[New Multicolumn] Layout support for column-span:all.

Source/core/rendering/RenderMultiColumnFlowThread.h

 /*
  * Copyright (C) 2012 Apple 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 130 matching lines @@
     void populate();
 
     // Empty the flow thread by moving everything to the parent. Remove all multicol specific
     // renderers. Then destroy the flow thread. Called when a multicol container becomes a regular
     // block.
     void evacuateAndDestroy();
 
     unsigned columnCount() const { return m_columnCount; }
     LayoutUnit columnHeightAvailable() const { return m_columnHeightAvailable; }
     void setColumnHeightAvailable(LayoutUnit available) { m_columnHeightAvailable = available; }
-    virtual bool heightIsAuto() const { return !columnHeightAvailable() || multiColumnBlockFlow()->style()->columnFill() == ColumnFillBalance; }
     bool progressionIsInline() const { return m_progressionIsInline; }
 
     virtual LayoutSize columnOffset(const LayoutPoint&) const override final;
 
     // Do we need to set a new width and lay out?
     virtual bool needsNewWidth() const;
 
+    virtual RenderMultiColumnSet* columnSetAtBlockOffset(LayoutUnit) const override final;
+
     void layoutColumns(bool relayoutChildren, SubtreeLayoutScope&);
 
     bool recalculateColumnHeights();
 
 protected:
     RenderMultiColumnFlowThread();
     void setProgressionIsInline(bool isInline) { m_progressionIsInline = isInline; }
 
     virtual void layout() override;
 
 private:
     void calculateColumnCountAndWidth(LayoutUnit& width, unsigned& count) const;
     void createAndInsertMultiColumnSet();
     void createAndInsertSpannerPlaceholder(RenderBox* spanner);
     virtual bool descendantIsValidColumnSpanner(RenderObject* descendant) const;
 
     virtual const char* renderName() const override;
     virtual void addRegionToThread(RenderMultiColumnSet*) override;
     virtual void willBeRemovedFromTree() override;
+    virtual LayoutUnit skipColumnSpanner(RenderBox*, LayoutUnit logicalTopInFlowThread) override;
     virtual void flowThreadDescendantWasInserted(RenderObject*) override;
     virtual void flowThreadDescendantWillBeRemoved(RenderObject*) override;
     virtual void computeLogicalHeight(LayoutUnit logicalHeight, LayoutUnit logicalTop, LogicalExtentComputedValues&) const override;
     virtual void updateLogicalWidth() override;
     virtual void setPageBreak(LayoutUnit offset, LayoutUnit spaceShortage) override;
     virtual void updateMinimumPageHeight(LayoutUnit offset, LayoutUnit minHeight) override;
-    virtual RenderMultiColumnSet* columnSetAtBlockOffset(LayoutUnit) const override;
     virtual bool addForcedRegionBreak(LayoutUnit, RenderObject* breakChild, bool isBefore, LayoutUnit* offsetBreakAdjustment = 0) override;
     virtual bool isPageLogicalHeightKnown() const override;
 
+    // The last set we worked on. It's not to be used as the "current set". The concept of a
+    // "current set" is difficult, since layout may jump back and forth in the tree, due to wrong
+    // top location estimates (due to e.g. margin collapsing), and possibly for other reasons.
+    RenderMultiColumnSet* m_lastSetWorkedOn;
+
     unsigned m_columnCount; // The used value of column-count
     LayoutUnit m_columnHeightAvailable; // Total height available to columns, or 0 if auto.
     bool m_inBalancingPass; // Set when relayouting for column balancing.
     bool m_needsColumnHeightsRecalculation; // Set when we need to recalculate the column set heights after layout.
     bool m_progressionIsInline; // Always true for regular multicol. False for paged-y overflow.
     bool m_isBeingEvacuated;
 };
 
 } // namespace blink
 
 #endif // RenderMultiColumnFlowThread_h