Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/dom/FullscreenElementStack.cpp

Index: Source/core/dom/FullscreenElementStack.cpp
diff --git a/Source/core/dom/FullscreenElementStack.cpp b/Source/core/dom/FullscreenElementStack.cpp
index 4868011a43ed6e851d5736782a4ad9b7cc9b24b8..1d2fc3202db56424c19779ee6b7cf42e5c61b9ff 100644
--- a/Source/core/dom/FullscreenElementStack.cpp
+++ b/Source/core/dom/FullscreenElementStack.cpp
@@ -126,7 +126,7 @@ void FullscreenElementStack::documentWasDetached()
 
 void FullscreenElementStack::documentWasDisposed()
 {
-    m_fullScreenElement = 0;
+    m_fullScreenElement = nullptr;
     m_fullScreenElementStack.clear();
 }
 
@@ -433,7 +433,7 @@ void FullscreenElementStack::webkitDidExitFullScreenForElement(Element*)
     if (m_fullScreenRenderer)
         m_fullScreenRenderer->unwrapRenderer();
 
-    m_fullScreenElement = 0;
+    m_fullScreenElement = nullptr;
     document()->setNeedsStyleRecalc(SubtreeStyleChange);
 
     // When webkitCancelFullScreen is called, we call webkitExitFullScreen on the topDocument(). That