Add registered custom property wrapping support to CSSAnimatableValueFactory

third_party/WebKit/Source/core/animation/animatable/AnimatableUnknown.h

Index: third_party/WebKit/Source/core/animation/animatable/AnimatableUnknown.h
diff --git a/third_party/WebKit/Source/core/animation/animatable/AnimatableUnknown.h b/third_party/WebKit/Source/core/animation/animatable/AnimatableUnknown.h
index af25e09ab73fe62903045110dffca5cfcf8d468b..1ec923dc82de9a8d2fb173ffce57325e8b1ef72e 100644
--- a/third_party/WebKit/Source/core/animation/animatable/AnimatableUnknown.h
+++ b/third_party/WebKit/Source/core/animation/animatable/AnimatableUnknown.h
@@ -41,14 +41,14 @@ class AnimatableUnknown final : public AnimatableValue {
  public:
   ~AnimatableUnknown() override {}
 
-  static PassRefPtr<AnimatableUnknown> create(CSSValue* value) {
+  static PassRefPtr<AnimatableUnknown> create(const CSSValue* value) {
     return adoptRef(new AnimatableUnknown(value));
   }
   static PassRefPtr<AnimatableUnknown> create(CSSValueID value) {
     return adoptRef(new AnimatableUnknown(CSSIdentifierValue::create(value)));
   }
 
-  CSSValue* toCSSValue() const { return m_value; }
+  const CSSValue* toCSSValue() const { return m_value; }
   CSSValueID toCSSValueID() const {
     return toCSSIdentifierValue(m_value.get())->getValueID();
   }
@@ -62,13 +62,11 @@ class AnimatableUnknown final : public AnimatableValue {
   bool usesDefaultInterpolationWith(const AnimatableValue*) const override;
 
  private:
-  explicit AnimatableUnknown(CSSValue* value) : m_value(value) {
-    DCHECK(m_value);
-  }
+  explicit AnimatableUnknown(const CSSValue* value) : m_value(value) {}
   AnimatableType type() const override { return TypeUnknown; }
   bool equalTo(const AnimatableValue*) const override;
 
-  const Persistent<CSSValue> m_value;
+  const Persistent<const CSSValue> m_value;
 };
 
 DEFINE_ANIMATABLE_VALUE_TYPE_CASTS(AnimatableUnknown, isUnknown());