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

Source/core/style/StylePendingImage.h

 /*
  * Copyright (C) 2010 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 31 matching lines @@
 class StylePendingImage final : public StyleImage {
 public:
     static PassRefPtrWillBeRawPtr<StylePendingImage> create(CSSValue* value)
     {
         return adoptRefWillBeNoop(new StylePendingImage(value));
     }
 
     WrappedImagePtr data() const override { return m_value; }
 
     PassRefPtrWillBeRawPtr<CSSValue> cssValue() const override { return m_value; }
+
+    PassRefPtrWillBeRawPtr<CSSValue> computedCSSValue() const override
+    {
+        ASSERT_NOT_REACHED();
+        return nullptr;
+    }
+
     CSSImageValue* cssImageValue() const { return m_value->isImageValue() ? toCSSImageValue(m_value) : 0; }
     CSSImageGeneratorValue* cssImageGeneratorValue() const { return m_value->isImageGeneratorValue() ? toCSSImageGeneratorValue(m_value) : 0; }
     CSSCursorImageValue* cssCursorImageValue() const { return m_value->isCursorImageValue() ? toCSSCursorImageValue(m_value) : 0; }
     CSSImageSetValue* cssImageSetValue() const { return m_value->isImageSetValue() ? toCSSImageSetValue(m_value) : 0; }
 
     LayoutSize imageSize(const LayoutObject*, float /*multiplier*/) const override { return LayoutSize(); }
     bool imageHasRelativeWidth() const override { return false; }
     bool imageHasRelativeHeight() const override { return false; }
     void computeIntrinsicDimensions(const LayoutObject*, Length& /* intrinsicWidth */ , Length& /* intrinsicHeight */, FloatSize& /* intrinsicRatio */) override { }
     bool usesImageContainerSize() const override { return false; }
@@ skipping 20 matching lines @@
         m_isPendingImage = true;
     }
 
     RawPtrWillBeMember<CSSValue> m_value; // Not retained; it owns us.
 };
 
 DEFINE_STYLE_IMAGE_TYPE_CASTS(StylePendingImage, isPendingImage());
 
 }
 #endif