Implement type inference for PropertySet.

pkg/front_end/testcases/inference/infer_assign_to_ref.dart

Index: pkg/front_end/testcases/inference/infer_assign_to_ref.dart
diff --git a/pkg/front_end/testcases/inference/infer_assign_to_ref.dart b/pkg/front_end/testcases/inference/infer_assign_to_ref.dart
index bfa6613de49c39e6ad0be325d6bb17dad6a4144d..1a958bc18500af1a0a8e913751bc5c93d554499b 100644
--- a/pkg/front_end/testcases/inference/infer_assign_to_ref.dart
+++ b/pkg/front_end/testcases/inference/infer_assign_to_ref.dart
@@ -10,7 +10,8 @@ class A {
 }
 
 A a = new A();
-var /*@topType=dynamic*/ b = (/*error:TOP_LEVEL_UNSUPPORTED*/ a.f = 1);
+var /*@topType=dynamic*/ b =
+    (/*error:TOP_LEVEL_UNSUPPORTED*/ a. /*@target=A::f*/ f = 1);
 var /*@topType=int*/ c = 0;
 var /*@topType=dynamic*/ d = (/*error:TOP_LEVEL_UNSUPPORTED*/ c = 1);