BackgroundImage incorrectly returns empty url() when created on-the-fly

Source/core/style/StyleFetchedImage.h

Index: Source/core/style/StyleFetchedImage.h
diff --git a/Source/core/style/StyleFetchedImage.h b/Source/core/style/StyleFetchedImage.h
index 4f6ecf2c0f9646d45c6c98424f8156f112c6f5b6..b68481d7fc61cd607f40cc412f52bef5d5d1dbfd 100644
--- a/Source/core/style/StyleFetchedImage.h
+++ b/Source/core/style/StyleFetchedImage.h
@@ -45,6 +45,7 @@ public:
     WrappedImagePtr data() const override { return m_image.get(); }
 
     PassRefPtrWillBeRawPtr<CSSValue> cssValue() const override;
+    PassRefPtrWillBeRawPtr<CSSValue> computedCSSValue() const override;
 
     bool canRender(const LayoutObject&, float multiplier) const override;
     bool isLoaded() const override;