Consider a thrown AsyncError from a future/stream handler a rethrow.

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 b5466c5659c30ed15f71566a0f40c5d5f2215d7d..c9377d5da2abd4d6aca92a760132e9f41de6a7df 100644
--- a/sdk/lib/async/stream.dart
+++ b/sdk/lib/async/stream.dart
@@ -181,7 +181,7 @@ abstract class Stream<T> {
         onError: onError,
         onDone: () {
           sink.close();
-          result.setValue(null);
+          result._setValue(null);
         },
         unsubscribeOnError: unsubscribeOnError);
     return result;