Roll Observatory packages and add a roll script

packages/matcher/lib/src/iterable_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 matcher.iterable_matchers;
 
 import 'core_matchers.dart';
 import 'description.dart';
 import 'interfaces.dart';
 import 'util.dart';
@@ skipping 247 matching lines @@
     } else {
       return mismatchDescription
           .add('has ')
           .addDescriptionOf(matchState["actual"])
           .add(' which is not $_description ')
           .addDescriptionOf(matchState["expected"])
           .add(' at index ${matchState["index"]}');
     }
   }
 }