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

tests/standalone/io/secure_server_socket_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 172 matching lines @@
           verifyTestData(dataReceived);
           socket.close();
           asyncEnd();
         });
     });
   });
 }
 
 main() {
   asyncStart();
-  String certificateDatabase = Platform.script.resolve('pkcert').toFilePath();
+  String certificateDatabase = join(dirname(Platform.script), 'pkcert');
   SecureSocket.initialize(database: certificateDatabase,
                           password: 'dartdart',
                           useBuiltinRoots: false);
   testSimpleBind();
   testInvalidBind();
   testSimpleConnect(CERTIFICATE);
   testSimpleConnect("CN=localhost");
   testSimpleConnectFail("not_a_nickname", false);
   testSimpleConnectFail("CN=notARealDistinguishedName", false);
   testSimpleConnectFail("not_a_nickname", true);
   testSimpleConnectFail("CN=notARealDistinguishedName", true);
   testServerListenAfterConnect();
   testSimpleReadWrite();
   asyncEnd();
 }