Add fields to platform library, implement them on runtime dart.

tests/lib/platform/script_test.dart

Index: tests/lib/platform/script_test.dart
diff --git a/tests/lib/platform/script_test.dart b/tests/lib/platform/script_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..0288be82ce64bdedbd73439d159c91cee406c7a8
--- /dev/null
+++ b/tests/lib/platform/script_test.dart
@@ -0,0 +1,16 @@
+// 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 "dart:platform" as platform;
+
+import "package:unittest/unittest.dart";
+
+main() {
+  if (platform.operatingSystem != null) {
+    expect(platform.script.replaceAll('\\', '/'),

[Anders Johnsen, 2013/10/24 17:21:01]

Consider using `new Uri.file(platform.script).toString()`.

[Bill Hesse, 2013/10/25 11:06:34]

Done.

+           endsWith('tests/lib/platform/script_test.dart'));
+  } else {
+    expect(platform.script, isNull);
+  }
+}