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

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 "dart:async";
@@ skipping 135 matching lines @@
       SecureSocket.connect(HOST_NAME, server.port).then((connection) {
         ends.add(connection);
         checkDone();
       });
     }
   });
 }
 
 
 main() {
-  String certificateDatabase = join(dirname(Platform.script), 'pkcert');
+  String certificateDatabase = Platform.script.resolve('pkcert').toFilePath();
   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.
 }