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

content/common/gpu/client/webgraphicscontext3d_command_buffer_impl.h

 // Copyright (c) 2012 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 CONTENT_COMMON_GPU_CLIENT_WEBGRAPHICSCONTEXT3D_COMMAND_BUFFER_IMPL_H_
 #define CONTENT_COMMON_GPU_CLIENT_WEBGRAPHICSCONTEXT3D_COMMAND_BUFFER_IMPL_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 112 matching lines @@
   // graphics context fails to create. Do not call from more than one thread.
   virtual bool makeContextCurrent();
 
   virtual int width();
   virtual int height();
 
   virtual unsigned int insertSyncPoint();
   virtual void waitSyncPoint(unsigned int sync_point);
   virtual void signalSyncPoint(unsigned sync_point,
                                WebGraphicsSyncPointCallback* callback);
+  virtual void signalQuery(unsigned query,
+                           WebGraphicsSyncPointCallback* callback);
 
   virtual void reshape(int width, int height);
   virtual void reshapeWithScaleFactor(
       int width, int height, float scale_factor);
 
   virtual bool readBackFramebuffer(unsigned char* pixels, size_t buffer_size);
   virtual bool readBackFramebuffer(unsigned char* pixels, size_t buffer_size,
                                    WebGLId framebuffer, int width, int height);
 
   virtual void prepareTexture();
@@ skipping 608 matching lines @@
   bool use_echo_for_swap_ack_;
   size_t command_buffer_size_;
   size_t start_transfer_buffer_size_;
   size_t min_transfer_buffer_size_;
   size_t max_transfer_buffer_size_;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_COMMON_GPU_CLIENT_WEBGRAPHICSCONTEXT3D_COMMAND_BUFFER_IMPL_H_