Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/fetch/CSSStyleSheetResource.cpp

Index: Source/core/fetch/CSSStyleSheetResource.cpp
diff --git a/Source/core/fetch/CSSStyleSheetResource.cpp b/Source/core/fetch/CSSStyleSheetResource.cpp
index 1370b3bcb575081c6f1010f5c8ca43daac71b92b..38dffed655f0f3b8975f979f5bb868bb7c97e4e7 100644
--- a/Source/core/fetch/CSSStyleSheetResource.cpp
+++ b/Source/core/fetch/CSSStyleSheetResource.cpp
@@ -151,11 +151,11 @@ bool CSSStyleSheetResource::canUseSheet(bool enforceMIMEType, bool* hasValidMIME
 PassRefPtrWillBeRawPtr<StyleSheetContents> CSSStyleSheetResource::restoreParsedStyleSheet(const CSSParserContext& context)
 {
     if (!m_parsedStyleSheetCache)
-        return 0;
+        return nullptr;
     if (m_parsedStyleSheetCache->hasFailedOrCanceledSubresources()) {
         m_parsedStyleSheetCache->removedFromMemoryCache();
         m_parsedStyleSheetCache.clear();
-        return 0;
+        return nullptr;
     }
 
     ASSERT(m_parsedStyleSheetCache->isCacheable());
@@ -163,7 +163,7 @@ PassRefPtrWillBeRawPtr<StyleSheetContents> CSSStyleSheetResource::restoreParsedS
 
     // Contexts must be identical so we know we would get the same exact result if we parsed again.
     if (m_parsedStyleSheetCache->parserContext() != context)
-        return 0;
+        return nullptr;
 
     didAccessDecodedData(currentTime());