Add a UseCounter for clip CSS or -webkit-clip-path that clips positioned descendants.

Source/core/paint/DeprecatedPaintLayerPaintingInfo.h

 /*
  * Copyright (C) 2003, 2009, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Intel Corporation. All rights reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
@@ skipping 67 matching lines @@
 struct DeprecatedPaintLayerPaintingInfo {
     STACK_ALLOCATED();
     DeprecatedPaintLayerPaintingInfo(DeprecatedPaintLayer* inRootLayer, const LayoutRect& inDirtyRect,
         GlobalPaintFlags globalPaintFlags, const LayoutSize& inSubPixelAccumulation,
         LayoutObject* inPaintingRoot = 0)
         : rootLayer(inRootLayer)
         , paintingRoot(inPaintingRoot)
         , paintDirtyRect(inDirtyRect)
         , subPixelAccumulation(inSubPixelAccumulation)
         , clipToDirtyRect(true)
+        , ancestorHasClipPathClipping(false)
         , m_globalPaintFlags(globalPaintFlags)
     { }
 
     GlobalPaintFlags globalPaintFlags() const { return m_globalPaintFlags; }
 
     // TODO(jchaffraix): We should encapsulate all these fields.
     DeprecatedPaintLayer* rootLayer;
     LayoutObject* paintingRoot; // only paint descendants of this object
     LayoutRect paintDirtyRect; // relative to rootLayer;
     LayoutSize subPixelAccumulation;
     IntSize scrollOffsetAccumulation;
     bool clipToDirtyRect;
+    bool ancestorHasClipPathClipping;
 
 private:
     const GlobalPaintFlags m_globalPaintFlags;
 };
 
 } // namespace blink
 
 #endif // DeprecatedPaintLayerPaintingInfo_h