Roll Observatory packages and add a roll script

packages/unittest/lib/src/matcher/core_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.core_matchers;
 
 import 'description.dart';
 import 'interfaces.dart';
 import 'util.dart';
 
@@ skipping 625 matching lines @@
         .addDescriptionOf(matchState['feature']);
     var innerDescription = new StringDescription();
     _matcher.describeMismatch(
         matchState['feature'], innerDescription, matchState['state'], verbose);
     if (innerDescription.length > 0) {
       mismatchDescription.add(' which ').add(innerDescription.toString());
     }
     return mismatchDescription;
   }
 }