Ensure that asyncStart is called before starting an async operation in test

tests/standalone/io/directory_test.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.
 //
 // Directory listing test.
 
 import "dart:async";
 import "dart:io";
 
 import "package:async_helper/async_helper.dart";
@@ skipping 106 matching lines @@
     }
     Directory.systemTemp.createTemp('dart_directory').then((d) {
       d.delete().then((ignore) {
         setupListerHandlers(d.list());
         setupListerHandlers(d.list(recursive: true));
       });
     });
   }
 
   static void testListTooLongName() {
+    asyncStart();
     Directory.systemTemp.createTemp('dart_directory').then((d) {
       var errors = 0;
-      asyncStart();
       setupListHandlers(Stream<FileSystemEntity> stream) {
         stream.listen(
           (_) => Expect.fail("Listing of non-existing directory should fail"),
           onError: (error) {
             Expect.isTrue(error is FileSystemException);
             if (++errors == 2) {
               d.delete(recursive: true).then((_) {
                 asyncEnd();
               });
             }
@@ skipping 477 matching lines @@
   DirectoryTest.testMain();
   NestedTempDirectoryTest.testMain();
   testCreateTempErrorSync();
   testCreateTempError();
   testCreateExistingSync();
   testCreateExisting();
   testCreateDirExistingFileSync();
   testCreateDirExistingFile();
   testRename();
 }