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

tests/language/identical_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.
 // Test efficient and correct implementation of !identical(a, b).
-// VMOptions=--optimization-counter-threshold=10
+// VMOptions=--optimization-counter-threshold=10 --no-background-compilation
 
 import 'package:expect/expect.dart';
 
 notIdenticalTest1(a) {
   if (!identical("ho", a)) {
     return 2;
   } else {
     return 1;
   }
 }
@@ skipping 14 matching lines @@
   return !x;
 }
 
 main() {
   for (int i = 0; i < 20; i++) {
     Expect.equals(1, notIdenticalTest1("ho"));
     Expect.equals(1, notIdenticalTest2("ho"));
     Expect.equals(false, notIdenticalTest3("ho"));
   }
 }