Fixing polymer element registration when extending tag extensions

pkg/polymer/test/register_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.
+
+import 'dart:html';
+import 'package:unittest/unittest.dart';
+import 'package:unittest/html_config.dart';
+import 'package:polymer/polymer.dart';
+
+@CustomTag('x-html')
+class XHtmlElement extends PolymerElement {
+  XHtmlElement.created() : super.created();
+}
+
+@CustomTag('x-html-two')
+class XHtml2Element extends XHtmlElement {
+  XHtml2Element.created() : super.created();
+}
+
+@CustomTag('x-div')
+class XDivElement extends DivElement with Polymer, Observable {
+  XDivElement.created() : super.created();
+}
+
+@CustomTag('x-div-two')
+class XDiv2lElement extends XDivElement {
+  XDiv2lElement.created() : super.created();
+}
+
+main() {
+  initPolymer();
+  useHtmlConfiguration();
+
+  setUp(() => Polymer.onReady);
+
+  test('elements upgraded', () {
+    expect(querySelector('x-html') is XHtmlElement, isTrue);
+    expect(querySelector('x-html-two') is XHtml2Element, isTrue);
+    expect(querySelector('#x-div') is XDivElement, isTrue);
+    expect(querySelector('#x-div-two') is XDiv2Element, isTrue);
+  });
+}