Add a new audio extension event OnLevelChanged.

extensions/browser/api/audio/audio_api.h

Index: extensions/browser/api/audio/audio_api.h
diff --git a/extensions/browser/api/audio/audio_api.h b/extensions/browser/api/audio/audio_api.h
index ddee1d5c75a0b13cf34fc8fb07016b9e42f11621..01d74ac0569c3953393b90cc35119dbdd3706deb 100644
--- a/extensions/browser/api/audio/audio_api.h
+++ b/extensions/browser/api/audio/audio_api.h
@@ -25,6 +25,7 @@ class AudioAPI : public BrowserContextKeyedAPI, public AudioService::Observer {
 
   // AudioService::Observer implementation.
   void OnDeviceChanged() override;
+  void OnOutputNodeVolumeChanged(const std::string& id, double volume) override;
 
  private:
   friend class BrowserContextKeyedAPIFactory<AudioAPI>;
@@ -70,6 +71,17 @@ class AudioSetPropertiesFunction : public SyncExtensionFunction {
   bool RunSync() override;
 };
 
+class AudioGetDeviceInfoFunction : public AsyncExtensionFunction {
+ public:
+  DECLARE_EXTENSION_FUNCTION("audio.getDeviceInfo", AUDIO_GETDEVICEINFO);
+
+ protected:
+  ~AudioGetDeviceInfoFunction() override {}
+  bool RunAsync() override;
+
+ private:
+  void OnGetDeviceInfoCompleted(const DevicesInfo& devices_info, bool success);
+};
 
 }  // namespace extensions