gpu: Add EGL fence support.

ui/gl/gl_fence.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 UI_GL_GL_FENCE_H_
 #define UI_GL_GL_FENCE_H_
 
 #include "base/basictypes.h"
 #include "ui/gl/gl_export.h"
 
 namespace gfx {
 
 class GL_EXPORT GLFence {
  public:
   GLFence();
   virtual ~GLFence();
 
   static GLFence* Create();
   virtual bool HasCompleted() = 0;
+  virtual void ClientWait() = 0;
 
  protected:
   static bool IsContextLost();
 
  private:
   DISALLOW_COPY_AND_ASSIGN(GLFence);
 };
 
 }  // namespace gfx
 
 #endif  // UI_GL_GL_FENCE_H_