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

tests/language/vm/optimized_polymorphic_list_access_test.dart

Index: tests/language/vm/optimized_polymorphic_list_access_test.dart
diff --git a/tests/language/vm/optimized_polymorphic_list_access_test.dart b/tests/language/vm/optimized_polymorphic_list_access_test.dart
index 6ab48f949f66c36d1afbb31bd147aeaea7958125..77e5c1287f50e75f81c9e29a1c423c984f300616 100644
--- a/tests/language/vm/optimized_polymorphic_list_access_test.dart
+++ b/tests/language/vm/optimized_polymorphic_list_access_test.dart
@@ -1,7 +1,7 @@
 // Copyright (c) 2013, 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
+// VMOptions=--optimization_counter_threshold=10 --no-background_compilation
 
 import "package:expect/expect.dart";