Expose stable_device_id in audio extension apis.

extensions/test/data/api_test/audio/remove_nodes/background.js

 // Copyright 2015 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.
 
 chrome.audio.OnDevicesChanged.addListener(function (devices) {
   if (devices.length === 2) {
     if (devices[0].id != "40001" ||
+      devices[0].stableDeviceId != "90001" ||
       devices[0].isInput != true ||
       devices[0].deviceType != "USB" ||
       devices[0].deviceName != "Jabra Mic" ||
       devices[0].displayName != "Jabra Mic 1") {
       console.error("Got wrong device property for device:" +
           JSON.stringify(devices[0]));
       chrome.test.sendMessage("failure");
     }
     if (devices[1].id != "40002" ||
+        devices[1].stableDeviceId != "90002" ||
         devices[1].isInput != true ||
         devices[1].deviceType != "USB" ||
         devices[1].deviceName != "Jabra Mic" ||
         devices[1].displayName != "Jabra Mic 2") {
       console.error("Got wrong device property for device:" +
           JSON.stringify(devices[1]));
       chrome.test.sendMessage("failure");
     }
     chrome.test.sendMessage("success");
   } else {
     console.error("Got unexpected OnNodesChanged event failed");
     chrome.test.sendMessage("failure");
   }
 });
 chrome.test.sendMessage("loaded");