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

Source/core/rendering/RenderBR.cpp

 /**
  * Copyright (C) 2000 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2006 Apple Computer, Inc.
  *
  * 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 26 matching lines @@
     , m_lineHeight(-1)
 {
 }
 
 RenderBR::~RenderBR()
 {
 }
 
 int RenderBR::lineHeight(bool firstLine) const
 {
-    if (firstLine && document()->styleSheetCollections()->usesFirstLineRules()) {
+    if (firstLine && document().styleSheetCollections()->usesFirstLineRules()) {
         RenderStyle* s = style(firstLine);
         if (s != style())
             return s->computedLineHeight(view());
     }
 
     if (m_lineHeight == -1)
         m_lineHeight = style()->computedLineHeight(view());
 
     return m_lineHeight;
 }
@@ skipping 13 matching lines @@
 {
     return 1;
 }
 
 PositionWithAffinity RenderBR::positionForPoint(const LayoutPoint&)
 {
     return createPositionWithAffinity(0, DOWNSTREAM);
 }
 
 } // namespace WebCore