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

Source/core/editing/InsertListCommand.cpp

 /*
  * Copyright (C) 2006, 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 360 matching lines @@
         if (listChild && listChild->hasTagName(liTag))
             insertionPos = positionInParentBeforeNode(listChild);
 
         insertNodeAt(listElement, insertionPos);
 
         // We inserted the list at the start of the content we're about to move
         // Update the start of content, so we don't try to move the list into itself.  bug 19066
         // Layout is necessary since start's node's inline renderers may have been destroyed by the insertion
         // The end of the content may have changed after the insertion and layout so update it as well.
         if (insertionPos == start.deepEquivalent()) {
-            listElement->document()->updateLayoutIgnorePendingStylesheets();
+            listElement->document().updateLayoutIgnorePendingStylesheets();
             start = startOfParagraph(originalStart, CanSkipOverEditingBoundary);
             end = endOfParagraph(start, CanSkipOverEditingBoundary);
         }
     }
 
     moveParagraph(start, end, positionBeforeNode(placeholder.get()), true);
 
     if (listElement)
         return mergeWithNeighboringLists(listElement);
 
     if (canMergeLists(previousList, nextList))
         mergeIdenticalElements(previousList, nextList);
 
     return listElement;
 }
 
 }