Roll Observatory packages and add a roll script

packages/barback/lib/src/utils/stream_replayer.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.
 
 library barback.utils.stream_replayer;
 
 import 'dart:async';
 import 'dart:collection';
 
 import '../utils.dart';
@@ skipping 63 matching lines @@
       }
     }, onDone: () {
       _isClosed = true;
       for (var controller in _controllers) {
         controller.close();
       }
       _controllers.clear();
     });
   }
 }