fix up tests

test/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.
 
 import 'dart:async';
 import 'package:logging/logging.dart';
 import 'package:observe/observe.dart';
 import 'package:observe/src/dirty_check.dart' as dirty_check;
 import 'package:unittest/unittest.dart';
 import 'observe_test_utils.dart';
 
-main() => dirtyCheckZone().run(_tests);
+import 'package:observe/mirrors_used.dart'; // make test smaller.
+import 'package:smoke/mirrors.dart';
+
+main() {
+  useMirrors();
+  dirtyCheckZone().run(_tests);
+}
 
 void _tests() {
   // Note: to test the basic Observable system, we use ObservableBox due to its
   // simplicity. We also test a variant that is based on dirty-checking.
 
   test('no observers at the start', () {
     expect(dirty_check.allObservablesCount, 0);
   });
 
   group('WatcherModel', () => _observeTests((x) => new WatcherModel(x)));
@@ skipping 239 matching lines @@
   @observable T value;
 
   WatcherModel([T initialValue]) : value = initialValue;
 
   String toString() => '#<$runtimeType value: $value>';
 }
 
 class ModelSubclass<T> extends WatcherModel<T> {
   ModelSubclass([T initialValue]) : super(initialValue);
 }