Update TodoMVC based on https://github.com/polymer/todomvc

samples/third_party/todomvc/test/utils.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 todomvc.test.utils;
+
+import 'dart:async';
+import 'package:observe/observe.dart';
+
+Future onPropertyInit(Observable obj, String path) {
+  final obs = new PathObserver(obj, path);
+  if (obs.value != null) return new Future.value(obs.value);
+
+  final c = new Completer();
+  StreamSubscription sub;
+  sub = obs.changes.listen((_) {
+    if (obs.value != null) {
+      sub.cancel();
+      c.complete(obs.value);
+    }
+  });
+  return c.future;
+}