AudioPlayer: Stop using Object.observe() and Array.observe().

ui/file_manager/audio_player/js/audio_player_model.js

-// Copyright 2014 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 model class for audio player.
- * @constructor
- */
-function AudioPlayerModel() {}
-
-AudioPlayerModel.prototype.initialize = function(callback) {
-  'use strict';
-
-  /**
-   * List of values to be stored into the model.
-   * @type {!Object<*>}
-   * @const
-   */
-  var VALUES =
-    /**
-     * They will be used as properties of AudioPlayerModel.
-     * @lends {AudioPlayerModel.prototype}
-     */
-    {
-      shuffle: false,
-      repeat: false,
-      volume: 100,
-      expanded: false,
-    };
-
-  /**
-   * Prefix of the stored values in the storage.
-   * @type {string}
-   */
-  var STORAGE_PREFIX = 'audioplayer-';
-
-  /**
-   * Save the values in the model into the storage.
-   * @param {AudioPlayerModel} model The model.
-   */
-  function saveModel(model) {
-    var objectToBeSaved = {};
-    for (var key in VALUES) {
-      objectToBeSaved[STORAGE_PREFIX + key] = model[key];
-    }
-
-    chrome.storage.local.set(objectToBeSaved);
-  };
-
-  /**
-   * Load the values in the model from the storage.
-   * @param {AudioPlayerModel} model The model.
-   * @param {function()} inCallback Called when the load is completed.
-   */
-  function loadModel(model, inCallback) {
-    // Restores the values from the storage
-    var objectsToBeRead = Object.keys(VALUES).
-                          map(function(a) {
-                            return STORAGE_PREFIX + a;
-                          });
-
-    chrome.storage.local.get(objectsToBeRead, function(result) {
-      for (var key in result) {
-        // Strips the prefix.
-        model[key.substr(STORAGE_PREFIX.length)] = result[key];
-      }
-      inCallback();
-    });
-  };
-
-  // Initializes values.
-  for (var key in VALUES) {
-    this[key] = VALUES[key];
-  }
-  Object.seal(this);
-
-  // Restores the values from the storage
-  var target = this;
-  loadModel(target, function() {
-    // Installs observer to watch changes of the values.
-    Object.observe(target, function(changes) {
-      saveModel(target);
-    });
-    callback();
-  });
-}