Switch on null-aware operators by default in analyzer.

tests/language/if_null_evaluation_order_test.dart

 // Copyright (c) 2015, 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.
 
 // Evaluation of an if-null expresion e of the form e1 ?? e2 is equivalent to
 // the evaluation of the expression ((x) => x == null ? e2 : x)(e1).
 //
 // Therefore, e1 should be evaluated first; if it is non-null, e2 should not
 // be evaluated.
 
-// SharedOptions=--enable-null-aware-operators
-
 import "package:expect/expect.dart";
 
 void bad() {
   throw new Exception();
 }
 
 bool firstExecuted = false;
 
 first() {
   firstExecuted = true;
   return null;
 }
 
 second() {
   Expect.isTrue(firstExecuted);
   return 2;
 }
 
 main() {
   // Make sure the "none" test fails if "??" is not implemented.  This makes
   // status files easier to maintain.
   var _ = null ?? null;
 
   Expect.equals(1, 1 ?? bad()); /// 01: ok
   Expect.equals(2, first() ?? second()); /// 02: ok
 }