@Override
  public KeyData newKeyData(ByteString serializedKeyFormat) throws GeneralSecurityException {
    HmacKey key = (HmacKey) newKey(serializedKeyFormat);
    return KeyData.newBuilder()
        .setTypeUrl(TYPE_URL)
        .setValue(key.toByteString())
        .setKeyMaterialType(KeyData.KeyMaterialType.SYMMETRIC)
        .build();
  }
@param serializedKeyFormat serialized {@code HmacKeyFormat} proto
@return {@code KeyData} with a new {@code HmacKey} proto
java_src/src/main/java/com/google/crypto/tink/mac/internal/LegacyHmacTestKeyManager.java