Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/page/PointerLockController.cpp

Index: Source/core/page/PointerLockController.cpp
diff --git a/Source/core/page/PointerLockController.cpp b/Source/core/page/PointerLockController.cpp
index 9866aa89dd23c7918b37e45b2c16707d90655c02..ab377a3fa5e96367817a9c903a82dc660922ea24 100644
--- a/Source/core/page/PointerLockController.cpp
+++ b/Source/core/page/PointerLockController.cpp
@@ -125,7 +125,7 @@ void PointerLockController::didLosePointerLock()
 {
     enqueueEvent(EventTypeNames::webkitpointerlockchange, m_element ? &m_element->document() : m_documentOfRemovedElementWhileWaitingForUnlock.get());
     clearElement();
-    m_documentOfRemovedElementWhileWaitingForUnlock = 0;
+    m_documentOfRemovedElementWhileWaitingForUnlock = nullptr;
 }
 
 void PointerLockController::dispatchLockedMouseEvent(const PlatformMouseEvent& event, const AtomicString& eventType)
@@ -143,7 +143,7 @@ void PointerLockController::dispatchLockedMouseEvent(const PlatformMouseEvent& e
 void PointerLockController::clearElement()
 {
     m_lockPending = false;
-    m_element = 0;
+    m_element = nullptr;
 }
 
 void PointerLockController::enqueueEvent(const AtomicString& type, Element* element)