fix custom elements that extend tags like "section"

tests/html/custom/created_callback_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 created_callback_test;
 import 'package:unittest/unittest.dart';
 import 'package:unittest/html_config.dart';
 import 'dart:html';
 import 'dart:js' as js;
 import '../utils.dart';
@@ skipping 138 matching lines @@
 
   test('cannot register created with params', () {
     expect(() {
       document.register('x-created-with-params', CreatedWithParametersElement);
     }, throws);
   });
 
   test('created cannot be called from nested constructor',
       NestedCreatedConstructorElement.test);
 
-
   // TODO(vsm): Port additional test from upstream here:
   // http://src.chromium.org/viewvc/blink/trunk/LayoutTests/fast/dom/custom/created-callback.html?r1=156141&r2=156185
 }
 
-
 class NestedElement extends HtmlElement {
   static final tag = 'x-nested';
 
   final Element b = new B();
 
   factory NestedElement() => new Element.tag(tag);
   NestedElement.created() : super.created();
 
   static void register() {
     document.register(tag, NestedElement);
@@ skipping 115 matching lines @@
   } catch(e) {
     rethrow;
   } finally {
     js.context['testExpectsGlobalError'] = false;
   }
   var errors = js.context['testSuppressedGlobalErrors'];
   expect(errors['length'], 1);
   // Clear out the errors;
   js.context['testSuppressedGlobalErrors']['length'] = 0;
 }