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

tests/language/vm/type_propagation_test.dart

Index: tests/language/vm/type_propagation_test.dart
diff --git a/tests/language/vm/type_propagation_test.dart b/tests/language/vm/type_propagation_test.dart
index 2783654c50158586721b9b75e92a2b9dba83372a..e42aca24afdeb8a18f4495b25ab0c3bc93b16e59 100644
--- a/tests/language/vm/type_propagation_test.dart
+++ b/tests/language/vm/type_propagation_test.dart
@@ -1,10 +1,10 @@
 // Copyright (c) 2015, 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=1000 --max-polymorphic-checks=1
+// VMOptions=--optimization-counter-threshold=1000 --max-polymorphic-checks=1 --no-background-compilation
 
 // Test correct loop invariant code motion and type propagation from is-checks
-// and null-comparisons. 
+// and null-comparisons.
 
 class B {
   var b;