Add toHTMLDocument() convenience methods that take a reference

Source/core/dom/Element.cpp

Index: Source/core/dom/Element.cpp
diff --git a/Source/core/dom/Element.cpp b/Source/core/dom/Element.cpp
index 416514120852be1468dafee7f501ea2cd9b4a870..5f7f5f287246394e7d84cb69ed2b5ff25f9c7e96 100644
--- a/Source/core/dom/Element.cpp
+++ b/Source/core/dom/Element.cpp
@@ -2878,10 +2878,10 @@ void Element::updateNamedItemRegistration(const AtomicString& oldName, const Ato
         return;
 
     if (!oldName.isEmpty())
-        toHTMLDocument(&document())->removeNamedItem(oldName);
+        toHTMLDocument(document()).removeNamedItem(oldName);
 
     if (!newName.isEmpty())
-        toHTMLDocument(&document())->addNamedItem(newName);
+        toHTMLDocument(document()).addNamedItem(newName);
 }
 
 void Element::updateExtraNamedItemRegistration(const AtomicString& oldId, const AtomicString& newId)
@@ -2890,10 +2890,10 @@ void Element::updateExtraNamedItemRegistration(const AtomicString& oldId, const
         return;
 
     if (!oldId.isEmpty())
-        toHTMLDocument(&document())->removeExtraNamedItem(oldId);
+        toHTMLDocument(document()).removeExtraNamedItem(oldId);
 
     if (!newId.isEmpty())
-        toHTMLDocument(&document())->addExtraNamedItem(newId);
+        toHTMLDocument(document()).addExtraNamedItem(newId);
 }
 
 PassRefPtr<HTMLCollection> Element::ensureCachedHTMLCollection(CollectionType type)