Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/loader/NavigationAction.h

Index: Source/core/loader/NavigationAction.h
diff --git a/Source/core/loader/NavigationAction.h b/Source/core/loader/NavigationAction.h
index e50716bfe9c14c1141ea4a93bb1bbe9c2ae1e2ba..966aa7b1c522dc15a1d8ed2c1452897aa0ff3bee 100644
--- a/Source/core/loader/NavigationAction.h
+++ b/Source/core/loader/NavigationAction.h
@@ -41,7 +41,7 @@ namespace WebCore {
     class NavigationAction {
     public:
         NavigationAction();
-        NavigationAction(const ResourceRequest&, FrameLoadType = FrameLoadTypeStandard, bool isFormSubmission = false, PassRefPtr<Event> = 0);
+        NavigationAction(const ResourceRequest&, FrameLoadType = FrameLoadTypeStandard, bool isFormSubmission = false, PassRefPtr<Event> = nullptr);
 
         const ResourceRequest& resourceRequest() const { return m_resourceRequest; }
         NavigationType type() const { return m_type; }