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

Source/core/layout/LayoutMultiColumnSet.h

Index: Source/core/layout/LayoutMultiColumnSet.h
diff --git a/Source/core/layout/LayoutMultiColumnSet.h b/Source/core/layout/LayoutMultiColumnSet.h
index 9de82f69b480a67ad052a56484ab4a8413b7664f..590ebd97a070d7c2e9dd33f1c4aac1721d76fa64 100644
--- a/Source/core/layout/LayoutMultiColumnSet.h
+++ b/Source/core/layout/LayoutMultiColumnSet.h
@@ -96,6 +96,8 @@ public:
     // get from flow thread coordinates to visual coordinates.
     LayoutSize flowThreadTranslationAtOffset(LayoutUnit) const;
 
+    LayoutPoint visualPointToFlowThreadPoint(const LayoutPoint& visualPoint) const;
+
     void updateMinimumColumnHeight(LayoutUnit offsetInFlowThread, LayoutUnit height);
 
     // Add a content run, specified by its end position. A content run is appended at every