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

Source/core/rendering/svg/ReferenceFilterBuilder.cpp

 /*
  * Copyright (C) 2013 Adobe Systems Inc. All rights reserved.
  * Copyright (C) 2013 Google Inc.  All rights reserved.
  * Copyright (C) 2011 Apple 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
@@ skipping 71 matching lines @@
     }
 
     return true;
 }
 
 PassRefPtr<FilterEffect> ReferenceFilterBuilder::build(Filter* parentFilter, RenderObject* renderer, FilterEffect* previousEffect, const ReferenceFilterOperation* filterOperation)
 {
     if (!renderer)
         return 0;
 
-    Document* document = renderer->document();
-    ASSERT(document);
+    Document* document = &renderer->document();
 
     DocumentResourceReference* documentResourceReference = filterOperation->documentResourceReference();
     DocumentResource* cachedSVGDocument = documentResourceReference ? documentResourceReference->document() : 0;
 
     // If we have an SVG document, this is an external reference. Otherwise
     // we look up the referenced node in the current document.
     if (cachedSVGDocument)
         document = cachedSVGDocument->document();
 
     if (!document)
@@ skipping 41 matching lines @@
         effect->setEffectBoundaries(SVGLengthContext::resolveRectangle<SVGFilterPrimitiveStandardAttributes>(effectElement, filterElement->primitiveUnitsCurrentValue(), parentFilter->sourceImageRect()));
         ColorSpace colorSpace = filterColorSpace;
         if (useFilterColorSpace || getSVGElementColorSpace(effectElement, colorSpace))
             effect->setOperatingColorSpace(colorSpace);
         builder->add(effectElement->resultCurrentValue(), effect);
     }
     return builder->lastEffect();
 }
 
 } // namespace WebCore