Adding strict mode for bookmark_manager file for better error checking.

chrome/browser/resources/bookmark_manager/js/bmm/bookmark_list.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.
 
 // TODO(arv): Now that this is driven by a data model, implement a data model
 //            that handles the loading and the events from the bookmark backend.
 
 /**
  * @typedef {{childIds: Array<string>}}
  *
  * @see chrome/common/extensions/api/bookmarks.json
  */
 var ReorderInfo;
 
 /**
  * @typedef {{parentId: string,
  *            index: number,
  *            oldParentId: string,
  *            oldIndex: number}}
  *
  * @see chrome/common/extensions/api/bookmarks.json
  */
 var MoveInfo;
 
 cr.define('bmm', function() {
+  'use strict';
+
   var List = cr.ui.List;
   var ListItem = cr.ui.ListItem;
   var ArrayDataModel = cr.ui.ArrayDataModel;
   var ContextMenuButton = cr.ui.ContextMenuButton;
 
   /**
    * Basic array data model for use with bookmarks.
    * @param {!Array<!BookmarkTreeNode>} items The bookmark items.
    * @constructor
    * @extends {ArrayDataModel}
@@ skipping 590 matching lines @@
         }
       }
     }
   };
 
   return {
     BookmarkList: BookmarkList,
     list: /** @type {Element} */(null),  // Set when decorated.
   };
 });