Relax typing on Stream.transform

sdk/lib/async/stream.dart

Index: sdk/lib/async/stream.dart
diff --git a/sdk/lib/async/stream.dart b/sdk/lib/async/stream.dart
index 3d58455d0ed101bb3ed31eb177524cf912d3e4f4..feef93c5e23ddef62fcd0a18cd5e5379af5d01c8 100644
--- a/sdk/lib/async/stream.dart
+++ b/sdk/lib/async/stream.dart
@@ -615,8 +615,8 @@ abstract class Stream<T> {
    * and which elements it will contain,
    * is entirely up to the transformation.
    */
-  Stream<S> transform<S>(StreamTransformer<T, S> streamTransformer) {
-    return streamTransformer.bind(this);
+  Stream<S> transform<S>(StreamTransformer<dynamic, S> streamTransformer) {
+    return streamTransformer.bind(this.map<T>((x) => x));

[vsm, 2017/06/26 18:28:51]

Actually, not sure the map is necessary at this point.  Seems to work without
it.

[Lasse Reichstein Nielsen, 2017/06/27 05:45:18]

It should work, the transformer claims to handle all types, so there should be
no need to change the type of elements put into it. 

It's only due to implicit down-cast that the map operation is allowed. You are
implicitly casting `dynamic` to `T` in the `=> x` return, so you'll get a
dynamic check there.

   }
 
   /**