Listen for OutputNodeVolumeChanged signal

chromeos/dbus/cras_audio_client.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_DBUS_CRAS_AUDIO_CLIENT_H_
 #define CHROMEOS_DBUS_CRAS_AUDIO_CLIENT_H_
 
 #include <stdint.h>
 
 #include "base/callback.h"
@@ skipping 24 matching lines @@
 
     // Called when audio nodes change.
     virtual void NodesChanged();
 
     // Called when active audio output node changed to new node with |node_id|.
     virtual void ActiveOutputNodeChanged(uint64_t node_id);
 
     // Called when active audio input node changed to new node with |node_id|.
     virtual void ActiveInputNodeChanged(uint64_t node_id);
 
+    // Called when output node's volume changed.
+    virtual void OutputNodeVolumeChanged(uint64_t node_id, int volume);
+
    protected:
     virtual ~Observer();
   };
 
   ~CrasAudioClient() override;
 
   // Adds and removes the observer.
   virtual void AddObserver(Observer* observer) = 0;
   virtual void RemoveObserver(Observer* observer) = 0;
   // Returns true if this object has the given observer.
@@ skipping 89 matching lines @@
   // Create() should be used instead.
   CrasAudioClient();
 
  private:
   DISALLOW_COPY_AND_ASSIGN(CrasAudioClient);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROMEOS_DBUS_CRAS_AUDIO_CLIENT_H_