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

Source/core/layout/LayoutMultiColumnSet.cpp

Index: Source/core/layout/LayoutMultiColumnSet.cpp
diff --git a/Source/core/layout/LayoutMultiColumnSet.cpp b/Source/core/layout/LayoutMultiColumnSet.cpp
index eadd7f014fd869eb8db696889b562dce5d083410..67bbec10c24ca118a669f368c73807aceaa44495 100644
--- a/Source/core/layout/LayoutMultiColumnSet.cpp
+++ b/Source/core/layout/LayoutMultiColumnSet.cpp
@@ -123,6 +123,12 @@ LayoutSize LayoutMultiColumnSet::flowThreadTranslationAtOffset(LayoutUnit blockO
     return row.offsetFromColumnSet() + row.flowThreadTranslationAtOffset(blockOffset);
 }
 
+LayoutPoint LayoutMultiColumnSet::visualPointToFlowThreadPoint(const LayoutPoint& visualPoint) const
+{
+    const MultiColumnFragmentainerGroup& row = fragmentainerGroupAtVisualPoint(visualPoint);
+    return row.visualPointToFlowThreadPoint(visualPoint - row.offsetFromColumnSet());
+}
+
 void LayoutMultiColumnSet::updateMinimumColumnHeight(LayoutUnit offsetInFlowThread, LayoutUnit height)
 {
     fragmentainerGroupAtFlowThreadOffset(offsetInFlowThread).updateMinimumColumnHeight(height);