Consolidate volume control code.

ash/volume_control_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_VOLUME_CONTROL_DELEGATE_H_
 #define ASH_VOLUME_CONTROL_DELEGATE_H_
 
 namespace ui {
 class Accelerator;
 }  // namespace ui
 
 namespace ash {
 
 // Delegate for controlling the volume.
 class VolumeControlDelegate {
  public:
   virtual ~VolumeControlDelegate() {}
 
   virtual bool HandleVolumeMute(const ui::Accelerator& accelerator) = 0;
   virtual bool HandleVolumeDown(const ui::Accelerator& accelerator) = 0;
   virtual bool HandleVolumeUp(const ui::Accelerator& accelerator) = 0;
 
+  // Is the system audio muted?
+  virtual bool IsAudioMuted() const = 0;
+
+  // Mutes/Unmutes the audio system.
+  virtual void SetAudioMuted(bool muted) = 0;
+
+  // Gets the volume level. The range is [0, 1.0].
+  virtual float GetVolumeLevel() const = 0;
+
+  // Sets the volume level. The range is [0, 1.0].
+  virtual void SetVolumeLevel(float level) = 0;
+
   // Requests that the volume be set to |percent|, in the range
   // [0.0, 100.0].
   virtual void SetVolumePercent(double percent) = 0;
 };
 
 }  // namespace ash
 
 #endif  // ASH_VOLUME_CONTROL_DELEGATE_H_