Migrate block 162 to Dart 2.0.

tests/language/type_propagation3_test.dart

-// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file

[eernst, 2017/09/04 17:04:56]

Lost coverage: don't delete this 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;
-  bool get isEmpty => false;
-  foo() => 42;
-  bar() => 54;
-}
-
-bool entered = false;
-
-class B extends A {
-  foo() => 54;
-  doIt() => new A();
-  bool get isEmpty => true;
-  bar() => entered = true;
-}
-
-// (1) At initialization phase of the type propagation, [a] would be
-//     marked as [exact A].
-// (2) Will make the loop phi [b] typed [null, exact A].
-// (3) Will create a [HTypeKnown] [exact A] for [b].
-// (4) Will create a [HTypeKnown] [exact A] for [b] and update users
-//     of [b] to use this [HTypeKnown] instead.
-// (5) [a] will be updated to [subclass A].
-// (6) Will change the [HTypeKnown] of [b] from [exact A] to [subclass A].
-// (7) Receiver is [subclass A] and it will refine it to
-//     [subclass A]. We used to wrongly assume there was
-//     no need to update the [HTypeKnown] created in (3).
-// (8) Consider that bar is called on an [exact A] (the [HTypeKnown]
-//     created in (3)) and remove the call because it does not have
-//     any side effects.
-
-main() {
-  var a = new A();
-  for (var i in [42]) {
-    a = a.next();
-  }
-
-  // (1, 5)
-
-  var b = a;
-  while (b.isEmpty) {
-    // (4, 6)
-    b.foo(); // (3, 7)
-    b.bar(); // (8)
-    b = b.doIt(); // (2)
-  }
-
-  if (!entered) throw 'Test failed';
-}