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

frog/tests/await/single_await2_test.dart

Index: frog/tests/await/single_await2_test.dart
diff --git a/frog/tests/await/single_await2_test.dart b/frog/tests/await/single_await2_test.dart
index 69f94613898342711e8c0fb9c7519f9480bc6c6e..6ad51ef68214d32f155d81fbc834f14073c1b2b7 100644
--- a/frog/tests/await/single_await2_test.dart
+++ b/frog/tests/await/single_await2_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
+
 // Linear await with the minimal required normalization in the code.
 #import("await_test_helper.dart");