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

tests/language/regress_11800_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 register allocation with a value used twice at the same
 // instruction.
 test(List a, int v) {
   a[v] = v;
 }
 
 main() {
   var list = new List(2);
   for (var i = 0; i < 20; i++) test(list, 1);
   Expect.equals(null, list[0]);
   Expect.equals(1, list[1]);
 }