Update {virtual,override} to follow C++11 style in media.

media/base/mock_audio_renderer_sink.h

Index: media/base/mock_audio_renderer_sink.h
diff --git a/media/base/mock_audio_renderer_sink.h b/media/base/mock_audio_renderer_sink.h
index 5f1c245c428610b356d6acfb73196b2224db22ce..3a85d528a033a779827c0217e691c145ae230df6 100644
--- a/media/base/mock_audio_renderer_sink.h
+++ b/media/base/mock_audio_renderer_sink.h
@@ -21,12 +21,12 @@ class MockAudioRendererSink : public AudioRendererSink {
   MOCK_METHOD0(Play, void());
   MOCK_METHOD1(SetVolume, bool(double volume));
 
-  virtual void Initialize(const AudioParameters& params,
-                          RenderCallback* renderer) override;
+  void Initialize(const AudioParameters& params,
+                  RenderCallback* renderer) override;
   AudioRendererSink::RenderCallback* callback() { return callback_; }
 
  protected:
-  virtual ~MockAudioRendererSink();
+  ~MockAudioRendererSink() override;
 
  private:
   RenderCallback* callback_;