Prepare for responsive CSS animations.

Source/core/animation/DeferredLegacyStyleInterpolation.h

Index: Source/core/animation/DeferredLegacyStyleInterpolation.h
diff --git a/Source/core/animation/DeferredLegacyStyleInterpolation.h b/Source/core/animation/DeferredLegacyStyleInterpolation.h
index 9f72bd71be0fe1aec041d49e9f08642c47e12847..18bfd0eff17a5b2f73405cf2f17100fc39aabc8c 100644
--- a/Source/core/animation/DeferredLegacyStyleInterpolation.h
+++ b/Source/core/animation/DeferredLegacyStyleInterpolation.h
@@ -5,6 +5,7 @@
 #ifndef DeferredLegacyStyleInterpolation_h
 #define DeferredLegacyStyleInterpolation_h
 
+#include "core/animation/LegacyStyleInterpolation.h"
 #include "core/animation/StyleInterpolation.h"
 #include "core/css/CSSValue.h"
 
@@ -36,18 +37,27 @@ public:
     static bool interpolationRequiresStyleResolve(const CSSValueList&);
     static bool interpolationRequiresStyleResolve(const CSSBasicShape&);
 
+    void underlyingStyleChanged() { m_outdated = true; }
+
+    virtual bool isDeferredLegacyStyleInterpolation() const override final { return true; }
+
 private:
     DeferredLegacyStyleInterpolation(PassRefPtrWillBeRawPtr<CSSValue> start, PassRefPtrWillBeRawPtr<CSSValue> end, CSSPropertyID id)
         : StyleInterpolation(InterpolableNumber::create(0), InterpolableNumber::create(1), id)
         , m_startCSSValue(start)
         , m_endCSSValue(end)
+        , m_outdated(true)
     {
     }
 
     RefPtrWillBeMember<CSSValue> m_startCSSValue;
     RefPtrWillBeMember<CSSValue> m_endCSSValue;
+    mutable RefPtrWillBeMember<LegacyStyleInterpolation> m_innerInterpolation;
+    mutable bool m_outdated;
 };
 
+DEFINE_TYPE_CASTS(DeferredLegacyStyleInterpolation, StyleInterpolation, value, value->isDeferredLegacyStyleInterpolation(), value.isDeferredLegacyStyleInterpolation());
+
 }
 
 #endif