cc: Make async readback path use async glRreadPixels.

cc/test/pixel_test.h

 // Copyright 2013 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.
 
 #include "base/file_util.h"
 #include "cc/quads/render_pass.h"
 #include "cc/test/pixel_comparator.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "ui/gfx/size.h"
 
@@ skipping 18 matching lines @@
 
   gfx::Size device_viewport_size_;
   scoped_ptr<OutputSurface> output_surface_;
   scoped_ptr<ResourceProvider> resource_provider_;
   class PixelTestRendererClient;
   scoped_ptr<PixelTestRendererClient> fake_client_;
   scoped_ptr<GLRenderer> renderer_;
   scoped_ptr<SkBitmap> result_bitmap_;
 
  private:
-  void ReadbackResult(scoped_ptr<SkBitmap> bitmap);
+  void ReadbackResult(base::Closure quit_run_loop, scoped_ptr<SkBitmap> bitmap);
 
   bool PixelsMatchReference(const base::FilePath& ref_file,
                             const PixelComparator& comparator);
 };
 
 }  // namespace cc
 
 #endif  // CC_TEST_PIXEL_TEST_H_