Enable top level inference of instance property gets/sets.

pkg/front_end/testcases/inference_new/infer_instance_field_ref_circular.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;
+
+// In the code below, there is a circularity between A.b and x.
+
+class A {
+  var /*@topType=dynamic*/ b = /*@returnType=dynamic*/ () => x;
+  var /*@topType=() -> dynamic*/ c = /*@returnType=dynamic*/ () => x;
+}
+
+var /*@topType=A*/ a = new A();
+var /*@topType=dynamic*/ x = /*@returnType=dynamic*/ () =>
+    a. /*@target=A::b*/ b;
+var /*@topType=() -> () -> dynamic*/ y = /*@returnType=() -> dynamic*/ () =>
+    a. /*@target=A::c*/ c;
+
+main() {}