Enable top level inference of instance property gets/sets.

pkg/front_end/testcases/inference_new/infer_instance_accessor_ref.dart

Index: pkg/front_end/testcases/inference_new/infer_instance_accessor_ref.dart
diff --git a/pkg/front_end/testcases/inference/infer_assign_to_ref.dart b/pkg/front_end/testcases/inference_new/infer_instance_accessor_ref.dart
similarity index 51%
copy from pkg/front_end/testcases/inference/infer_assign_to_ref.dart
copy to pkg/front_end/testcases/inference_new/infer_instance_accessor_ref.dart
index 9ef7bb7f0e3bd8958681000bebac90b71bdcf9d7..d7b652f5bddf77b2e65078fc96ecd52e9c12cd3b 100644
--- a/pkg/front_end/testcases/inference/infer_assign_to_ref.dart
+++ b/pkg/front_end/testcases/inference_new/infer_instance_accessor_ref.dart
@@ -6,16 +6,20 @@
 library test;
 
 class A {
-  int f;
+  B b;
 }
 
-A a = new A();
-var /*@topType=dynamic*/ b =
-    (/*error:TOP_LEVEL_UNSUPPORTED*/ a. /*@target=A::f*/ f = 1);
-var /*@topType=int*/ c = 0;
-
-main() {
-  a;
-  b;
-  c;
+class B {
+  C get c => null;
+  void set(C value) {}
 }
+
+class C {}
+
+class D extends C {}
+
+var /*@topType=A*/ a = new A();
+var /*@topType=C*/ x = a. /*@target=A::b*/ b. /*@target=B::c*/ c;
+var /*@topType=dynamic*/ y = a. /*@target=A::b*/ b.c ??= new D();
+
+main() {}