getClientRects() shouldn't clip against any ancestors.

third_party/WebKit/Source/core/layout/MultiColumnFragmentainerGroup.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef MultiColumnFragmentainerGroup_h
 #define MultiColumnFragmentainerGroup_h
 
 #include "core/layout/LayoutMultiColumnFlowThread.h"
 #include "wtf/Allocator.h"
 
@@ skipping 85 matching lines @@
   // that positionForPoint() depends on.
   enum SnapToColumnPolicy { DontSnapToColumn, SnapToColumn };
   LayoutPoint visualPointToFlowThreadPoint(
       const LayoutPoint& visualPoint,
       SnapToColumnPolicy = DontSnapToColumn) const;
 
   LayoutRect fragmentsBoundingBox(
       const LayoutRect& boundingBoxInFlowThread) const;
 
   LayoutRect flowThreadPortionRectAt(unsigned columnIndex) const;
-  LayoutRect flowThreadPortionOverflowRectAt(unsigned columnIndex) const;
+
+  enum ClipRectAxesSelector {
+    // Only limit the clip rectangle in the block direction. Leave inline
+    // position and length at infinity. Certain operations require this. Those
+    // operations would typically ideally want no clipping at all, but in our
+    // implementation we have to clip in the block direction, in order to slice
+    // the flow thread properly into columns.
+    BlockDirectionAxis,
+
+    // Limit the clip rectangle along both axes. This is what to use for
+    // painting and hit testing.
+    BothAxes
+  };
+
+  LayoutRect flowThreadPortionOverflowRectAt(
+      unsigned columnIndex,
+      ClipRectAxesSelector = BothAxes) const;
 
   // Get the first and the last column intersecting the specified block range.
   // Note that |logicalBottomInFlowThread| is an exclusive endpoint.
   void columnIntervalForBlockRangeInFlowThread(
       LayoutUnit logicalTopInFlowThread,
       LayoutUnit logicalBottomInFlowThread,
       unsigned& firstColumn,
       unsigned& lastColumn) const;
 
   // Get the first and the last column intersecting the specified visual
@@ skipping 87 matching lines @@
 
  private:
   LayoutMultiColumnSet& m_columnSet;
 
   Vector<MultiColumnFragmentainerGroup, 1> m_groups;
 };
 
 }  // namespace blink
 
 #endif  // MultiColumnFragmentainerGroup_h