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

Source/core/accessibility/AccessibilityTable.cpp

 /*
  * Copyright (C) 2008 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
@@ skipping 313 matching lines @@
         return;
     }
 
     ASSERT(!m_haveChildren);
 
     m_haveChildren = true;
     if (!m_renderer || !m_renderer->isTable())
         return;
 
     RenderTable* table = toRenderTable(m_renderer);
-    AXObjectCache* axCache = m_renderer->document()->axObjectCache();
+    AXObjectCache* axCache = m_renderer->document().axObjectCache();
 
     // Go through all the available sections to pull out the rows and add them as children.
     table->recalcSectionsIfNeeded();
     RenderTableSection* tableSection = table->topSection();
     if (!tableSection)
         return;
 
     RenderTableSection* initialTableSection = tableSection;
     while (tableSection) {
 
@@ skipping 196 matching lines @@
     }
 
     // try the standard
     if (title.isEmpty())
         title = AccessibilityRenderObject::title();
 
     return title;
 }
 
 } // namespace WebCore