Fix for issue 21398 (only send "literal like" objects across isolates spawned using spawnURI

sdk/lib/io/directory_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.io;
 
 class _Directory extends FileSystemEntity implements Directory {
   final String path;
 
   _Directory(this.path) {
@@ skipping 268 matching lines @@
   }
 
   Stream get stream => controller.stream;
 
   void onListen() {
     _IOService.dispatch(_DIRECTORY_LIST_START, [path, recursive, followLinks])
         .then((response) {
           if (response is int) {
             id = response;
             next();
+          } else if (response is Error) {
+            controller.addError(response);
+            close();
           } else {
             error(response);
             close();
           }
         });
   }
 
   void onResume() {
     if (!nextRunning) next();
   }
@@ skipping 78 matching lines @@
       controller.addError(
           new FileSystemException("Directory listing failed",
                                  errorPath,
                                  err));
     } else {
       controller.addError(
           new FileSystemException("Internal error"));
     }
   }
 }