Enable top level inference of instance property gets/sets.

pkg/front_end/testcases/inference/infer_assign_to_ref.dart

 // Copyright (c) 2017, 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.
 
 /*@testedFeatures=inference*/
 library test;
 
 class A {
   int f;
 }
 
 A a = new A();
-var /*@topType=dynamic*/ b =
-    (/*error:TOP_LEVEL_UNSUPPORTED*/ a. /*@target=A::f*/ f = 1);

[Siggi Cherem (dart-lang), 2017/06/16 03:40:03]

I wonder if there is value in also keeping the old tests around by passing
another flag to the test framework. For instance, have
testedFeatures=inference_old or =inference_new to toggle the flags and continue
to test the old behavior until it gets deleted.

[Paul Berry, 2017/06/16 03:44:09]

Acknowledged.

 var /*@topType=int*/ c = 0;
 
 main() {
   a;
-  b;
   c;
 }