Perform glReadPixels with PBOs in the gpu, if PBOs are available.

cc/output/gl_renderer.h

 // Copyright 2010 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.
 
 #ifndef CC_OUTPUT_GL_RENDERER_H_
 #define CC_OUTPUT_GL_RENDERER_H_
 
 #include "base/cancelable_callback.h"
 #include "cc/base/cc_export.h"
 #include "cc/base/scoped_ptr_vector.h"
@@ skipping 186 matching lines @@
   typedef base::Callback<void(scoped_ptr<CopyOutputRequest> copy_request,
                               bool success)>
       AsyncGetFramebufferPixelsCleanupCallback;
   void DoGetFramebufferPixels(
       uint8* pixels,
       gfx::Rect window_rect,
       const AsyncGetFramebufferPixelsCleanupCallback& cleanup_callback);
   void FinishedReadback(
       const AsyncGetFramebufferPixelsCleanupCallback& cleanup_callback,
       unsigned source_buffer,
+      unsigned query,
       uint8_t* dest_pixels,
       gfx::Size size);
   void PassOnSkBitmap(scoped_ptr<SkBitmap> bitmap,
                       scoped_ptr<SkAutoLockPixels> lock,
                       scoped_ptr<CopyOutputRequest> request,
                       bool success);
   void DeleteTextureReleaseCallback(unsigned texture_id,
                                     unsigned sync_point,
                                     bool lost_resource);
 
@@ skipping 231 matching lines @@
 #if DEBUG_GL_CALLS && !defined(NDEBUG)
 #define GLC(context, x)                                                        \
   (x, GLRenderer::DebugGLCall(&* context, #x, __FILE__, __LINE__))
 #else
 #define GLC(context, x) (x)
 #endif
 
 }  // namespace cc
 
 #endif  // CC_OUTPUT_GL_RENDERER_H_