Web Animations: Add Interpolation class.

Source/core/animation/Interpolation.h

+// Copyright 2014 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 Interpolation_h
+#define Interpolation_h
+
+#include "core/animation/InterpolableValue.h"
+#include "core/css/resolver/StyleResolverState.h"
+#include "wtf/RefCounted.h"
+
+namespace WebCore {
+
+class Interpolation : public RefCounted<Interpolation> {
+public:
+    static PassRefPtr<Interpolation> create(PassOwnPtr<InterpolableValue> start, PassOwnPtr<InterpolableValue> end)
+    {
+        return adoptRef(new Interpolation(start, end));
+    }
+
+    void interpolate(double fraction) const;
+
+protected:
+    const OwnPtr<InterpolableValue> m_start;
+    const OwnPtr<InterpolableValue> m_end;
+
+    mutable double m_cachedFraction;
+    mutable OwnPtr<InterpolableValue> m_cachedValue;
+
+    Interpolation(PassOwnPtr<InterpolableValue> start, PassOwnPtr<InterpolableValue> end);
+
+private:
+    InterpolableValue* getCachedValueForTesting() const { return m_cachedValue.get(); }
+
+    friend class AnimationInterpolableValueTest;
+};
+
+class StyleInterpolation : public Interpolation {
+public:
+    // 1) convert m_cachedValue into an X
+    // 2) shove X into StyleResolverState
+    // X can be:
+    // (1) a CSSValue (and applied via StyleBuilder::applyProperty)
+    // (2) an AnimatableValue (and applied via // AnimatedStyleBuilder::applyProperty)
+    // (3) a custom value that is inserted directly into the StyleResolverState.
+    virtual void apply(StyleResolverState&) = 0;
+
+protected:
+    CSSPropertyID m_id;
+
+    StyleInterpolation(PassOwnPtr<InterpolableValue> start, PassOwnPtr<InterpolableValue> end, CSSPropertyID id)
+        : Interpolation(start, end)
+        , m_id(id)
+    { }
+};
+
+}
+#endif