Have Node::document() return a reference instead of a pointer

Source/core/html/FormAssociatedElement.cpp

Index: Source/core/html/FormAssociatedElement.cpp
diff --git a/Source/core/html/FormAssociatedElement.cpp b/Source/core/html/FormAssociatedElement.cpp
index 58f6654ae4c23ac31828a3864cf80c145e95f9f6..25ab4a5405a433c2c9c2bcc63ec8b4153a84ef09 100644
--- a/Source/core/html/FormAssociatedElement.cpp
+++ b/Source/core/html/FormAssociatedElement.cpp
@@ -163,7 +163,7 @@ void FormAssociatedElement::resetFormOwner()
     setForm(findAssociatedForm(toHTMLElement(this), m_form));
     HTMLElement* element = toHTMLElement(this);
     if (m_form && m_form != originalForm && m_form->inDocument())
-        element->document()->didAssociateFormControl(element);
+        element->document().didAssociateFormControl(element);
 }
 
 void FormAssociatedElement::formAttributeChanged()
@@ -175,7 +175,7 @@ void FormAssociatedElement::formAttributeChanged()
         setForm(element->findFormAncestor());
         HTMLElement* element = toHTMLElement(this);
         if (m_form && m_form != originalForm && m_form->inDocument())
-            element->document()->didAssociateFormControl(element);
+            element->document().didAssociateFormControl(element);
         m_formAttributeTargetObserver = nullptr;
     } else {
         resetFormOwner();