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

ash/system/audio/tray_audio_delegate.h

+// Copyright (c) 2012 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_H_
+#define ASH_SYSTEM_AUDIO_TRAY_AUDIO_DELEGATE_H_
+
+namespace ash {
+namespace system {
+
+class TrayAudioDelegate {
+ public:
+
+  enum { kNoAudioDeviceIcon = -1 };
+
+  virtual ~TrayAudioDelegate() {}
+
+  // Sets the volume level of the output device to the minimum level which is
+  // deemed to be audible.
+  virtual void AdjustOutputVolumeToAudibleLevel() = 0;
+
+  // Gets the default level in the range 0%-100% at which the output device
+  // should be muted.
+  virtual int GetOutputDefaultVolumeMuteLevel() = 0;
+
+  // Gets the icon to use for the current device.
+  virtual int GetDeviceIconId() = 0;

[jennyz, 2014/02/14 21:36:43]

The name is not accurate, how about lGetActiveOutputDeviceIconId? And please up
the comment accordingly.

[jennyz, 2014/02/14 21:40:05]

Sorry for the typo. No l before GetActiveOutputDeviceIconId.

[zturner, 2014/02/15 00:57:45]

Done.

+
+  // Returns the volume level of the output device in the range 0%-100%.
+  virtual int GetOutputVolumeLevel() = 0;
+
+  // Returns true if the device has alternative inputs or outputs.
+  virtual bool HasAlternativeSources() = 0;
+
+  // Returns whether the output volume is muted.
+  virtual bool IsOutputAudioMuted() = 0;
+
+  // Sets the mute state of the output device.
+  virtual void SetOutputAudioIsMuted(bool is_muted) = 0;
+
+  // Sets the volume level of the output device in the range 0%-100%
+  virtual void SetOutputVolumeLevel(int level) = 0;
+};
+
+}  // namespace system
+}  // namespace ash
+
+#endif  // ASH_SYSTEM_AUDIO_TRAY_AUDIO_DELEGATE_H_