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

tests/standalone/io/skipping_dart2js_compilations_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.
 
 /*
  * This test makes sure that the "skipping Dart2Js compilations if the output is
  * already up to date" feature does work as it should.
  * Therefore this test ensures that compilations are only skipped if the last
  * modified date of the output of a dart2js compilation is newer than
  *   - the the dart application to compile (including it's dependencies)
@@ skipping 130 matching lines @@
           .existsSync());
     } else {
       Expect.isFalse(new File(fileUtils.scriptOutputPath.toNativePath())
           .existsSync());
     }
   }
 }
 
 runner.Command makeCompilationCommand(String testName, FileUtils fileUtils) {
   var config = new options.TestOptionsParser().parse(['--timeout', '2'])[0];
-  var createFileScript = join(dirname(Platform.script),
-      'skipping_dart2js_compilations_helper.dart');
+  var createFileScript = Platform.script
+      .resolve('skipping_dart2js_compilations_helper.dart').toFilePath();
   var executable = Platform.executable;
   var arguments = [createFileScript, fileUtils.scriptOutputPath.toNativePath()];
   var bootstrapDeps = [
       Uri.parse("file://${fileUtils.testSnapshotFilePath}")];
   return runner.CommandBuilder.instance.getCompilationCommand(
       'dart2js',
       fileUtils.testJsFilePath.toNativePath(),
       false,
       bootstrapDeps,
       executable,
@@ skipping 74 matching lines @@
       cleanup();
       throw error;
     }).then((_) {
       cleanup();
     });
   }
   // We need to wait some time to make sure that the files we 'touch' get a
   // bigger timestamp than the old ones
   new Timer(new Duration(seconds: 1), touchFilesAndRunTests);
 }