Use Object.observe() instead of Polyfills

ui/file_manager/audio_player/js/audio_player_scripts.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.
 
 <include src="../../../webui/resources/js/cr.js"/>
 <include src="../../../webui/resources/js/cr/event_target.js"/>
 <include src="../../../webui/resources/js/cr/ui/array_data_model.js"/>
 
 // Hack for polymer, notifying that CSP is enabled here.
 // TODO(yoshiki): Find a way to remove the hack.
 if (!('securityPolicy' in document))
   document['securityPolicy'] = {};
 if (!('allowsEval' in document.securityPolicy))
   document.securityPolicy['allowsEval'] = false;
 
-// Force Polymer into dirty-checking mode, see http://crbug.com/351967
-Object['observe'] = undefined;
-
 <include src="../../../../third_party/polymer/components/polymer/polymer.js">
 
 (function() {
 
 // 'strict mode' is invoked for this scope.
 'use strict';
 
 // Base classes.
 <include src="../../file_manager/foreground/js/metadata/metadata_cache_set.js">
 <include src="../../file_manager/foreground/js/metadata/new_metadata_provider.js">
@@ skipping 19 matching lines @@
 <include src="../elements/track_list.js"/>
 <include src="../elements/control_panel.js"/>
 <include src="../elements/volume_controller.js"/>
 <include src="../elements/audio_player.js"/>
 
 window.reload = reload;
 window.unload = unload;
 window.AudioPlayer = AudioPlayer;
 
 })();