anchor.diff:        },
         onPause: () { subscription.pause(); },
         onResume: () { subscription.resume(); },
  -      onCancel: () { subscription.cancel(); }
  +      onCancel: () { subscription.cancel(); },
  +      sync: true
       );
       return controller.stream;
     }
  
positive.code:   Stream asyncMap(convert(T event)) {
      StreamController controller;
      StreamSubscription subscription;
      controller = new StreamController(sync: true,
        onListen: () {
          var add = controller.add;
          var addError = controller.addError;
  
negative.code:   Stream asyncExpand(Stream convert(T event)) {
      StreamController controller;
      StreamSubscription subscription;
      controller = new StreamController(
        onListen: () {
          subscription = this.listen(
              (T event) {
  