Adding Element.created constructor

tests/html/custom/entered_left_view_test.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 entered_left_view_test;
 
 import 'dart:async';
 import 'dart:html';
 import 'dart:js' as js;
 import 'package:unittest/html_individual_config.dart';
 import 'package:unittest/unittest.dart';
 import '../utils.dart';
 
 var invocations = [];
 class Foo extends HtmlElement {
   factory Foo() => null;
+  Foo.created() : super.created();
 
-  void created() {
+  void createdCallback() {
     invocations.add('created');
   }
 
   void enteredView() {
     invocations.add('entered');
   }
 
   void leftView() {
     invocations.add('left');
   }
@@ skipping 208 matching lines @@
       Platform.upgradeCustomElements(div);
       invocations = [];
       document.body.append(div);
       customElementsTakeRecords();
       expect(invocations, ['entered'],
           reason: 'the entered callback should be invoked when inserted into a '
           'document with a view as part of a subtree');
     });
   });
 }