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

Source/core/accessibility/AccessibilityObject.cpp

 /*
  * Copyright (C) 2008, 2009, 2011 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 487 matching lines @@
     }
 
     return parent;
 }
 
 AccessibilityObject* AccessibilityObject::firstAccessibleObjectFromNode(const Node* node)
 {
     if (!node)
         return 0;
 
-    AXObjectCache* cache = node->document()->axObjectCache();
+    AXObjectCache* cache = node->document().axObjectCache();
     AccessibilityObject* accessibleObject = cache->getOrCreate(node->renderer());
     while (accessibleObject && accessibleObject->accessibilityIsIgnored()) {
         node = NodeTraversal::next(node);
 
         while (node && !node->renderer())
             node = NodeTraversal::nextSkippingChildren(node);
 
         if (!node)
             return 0;
 
@@ skipping 357 matching lines @@
 }
 
 static bool replacedNodeNeedsCharacter(Node* replacedNode)
 {
     // we should always be given a rendered node and a replaced node, but be safe
     // replaced nodes are either attachments (widgets) or images
     if (!replacedNode || !replacedNode->renderer() || !replacedNode->renderer()->isReplaced() || replacedNode->isTextNode())
         return false;
 
     // create an AX object, but skip it if it is not supposed to be seen
-    AccessibilityObject* object = replacedNode->renderer()->document()->axObjectCache()->getOrCreate(replacedNode);
+    AccessibilityObject* object = replacedNode->renderer()->document().axObjectCache()->getOrCreate(replacedNode);
     if (object->accessibilityIsIgnored())
         return false;
 
     return true;
 }
 
 #if HAVE(ACCESSIBILITY)
 int AccessibilityObject::lineForPosition(const VisiblePosition& visiblePos) const
 {
     if (visiblePos.isNull() || !node())
@@ skipping 85 matching lines @@
 
     for (AccessibilityObject* object = parentObject(); object; object = object->parentObject()) {
         if (equalIgnoringCase(object->getAttribute(aria_hiddenAttr), "true"))
             return true;
     }
 
     return false;
 }
 
 } // namespace WebCore