Enable top level inference of instance property gets/sets.

pkg/front_end/testcases/inference/infer_assign_to_property.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;
-}
-
-var /*@topType=dynamic*/ v_assign =
-    (/*error:TOP_LEVEL_UNSUPPORTED*/ new A(). /*@target=A::f*/ f = 1);
-var /*@topType=dynamic*/ v_plus =
-    (/*error:TOP_LEVEL_UNSUPPORTED*/ new A(). /*@target=A::f*/ f += 1);
-var /*@topType=dynamic*/ v_minus =
-    (/*error:TOP_LEVEL_UNSUPPORTED*/ new A(). /*@target=A::f*/ f -= 1);
-var /*@topType=dynamic*/ v_multiply =
-    (/*error:TOP_LEVEL_UNSUPPORTED*/ new A(). /*@target=A::f*/ f *= 1);
-var /*@topType=dynamic*/ v_prefix_pp =
-    (++new A(). /*error:TOP_LEVEL_INSTANCE_GETTER*/ /*@target=A::f*/ f);
-var /*@topType=dynamic*/ v_prefix_mm =
-    (--new A(). /*error:TOP_LEVEL_INSTANCE_GETTER*/ /*@target=A::f*/ f);
-var /*@topType=dynamic*/ v_postfix_pp =
-    (new A(). /*error:TOP_LEVEL_INSTANCE_GETTER*/ /*@target=A::f*/ f++);
-var /*@topType=dynamic*/ v_postfix_mm =
-    (new A(). /*error:TOP_LEVEL_INSTANCE_GETTER*/ /*@target=A::f*/ f--);
-
-main() {}