Listen for OutputNodeVolumeChanged signal

chromeos/audio/cras_audio_handler.h

 // Copyright (c) 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 CHROMEOS_AUDIO_CRAS_AUDIO_HANDLER_H_
 #define CHROMEOS_AUDIO_CRAS_AUDIO_HANDLER_H_
 
 #include <stddef.h>
 #include <stdint.h>
 #include <queue>
@@ skipping 213 matching lines @@
   ~CrasAudioHandler() override;
 
  private:
   friend class CrasAudioHandlerTest;
 
   // CrasAudioClient::Observer overrides.
   void AudioClientRestarted() override;
   void NodesChanged() override;
   void ActiveOutputNodeChanged(uint64_t node_id) override;
   void ActiveInputNodeChanged(uint64_t node_id) override;
+  void OutputNodeVolumeChanged(uint64_t node_id, int volume) override;
 
   // AudioPrefObserver overrides.
   void OnAudioPolicyPrefChanged() override;
 
   // SessionManagerClient::Observer overrides.
   void EmitLoginPromptVisibleCalled() override;
 
   // Sets the |active_device| to be active.
   // If |notify|, notifies Active*NodeChange.
   // Saves device active states in prefs. |activate_by| indicates how
@@ skipping 174 matching lines @@
   bool cras_service_available_ = false;
 
   base::WeakPtrFactory<CrasAudioHandler> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(CrasAudioHandler);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROMEOS_AUDIO_CRAS_AUDIO_HANDLER_H_