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

cc/resources/sync_point_helper.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.
 
 #ifndef CC_RESOURCES_SYNC_POINT_HELPER_H_
 #define CC_RESOURCES_SYNC_POINT_HELPER_H_
 
 #include "base/callback.h"
 #include "cc/base/cc_export.h"
-
-namespace WebKit { class WebGraphicsContext3D; }
+#include "third_party/WebKit/public/platform/WebGraphicsContext3D.h"
 
 namespace cc {
 
 class CC_EXPORT SyncPointHelper {
  public:
   // Requests a callback to |closure| when the |sync_point| is reached by the
   // |context3d|.
   //
   // If the |context3d| is destroyed or lost before the callback fires, then
   // AbortBecauseDidLoseOrDestroyContext() must be called to clean up the
   // callback's resources.
   static void SignalSyncPoint(
       WebKit::WebGraphicsContext3D* context3d,
       unsigned sync_point,
       const base::Closure& closure);
 
+  static void SignalQuery(

[danakj, 2013/06/17 18:36:48]

nit: add a comment here to describe the function?

[hubbe, 2013/06/17 19:47:19]

Done.

+      WebKit::WebGraphicsContext3D* context3d,
+      WebKit::WebGLId query,
+      const base::Closure& closure);
+
  private:
   SyncPointHelper();
 
   DISALLOW_COPY_AND_ASSIGN(SyncPointHelper);
 };
 
 }  // namespace cc
 
 #endif  // CC_RESOURCES_SYNC_POINT_HELPER_H_