDirectlyOwnedAnonBoxes(
+    nsTArray<OwnedAnonBox>& aResult) {
+  if (auto* rubyContentPseudoFrame = GetRubyContentPseudoFrame()) {
+    aResult.AppendElement(OwnedAnonBox(rubyContentPseudoFrame));
+  }
+}
+
+void nsBlockFrame::RemoveFloatFromFloatCache(nsIFrame* aFloat) {
+  // Find which line contains the float, so we can update
+  // the float cache.
+  for (auto& line : Lines()) {
+    if (line.IsInline() && line.RemoveFloat(aFloat)) {
+      break;
+    }
+  }
+}
+
+void nsBlockFrame::RemoveFloat(nsIFrame* aFloat) {
+#ifdef DEBUG
+  // Floats live in mFloats, or in the PushedFloat or OverflowOutOfFlows
+  // frame list properties.
+  if (!mFloats.ContainsFrame(aFloat)) {
+    MOZ_ASSERT(
+        (GetOverflowOutOfFlows() &&
+         GetOverflowOutOfFlows()->ContainsFrame(aFloat)) ||
+            (GetPushedFloats() && GetPushedFloats()->ContainsFrame(aFloat)),
+        "aFloat is not our child or on an unexpected frame list");
+  }
+#endif
+
+  if (mFloats.StartRemoveFrame(aFloat)) {
+    return;
+  }
+
+  nsFrameList* list = GetPushedFloats();
+  if (list && list->ContinueRemoveFrame(aFloat)) {
+#if 0
+    // XXXmats not yet - need to investigate BlockReflowState::mPushedFloats
+    // first so we don't leave it pointing to a deleted list.
+    if (list->IsEmpty()) {
+      delete RemovePushedFloats();
+    }
+#endif
+    return;
+  }
+
+  {
+    nsAutoOOFFrameList oofs(this);
+    if (oofs.mList.ContinueRemoveFrame(aFloat)) {
+      return;
+    }
+  }
+}
+
+void nsBlockFrame::DoRemoveOutOfFlowFrame(DestroyContext& aContext,
+                                          nsIFrame* aFrame) {
+  // The containing block is always the parent of aFrame.
+  nsBlockFrame* block = (nsBlockFrame*)aFrame->GetParent();
+
+  // Remove aFrame from the appropriate list.
+  if (aFrame->IsAbsolutelyPositioned()) {
+    // This also deletes the next-in-flows
+    block->GetAbsoluteContainingBlock()->RemoveFrame(
+        aContext, FrameChildListID::Absolute, aFrame);
+  } else {
+    // First remove aFrame's next-in-flows.
+    if (nsIFrame* nif = aFrame->GetNextInFlow()) {
+      nif->GetParent()->DeleteNextInFlowChild(aContext, nif, false);
+    }
+    // Now remove aFrame from its child list and Destroy it.
+    block->RemoveFloatFromFloatCache(aFrame);
+    block->RemoveFloat(aFrame);
+    aFrame->Destroy(aContext);
+  }
+}
+
+/**
+ * This helps us iterate over the list of all normal + overflow lines
+ */
+void nsBlockFrame::TryAllLines(nsLineList::iterator* aIterator,
+                               nsLineList::iterator* aStartIterator,
+                               nsLineList::iterator* aEndIterator,
+                               bool* aInOverflowLines,
+                               FrameLines** aOverflowLines) {
+  if (*aIterator == *aEndIterator) {
+    if (!*aInOverflowLines) {
+      // Try the overflow lines
+      *aInOverflowLines = true;
+      FrameLines* lines = GetOverflowLines();
+      if (lines) {
+        *aStartIterator = lines->mLines.begin();
+        *aIterator = *aStartIterator;
+        *aEndIterator = lines->mLines.end();
+        *aOverflowLines = lines;
+      }
+    }
+  }
+}
+
+nsBlockInFlowLineIterator::nsBlockInFlowLineIterator(nsBlockFrame* aFrame,
+                                                     LineIterator aLine)
+    : mFrame(aFrame), mLine(aLine), mLineList(&aFrame->mLines) {
+  // This will assert if aLine isn't in mLines of aFrame:
+  DebugOnly<bool> check = aLine == mFrame->LinesBegin();
+}
+
+nsBlockInFlowLineIterator::nsBlockInFlowLineIterator(nsBlockFrame* aFrame,
+                                                     LineIterator aLine,
+                                                     bool aInOverflow)
+    : mFrame(aFrame),
+      mLine(aLine),
+      mLineList(aInOverflow ? &aFrame->GetOverflowLines()->mLines
+                            : &aFrame->mLines) {}
+
+nsBlockInFlowLineIterator::nsBlockInFlowLineIterator(nsBlockFrame* aFrame,
+                                                     bool* aFoundValidLine)
+    : mFrame(aFrame), mLineList(&aFrame->mLines) {
+  mLine = aFrame->LinesBegin();
+  *aFoundValidLine = FindValidLine();
+}
+
+static bool StyleEstablishesBFC(const ComputedStyle* aStyle) {
+  // paint/layout containment boxes and multi-column containers establish an
+  // independent formatting context.
+  // https://drafts.csswg.org/css-contain/#containment-paint
+  // https://drafts.csswg.org/css-contain/#containment-layout
+  // https://drafts.csswg.org/css-multicol/#columns
+  return aStyle->StyleDisplay()->IsContainPaint() ||
+         aStyle->StyleDisplay()->IsContainLayout() ||
+         aStyle->GetPseudoType() == PseudoStyleType::columnContent;
+}
+
+void nsBlockFrame::DidSetComputedStyle(ComputedStyle* aOldStyle) {
+  nsContainerFrame::DidSetComputedStyle(aOldStyle);
+  if (!aOldStyle) {
+    return;
+  }
+
+  // If NS_BLOCK_STATIC_BFC flag was set when the frame was initialized, it
+  // remains set during the lifetime of the frame and always forces it to be
+  // treated as a BFC, independently of the value of NS_BLOCK_DYNAMIC_BFC.
+  // Consequently, we don't bother invalidating or updating that latter flag.
+  if (HasAnyStateBits(NS_BLOCK_STATIC_BFC)) {
+    return;
+  }
+
+  bool isBFC = StyleEstablishesBFC(Style());
+  if (StyleEstablishesBFC(aOldStyle) != isBFC) {
+    if (MaybeHasFloats()) {
+      // If the frame contains floats, this update may change their float
+      // manager. Be safe by dirtying all descendant lines of the nearest
+      // ancestor's float manager.
+      RemoveStateBits(NS_BLOCK_DYNAMIC_BFC);
+      MarkSameFloatManagerLinesDirty(this);
+    }
+    AddOrRemoveStateBits(NS_BLOCK_DYNAMIC_BFC, isBFC);
+  }
+}
+
+void nsBlockFrame::UpdateFirstLetterStyle(ServoRestyleState& aRestyleState) {
+  nsIFrame* letterFrame = GetFirstLetter();
+  if (!letterFrame) {
+    return;
+  }
+
+  // Figure out what the right style parent is.  This needs to match
+  // nsCSSFrameConstructor::CreateLetterFrame.
+  nsIFrame* inFlowFrame = letterFrame;
+  if (inFlowFrame->HasAnyStateBits(NS_FRAME_OUT_OF_FLOW)) {
+    inFlowFrame = inFlowFrame->GetPlaceholderFrame();
+  }
+  nsIFrame* styleParent = CorrectStyleParentFrame(inFlowFrame->GetParent(),
+                                                  PseudoStyleType::firstLetter);
+  ComputedStyle* parentStyle = styleParent->Style();
+  RefPtr<ComputedStyle> firstLetterStyle =
+      aRestyleState.StyleSet().ResolvePseudoElementStyle(
+          *mContent->AsElement(), PseudoStyleType::firstLetter, nullptr,
+          parentStyle);
+  // Note that we don't need to worry about changehints for the continuation
+  // styles: those will be handled by the styleParent already.
+  RefPtr<ComputedStyle> continuationStyle =
+      aRestyleState.StyleSet().ResolveStyleForFirstLetterContinuation(
+          parentStyle);
+  UpdateStyleOfOwnedChildFrame(letterFrame, firstLetterStyle, aRestyleState,
+                               Some(continuationStyle.get()));
+
+  // We also want to update the style on the textframe inside the first-letter.
+  // We don't need to compute a changehint for this, though, since any changes
+  // to it are handled by the first-letter anyway.
+  nsIFrame* textFrame = letterFrame->PrincipalChildList().FirstChild();
+  RefPtr<ComputedStyle> firstTextStyle =
+      aRestyleState.StyleSet().ResolveStyleForText(textFrame->GetContent(),
+                                                   firstLetterStyle);
+  textFrame->SetComputedStyle(firstTextStyle);
+
+  // We don't need to update style for textFrame's continuations: it's already
+  // set up to inherit from parentStyle, which is what we want.
+}
+
+static nsIFrame* FindChildContaining(nsBlockFrame* aFrame,
+                                     nsIFrame* aFindFrame) {
+  NS_ASSERTION(aFrame, "must have frame");
+  nsIFrame* child;
+  while (true) {
+    nsIFrame* block = aFrame;
+    do {
+      child = nsLayoutUtils::FindChildContainingDescendant(block, aFindFrame);
+      if (child) {
+        break;
+      }
+      block = block->GetNextContinuation();
+    } while (block);
+    if (!child) {
+      return nullptr;
+    }
+    if (!child->HasAnyStateBits(NS_FRAME_OUT_OF_FLOW)) {
+      break;
+    }
+    aFindFrame = child->GetPlaceholderFrame();
+  }
+
+  return child;
+}
+
+nsBlockInFlowLineIterator::nsBlockInFlowLineIterator(nsBlockFrame* aFrame,
+                                                     nsIFrame* aFindFrame,
+                                                     bool* aFoundValidLine)
+    : mFrame(aFrame), mLineList(&aFrame->mLines) {
+  *aFoundValidLine = false;
+
+  nsIFrame* child = FindChildContaining(aFrame, aFindFrame);
+  if (!child) {
+    return;
+  }
+
+  LineIterator line_end = aFrame->LinesEnd();
+  mLine = aFrame->LinesBegin();
+  if (mLine != line_end && mLine.next() == line_end &&
+      !aFrame->HasOverflowLines()) {
+    // The block has a single line - that must be it!
+    *aFoundValidLine = true;
+    return;
+  }
+
+  // Try to use the cursor if it exists, otherwise fall back to the first line
+  if (nsLineBox* const cursor = aFrame->GetLineCursorForQuery()) {
+    mLine = line_end;
+    // Perform a simultaneous forward and reverse search starting from the
+    // line cursor.
+    nsBlockFrame::LineIterator line = aFrame->LinesBeginFrom(cursor);
+    nsBlockFrame::ReverseLineIterator rline = aFrame->LinesRBeginFrom(cursor);
+    nsBlockFrame::ReverseLineIterator rline_end = aFrame->LinesREnd();
+    // rline is positioned on the line containing 'cursor', so it's not
+    // rline_end. So we can safely increment it (i.e. move it to one line
+    // earlier) to start searching there.
+    ++rline;
+    while (line != line_end || rline != rline_end) {
+      if (line != line_end) {
+        if (line->Contains(child)) {
+          mLine = line;
+          break;
+        }
+        ++line;
+      }
+      if (rline != rline_end) {
+        if (rline->Contains(child)) {
+          mLine = rline;
+          break;
+        }
+        ++rline;
+      }
+    }
+    if (mLine != line_end) {
+      *aFoundValidLine = true;
+      if (mLine != cursor) {
+        aFrame->SetProperty(nsBlockFrame::LineCursorPropertyQuery(), mLine);
+      }
+      return;
+    }
+  } else {
+    for (mLine = aFrame->LinesBegin(); mLine != line_end; ++mLine) {
+      if (mLine->Contains(child)) {
+        *aFoundValidLine = true;
+        return;
+      }
+    }
+  }
+  // Didn't find the line
+  MOZ_ASSERT(mLine == line_end, "mLine should be line_end at this point");
+
+  // If we reach here, it means that we have not been able to find the
+  // desired frame in our in-flow lines.  So we should start looking at
+  // our overflow lines. In order to do that, we set mLine to the end
+  // iterator so that FindValidLine starts to look at overflow lines,
+  // if any.
+
+  if (!FindValidLine()) {
+    return;
+  }
+
+  do {
+    if (mLine->Contains(child)) {
+      *aFoundValidLine = true;
+      return;
+    }
+  } while (Next());
+}
+
+nsBlockFrame::LineIterator nsBlockInFlowLineIterator::End() {
+  return mLineList->end();
+}
+
+bool nsBlockInFlowLineIterator::IsLastLineInList() {
+  LineIterator end = End();
+  return mLine != end && mLine.next() == end;
+}
+
+bool nsBlockInFlowLineIterator::Next() {
+  ++mLine;
+  return FindValidLine();
+}
+
+bool nsBlockInFlowLineIterator::Prev() {
+  LineIterator begin = mLineList->begin();
+  if (mLine != begin) {
+    --mLine;
+    return true;
+  }
+  bool currentlyInOverflowLines = GetInOverflow();
+  while (true) {
+    if (currentlyInOverflowLines) {
+      mLineList = &mFrame->mLines;
+      mLine = mLineList->end();
+      if (mLine != mLineList->begin()) {
+        --mLine;
+        return true;
+      }
+    } else {
+      mFrame = static_cast<nsBlockFrame*>(mFrame->GetPrevInFlow());
+      if (!mFrame) {
+        return false;
+      }
+      nsBlockFrame::FrameLines* overflowLines = mFrame->GetOverflowLines();
+      if (overflowLines) {
+        mLineList = &overflowLines->mLines;
+        mLine = mLineList->end();
+        NS_ASSERTION(mLine != mLineList->begin(), "empty overflow line list?");
+        --mLine;
+        return true;
+      }
+    }
+    currentlyInOverflowLines = !currentlyInOverflowLines;
+  }
+}
+
+bool nsBlockInFlowLineIterator::FindValidLine() {
+  LineIterator end = mLineList->end();
+  if (mLine != end) {
+    return true;
+  }
+  bool currentlyInOverflowLines = GetInOverflow();
+  while (true) {
+    if (currentlyInOverflowLines) {
+      mFrame = static_cast<nsBlockFrame*>(mFrame->GetNextInFlow());
+      if (!mFrame) {
+        return false;
+      }
+      mLineList = &mFrame->mLines;
+      mLine = mLineList->begin();
+      if (mLine != mLineList->end()) {
+        return true;
+      }
+    } else {
+      nsBlockFrame::FrameLines* overflowLines = mFrame->GetOverflowLines();
+      if (overflowLines) {
+        mLineList = &overflowLines->mLines;
+        mLine = mLineList->begin();
+        NS_ASSERTION(mLine != mLineList->end(), "empty overflow line list?");
+        return true;
+      }
+    }
+    currentlyInOverflowLines = !currentlyInOverflowLines;
+  }
+}
+
+// This function removes aDeletedFrame and all its continuations.  It
+// is optimized for deleting a whole series of frames. The easy
+// implementation would invoke itself recursively on
+// aDeletedFrame->GetNextContinuation, then locate the line containing
+// aDeletedFrame and remove aDeletedFrame from that line. But here we
+// start by locating aDeletedFrame and then scanning from that point
+// on looking for continuations.
+void nsBlockFrame::DoRemoveFrame(DestroyContext& aContext,
+                                 nsIFrame* aDeletedFrame, uint32_t aFlags) {
+  // Clear our line cursor, since our lines may change.
+  ClearLineCursors();
+
+  if (aDeletedFrame->HasAnyStateBits(NS_FRAME_OUT_OF_FLOW |
+                                     NS_FRAME_IS_OVERFLOW_CONTAINER)) {
+    if (!aDeletedFrame->GetPrevInFlow()) {
+      NS_ASSERTION(aDeletedFrame->HasAnyStateBits(NS_FRAME_OUT_OF_FLOW),
+                   "Expected out-of-flow frame");
+      DoRemoveOutOfFlowFrame(aContext, aDeletedFrame);
+    } else {
+      // FIXME(emilio): aContext is lost here, maybe it's not a big deal?
+      nsContainerFrame::DeleteNextInFlowChild(aContext, aDeletedFrame,
+                                              (aFlags & FRAMES_ARE_EMPTY) != 0);
+    }
+    return;
+  }
+
+  // Find the line that contains deletedFrame
+  nsLineList::iterator line_start = mLines.begin(), line_end = mLines.end();
+  nsLineList::iterator line = line_start;
+  FrameLines* overflowLines = nullptr;
+  bool searchingOverflowList = false;
+  // Make sure we look in the overflow lines even if the normal line
+  // list is empty
+  TryAllLines(&line, &line_start, &line_end, &searchingOverflowList,
+              &overflowLines);
+  while (line != line_end) {
+    if (line->Contains(aDeletedFrame)) {
+      break;
+    }
+    ++line;
+    TryAllLines(&line, &line_start, &line_end, &searchingOverflowList,
+                &overflowLines);
+  }
+
+  if (line == line_end) {
+    NS_ERROR("can't find deleted frame in lines");
+    return;
+  }
+
+  if (!(aFlags & FRAMES_ARE_EMPTY)) {
+    if (line != line_start) {
+      line.prev()->MarkDirty();
+      line.prev()->SetInvalidateTextRuns(true);
+    } else if (searchingOverflowList && !mLines.empty()) {
+      mLines.back()->MarkDirty();
+      mLines.back()->SetInvalidateTextRuns(true);
+    }
+  }
+
+  while (line != line_end && aDeletedFrame) {
+    MOZ_ASSERT(this == aDeletedFrame->GetParent(), "messed up delete code");
+    MOZ_ASSERT(line->Contains(aDeletedFrame), "frame not in line");
+
+    if (!(aFlags & FRAMES_ARE_EMPTY)) {
+      line->MarkDirty();
+      line->SetInvalidateTextRuns(true);
+    }
+
+    // If the frame being deleted is the last one on the line then
+    // optimize away the line->Contains(next-in-flow) call below.
+    bool isLastFrameOnLine = 1 == line->GetChildCount();
+    if (!isLastFrameOnLine) {
+      LineIterator next = line.next();
+      nsIFrame* lastFrame =
+          next != line_end
+              ? next->mFirstChild->GetPrevSibling()
+              : (searchingOverflowList ? overflowLines->mFrames.LastChild()
+                                       : mFrames.LastChild());
+      NS_ASSERTION(next == line_end || lastFrame == line->LastChild(),
+                   "unexpected line frames");
+      isLastFrameOnLine = lastFrame == aDeletedFrame;
+    }
+
+    // Remove aDeletedFrame from the line
+    if (line->mFirstChild == aDeletedFrame) {
+      // We should be setting this to null if aDeletedFrame
+      // is the only frame on the line. HOWEVER in that case
+      // we will be removing the line anyway, see below.
+      line->mFirstChild = aDeletedFrame->GetNextSibling();
+    }
+
+    // Hmm, this won't do anything if we're removing a frame in the first
+    // overflow line... Hopefully doesn't matter
+    --line;
+    if (line != line_end && !line->IsBlock()) {
+      // Since we just removed a frame that follows some inline
+      // frames, we need to reflow the previous line.
+      line->MarkDirty();
+    }
+    ++line;
+
+    // Take aDeletedFrame out of the sibling list. Note that
+    // prevSibling will only be nullptr when we are deleting the very
+    // first frame in the main or overflow list.
+    if (searchingOverflowList) {
+      overflowLines->mFrames.RemoveFrame(aDeletedFrame);
+    } else {
+      mFrames.RemoveFrame(aDeletedFrame);
+    }
+
+    // Update the child count of the line to be accurate
+    line->NoteFrameRemoved(aDeletedFrame);
+
+    // Destroy frame; capture its next continuation first in case we need
+    // to destroy that too.
+    nsIFrame* deletedNextContinuation =
+        (aFlags & REMOVE_FIXED_CONTINUATIONS)
+            ? aDeletedFrame->GetNextContinuation()
+            : aDeletedFrame->GetNextInFlow();
+#ifdef NOISY_REMOVE_FRAME
+    printf("DoRemoveFrame: %s line=%p frame=",
+           searchingOverflowList ? "overflow" : "normal", line.get());
+    aDeletedFrame->ListTag(stdout);
+    printf(" prevSibling=%p deletedNextContinuation=%p\n",
+           aDeletedFrame->GetPrevSibling(), deletedNextContinuation);
+#endif
+
+    // If next-in-flow is an overflow container, must remove it first.
+    // FIXME: Can we do this unconditionally?
+    if (deletedNextContinuation && deletedNextContinuation->HasAnyStateBits(
+                                       NS_FRAME_IS_OVERFLOW_CONTAINER)) {
+      deletedNextContinuation->GetParent()->DeleteNextInFlowChild(
+          aContext, deletedNextContinuation, false);
+      deletedNextContinuation = nullptr;
+    }
+
+    aDeletedFrame->Destroy(aContext);
+    aDeletedFrame = deletedNextContinuation;
+
+    bool haveAdvancedToNextLine = false;
+    // If line is empty, remove it now.
+    if (0 == line->GetChildCount()) {
+#ifdef NOISY_REMOVE_FRAME
+      printf("DoRemoveFrame: %s line=%p became empty so it will be removed\n",
+             searchingOverflowList ? "overflow" : "normal", line.get());
+#endif
+      nsLineBox* cur = line;
+      if (!searchingOverflowList) {
+        line = mLines.erase(line);
+        // Invalidate the space taken up by the line.
+        // XXX We need to do this if we're removing a frame as a result of
+        // a call to RemoveFrame(), but we may not need to do this in all
+        // cases...
+#ifdef NOISY_BLOCK_INVALIDATE
+        nsRect inkOverflow(cur->InkOverflowRect());
+        printf("%p invalidate 10 (%d, %d, %d, %d)\n", this, inkOverflow.x,
+               inkOverflow.y, inkOverflow.width, inkOverflow.height);
+#endif
+      } else {
+        line = overflowLines->mLines.erase(line);
+        if (overflowLines->mLines.empty()) {
+          DestroyOverflowLines();
+          overflowLines = nullptr;
+          // We just invalidated our iterators.  Since we were in
+          // the overflow lines list, which is now empty, set them
+          // so we're at the end of the regular line list.
+          line_start = mLines.begin();
+          line_end = mLines.end();
+          line = line_end;
+        }
+      }
+      FreeLineBox(cur);
+
+      // If we're removing a line, ReflowDirtyLines isn't going to
+      // know that it needs to slide lines unless something is marked
+      // dirty.  So mark the previous margin of the next line dirty if
+      // there is one.
+      if (line != line_end) {
+        line->MarkPreviousMarginDirty();
+      }
+      haveAdvancedToNextLine = true;
+    } else {
+      // Make the line that just lost a frame dirty, and advance to
+      // the next line.
+      if (!deletedNextContinuation || isLastFrameOnLine ||
+          !line->Contains(deletedNextContinuation)) {
+        line->MarkDirty();
+        ++line;
+        haveAdvancedToNextLine = true;
+      }
+    }
+
+    if (deletedNextContinuation) {
+      // See if we should keep looking in the current flow's line list.
+      if (deletedNextContinuation->GetParent() != this) {
+        // The deceased frames continuation is not a child of the
+        // current block. So break out of the loop so that we advance
+        // to the next parent.
+        //
+        // If we have a continuation in a different block then all bets are
+        // off regarding whether we are deleting frames without actual content,
+        // so don't propagate FRAMES_ARE_EMPTY any further.
+        aFlags &= ~FRAMES_ARE_EMPTY;
+        break;
+      }
+
+      // If we advanced to the next line then check if we should switch to the
+      // overflow line list.
+      if (haveAdvancedToNextLine) {
+        if (line != line_end && !searchingOverflowList &&
+            !line->Contains(deletedNextContinuation)) {
+          // We have advanced to the next *normal* line but the next-in-flow
+          // is not there - force a switch to the overflow line list.
+          line = line_end;
+        }
+
+        TryAllLines(&line, &line_start, &line_end, &searchingOverflowList,
+                    &overflowLines);
+#ifdef NOISY_REMOVE_FRAME
+        printf("DoRemoveFrame: now on %s line=%p\n",
+               searchingOverflowList ? "overflow" : "normal", line.get());
+#endif
+      }
+    }
+  }
+
+  if (!(aFlags & FRAMES_ARE_EMPTY) && line.next() != line_end) {
+    line.next()->MarkDirty();
+    line.next()->SetInvalidateTextRuns(true);
+  }
+
+#ifdef DEBUG
+  VerifyLines(true);
+  VerifyOverflowSituation();
+#endif
+
+  // Advance to next flow block if the frame has more continuations.
+  if (!aDeletedFrame) {
+    return;
+  }
+  nsBlockFrame* nextBlock = do_QueryFrame(aDeletedFrame->GetParent());
+  NS_ASSERTION(nextBlock, "Our child's continuation's parent is not a block?");
+  uint32_t flags = (aFlags & REMOVE_FIXED_CONTINUATIONS);
+  nextBlock->DoRemoveFrame(aContext, aDeletedFrame, flags);
+}
+
+static bool FindBlockLineFor(nsIFrame* aChild, nsLineList::iterator aBegin,
+                             nsLineList::iterator aEnd,
+                             nsLineList::iterator* aResult) {
+  MOZ_ASSERT(aChild->IsBlockOutside());
+  for (nsLineList::iterator line = aBegin; line != aEnd; ++line) {
+    MOZ_ASSERT(line->GetChildCount() > 0);
+    if (line->IsBlock() && line->mFirstChild == aChild) {
+      MOZ_ASSERT(line->GetChildCount() == 1);
+      *aResult = line;
+      return true;
+    }
+  }
+  return false;
+}
+
+static bool FindInlineLineFor(nsIFrame* aChild, const nsFrameList& aFrameList,
+                              nsLineList::iterator aBegin,
+                              nsLineList::iterator aEnd,
+                              nsLineList::iterator* aResult) {
+  MOZ_ASSERT(!aChild->IsBlockOutside());
+  for (nsLineList::iterator line = aBegin; line != aEnd; ++line) {
+    MOZ_ASSERT(line->GetChildCount() > 0);
+    if (!line->IsBlock()) {
+      // Optimize by comparing the line's last child first.
+      nsLineList::iterator next = line.next();
+      if (aChild == (next == aEnd ? aFrameList.LastChild()
+                                  : next->mFirstChild->GetPrevSibling()) ||
+          line->Contains(aChild)) {
+        *aResult = line;
+        return true;
+      }
+    }
+  }
+  return false;
+}
+
+static bool FindLineFor(nsIFrame* aChild, const nsFrameList& aFrameList,
+                        nsLineList::iterator aBegin, nsLineList::iterator aEnd,
+                        nsLineList::iterator* aResult) {
+  return aChild->IsBlockOutside()
+             ? FindBlockLineFor(aChild, aBegin, aEnd, aResult)
+             : FindInlineLineFor(aChild, aFrameList, aBegin, aEnd, aResult);
+}
+
+void nsBlockFrame::StealFrame(nsIFrame* aChild) {
+  MOZ_ASSERT(aChild->GetParent() == this);
+
+  if (aChild->IsFloating()) {
+    RemoveFloat(aChild);
+    return;
+  }
+
+  if (MaybeStealOverflowContainerFrame(aChild)) {
+    return;
+  }
+
+  MOZ_ASSERT(!aChild->HasAnyStateBits(NS_FRAME_OUT_OF_FLOW));
+
+  nsLineList::iterator line;
+  if (FindLineFor(aChild, mFrames, mLines.begin(), mLines.end(), &line)) {
+    RemoveFrameFromLine(aChild, line, mFrames, mLines);
+  } else {
+    FrameLines* overflowLines = GetOverflowLines();
+    DebugOnly<bool> found;
+    found = FindLineFor(aChild, overflowLines->mFrames,
+                        overflowLines->mLines.begin(),
+                        overflowLines->mLines.end(), &line);
+    MOZ_ASSERT(found, "Why can't we find aChild in our overflow lines?");
+    RemoveFrameFromLine(aChild, line, overflowLines->mFrames,
+                        overflowLines->mLines);
+    if (overflowLines->mLines.empty()) {
+      DestroyOverflowLines();
+    }
+  }
+}
+
+void nsBlockFrame::RemoveFrameFromLine(nsIFrame* aChild,
+                                       nsLineList::iterator aLine,
+                                       nsFrameList& aFrameList,
+                                       nsLineList& aLineList) {
+  aFrameList.RemoveFrame(aChild);
+  if (aChild == aLine->mFirstChild) {
+    aLine->mFirstChild = aChild->GetNextSibling();
+  }
+  aLine->NoteFrameRemoved(aChild);
+  if (aLine->GetChildCount() > 0) {
+    aLine->MarkDirty();
+  } else {
+    // The line became empty - destroy it.
+    nsLineBox* lineBox = aLine;
+    aLine = aLineList.erase(aLine);
+    if (aLine != aLineList.end()) {
+      aLine->MarkPreviousMarginDirty();
+    }
+    FreeLineBox(lineBox);
+  }
+}
+
+void nsBlockFrame::DeleteNextInFlowChild(DestroyContext& aContext,
+                                         nsIFrame* aNextInFlow,
+                                         bool aDeletingEmptyFrames) {
+  MOZ_ASSERT(aNextInFlow->GetPrevInFlow(), "bad next-in-flow");
+
+  if (aNextInFlow->HasAnyStateBits(NS_FRAME_OUT_OF_FLOW |
+                                   NS_FRAME_IS_OVERFLOW_CONTAINER)) {
+    nsContainerFrame::DeleteNextInFlowChild(aContext, aNextInFlow,
+                                            aDeletingEmptyFrames);
+  } else {
+#ifdef DEBUG
+    if (aDeletingEmptyFrames) {
+      nsLayoutUtils::AssertTreeOnlyEmptyNextInFlows(aNextInFlow);
+    }
+#endif
+    DoRemoveFrame(aContext, aNextInFlow,
+                  aDeletingEmptyFrames ? FRAMES_ARE_EMPTY : 0);
+  }
+}
+
+const nsStyleText* nsBlockFrame::StyleTextForLineLayout() {
+  // Return the pointer to an unmodified style text
+  return StyleText();
+}
+
+void nsBlockFrame::ReflowFloat(BlockReflowState& aState, ReflowInput& aFloatRI,
+                               nsIFrame* aFloat,
+                               nsReflowStatus& aReflowStatus) {
+  MOZ_ASSERT(aReflowStatus.IsEmpty(),
+             "Caller should pass a fresh reflow status!");
+  MOZ_ASSERT(aFloat->HasAnyStateBits(NS_FRAME_OUT_OF_FLOW),
+             "aFloat must be an out-of-flow frame");
+
+  WritingMode wm = aState.mReflowInput.GetWritingMode();
+
+  // Setup a block reflow context to reflow the float.
+  nsBlockReflowContext brc(aState.mPresContext, aState.mReflowInput);
+
+  nsIFrame* clearanceFrame = nullptr;
+  do {
+    nsCollapsingMargin margin;
+    bool mayNeedRetry = false;
+    aFloatRI.mDiscoveredClearance = nullptr;
+    // Only first in flow gets a block-start margin.
+    if (!aFloat->GetPrevInFlow()) {
+      brc.ComputeCollapsedBStartMargin(aFloatRI, &margin, clearanceFrame,
+                                       &mayNeedRetry);
+
+      if (mayNeedRetry && !clearanceFrame) {
+        aFloatRI.mDiscoveredClearance = &clearanceFrame;
+        // We don't need to push the float manager state because the the block
+        // has its own float manager that will be destroyed and recreated
+      }
+    }
+
+    // When reflowing a float, aSpace argument doesn't matter because we pass
+    // nullptr to aLine and we don't call nsBlockReflowContext::PlaceBlock()
+    // later.
+    brc.ReflowBlock(LogicalRect(wm), true, margin, 0, nullptr, aFloatRI,
+                    aReflowStatus, aState);
+  } while (clearanceFrame);
+
+  if (aFloat->IsLetterFrame()) {
+    // We never split floating first letters; an incomplete status for such
+    // frames simply means that there is more content to be reflowed on the
+    // line.
+    if (aReflowStatus.IsIncomplete()) {
+      aReflowStatus.Reset();
+    }
+  }
+
+  NS_ASSERTION(aReflowStatus.IsFullyComplete() ||
+                   aFloatRI.AvailableBSize() != NS_UNCONSTRAINEDSIZE,
+               "The status can only be incomplete or overflow-incomplete if "
+               "the available block-size is constrained!");
+
+  if (aReflowStatus.NextInFlowNeedsReflow()) {
+    aState.mReflowStatus.SetNextInFlowNeedsReflow();
+  }
+
+  const ReflowOutput& metrics = brc.GetMetrics();
+
+  // Set the rect, make sure the view is properly sized and positioned,
+  // and tell the frame we're done reflowing it
+  // XXXldb This seems like the wrong place to be doing this -- shouldn't
+  // we be doing this in BlockReflowState::FlowAndPlaceFloat after
+  // we've positioned the float, and shouldn't we be doing the equivalent
+  // of |PlaceFrameView| here?
+  WritingMode metricsWM = metrics.GetWritingMode();
+  aFloat->SetSize(metricsWM, metrics.Size(metricsWM));
+  if (aFloat->HasView()) {
+    nsContainerFrame::SyncFrameViewAfterReflow(
+        aState.mPresContext, aFloat, aFloat->GetView(), metrics.InkOverflow(),
+        ReflowChildFlags::NoMoveView);
+  }
+  aFloat->DidReflow(aState.mPresContext, &aFloatRI);
+}
+
+StyleClear nsBlockFrame::FindTrailingClear() {
+  for (nsBlockFrame* b = this; b;
+       b = static_cast<nsBlockFrame*>(b->GetPrevInFlow())) {
+    auto endLine = b->LinesRBegin();
+    if (endLine != b->LinesREnd()) {
+      return endLine->FloatClearTypeAfter();
+    }
+  }
+  return StyleClear::None;
+}
+
+void nsBlockFrame::ReflowPushedFloats(BlockReflowState& aState,
+                                      OverflowAreas& aOverflowAreas) {
+  // Pushed floats live at the start of our float list; see comment
+  // above nsBlockFrame::DrainPushedFloats.
+  nsIFrame* f = mFloats.FirstChild();
+  nsIFrame* prev = nullptr;
+  while (f && f->HasAnyStateBits(NS_FRAME_IS_PUSHED_FLOAT)) {
+    MOZ_ASSERT(prev == f->GetPrevSibling());
+    // When we push a first-continuation float in a non-initial reflow,
+    // it's possible that we end up with two continuations with the same
+    // parent.  This happens if, on the previous reflow of the block or
+    // a previous reflow of the line containing the block, the float was
+    // split between continuations A and B of the parent, but on the
+    // current reflow, none of the float can fit in A.
+    //
+    // When this happens, we might even have the two continuations
+    // out-of-order due to the management of the pushed floats.  In
+    // particular, if the float's placeholder was in a pushed line that
+    // we reflowed before it was pushed, and we split the float during
+    // that reflow, we might have the continuation of the float before
+    // the float itself.  (In the general case, however, it's correct
+    // for floats in the pushed floats list to come before floats
+    // anchored in pushed lines; however, in this case it's wrong.  We
+    // should probably find a way to fix it somehow, since it leads to
+    // incorrect layout in some cases.)
+    //
+    // When we have these out-of-order continuations, we might hit the
+    // next-continuation before the previous-continuation.  When that
+    // happens, just push it.  When we reflow the next continuation,
+    // we'll either pull all of its content back and destroy it (by
+    // calling DeleteNextInFlowChild), or nsBlockFrame::SplitFloat will
+    // pull it out of its current position and push it again (and
+    // potentially repeat this cycle for the next continuation, although
+    // hopefully then they'll be in the right order).
+    //
+    // We should also need this code for the in-order case if the first
+    // continuation of a float gets moved across more than one
+    // continuation of the containing block.  In this case we'd manage
+    // to push the second continuation without this check, but not the
+    // third and later.
+    nsIFrame* prevContinuation = f->GetPrevContinuation();
+    if (prevContinuation && prevContinuation->GetParent() == f->GetParent()) {
+      mFloats.RemoveFrame(f);
+      aState.AppendPushedFloatChain(f);
+      f = !prev ? mFloats.FirstChild() : prev->GetNextSibling();
+      continue;
+    }
+
+    // Always call FlowAndPlaceFloat; we might need to place this float if it
+    // didn't belong to this block the last time it was reflowed.  Note that if
+    // the float doesn't get placed, we don't consider its overflow areas.
+    // (Not-getting-placed means it didn't fit and we pushed it instead of
+    // placing it, and its position could be stale.)
+    if (aState.FlowAndPlaceFloat(f) ==
+        BlockReflowState::PlaceFloatResult::Placed) {
+      ConsiderChildOverflow(aOverflowAreas, f);
+    }
+
+    nsIFrame* next = !prev ? mFloats.FirstChild() : prev->GetNextSibling();
+    if (next == f) {
+      // We didn't push |f| so its next-sibling is next.
+      next = f->GetNextSibling();
+      prev = f;
+    }  // else: we did push |f| so |prev|'s new next-sibling is next.
+    f = next;
+  }
+
+  // If there are pushed or split floats, then we may need to continue BR
+  // clearance
+  if (auto [bCoord, result] = aState.ClearFloats(0, StyleClear::Both);
+      result != ClearFloatsResult::BCoordNoChange) {
+    Unused << bCoord;
+    if (auto* prevBlock = static_cast<nsBlockFrame*>(GetPrevInFlow())) {
+      aState.mTrailingClearFromPIF = prevBlock->FindTrailingClear();
+    }
+  }
+}
+
+void nsBlockFrame::RecoverFloats(nsFloatManager& aFloatManager, WritingMode aWM,
+                                 const nsSize& aContainerSize) {
+  // Recover our own floats
+  nsIFrame* stop = nullptr;  // Stop before we reach pushed floats that
+                             // belong to our next-in-flow
+  for (nsIFrame* f = mFloats.FirstChild(); f && f != stop;
+       f = f->GetNextSibling()) {
+    LogicalRect region = nsFloatManager::GetRegionFor(aWM, f, aContainerSize);
+    aFloatManager.AddFloat(f, region, aWM, aContainerSize);
+    if (!stop && f->GetNextInFlow()) {
+      stop = f->GetNextInFlow();
+    }
+  }
+
+  // Recurse into our overflow container children
+  for (nsIFrame* oc =
+           GetChildList(FrameChildListID::OverflowContainers).FirstChild();
+       oc; oc = oc->GetNextSibling()) {
+    RecoverFloatsFor(oc, aFloatManager, aWM, aContainerSize);
+  }
+
+  // Recurse into our normal children
+  for (const auto& line : Lines()) {
+    if (line.IsBlock()) {
+      RecoverFloatsFor(line.mFirstChild, aFloatManager, aWM, aContainerSize);
+    }
+  }
+}
+
+void nsBlockFrame::RecoverFloatsFor(nsIFrame* aFrame,
+                                    nsFloatManager& aFloatManager,
+                                    WritingMode aWM,
+                                    const nsSize& aContainerSize) {
+  MOZ_ASSERT(aFrame, "null frame");
+
+  // Only blocks have floats
+  nsBlockFrame* block = do_QueryFrame(aFrame);
+  // Don't recover any state inside a block that has its own float manager
+  // (we don't currently have any blocks like this, though, thanks to our
+  // use of extra frames for 'overflow')
+  if (block && !nsBlockFrame::BlockNeedsFloatManager(block)) {
+    // If the element is relatively positioned, then adjust x and y
+    // accordingly so that we consider relatively positioned frames
+    // at their original position.
+
+    const LogicalRect rect = block->GetLogicalNormalRect(aWM, aContainerSize);
+    nscoord lineLeft = rect.LineLeft(aWM, aContainerSize);
+    nscoord blockStart = rect.BStart(aWM);
+    aFloatManager.Translate(lineLeft, blockStart);
+    block->RecoverFloats(aFloatManager, aWM, aContainerSize);
+    aFloatManager.Translate(-lineLeft, -blockStart);
+  }
+}
+
+bool nsBlockFrame::HasPushedFloatsFromPrevContinuation() const {
+  if (!mFloats.IsEmpty()) {
+    // If we have pushed floats, then they should be at the beginning of our
+    // float list.
+    if (mFloats.FirstChild()->HasAnyStateBits(NS_FRAME_IS_PUSHED_FLOAT)) {
+      return true;
+    }
+  }
+
+#ifdef DEBUG
+  // Double-check the above assertion that pushed floats should be at the
+  // beginning of our floats list.
+  for (nsIFrame* f : mFloats) {
+    NS_ASSERTION(!f->HasAnyStateBits(NS_FRAME_IS_PUSHED_FLOAT),
+                 "pushed floats must be at the beginning of the float list");
+  }
+#endif
+
+  // We may have a pending push of pushed floats too:
+  if (HasPushedFloats()) {
+    // XXX we can return 'true' here once we make HasPushedFloats
+    // not lie.  (see nsBlockFrame::RemoveFloat)
+    auto* pushedFloats = GetPushedFloats();
+    return pushedFloats && !pushedFloats->IsEmpty();
+  }
+  return false;
+}
+
+//////////////////////////////////////////////////////////////////////
+// Painting, event handling
+
+#ifdef DEBUG
+static void ComputeInkOverflowArea(nsLineList& aLines, nscoord aWidth,
+                                   nscoord aHeight, nsRect& aResult) {
+  nscoord xa = 0, ya = 0, xb = aWidth, yb = aHeight;
+  for (nsLineList::iterator line = aLines.begin(), line_end = aLines.end();
+       line != line_end; ++line) {
+    // Compute min and max x/y values for the reflowed frame's
+    // combined areas
+    nsRect inkOverflow(line->InkOverflowRect());
+    nscoord x = inkOverflow.x;
+    nscoord y = inkOverflow.y;
+    nscoord xmost = x + inkOverflow.width;
+    nscoord ymost = y + inkOverflow.height;
+    if (x < xa) {
+      xa = x;
+    }
+    if (xmost > xb) {
+      xb = xmost;
+    }
+    if (y < ya) {
+      ya = y;
+    }
+    if (ymost > yb) {
+      yb = ymost;
+    }
+  }
+
+  aResult.x = xa;
+  aResult.y = ya;
+  aResult.width = xb - xa;
+  aResult.height = yb - ya;
+}
+#endif
+
+#ifdef DEBUG
+static void DebugOutputDrawLine(int32_t aDepth, nsLineBox* aLine, bool aDrawn) {
+  if (nsBlockFrame::gNoisyDamageRepair) {
+    nsIFrame::IndentBy(stdout, aDepth + 1);
+    nsRect lineArea = aLine->InkOverflowRect();
+    printf("%s line=%p bounds=%d,%d,%d,%d ca=%d,%d,%d,%d\n",
+           aDrawn ? "draw" : "skip", static_cast<void*>(aLine), aLine->IStart(),
+           aLine->BStart(), aLine->ISize(), aLine->BSize(), lineArea.x,
+           lineArea.y, lineArea.width, lineArea.height);
+  }
+}
+#endif
+
+static void DisplayLine(nsDisplayListBuilder* aBuilder,
+                        nsBlockFrame::LineIterator& aLine,
+                        const bool aLineInLine, const nsDisplayListSet& aLists,
+                        nsBlockFrame* aFrame, TextOverflow* aTextOverflow,
+                        uint32_t aLineNumberForTextOverflow, int32_t aDepth,
+                        int32_t& aDrawnLines) {
+#ifdef DEBUG
+  if (nsBlockFrame::gLamePaintMetrics) {
+    aDrawnLines++;
+  }
+  const bool intersect =
+      aLine->InkOverflowRect().Intersects(aBuilder->GetDirtyRect());
+  DebugOutputDrawLine(aDepth, aLine.get(), intersect);
+#endif
+
+  // Collect our line's display items in a temporary nsDisplayListCollection,
+  // so that we can apply any "text-overflow" clipping to the entire collection
+  // without affecting previous lines.
+  nsDisplayListCollection collection(aBuilder);
+
+  // Block-level child backgrounds go on the blockBorderBackgrounds list ...
+  // Inline-level child backgrounds go on the regular child content list.
+  nsDisplayListSet childLists(
+      collection,
+      aLineInLine ? collection.Content() : collection.BlockBorderBackgrounds());
+
+  auto flags =
+      aLineInLine
+          ? nsIFrame::DisplayChildFlags(nsIFrame::DisplayChildFlag::Inline)
+          : nsIFrame::DisplayChildFlags();
+
+  nsIFrame* kid = aLine->mFirstChild;
+  int32_t n = aLine->GetChildCount();
+  while (--n >= 0) {
+    aFrame->BuildDisplayListForChild(aBuilder, kid, childLists, flags);
+    kid = kid->GetNextSibling();
+  }
+
+  if (aTextOverflow && aLineInLine) {
+    aTextOverflow->ProcessLine(collection, aLine.get(),
+                               aLineNumberForTextOverflow);
+  }
+
+  collection.MoveTo(aLists);
+}
+
+void nsBlockFrame::BuildDisplayList(nsDisplayListBuilder* aBuilder,
+                                    const nsDisplayListSet& aLists) {
+  int32_t drawnLines;  // Will only be used if set (gLamePaintMetrics).
+  int32_t depth = 0;
+#ifdef DEBUG
+  if (gNoisyDamageRepair) {
+    nsRect dirty = aBuilder->GetDirtyRect();
+    depth = GetDepth();
+    nsRect ca;
+    ::ComputeInkOverflowArea(mLines, mRect.width, mRect.height, ca);
+    nsIFrame::IndentBy(stdout, depth);
+    ListTag(stdout);
+    printf(": bounds=%d,%d,%d,%d dirty(absolute)=%d,%d,%d,%d ca=%d,%d,%d,%d\n",
+           mRect.x, mRect.y, mRect.width, mRect.height, dirty.x, dirty.y,
+           dirty.width, dirty.height, ca.x, ca.y, ca.width, ca.height);
+  }
+  PRTime start = 0;  // Initialize these variables to silence the compiler.
+  if (gLamePaintMetrics) {
+    start = PR_Now();
+    drawnLines = 0;
+  }
+#endif
+
+  // TODO(heycam): Should we boost the load priority of any shape-outside
+  // images using CATEGORY_DISPLAY, now that this block is being displayed?
+  // We don't have a float manager here.
+
+  DisplayBorderBackgroundOutline(aBuilder, aLists);
+
+  if (GetPrevInFlow()) {
+    DisplayOverflowContainers(aBuilder, aLists);
+    for (nsIFrame* f : mFloats) {
+      if (f->HasAnyStateBits(NS_FRAME_IS_PUSHED_FLOAT)) {
+        BuildDisplayListForChild(aBuilder, f, aLists);
+      }
+    }
+  }
+
+  aBuilder->MarkFramesForDisplayList(this, mFloats);
+
+  if (HasOutsideMarker()) {
+    // Display outside ::marker manually.
+    BuildDisplayListForChild(aBuilder, GetOutsideMarker(), aLists);
+  }
+
+  // Prepare for text-overflow processing.
+  Maybe<TextOverflow> textOverflow =
+      TextOverflow::WillProcessLines(aBuilder, this);
+
+  const bool hasDescendantPlaceHolders =
+      HasAnyStateBits(NS_FRAME_FORCE_DISPLAY_LIST_DESCEND_INTO) ||
+      ForceDescendIntoIfVisible() || aBuilder->GetIncludeAllOutOfFlows();
+
+  const auto ShouldDescendIntoLine = [&](const nsRect& aLineArea) -> bool {
+    // TODO(miko): Unfortunately |descendAlways| cannot be cached, because with
+    // some frame trees, building display list for child lines can change it.
+    // See bug 1552789.
+    const bool descendAlways =
+        HasAnyStateBits(NS_FRAME_FORCE_DISPLAY_LIST_DESCEND_INTO) ||
+        aBuilder->GetIncludeAllOutOfFlows();
+
+    return descendAlways || aLineArea.Intersects(aBuilder->GetDirtyRect()) ||
+           (ForceDescendIntoIfVisible() &&
+            aLineArea.Intersects(aBuilder->GetVisibleRect()));
+  };
+
+  Maybe<nscolor> backplateColor;
+
+  // We'll try to draw an accessibility backplate behind text (to ensure it's
+  // readable over any possible background-images), if all of the following
+  // hold:
+  //    (A) the backplate feature is preffed on
+  //    (B) we are not honoring the document colors
+  //    (C) the force color adjust property is set to auto
+  if (StaticPrefs::browser_display_permit_backplate() &&
+      PresContext()->ForcingColors() && !IsComboboxControlFrame() &&
+      StyleText()->mForcedColorAdjust != StyleForcedColorAdjust::None) {
+    backplateColor.emplace(GetBackplateColor(this));
+  }
+
+  // Don't use the line cursor if we might have a descendant placeholder ...
+  // it might skip lines that contain placeholders but don't themselves
+  // intersect with the dirty area.
+  // In particular, we really want to check ShouldDescendIntoFrame()
+  // on all our child frames, but that might be expensive.  So we
+  // approximate it by checking it on |this|; if it's true for any
+  // frame in our child list, it's also true for |this|.
+  // Also skip the cursor if we're creating text overflow markers,
+  // since we need to know what line number we're up to in order
+  // to generate unique display item keys.
+  // Lastly, the cursor should be skipped if we're drawing
+  // backplates behind text. When backplating we consider consecutive
+  // runs of text as a whole, which requires we iterate through all lines
+  // to find our backplate size.
+  nsLineBox* cursor =
+      (hasDescendantPlaceHolders || textOverflow.isSome() || backplateColor)
+          ? nullptr
+          : GetFirstLineContaining(aBuilder->GetDirtyRect().y);
+  LineIterator line_end = LinesEnd();
+
+  TextOverflow* textOverflowPtr = textOverflow.ptrOr(nullptr);
+
+  if (cursor) {
+    for (LineIterator line = mLines.begin(cursor); line != line_end; ++line) {
+      const nsRect lineArea = line->InkOverflowRect();
+      if (!lineArea.IsEmpty()) {
+        // Because we have a cursor, the combinedArea.ys are non-decreasing.
+        // Once we've passed aDirtyRect.YMost(), we can never see it again.
+        if (lineArea.y >= aBuilder->GetDirtyRect().YMost()) {
+          break;
+        }
+        MOZ_ASSERT(textOverflow.isNothing());
+
+        if (ShouldDescendIntoLine(lineArea)) {
+          DisplayLine(aBuilder, line, line->IsInline(), aLists, this, nullptr,
+                      0, depth, drawnLines);
+        }
+      }
+    }
+  } else {
+    bool nonDecreasingYs = true;
+    uint32_t lineCount = 0;
+    nscoord lastY = INT32_MIN;
+    nscoord lastYMost = INT32_MIN;
+
+    // A frame's display list cannot contain more than one copy of a
+    // given display item unless the items are uniquely identifiable.
+    // Because backplate occasionally requires multiple
+    // SolidColor items, we use an index (backplateIndex) to maintain
+    // uniqueness among them. Note this is a mapping of index to
+    // item, and the mapping is stable even if the dirty rect changes.
+    uint16_t backplateIndex = 0;
+    nsRect curBackplateArea;
+
+    auto AddBackplate = [&]() {
+      aLists.BorderBackground()->AppendNewToTopWithIndex<nsDisplaySolidColor>(
+          aBuilder, this, backplateIndex, curBackplateArea,
+          backplateColor.value());
+    };
+
+    for (LineIterator line = LinesBegin(); line != line_end; ++line) {
+      const nsRect lineArea = line->InkOverflowRect();
+      const bool lineInLine = line->IsInline();
+
+      if ((lineInLine && textOverflowPtr) || ShouldDescendIntoLine(lineArea)) {
+        DisplayLine(aBuilder, line, lineInLine, aLists, this, textOverflowPtr,
+                    lineCount, depth, drawnLines);
+      }
+
+      if (!lineInLine && !curBackplateArea.IsEmpty()) {
+        // If we have encountered a non-inline line but were previously
+        // forming a backplate, we should add the backplate to the display
+        // list as-is and render future backplates disjointly.
+        MOZ_ASSERT(backplateColor,
+                   "if this master switch is off, curBackplateArea "
+                   "must be empty and we shouldn't get here");
+        AddBackplate();
+        backplateIndex++;
+        curBackplateArea = nsRect();
+      }
+
+      if (!lineArea.IsEmpty()) {
+        if (lineArea.y < lastY || lineArea.YMost() < lastYMost) {
+          nonDecreasingYs = false;
+        }
+        lastY = lineArea.y;
+        lastYMost = lineArea.YMost();
+        if (lineInLine && backplateColor && LineHasVisibleInlineContent(line)) {
+          nsRect lineBackplate = GetLineTextArea(line, aBuilder) +
+                                 aBuilder->ToReferenceFrame(this);
+          if (curBackplateArea.IsEmpty()) {
+            curBackplateArea = lineBackplate;
+          } else {
+            curBackplateArea.OrWith(lineBackplate);
+          }
+        }
+      }
+      lineCount++;
+    }
+
+    if (nonDecreasingYs && lineCount >= MIN_LINES_NEEDING_CURSOR) {
+      SetupLineCursorForDisplay();
+    }
+
+    if (!curBackplateArea.IsEmpty()) {
+      AddBackplate();
+    }
+  }
+
+  if (textOverflow.isSome()) {
+    // Put any text-overflow:ellipsis markers on top of the non-positioned
+    // content of the block's lines. (If we ever start sorting the Content()
+    // list this will end up in the wrong place.)
+    aLists.Content()->AppendToTop(&textOverflow->GetMarkers());
+  }
+
+#ifdef DEBUG
+  if (gLamePaintMetrics) {
+    PRTime end = PR_Now();
+
+    int32_t numLines = mLines.size();
+    if (!numLines) {
+      numLines = 1;
+    }
+    PRTime lines, deltaPerLine, delta;
+    lines = int64_t(numLines);
+    delta = end - start;
+    deltaPerLine = delta / lines;
+
+    ListTag(stdout);
+    char buf[400];
+    SprintfLiteral(buf,
+                   ": %" PRId64 " elapsed (%" PRId64
+                   " per line) lines=%d drawn=%d skip=%d",
+                   delta, deltaPerLine, numLines, drawnLines,
+                   numLines - drawnLines);
+    printf("%s\n", buf);
+  }
+#endif
+}
+
+#ifdef ACCESSIBILITY
+a11y::AccType nsBlockFrame::AccessibleType() {
+  if (IsTableCaption()) {
+    return GetRect().IsEmpty() ? a11y::eNoType : a11y::eHTMLCaptionType;
+  }
+
+  // block frame may be for <hr>
+  if (mContent->IsHTMLElement(nsGkAtoms::hr)) {
+    return a11y::eHTMLHRType;
+  }
+
+  if (!HasMarker() || !PresContext()) {
+    // XXXsmaug What if we're in the shadow dom?
+    if (!mContent->GetParent()) {
+      // Don't create accessible objects for the root content node, they are
+      // redundant with the nsDocAccessible object created with the document
+      // node
+      return a11y::eNoType;
+    }
+
+    if (mContent == mContent->OwnerDoc()->GetBody()) {
+      // Don't create accessible objects for the body, they are redundant with
+      // the nsDocAccessible object created with the document node
+      return a11y::eNoType;
+    }
+
+    // Not a list item with a ::marker, treat as normal HTML container.
+    return a11y::eHyperTextType;
+  }
+
+  // Create special list item accessible since we have a ::marker.
+  return a11y::eHTMLLiType;
+}
+#endif
+
+void nsBlockFrame::SetupLineCursorForDisplay() {
+  if (mLines.empty() || HasProperty(LineCursorPropertyDisplay())) {
+    return;
+  }
+
+  SetProperty(LineCursorPropertyDisplay(), mLines.front());
+  AddStateBits(NS_BLOCK_HAS_LINE_CURSOR);
+}
+
+void nsBlockFrame::SetupLineCursorForQuery() {
+  if (mLines.empty() || HasProperty(LineCursorPropertyQuery())) {
+    return;
+  }
+
+  SetProperty(LineCursorPropertyQuery(), mLines.front());
+  AddStateBits(NS_BLOCK_HAS_LINE_CURSOR);
+}
+
+nsLineBox* nsBlockFrame::GetFirstLineContaining(nscoord y) {
+  // Although this looks like a "querying" method, it is used by the
+  // display-list building code, so uses the Display cursor.
+  nsLineBox* property = GetLineCursorForDisplay();
+  if (!property) {
+    return nullptr;
+  }
+  LineIterator cursor = mLines.begin(property);
+  nsRect cursorArea = cursor->InkOverflowRect();
+
+  while ((cursorArea.IsEmpty() || cursorArea.YMost() > y) &&
+         cursor != mLines.front()) {
+    cursor = cursor.prev();
+    cursorArea = cursor->InkOverflowRect();
+  }
+  while ((cursorArea.IsEmpty() || cursorArea.YMost() <= y) &&
+         cursor != mLines.back()) {
+    cursor = cursor.next();
+    cursorArea = cursor->InkOverflowRect();
+  }
+
+  if (cursor.get() != property) {
+    SetProperty(LineCursorPropertyDisplay(), cursor.get());
+  }
+
+  return cursor.get();
+}
+
+/* virtual */
+void nsBlockFrame::ChildIsDirty(nsIFrame* aChild) {
+  // See if the child is absolutely positioned
+  if (aChild->IsAbsolutelyPositioned()) {
+    // do nothing
+  } else if (aChild == GetOutsideMarker()) {
+    // The ::marker lives in the first line, unless the first line has
+    // height 0 and there is a second line, in which case it lives
+    // in the second line.
+    LineIterator markerLine = LinesBegin();
+    if (markerLine != LinesEnd() && markerLine->BSize() == 0 &&
+        markerLine != mLines.back()) {
+      markerLine = markerLine.next();
+    }
+
+    if (markerLine != LinesEnd()) {
+      MarkLineDirty(markerLine, &mLines);
+    }
+    // otherwise we have an empty line list, and ReflowDirtyLines
+    // will handle reflowing the ::marker.
+  } else {
+    // Note that we should go through our children to mark lines dirty
+    // before the next reflow.  Doing it now could make things O(N^2)
+    // since finding the right line is O(N).
+    // We don't need to worry about marking lines on the overflow list
+    // as dirty; we're guaranteed to reflow them if we take them off the
+    // overflow list.
+    // However, we might have gotten a float, in which case we need to
+    // reflow the line containing its placeholder.  So find the
+    // ancestor-or-self of the placeholder that's a child of the block,
+    // and mark it as NS_FRAME_HAS_DIRTY_CHILDREN too, so that we mark
+    // its line dirty when we handle NS_BLOCK_LOOK_FOR_DIRTY_FRAMES.
+    // We need to take some care to handle the case where a float is in
+    // a different continuation than its placeholder, including marking
+    // an extra block with NS_BLOCK_LOOK_FOR_DIRTY_FRAMES.
+    if (!aChild->HasAnyStateBits(NS_FRAME_OUT_OF_FLOW)) {
+      AddStateBits(NS_BLOCK_LOOK_FOR_DIRTY_FRAMES);
+    } else {
+      NS_ASSERTION(aChild->IsFloating(), "should be a float");
+      nsIFrame* thisFC = FirstContinuation();
+      nsIFrame* placeholderPath = aChild->GetPlaceholderFrame();
+      // SVG code sometimes sends FrameNeedsReflow notifications during
+      // frame destruction, leading to null placeholders, but we're safe
+      // ignoring those.
+      if (placeholderPath) {
+        for (;;) {
+          nsIFrame* parent = placeholderPath->GetParent();
+          if (parent->GetContent() == mContent &&
+              parent->FirstContinuation() == thisFC) {
+            parent->AddStateBits(NS_BLOCK_LOOK_FOR_DIRTY_FRAMES);
+            break;
+          }
+          placeholderPath = parent;
+        }
+        placeholderPath->AddStateBits(NS_FRAME_HAS_DIRTY_CHILDREN);
+      }
+    }
+  }
+
+  nsContainerFrame::ChildIsDirty(aChild);
+}
+
+static bool AlwaysEstablishesBFC(const nsBlockFrame* aFrame) {
+  switch (aFrame->Type()) {
+    case LayoutFrameType::ColumnSetWrapper:
+      // CSS Multi-column level 1 section 2: A multi-column container
+      // establishes a new block formatting context, as per CSS 2.1 section
+      // 9.4.1.
+    case LayoutFrameType::ComboboxControl:
+      return true;
+    case LayoutFrameType::Block:
+      return static_cast<const nsFileControlFrame*>(do_QueryFrame(aFrame)) ||
+             // Ensure that the options inside the select aren't expanded by
+             // right floats outside the select.
+             static_cast<const nsSelectsAreaFrame*>(do_QueryFrame(aFrame)) ||
+             // See bug 1373767 and bug 353894.
+             static_cast<const nsMathMLmathBlockFrame*>(do_QueryFrame(aFrame));
+    default:
+      return false;
+  }
+}
+
+void nsBlockFrame::Init(nsIContent* aContent, nsContainerFrame* aParent,
+                        nsIFrame* aPrevInFlow) {
+  // These are all the block specific frame bits, they are copied from
+  // the prev-in-flow to a newly created next-in-flow, except for the
+  // NS_BLOCK_FLAGS_NON_INHERITED_MASK bits below.
+  constexpr nsFrameState NS_BLOCK_FLAGS_MASK =
+      NS_BLOCK_BFC_STATE_BITS | NS_BLOCK_CLIP_PAGINATED_OVERFLOW |
+      NS_BLOCK_HAS_FIRST_LETTER_STYLE | NS_BLOCK_FRAME_HAS_OUTSIDE_MARKER |
+      NS_BLOCK_HAS_FIRST_LETTER_CHILD | NS_BLOCK_FRAME_HAS_INSIDE_MARKER;
+
+  // This is the subset of NS_BLOCK_FLAGS_MASK that is NOT inherited
+  // by default.  They should only be set on the first-in-flow.
+  constexpr nsFrameState NS_BLOCK_FLAGS_NON_INHERITED_MASK =
+      NS_BLOCK_FRAME_HAS_OUTSIDE_MARKER | NS_BLOCK_HAS_FIRST_LETTER_CHILD |
+      NS_BLOCK_FRAME_HAS_INSIDE_MARKER;
+
+  if (aPrevInFlow) {
+    // Copy over the inherited block frame bits from the prev-in-flow.
+    RemoveStateBits(NS_BLOCK_FLAGS_MASK);
+    AddStateBits(aPrevInFlow->GetStateBits() &
+                 (NS_BLOCK_FLAGS_MASK & ~NS_BLOCK_FLAGS_NON_INHERITED_MASK));
+  }
+
+  nsContainerFrame::Init(aContent, aParent, aPrevInFlow);
+
+  if (!aPrevInFlow ||
+      aPrevInFlow->HasAnyStateBits(NS_BLOCK_NEEDS_BIDI_RESOLUTION)) {
+    AddStateBits(NS_BLOCK_NEEDS_BIDI_RESOLUTION);
+  }
+
+  // A display:flow-root box establishes a block formatting context.
+  //
+  // If a box has a different writing-mode value than its containing block:
+  // ...
+  //   If the box is a block container, then it establishes a new block
+  //   formatting context.
+  // (https://drafts.csswg.org/css-writing-modes/#block-flow)
+  //
+  // If the box has contain: paint or contain:layout (or contain:strict),
+  // then it should also establish a formatting context.
+  //
+  // Per spec, a column-span always establishes a new block formatting context.
+  //
+  // Other more specific frame types also always establish a BFC.
+  //
+  if (StyleDisplay()->mDisplay == mozilla::StyleDisplay::FlowRoot ||
+      (GetParent() &&
+       (GetWritingMode().GetBlockDir() !=
+            GetParent()->GetWritingMode().GetBlockDir() ||
+        GetWritingMode().IsVerticalSideways() !=
+            GetParent()->GetWritingMode().IsVerticalSideways())) ||
+      IsColumnSpan() || AlwaysEstablishesBFC(this)) {
+    AddStateBits(NS_BLOCK_STATIC_BFC);
+  }
+
+  if (StyleEstablishesBFC(Style())) {
+    AddStateBits(NS_BLOCK_DYNAMIC_BFC);
+  }
+
+  if (HasAnyStateBits(NS_FRAME_FONT_INFLATION_CONTAINER) &&
+      HasAnyStateBits(NS_BLOCK_BFC_STATE_BITS)) {
+    AddStateBits(NS_FRAME_FONT_INFLATION_FLOW_ROOT);
+  }
+}
+
+void nsBlockFrame::SetInitialChildList(ChildListID aListID,
+                                       nsFrameList&& aChildList) {
+  if (FrameChildListID::Float == aListID) {
+    mFloats = std::move(aChildList);
+  } else if (FrameChildListID::Principal == aListID) {
+#ifdef DEBUG
+    // The only times a block that is an anonymous box is allowed to have a
+    // first-letter frame are when it's the block inside a non-anonymous cell,
+    // the block inside a fieldset, button or column set, or a scrolled content
+    // block, except for <select>.  Note that this means that blocks which are
+    // the anonymous block in {ib} splits do NOT get first-letter frames.
+    // Note that NS_BLOCK_HAS_FIRST_LETTER_STYLE gets set on all continuations
+    // of the block.
+    auto pseudo = Style()->GetPseudoType();
+    bool haveFirstLetterStyle =
+        (pseudo == PseudoStyleType::NotPseudo ||
+         (pseudo == PseudoStyleType::cellContent &&
+          !GetParent()->Style()->IsPseudoOrAnonBox()) ||
+         pseudo == PseudoStyleType::fieldsetContent ||
+         pseudo == PseudoStyleType::buttonContent ||
+         pseudo == PseudoStyleType::columnContent ||
+         (pseudo == PseudoStyleType::scrolledContent &&
+          !GetParent()->IsListControlFrame()) ||
+         pseudo == PseudoStyleType::mozSVGText) &&
+        !IsComboboxControlFrame() && !IsMathMLFrame() &&
+        !IsColumnSetWrapperFrame() &&
+        RefPtr<ComputedStyle>(GetFirstLetterStyle(PresContext())) != nullptr;
+    NS_ASSERTION(haveFirstLetterStyle ==
+                     HasAnyStateBits(NS_BLOCK_HAS_FIRST_LETTER_STYLE),
+                 "NS_BLOCK_HAS_FIRST_LETTER_STYLE state out of sync");
+#endif
+
+    AddFrames(std::move(aChildList), nullptr, nullptr);
+  } else {
+    nsContainerFrame::SetInitialChildList(aListID, std::move(aChildList));
+  }
+}
+
+void nsBlockFrame::SetMarkerFrameForListItem(nsIFrame* aMarkerFrame) {
+  MOZ_ASSERT(aMarkerFrame);
+  MOZ_ASSERT(!HasAnyStateBits(NS_BLOCK_FRAME_HAS_INSIDE_MARKER |
+                              NS_BLOCK_FRAME_HAS_OUTSIDE_MARKER),
+             "How can we have a ::marker frame already?");
+
+  if (StyleList()->mListStylePosition == StyleListStylePosition::Inside) {
+    SetProperty(InsideMarkerProperty(), aMarkerFrame);
+    AddStateBits(NS_BLOCK_FRAME_HAS_INSIDE_MARKER);
+  } else {
+    if (nsBlockFrame* marker = do_QueryFrame(aMarkerFrame)) {
+      // An outside ::marker needs to be an independent formatting context
+      // to avoid being influenced by the float manager etc.
+      marker->AddStateBits(NS_BLOCK_STATIC_BFC);
+    }
+    SetProperty(OutsideMarkerProperty(),
+                new (PresShell()) nsFrameList(aMarkerFrame, aMarkerFrame));
+    AddStateBits(NS_BLOCK_FRAME_HAS_OUTSIDE_MARKER);
+  }
+}
+
+bool nsBlockFrame::MarkerIsEmpty() const {
+  NS_ASSERTION(mContent->GetPrimaryFrame()->StyleDisplay()->IsListItem() &&
+                   HasOutsideMarker(),
+               "should only care when we have an outside ::marker");
+  nsIFrame* marker = GetMarker();
+  const nsStyleList* list = marker->StyleList();
+  return marker->StyleContent()->mContent.IsNone() ||
+         (list->mCounterStyle.IsNone() && list->mListStyleImage.IsNone() &&
+          marker->StyleContent()->ContentCount() == 0);
+}
+
+void nsBlockFrame::ReflowOutsideMarker(nsIFrame* aMarkerFrame,
+                                       BlockReflowState& aState,
+                                       ReflowOutput& aMetrics,
+                                       nscoord aLineTop) {
+  const ReflowInput& ri = aState.mReflowInput;
+
+  WritingMode markerWM = aMarkerFrame->GetWritingMode();
+  LogicalSize availSize(markerWM);
+  // Make up an inline-size since it doesn't really matter (XXX).
+  availSize.ISize(markerWM) = aState.ContentISize();
+  availSize.BSize(markerWM) = NS_UNCONSTRAINEDSIZE;
+
+  ReflowInput reflowInput(aState.mPresContext, ri, aMarkerFrame, availSize,
+                          Nothing(), {}, {}, {ComputeSizeFlag::ShrinkWrap});
+  nsReflowStatus status;
+  aMarkerFrame->Reflow(aState.mPresContext, aMetrics, reflowInput, status);
+
+  // Get the float available space using our saved state from before we
+  // started reflowing the block, so that we ignore any floats inside
+  // the block.
+  // FIXME: aLineTop isn't actually set correctly by some callers, since
+  // they reposition the line.
+  LogicalRect floatAvailSpace =
+      aState
+          .GetFloatAvailableSpaceWithState(aLineTop, ShapeType::ShapeOutside,
+                                           &aState.mFloatManagerStateBefore)
+          .mRect;
+  // FIXME (bug 25888): need to check the entire region that the first
+  // line overlaps, not just the top pixel.
+
+  // Place the ::marker now.  We want to place the ::marker relative to the
+  // border-box of the associated block (using the right/left margin of
+  // the ::marker frame as separation).  However, if a line box would be
+  // displaced by floats that are *outside* the associated block, we
+  // want to displace it by the same amount.  That is, we act as though
+  // the edge of the floats is the content-edge of the block, and place
+  // the ::marker at a position offset from there by the block's padding,
+  // the block's border, and the ::marker frame's margin.
+
+  // IStart from floatAvailSpace gives us the content/float start edge
+  // in the current writing mode. Then we subtract out the start
+  // border/padding and the ::marker's width and margin to offset the position.
+  WritingMode wm = ri.GetWritingMode();
+  // Get the ::marker's margin, converted to our writing mode so that we can
+  // combine it with other logical values here.
+  LogicalMargin markerMargin = reflowInput.ComputedLogicalMargin(wm);
+  nscoord iStart = floatAvailSpace.IStart(wm) -
+                   ri.ComputedLogicalBorderPadding(wm).IStart(wm) -
+                   markerMargin.IEnd(wm) - aMetrics.ISize(wm);
+
+  // Approximate the ::marker's position; vertical alignment will provide
+  // the final vertical location. We pass our writing-mode here, because
+  // it may be different from the ::marker frame's mode.
+  nscoord bStart = floatAvailSpace.BStart(wm);
+  aMarkerFrame->SetRect(
+      wm,
+      LogicalRect(wm, iStart, bStart, aMetrics.ISize(wm), aMetrics.BSize(wm)),
+      aState.ContainerSize());
+  aMarkerFrame->DidReflow(aState.mPresContext, &aState.mReflowInput);
+}
+
+// This is used to scan frames for any float placeholders, add their
+// floats to the list represented by aList, and remove the
+// floats from whatever list they might be in. We don't search descendants
+// that are float containing blocks.  Floats that or not children of 'this'
+// are ignored (they are not added to aList).
+void nsBlockFrame::DoCollectFloats(nsIFrame* aFrame, nsFrameList& aList,
+                                   bool aCollectSiblings) {
+  while (aFrame) {
+    // Don't descend into float containing blocks.
+    if (!aFrame->IsFloatContainingBlock()) {
+      nsIFrame* outOfFlowFrame =
+          aFrame->IsPlaceholderFrame()
+              ? nsLayoutUtils::GetFloatFromPlaceholder(aFrame)
+              : nullptr;
+      while (outOfFlowFrame && outOfFlowFrame->GetParent() == this) {
+        RemoveFloat(outOfFlowFrame);
+        // Remove the IS_PUSHED_FLOAT bit, in case |outOfFlowFrame| came from
+        // the PushedFloats list.
+        outOfFlowFrame->RemoveStateBits(NS_FRAME_IS_PUSHED_FLOAT);
+        aList.AppendFrame(nullptr, outOfFlowFrame);
+        outOfFlowFrame = outOfFlowFrame->GetNextInFlow();
+        // FIXME: By not pulling floats whose parent is one of our
+        // later siblings, are we risking the pushed floats getting
+        // out-of-order?
+        // XXXmats nsInlineFrame's lazy reparenting depends on NOT doing that.
+      }
+
+      DoCollectFloats(aFrame->PrincipalChildList().FirstChild(), aList, true);
+      DoCollectFloats(
+          aFrame->GetChildList(FrameChildListID::Overflow).FirstChild(), aList,
+          true);
+    }
+    if (!aCollectSiblings) {
+      break;
+    }
+    aFrame = aFrame->GetNextSibling();
+  }
+}
+
+void nsBlockFrame::CheckFloats(BlockReflowState& aState) {
+#ifdef DEBUG
+  // If any line is still dirty, that must mean we're going to reflow this
+  // block again soon (e.g. because we bailed out after noticing that
+  // clearance was imposed), so don't worry if the floats are out of sync.
+  bool anyLineDirty = false;
+
+  // Check that the float list is what we would have built
+  AutoTArray<nsIFrame*, 8> lineFloats;
+  for (auto& line : Lines()) {
+    if (line.HasFloats()) {
+      lineFloats.AppendElements(line.Floats());
+    }
+    if (line.IsDirty()) {
+      anyLineDirty = true;
+    }
+  }
+
+  AutoTArray<nsIFrame*, 8> storedFloats;
+  bool equal = true;
+  bool hasHiddenFloats = false;
+  uint32_t i = 0;
+  for (nsIFrame* f : mFloats) {
+    if (f->HasAnyStateBits(NS_FRAME_IS_PUSHED_FLOAT)) {
+      continue;
+    }
+    // There are chances that the float children won't be added to lines,
+    // because in nsBlockFrame::ReflowLine, it skips reflow line if the first
+    // child of the line is IsHiddenByContentVisibilityOfInFlowParentForLayout.
+    // There are also chances that the floats in line are out of date, for
+    // instance, lines could reflow if
+    // PresShell::IsForcingLayoutForHiddenContent, and after forcingLayout is
+    // off, the reflow of lines could be skipped, but the floats are still in
+    // there. Here we can't know whether the floats hidden by c-v are included
+    // in the lines or not. So we use hasHiddenFloats to skip the float length
+    // checking.
+    if (!hasHiddenFloats &&
+        f->IsHiddenByContentVisibilityOfInFlowParentForLayout()) {
+      hasHiddenFloats = true;
+    }
+    storedFloats.AppendElement(f);
+    if (i < lineFloats.Length() && lineFloats.ElementAt(i) != f) {
+      equal = false;
+    }
+    ++i;
+  }
+
+  if ((!equal || lineFloats.Length() != storedFloats.Length()) &&
+      !anyLineDirty && !hasHiddenFloats) {
+    NS_ERROR(
+        "nsBlockFrame::CheckFloats: Explicit float list is out of sync with "
+        "float cache");
+#  if defined(DEBUG_roc)
+    nsIFrame::RootFrameList(PresContext(), stdout, 0);
+    for (i = 0; i < lineFloats.Length(); ++i) {
+      printf("Line float: %p\n", lineFloats.ElementAt(i));
+    }
+    for (i = 0; i < storedFloats.Length(); ++i) {
+      printf("Stored float: %p\n", storedFloats.ElementAt(i));
+    }
+#  endif
+  }
+#endif
+
+  const nsFrameList* oofs = GetOverflowOutOfFlows();
+  if (oofs && oofs->NotEmpty()) {
+    // Floats that were pushed should be removed from our float
+    // manager.  Otherwise the float manager's YMost or XMost might
+    // be larger than necessary, causing this block to get an
+    // incorrect desired height (or width).  Some of these floats
+    // may not actually have been added to the float manager because
+    // they weren't reflowed before being pushed; that's OK,
+    // RemoveRegions will ignore them. It is safe to do this here
+    // because we know from here on the float manager will only be
+    // used for its XMost and YMost, not to place new floats and
+    // lines.
+    aState.FloatManager()->RemoveTrailingRegions(oofs->FirstChild());
+  }
+}
+
+void nsBlockFrame::IsMarginRoot(bool* aBStartMarginRoot,
+                                bool* aBEndMarginRoot) {
+  nsIFrame* parent = GetParent();
+  if (!HasAnyStateBits(NS_BLOCK_BFC_STATE_BITS)) {
+    if (!parent || parent->IsFloatContainingBlock()) {
+      *aBStartMarginRoot = false;
+      *aBEndMarginRoot = false;
+      return;
+    }
+  }
+
+  if (parent && parent->IsColumnSetFrame()) {
+    // The first column is a start margin root and the last column is an end
+    // margin root.  (If the column-set is split by a column-span:all box then
+    // the first and last column in each column-set fragment are margin roots.)
+    *aBStartMarginRoot = GetPrevInFlow() == nullptr;
+    *aBEndMarginRoot = GetNextInFlow() == nullptr;
+    return;
+  }
+
+  *aBStartMarginRoot = true;
+  *aBEndMarginRoot = true;
+}
+
+/* static */
+bool nsBlockFrame::BlockNeedsFloatManager(nsIFrame* aBlock) {
+  MOZ_ASSERT(aBlock, "Must have a frame");
+  NS_ASSERTION(aBlock->IsBlockFrameOrSubclass(), "aBlock must be a block");
+
+  nsIFrame* parent = aBlock->GetParent();
+  return aBlock->HasAnyStateBits(NS_BLOCK_BFC_STATE_BITS) ||
+         (parent && !parent->IsFloatContainingBlock());
+}
+
+/* static */
+bool nsBlockFrame::BlockCanIntersectFloats(nsIFrame* aFrame) {
+  return aFrame->IsBlockFrameOrSubclass() && !aFrame->IsReplaced() &&
+         !aFrame->HasAnyStateBits(NS_BLOCK_BFC_STATE_BITS);
+}
+
+// Note that this width can vary based on the vertical position.
+// However, the cases where it varies are the cases where the width fits
+// in the available space given, which means that variation shouldn't
+// matter.
+/* static */
+nsBlockFrame::FloatAvoidingISizeToClear nsBlockFrame::ISizeToClearPastFloats(
+    const BlockReflowState& aState, const LogicalRect& aFloatAvailableSpace,
+    nsIFrame* aFloatAvoidingBlock) {
+  nscoord inlineStartOffset, inlineEndOffset;
+  WritingMode wm = aState.mReflowInput.GetWritingMode();
+
+  FloatAvoidingISizeToClear result;
+  aState.ComputeFloatAvoidingOffsets(aFloatAvoidingBlock, aFloatAvailableSpace,
+                                     inlineStartOffset, inlineEndOffset);
+  nscoord availISize =
+      aState.mContentArea.ISize(wm) - inlineStartOffset - inlineEndOffset;
+
+  // We actually don't want the min width here; see bug 427782; we only
+  // want to displace if the width won't compute to a value small enough
+  // to fit.
+  // All we really need here is the result of ComputeSize, and we
+  // could *almost* get that from an SizeComputationInput, except for the
+  // last argument.
+  WritingMode frWM = aFloatAvoidingBlock->GetWritingMode();
+  LogicalSize availSpace =
+      LogicalSize(wm, availISize, NS_UNCONSTRAINEDSIZE).ConvertTo(frWM, wm);
+  ReflowInput reflowInput(aState.mPresContext, aState.mReflowInput,
+                          aFloatAvoidingBlock, availSpace);
+  result.borderBoxISize =
+      reflowInput.ComputedSizeWithBorderPadding(wm).ISize(wm);
+
+  // Use the margins from sizingInput rather than reflowInput so that
+  // they aren't reduced by ignoring margins in overconstrained cases.
+  SizeComputationInput sizingInput(aFloatAvoidingBlock,
+                                   aState.mReflowInput.mRenderingContext, wm,
+                                   aState.mContentArea.ISize(wm));
+  const LogicalMargin computedMargin = sizingInput.ComputedLogicalMargin(wm);
+
+  nscoord marginISize = computedMargin.IStartEnd(wm);
+  const auto& iSize = reflowInput.mStylePosition->ISize(wm);
+  if (marginISize < 0 && (iSize.IsAuto() || iSize.IsMozAvailable())) {
+    // If we get here, floatAvoidingBlock has a negative amount of inline-axis
+    // margin and an 'auto' (or ~equivalently, -moz-available) inline
+    // size. Under these circumstances, we use the margin to establish a
+    // (positive) minimum size for the border-box, in order to satisfy the
+    // equation in CSS2 10.3.3.  That equation essentially simplifies to the
+    // following:
+    //
+    //   iSize of margins + iSize of borderBox = iSize of containingBlock
+    //
+    // ...where "iSize of borderBox" is the sum of floatAvoidingBlock's
+    // inline-axis components of border, padding, and {width,height}.
+    //
+    // Right now, in the above equation, "iSize of margins" is the only term
+    // that we know for sure. (And we also know that it's negative, since we
+    // got here.) The other terms are as-yet unresolved, since the frame has an
+    // 'auto' iSize, and since we aren't yet sure if we'll clear this frame
+    // beyond floats or place it alongside them.
+    //
+    // However: we *do* know that the equation's "iSize of containingBlock"
+    // term *must* be non-negative, since boxes' widths and heights generally
+    // can't be negative in CSS.  To satisfy that requirement, we can then
+    // infer that the equation's "iSize of borderBox" term *must* be large
+    // enough to cancel out the (known-to-be-negative) "iSize of margins"
+    // term. Therefore, marginISize value (negated to make it positive)
+    // establishes a lower-bound for how much inline-axis space our border-box
+    // will really require in order to fit alongside any floats.
+    //
+    // XXXdholbert This explanation is admittedly a bit hand-wavy and may not
+    // precisely match what any particular spec requires. It's the best
+    // reasoning I could come up with to explain engines' behavior.  Also, our
+    // behavior with -moz-available doesn't seem particularly correct here, per
+    // bug 1767217, though that's probably due to a bug elsewhere in our float
+    // handling code...
+    result.borderBoxISize = std::max(result.borderBoxISize, -marginISize);
+  }
+
+  result.marginIStart = computedMargin.IStart(wm);
+  return result;
+}
+
+/* static */
+nsBlockFrame* nsBlockFrame::GetNearestAncestorBlock(nsIFrame* aCandidate) {
+  nsBlockFrame* block = nullptr;
+  while (aCandidate) {
+    block = do_QueryFrame(aCandidate);
+    if (block) {
+      // yay, candidate is a block!
+      return block;
+    }
+    // Not a block. Check its parent next.
+    aCandidate = aCandidate->GetParent();
+  }
+  MOZ_ASSERT_UNREACHABLE("Fell off frame tree looking for ancestor block!");
+  return nullptr;
+}
+
+nscoord nsBlockFrame::ComputeFinalBSize(BlockReflowState& aState,
+                                        nscoord aBEndEdgeOfChildren) {
+  const WritingMode wm = aState.mReflowInput.GetWritingMode();
+
+  const nscoord effectiveContentBoxBSize =
+      GetEffectiveComputedBSize(aState.mReflowInput, aState.mConsumedBSize);
+  const nscoord blockStartBP = aState.BorderPadding().BStart(wm);
+  const nscoord blockEndBP = aState.BorderPadding().BEnd(wm);
+
+  NS_ASSERTION(
+      !IsTrueOverflowContainer() || (effectiveContentBoxBSize == 0 &&
+                                     blockStartBP == 0 && blockEndBP == 0),
+      "An overflow container's effective content-box block-size, block-start "
+      "BP, and block-end BP should all be zero!");
+
+  const nscoord effectiveContentBoxBSizeWithBStartBP =
+      NSCoordSaturatingAdd(blockStartBP, effectiveContentBoxBSize);
+  const nscoord effectiveBorderBoxBSize =
+      NSCoordSaturatingAdd(effectiveContentBoxBSizeWithBStartBP, blockEndBP);
+
+  if (HasColumnSpanSiblings()) {
+    MOZ_ASSERT(LastInFlow()->GetNextContinuation(),
+               "Frame constructor should've created column-span siblings!");
+
+    // If a block is split by any column-spans, we calculate the final
+    // block-size by shrinkwrapping our children's block-size for all the
+    // fragments except for those after the final column-span, but we should
+    // take no more than our effective border-box block-size. If there's any
+    // leftover block-size, our next continuations will take up rest.
+    //
+    // We don't need to adjust aBri.mReflowStatus because our children's status
+    // is the same as ours.
+    return std::min(effectiveBorderBoxBSize, aBEndEdgeOfChildren);
+  }
+
+  const nscoord availBSize = aState.mReflowInput.AvailableBSize();
+  if (availBSize == NS_UNCONSTRAINEDSIZE) {
+    return effectiveBorderBoxBSize;
+  }
+
+  // Save our children's reflow status.
+  const bool isChildStatusComplete = aState.mReflowStatus.IsComplete();
+  if (isChildStatusComplete && effectiveContentBoxBSize > 0 &&
+      effectiveBorderBoxBSize > availBSize &&
+      ShouldAvoidBreakInside(aState.mReflowInput)) {
+    aState.mReflowStatus.SetInlineLineBreakBeforeAndReset();
+    return effectiveBorderBoxBSize;
+  }
+
+  const bool isBDBClone =
+      aState.mReflowInput.mStyleBorder->mBoxDecorationBreak ==
+      StyleBoxDecorationBreak::Clone;
+
+  // The maximum value our content-box block-size can take within the given
+  // available block-size.
+  const nscoord maxContentBoxBSize = aState.ContentBSize();
+
+  // The block-end edge of our content-box (relative to this frame's origin) if
+  // we consumed the maximum block-size available to us (maxContentBoxBSize).
+  const nscoord maxContentBoxBEnd = aState.ContentBEnd();
+
+  // These variables are uninitialized intentionally so that the compiler can
+  // check they are assigned in every if-else branch below.
+  nscoord finalContentBoxBSizeWithBStartBP;
+  bool isOurStatusComplete;
+
+  if (effectiveBorderBoxBSize <= availBSize) {
+    // Our effective border-box block-size can fit in the available block-size,
+    // so we are complete.
+    finalContentBoxBSizeWithBStartBP = effectiveContentBoxBSizeWithBStartBP;
+    isOurStatusComplete = true;
+  } else if (effectiveContentBoxBSizeWithBStartBP <= maxContentBoxBEnd) {
+    // Note: The following assertion should generally hold because, for
+    // box-decoration-break:clone, this "else if" branch is mathematically
+    // equivalent to the initial "if".
+    NS_ASSERTION(!isBDBClone,
+                 "This else-if branch is handling a situation that's specific "
+                 "to box-decoration-break:slice, i.e. a case when we can skip "
+                 "our block-end border and padding!");
+
+    // Our effective content-box block-size plus the block-start border and
+    // padding can fit in the available block-size, but it cannot fit after
+    // adding the block-end border and padding. Thus, we need a continuation
+    // (unless we already weren't asking for any block-size, in which case we
+    // stay complete to avoid looping forever).
+    finalContentBoxBSizeWithBStartBP = effectiveContentBoxBSizeWithBStartBP;
+    isOurStatusComplete = effectiveContentBoxBSize == 0;
+  } else {
+    // We aren't going to be able to fit our content-box in the space available
+    // to it, which means we'll probably call ourselves incomplete to request a
+    // continuation. But before making that decision, we check for certain
+    // conditions which would force us to overflow beyond the available space --
+    // these might result in us actually being complete if we're forced to
+    // overflow far enough.
+    if (MOZ_UNLIKELY(aState.mReflowInput.mFlags.mIsTopOfPage && isBDBClone &&
+                     maxContentBoxBSize <= 0 &&
+                     aBEndEdgeOfChildren == blockStartBP)) {
+      // In this rare case, we are at the top of page/column, we have
+      // box-decoration-break:clone and zero available block-size for our
+      // content-box (e.g. our own block-start border and padding already exceed
+      // the available block-size), and we didn't lay out any child to consume
+      // our content-box block-size. To ensure we make progress (avoid looping
+      // forever), use 1px as our content-box block-size regardless of our
+      // effective content-box block-size, in the spirit of
+      // https://drafts.csswg.org/css-break/#breaking-rules.
+      finalContentBoxBSizeWithBStartBP = blockStartBP + AppUnitsPerCSSPixel();
+      isOurStatusComplete = effectiveContentBoxBSize <= AppUnitsPerCSSPixel();
+    } else if (aBEndEdgeOfChildren > maxContentBoxBEnd) {
+      // We have a unbreakable child whose block-end edge exceeds the available
+      // block-size for children.
+      if (aBEndEdgeOfChildren >= effectiveContentBoxBSizeWithBStartBP) {
+        // The unbreakable child's block-end edge forces us to consume all of
+        // our effective content-box block-size.
+        finalContentBoxBSizeWithBStartBP = effectiveContentBoxBSizeWithBStartBP;
+
+        // Even though we've consumed all of our effective content-box
+        // block-size, we may still need to report an incomplete status in order
+        // to get another continuation, which will be responsible for laying out
+        // & drawing our block-end border & padding. But if we have no such
+        // border & padding, or if we're forced to apply that border & padding
+        // on this frame due to box-decoration-break:clone, then we don't need
+        // to bother with that additional continuation.
+        isOurStatusComplete = (isBDBClone || blockEndBP == 0);
+      } else {
+        // The unbreakable child's block-end edge doesn't force us to consume
+        // all of our effective content-box block-size.
+        finalContentBoxBSizeWithBStartBP = aBEndEdgeOfChildren;
+        isOurStatusComplete = false;
+      }
+    } else {
+      // The children's block-end edge can fit in the content-box space that we
+      // have available for it. Consume all the space that is available so that
+      // our inline-start/inline-end borders extend all the way to the block-end
+      // edge of column/page.
+      finalContentBoxBSizeWithBStartBP = maxContentBoxBEnd;
+      isOurStatusComplete = false;
+    }
+  }
+
+  nscoord finalBorderBoxBSize = finalContentBoxBSizeWithBStartBP;
+  if (isOurStatusComplete) {
+    finalBorderBoxBSize = NSCoordSaturatingAdd(finalBorderBoxBSize, blockEndBP);
+    if (isChildStatusComplete) {
+      // We want to use children's reflow status as ours, which can be overflow
+      // incomplete. Suppress the urge to call aBri.mReflowStatus.Reset() here.
+    } else {
+      aState.mReflowStatus.SetOverflowIncomplete();
+    }
+  } else {
+    NS_ASSERTION(!IsTrueOverflowContainer(),
+                 "An overflow container should always be complete because of "
+                 "its zero border-box block-size!");
+    if (isBDBClone) {
+      finalBorderBoxBSize =
+          NSCoordSaturatingAdd(finalBorderBoxBSize, blockEndBP);
+    }
+    aState.mReflowStatus.SetIncomplete();
+    if (!GetNextInFlow()) {
+      aState.mReflowStatus.SetNextInFlowNeedsReflow();
+    }
+  }
+
+  return finalBorderBoxBSize;
+}
+
+nsresult nsBlockFrame::ResolveBidi() {
+  NS_ASSERTION(!GetPrevInFlow(),
+               "ResolveBidi called on non-first continuation");
+  MOZ_ASSERT(PresContext()->BidiEnabled());
+  return nsBidiPresUtils::Resolve(this);
+}
+
+void nsBlockFrame::UpdatePseudoElementStyles(ServoRestyleState& aRestyleState) {
+  // first-letter needs to be updated before first-line, because first-line can
+  // change the style of the first-letter.
+  if (HasFirstLetterChild()) {
+    UpdateFirstLetterStyle(aRestyleState);
+  }
+
+  if (nsIFrame* firstLineFrame = GetFirstLineFrame()) {
+    nsIFrame* styleParent = CorrectStyleParentFrame(firstLineFrame->GetParent(),
+                                                    PseudoStyleType::firstLine);
+
+    ComputedStyle* parentStyle = styleParent->Style();
+    RefPtr<ComputedStyle> firstLineStyle =
+        aRestyleState.StyleSet().ResolvePseudoElementStyle(
+            *mContent->AsElement(), PseudoStyleType::firstLine, nullptr,
+            parentStyle);
+
+    // FIXME(bz): Can we make first-line continuations be non-inheriting anon
+    // boxes?
+    RefPtr<ComputedStyle> continuationStyle =
+        aRestyleState.StyleSet().ResolveInheritingAnonymousBoxStyle(
+            PseudoStyleType::mozLineFrame, parentStyle);
+
+    UpdateStyleOfOwnedChildFrame(firstLineFrame, firstLineStyle, aRestyleState,
+                                 Some(continuationStyle.get()));
+
+    // We also want to update the styles of the first-line's descendants.  We
+    // don't need to compute a changehint for this, though, since any changes to
+    // them are handled by the first-line anyway.
+    RestyleManager* manager = PresContext()->RestyleManager();
+    for (nsIFrame* kid : firstLineFrame->PrincipalChildList()) {
+      manager->ReparentComputedStyleForFirstLine(kid);
+    }
+  }
+}
+
+nsIFrame* nsBlockFrame::GetFirstLetter() const {
+  if (!HasAnyStateBits(NS_BLOCK_HAS_FIRST_LETTER_STYLE)) {
+    // Certainly no first-letter frame.
+    return nullptr;
+  }
+
+  return GetProperty(FirstLetterProperty());
+}
+
+nsIFrame* nsBlockFrame::GetFirstLineFrame() const {
+  nsIFrame* maybeFirstLine = PrincipalChildList().FirstChild();
+  if (maybeFirstLine && maybeFirstLine->IsLineFrame()) {
+    return maybeFirstLine;
+  }
+
+  return nullptr;
+}
+
+#ifdef DEBUG
+void nsBlockFrame::VerifyLines(bool aFinalCheckOK) {
+  if (!gVerifyLines) {
+    return;
+  }
+  if (mLines.empty()) {
+    return;
+  }
+
+  nsLineBox* cursor = GetLineCursorForQuery();
+
+  // Add up the counts on each line. Also validate that IsFirstLine is
+  // set properly.
+  int32_t count = 0;
+  for (const auto& line : Lines()) {
+    if (&line == cursor) {
+      cursor = nullptr;
+    }
+    if (aFinalCheckOK) {
+      MOZ_ASSERT(line.GetChildCount(), "empty line");
+      if (line.IsBlock()) {
+        NS_ASSERTION(1 == line.GetChildCount(), "bad first line");
+      }
+    }
+    count += line.GetChildCount();
+  }
+
+  // Then count the frames
+  int32_t frameCount = 0;
+  nsIFrame* frame = mLines.front()->mFirstChild;
+  while (frame) {
+    frameCount++;
+    frame = frame->GetNextSibling();
+  }
+  NS_ASSERTION(count == frameCount, "bad line list");
+
+  // Next: test that each line has right number of frames on it
+  for (LineIterator line = LinesBegin(), line_end = LinesEnd();
+       line != line_end;) {
+    count = line->GetChildCount();
+    frame = line->mFirstChild;
+    while (--count >= 0) {
+      frame = frame->GetNextSibling();
+    }
+    ++line;
+    if ((line != line_end) && (0 != line->GetChildCount())) {
+      NS_ASSERTION(frame == line->mFirstChild, "bad line list");
+    }
+  }
+
+  if (cursor) {
+    FrameLines* overflowLines = GetOverflowLines();
+    if (overflowLines) {
+      LineIterator line = overflowLines->mLines.begin();
+      LineIterator line_end = overflowLines->mLines.end();
+      for (; line != line_end; ++line) {
+        if (line == cursor) {
+          cursor = nullptr;
+          break;
+        }
+      }
+    }
+  }
+  NS_ASSERTION(!cursor, "stale LineCursorProperty");
+}
+
+void nsBlockFrame::VerifyOverflowSituation() {
+  // Overflow out-of-flows must not have a next-in-flow in mFloats or mFrames.
+  nsFrameList* oofs = GetOverflowOutOfFlows();
+  if (oofs) {
+    for (nsIFrame* f : *oofs) {
+      nsIFrame* nif = f->GetNextInFlow();
+      MOZ_ASSERT(!nif ||
+                 (!mFloats.ContainsFrame(nif) && !mFrames.ContainsFrame(nif)));
+    }
+  }
+
+  // Pushed floats must not have a next-in-flow in mFloats or mFrames.
+  oofs = GetPushedFloats();
+  if (oofs) {
+    for (nsIFrame* f : *oofs) {
+      nsIFrame* nif = f->GetNextInFlow();
+      MOZ_ASSERT(!nif ||
+                 (!mFloats.ContainsFrame(nif) && !mFrames.ContainsFrame(nif)));
+    }
+  }
+
+  // A child float next-in-flow's parent must be |this| or a next-in-flow of
+  // |this|. Later next-in-flows must have the same or later parents.
+  ChildListID childLists[] = {FrameChildListID::Float,
+                              FrameChildListID::PushedFloats};
+  for (size_t i = 0; i < ArrayLength(childLists); ++i) {
+    const nsFrameList& children = GetChildList(childLists[i]);
+    for (nsIFrame* f : children) {
+      nsIFrame* parent = this;
+      nsIFrame* nif = f->GetNextInFlow();
+      for (; nif; nif = nif->GetNextInFlow()) {
+        bool found = false;
+        for (nsIFrame* p = parent; p; p = p->GetNextInFlow()) {
+          if (nif->GetParent() == p) {
+            parent = p;
+            found = true;
+            break;
+          }
+        }
+        MOZ_ASSERT(
+            found,
+            "next-in-flow is a child of parent earlier in the frame tree?");
+      }
+    }
+  }
+
+  nsBlockFrame* flow = static_cast<nsBlockFrame*>(FirstInFlow());
+  while (flow) {
+    FrameLines* overflowLines = flow->GetOverflowLines();
+    if (overflowLines) {
+      NS_ASSERTION(!overflowLines->mLines.empty(),
+                   "should not be empty if present");
+      NS_ASSERTION(overflowLines->mLines.front()->mFirstChild,
+                   "bad overflow lines");
+      NS_ASSERTION(overflowLines->mLines.front()->mFirstChild ==
+                       overflowLines->mFrames.FirstChild(),
+                   "bad overflow frames / lines");
+    }
+    auto checkCursor = [&](nsLineBox* cursor) -> bool {
+      if (!cursor) {
+        return true;
+      }
+      LineIterator line = flow->LinesBegin();
+      LineIterator line_end = flow->LinesEnd();
+      for (; line != line_end && line != cursor; ++line)
+        ;
+      if (line == line_end && overflowLines) {
+        line = overflowLines->mLines.begin();
+        line_end = overflowLines->mLines.end();
+        for (; line != line_end && line != cursor; ++line)
+          ;
+      }
+      return line != line_end;
+    };
+    MOZ_ASSERT(checkCursor(flow->GetLineCursorForDisplay()),
+               "stale LineCursorPropertyDisplay");
+    MOZ_ASSERT(checkCursor(flow->GetLineCursorForQuery()),
+               "stale LineCursorPropertyQuery");
+    flow = static_cast<nsBlockFrame*>(flow->GetNextInFlow());
+  }
+}
+
+int32_t nsBlockFrame::GetDepth() const {
+  int32_t depth = 0;
+  nsIFrame* parent = GetParent();
+  while (parent) {
+    parent = parent->GetParent();
+    depth++;
+  }
+  return depth;
+}
+
+already_AddRefed<ComputedStyle> nsBlockFrame::GetFirstLetterStyle(
+    nsPresContext* aPresContext) {
+  return aPresContext->StyleSet()->ProbePseudoElementStyle(
+      *mContent->AsElement(), PseudoStyleType::firstLetter, nullptr, Style());
+}
+#endif