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

ash/system/win/audio/tray_audio_delegate_win.h

Index: ash/system/win/audio/tray_audio_delegate_win.h
diff --git a/ash/system/win/audio/tray_audio_delegate_win.h b/ash/system/win/audio/tray_audio_delegate_win.h
index a299b7db33b3a1cf0905e6b93182287d63de18ba..9ab0208f9a12f098a4bdbd6b6d035e3e3b150104 100644
--- a/ash/system/win/audio/tray_audio_delegate_win.h
+++ b/ash/system/win/audio/tray_audio_delegate_win.h
@@ -18,18 +18,18 @@ namespace system {
 
 class ASH_EXPORT TrayAudioDelegateWin : public TrayAudioDelegate {
  public:
-  virtual ~TrayAudioDelegateWin() {}
+  ~TrayAudioDelegateWin() override {}
 
   // Overridden from TrayAudioDelegate.
-  virtual void AdjustOutputVolumeToAudibleLevel() override;
-  virtual int GetOutputDefaultVolumeMuteLevel() override;
-  virtual int GetOutputVolumeLevel() override;
-  virtual int GetActiveOutputDeviceIconId() override;
-  virtual bool HasAlternativeSources() override;
-  virtual bool IsOutputAudioMuted() override;
-  virtual void SetOutputAudioIsMuted(bool is_muted) override;
-  virtual void SetOutputVolumeLevel(int level) override;
-  virtual void SetInternalSpeakerChannelMode(AudioChannelMode mode) override;
+  void AdjustOutputVolumeToAudibleLevel() override;
+  int GetOutputDefaultVolumeMuteLevel() override;
+  int GetOutputVolumeLevel() override;
+  int GetActiveOutputDeviceIconId() override;
+  bool HasAlternativeSources() override;
+  bool IsOutputAudioMuted() override;
+  void SetOutputAudioIsMuted(bool is_muted) override;
+  void SetOutputVolumeLevel(int level) override;
+  void SetInternalSpeakerChannelMode(AudioChannelMode mode) override;
 
  private:
   base::win::ScopedComPtr<ISimpleAudioVolume> CreateDefaultVolumeControl();