Change dart:io Platform.script to return a Uri.

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";
@@ skipping 37 matching lines @@
   Expect.throws(() => RawSecureSocket.connect(SERVER_ADDRESS, 0,
                                               sendClientCertificate: 'fisk'),
                 isArgOrTypeError);
   Expect.throws(() => RawSecureSocket.connect(SERVER_ADDRESS, 0,
                                               onBadCertificate: 'hund'),
                 isArgOrTypeError);
 }
 
 
 main() {
-  var certificateDatabase = join(dirname(Platform.script), 'pkcert');
+  var certificateDatabase = Platform.script.resolve('pkcert').toFilePath();
   SecureSocket.initialize(database: certificateDatabase,
                           password: 'dartdart',
                           useBuiltinRoots: false);
   testArguments();
 }