Implement type inference for PropertyGet.

pkg/front_end/testcases/inference/propagate_inference_to_field_in_class.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 x = 2;
 }
 
-test() {
+main() {
   var /*@type=A*/ a = new A();
   A b = a; // doesn't require down cast
-  print(a.x); // doesn't require dynamic invoke
-  print(a.x /*@target=num::+*/ + 2); // ok to use in bigger expression
+  print(a. /*@target=A::x*/ x); // doesn't require dynamic invoke
+  print(a. /*@target=A::x*/ x /*@target=num::+*/ +
+      2); // ok to use in bigger expression
 }