Add a new audio extension event OnLevelChanged.

extensions/browser/api/audio/audio_service.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 EXTENSIONS_BROWSER_API_AUDIO_AUDIO_SERVICE_H_
 #define EXTENSIONS_BROWSER_API_AUDIO_AUDIO_SERVICE_H_
 
 #include <string>
 #include <vector>
 
 #include "base/callback.h"
 #include "base/macros.h"
 #include "base/memory/linked_ptr.h"
 #include "extensions/common/api/audio.h"
 
 namespace extensions {
 
 using OutputInfo = std::vector<linked_ptr<core_api::audio::OutputDeviceInfo>>;
 using InputInfo = std::vector<linked_ptr<core_api::audio::InputDeviceInfo>>;
+using DevicesInfo = std::vector<linked_ptr<core_api::audio::AudioDeviceInfo>>;
 using DeviceIdList = std::vector<std::string>;
 
 class AudioService {
  public:
   class Observer {
    public:
     // Called when anything changes to the audio device configuration.
     virtual void OnDeviceChanged() = 0;
 
+    // Called when the volume of an active output node changes.
+    virtual void OnOutputNodeVolumeChanged(const std::string& id,
+                                           double volume) = 0;
+
    protected:
     virtual ~Observer() {}
   };
 
   // Callback type for completing to get audio device information.
   typedef base::Callback<void(const OutputInfo&, const InputInfo&, bool)>
       GetInfoCallback;
 
+  // Callback type for completing to get audio devices information.
+  typedef base::Callback<void(const DevicesInfo&, bool)> GetDeviceInfoCallback;
+
   // Creates a platform-specific AudioService instance.
   static AudioService* CreateInstance();
 
   virtual ~AudioService() {}
 
   // Called by listeners to this service to add/remove themselves as observers.
   virtual void AddObserver(Observer* observer) = 0;
   virtual void RemoveObserver(Observer* observer) = 0;
 
   // Start to query audio device information. Should be called on UI thread.
   // The |callback| will be invoked once the query is completed.
   virtual void StartGetInfo(const GetInfoCallback& callback) = 0;
 
   // Sets the active nodes to the nodes specified by |device_list|.
   // It can pass in the "complete" active node list of either input
   // nodes, or output nodes, or both. If only input nodes are passed in,
   // it will only change the input nodes' active status, output nodes will NOT
   // be changed; similarly for the case if only output nodes are passed.
   // If the nodes specified in |new_active_ids| are already active, they will
   // remain active. Otherwise, the old active nodes will be de-activated before
   // we activate the new nodes with the same type(input/output).
   virtual void SetActiveDevices(const DeviceIdList& device_list) = 0;
 
   // Set the muted and volume/gain properties of a device.
   virtual bool SetDeviceProperties(const std::string& device_id,
                                    bool muted,
                                    int volume,
                                    int gain) = 0;
 
+  // Starts to query audio devices information. Should be called on UI thread.
+  // The |callback| will be invoked once the query is completed.
+  virtual void StartGetDeviceInfo(const GetDeviceInfoCallback& callback) = 0;
+
  protected:
   AudioService() {}
 
  private:
   DISALLOW_COPY_AND_ASSIGN(AudioService);
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_BROWSER_API_AUDIO_AUDIO_SERVICE_H_