Migrate block 162 to Dart 2.0.

tests/language_2/type_propagation_test.dart

 // Copyright (c) 2013, 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.
 
 // dart2js used to have an infinite loop in its type propagation
 // algorithm due to types becoming broader instead of narrower.
 
 import "package:expect/expect.dart";
 
 class A {
@@ skipping 23 matching lines @@
 var a = 43;
 
 class B {
   var getter = a == 42 ? new A() : null;
 }
 
 main() {
   Expect.isTrue(new A().visitSend(new A()) is A);
   Expect.isTrue(new A().visitSend(null) is B);
 }