Intersect with the dirty rect before deciding which columns to examine for collection.

Source/core/layout/MultiColumnFragmentainerGroup.h

Index: Source/core/layout/MultiColumnFragmentainerGroup.h
diff --git a/Source/core/layout/MultiColumnFragmentainerGroup.h b/Source/core/layout/MultiColumnFragmentainerGroup.h
index c55994764c3d818caf258bc9eb9bd5b7fa67f5ce..8912e8328a88488613f318046a61e9732a7ffa48 100644
--- a/Source/core/layout/MultiColumnFragmentainerGroup.h
+++ b/Source/core/layout/MultiColumnFragmentainerGroup.h
@@ -99,6 +99,9 @@ private:
     // not inside any of the columns.
     unsigned columnIndexAtVisualPoint(const LayoutPoint& visualPoint) const;
 
+    // Get the first and the last column intersecting the specified visual rectangle.
+    void columnIntervalForVisualRect(const LayoutRect&, unsigned& firstColumn, unsigned& lastColumn) const;
+
     LayoutMultiColumnSet& m_columnSet;
 
     LayoutUnit m_logicalTop;