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

Source/core/html/HTMLTitleElement.cpp

Index: Source/core/html/HTMLTitleElement.cpp
diff --git a/Source/core/html/HTMLTitleElement.cpp b/Source/core/html/HTMLTitleElement.cpp
index 7b142611e7744458b266bc86c2e4f20895701c68..caf8783826aeca23fc16db4e47048abdff91a0a4 100644
--- a/Source/core/html/HTMLTitleElement.cpp
+++ b/Source/core/html/HTMLTitleElement.cpp
@@ -52,7 +52,7 @@ Node::InsertionNotificationRequest HTMLTitleElement::insertedInto(ContainerNode*
 {
     HTMLElement::insertedInto(insertionPoint);
     if (inDocument() && !isInShadowTree())
-        document()->setTitleElement(text(), this);
+        document().setTitleElement(text(), this);
     return InsertionDone;
 }
 
@@ -60,14 +60,14 @@ void HTMLTitleElement::removedFrom(ContainerNode* insertionPoint)
 {
     HTMLElement::removedFrom(insertionPoint);
     if (insertionPoint->inDocument() && !insertionPoint->isInShadowTree())
-        document()->removeTitle(this);
+        document().removeTitle(this);
 }
 
 void HTMLTitleElement::childrenChanged(bool changedByParser, Node* beforeChange, Node* afterChange, int childCountDelta)
 {
     HTMLElement::childrenChanged(changedByParser, beforeChange, afterChange, childCountDelta);
     if (inDocument() && !isInShadowTree())
-        document()->setTitleElement(text(), this);
+        document().setTitleElement(text(), this);
 }
 
 String HTMLTitleElement::text() const
@@ -99,7 +99,7 @@ void HTMLTitleElement::setText(const String &value)
         if (numChildren > 0)
             removeChildren();
 
-        appendChild(document()->createTextNode(valueCopy.impl()), IGNORE_EXCEPTION);
+        appendChild(document().createTextNode(valueCopy.impl()), IGNORE_EXCEPTION);
     }
 }