Column balancing support in the region based multicol implementation.

Source/core/rendering/RenderFlowThread.h

 /*
  * Copyright (C) 2011 Adobe Systems Incorporated. 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.
@@ skipping 86 matching lines @@
     void styleDidChange(StyleDifference, const RenderStyle* oldStyle);
 
     void repaintRectangleInRegions(const LayoutRect&) const;
 
     LayoutPoint adjustedPositionRelativeToOffsetParent(const RenderBoxModelObject&, const LayoutPoint&);
 
     LayoutUnit pageLogicalTopForOffset(LayoutUnit);
     LayoutUnit pageLogicalWidthForOffset(LayoutUnit);
     LayoutUnit pageLogicalHeightForOffset(LayoutUnit);
     LayoutUnit pageRemainingLogicalHeightForOffset(LayoutUnit, PageBoundaryRule = IncludePageBoundary);
-    
+
+    virtual void setPageBreak(LayoutUnit /*offset*/, LayoutUnit /*spaceShortage*/) { }
+    virtual void updateMinimumPageHeight(LayoutUnit /*offset*/, LayoutUnit /*minHeight*/) { }
+
     enum RegionAutoGenerationPolicy {
         AllowRegionAutoGeneration,
         DisallowRegionAutoGeneration,
     };
     RenderRegion* regionAtBlockOffset(LayoutUnit, bool extendLastRegion = false, RegionAutoGenerationPolicy = AllowRegionAutoGeneration);
 
     bool regionsHaveUniformLogicalWidth() const { return m_regionsHaveUniformLogicalWidth; }
     bool regionsHaveUniformLogicalHeight() const { return m_regionsHaveUniformLogicalHeight; }
 
     RenderRegion* mapFromFlowToRegion(TransformState&) const;
@@ skipping 176 matching lines @@
 };
 
 template <> struct ValueToString<RenderRegion*> {
     static String string(const RenderRegion* value) { return String::format("%p", value); }
 };
 #endif
 
 } // namespace WebCore
 
 #endif // RenderFlowThread_h