Add a new audio extension event OnLevelChanged.

ash/system/audio/tray_audio.cc

 // Copyright 2014 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/audio/tray_audio.h"
 
 #include <cmath>
 
 #include "ash/ash_constants.h"
 #include "ash/display/display_manager.h"
@@ skipping 79 matching lines @@
 }
 
 bool TrayAudio::ShouldHideArrow() const {
   return true;
 }
 
 bool TrayAudio::ShouldShowShelf() const {
   return TrayAudio::ShowAudioDeviceMenu() && !pop_up_volume_view_;
 }
 
-void TrayAudio::OnOutputVolumeChanged() {
+void TrayAudio::OnOutputNodeVolumeChanged(uint64 node_id, double volume) {

[stevenjb, 2015/02/23 22:16:19]

Comment out node_id and volume to indicate that they are unused.

[jennyz, 2015/02/24 00:05:38]

Done.

   float percent =
       static_cast<float>(audio_delegate_->GetOutputVolumeLevel()) / 100.0f;
   if (tray_view())
     tray_view()->SetVisible(GetInitialVisibility());
 
   if (volume_view_) {
     volume_view_->SetVolumeLevel(percent);
     SetDetailedViewCloseDelay(kTrayPopupAutoCloseDelayInSeconds);
     return;
   }
@@ skipping 66 matching lines @@
   if (tray_view())
       tray_view()->SetVisible(GetInitialVisibility());
   if (volume_view_) {
     volume_view_->SetVolumeLevel(
         static_cast<float>(audio_delegate_->GetOutputVolumeLevel()) / 100.0f);
     volume_view_->Update();
   }
 }
 
 }  // namespace ash