Roll Observatory packages and add a roll script

packages/quiver/lib/src/async/future_stream.dart

 // Copyright 2014 Google Inc. All Rights Reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //     http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
@@ skipping 62 matching lines @@
   }
 
   StreamSubscription<T> listen(void onData(T event),
       {Function onError, void onDone(), bool cancelOnError}) {
     return _controller.stream.listen(onData,
         onError: onError, onDone: onDone, cancelOnError: cancelOnError);
   }
 
   bool get isBroadcast => _controller.stream.isBroadcast;
 }