Adding strict mode for bookmark_manager file for better error checking.

chrome/browser/resources/bookmark_manager/js/main.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';
+
 (function() {
 /** @const */ var BookmarkList = bmm.BookmarkList;
 /** @const */ var BookmarkTree = bmm.BookmarkTree;
 /** @const */ var Command = cr.ui.Command;
 /** @const */ var LinkKind = cr.LinkKind;
 /** @const */ var ListItem = cr.ui.ListItem;
 /** @const */ var Menu = cr.ui.Menu;
 /** @const */ var MenuButton = cr.ui.MenuButton;
 /** @const */ var Splitter = cr.ui.Splitter;
 /** @const */ var TreeItem = cr.ui.TreeItem;
@@ skipping 1500 matching lines @@
 
   cr.ui.FocusOutlineManager.forDocument(document);
   initializeSplitter();
   bmm.addBookmarkModelListeners();
   dnd.init(selectItemsAfterUserAction);
   bmm.tree.reload();
 }
 
 initializeBookmarkManager();
 })();