Migrate test block 3 to Dart 2.0.

tests/corelib_2/bit_twiddling_bigint_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.
 // Testing Bigints.
 
 library bit_twiddling_test;
 
 import "package:expect/expect.dart";
 
 // See bit_twiddling_test.dart first.  This file contains only the tests that
@@ skipping 41 matching lines @@
   checkS(0x100000200000000000001, 59, 0x200000000000001);
   checkS(0x100000200000000000001, 58, -0x200000000000000 + 1);
   checkS(0x100000200000000000001, 57, 1);
 }
 
 main() {
   testBitLength();
   testToUnsigned();
   testToSigned();
 }