Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/modules/webmidi/NavigatorWebMIDI.cpp

 /*
  * Copyright (C) 2013 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 53 matching lines @@
 }
 
 PassRefPtrWillBeRawPtr<MIDIAccessPromise> NavigatorWebMIDI::requestMIDIAccess(Navigator& navigator, const Dictionary& options)
 {
     return NavigatorWebMIDI::from(navigator).requestMIDIAccess(options);
 }
 
 PassRefPtrWillBeRawPtr<MIDIAccessPromise> NavigatorWebMIDI::requestMIDIAccess(const Dictionary& options)
 {
     if (!frame())
-        return 0;
+        return nullptr;
 
     ExecutionContext* context = frame()->document();
     ASSERT(context);
 
     return MIDIAccessPromise::create(context, options);
 }
 
 } // namespace WebCore