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

tests/standalone/io/secure_client_raw_server_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 60 matching lines @@
       onDone: () {
         String reply = chunks.join();
         Expect.equals("Hello server.", reply);
         success.complete(server);
       });
   });
   return success.future;
 }
 
 void main() {
-  String certificateDatabase = Platform.script.resolve('pkcert').toFilePath();
+  String certificateDatabase = join(dirname(Platform.script), 'pkcert');
   SecureSocket.initialize(database: certificateDatabase,
                           password: 'dartdart');
 
   startEchoServer()
       .then(testClient)
       .then((server) {
         server.close();
       });
 }