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

Source/core/accessibility/AccessibilityARIAGrid.cpp

 /*
  * Copyright (C) 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
@@ skipping 75 matching lines @@
 
     if (!isAccessibilityTable()) {
         AccessibilityRenderObject::addChildren();
         return;
     }
 
     m_haveChildren = true;
     if (!m_renderer)
         return;
 
-    AXObjectCache* axCache = m_renderer->document()->axObjectCache();
+    AXObjectCache* axCache = m_renderer->document().axObjectCache();
 
     // add only rows that are labeled as aria rows
     HashSet<AccessibilityObject*> appendedRows;
     unsigned columnCount = 0;
     for (RefPtr<AccessibilityObject> child = firstChild(); child; child = child->nextSibling()) {
 
         if (!addTableCellChild(child.get(), appendedRows, columnCount)) {
 
             // in case the render tree doesn't match the expected ARIA hierarchy, look at the children
             if (!child->hasChildren())
@@ skipping 17 matching lines @@
         if (!column->accessibilityIsIgnored())
             m_children.append(column);
     }
 
     AccessibilityObject* headerContainerObject = headerContainer();
     if (headerContainerObject && !headerContainerObject->accessibilityIsIgnored())
         m_children.append(headerContainerObject);
 }
 
 } // namespace WebCore