Add a new audio extension event OnLevelChanged.

extensions/browser/api/audio/audio_api.cc

Index: extensions/browser/api/audio/audio_api.cc
diff --git a/extensions/browser/api/audio/audio_api.cc b/extensions/browser/api/audio/audio_api.cc
index 659ae6ce67637ac20228a53e47681c1ab558b37a..4b4fa7d6384b186e9ab369f62db0c7963464e7dc 100644
--- a/extensions/browser/api/audio/audio_api.cc
+++ b/extensions/browser/api/audio/audio_api.cc
@@ -45,6 +45,15 @@ void AudioAPI::OnDeviceChanged() {
   }
 }
 
+void AudioAPI::OnLevelChanged(const std::string& id, int level) {
+  if (browser_context_ && EventRouter::Get(browser_context_)) {
+    scoped_ptr<base::ListValue> args = audio::OnLevelChanged::Create(id, level);
+    scoped_ptr<Event> event(
+        new Event(audio::OnLevelChanged::kEventName, args.Pass()));
+    EventRouter::Get(browser_context_)->BroadcastEvent(event.Pass());
+  }
+}
+
 ///////////////////////////////////////////////////////////////////////////////
 
 bool AudioGetInfoFunction::RunAsync() {
@@ -107,4 +116,6 @@ bool AudioSetPropertiesFunction::RunSync() {
     return true;
 }
 
+///////////////////////////////////////////////////////////////////////////////
+
 }  // namespace extensions