Add OVERRIDE to media/.

media/filters/null_video_renderer.h

 // Copyright (c) 2011 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 MEDIA_FILTERS_NULL_VIDEO_RENDERER_H_
 #define MEDIA_FILTERS_NULL_VIDEO_RENDERER_H_
 
 #include "media/filters/video_renderer_base.h"
 
 namespace media {
 
 class NullVideoRenderer : public VideoRendererBase {
  public:
   NullVideoRenderer();
 
   // VideoRendererBase implementation.
-  virtual bool OnInitialize(VideoDecoder* decoder);
-  virtual void OnStop(const base::Closure& callback);
-  virtual void OnFrameAvailable();
+  virtual bool OnInitialize(VideoDecoder* decoder) OVERRIDE;
+  virtual void OnStop(const base::Closure& callback) OVERRIDE;
+  virtual void OnFrameAvailable() OVERRIDE;
 
  private:
   // Only allow to be deleted by reference counting.
   friend class scoped_refptr<NullVideoRenderer>;
   virtual ~NullVideoRenderer();
 
   DISALLOW_COPY_AND_ASSIGN(NullVideoRenderer);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_FILTERS_NULL_VIDEO_RENDERER_H_