[New Multicolumn] balancer confused by content with top margins.

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 dc0e663ea045ab6a428a9b7dd9b2c82814936abd..12d9cea7f18fdc978c5a13bffe52e36e8cd7bdb5 100644
--- a/Source/core/rendering/RenderMultiColumnFlowThread.cpp
+++ b/Source/core/rendering/RenderMultiColumnFlowThread.cpp
@@ -229,4 +229,13 @@ bool RenderMultiColumnFlowThread::addForcedRegionBreak(LayoutUnit offset, Render
     return false;
 }
 
+bool RenderMultiColumnFlowThread::isPageLogicalHeightKnown() const
+{
+    for (RenderBox* renderer = parentBox()->lastChildBox(); renderer; renderer = renderer->previousSiblingBox()) {
+        if (renderer->isRenderMultiColumnSet())
+            return toRenderMultiColumnSet(renderer)->computedColumnHeight();
+    }
+    return true;
+}
+
 }