Migrating another batch of tests to dart 2.

tests/language_strong/compile_time_constant13_test.dart

-// Copyright (c) 2014, 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.
-
-class A {
-  final x; //      //# 01: ok
-  /// 02: compile-time error
-  var x; //        //# 03: compile-time error
-  get x => null; //# 04: compile-time error
-  set x(v) {} //   //# 05: compile-time error
-
-  const A()
-    : x = 'foo' // //# 01: continued
-    : x = 'foo' // //# 02: continued
-    : x = 'foo' // //# 03: continued
-    : x = 'foo' // //# 04: continued
-    : x = 'foo' // //# 05: continued
-  ;
-}
-
-use(x) => x;
-
-A a = const A();
-
-main() {
-  use(a);
-}