Migrate test block 10 to Dart 2.0.

tests/corelib_2/integer_to_radix_string_test.dart

 // Copyright (c) 2012, 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";
 
 main() {
   // Test that we accept radix 2 to 36 and that we use lower-case
   // letters.
   var expected = [
@@ skipping 75 matching lines @@
   ];
   for (var bignum in bignums) {
     for (int radix = 2; radix <= 36; radix++) {
       String digits = bignum.toRadixString(radix);
       int result = int.parse(digits, radix: radix);
       Expect.equals(
           bignum, result, "${bignum.toRadixString(16)} -> $digits/$radix");
     }
   }
 }