Add StreamChannelTransformer.

test/stream_channel_test.dart

Index: test/stream_channel_test.dart
diff --git a/test/stream_channel_test.dart b/test/stream_channel_test.dart
index 30a7db4fafb508dc9d92cd3637897e157f31147c..5f006c39c64a4ecf400a6bd7af4c4b34b9da48fb 100644
--- a/test/stream_channel_test.dart
+++ b/test/stream_channel_test.dart
@@ -44,7 +44,8 @@ void main() {
   });
 
   test("transform() transforms the channel", () {
-    var transformed = channel.transform(UTF8);
+    var transformed = channel.transform(
+        new StreamChannelTransformer.fromCodec(UTF8));
 
     streamController.add([102, 111, 111, 98, 97, 114]);
     streamController.close();