Implement HKDF for WebCrypto (blink-side)

Source/platform/exported/WebCryptoKeyAlgorithm.cpp

Index: Source/platform/exported/WebCryptoKeyAlgorithm.cpp
diff --git a/Source/platform/exported/WebCryptoKeyAlgorithm.cpp b/Source/platform/exported/WebCryptoKeyAlgorithm.cpp
index bef587d0d25dbd6e796cacba6688ed7e2bc256b6..f675939b84b0a5970acb52f8f125090d97fc1d25 100644
--- a/Source/platform/exported/WebCryptoKeyAlgorithm.cpp
+++ b/Source/platform/exported/WebCryptoKeyAlgorithm.cpp
@@ -93,6 +93,13 @@ WebCryptoKeyAlgorithm WebCryptoKeyAlgorithm::createEc(WebCryptoAlgorithmId id, W
     return WebCryptoKeyAlgorithm(id, adoptPtr(new WebCryptoEcKeyAlgorithmParams(namedCurve)));
 }
 
+WebCryptoKeyAlgorithm WebCryptoKeyAlgorithm::createKdf(WebCryptoAlgorithmId kdf)
+{
+    if (!WebCryptoAlgorithm::isKdf(kdf))
+        return WebCryptoKeyAlgorithm();
+    return WebCryptoKeyAlgorithm(kdf, adoptPtr(new WebCryptoKdfKeyAlgorithmParams()));
+}
+
 bool WebCryptoKeyAlgorithm::isNull() const
 {
     return m_private.isNull();
@@ -144,11 +151,20 @@ WebCryptoEcKeyAlgorithmParams* WebCryptoKeyAlgorithm::ecParams() const
     return 0;
 }
 
+WebCryptoKdfKeyAlgorithmParams* WebCryptoKeyAlgorithm::kdfParams() const
+{
+    ASSERT(!isNull());
+    if (paramsType() == WebCryptoKeyAlgorithmParamsTypeKdf)
+        return static_cast<WebCryptoKdfKeyAlgorithmParams*>(m_private->params.get());
+    return 0;
+}
+
 void WebCryptoKeyAlgorithm::writeToDictionary(WebCryptoKeyAlgorithmDictionary* dict) const
 {
     ASSERT(!isNull());
     dict->setString("name", WebCryptoAlgorithm::lookupAlgorithmInfo(id())->name);
-    m_private->params.get()->writeToDictionary(dict);
+    if (m_private->params.get())

[eroman, 2015/01/07 00:40:31]

This change seems like it is sufficient, rather than defining an HkdfKeyParams.
See later comments. (To be clear I am cool with this changed line, but not
convinced on the addition of the new KdfKeyParams).

[nharper, 2015/01/08 00:58:39]

The introduction of KdfKeyParams was to make something marginally easier in
ScriptValueSerializerForModules.cpp, but I agree that there's no need for
creating a new class that stores nothing in it.

+        m_private->params.get()->writeToDictionary(dict);
 }
 
 void WebCryptoKeyAlgorithm::assign(const WebCryptoKeyAlgorithm& other)