Clean up after getPropertyCSSValue

Source/core/css/CSSImageSetValue.h

Index: Source/core/css/CSSImageSetValue.h
diff --git a/Source/core/css/CSSImageSetValue.h b/Source/core/css/CSSImageSetValue.h
index 427b8391af02a0bde146bc038a4d5eeac3de5262..e37fa24abbbe52ac4e2e9a9e240f37b6a3382985 100644
--- a/Source/core/css/CSSImageSetValue.h
+++ b/Source/core/css/CSSImageSetValue.h
@@ -63,8 +63,6 @@ public:
 
     bool hasFailedOrCanceledSubresources() const;
 
-    PassRefPtrWillBeRawPtr<CSSImageSetValue> cloneForCSSOM() const;
-
     void traceAfterDispatch(Visitor* visitor) { CSSValueList::traceAfterDispatch(visitor); }
 
 protected:
@@ -72,7 +70,6 @@ protected:
 
 private:
     CSSImageSetValue();
-    explicit CSSImageSetValue(const CSSImageSetValue& cloneFrom);
 
     void fillImageSet();
     static inline bool compareByScaleFactor(ImageWithScale first, ImageWithScale second) { return first.scaleFactor < second.scaleFactor; }