Need deeper layout passes inside flexboxes when fragmenting (pagination, multicol).

Source/core/layout/LayoutFlexibleBox.h

 /*
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
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     void setFlowAwareLocationForChild(LayoutBox& child, const LayoutPoint&);
     void adjustAlignmentForChild(LayoutBox& child, LayoutUnit);
     ItemPosition alignmentForChild(LayoutBox& child) const;
     LayoutUnit mainAxisBorderAndPaddingExtentForChild(LayoutBox& child) const;
     LayoutUnit computeInnerFlexBaseSizeForChild(LayoutBox& child, ChildLayoutType = LayoutIfNeeded);
     bool mainAxisLengthIsIndefinite(const Length& flexBasis) const;
     bool childFlexBaseSizeRequiresLayout(LayoutBox& child) const;
     bool needToStretchChildLogicalHeight(LayoutBox& child) const;
     EOverflow mainAxisOverflowForChild(LayoutBox& child) const;
 
-    void layoutFlexItems(bool relayoutChildren);
+    void layoutFlexItems(bool relayoutChildren, SubtreeLayoutScope&);
     LayoutUnit autoMarginOffsetInMainAxis(const OrderedFlexItemList&, LayoutUnit& availableFreeSpace);
     void updateAutoMarginsInMainAxis(LayoutBox& child, LayoutUnit autoMarginOffset);
     bool hasAutoMarginsInCrossAxis(LayoutBox& child) const;
     bool updateAutoMarginsInCrossAxis(LayoutBox& child, LayoutUnit availableAlignmentSpace);
     void repositionLogicalHeightDependentFlexItems(Vector<LineContext>&);
     LayoutUnit clientLogicalBottomAfterRepositioning();
     void appendChildFrameRects(ChildFrameRects&);
 
     LayoutUnit availableAlignmentSpaceForChild(LayoutUnit lineCrossAxisExtent, LayoutBox& child);
     LayoutUnit availableAlignmentSpaceForChildBeforeStretching(LayoutUnit lineCrossAxisExtent, LayoutBox& child);
     LayoutUnit marginBoxAscentForChild(LayoutBox& child);
 
     LayoutUnit computeChildMarginValue(Length margin);
     void prepareOrderIteratorAndMargins();
     LayoutUnit adjustChildSizeForMinAndMax(LayoutBox& child, LayoutUnit childSize, bool childShrunk = false);
     // The hypothetical main size of an item is the flex base size clamped according to its min and max main size properties
     bool computeNextFlexLine(OrderedFlexItemList& orderedChildren, LayoutUnit& sumFlexBaseSize, double& totalFlexGrow, double& totalWeightedFlexShrink, LayoutUnit& sumHypotheticalMainSize, bool relayoutChildren);
 
     bool resolveFlexibleLengths(FlexSign, const OrderedFlexItemList&, LayoutUnit& availableFreeSpace, double& totalFlexGrow, double& totalWeightedFlexShrink, InflexibleFlexItemSize&, Vector<LayoutUnit, 16>& childSizes);
     void freezeViolations(const Vector<Violation>&, LayoutUnit& availableFreeSpace, double& totalFlexGrow, double& totalWeightedFlexShrink, InflexibleFlexItemSize&);
 
     void resetAutoMarginsAndLogicalTopInCrossAxis(LayoutBox& child);
     void setOverrideMainAxisSizeForChild(LayoutBox& child, LayoutUnit childPreferredSize);
     void prepareChildForPositionedLayout(LayoutBox& child, LayoutUnit mainAxisOffset, LayoutUnit crossAxisOffset, PositionedLayoutMode);
     size_t numberOfInFlowPositionedChildren(const OrderedFlexItemList&) const;
-    void layoutAndPlaceChildren(LayoutUnit& crossAxisOffset, const OrderedFlexItemList&, const Vector<LayoutUnit, 16>& childSizes, LayoutUnit availableFreeSpace, bool relayoutChildren, Vector<LineContext>&);
+    void layoutAndPlaceChildren(LayoutUnit& crossAxisOffset, const OrderedFlexItemList&, const Vector<LayoutUnit, 16>& childSizes, LayoutUnit availableFreeSpace, bool relayoutChildren, SubtreeLayoutScope&, Vector<LineContext>&);
     void layoutColumnReverse(const OrderedFlexItemList&, LayoutUnit crossAxisOffset, LayoutUnit availableFreeSpace);
     void alignFlexLines(Vector<LineContext>&);
     void alignChildren(const Vector<LineContext>&);
     void applyStretchAlignmentToChild(LayoutBox& child, LayoutUnit lineCrossAxisExtent);
     void flipForRightToLeftColumn();
     void flipForWrapReverse(const Vector<LineContext>&, LayoutUnit crossAxisStartEdge);
 
     // This is used to cache the preferred size for orthogonal flow children so we don't have to relayout to get it
     HashMap<const LayoutObject*, LayoutUnit> m_intrinsicSizeAlongMainAxis;
 
     mutable OrderIterator m_orderIterator;
     int m_numberOfInFlowChildrenOnFirstLine;
 };
 
 DEFINE_LAYOUT_OBJECT_TYPE_CASTS(LayoutFlexibleBox, isFlexibleBox());
 
 } // namespace blink
 
 #endif // LayoutFlexibleBox_h