Add support for the column-fill property.

Source/core/rendering/RenderMultiColumnBlock.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 26 matching lines @@
 public:
     RenderMultiColumnBlock(Element*);
 
     LayoutUnit columnHeightAvailable() const { return m_columnHeightAvailable; }
 
     LayoutUnit columnWidth() const { return m_columnWidth; }
     unsigned columnCount() const { return m_columnCount; }
 
     RenderMultiColumnFlowThread* flowThread() const { return m_flowThread; }
 
-    bool requiresBalancing() const { return !m_columnHeightAvailable; }
+    bool requiresBalancing() const { return !m_columnHeightAvailable || style()->columnFill() == ColumnFillBalance; }
 
 private:
     virtual bool isRenderMultiColumnBlock() const { return true; }
 
     virtual const char* renderName() const;
 
     virtual RenderObject* layoutSpecialExcludedChild(bool relayoutChildren, SubtreeLayoutScope&) OVERRIDE;
 
     virtual void styleDidChange(StyleDifference, const RenderStyle*) OVERRIDE;
 
@@ skipping 29 matching lines @@
     return static_cast<const RenderMultiColumnBlock*>(object);
 }
 
 // This will catch anyone doing an unnecessary cast.
 void toRenderMultiColumnBlock(const RenderMultiColumnBlock*);
 
 } // namespace WebCore
 
 #endif // RenderMultiColumnBlock_h