Region based multicol: support explicit column breaks

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 98 matching lines @@
     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);
 }
 
+bool RenderMultiColumnFlowThread::addForcedRegionBreak(LayoutUnit offset, RenderObject* /*breakChild*/, bool /*isBefore*/, LayoutUnit* offsetBreakAdjustment)
+{
+    if (RenderMultiColumnSet* multicolSet = toRenderMultiColumnSet(regionAtBlockOffset(offset))) {
+        multicolSet->addForcedBreak(offset);
+        if (offsetBreakAdjustment)
+            *offsetBreakAdjustment = pageLogicalHeightForOffset(offset) ? pageRemainingLogicalHeightForOffset(offset, IncludePageBoundary) : LayoutUnit();
+        return true;
+    }
+    return false;
 }
+
+}