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

frog/tests/await/doubly_nested_function_test.dart

Index: frog/tests/await/doubly_nested_function_test.dart
diff --git a/frog/tests/await/doubly_nested_function_test.dart b/frog/tests/await/doubly_nested_function_test.dart
index 3a41fac62dfc9c18904407116f109f123b889863..20c9419aad5104c1a203ff44667f8b2e840e276a 100644
--- a/frog/tests/await/doubly_nested_function_test.dart
+++ b/frog/tests/await/doubly_nested_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 in doubly-nested functions.
 
 #import("await_test_helper.dart");