Column balancing support in the region based multicol implementation.

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 77 matching lines @@
     RenderMultiColumnSet* firstSet = toRenderMultiColumnSet(firstRegion());
     if (firstSet)
         return;
     
     invalidateRegions();
 
     RenderMultiColumnBlock* parentBlock = toRenderMultiColumnBlock(parent());
     firstSet = RenderMultiColumnSet::createAnonymous(this);
     firstSet->setStyle(RenderStyle::createAnonymousStyleWithDisplay(parentBlock->style(), BLOCK));
     parentBlock->RenderBlock::addChild(firstSet);
-    
-    // Even though we aren't placed yet, we can go ahead and set up our size.
-    firstSet->updateLogicalWidth();
-    firstSet->updateLogicalHeight();
 
-    firstSet->setRequiresBalancing(parentBlock->requiresBalancing());
-    
+    // Even though we aren't placed yet, we can go ahead and set up our size. At this point we're
+    // typically in the middle of laying out the thread, attempting to paginate, and we need to do
+    // some rudimentary "layout" of the set now, so that pagination will work.
+    firstSet->prepareForLayout();
+
     validateRegions();
 }
 
+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);
+}
+
+}