Migrate block 162 to Dart 2.0.

tests/language_2/type_propagation3_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.
 
 // Regression test for dart2js that used to generate wrong code for
 // it. The bug happened in the SSA type propagation.
 
 class A {
   next() => new B();
   doIt() => null;
@@ skipping 37 matching lines @@
   var b = a;
   while (b.isEmpty) {
     // (4, 6)
     b.foo(); // (3, 7)
     b.bar(); // (8)
     b = b.doIt(); // (2)
   }
 
   if (!entered) throw 'Test failed';
 }