Roll Observatory packages and add a roll script

packages/barback/lib/src/utils/file_pool.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.file_pool;
 
 import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
 
@@ skipping 46 matching lines @@
     var completer = new Completer<List<int>>();
     var builder = new BytesBuilder();
 
     openRead(path).listen(builder.add, onDone: () {
       completer.complete(builder.takeBytes());
     }, onError: completer.completeError, cancelOnError: true);
 
     return completer.future;
   }
 }