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

content/common/gpu/client/command_buffer_proxy_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_COMMAND_BUFFER_PROXY_IMPL_H_
 #define CONTENT_COMMON_GPU_CLIENT_COMMAND_BUFFER_PROXY_IMPL_H_
 
 #include <map>
 #include <queue>
 #include <string>
@@ skipping 96 matching lines @@
   void RemoveDeletionObserver(DeletionObserver* observer);
 
   bool DiscardBackbuffer();
   bool EnsureBackbuffer();
 
   // Makes this command buffer invoke a task when a sync point is reached, or
   // the command buffer that inserted that sync point is destroyed.
   bool SignalSyncPoint(uint32 sync_point,
                        const base::Closure& callback);
 
+  // Makes this command buffer invoke a task when a query is completed, or
+  // the command buffer that inserted that sync point is destroyed.
+  // Should be invoked between begin/end query for reliable operation.
+  bool SignalQuery(unsigned query,
+                   const base::Closure& callback);
+
   // Generates n unique mailbox names that can be used with
   // GL_texture_mailbox_CHROMIUM. Unlike genMailboxCHROMIUM, this IPC is
   // handled only on the GPU process' IO thread, and so is not effectively
   // a finish.
   bool GenerateMailboxNames(unsigned num, std::vector<gpu::Mailbox>* names);
 
   // Sends an IPC message with the new state of surface visibility.
   bool SetSurfaceVisible(bool visible);
 
   void SetOnConsoleMessageCallback(
@@ skipping 70 matching lines @@
   // Tasks to be invoked in SignalSyncPoint responses.
   uint32 next_signal_id_;
   SignalTaskMap signal_tasks_;
 
   DISALLOW_COPY_AND_ASSIGN(CommandBufferProxyImpl);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_COMMON_GPU_CLIENT_COMMAND_BUFFER_PROXY_IMPL_H_