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

Source/core/html/parser/HTMLConstructionSite.h

 /*
  * Copyright (C) 2010 Google, Inc. All Rights Reserved.
  * Copyright (C) 2011 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 125 matching lines @@
     void generateImpliedEndTagsWithExclusion(const AtomicString& tagName);
 
     bool inQuirksMode();
 
     bool isEmpty() const { return !m_openElements.stackDepth(); }
     HTMLElementStack::ElementRecord* currentElementRecord() const { return m_openElements.topRecord(); }
     Element* currentElement() const { return m_openElements.top(); }
     ContainerNode* currentNode() const { return m_openElements.topNode(); }
     HTMLStackItem* currentStackItem() const { return m_openElements.topStackItem(); }
     HTMLStackItem* oneBelowTop() const { return m_openElements.oneBelowTop(); }
-    Document* ownerDocumentForCurrentNode();
+    Document& ownerDocumentForCurrentNode();
     HTMLElementStack* openElements() const { return &m_openElements; }
     HTMLFormattingElementList* activeFormattingElements() const { return &m_activeFormattingElements; }
     bool currentIsRootNode() { return m_openElements.topNode() == m_openElements.rootNode(); }
 
     Element* head() const { return m_head->element(); }
     HTMLStackItem* headStackItem() const { return m_head.get(); }
 
     void setForm(HTMLFormElement*);
     HTMLFormElement* form() const { return m_form.get(); }
     PassRefPtr<HTMLFormElement> takeForm();
@@ skipping 60 matching lines @@
     // "whenever a node would be inserted into the current node, it must instead
     // be foster parented."  This flag tracks whether we're in that state.
     bool m_redirectAttachToFosterParent;
 
     bool m_inQuirksMode;
 };
 
 } // namespace WebCore
 
 #endif