Fix File Copy Manager Wrapper to work in the strict mode.

chrome/browser/resources/file_manager/js/file_copy_manager_wrapper.js

 // Copyright (c) 2012 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.
 
 'use strict';
 
-var fileCopyManagerWrapper = null;
-
 /**
  * While FileCopyManager is run in the background page, this class is used to
  * communicate with it.
  * @param {DirectoryEntry} root Root directory entry.
  * @constructor
  */
 function FileCopyManagerWrapper(root) {
   this.root_ = root;
 
   this.status_ = {
@@ skipping 23 matching lines @@
  * Extending cr.EventTarget.
  */
 FileCopyManagerWrapper.prototype.__proto__ = cr.EventTarget.prototype;
 
 /**
  * Create a new instance or get existing instance of FCMW.
  * @param {DirectoryEntry} root Root directory entry.
  * @return {FileCopyManagerWrapper}  A FileCopyManagerWrapper instance.
  */
 FileCopyManagerWrapper.getInstance = function(root) {
-  if (fileCopyManagerWrapper === null) {
-    fileCopyManagerWrapper = new FileCopyManagerWrapper(root);
-  }
-  return fileCopyManagerWrapper;
+  if (!FileCopyManagerWrapper.instance_)
+    FileCopyManagerWrapper.instance_ = new FileCopyManagerWrapper(root);
+
+  return FileCopyManagerWrapper.instance_;
 };
 
 /**
  * Load background page and call callback with copy manager as an argument.
  * @param {function} callback Function with FileCopyManager as a parameter.
  * @private
  */
 FileCopyManagerWrapper.prototype.getCopyManagerAsync_ = function(callback) {
   var MAX_RETRIES = 10;
   var TIMEOUT = 100;
@@ skipping 58 matching lines @@
     });
   };
 };
 
 FileCopyManagerWrapper.decorateAsyncMethod('requestCancel');
 FileCopyManagerWrapper.decorateAsyncMethod('paste');
 FileCopyManagerWrapper.decorateAsyncMethod('deleteEntries');
 FileCopyManagerWrapper.decorateAsyncMethod('forceDeleteTask');
 FileCopyManagerWrapper.decorateAsyncMethod('cancelDeleteTask');
 FileCopyManagerWrapper.decorateAsyncMethod('zipSelection');