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

sdk/lib/async/stream.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of dart.async;
 
 // -------------------------------------------------------------------
 // Core Stream types
 // -------------------------------------------------------------------
 
@@ skipping 163 matching lines @@
   // Deprecated method, previously called 'pipe', retained for compatibility.
   Future pipeInto(Sink<T> sink,
                   {void onError(AsyncError error),
                    bool unsubscribeOnError}) {
     _FutureImpl<T> result = new _FutureImpl<T>();
     this.listen(
         sink.add,
         onError: onError,
         onDone: () {
           sink.close();
-          result.setValue(null);
+          result._setValue(null);
         },
         unsubscribeOnError: unsubscribeOnError);
     return result;
   }
 
 
   /**
    * Check whether [match] occurs in the elements provided by this stream.
    *
    * Completes the [Future] when the answer is known.
@@ skipping 657 matching lines @@
     sink.signalError(error);
   }
 
   /**
    * Handle an incoming done event.
    */
   void handleDone(StreamSink<T> sink) {
     sink.close();
   }
 }