Add toHTMLDocument() convenience methods that take a reference

Source/core/html/HTMLObjectElement.cpp

Index: Source/core/html/HTMLObjectElement.cpp
diff --git a/Source/core/html/HTMLObjectElement.cpp b/Source/core/html/HTMLObjectElement.cpp
index 4731b19b182dfe0326467850776a554a9ba951b1..7b2278b1d66f004504d8b8b9b1cc676fdb883a07 100644
--- a/Source/core/html/HTMLObjectElement.cpp
+++ b/Source/core/html/HTMLObjectElement.cpp
@@ -438,13 +438,13 @@ void HTMLObjectElement::updateDocNamedItem()
         child = child->nextSibling();
     }
     if (isNamedItem != wasNamedItem && document().isHTMLDocument()) {
-        HTMLDocument* document = toHTMLDocument(&this->document());
+        HTMLDocument& document = toHTMLDocument(this->document());
         if (isNamedItem) {
-            document->addNamedItem(getNameAttribute());
-            document->addExtraNamedItem(getIdAttribute());
+            document.addNamedItem(getNameAttribute());
+            document.addExtraNamedItem(getIdAttribute());
         } else {
-            document->removeNamedItem(getNameAttribute());
-            document->removeExtraNamedItem(getIdAttribute());
+            document.removeNamedItem(getNameAttribute());
+            document.removeExtraNamedItem(getIdAttribute());
         }
     }
     m_docNamedItem = isNamedItem;