MD Settings: Fix Reset profile dialog scenario that causes a crash.

chrome/browser/resources/settings/reset_page/powerwash_dialog.js

 // Copyright 2015 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-reset-page' is the settings page containing reset
  * settings.
  */
 Polymer({
   is: 'settings-powerwash-dialog',
 
-  open: function() {
+  /** @override */
+  attached: function() {
     settings.ResetBrowserProxyImpl.getInstance().onPowerwashDialogShow();
     this.$.dialog.showModal();
   },
 
   /** @private */
   onCancelTap_: function() {
     this.$.dialog.close();
   },
 
   /** @private */
   onRestartTap_: function() {
     settings.LifetimeBrowserProxyImpl.getInstance().factoryReset();
   },
 });