Updating Polymer to derive from custom elements.

samples/third_party/todomvc/web/editable_label.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. 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.editable_label;
 
 import 'dart:html';
 import 'package:polymer/polymer.dart';
 
 /**
  * Label whose [value] can be edited by double clicking. When editing, it
  * displays a form and input element, otherwise it displays the label.
  */
 class EditableLabel extends PolymerElement {
   @observable bool editing = false;
   @published String value = '';
 
+  factory EditableLabel() => new Element.tag('editable-label');
+
+  EditableLabel.created() : super.created();
+
   bool get applyAuthorStyles => true;
 
   InputElement get _editBox => getShadowRoot("editable-label").query('#edit');
 
   void edit() {
     editing = true;
 
     // This causes _editBox to be inserted.
     performMicrotaskCheckpoint();
 
@@ skipping 13 matching lines @@
 
   void maybeCancel(KeyboardEvent e) {
     if (e.keyCode == KeyCode.ESC) {
       editing = false;
     }
   }
 }
 
 @initMethod
 void _init() {
-  Polymer.register('editable-label', EditableLabel);
+  Polymer.register('editable-label', type: EditableLabel);
 }