Implement new slider control and disable the volume control when audio is muted.

chrome/browser/chromeos/system/ash_system_tray_delegate.cc

Index: chrome/browser/chromeos/system/ash_system_tray_delegate.cc
diff --git a/chrome/browser/chromeos/system/ash_system_tray_delegate.cc b/chrome/browser/chromeos/system/ash_system_tray_delegate.cc
index dc7e9f6341dc4626fcef64d2b2bcc8b618607be0..38a81a2d3e12da9a5f5fd1dfb708689e78a8e1a2 100644
--- a/chrome/browser/chromeos/system/ash_system_tray_delegate.cc
+++ b/chrome/browser/chromeos/system/ash_system_tray_delegate.cc
@@ -944,6 +944,11 @@ class SystemTrayDelegate : public ash::SystemTrayDelegate,
     tray_->audio_observer()->OnVolumeChanged(level);
   }
 
+  // Overridden from AudioHandler::VolumeObserver.
+  virtual void OnMuteToggled() OVERRIDE {
+    tray_->audio_observer()->OnMuteToggled();
+  }
+
   // Overridden from PowerManagerClient::Observer.
   virtual void BrightnessChanged(int level, bool user_initiated) OVERRIDE {
     tray_->brightness_observer()->