Apply DEFINE_NODE_TYPE_CASTS_WITH_FUNCTION to HTMLUnknownElement

Source/core/html/HTMLUnknownElement.h

Index: Source/core/html/HTMLUnknownElement.h
diff --git a/Source/core/html/HTMLUnknownElement.h b/Source/core/html/HTMLUnknownElement.h
index be493b1bf4e48fbe3e83c8305565e96733aeadb6..1c1794c0ed5496463c537abb7519e896815e8899 100644
--- a/Source/core/html/HTMLUnknownElement.h
+++ b/Source/core/html/HTMLUnknownElement.h
@@ -51,12 +51,13 @@ private:
     }
 };
 
-inline HTMLUnknownElement* toHTMLUnknownElement(HTMLElement* element)
+inline bool isHTMLUnknownElement(const Node& node)
 {
-    ASSERT_WITH_SECURITY_IMPLICATION(!element || element->isHTMLUnknownElement());
-    return static_cast<HTMLUnknownElement*>(element);
+    return node.isElementNode() && toHTMLElement(node).isHTMLUnknownElement();
 }
 
+DEFINE_NODE_TYPE_CASTS_WITH_FUNCTION(HTMLUnknownElement);
+
 } // namespace
 
 #endif