Add a new audio extension event OnLevelChanged.

chromeos/audio/cras_audio_handler.cc

Index: chromeos/audio/cras_audio_handler.cc
diff --git a/chromeos/audio/cras_audio_handler.cc b/chromeos/audio/cras_audio_handler.cc
index c3e7c2dafe2ef876611420e4c671a3bb05be331c..52e5e67a2cf6d52720a3bc8a0348c46dd93b1b3f 100644
--- a/chromeos/audio/cras_audio_handler.cc
+++ b/chromeos/audio/cras_audio_handler.cc
@@ -55,7 +55,8 @@ CrasAudioHandler::AudioObserver::AudioObserver() {
 CrasAudioHandler::AudioObserver::~AudioObserver() {
 }
 
-void CrasAudioHandler::AudioObserver::OnOutputVolumeChanged() {
+void CrasAudioHandler::AudioObserver::OnOutputNodeVolumeChanged(uint64 node_id,
+                                                                double volume) {
 }
 
 void CrasAudioHandler::AudioObserver::OnInputGainChanged() {
@@ -636,7 +637,8 @@ void CrasAudioHandler::SetOutputNodeVolumePercent(uint64 node_id,
 
   if (device->active) {
     SetOutputNodeVolume(node_id, volume_percent);
-    FOR_EACH_OBSERVER(AudioObserver, observers_, OnOutputVolumeChanged());
+    FOR_EACH_OBSERVER(AudioObserver, observers_,
+                      OnOutputNodeVolumeChanged(node_id, volume_percent));
   }
 }