WIP: Implement CSS transitions on top of InterpolationTypes instead of AnimatableValues

third_party/WebKit/Source/core/animation/StackableInterpolation.h

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef StackableInterpolation_h
+#define StackableInterpolation_h
+
+#include "core/animation/Interpolation.h"
+
+namespace blink {
+
+class InterpolationEnvironment;
+class TypedInterpolationValue;
+class UnderlyingValueOwner;
+
+class StackableInterpolation : public Interpolation {
+public:
+    static void applyStack(const ActiveInterpolations&, InterpolationEnvironment&);
+
+    virtual bool isStackableInterpolation() const { return true; }
+
+protected:
+    virtual std::unique_ptr<TypedInterpolationValue> maybeConvertUnderlyingValue(const InterpolationEnvironment&) const = 0;
+    virtual const TypedInterpolationValue* ensureValidInterpolation(const InterpolationEnvironment&, const UnderlyingValueOwner&) const = 0;
+    virtual void setFlagIfInheritUsed(InterpolationEnvironment&) const {}
+    virtual double underlyingFraction() const = 0;
+};
+
+DEFINE_TYPE_CASTS(StackableInterpolation, Interpolation, value, value->isStackableInterpolation(), value.isStackableInterpolation());
+
+} // namespace blink
+
+#endif // StackableInterpolation_h