Migrate <cr-dialog> from PaperDialogBehavior to native <dialog>.

chrome/browser/resources/settings/people_page/users_add_user_dialog.js

 // Copyright 2016 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.
 
 /**
  * @fileoverview
  * 'settings-users-add-user-dialog' is the dialog shown for adding new allowed
  * users to a ChromeOS device.
  */
 (function() {
@@ skipping 15 matching lines @@
  * @const {!RegExp}
  */
 var EMAIL_REGEX = new RegExp(
     '^\\s*([\\w\\.!#\\$%&\'\\*\\+-\\/=\\?\\^`\\{\\|\\}~]+)@' +
     '([A-Za-z0-9\-]{2,63}\\..+)\\s*$');
 
 Polymer({
   is: 'settings-users-add-user-dialog',
 
   open: function() {
-    this.$.dialog.open();
+    this.$.dialog.showModal();
   },
 
   /** @private */
   onCancelTap_: function() {
     this.$.dialog.cancel();
   },
 
   /**
    * Validates that the new user entered is valid.
    * @private
@@ skipping 27 matching lines @@
 
     chrome.usersPrivate.addWhitelistedUser(
         userEmail,
         /* callback */ function(success) {});
     this.$.addUserInput.value = '';
     this.$.dialog.close();
   },
 });
 
 })();