Refactor how "length" parameter is obtained for HmacKeyParams.

public/platform/WebCryptoAlgorithmParams.h

 /*
  * 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 97 matching lines @@
         , m_hash(hash)
         , m_hasLength(hasLength)
         , m_length(length)
     {
     }
 
     const WebCryptoAlgorithm& hash() const { return m_hash; }
 
     bool hasLength() const { return m_hasLength; }
 
-    unsigned length() const
+    bool getLength(unsigned& length) const
     {
-        WEBKIT_ASSERT(m_length);
-        return m_length;
+        if (!m_hasLength)
+            return false;
+        length = m_length;
+        return true;
     }
 
 private:
     WebCryptoAlgorithm m_hash;
     bool m_hasLength;
-    int m_length;
+    unsigned m_length;
 };
 
 class WebCryptoRsaSsaParams : public WebCryptoAlgorithmParams {
 public:
     explicit WebCryptoRsaSsaParams(const WebCryptoAlgorithm& hash)
         : WebCryptoAlgorithmParams(WebCryptoAlgorithmParamsTypeRsaSsaParams)
         , m_hash(hash)
     {
     }
 
@@ skipping 16 matching lines @@
     const WebVector<unsigned char>& publicExponent() const { return m_publicExponent; }
 
 private:
     const unsigned m_modulusLength;
     const WebVector<unsigned char> m_publicExponent;
 };
 
 } // namespace WebKit
 
 #endif