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

tests/language/vm/reusable_boxes_test.dart

Index: tests/language/vm/reusable_boxes_test.dart
diff --git a/tests/language/vm/reusable_boxes_test.dart b/tests/language/vm/reusable_boxes_test.dart
index a70cade673038210f531dc27ac1a6bb45a0b225c..4e88e4ad060f7123ffa0a409a6bd4f363a9184df 100644
--- a/tests/language/vm/reusable_boxes_test.dart
+++ b/tests/language/vm/reusable_boxes_test.dart
@@ -2,7 +2,7 @@
 // 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.
 // Test correct handling reusable boxes.
-// VMOptions=--optimization_counter_threshold=100
+// VMOptions=--optimization_counter_threshold=100 --no-background_compilation
 
 library reusable_boxes_test;