Switch on null-aware operators by default in analyzer.

tests/language/conditional_property_access_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.
 
 // Verify semantics of the ?. operator when it does not appear on the LHS of an
 // assignment.
 
-// SharedOptions=--enable-null-aware-operators
-
 import "package:expect/expect.dart";
 import "conditional_access_helper.dart" as h;
 
 noMethod(e) => e is NoSuchMethodError;
 
 class B {}
 
 class C extends B {
   int v;
   C(this.v);
@@ skipping 26 matching lines @@
   Expect.throws(() => h.C?.staticField, noMethod); /// 08: static type warning
 
   // Nor can it be used to access toplevel properties in libraries imported via
   // prefix.
   var x = h?.topLevelVar; /// 09: compile-time error
 
   // However, '?.' can be used to access the hashCode getter on the class Type.
   Expect.equals(C?.hashCode, (C).hashCode); /// 10: ok
   Expect.equals(h.C?.hashCode, (h.C).hashCode); /// 11: ok
 }