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

Source/core/html/HTMLLinkElement.h

Index: Source/core/html/HTMLLinkElement.h
diff --git a/Source/core/html/HTMLLinkElement.h b/Source/core/html/HTMLLinkElement.h
index 213a40d8c63167117bee613d49264f4a16102e7c..46fb948ba2c720bf9ba87fb0c51879ccb27ad5e3 100644
--- a/Source/core/html/HTMLLinkElement.h
+++ b/Source/core/html/HTMLLinkElement.h
@@ -106,7 +106,7 @@ private:
     void clearSheet();
     void addPendingSheet(PendingSheetType);
     void removePendingSheet(RemovePendingSheetNotificationType = RemovePendingSheetNotifyImmediately);
-    Document* document();
+    Document& document();
 
     ResourcePtr<CSSStyleSheetResource> m_resource;
     RefPtr<CSSStyleSheet> m_sheet;
@@ -156,7 +156,7 @@ public:
     virtual bool shouldLoadLink() OVERRIDE;
 
     // For LinkStyle
-    bool loadLink(const String& type, const KURL& url) { return m_linkLoader.loadLink(m_relAttribute, type, url, document()); }
+    bool loadLink(const String& type, const KURL& url) { return m_linkLoader.loadLink(m_relAttribute, type, url, &document()); }
     bool isAlternate() const { return linkStyle()->isUnset() && m_relAttribute.isAlternate(); }
     bool shouldProcessStyle() { return linkResourceToProcess() && linkStyle(); }