[New Multicolumn] Rebalance properly when child content changes.

Source/core/rendering/RenderMultiColumnSet.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 90 matching lines @@
     bool recalculateColumnHeight(bool initial);
 
     // Record space shortage (the amount of space that would have been enough to prevent some
     // element from being moved to the next column) at a column break. The smallest amount of space
     // shortage we find is the amount with which we will stretch the column height, if it turns out
     // after layout that the columns weren't tall enough.
     void recordSpaceShortage(LayoutUnit spaceShortage);
 
     virtual void updateLogicalWidth() OVERRIDE;
 
-    void prepareForLayout();
+    void prepareForLayout(bool initial);
 
     // Expand this set's flow thread portion rectangle to contain all trailing flow thread
     // overflow. Only to be called on the last set.
     void expandToEncompassFlowThreadContentsIfNeeded();
 
 private:
     RenderMultiColumnSet(RenderFlowThread*);
 
     virtual void layout() OVERRIDE;
     virtual void computeLogicalHeight(LayoutUnit logicalHeight, LayoutUnit logicalTop, LogicalExtentComputedValues&) const OVERRIDE;
 
     virtual void paintObject(PaintInfo&, const LayoutPoint& paintOffset) OVERRIDE;
 
     virtual LayoutUnit pageLogicalWidth() const OVERRIDE { return m_computedColumnWidth; }
     virtual LayoutUnit pageLogicalHeight() const OVERRIDE { return m_computedColumnHeight; }
 
     virtual LayoutUnit pageLogicalTopForOffset(LayoutUnit offset) const OVERRIDE;
 
     virtual LayoutUnit logicalHeightOfAllFlowThreadContent() const OVERRIDE { return logicalHeightInFlowThread(); }
 
     virtual void repaintFlowThreadContent(const LayoutRect& repaintRect) const OVERRIDE;
 
     virtual void collectLayerFragments(LayerFragments&, const LayoutRect& layerBoundingBox, const LayoutRect& dirtyRect) OVERRIDE;
 
     virtual const char* renderName() const OVERRIDE;
 
     void paintColumnRules(PaintInfo&, const LayoutPoint& paintOffset);
 
+    LayoutUnit calculateMaxColumnHeight() const;
     LayoutUnit columnGap() const;
     LayoutRect columnRectAt(unsigned index) const;
     unsigned columnCount() const;
 
     LayoutRect flowThreadPortionRectAt(unsigned index) const;
     LayoutRect flowThreadPortionOverflowRect(const LayoutRect& flowThreadPortion, unsigned index, unsigned colCount, LayoutUnit colGap) const;
 
     enum ColumnIndexCalculationMode {
         ClampToExistingColumns, // Stay within the range of already existing columns.
         AssumeNewColumns // Allow column indices outside the range of already existing columns.
@@ skipping 49 matching lines @@
     };
     Vector<ContentRun, 1> m_contentRuns;
 };
 
 DEFINE_RENDER_OBJECT_TYPE_CASTS(RenderMultiColumnSet, isRenderMultiColumnSet());
 
 } // namespace WebCore
 
 #endif // RenderMultiColumnSet_h