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

Source/core/dom/Position.h

Index: Source/core/dom/Position.h
diff --git a/Source/core/dom/Position.h b/Source/core/dom/Position.h
index 4189054d17e94e19de110fdd6fc2d37b23cbb3b8..1f4ed778723f574629de99ff3488b5911b449f8e 100644
--- a/Source/core/dom/Position.h
+++ b/Source/core/dom/Position.h
@@ -127,7 +127,7 @@ public:
     // will be treated as before ignoredNode (thus node() is really after the position, not containing it).
     Node* deprecatedNode() const { return m_anchorNode.get(); }
 
-    Document* document() const { return m_anchorNode ? m_anchorNode->document() : 0; }
+    Document* document() const { return m_anchorNode ? &m_anchorNode->document() : 0; }
     Element* rootEditableElement() const
     {
         Node* container = containerNode();