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

Source/core/rendering/RenderVideo.cpp

 /*
  * Copyright (C) 2007, 2008, 2009, 2010 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 171 matching lines @@
     contentRect.moveBy(paintOffset);
     GraphicsContext* context = paintInfo.context;
     bool clip = !contentRect.contains(rect);
     if (clip) {
         context->save();
         context->clip(contentRect);
     }
 
     if (displayingPoster)
         paintIntoRect(context, rect);
-    else if (document()->view() && document()->view()->paintBehavior() & PaintBehaviorFlattenCompositingLayers)
+    else if (document().view() && document().view()->paintBehavior() & PaintBehaviorFlattenCompositingLayers)
         mediaPlayer->paintCurrentFrameInContext(context, pixelSnappedIntRect(rect));
     else
         mediaPlayer->paint(context, pixelSnappedIntRect(rect));
 
     if (clip)
         context->restore();
 }
 
 void RenderVideo::layout()
 {
@@ skipping 86 matching lines @@
 }
 
 LayoutUnit RenderVideo::offsetHeight() const
 {
     if (const RenderBlock* block = rendererPlaceholder(this))
         return block->offsetHeight();
     return RenderMedia::offsetHeight();
 }
 
 } // namespace WebCore