CSSValue Immediates: Replace CSSValue usage with const references

Source/core/animation/animatable/AnimatableUnknown.h

Index: Source/core/animation/animatable/AnimatableUnknown.h
diff --git a/Source/core/animation/animatable/AnimatableUnknown.h b/Source/core/animation/animatable/AnimatableUnknown.h
index a2e16a52670cad218921244ec0c5511eb58e7f4d..5c3fe7e6104e4f53e31b7ed61ce87ace9cf29279 100644
--- a/Source/core/animation/animatable/AnimatableUnknown.h
+++ b/Source/core/animation/animatable/AnimatableUnknown.h
@@ -41,7 +41,7 @@ class AnimatableUnknown final : public AnimatableValue {
 public:
     virtual ~AnimatableUnknown() { }
 
-    static PassRefPtrWillBeRawPtr<AnimatableUnknown> create(CSSValue value)
+    static PassRefPtrWillBeRawPtr<AnimatableUnknown> create(const CSSValue& value)
     {
         return adoptRefWillBeNoop(new AnimatableUnknown(value));
     }
@@ -68,7 +68,7 @@ protected:
     virtual bool usesDefaultInterpolationWith(const AnimatableValue*) const override { return true; }
 
 private:
-    explicit AnimatableUnknown(CSSValue value)
+    explicit AnimatableUnknown(const CSSValue& value)
         : m_value(value)
     {
     }