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

Source/core/css/SVGCSSComputedStyleDeclaration.cpp

 /*
     Copyright (C) 2007 Eric Seidel <eric@webkit.org>
     Copyright (C) 2007 Alexey Proskuryakov <ap@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 81 matching lines @@
 }
 
 PassRefPtr<CSSValue> CSSComputedStyleDeclaration::getSVGPropertyCSSValue(CSSPropertyID propertyID, EUpdateLayout updateLayout) const
 {
     Node* node = m_node.get();
     if (!node)
         return 0;
 
     // Make sure our layout is up to date before we allow a query on these attributes.
     if (updateLayout)
-        node->document()->updateLayout();
+        node->document().updateLayout();
 
     RenderStyle* style = node->computedStyle();
     if (!style)
         return 0;
 
     const SVGRenderStyle* svgStyle = style->svgStyle();
     if (!svgStyle)
         return 0;
 
     switch (propertyID) {
@@ skipping 114 matching lines @@
     default:
         // If you crash here, it's because you added a css property and are not handling it
         // in either this switch statement or the one in CSSComputedStyleDelcaration::getPropertyCSSValue
         ASSERT_WITH_MESSAGE(0, "unimplemented propertyID: %d", propertyID);
     }
     LOG_ERROR("unimplemented propertyID: %d", propertyID);
     return 0;
 }
 
 }