CSSValue Immediates: Replace CSSPrimitiveValue 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 91d46e4410a5bb0156425c42eef0bbce43154563..1e9429091ef87cc52a5793d20de4301cdf58ec55 100644
--- a/Source/core/animation/animatable/AnimatableUnknown.h
+++ b/Source/core/animation/animatable/AnimatableUnknown.h
@@ -42,7 +42,7 @@ class AnimatableUnknown final : public AnimatableValue {
 public:
     virtual ~AnimatableUnknown() { }
 
-    static PassRefPtrWillBeRawPtr<AnimatableUnknown> create(CSSPrimitiveValue value)
+    static PassRefPtrWillBeRawPtr<AnimatableUnknown> create(const CSSPrimitiveValue& value)
     {
         return adoptRefWillBeNoop(new AnimatableUnknown(value));
     }
@@ -51,7 +51,7 @@ public:
         return adoptRefWillBeNoop(new AnimatableUnknown(cssValuePool().createIdentifierValue(value)));
     }
 
-    CSSPrimitiveValue toCSSValue() const { return toCSSPrimitiveValue(m_value); }
+    const CSSPrimitiveValue& toCSSValue() const { return toCSSPrimitiveValue(m_value); }
     CSSValueID toCSSValueID() const { return toCSSPrimitiveValue(m_value).getValueID(); }
 
     DEFINE_INLINE_VIRTUAL_TRACE()
@@ -69,7 +69,7 @@ protected:
     virtual bool usesDefaultInterpolationWith(const AnimatableValue*) const override { return true; }
 
 private:
-    explicit AnimatableUnknown(CSSPrimitiveValue value)
+    explicit AnimatableUnknown(const CSSPrimitiveValue& value)
         : m_value(value)
     {
     }