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

tests/standalone/io/http_cross_process_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 'dart:async';
 import 'dart:io';
 
 const int NUM_SERVERS = 10;
@@ skipping 18 matching lines @@
     server.listen((request) {
       request.pipe(request.response);
     });
     return server;
   });
 }
 
 Future runClientProcess(int port) {
   return Process.run(Platform.executable,
                      []..addAll(Platform.executableArguments)
-                       ..add(Platform.script)
+                       ..add(Platform.script.toFilePath())
                        ..add('--client')
                        ..add(port.toString())).then((ProcessResult result) {
     if (result.exitCode != 0 || !result.stdout.contains('SUCCESS')) {
       print("Client failed, exit code ${result.exitCode}");
       print("  stdout:");
       print(result.stdout);
       print("  stderr:");
       print(result.stderr);
       Expect.fail('Client subprocess exit code: ${result.exitCode}');
     }
   });
 }
 
 runClient(int port) {
   var client = new HttpClient();
   client.get('127.0.0.1', port, "/")
       .then((request) => request.close())
       .then((response) => response.listen((data) {},
                                           onDone: () => print('SUCCESS')));
 }