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

tests/language/vm/regress_14903_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 identical comparisons in optimized code. Registers must be preserved
 // when calling the runtime.
 
 cmp(a, b, c) {
   var v = c + 1;
   var w = v + 1;
   var x = w + 1;
   var y = x + 1;
   var z = y + 1;
   if (identical(a, b)) {
     c++;
   }
   return c + v + w + x + y + z;
 }
 
 
 main() {
   var big = 100000000000000000000000000000000000;
   var before = cmp(big, big, 0);
   Expect.equals(16, before);
   for (var i = 0; i < 20; i++) cmp(big, big + 1, 0);
   Expect.equals(before, cmp(big, big, 0));
 }