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

tests/language/null_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.
 // Second dart test program.
 
-// VMOptions=--optimization-counter-threshold=5
+// VMOptions=--optimization-counter-threshold=5 --no-background-compilation
 
 import "dart:mirrors";
 import "package:expect/expect.dart";
 
 class BadInherit
   extends Null     /// 01: compile-time error
   implements Null  /// 02: compile-time error
   extends Object with Null  /// 03: compile-time error
     {}
 
@@ skipping 177 matching lines @@
   var capture = new CaptureInvocationMirror();
   var mirror = capture.notDeclared();
   Expect.throws(() => noSuchMethod(mirror));
   Expect.throws(() => Function.apply(noSuchMethod, [mirror]));
 }
 
 
 class CaptureInvocationMirror {
   noSuchMethod(mirror) => mirror;
 }