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

tests/language/vm/optimized_polymorphic_list_access_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.
-// VMOptions=--optimization_counter_threshold=10
+// VMOptions=--optimization_counter_threshold=10 --no-background_compilation
 
 import "package:expect/expect.dart";
 
 // Test correct polymorphic inlining of recognized methods like list access.
 
 test(arr) {
   var r = 0;
   for (var i = 0; i < 1; ++i) {
     r += arr[0];
   }
   return r;
 }
 
 
 main() {
   var a = new List<int>(1);
   a[0] = 0;
   var b = <int>[0];
   Expect.equals(0, test(a));
   Expect.equals(0, test(b));
   for (var i = 0; i < 20; ++i) test(a);
   Expect.equals(0, test(a));
   Expect.equals(0, test(b));
 }