[New Multicolumn] Remove RenderRegionSet.

Source/core/rendering/RenderMultiColumnFlowThread.cpp

 /*
  * 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 251 matching lines @@
     // We simply remain at our intrinsic height.
     computedValues.m_extent = logicalHeight;
     computedValues.m_position = logicalTop;
 }
 
 LayoutUnit RenderMultiColumnFlowThread::initialLogicalWidth() const
 {
     return columnWidth();
 }
 
+void RenderMultiColumnFlowThread::layout()
+{
+    RenderFlowThread::layout();
+    if (RenderMultiColumnSet* lastSet = lastMultiColumnSet())
+        lastSet->expandToEncompassFlowThreadContentsIfNeeded();
+}
+
 void RenderMultiColumnFlowThread::setPageBreak(LayoutUnit offset, LayoutUnit spaceShortage)
 {
     if (RenderMultiColumnSet* multicolSet = toRenderMultiColumnSet(regionAtBlockOffset(offset)))
         multicolSet->recordSpaceShortage(spaceShortage);
 }
 
 void RenderMultiColumnFlowThread::updateMinimumPageHeight(LayoutUnit offset, LayoutUnit minHeight)
 {
     if (RenderMultiColumnSet* multicolSet = toRenderMultiColumnSet(regionAtBlockOffset(offset)))
         multicolSet->updateMinimumColumnHeight(minHeight);
@@ skipping 17 matching lines @@
 }
 
 bool RenderMultiColumnFlowThread::isPageLogicalHeightKnown() const
 {
     if (RenderMultiColumnSet* columnSet = lastMultiColumnSet())
         return columnSet->computedColumnHeight();
     return false;
 }
 
 }