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

Source/core/rendering/RenderScrollbar.cpp

 /*
  * Copyright (C) 2008, 2009 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.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 234 matching lines @@
                 needRenderer = (buttonsPlacement == ScrollbarButtonsSingle || buttonsPlacement == ScrollbarButtonsDoubleEnd ||
                                 buttonsPlacement == ScrollbarButtonsDoubleBoth);
                 break;
             default:
                 break;
         }
     }
 
     RenderScrollbarPart* partRenderer = m_parts.get(partType);
     if (!partRenderer && needRenderer) {
-        partRenderer = RenderScrollbarPart::createAnonymous(owningRenderer()->document(), this, partType);
+        partRenderer = RenderScrollbarPart::createAnonymous(&owningRenderer()->document(), this, partType);
         m_parts.set(partType, partRenderer);
     } else if (partRenderer && !needRenderer) {
         m_parts.remove(partType);
         partRenderer->destroy();
         partRenderer = 0;
     }
 
     if (partRenderer)
         partRenderer->setStyle(partStyle.release());
 }
@@ skipping 84 matching lines @@
 int RenderScrollbar::minimumThumbLength()
 {
     RenderScrollbarPart* partRenderer = m_parts.get(ThumbPart);
     if (!partRenderer)
         return 0;
     partRenderer->layout();
     return orientation() == HorizontalScrollbar ? partRenderer->width() : partRenderer->height();
 }
 
 }