Revert "Switch libraries to using new tags."

sdk/lib/crypto/hmac.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.
 
-part of dart.crypto;
-
 class _HMAC implements HMAC {
   _HMAC(Hash this._hash, List<int> this._key) : _message = [];
 
   HMAC update(List<int> data) {
     _message.addAll(data);
     return this;
   }
 
   List<int> digest() {
     var blockSize = _hash.blockSize;
@@ skipping 46 matching lines @@
       result |= digest[i] ^ computedDigest[i];
     }
     return result == 0;
   }
 
   // HMAC internal state.
   Hash _hash;
   List<int> _key;
   List<int> _message;
 }