anchor.diff:  ///
   /// The [close] method is also called immediately when the source stream
   /// is done.
  -abstract class _EventRequest implements EventSink {
  +abstract class _EventRequest {
     /// Handle available events.
     ///
     /// The available events are provided as a queue. The `addEvents` function
  
positive.code:   /// Ensures that we are listening on events from [_sourceStream].
    ///
    /// Resumes subscription on [_sourceStream], or creates it if necessary.
    StreamSubscription _ensureListening() {
      assert(!_isDone);
      if (_subscription == null) {
        _subscription =
  
negative.code:     return true;
    }
  
    void close(Queue<Result> events) {
      _completer.complete(_list);
    }
  }
  