Support for showing/hiding status area volume controls in desktop devices

chrome/browser/chromeos/status/volume_menu_button.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 CHROME_BROWSER_CHROMEOS_STATUS_VOLUME_MENU_BUTTON_H_
 #define CHROME_BROWSER_CHROMEOS_STATUS_VOLUME_MENU_BUTTON_H_
 #pragma once
 
 #include "base/compiler_specific.h"
+#include "chrome/browser/chromeos/audio/audio_handler.h"
 #include "chrome/browser/chromeos/status/status_area_button.h"
 #include "ui/views/controls/menu/menu_delegate.h"
 #include "ui/views/controls/menu/view_menu_delegate.h"
 
 namespace chromeos {
 
 // The volume button in the status area.
 class VolumeMenuButton : public StatusAreaButton,
                          public views::MenuDelegate,
-                         public views::ViewMenuDelegate {
+                         public views::ViewMenuDelegate,
+                         public AudioHandler::VolumeObserver {
  public:
   explicit VolumeMenuButton(StatusAreaButton::Delegate* delegate);
   virtual ~VolumeMenuButton();
 
   // Update the volume icon.
   void UpdateIcon();
 
  protected:
   // StatusAreaButton implementation.
   virtual int icon_width() OVERRIDE;
 
  private:
   // views::View implementation.
   virtual void OnLocaleChanged() OVERRIDE;
 
   // views::ViewMenuDelegate implementation.
   virtual void RunMenu(views::View* source, const gfx::Point& pt) OVERRIDE;
 
+  // AudioHandler::VolumeObserver implementation.
+  virtual void OnVolumeChanged() OVERRIDE;
+
   DISALLOW_COPY_AND_ASSIGN(VolumeMenuButton);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_STATUS_VOLUME_MENU_BUTTON_H_