Refactor the TrayAudio code so that it can be used by other platforms.

ash/system/chromeos/audio/tray_audio_delegate_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_AUDIO_TRAY_AUDIO_DELEGATE_CHROMEOS_H_
+#define ASH_SYSTEM_AUDIO_TRAY_AUDIO_DELEGATE_CHROMEOS_H_
+
+#include "ash/ash_export.h"
+#include "ash/system/audio/tray_audio_delegate.h"
+#include "base/compiler_specific.h"
+
+namespace ash {
+namespace system {
+
+class ASH_EXPORT TrayAudioDelegateChromeOs : public TrayAudioDelegate {
+ public:
+  virtual ~TrayAudioDelegateChromeOs() {}
+
+  // 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;
+};
+
+}  // namespace system
+}  // namespace ash
+
+#endif  // ASH_SYSTEM_AUDIO_TRAY_AUDIO_DELEGATE_CHROMEOS_H_