Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/accessibility/AXNodeObject.cpp

 /*
 * Copyright (C) 2012, Google 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 1491 matching lines @@
     return 0;
 }
 
 void AXNodeObject::setFocused(bool on)
 {
     if (!canSetFocusAttribute())
         return;
 
     Document* document = this->document();
     if (!on) {
-        document->setFocusedElement(0);
+        document->setFocusedElement(nullptr);
     } else {
         Node* node = this->node();
         if (node && node->isElementNode()) {
             // If this node is already the currently focused node, then calling focus() won't do anything.
             // That is a problem when focus is removed from the webpage to chrome, and then returns.
             // In these cases, we need to do what keyboard and mouse focus do, which is reset focus first.
             if (document->focusedElement() == node)
-                document->setFocusedElement(0);
+                document->setFocusedElement(nullptr);
 
             toElement(node)->focus();
         } else {
-            document->setFocusedElement(0);
+            document->setFocusedElement(nullptr);
         }
     }
 }
 
 void AXNodeObject::increment()
 {
     UserGestureIndicator gestureIndicator(DefinitelyProcessingNewUserGesture);
     alterSliderValue(true);
 }
 
@@ skipping 269 matching lines @@
         useTextUnderElement = true;
 
     if (useTextUnderElement) {
         String text = textUnderElement();
         if (!text.isEmpty())
             textOrder.append(AccessibilityText(text, ChildrenText));
     }
 }
 
 } // namespace WebCore