Roll Observatory packages and add a roll script

packages/barback/lib/src/transformer/base_transform.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.transformer.base_transform;
 
 import 'dart:async';
 
 import '../asset/asset_id.dart';
 import '../graph/transform_node.dart';
@@ skipping 95 matching lines @@
   ///
   /// This will close any streams and release any resources that were allocated
   /// for the duration of the transformation. Unlike [done], this indicates that
   /// the transformation is no longer relevant; either it has returned, or
   /// something external has preemptively invalidated its results.
   void cancel() {
     done();
     transform._onLogController.close();
   }
 }