Merge 120640 - [chromium] REGRESSION(r120346) ContentLayerPainter should clear rect to be painted

Source/WebCore/platform/graphics/chromium/OpaqueRectTrackingContentLayerDelegate.cpp

 /*
  * Copyright (C) 2012 Google Inc. 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.
  * 2.  Redistributions in binary form must reproduce the above copyright
  *     notice, this list of conditions and the following disclaimer in the
@@ skipping 32 matching lines @@
 OpaqueRectTrackingContentLayerDelegate::~OpaqueRectTrackingContentLayerDelegate()
 {
 }
 
 void OpaqueRectTrackingContentLayerDelegate::paintContents(SkCanvas* canvas, const IntRect& clip, IntRect& opaque)
 {
     PlatformContextSkia platformContext(canvas);
     platformContext.setTrackOpaqueRegion(!m_opaque);
     GraphicsContext context(&platformContext);
 
-    context.clearRect(clip);
-    context.clip(clip);
-
     // Record transform prior to painting, as all opaque tracking will be
     // relative to this current value.
     AffineTransform canvasToContentTransform = context.getCTM().inverse();
 
     m_painter->paint(context, clip);
 
     // Transform tracked opaque paints back to our layer's content space.
     ASSERT(canvasToContentTransform.isInvertible());
     ASSERT(canvasToContentTransform.preservesAxisAlignment());
     FloatRect opaqueCanvasRect = platformContext.opaqueRegion().asRect();
     opaque = enclosedIntRect(canvasToContentTransform.mapRect(opaqueCanvasRect));
 }
 
 }