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

frog/tests/await/single_await_normalization_test.dart

Index: frog/tests/await/single_await_normalization_test.dart
diff --git a/frog/tests/await/single_await_normalization_test.dart b/frog/tests/await/single_await_normalization_test.dart
index 9bdd99cfe5c176ef1c4baf3a780d9a029bf5bbc4..d2907f4466ed9e06b0a8f2850bd8183a541086ce 100644
--- a/frog/tests/await/single_await_normalization_test.dart
+++ b/frog/tests/await/single_await_normalization_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 not-normalized await expression
 #import("await_test_helper.dart");