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

Source/core/html/shadow/SliderThumbElement.h

 /*
  * Copyright (C) 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2010 Google 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
@@ skipping 57 matching lines @@
     virtual bool matchesReadWritePseudoClass() const OVERRIDE;
     virtual Node* focusDelegate();
     void startDragging();
     void stopDragging();
 
     bool m_inDragMode;
 };
 
 inline PassRefPtr<Element> SliderThumbElement::cloneElementWithoutAttributesAndChildren()
 {
-    return create(document());
+    return create(&document());
 }
 
 inline SliderThumbElement* toSliderThumbElement(Node* node)
 {
     ASSERT_WITH_SECURITY_IMPLICATION(!node || node->isHTMLElement());
     return static_cast<SliderThumbElement*>(node);
 }
 
 // --------------------------------
 
@@ skipping 14 matching lines @@
 
 private:
     SliderContainerElement(Document*);
     virtual RenderObject* createRenderer(RenderStyle*);
     virtual const AtomicString& part() const;
 };
 
 }
 
 #endif