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

tests/language/vm/regress_21245_test.dart

 // Copyright (c) 2014, 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=10 --no-use-osr
+// VMOptions=--optimization_counter_threshold=10 --no-use-osr --no-background_compilation
 
 test(a) {
   var e;
   for (var i = 0; i < a.length; i++) {
     e = a[i];
     for (var j = 0; j < i; j++) {
       e = a[j];
     }
   }
   return e;
 }
 
 main() {
   var a = [0, 1, 2, 3, 4, 5];
   for (var i = 0; i < 20; i++) {
     test(a);
   }
 }