Turn on Polymer TodoMVC tests on Dart buildbots

samples/tests/samples/todomvc/markdone_shadow_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 testrunner_test;
+library todomvc.test.markdone_shadow_test;
 
+// We don't use this import, but it signals to the test framework that this is
+// a web test.
 import 'dart:html';
-import 'package:unittest/unittest.dart';
+import 'markdone_test.dart' as markdone_test;
 
-main() {
-  test("layout", () {
-    var lbl = new LabelElement();
-    lbl.text = 'Hello Dart!';
-    document.body.nodes.add(lbl);
-  });
-}
-
+main() => markdone_test.main();