CSSValue Immediates: Replace CSSValue usage with const references

Source/core/animation/ImageStyleInterpolation.h

Index: Source/core/animation/ImageStyleInterpolation.h
diff --git a/Source/core/animation/ImageStyleInterpolation.h b/Source/core/animation/ImageStyleInterpolation.h
index 414ca825f3c1271e00b03d70ad71800a0c870cb5..a2b2d5c46f26086f56a91cc179be4668160959d1 100644
--- a/Source/core/animation/ImageStyleInterpolation.h
+++ b/Source/core/animation/ImageStyleInterpolation.h
@@ -11,7 +11,7 @@
 namespace blink {
 class ImageStyleInterpolation : public StyleInterpolation {
 public:
-    static PassRefPtrWillBeRawPtr<ImageStyleInterpolation> create(CSSValue& start, CSSValue& end, CSSPropertyID id)
+    static PassRefPtrWillBeRawPtr<ImageStyleInterpolation> create(const CSSValue& start, const CSSValue& end, CSSPropertyID id)
     {
         return adoptRefWillBeNoop(new ImageStyleInterpolation(start, end, id));
     }
@@ -22,7 +22,7 @@ public:
     virtual void apply(StyleResolverState&) const override;
 
 private:
-    ImageStyleInterpolation(CSSValue start, CSSValue end, CSSPropertyID id)
+    ImageStyleInterpolation(const CSSValue& start, const CSSValue& end, CSSPropertyID id)
         : StyleInterpolation(InterpolableNumber::create(0.0), InterpolableNumber::create(1.0), id)
         , m_initialImage(start)
         , m_finalImage(end)