Don't consider controller.addError to be a zone-crossing.

sdk/lib/async/stream_impl.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;
 
 /** Abstract and private interface for a place to put events. */
 abstract class _EventSink<T> {
   void _add(T data);
   void _addError(Object error, StackTrace stackTrace);
@@ skipping 336 matching lines @@
     assert(!_isCanceled);
     assert(!_isPaused);
     assert(!_inCallback);
     bool wasInputPaused = _isInputPaused;
 
     void sendError() {
       // If the subscription has been canceled while waiting for the cancel
       // future to finish we must not report the error.
       if (_isCanceled && !_waitsForCancel) return;
       _state |= _STATE_IN_CALLBACK;
-      if (!_zone.inSameErrorZone(Zone.current)) {
-        // Errors are not allowed to traverse zone boundaries.
-        Zone.current.handleUncaughtError(error, stackTrace);
-      } else if (_onError is ZoneBinaryCallback) {
+      if (_onError is ZoneBinaryCallback) {
         _zone.runBinaryGuarded(_onError, error, stackTrace);
       } else {
         _zone.runUnaryGuarded(_onError, error);
       }
       _state &= ~_STATE_IN_CALLBACK;
     }
 
     if (_cancelOnError) {
       _state |= _STATE_WAIT_FOR_CANCEL;
       _cancel();
@@ skipping 704 matching lines @@
       _Future<bool> hasNext = _futureOrPrefetch;
       _clear();
       hasNext._complete(false);
       return;
     }
     _subscription.pause();
     _futureOrPrefetch = null;
     _state = _STATE_EXTRA_DONE;
   }
 }