Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/events/MessageEvent.cpp

Index: Source/core/events/MessageEvent.cpp
diff --git a/Source/core/events/MessageEvent.cpp b/Source/core/events/MessageEvent.cpp
index 883b1f969e5703fabc77322637f12b4bdf6ad94e..52e609ccf0c813a21896bb30616c06d5a9a11249 100644
--- a/Source/core/events/MessageEvent.cpp
+++ b/Source/core/events/MessageEvent.cpp
@@ -54,7 +54,7 @@ MessageEvent::MessageEvent(const AtomicString& type, const MessageEventInit& ini
     , m_dataType(DataTypeScriptValue)
     , m_origin(initializer.origin)
     , m_lastEventId(initializer.lastEventId)
-    , m_source(isValidSource(initializer.source.get()) ? initializer.source : 0)
+    , m_source(isValidSource(initializer.source.get()) ? initializer.source : nullptr)
     , m_ports(adoptPtr(new MessagePortArray(initializer.ports)))
 {
     ScriptWrappable::init(this);
@@ -138,7 +138,7 @@ PassRefPtr<MessageEvent> MessageEvent::create(const AtomicString& type, const Me
 {
     if (initializer.source.get() && !isValidSource(initializer.source.get())) {
         exceptionState.throwTypeError("The optional 'source' property is neither a Window nor MessagePort.");
-        return 0;
+        return nullptr;
     }
     return adoptRef(new MessageEvent(type, initializer));
 }