Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/web/WebIDBKeyRange.cpp

 /*
  * Copyright (C) 2011 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 23 matching lines @@
 
 namespace blink {
 
 void WebIDBKeyRange::assign(const WebIDBKeyRange& other)
 {
     m_private = other.m_private;
 }
 
 void WebIDBKeyRange::assign(const WebIDBKey& lower, const WebIDBKey& upper, bool lowerOpen, bool upperOpen)
 {
-    // FIXME: replace reset() with nullptr assignment (cf. https://codereview.chromium.org/170603003/ )
     if (!lower.isValid() && !upper.isValid())
         m_private.reset();
     else
         m_private = IDBKeyRange::create(lower, upper, lowerOpen ? IDBKeyRange::LowerBoundOpen : IDBKeyRange::LowerBoundClosed, upperOpen ? IDBKeyRange::UpperBoundOpen : IDBKeyRange::UpperBoundClosed);
 }
 
 void WebIDBKeyRange::reset()
 {
     m_private.reset();
 }
@@ skipping 32 matching lines @@
     m_private = value;
     return *this;
 }
 
 WebIDBKeyRange::operator PassRefPtr<IDBKeyRange>() const
 {
     return m_private.get();
 }
 
 } // namespace blink