[New Multicolumn] mapAbsoluteToLocalPoint() needs to convert to flow thread coordinates.

Source/core/layout/LayoutMultiColumnFlowThread.h

Index: Source/core/layout/LayoutMultiColumnFlowThread.h
diff --git a/Source/core/layout/LayoutMultiColumnFlowThread.h b/Source/core/layout/LayoutMultiColumnFlowThread.h
index b16b66c688e03c06fda32a69ea3564f53780488e..4f7a038cc6453a215ed1cdda8d27cad6c87323ca 100644
--- a/Source/core/layout/LayoutMultiColumnFlowThread.h
+++ b/Source/core/layout/LayoutMultiColumnFlowThread.h
@@ -167,6 +167,8 @@ public:
     // Do we need to set a new width and lay out?
     virtual bool needsNewWidth() const;
 
+    virtual LayoutPoint visualPointToFlowThreadPoint(const LayoutPoint& visualPoint) const override;
+
     virtual LayoutMultiColumnSet* columnSetAtBlockOffset(LayoutUnit) const override final;
 
     void layoutColumns(bool relayoutChildren, SubtreeLayoutScope&);