Fix checked mode error in socket_bind_test.

tests/standalone/io/socket_bind_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 'dart:async';
 import 'dart:io';
 import 'dart:convert';
 
 import 'package:async_helper/async_helper.dart';
 import 'package:expect/expect.dart';
@@ skipping 95 matching lines @@
   });
 
   Socket client = await Socket.connect(host, socket2.port);
   await client.close();
   await client.drain();
 
   asyncEnd();
 }
 
 Future<int> freeIPv4AndIPv6Port() async {
-  var socket = await ServerSocket.bind(InternetAddress.ANY_IP_V6, 0, v6Only: false);
+  var socket =
+    await ServerSocket.bind(InternetAddress.ANY_IP_V6, 0, v6Only: false);
   int port = socket.port;
   await socket.close();
   return port;
 }
 
-void main() async {
+main() async {
   asyncStart();
   await testBindDifferentAddresses(InternetAddress.ANY_IP_V6,
                                    InternetAddress.ANY_IP_V4,
                                    true,
                                    false);
   await testBindDifferentAddresses(InternetAddress.ANY_IP_V4,
                                    InternetAddress.ANY_IP_V6,
                                    false,
                                    true);
 
   for (var host in ['127.0.0.1', '::1']) {
     testBindShared(host, false);
     testBindShared(host, true);
 
     negTestBindSharedMismatch(host, false);
     negTestBindSharedMismatch(host, true);
 
     negTestBindV6OnlyMismatch(host, true);
     negTestBindV6OnlyMismatch(host, false);
 
     testListenCloseListenClose(host);
   }
   asyncEnd();
 }