Abort unit tests in the event of async failure while awaiting a future.

pkg/unittest/test/utils.dart

 // Copyright (c) 2013, 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 unittestTest;
 
+/**
+ * Schedule [fn] for future execution in an event handler.
+ */
 Future _defer(void fn()) {
-  return new Future.sync(fn);
+  return new Future(fn);
 }
 
 String buildStatusString(int passed, int failed, int errors,
                          var results,
                          {int count: 0,
                          String setup: '', String teardown: '',
                          String uncaughtError: null,
                          String message: ''}) {
   var totalTests = 0;
   var testDetails = new StringBuffer();
@@ skipping 65 matching lines @@
   testFunction(testConfig);
 }
 
 void main() {
   var replyPort = new ReceivePort();
   Isolate.spawn(runTestInIsolate, replyPort.sendPort);
   replyPort.first.then((String msg) {
     expect(msg.trim(), expected);
   });
 }