Migrate test block 3 to Dart 2.0.

tests/corelib/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
-// need Bigint or would fail in dart2js compatibility mode.
-
-testBitLength() {
-  check(int i, width) {
-    Expect.equals(width, i.bitLength, '$i.bitLength ==  $width');
-    // (~i) written as (-i-1) to avoid issues with limited range of dart2js ops.
-    Expect.equals(width, (-i - 1).bitLength, '(~$i).bitLength == $width');
-  }
-
-  check(0xffffffffffffff, 56);
-  check(0xffffffffffffffff, 64);
-  check(0xffffffffffffffffff, 72);
-  check(0x1000000000000000000, 73);
-  check(0x1000000000000000001, 73);
-
-  check(0xfffffffffffffffffffffffffffffffffffffe, 152);
-  check(0xffffffffffffffffffffffffffffffffffffff, 152);
-  check(0x100000000000000000000000000000000000000, 153);
-  check(0x100000000000000000000000000000000000001, 153);
-}
-
-testToUnsigned() {
-  checkU(src, width, expected) {
-    Expect.equals(expected, src.toUnsigned(width));
-  }
-
-  checkU(0x100000100000000000001, 2, 1);
-  checkU(0x100000200000000000001, 60, 0x200000000000001);
-  checkU(0x100000200000000000001, 59, 0x200000000000001);
-  checkU(0x100000200000000000001, 58, 0x200000000000001);
-  checkU(0x100000200000000000001, 57, 1);
-}
-
-testToSigned() {
-  checkS(src, width, expected) {
-    Expect.equals(
-        expected, src.toSigned(width), '$src.toSigned($width) == $expected');
-  }
-
-  checkS(0x100000100000000000001, 2, 1);
-  checkS(0x100000200000000000001, 60, 0x200000000000001);
-  checkS(0x100000200000000000001, 59, 0x200000000000001);
-  checkS(0x100000200000000000001, 58, -0x200000000000000 + 1);
-  checkS(0x100000200000000000001, 57, 1);
-}
-
-main() {
-  testBitLength();
-  testToUnsigned();
-  testToSigned();
-}