Remove uses of Path class from tests/standalone.

tests/standalone/io/secure_server_closing_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:expect/expect.dart";
+import "package:path/path.dart";
 import "dart:async";
 import "dart:io";
 import "dart:isolate";
 
 const HOST_NAME = "localhost";
 const CERTIFICATE = "localhost_cert";
 
 void testCloseOneEnd(String toClose) {
   ReceivePort port = new ReceivePort();
   Completer serverDone = new Completer();
@@ skipping 123 matching lines @@
       SecureSocket.connect(HOST_NAME, server.port).then((connection) {
         ends.add(connection);
         checkDone();
       });
     }
   });
 }
 
 
 main() {
-  Path scriptDir = new Path(Platform.script).directoryPath;
-  Path certificateDatabase = scriptDir.append('pkcert');
-  SecureSocket.initialize(database: certificateDatabase.toNativePath(),
+  String certificateDatabase = join(dirname(Platform.script), 'pkcert');
+  SecureSocket.initialize(database: certificateDatabase,
                           password: 'dartdart',
                           useBuiltinRoots: false);
 
   testCloseOneEnd("client");
   testCloseOneEnd("server");
   testCloseBothEnds();
   testPauseServerSocket();
   testCloseServer();
   // TODO(whesse): Add testPauseSocket from raw_socket_test.dart.
   // TODO(whesse): Add testCancelResubscribeSocket from raw_socket_test.dart.
 }