[New multicol] Eliminate the need for RenderMultiColumnBlock.

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 30 matching lines @@
 // as well).
 //
 // Column spans result in the creation of new column sets as well, since a spanning region has to be placed in between the column sets that
 // come before and after the span.
 class RenderMultiColumnSet FINAL : public RenderRegionSet {
 public:
     static RenderMultiColumnSet* createAnonymous(RenderFlowThread*);
 
     virtual bool isRenderMultiColumnSet() const OVERRIDE { return true; }
 
+    RenderBlockFlow* multiColumnBlockFlow() const { return toRenderBlockFlow(parent()); }
+    RenderMultiColumnFlowThread* multiColumnFlowThread() const { return multiColumnBlockFlow()->multiColumnFlowThread(); }
     unsigned computedColumnCount() const { return m_computedColumnCount; }
     LayoutUnit computedColumnWidth() const { return m_computedColumnWidth; }
     LayoutUnit computedColumnHeight() const { return m_computedColumnHeight; }
 
     void setComputedColumnWidthAndCount(LayoutUnit width, unsigned count)
     {
         m_computedColumnWidth = width;
         m_computedColumnCount = count;
     }
 
@@ skipping 106 matching lines @@
     };
     Vector<ContentRun, 1> m_contentRuns;
 };
 
 DEFINE_RENDER_OBJECT_TYPE_CASTS(RenderMultiColumnSet, isRenderMultiColumnSet());
 
 } // namespace WebCore
 
 #endif // RenderMultiColumnSet_h