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

Source/core/svg/SVGZoomAndPan.h

 /*
  * Copyright (C) 2004, 2005, 2008 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007 Rob Buis <buis@kde.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 41 matching lines @@
         return static_cast<SVGZoomAndPanType>(number);
     }
 
     static bool parseZoomAndPan(const LChar*& start, const LChar* end, SVGZoomAndPanType&);
     static bool parseZoomAndPan(const UChar*& start, const UChar* end, SVGZoomAndPanType&);
 
     template<class SVGElementTarget>
     static bool parseAttribute(SVGElementTarget* target, const QualifiedName& name, const AtomicString& value)
     {
         ASSERT(target);
-        ASSERT(target->document());
         if (name == SVGNames::zoomAndPanAttr) {
             SVGZoomAndPanType zoomAndPan = SVGZoomAndPanUnknown;
             if (!value.isEmpty()) {
                 if (value.is8Bit()) {
                     const LChar* start = value.characters8();
                     parseZoomAndPan(start, start + value.length(), zoomAndPan);
                 } else {
                     const UChar* start = value.characters16();
                     parseZoomAndPan(start, start + value.length(), zoomAndPan);
                 }
@@ skipping 10 matching lines @@
     // These methods only exist to allow us to compile V8/JSSVGZoomAndPan.*.
     // These are never called, and thus ASSERT_NOT_REACHED.
     void ref();
     void deref();
     void setZoomAndPan(unsigned short);
 };
 
 } // namespace WebCore
 
 #endif // SVGZoomAndPan_h