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

tests/language/vm/reusable_boxes_test.dart

 // 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.
 // Test correct handling reusable boxes.
-// VMOptions=--optimization_counter_threshold=100
+// VMOptions=--optimization_counter_threshold=100 --no-background_compilation
 
 library reusable_boxes_test;
 
 import 'dart:typed_data';
 import 'package:expect/expect.dart';
 
 class D {
   var a = 0.0;
   var b = 1.0;
   var c = 2.0;
@@ skipping 67 matching lines @@
   Expect.equals(40.0, r.y);
   Expect.equals(60.0, r.z);
   Expect.equals(80.0, r.w);
 }
 
 
 main() {
   testD();
   testF();
 }