Use mojo volume interfaces for mash and classic ash.

chrome/browser/chromeos/extensions/extension_system_event_observer.h

 // Copyright 2013 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.
 
 #ifndef CHROME_BROWSER_CHROMEOS_EXTENSIONS_EXTENSION_SYSTEM_EVENT_OBSERVER_H_
 #define CHROME_BROWSER_CHROMEOS_EXTENSIONS_EXTENSION_SYSTEM_EVENT_OBSERVER_H_
 
-#include "base/compiler_specific.h"
 #include "base/macros.h"
+#include "chromeos/audio/cras_audio_handler.h"
 #include "chromeos/dbus/power_manager_client.h"
 #include "chromeos/dbus/session_manager_client.h"
 
 namespace chromeos {
 
 // Dispatches extension events in response to system events.
 class ExtensionSystemEventObserver : public PowerManagerClient::Observer,
-                                     public SessionManagerClient::Observer {
+                                     public SessionManagerClient::Observer,
+                                     public CrasAudioHandler::AudioObserver {
  public:
   // This class registers/unregisters itself as an observer in ctor/dtor.
   ExtensionSystemEventObserver();
   ~ExtensionSystemEventObserver() override;
 
-  // PowerManagerClient::Observer overrides:
+  // PowerManagerClient::Observer:
   void BrightnessChanged(int level, bool user_initiated) override;
   void SuspendDone(const base::TimeDelta& sleep_duration) override;
 
-  // SessionManagerClient::Observer override.
+  // SessionManagerClient::Observer:
   void ScreenIsUnlocked() override;
 
+  // CrasAudioHandler::AudioObserver:
+  void OnOutputNodeVolumeChanged(uint64_t node_id, int volume) override;
+  void OnOutputMuteChanged(bool mute_on, bool system_adjust) override;
+
  private:
   DISALLOW_COPY_AND_ASSIGN(ExtensionSystemEventObserver);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_EXTENSIONS_EXTENSION_SYSTEM_EVENT_OBSERVER_H_