Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/css/Counter.h

Index: Source/core/css/Counter.h
diff --git a/Source/core/css/Counter.h b/Source/core/css/Counter.h
index d27ff184e788ef5b9b324dfa87357291bca48ade..a6d5bc4ad20af8ed55d24173e4c46f225da773c0 100644
--- a/Source/core/css/Counter.h
+++ b/Source/core/css/Counter.h
@@ -53,9 +53,9 @@ public:
 
     PassRefPtrWillBeRawPtr<Counter> cloneForCSSOM() const
     {
-        return create(m_identifier ? m_identifier->cloneForCSSOM() : 0
-            , m_listStyle ? m_listStyle->cloneForCSSOM() : 0
-            , m_separator ? m_separator->cloneForCSSOM() : 0);
+        return create(m_identifier ? m_identifier->cloneForCSSOM() : nullptr
+            , m_listStyle ? m_listStyle->cloneForCSSOM() : nullptr
+            , m_separator ? m_separator->cloneForCSSOM() : nullptr);
     }
 
     void trace(Visitor*);