Revert usage of delegating generative constructor, still not supported by VM.

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 b8e4e38d4d21807e9791a3acd8670c166db0ed3b..428e87835bb69938ed2d2a6e1b9d30260e8575e3 100644
--- a/sdk/lib/async/stream.dart
+++ b/sdk/lib/async/stream.dart
@@ -1673,7 +1673,10 @@ abstract class StreamTransformer<S, T> {
 abstract class StreamIterator<T> {
 
   /** Create a [StreamIterator] on [stream]. */
-  factory StreamIterator(Stream<T> stream) = _StreamIteratorImpl<T>;
+  factory StreamIterator(Stream<T> stream)
+      // TODO(lrn): use redirecting factory constructor when type
+      // arguments are supported.
+      => new _StreamIteratorImpl<T>(stream);
 
   /**
    * Wait for the next stream value to be available.