Fix types in test.

tests/standalone/io/async_catch_errors_test.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.
 
 import "package:expect/expect.dart";
 import 'dart:async';
 import 'dart:isolate';
 import 'dart:io';
 
 var events = [];
 
-void testSocketException() {
+Future testSocketException() {
   var completer = new Completer();
   runZonedExperimental(() {
     Socket.connect("4", 1).then((Socket s) {
       Expect.fail("Socket should not be able to connect");
     });
   }, onError: (err) {
     if (err is! SocketException) Expect.fail("Not expected error: $err");
     completer.complete("socket test, ok.");
     events.add("SocketException");
   });
   return completer.future;
 }
 
-void testFileException() {
+Future testFileException() {
   var completer = new Completer();
   runZonedExperimental(() {
     new File("lol it's not a file\n").openRead().listen(null);
   }, onError: (err) {
     if (err is! FileException) Expect.fail("Not expected error: $err");
     completer.complete("file test, ok.");
     events.add("FileException");
   });
   return completer.future;
 }
 
 main() {
   // We keep a ReceivePort open until all tests are done. This way the VM will
   // hang if the callbacks are not invoked and the test will time out.
   var timeOutPort = new ReceivePort();
   testSocketException()
     .then((_) => testFileException())
     .then((_) {
       timeOutPort.close();
       Expect.listEquals(["SocketException", "FileException"],
                         events);
     });
 }