Fix bad onSuccess calls after an exception.

sdk/lib/async/stream_pipe.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;
 
 /** Utility function to create an [AsyncError] if [error] isn't one already. */
 AsyncError _asyncError(Object error, Object stackTrace, [AsyncError cause]) {
   if (error is AsyncError) return error;
   if (cause == null) return new AsyncError(error, stackTrace);
   return new AsyncError.withCause(error, stackTrace, cause);
 }
 
 /** Runs user code and takes actions depending on success or failure. */
 _runUserCode(userCode(), onSuccess(value), onError(AsyncError error),
              { AsyncError cause }) {
   var result;
   try {
     result = userCode();
   } on AsyncError catch (e) {
     return onError(e);
   } catch (e, s) {
     if (cause == null) {
       onError(new AsyncError(e, s));
     } else {
       onError(new AsyncError.withCause(e, s, cause));
     }
+    // onError is allowed to return. Don't execute the onSuccess below.
+    return;
   }
   onSuccess(result);
 }
 
 /** Helper function to make an onError argument to [_runUserCode]. */
 _cancelAndError(StreamSubscription subscription, _FutureImpl future) =>
   (AsyncError error) {
     subscription.cancel();
     future._setError(error);
   };
@@ skipping 475 matching lines @@
 
   void handleError(AsyncError error, EventSink<T> sink) {
     _handleError(error, sink);
   }
 
   void handleDone(EventSink<T> sink) {
     _handleDone(sink);
   }
 }