Add executable to Options interface to get the name of the executable used to execute the script.

tests/standalone/io/process_stderr_test.dart

Index: tests/standalone/io/process_stderr_test.dart
diff --git a/tests/standalone/io/process_stderr_test.dart b/tests/standalone/io/process_stderr_test.dart
index 6181c1cc82cecf6f16ad1839d209bf22b0b5a636..47a030b49dc098de6b3e2a47310250282c0a1410 100644
--- a/tests/standalone/io/process_stderr_test.dart
+++ b/tests/standalone/io/process_stderr_test.dart
@@ -67,5 +67,5 @@ main() {
     scriptFile = new File("../tests/standalone/io/process_std_io_script.dart");
   }
   Expect.isTrue(scriptFile.existsSync());
-  test(new Process.start(getDartFileName(), [scriptFile.name, "1"]), 0);
+  test(new Process.start(new Options().executable, [scriptFile.name, "1"]), 0);
 }