Remove use of deprecated property in TodoMVC

samples/third_party/todomvc_performance/web/lib-elements/simple_router.dart

 // Copyright 2013 The Polymer Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 library todomvc.web.lib_elements.simple_router;
 
 import 'dart:async';
 import 'dart:html';
 import 'package:polymer/polymer.dart';
 
 // A very simple router for TodoMVC. Real app should use package:route, but it
 // does not currently support Shadow DOM.
 @CustomTag('simple-router')
 class SimpleRouter extends PolymerElement {
   @published String route = '';
 
   StreamSubscription _sub;
 
   factory SimpleRouter() => new Element.tag('simple-router');
   SimpleRouter.created() : super.created();
 
-  enteredView() {
+  attached() {
+    super.attached();
     _sub = windowLocation.changes.listen((_) {
       var hash = window.location.hash;
       if (hash.startsWith('#/')) hash = hash.substring(2);
       // TODO(jmesserly): empty string is not triggering a call to TodoList
       // routeChanged after deployment. Use 'all' as a workaround.
       if (hash == '') hash = 'all';
       route = hash;
     });
   }
 
-  leftView() {
+  detached() {
+    super.detached();
     _sub.cancel();
   }
 
   routeChanged() {
     fire('route', detail: route);
   }
 }