[New multicol] Eliminate the need for RenderMultiColumnBlock.

Source/core/rendering/RenderBlock.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2007 David Smith (catfish.man@gmail.com)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
@@ skipping 371 matching lines @@
     virtual void addChildIgnoringContinuation(RenderObject* newChild, RenderObject* beforeChild) OVERRIDE;
     void addChildToAnonymousColumnBlocks(RenderObject* newChild, RenderObject* beforeChild);
 
     void addChildIgnoringAnonymousColumnBlocks(RenderObject* newChild, RenderObject* beforeChild = 0);
 
     virtual bool isSelfCollapsingBlock() const OVERRIDE;
 
     void insertIntoTrackedRendererMaps(RenderBox* descendant, TrackedDescendantsMap*&, TrackedContainerMap*&);
     static void removeFromTrackedRendererMaps(RenderBox* descendant, TrackedDescendantsMap*&, TrackedContainerMap*&);
 
-    // Called to lay out the legend for a fieldset or the ruby text of a ruby run.
-    virtual RenderObject* layoutSpecialExcludedChild(bool /*relayoutChildren*/, SubtreeLayoutScope&) { return 0; }
-
     void createFirstLetterRenderer(RenderObject* firstLetterBlock, RenderObject* currentChild, unsigned length);
     void updateFirstLetterStyle(RenderObject* firstLetterBlock, RenderObject* firstLetterContainer);
 
     Node* nodeForHitTest() const;
 
     // FIXME-BLOCKFLOW: Remove virtualizaion when all callers have moved to RenderBlockFlow
     virtual void paintFloats(PaintInfo&, const LayoutPoint&, bool) { }
     void paintContents(PaintInfo&, const LayoutPoint&);
     void paintColumnContents(PaintInfo&, const LayoutPoint&, bool paintFloats = false);
     void paintColumnRules(PaintInfo&, const LayoutPoint&);
@@ skipping 182 matching lines @@
             return false;
     }
     return true;
 }
 
 DEFINE_RENDER_OBJECT_TYPE_CASTS(RenderBlock, isRenderBlock());
 
 } // namespace WebCore
 
 #endif // RenderBlock_h