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

ash/system/chromeos/audio/tray_audio_chromeos.h

 // Copyright 2014 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 ASH_SYSTEM_CHROMEOS_AUDIO_TRAY_AUDIO_CHROMEOS_H_
 #define ASH_SYSTEM_CHROMEOS_AUDIO_TRAY_AUDIO_CHROMEOS_H_
 
 #include "ash/ash_export.h"
 #include "ash/system/audio/tray_audio.h"
 #include "base/memory/scoped_ptr.h"
 
 namespace ash {
 namespace tray {
 class AudioDetailedView;
 }
 
 class ASH_EXPORT TrayAudioChromeOs : public TrayAudio {
  public:
   explicit TrayAudioChromeOs(SystemTray* system_tray);
-  virtual ~TrayAudioChromeOs();
+  ~TrayAudioChromeOs() override;
 
  protected:
   // Overridden from TrayAudio
-  virtual void Update() override;
+  void Update() override;
 
  private:
   // Overridden from SystemTrayItem.
-  virtual views::View* CreateDetailedView(user::LoginStatus status) override;
-  virtual void DestroyDetailedView() override;
+  views::View* CreateDetailedView(user::LoginStatus status) override;
+  void DestroyDetailedView() override;
 
   tray::AudioDetailedView* audio_detail_view_;
 
   DISALLOW_COPY_AND_ASSIGN(TrayAudioChromeOs);
 };
 
 }  // namespace ash
 
 #endif  // ASH_SYSTEM_CHROMEOS_AUDIO_TRAY_AUDIO_CHROMEOS_H_