Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/modules/webdatabase/DatabaseBackend.cpp

 /*
  * Copyright (C) 2013 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
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 86 matching lines @@
 
     closeDatabase();
     databaseContext()->databaseThread()->recordDatabaseClosed(this);
 }
 
 PassRefPtr<SQLTransactionBackend> DatabaseBackend::runTransaction(PassRefPtr<SQLTransaction> transaction,
     bool readOnly, const ChangeVersionData* data)
 {
     MutexLocker locker(m_transactionInProgressMutex);
     if (!m_isTransactionQueueEnabled)
-        return 0;
+        return nullptr;
 
     RefPtr<SQLTransactionWrapper> wrapper;
     if (data)
         wrapper = ChangeVersionWrapper::create(data->oldVersion(), data->newVersion());
 
     RefPtr<SQLTransactionBackend> transactionBackend = SQLTransactionBackend::create(this, transaction, wrapper, readOnly);
     m_transactionQueue.append(transactionBackend);
     if (!m_transactionInProgress)
         scheduleTransaction();
 
@@ skipping 38 matching lines @@
 {
     return databaseContext()->databaseThread()->transactionClient();
 }
 
 SQLTransactionCoordinator* DatabaseBackend::transactionCoordinator() const
 {
     return databaseContext()->databaseThread()->transactionCoordinator();
 }
 
 } // namespace WebCore