Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/css/CSSValuePool.cpp

Index: Source/core/css/CSSValuePool.cpp
diff --git a/Source/core/css/CSSValuePool.cpp b/Source/core/css/CSSValuePool.cpp
index 4e6e9f227dd6bbba515515613b6a7ed3e7c21e68..89630e487fadc1238b34fcef31bcbdad350d27ee 100644
--- a/Source/core/css/CSSValuePool.cpp
+++ b/Source/core/css/CSSValuePool.cpp
@@ -131,7 +131,7 @@ PassRefPtrWillBeRawPtr<CSSPrimitiveValue> CSSValuePool::createValue(const Length
 
 PassRefPtrWillBeRawPtr<CSSPrimitiveValue> CSSValuePool::createFontFamilyValue(const String& familyName)
 {
-    RefPtrWillBeMember<CSSPrimitiveValue>& value = m_fontFamilyValueCache.add(familyName, 0).storedValue->value;
+    RefPtrWillBeMember<CSSPrimitiveValue>& value = m_fontFamilyValueCache.add(familyName, nullptr).storedValue->value;
     if (!value)
         value = CSSPrimitiveValue::create(familyName, CSSPrimitiveValue::CSS_STRING);
     return value;
@@ -144,7 +144,7 @@ PassRefPtrWillBeRawPtr<CSSValueList> CSSValuePool::createFontFaceValue(const Ato
     if (m_fontFaceValueCache.size() > maximumFontFaceCacheSize)
         m_fontFaceValueCache.clear();
 
-    RefPtrWillBeMember<CSSValueList>& value = m_fontFaceValueCache.add(string, 0).storedValue->value;
+    RefPtrWillBeMember<CSSValueList>& value = m_fontFaceValueCache.add(string, nullptr).storedValue->value;
     if (!value)
         value = BisonCSSParser::parseFontFaceValue(string);
     return value;