Region based multicol: support explicit column breaks

Source/core/rendering/RenderMultiColumnFlowThread.cpp

Index: Source/core/rendering/RenderMultiColumnFlowThread.cpp
diff --git a/Source/core/rendering/RenderMultiColumnFlowThread.cpp b/Source/core/rendering/RenderMultiColumnFlowThread.cpp
index 1a2fc6f74b2def7b33634f373588b4b9dffea524..86ee4ed2de560f24e7de7dccc96a1a1d0f2aa7c1 100644
--- a/Source/core/rendering/RenderMultiColumnFlowThread.cpp
+++ b/Source/core/rendering/RenderMultiColumnFlowThread.cpp
@@ -116,4 +116,15 @@ void RenderMultiColumnFlowThread::updateMinimumPageHeight(LayoutUnit offset, Lay
         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;
+}
+
 }