CSSValue Immediates: Change CSSValue to an object instead of a pointer

Source/core/style/StyleGeneratedImage.h

Index: Source/core/style/StyleGeneratedImage.h
diff --git a/Source/core/style/StyleGeneratedImage.h b/Source/core/style/StyleGeneratedImage.h
index ffa5b5ac4a0eef2e04c00f2577eb05a456b1d4f9..01579e9059fc988c19c76025385fa8d77ef4d971 100644
--- a/Source/core/style/StyleGeneratedImage.h
+++ b/Source/core/style/StyleGeneratedImage.h
@@ -41,7 +41,7 @@ public:
 
     virtual WrappedImagePtr data() const override { return m_imageGeneratorValue.get(); }
 
-    virtual PassRefPtrWillBeRawPtr<CSSValue> cssValue() const override;
+    virtual NullableCSSValue cssValue() const override;
 
     virtual LayoutSize imageSize(const LayoutObject*, float multiplier) const override;
     virtual bool imageHasRelativeWidth() const override { return !m_fixedSize; }