[New Multicolumn] Add support for column-span:all

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 49 matching lines @@
     virtual bool isRenderFlowThread() const OVERRIDE FINAL { return true; }
     virtual bool isRenderMultiColumnFlowThread() const { return false; }
     virtual bool isRenderPagedFlowThread() const { return false; }
 
     virtual void layout() OVERRIDE;
 
     // Always create a RenderLayer for the RenderFlowThread so that we
     // can easily avoid drawing the children directly.
     virtual LayerType layerTypeRequired() const OVERRIDE FINAL { return NormalLayer; }
 
+    // Some renderers (column spanners) are moved out of the flow thread to live among column
+    // sets. If |child| is such a renderer, resolve it to the placeholder that lives at the original
+    // location in the tree.
+    virtual RenderObject* resolveMovedChild(RenderObject* child) const { return child; }
+    // Called when a descendant of the flow thread has been inserted.
+    virtual void flowThreadDescendantInserted(RenderObject*) { }
+    // Called when a sibling or descendant of the flow thread is about to be removed.
+    virtual void flowThreadRelativeWillBeRemoved(RenderObject*) { }
+    // Called when a descendant box's layout is finished and it has been positioned within its container.
+    virtual void flowThreadDescendantBoxLaidOut(RenderBox*, LayoutUnit /*logicalBottomInFlowThread*/) { }
+
     virtual bool nodeAtPoint(const HitTestRequest&, HitTestResult&, const HitTestLocation& locationInContainer, const LayoutPoint& accumulatedOffset, HitTestAction) OVERRIDE FINAL;
 
     virtual void addRegionToThread(RenderRegion*) = 0;
     virtual void removeRegionFromThread(RenderRegion*);
     const RenderRegionList& renderRegionList() const { return m_regionList; }
 
     virtual void computeLogicalHeight(LayoutUnit logicalHeight, LayoutUnit logicalTop, LogicalExtentComputedValues&) const OVERRIDE;
 
     bool hasRegions() const { return m_regionList.size(); }
 
@@ skipping 136 matching lines @@
 };
 
 template <> struct ValueToString<RenderRegion*> {
     static String string(const RenderRegion* value) { return String::format("%p", value); }
 };
 #endif
 
 } // namespace WebCore
 
 #endif // RenderFlowThread_h