Retain script path of parent isolate when spawnFunction is called so that

tests/standalone/io/platform_test.dart

 // Copyright (c) 2012, 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 "dart:async";
 import "dart:io";
 import "dart:isolate";
 
 import "package:async_helper/async_helper.dart";
 import "package:expect/expect.dart";
@@ skipping 47 matching lines @@
 testIsolate() {
   asyncStart();
   var sendPort = spawnFunction(f);
   Future.wait([sendPort.call("Platform.executable"),
                sendPort.call("Platform.script"),
                sendPort.call("Platform.packageRoot"),
                sendPort.call("Platform.executableArguments")])
   .then((results) {
     Expect.equals(Platform.executable, results[0]);
     Uri uri = Uri.parse(results[1]);
-    Expect.equals("file", uri.scheme);
+    // SpawnFunction retains the script url of the parent which in this
+    // case was a relative path.
+    Expect.equals("", uri.scheme);
     Expect.isTrue(uri.path.endsWith('tests/standalone/io/platform_test.dart'));
     Expect.equals(Platform.packageRoot, results[2]);
     Expect.listEquals(Platform.executableArguments, results[3]);
     sendPort.call("close").then((_) => asyncEnd());
   });
 }
 
 main() {
   test();
   testIsolate();
 }