Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/xml/XMLHttpRequestProgressEventThrottle.cpp

Index: Source/core/xml/XMLHttpRequestProgressEventThrottle.cpp
diff --git a/Source/core/xml/XMLHttpRequestProgressEventThrottle.cpp b/Source/core/xml/XMLHttpRequestProgressEventThrottle.cpp
index 9a3c16c074494eac5b80e006e63d075eb1c0af61..73b01f1e1d6d1f928b6da3801add5e3c782719de 100644
--- a/Source/core/xml/XMLHttpRequestProgressEventThrottle.cpp
+++ b/Source/core/xml/XMLHttpRequestProgressEventThrottle.cpp
@@ -111,7 +111,7 @@ bool XMLHttpRequestProgressEventThrottle::flushDeferredProgressEvent()
     if (m_deferEvents && m_deferredProgressEvent) {
         // Move the progress event to the queue, to get it in the right order on resume.
         m_deferredEvents.append(m_deferredProgressEvent);
-        m_deferredProgressEvent = 0;
+        m_deferredProgressEvent = nullptr;
         return true;
     }
     return false;
@@ -143,7 +143,7 @@ void XMLHttpRequestProgressEventThrottle::dispatchDeferredEvents(Timer<XMLHttpRe
     m_deferredEvents.swap(deferredEvents);
 
     RefPtr<Event> deferredProgressEvent = m_deferredProgressEvent;
-    m_deferredProgressEvent = 0;
+    m_deferredProgressEvent = nullptr;
 
     Vector<RefPtr<Event> >::const_iterator it = deferredEvents.begin();
     const Vector<RefPtr<Event> >::const_iterator end = deferredEvents.end();