Perf Tryjob: CSSValue refactor step 1

Source/core/html/canvas/CanvasFontCache.cpp

Index: Source/core/html/canvas/CanvasFontCache.cpp
diff --git a/Source/core/html/canvas/CanvasFontCache.cpp b/Source/core/html/canvas/CanvasFontCache.cpp
index 36ae3387adf84925c18a1a8b5e6d1484aeebb2f8..f4e4bd5d1940222e7b11bd16654edff5f7eeae49 100644
--- a/Source/core/html/canvas/CanvasFontCache.cpp
+++ b/Source/core/html/canvas/CanvasFontCache.cpp
@@ -58,7 +58,7 @@ MutableStylePropertySet* CanvasFontCache::parseFont(const String& fontString)
             return nullptr;
         // According to http://lists.w3.org/Archives/Public/public-html/2009Jul/0947.html,
         // the "inherit" and "initial" values must be ignored.
-        RefPtrWillBeRawPtr<CSSValue> fontValue = parsedStyle->getPropertyCSSValue(CSSPropertyFontSize);
+        NullableCSSValue fontValue = parsedStyle->getPropertyCSSValue(CSSPropertyFontSize);
         if (fontValue && (fontValue->isInitialValue() || fontValue->isInheritedValue()))
             return nullptr;
         m_fetchedFonts.add(fontString, parsedStyle);