Oilpan: fix build after r184449.

Source/core/css/parser/CSSPropertyParser.cpp

Index: Source/core/css/parser/CSSPropertyParser.cpp
diff --git a/Source/core/css/parser/CSSPropertyParser.cpp b/Source/core/css/parser/CSSPropertyParser.cpp
index a4fe06d622f8d7d7c940f78e1c68d7bed7ecfe8e..5d6cccd27dca3f744281230be43bd04a26fc5e1e 100644
--- a/Source/core/css/parser/CSSPropertyParser.cpp
+++ b/Source/core/css/parser/CSSPropertyParser.cpp
@@ -4456,7 +4456,7 @@ void CSSPropertyParser::parseSystemFont(bool important)
     addProperty(CSSPropertyFontStyle, cssValuePool().createIdentifierValue(fontStyle == FontStyleItalic ? CSSValueItalic : CSSValueNormal), important);
     addProperty(CSSPropertyFontWeight, cssValuePool().createValue(fontWeight), important);
     addProperty(CSSPropertyFontSize, cssValuePool().createValue(fontSize, CSSPrimitiveValue::CSS_PX), important);
-    RefPtr<CSSValueList> fontFamilyList = CSSValueList::createCommaSeparated();
+    RefPtrWillBeRawPtr<CSSValueList> fontFamilyList = CSSValueList::createCommaSeparated();
     fontFamilyList->append(cssValuePool().createFontFamilyValue(fontFamily));
     addProperty(CSSPropertyFontFamily, fontFamilyList.release(), important);
     addProperty(CSSPropertyFontVariant, cssValuePool().createIdentifierValue(CSSValueNormal), important);