anchor.diff:      _cancel();
       _state |= _STATE_WAIT_FOR_CANCEL;
       var cancelFuture = _cancelFuture;
  -    if (cancelFuture != null &&
  -        !identical(cancelFuture, Future._nullFuture)) {
  +    if (cancelFuture != null && !identical(cancelFuture, Future._nullFuture)) {
         cancelFuture.whenComplete(sendDone);
       } else {
         sendDone();
  
positive.code:   bool _isPaused = false;
  
    _StreamIterator(final Stream<T> stream)
        : _stateData = stream;
  
    T get current {
      if (_subscription != null && _isPaused) {
  
negative.code:       this._source,
        void onListenHandler(StreamSubscription<T> subscription)?,
        void onCancelHandler(StreamSubscription<T> subscription)?)
        : _onListenHandler = onListenHandler == null
              ? null
              : Zone.current.registerUnaryCallback<void, StreamSubscription<T>>(
                  onListenHandler),
          _onCancelHandler = onCancelHandler == null
              ? null
              : Zone.current.registerUnaryCallback<void, StreamSubscription<T>>(
                  onCancelHandler),
          _zone = Zone.current {
      _controller = new _AsBroadcastStreamController<T>(_onListen, _onCancel);
  