Use fragmented bounding box for hit-test/paint clipping.

Source/core/rendering/RenderLayer.h

Index: Source/core/rendering/RenderLayer.h
diff --git a/Source/core/rendering/RenderLayer.h b/Source/core/rendering/RenderLayer.h
index c46a78166e4697a19093bd3d6e9571c80cde24b8..f9bd3c9cedaf18153d92735d0a6cd6f4b637780d 100644
--- a/Source/core/rendering/RenderLayer.h
+++ b/Source/core/rendering/RenderLayer.h
@@ -230,6 +230,7 @@ public:
     // Bounding box relative to some ancestor layer. Pass offsetFromRoot if known.
     LayoutRect physicalBoundingBox(const RenderLayer* ancestorLayer, const LayoutPoint* offsetFromRoot = 0) const;
     LayoutRect physicalBoundingBoxIncludingReflectionAndStackingChildren(const RenderLayer* ancestorLayer, const LayoutPoint& offsetFromRoot) const;
+    LayoutRect fragmentsBoundingBox(const RenderLayer* ancestorLayer) const;
 
     // FIXME: This function is inconsistent as to whether the returned rect has been flipped for writing mode.
     LayoutRect boundingBoxForCompositingOverlapTest() const { return overlapBoundsIncludeChildren() ? boundingBoxForCompositing() : logicalBoundingBox(); }
@@ -543,6 +544,7 @@ public:
 private:
     // Bounding box in the coordinates of this layer.
     LayoutRect logicalBoundingBox() const;
+    LayoutRect flippedLogicalBoundingBox() const;
 
     bool hasOverflowControls() const;