Implement type inference for PropertySet.

pkg/front_end/testcases/inference/downwards_inference_inside_top_level.dart

Index: pkg/front_end/testcases/inference/downwards_inference_inside_top_level.dart
diff --git a/pkg/front_end/testcases/inference/downwards_inference_inside_top_level.dart b/pkg/front_end/testcases/inference/downwards_inference_inside_top_level.dart
index 1737447c782b130464bec58b54d65881b476bf7a..f885364bf273e549c67230d56d2eaa1116738569 100644
--- a/pkg/front_end/testcases/inference/downwards_inference_inside_top_level.dart
+++ b/pkg/front_end/testcases/inference/downwards_inference_inside_top_level.dart
@@ -13,9 +13,12 @@ class B<T> {
   B(T x);
 }
 
-var /*@topType=A*/ t1 = new A()..b = new /*@typeArgs=int*/ B(1);
+var /*@topType=A*/ t1 = new A()
+  .. /*@target=A::b*/ b = new /*@typeArgs=int*/ B(1);
 var /*@topType=List<B<int>>*/ t2 = <B<int>>[new /*@typeArgs=int*/ B(2)];
 var /*@topType=List<B<dynamic>>*/ t3 = /*@typeArgs=B<dynamic>*/ [
   new
       /*error:TOP_LEVEL_TYPE_ARGUMENTS*/ /*@typeArgs=dynamic*/ B(3)
 ];
+
+main() {}