Add a new audio extension event OnLevelChanged.

ash/system/tray/system_tray_notifier.cc

 // 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.
 
 #include "ash/system/tray/system_tray_notifier.h"
 
 namespace ash {
 
 SystemTrayNotifier::SystemTrayNotifier() {
 }
@@ skipping 177 matching lines @@
 #endif
 
 void SystemTrayNotifier::NotifyAccessibilityModeChanged(
     ui::AccessibilityNotificationVisibility notify) {
   FOR_EACH_OBSERVER(
       AccessibilityObserver,
       accessibility_observers_,
       OnAccessibilityModeChanged(notify));
 }
 
-void SystemTrayNotifier::NotifyAudioOutputVolumeChanged() {
-  FOR_EACH_OBSERVER(
-      AudioObserver,
-      audio_observers_,
-      OnOutputVolumeChanged());
+void SystemTrayNotifier::NotifyAudioOutputVolumeChanged(uint64 node_id,
+                                                        double volume) {
+  FOR_EACH_OBSERVER(AudioObserver, audio_observers_,
+                    OnOutputNodeVolumeChanged(node_id, volume));
 }
 
 void SystemTrayNotifier::NotifyAudioOutputMuteChanged() {
   FOR_EACH_OBSERVER(
       AudioObserver,
       audio_observers_,
       OnOutputMuteChanged());
 }
 
 void SystemTrayNotifier::NotifyAudioNodesChanged() {
@@ skipping 175 matching lines @@
 void SystemTrayNotifier::NotifyVirtualKeyboardSuppressionChanged(
     bool suppressed) {
   FOR_EACH_OBSERVER(VirtualKeyboardObserver,
                     virtual_keyboard_observers_,
                     OnKeyboardSuppressionChanged(suppressed));
 }
 
 #endif  // OS_CHROMEOS
 
 }  // namespace ash