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

tests/language/optimized_constant_array_string_access_test.dart

 // Copyright (c) 2012, 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
 
 import "package:expect/expect.dart";
 
 // Test optimized constant string and constant array access.
 
 int testConstantStringAndIndexCodeUnitAt() {
   int test(b) {
     if (b) return "hest".codeUnitAt(400);
     return "hest".codeUnitAt(2);
   }
@@ skipping 38 matching lines @@
   for (int i = 0; i < 20; i++) { foo(1); }
   Expect.throws(() => foo(2));
 }
 
 
 main() {
   testConstantStringAndIndexCodeUnitAt();
   testConstantArrayAndIndexAt();
   testNonSmiIndex();
 }