Enable top level inference of instance property gets/sets.

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