Fixing Node.clone not returning upgraded custom elements.

tests/html/custom/constructor_calls_created_synchronously_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 constructor_calls_created_synchronously_test;
 import 'package:unittest/unittest.dart';
 import 'package:unittest/html_config.dart';
 import 'dart:html';
 import '../utils.dart';
 import 'dart:mirrors';
 
 class A extends HtmlElement {
   static final tag = 'x-a';
   factory A() => new Element.tag(tag);
   A.created() : super.created();
 
   static int ncallbacks = 0;
 
   void createdCallback() {
     ncallbacks++;
   }
 }
 
 main() {
   useHtmlConfiguration();
 
   // Adapted from Blink's
   // fast/dom/custom/constructor-calls-created-synchronously test.
 
-  setUp(loadPolyfills);
+  var registered = false;
+  setUp(() {
+    return loadPolyfills().then((_) {
+      if (!registered) {
+        registered = true;
+        document.register(A.tag, A);
+      }
+    });
+  });
 
   test('createdCallback', () {
-    document.register(A.tag, A);
     var x = new A();
     expect(A.ncallbacks, 1);
   });
+
+  test('clone node', () {
+    A.ncallbacks = 0;
+
+    var a = new A();
+    expect(A.ncallbacks, 1);
+    var b = a.clone(false);
+    expect(A.ncallbacks, 2);
+    expect(b is A, isTrue);
+  });
 }