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

Source/core/page/SpatialNavigation.h

Index: Source/core/page/SpatialNavigation.h
diff --git a/Source/core/page/SpatialNavigation.h b/Source/core/page/SpatialNavigation.h
index 77dd3b08e32dc726628c5d19ce8fb70b1945b5fd..e56c734ca560c3fb9588c1e1ef0c639db86780f5 100644
--- a/Source/core/page/SpatialNavigation.h
+++ b/Source/core/page/SpatialNavigation.h
@@ -116,7 +116,7 @@ struct FocusCandidate {
     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.