Add --no-background-compilation to tests that expect to run code in optimized form

tests/language/vm/regress_21245_test.dart

Index: tests/language/vm/regress_21245_test.dart
diff --git a/tests/language/vm/regress_21245_test.dart b/tests/language/vm/regress_21245_test.dart
index 8fa7bb086c4d2ffafd8e061c246373f04f419b61..2e588fb631f0d9286643ba3f9d26daacbebec5c0 100644
--- a/tests/language/vm/regress_21245_test.dart
+++ b/tests/language/vm/regress_21245_test.dart
@@ -1,7 +1,7 @@
 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // 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.
-// VMOptions=--optimization_counter_threshold=10 --no-use-osr
+// VMOptions=--optimization_counter_threshold=10 --no-use-osr --no-background_compilation
 
 test(a) {
   var e;