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

chrome/browser/chromeos/status/volume_menu_button.h

Index: chrome/browser/chromeos/status/volume_menu_button.h
===================================================================
--- chrome/browser/chromeos/status/volume_menu_button.h	(revision 119435)
+++ chrome/browser/chromeos/status/volume_menu_button.h	(working copy)
@@ -7,6 +7,7 @@
 #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"
@@ -16,7 +17,8 @@
 // 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();
@@ -35,6 +37,9 @@
   // 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);
 };