Remove uses of Path class from tests/standalone.

tests/standalone/io/https_client_certificate_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 "package:expect/expect.dart";
+import "package:path/path.dart";
 import "dart:async";
 import "dart:io";
 import "dart:isolate";
 
 const HOST_NAME = "localhost";
 
 
 Function test() {
   var keepAlive = new ReceivePort();
   HttpServer.bindSecure(HOST_NAME,
@@ skipping 21 matching lines @@
           String received = new String.fromCharCodes(message);
           Expect.equals(received, "Hello");
           client.close();
           server.close();
           keepAlive.close();
         });
   });
 }
 
 void InitializeSSL() {
-  var testPkcertDatabase =
-      new Path(Platform.script).directoryPath.append('pkcert/');
-  SecureSocket.initialize(database: testPkcertDatabase.toNativePath(),
+  var testPkcertDatabase = join(dirname(Platform.script), 'pkcert');
+  SecureSocket.initialize(database: testPkcertDatabase,
                           password: 'dartdart');
 }
 
 void main() {
   InitializeSSL();
   test();
 }