Revert 251959 "Refactor the TrayAudio code so that it can be use..."

trunk/src/ash/system/audio/audio_observer.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_AUDIO_AUDIO_OBSERVER_H_
-#define ASH_SYSTEM_AUDIO_AUDIO_OBSERVER_H_
-
-namespace ash {
-
-class AudioObserver {
- public:
-  virtual ~AudioObserver() {}
-
-  // Called when output volume changed.
-  virtual void OnOutputVolumeChanged() = 0;
-
-  // Called when output mute state changed.
-  virtual void OnOutputMuteChanged() = 0;
-
-  // Called when audio nodes changed.
-  virtual void OnAudioNodesChanged() = 0;
-
-  // Called when active audio output node changed.
-  virtual void OnActiveOutputNodeChanged() = 0;
-
-  // Called when active audio input node changed.
-  virtual void OnActiveInputNodeChanged() = 0;
-};
-
-}  // namespace ash
-
-#endif  // ASH_SYSTEM_AUDIO_AUDIO_OBSERVER_H_