Refactor how "length" parameter is obtained for HmacKeyParams.

Source/modules/crypto/HmacKeyParams.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 26 matching lines @@
 
 Algorithm* HmacKeyParams::hash()
 {
     if (!m_hash)
         m_hash = Algorithm::create(m_algorithm.hmacKeyParams()->hash());
     return m_hash.get();
 }
 
 unsigned HmacKeyParams::length(bool& isNull)
 {
-    isNull = !m_algorithm.hmacKeyParams()->hasLength();
-    return isNull ? 0 : m_algorithm.hmacKeyParams()->length();
+    unsigned length;
+    isNull = !m_algorithm.hmacKeyParams()->getLength(length);
+    return length;
 }
 
 HmacKeyParams::HmacKeyParams(const WebKit::WebCryptoAlgorithm& algorithm)
     : Algorithm(algorithm)
 {
     ASSERT(algorithm.hmacKeyParams());
     ScriptWrappable::init(this);
 }
 
 } // namespace WebCore