[New Multicolumn] Update sets' flow thread portion rectangles properly.

Source/core/rendering/RenderMultiColumnSet.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 268 matching lines @@
     } else {
         setAndConstrainColumnHeight(heightAdjustedForSetOffset(multiColumnFlowThread()->columnHeightAvailable()));
     }
 
     clearForcedBreaks();
 
     // Nuke previously stored minimum column height. Contents may have changed for all we know.
     m_minimumColumnHeight = 0;
 }
 
+void RenderMultiColumnSet::layout()
+{
+    RenderRegion::layout();
+
+    if (!nextSiblingMultiColumnSet()) {
+        // This is the last set, i.e. the last region. Seize the opportunity to validate them.
+        multiColumnFlowThread()->validateRegions();

[Julien - ping for review, 2014/05/06 23:46:00]

RenderFlowThread::layout calls this function already so why would we need to
call it twice?

[mstensho (USE GERRIT), 2014/05/07 07:35:11]

Done.

+    }
+}
+
 void RenderMultiColumnSet::computeLogicalHeight(LayoutUnit, LayoutUnit logicalTop, LogicalExtentComputedValues& computedValues) const
 {
     computedValues.m_extent = m_computedColumnHeight;
     computedValues.m_position = logicalTop;
 }
 
 LayoutUnit RenderMultiColumnSet::columnGap() const
 {
     RenderBlockFlow* parentBlock = multiColumnBlockFlow();
     if (parentBlock->style()->hasNormalColumnGap())
@@ skipping 305 matching lines @@
         fragments.append(fragment);
     }
 }
 
 const char* RenderMultiColumnSet::renderName() const
 {
     return "RenderMultiColumnSet";
 }
 
 }