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

Source/core/html/HTMLCanvasElement.cpp

 /*
  * Copyright (C) 2004, 2006, 2007 Apple Inc. All rights reserved.
  * Copyright (C) 2007 Alp Toker <alp@atoker.com>
  * Copyright (C) 2010 Torch Mobile (Beijing) Co. Ltd. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
@@ skipping 573 matching lines @@
 
 bool HTMLCanvasElement::originClean() const
 {
     if (document().settings() && document().settings()->disableReadingFromCanvas())
         return false;
     return m_originClean;
 }
 
 bool HTMLCanvasElement::shouldAccelerate(const IntSize& size) const
 {
+    fprintf(stderr, "shouldAccelerate?\n");
     if (m_context && !m_context->is2d())
         return false;
 
     if (m_accelerationDisabled)
         return false;
 
     if (RuntimeEnabledFeatures::forceDisplayList2dCanvasEnabled())
         return false;
 
     Settings* settings = document().settings();
@@ skipping 339 matching lines @@
 {
     return FloatSize(width(), height());
 }
 
 bool HTMLCanvasElement::isOpaque() const
 {
     return m_context && !m_context->hasAlpha();
 }
 
 } // blink