[New Multicolumn] Remove RenderRegionSet.

Source/core/rendering/RenderFlowThread.cpp

 /*
  * 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 116 matching lines @@
 void RenderFlowThread::layout()
 {
     m_pageLogicalSizeChanged = m_regionsInvalidated && everHadLayout();
 
     validateRegions();
 
     CurrentRenderFlowThreadMaintainer currentFlowThreadSetter(this);
     RenderBlockFlow::layout();
 
     m_pageLogicalSizeChanged = false;
-
-    if (lastRegion())
-        lastRegion()->expandToEncompassFlowThreadContentsIfNeeded();
 }
 
 void RenderFlowThread::updateLogicalWidth()
 {
     setLogicalWidth(initialLogicalWidth());
 }
 
 void RenderFlowThread::computeLogicalHeight(LayoutUnit, LayoutUnit logicalTop, LogicalExtentComputedValues& computedValues) const
 {
     computedValues.m_position = logicalTop;
@@ skipping 398 matching lines @@
 {
     if (!m_renderFlowThread)
         return;
     RenderView* view = m_renderFlowThread->view();
     ASSERT(view->flowThreadController()->currentRenderFlowThread() == m_renderFlowThread);
     view->flowThreadController()->setCurrentRenderFlowThread(m_previousRenderFlowThread);
 }
 
 
 } // namespace WebCore