Implement HMAC support in lib/crypto.

tests/lib/test_config.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.
 
 #library("lib_test_config");
 
 #import("../../tools/testing/dart/test_suite.dart");
 
 class LibTestSuite extends StandardTestSuite {
   LibTestSuite(Map configuration)
       : super(configuration,
               "lib",
               "tests/lib/src",
-              ["tests/lib/lib.status"]);
+              ["tests/lib/lib.status"],
+              (s) => s.endsWith('_test.dart'));
 
   bool listRecursively() => true;
 }