Remove uses of Path class from tests/standalone.

tests/standalone/io/raw_secure_server_socket_argument_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 SERVER_ADDRESS = "127.0.0.1";
 const CERTIFICATE = "localhost_cert";
 
 
 void testArguments() {
   bool isArgOrTypeError(e) => e is ArgumentError || e is TypeError;
@@ skipping 26 matching lines @@
   Expect.throws(() => RawSecureSocket.connect(SERVER_ADDRESS, 0,
                                               sendClientCertificate: 'fisk'),
                 isArgOrTypeError);
   Expect.throws(() => RawSecureSocket.connect(SERVER_ADDRESS, 0,
                                               onBadCertificate: 'hund'),
                 isArgOrTypeError);
 }
 
 
 main() {
-  Path scriptDir = new Path(Platform.script).directoryPath;
-  Path certificateDatabase = scriptDir.append('pkcert');
-  SecureSocket.initialize(database: certificateDatabase.toNativePath(),
+  var certificateDatabase = join(dirname(Platform.script), 'pkcert');
+  SecureSocket.initialize(database: certificateDatabase,
                           password: 'dartdart',
                           useBuiltinRoots: false);
   testArguments();
 }