Roll Observatory packages and add a roll script

packages/unittest/lib/src/matcher/future_matchers.dart

 // Copyright (c) 2012, 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 unittest.matcher.future_matchers;
 
 import 'dart:async';
 
 import 'expect.dart';
 import 'interfaces.dart';
@@ skipping 55 matching lines @@
 
   Description describe(Description description) {
     if (_matcher == null) {
       description.add('completes successfully');
     } else {
       description.add('completes to a value that ').addDescriptionOf(_matcher);
     }
     return description;
   }
 }