Adding strict mode for bookmark_manager file for better error checking.

chrome/browser/resources/bookmark_manager/js/bmm.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.
 
 cr.define('bmm', function() {
+  'use strict';
+
   /**
    * Whether a node contains another node.
    * TODO(yosin): Once JavaScript style guide is updated and linter follows
    * that, we'll remove useless documentations for |parent| and |descendant|.
    * TODO(yosin): bmm.contains() should be method of BookmarkTreeNode.
    * @param {!BookmarkTreeNode} parent .
    * @param {!BookmarkTreeNode} descendant .
    * @return {boolean} Whether the parent contains the descendant.
    */
   function contains(parent, descendant) {
@@ skipping 234 matching lines @@
   };
 
   return {
     contains: contains,
     isFolder: isFolder,
     loadSubtree: loadSubtree,
     loadTree: loadTree,
     addBookmarkModelListeners: addBookmarkModelListeners
   };
 });