fix transform

Samples/UIWidgetsSamples_2019_4/Assets/Editor/Tests/Stream/TestMain.cs

                     Debug.Log("val = " + val);
                 });
             }
+
+            private void test10()
+            {
+                Stream<int> numbers = Stream<int>.fromIterable(new List<int> {0, 1, 2, 2, 3, 4, 5, 5});
+                var transformer = StreamTransformer<int, string>.fromHandlers(handleData: (val, sink) =>
+                {
+                    sink.add("My number is " + val);
+                });
+
+                numbers.transform(transformer).listen(val =>
+                {
+                    Debug.Log("val = " + val);
+                });
+            }
-                test9();
+                test10();
                 return new Container();
             }
         }

com.unity.uiwidgets/Runtime/async/stream.cs

             return streamConsumer.addStream(this).then((_) => streamConsumer.close(), (_) => FutureOr.nil);
         }
 
-        Stream<S> transform<S>(StreamTransformer<T, S> streamTransformer) where S : class {
+        public Stream<S> transform<S>(StreamTransformer<T, S> streamTransformer) where S : class {
             return streamTransformer.bind(this);
         }
 

com.unity.uiwidgets/Runtime/async/stream_transformers.cs

 
 namespace Unity.UIWidgets.async {
     class _EventSinkWrapper<T> : EventSink<T> {
-        _EventSink<object> _sink;
+        _EventSink<T> _sink;
-        internal _EventSinkWrapper(_EventSink<object> _sink) {
+        internal _EventSinkWrapper(_EventSink<T> _sink) {
             this._sink = _sink;
         }
 
                 Action<T> onData, Action<object, string> onError, Action onDone, bool cancelOnError)
             // We set the adapter's target only when the user is allowed to send data.
             : base(onData, onError, onDone, cancelOnError) {
-            _EventSinkWrapper<T> eventSink = new _EventSinkWrapper<T>((_EventSink<object>) this);
+            _EventSinkWrapper<T> eventSink = new _EventSinkWrapper<T>(this);
             _transformerSink = mapper(eventSink);
             _subscription =
                 source.listen(_handleData, onError: _handleError, onDone: _handleDone);