Reduce flakiness of http_client_stays_alive_test.

tests/standalone/io/socket_ipv6_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:io';
 
 import "package:async_helper/async_helper.dart";
 import "package:expect/expect.dart";
 
 const ANY = InternetAddressType.ANY;
@@ skipping 106 matching lines @@
               });
               Socket.connect("127.0.0.1", server.port).catchError((error) {
                 server.close();
                 asyncEnd();
               });
             });
       });
 }
 
 void main() {
-  testIPv6toIPv6();
-  testIPv4toIPv6();
-  testIPv6toIPv4();
-  testIPv4toIPv4();
-  testIPv6Lookup();
-  testIPv4Lookup();
+  testIPv6toIPv6();           /// none: ok

[Florian Schneider, 2016/12/12 21:05:14]

Unrelated, but seems good in general to split up tests like this into smaller
units.

+  testIPv4toIPv6();           /// 01: ok
+  testIPv6toIPv4();           /// 02: ok
+  testIPv4toIPv4();           /// 03: ok
+  testIPv6Lookup();           /// 04: ok
+  testIPv4Lookup();           /// 05: ok
 
-  testIPv4toIPv6_IPV6Only();
+  testIPv4toIPv6_IPV6Only();  /// 06: ok
 }