VM: Fix --no-use-field-guards.

tests/corelib/num_sign_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 num.clamp.
+// VMOptions=--no-use-field-guards
+// VMOptions=
 
 import "package:expect/expect.dart";
 
 // Pedestrian implementation of sign, following its specification directly.
 num sign(num value) {
   if (value is int) {
     if (value < 0) return -1;
     if (value > 0) return 1;
     return 0;
   }
@@ skipping 83 matching lines @@
     Expect.equals(number.isNegative, actualSign.isNegative, "$number:negative");
     var renumber = actualSign * number.abs();
     Expect.equals(number, renumber, "$number (sign*abs)");
     if (number is int) {
       Expect.isTrue(renumber is int, "$number (sign*abs) is int");
     } else {
       Expect.isTrue(renumber is double, "$number (sign*abs) is double");
     }
   }
 }