Supervised user import dialog: disable "ok" button when no user is selected

chrome/browser/resources/options/supervised_user_import.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.
 
 cr.define('options', function() {
   var Page = cr.ui.pageManager.Page;
   var PageManager = cr.ui.pageManager.PageManager;
   var ArrayDataModel = cr.ui.ArrayDataModel;
 
   /**
@@ skipping 27 matching lines @@
       options.supervisedUserOptions.SupervisedUserList.decorate(
           supervisedUserList);
 
       var avatarGrid = $('select-avatar-grid');
       options.ProfilesIconGrid.decorate(avatarGrid);
       var avatarIcons = loadTimeData.getValue('avatarIcons');
       avatarGrid.dataModel = new ArrayDataModel(avatarIcons);
 
       supervisedUserList.addEventListener('change', function(event) {
         var supervisedUser = supervisedUserList.selectedItem;
-        if (!supervisedUser)
-          return;
-
         $('supervised-user-import-ok').disabled =
-          supervisedUserList.selectedItem.onCurrentDevice;
+            !supervisedUser || supervisedUser.onCurrentDevice;
       });
 
       var self = this;
       $('supervised-user-import-cancel').onclick = function(event) {
         if (self.inProgress_) {
           self.updateImportInProgress_(false);
 
           // 'cancelCreateProfile' is handled by CreateProfileHandler.
           chrome.send('cancelCreateProfile');
         }
@@ skipping 170 matching lines @@
   cr.makePublic(SupervisedUserImportOverlay, [
     'onError',
     'onSuccess',
   ]);
 
   // Export
   return {
     SupervisedUserImportOverlay: SupervisedUserImportOverlay,
   };
 });