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

Source/core/page/SpatialNavigation.h

 /*
  * Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2009 Antonio Gomes <tonikitoo@webkit.org>
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 98 matching lines @@
         , isOffscreen(true)
         , isOffscreenAfterScrolling(true)
     {
     }
 
     FocusCandidate(Node* n, FocusDirection);
     explicit FocusCandidate(HTMLAreaElement* area, FocusDirection);
     bool isNull() const { return !visibleNode; }
     bool inScrollableContainer() const { return visibleNode && enclosingScrollableBox; }
     bool isFrameOwnerElement() const { return visibleNode && visibleNode->isFrameOwnerElement(); }
-    Document* document() const { return visibleNode ? visibleNode->document() : 0; }
+    Document* document() const { return visibleNode ? &visibleNode->document() : 0; }
 
     // We handle differently visibleNode and FocusableNode to properly handle the areas of imagemaps,
     // where visibleNode would represent the image element and focusableNode would represent the area element.
     // In all other cases, visibleNode and focusableNode are one and the same.
     Node* visibleNode;
     Node* focusableNode;
     Node* enclosingScrollableBox;
     long long distance;
     long long parentDistance;
     RectsAlignment alignment;
@@ skipping 14 matching lines @@
 Node* scrollableEnclosingBoxOrParentFrameForNodeInDirection(FocusDirection, Node*);
 LayoutRect nodeRectInAbsoluteCoordinates(Node*, bool ignoreBorder = false);
 LayoutRect frameRectInAbsoluteCoordinates(Frame*);
 LayoutRect virtualRectForDirection(FocusDirection, const LayoutRect& startingRect, LayoutUnit width = 0);
 LayoutRect virtualRectForAreaElementAndDirection(HTMLAreaElement*, FocusDirection);
 HTMLFrameOwnerElement* frameOwnerElement(FocusCandidate&);
 
 } // namspace WebCore
 
 #endif // SpatialNavigation_h