Roll Observatory packages and add a roll script

packages/barback/lib/src/graph/node_streams.dart

 // Copyright (c) 2014, 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.graph.node_streams;
 
 import 'dart:async';
 
 import '../asset/asset_node.dart';
 import '../log.dart';
@@ skipping 46 matching lines @@
 
   /// Closes all the streams.
   void close() {
     _onStatusChangeController.close();
     onAssetController.close();
     onAssetPool.close();
     onLogController.close();
     onLogPool.close();
   }
 }