watch the registration queue and print if it has no progress

pkg/polymer/test/inject_bound_html_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:async';
 import 'dart:html';
 import 'package:unittest/unittest.dart';
 import 'package:unittest/html_config.dart';
 import 'package:polymer/polymer.dart';
 
 @CustomTag('x-foo')
 class XFoo extends PolymerElement {
   @observable String bar = "baz";
 
   XFoo.created() : super.created();
 
   @ComputedProperty('bar')
   String get ignore => readValue(#bar);
-
 }
 
 main() => initPolymer().run(() {
   useHtmlConfiguration();
 
   setUp(() => Polymer.onReady);
 
   test('can inject bound html fragments', () {
     XFoo xFoo = querySelector('x-foo');
     DivElement injectDiv = xFoo.$['inject'];
     xFoo.injectBoundHTML('<span>{{bar}}</span>', injectDiv);
     expect(injectDiv.innerHtml, '<span>baz</span>');
 
     xFoo.bar = 'bat';
     return new Future(() {}).then((_) {
       expect(injectDiv.innerHtml, '<span>bat</span>');
     });
   });
 });