Migrate block 163 to Dart 2.0.

tests/language_2/unicode_bom_middle_test.dart

 // Copyright (c) 2011, 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.
 
 import "package:expect/expect.dart";
 
 int inscrutable(int x) => x == 0 ? 0 : x | inscrutable(x & (x - 1));
 
 foo(x) {
   if (inscrutable(1999) == 1999) return x;
   return 499;
 }
 
 main() {
   Expect.equals(3, "xx".length); // BOM character between the xs.
   Expect.equals(3, foo("xx").length); // BOM character between the xs.
 }