Add a new audio extension event OnLevelChanged.

extensions/common/api/audio.idl

 // 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.
 
 // The <code>chrome.audio</code> API is provided to allow users to
 // get information about and control the audio devices attached to the
 // system. This API is currently only implemented for ChromeOS.
 namespace audio {
 
   dictionary OutputDeviceInfo {
@@ skipping 26 matching lines @@
     // True if this is muted.
     boolean isMuted;
     // If this is an output device then this field indicates the output volume.
     // If this is an input device then this field is ignored.
     double? volume;
     // If this is an input device then this field indicates the input gain.
     // If this is an output device then this field is ignored.
     double? gain;
   };
 
+  dictionary AudioDeviceInfo {
+    // The unique identifier of the audio device.
+    DOMString id;
+    // True if the device is an input device; False if it is an output device.
+    boolean isInput;
+    // Display name of the device,  (e.g. "Bose Amplifier").
+    DOMString displayName;
+    // Device name of the device.
+    DOMString deviceName;
+    // True if the device is active.
+    boolean isActive;
+    // True if the device is muted.
+    boolean isMuted;
+    // Volume if this is an output device, Gain if this is an input device.
+    double volumeGain;
+  };
+
   callback GetInfoCallback = void(OutputDeviceInfo[] outputInfo,
                                   InputDeviceInfo[] inputInfo);
   callback SetActiveDevicesCallback = void();
   callback SetPropertiesCallback = void();
+  callback GetDeviceInfoCallback = void(AudioDeviceInfo[] deviceInfo);
 
   interface Functions {
-    // Get the information of all audio output and input devices.
+    // Gets the information of all audio output and input devices.
     static void getInfo(GetInfoCallback callback);
 
-    // Select a subset of audio devices as active.
+  // Sets the active nodes to the nodes specified by |ids|.
+  // It can pass in the "complete" active node id list of either input
+  // nodes, or output nodes, or both. If only input node ids 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).
     static void setActiveDevices(DOMString[] ids,
                                  SetActiveDevicesCallback callback);
 
     // Sets the properties for the input or output device.
     static void setProperties(DOMString id,
                               DeviceProperties properties,
                               SetPropertiesCallback callback);
+   
+    // Gets the information of all audio devices.
+    static void getDeviceInfo(GetDeviceInfoCallback callback);
   };
 
   interface Events {
     // Fired when anything changes to the audio device configuration.
     static void onDeviceChanged();
+
+    // Fired when output volume changes for a particular node.
+    // |id|: id of the output node.
+    // |volume|: new volume of the output node.
+    static void OnOutputNodeVolumeChanged(DOMString id, double volume);
   };
 };