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

tests/standalone/io/process_sync_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 'package:path/path.dart';
 import "dart:io";
 
 test(int blockCount,
      int stdoutBlockSize,
      int stderrBlockSize,
      int exitCode,
      [int nonWindowsExitCode]) {
   // Get the Dart script file that generates output.
-  var scriptFile = new File(join(dirname(Platform.script),
-                                 "process_sync_script.dart"));
+  var scriptFile = new File(Platform.script
+                                    .resolve("process_sync_script.dart")
+                                    .toFilePath());
   var args = [scriptFile.path,
               blockCount.toString(),
               stdoutBlockSize.toString(),
               stderrBlockSize.toString(),
               exitCode.toString()];
   ProcessResult syncResult = Process.runSync(Platform.executable, args);
   Expect.equals(blockCount * stdoutBlockSize, syncResult.stdout.length);
   Expect.equals(blockCount * stderrBlockSize, syncResult.stderr.length);
   if (Platform.isWindows) {
     Expect.equals(exitCode, syncResult.exitCode);
@@ skipping 25 matching lines @@
   test(1, kBufferSize, kBufferSize, 0);
   test(1, kBufferSize - 1, kBufferSize - 1, 0);
   test(1, kBufferSize + 1, kBufferSize + 1, 0);
 
   test(10, 10, 10, 1);
   test(10, 10, 10, 255);
   test(10, 10, 10, -1, 255);
   test(10, 10, 10, -255, 1);
 }