pkg/polymer[_expressions] unittest fixes

pkg/polymer/test/property_observe_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 polymer.test.property_change_test;
 
 import 'dart:async';
 import 'dart:html';
 import 'package:polymer/polymer.dart';
 import 'package:unittest/unittest.dart';
 import 'package:unittest/html_config.dart';
-import 'package:unittest/matcher.dart';
 
 var _changes = 0;
 final _done = new Completer();
 
 checkDone() {
   if (6 == ++_changes) {
     _done.complete();
   }
 }
 
@@ skipping 60 matching lines @@
 }
 
 @initMethod
 main() {
   useHtmlConfiguration();
 
   setUp(() => Polymer.onReady);
 
   test('changes detected', () => _done.future);
 }