Fix test timeouts. I forgot to include observe/mirrors_used.dart in tests from

pkg/polymer_expressions/test/globals_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:observe/observe.dart';
+import 'package:observe/mirrors_used.dart'; // make test smaller.
 import 'package:polymer_expressions/polymer_expressions.dart';
 import 'package:template_binding/template_binding.dart';
 import 'package:unittest/unittest.dart';
 import 'package:unittest/html_config.dart';
 
 main() {
   useHtmlConfiguration();
 
   var testDiv;
   group('enumerate', () {
@@ skipping 63 matching lines @@
             'Item 3 is a',
             'Item 4 is b',
             'Item 5 is e',
             'Item 6 is c',
           ]);
         });
       });
     });
   });
 }