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

tests/language/double_nan_comparison_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.
 // Tests double comparisons with NaN in different contexts.
-// VMOptions=--optimization-counter-threshold=10
+// VMOptions=--optimization-counter-threshold=10 --no-background-compilation
 
 import "package:expect/expect.dart";
 
 test_expr(a, b) => a != b;
 
 test_conditional(a, b) => a != b ? true : false;
 
 test_branch(a, b) {
   if (a != b) {
     return true;
   }
   return false;
 }
 
 
 main() {
   Expect.equals(true, test_expr(0.5, double.NAN));
   for (var i = 0; i < 20; i++) test_expr(0.5, double.NAN);
   Expect.equals(true, test_expr(0.5, double.NAN));
 
   Expect.equals(true, test_conditional(0.5, double.NAN));
   for (var i = 0; i < 20; i++) test_conditional(0.5, double.NAN);
   Expect.equals(true, test_conditional(0.5, double.NAN));
 
   Expect.equals(true, test_branch(0.5, double.NAN));
   for (var i = 0; i < 20; i++) test_branch(0.5, double.NAN);
   Expect.equals(true, test_branch(0.5, double.NAN));
 }