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

tests/language/async_control_structures_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
+// VMOptions=--optimization-counter-threshold=10 --no-background-compilation
 
 import 'package:expect/expect.dart';
 
 import 'dart:async';
 
 expectThenValue(future, value) {
   Expect.isTrue(future is Future);
   future.then((result) {
     Expect.equals(value, result);
   });
@@ skipping 72 matching lines @@
     expectThenValue(asyncReturn, 3);
     asyncReturn = asyncTryCatchFinally(false, true);
     expectThenValue(asyncReturn, 444);
     asyncReturn = asyncTryCatchLoop();
     expectThenValue(asyncReturn, 13);
 
     asyncReturn = asyncImplicitReturn();
     expectThenValue(asyncReturn, null);
   }
 }