Consolidate volume control code.

ash/system/status_area_widget.cc

Index: ash/system/status_area_widget.cc
diff --git a/ash/system/status_area_widget.cc b/ash/system/status_area_widget.cc
index 4209f387ba12823a5bf77ef9cda35f4ffbe36259..f706da88936e364635db849728413b4ba1b0d80b 100644
--- a/ash/system/status_area_widget.cc
+++ b/ash/system/status_area_widget.cc
@@ -91,22 +91,6 @@ class DummySystemTrayDelegate : public SystemTrayDelegate {
   virtual void ShowHelp() OVERRIDE {
   }
 
-  virtual bool IsAudioMuted() const OVERRIDE {
-    return muted_;
-  }
-
-  virtual void SetAudioMuted(bool muted) OVERRIDE {
-    muted_ = muted;
-  }
-
-  virtual float GetVolumeLevel() const OVERRIDE {
-    return volume_;
-  }
-
-  virtual void SetVolumeLevel(float volume) OVERRIDE {
-    volume_ = volume;
-  }
-
   virtual bool IsCapsLockOn() const OVERRIDE {
     return caps_lock_enabled_;
   }