Add glReadPixel service implemenation....

gpu/command_buffer/client/gles2_implementation.h

 // Copyright (c) 2006-2009 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 GPU_COMMAND_BUFFER_CLIENT_GLES2_IMPLEMENTATION_H
 #define GPU_COMMAND_BUFFER_CLIENT_GLES2_IMPLEMENTATION_H
 
 #include "base/shared_memory.h"
 #include "gpu/command_buffer/common/gles2_cmd_utils.h"
 #include "gpu/command_buffer/client/gles2_cmd_helper.h"
@@ skipping 10 matching lines @@
 // GLES2CmdHelper but that entails changing your code to use and deal with
 // shared memory and synchronization issues.
 class GLES2Implementation {
  public:
   GLES2Implementation(
       GLES2CmdHelper* helper,
       size_t transfer_buffer_size,
       void* transfer_buffer,
       int32 transfer_buffer_id);
 
+  // The GLES2CmdHelper being used by this GLES2Implementation. You can use
+  // this to issue cmds at a lower level for certain kinds of optimization.
+  GLES2CmdHelper* helper() const {
+    return helper_;
+  }
+
   // Include the auto-generated part of this class. We split this because
   // it means we can easily edit the non-auto generated parts right here in
   // this file instead of having to edit some template or the code generator.
   #include "gpu/command_buffer/client/gles2_implementation_autogen.h"
 
  private:
   // Makes a set of Ids for glGen___ functions.
   void MakeIds(GLsizei n, GLuint* ids);
 
   // Frees a set of Ids for glDelete___ functions.
@@ skipping 37 matching lines @@
 
   DISALLOW_COPY_AND_ASSIGN(GLES2Implementation);
 };
 
 
 }  // namespace gles2
 }  // namespace command_buffer
 
 #endif  // GPU_COMMAND_BUFFER_CLIENT_GLES2_IMPLEMENTATION_H