[New Multicolumn] Let a spanner's containing block be the multicol container.

Source/core/rendering/RenderBlockFlow.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) 2003-2013 Apple Inc. All rights reserved.
  * Copyright (C) Research In Motion Limited 2010. All rights reserved.
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
@@ skipping 216 matching lines @@
 
 protected:
     void rebuildFloatsFromIntruding();
     void layoutInlineChildren(bool relayoutChildren, LayoutUnit& paintInvalidationLogicalTop, LayoutUnit& paintInvalidationLogicalBottom, LayoutUnit afterEdge);
 
     void createFloatingObjects();
 
     virtual void styleWillChange(StyleDifference, const RenderStyle& newStyle) override;
     virtual void styleDidChange(StyleDifference, const RenderStyle* oldStyle) override;
 
+    void updateBlockChildDirtyBitsBeforeLayout(bool relayoutChildren, RenderBox&);
+
     void addOverflowFromFloats();
 
     LayoutUnit logicalRightOffsetForLine(LayoutUnit logicalTop, LayoutUnit fixedOffset, bool applyTextIndent, LayoutUnit logicalHeight = 0) const
     {
         return adjustLogicalRightOffsetForLine(logicalRightFloatOffsetForLine(logicalTop, fixedOffset, logicalHeight), applyTextIndent);
     }
     LayoutUnit logicalLeftOffsetForLine(LayoutUnit logicalTop, LayoutUnit fixedOffset, bool applyTextIndent, LayoutUnit logicalHeight = 0) const
     {
         return adjustLogicalLeftOffsetForLine(logicalLeftFloatOffsetForLine(logicalTop, fixedOffset, logicalHeight), applyTextIndent);
     }
@@ skipping 276 matching lines @@
 
 // END METHODS DEFINED IN RenderBlockLineLayout
 
 };
 
 DEFINE_RENDER_OBJECT_TYPE_CASTS(RenderBlockFlow, isRenderBlockFlow());
 
 } // namespace blink
 
 #endif // RenderBlockFlow_h