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

ui/file_manager/externs/es7_workaround.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.
 
 /**
 * @fileoverview Partial definitions for ECMAScript 7. To compile Files.app, some
 *     definitions are defined in this file. They should be removed once ES7
 *     definitions are ready in closure compiler by default.
 * @externs
 */
 
 /**
- * @param {!Object} obj
- * @param {function(!Array<!Object>)} callback
- * @param {!Array<string>=} acceptList
- */
-Object.observe = function(obj, callback, acceptList) {};
-
-/**
- * @param {!Object} obj
- * @param {function(!Array<!Object>)} callback
- */
-Object.unobserve = function(obj, callback) {};
-
-/**
  * @param {!Array} arr
  * @param {function(!Array<!Object>)} callback
  */
 Array.observe = function(arr, callback) {};

[yoshiki, 2015/12/07 05:39:21]

Could you remove them as well?

[fukino, 2015/12/07 07:21:01]

Done.

I think we can simple stop listening to the internal modification of tracks
property.
Whenever the audio player changes the track list, the object for the track
property is replaced, not modified.
https://code.google.com/p/chromium/codesearch#chromium/src/ui/file_manager/au...

So, I think we don't need to listen to the modification of the tracks object,
and simply remove Array.observe().

 
 /**
  * @param {!Array} arr
  * @param {function(!Array<!Object>)} callback
  */
 Array.unobserve = function(arr, callback) {};