Implements secure sockets on Mac OS with SecureTransport API

tests/standalone/io/secure_socket_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.
 //
 // VMOptions=
 // VMOptions=--short_socket_read
 // VMOptions=--short_socket_write
 // VMOptions=--short_socket_read --short_socket_write
 
 import "package:async_helper/async_helper.dart";
@@ skipping 32 matching lines @@
           }
           request.response.close();
         });
     });
     return server;
   });
 }
 
 Future test(String certType, String password) {
   List<int> body = <int>[];
+  Completer completer = new Completer();
   startServer(certType, password).then((server) {
     SecureSocket.connect(
         "localhost", server.port, context: clientContext(certType, password))
     .then((socket) {
       socket.write("GET / HTTP/1.0\r\nHost: localhost\r\n\r\n");
       socket.close();
       socket.listen(
         (List<int> data) {
           body.addAll(data);
         },
         onDone: () {
           Expect.isTrue(body.length > 100, "$body\n${body.length}");
           Expect.equals(72, body[0]);
           Expect.equals(9, body[body.length - 1]);
           server.close();
+          completer.complete(null);
         },
         onError: (e, trace) {
           String msg = "Unexpected error $e";
           if (trace != null) msg += "\nStackTrace: $trace";
           Expect.fail(msg);
+          completer.complete(null);
         });
     });
   });
+  return completer.future;
 }
 
 main() async {
   asyncStart();
   await test('pem', 'dartdart');
   await test('p12', 'dartdart');
   asyncEnd();
 }