Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/html/HTMLDialogElement.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 56 matching lines @@
     if (focusableDescendant) {
         focusableDescendant->focus();
         return;
     }
 
     if (dialog->isFocusable()) {
         dialog->focus();
         return;
     }
 
-    dialog->document().setFocusedElement(0);
+    dialog->document().setFocusedElement(nullptr);
 }
 
 static void inertSubtreesChanged(Document& document)
 {
     // When a modal dialog opens or closes, nodes all over the accessibility
     // tree can change inertness which means they must be added or removed from
     // the tree. The most foolproof way is to clear the entire tree and rebuild
     // it, though a more clever way is probably possible.
     Document* topDocument = document.topDocument();
     topDocument->clearAXObjectCache();
@@ skipping 111 matching lines @@
 {
     if (event->type() == EventTypeNames::cancel) {
         closeDialog();
         event->setDefaultHandled();
         return;
     }
     HTMLElement::defaultEventHandler(event);
 }
 
 } // namespace WebCore