[Mojo] Fix race condition in sample_app's SwapBuffers

mojo/examples/sample_app/sample_gles2_delegate.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 MOJO_EXAMPLES_SAMPLE_APP_SAMPLE_GLES2_DELEGATE_H_
 #define MOJO_EXAMPLES_SAMPLE_APP_SAMPLE_GLES2_DELEGATE_H_
 
 #include "base/timer/timer.h"
 #include "mojo/examples/sample_app/spinning_cube.h"
 #include "mojo/public/bindings/gles2_client/gles2_client_impl.h"
 
 namespace mojo {
 namespace examples {
 
 class SampleGLES2Delegate : public GLES2Delegate {
  public:
   SampleGLES2Delegate();
   virtual ~SampleGLES2Delegate();
 
  private:
   virtual void DidCreateContext(
-      GLES2* gl, uint32_t width, uint32_t height) MOJO_OVERRIDE;
-  virtual void ContextLost(GLES2* gl) MOJO_OVERRIDE;
+      GLES2ClientImpl* gl, uint32_t width, uint32_t height) MOJO_OVERRIDE;
+  virtual void ContextLost(GLES2ClientImpl* gl) MOJO_OVERRIDE;
 
   void Draw();
 
   base::Time last_time_;
   base::RepeatingTimer<SampleGLES2Delegate> timer_;
-  GLES2* gl_;
   SpinningCube cube_;
+  GLES2ClientImpl* gl_;
 };
 
 }  // namespace examples
 }  // namespace mojo
 
 #endif  // MOJO_EXAMPLES_SAMPLE_APP_SAMPLE_GLES2_DELEGATE_H_