lingering step 2 of the test rename overhaul: make await tests also a directory

frog/tests/await/top_level_function_test.dart

Index: frog/tests/await/top_level_function_test.dart
diff --git a/frog/tests/await/top_level_function_test.dart b/frog/tests/await/top_level_function_test.dart
index b0e5e319342769be40b8489f20d48ed6976f0ecc..0e468a28881d73c2ba7060a7ff78902a036d8328 100644
--- a/frog/tests/await/top_level_function_test.dart
+++ b/frog/tests/await/top_level_function_test.dart
@@ -2,6 +2,11 @@
 // 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.
 
+// The next line is used to tell test.dart that this test is run by invoking
+// awaitc.dart and passing this file as an argument (e.g. frog
+// frog/await/awaitc.dart test.dart):
+// VMOptions=frog/await/awaitc.dart
+
 // Await within a top-level function.
 
 #import("await_test_helper.dart");