Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/events/PopStateEvent.cpp

Index: Source/core/events/PopStateEvent.cpp
diff --git a/Source/core/events/PopStateEvent.cpp b/Source/core/events/PopStateEvent.cpp
index 2ab213a18f2d64fbd07d015ac88ade5fc75d21d8..63b50cf6d08a37d411cc7d9c62d4e00bf8616b86 100644
--- a/Source/core/events/PopStateEvent.cpp
+++ b/Source/core/events/PopStateEvent.cpp
@@ -35,15 +35,15 @@ namespace WebCore {
 
 PopStateEvent::PopStateEvent()
     : Event(EventTypeNames::popstate, false, true)
-    , m_serializedState(0)
-    , m_history(0)
+    , m_serializedState(nullptr)
+    , m_history(nullptr)
 {
     ScriptWrappable::init(this);
 }
 
 PopStateEvent::PopStateEvent(const AtomicString& type, const PopStateEventInit& initializer)
     : Event(type, initializer)
-    , m_history(0)
+    , m_history(nullptr)
 {
     ScriptWrappable::init(this);
 }