Implement type inference for PropertyGet.

pkg/front_end/testcases/inference/propagate_inference_transitively2.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 = 42;
 }
 
 class B {
   A a = new A();
 }
 
 class C {
   B b = new B();
 }
 
 class D {
   C c = new C();
 }
 
 void main() {
   var /*@type=D*/ d1 = new D();
-  print(d1.c.b.a.x);
+  print(d1. /*@target=D::c*/ c. /*@target=C::b*/ b. /*@target=B::a*/ a
+      . /*@target=A::x*/ x);
 
   D d2 = new D();
-  print(d2.c.b.a.x);
+  print(d2. /*@target=D::c*/ c. /*@target=C::b*/ b. /*@target=B::a*/ a
+      . /*@target=A::x*/ x);
 }