WebCrypto: Add parsing for the algorithm parameter AesDerivedKey.

Source/platform/exported/WebCryptoAlgorithm.cpp

Index: Source/platform/exported/WebCryptoAlgorithm.cpp
diff --git a/Source/platform/exported/WebCryptoAlgorithm.cpp b/Source/platform/exported/WebCryptoAlgorithm.cpp
index f999795fd094ac23b8f6736d478be22017befc64..a615101a550f0fd9c5737257be0aec887a6384a4 100644
--- a/Source/platform/exported/WebCryptoAlgorithm.cpp
+++ b/Source/platform/exported/WebCryptoAlgorithm.cpp
@@ -429,6 +429,14 @@ const WebCryptoEcdhKeyDeriveParams* WebCryptoAlgorithm::ecdhKeyDeriveParams() co
     return 0;
 }
 
+const WebCryptoAesDerivedKeyParams* WebCryptoAlgorithm::aesDerivedKeyParams() const
+{
+    ASSERT(!isNull());
+    if (paramsType() == WebCryptoAlgorithmParamsTypeAesDerivedKeyParams)
+        return static_cast<WebCryptoAesDerivedKeyParams*>(m_private->params.get());
+    return 0;
+}
+
 bool WebCryptoAlgorithm::isHash(WebCryptoAlgorithmId id)
 {
     switch (id) {