Add additive animation support for CSS property transform-origin

third_party/WebKit/Source/core/animation/CSSTransformOriginInterpolationType.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 CSSTransformOriginInterpolationType_h
+#define CSSTransformOriginInterpolationType_h
+
+#include "core/animation/CSSLengthInterpolationType.h"
+#include "core/animation/CSSLengthListInterpolationType.h"
+#include "core/animation/CSSPositionAxisListInterpolationType.h"
+#include "core/animation/ListInterpolationFunctions.h"
+#include "core/css/CSSValueList.h"
+
+namespace blink {
+
+class CSSTransformOriginInterpolationType : public CSSLengthListInterpolationType {
+public:
+    CSSTransformOriginInterpolationType(CSSPropertyID property)
+        : CSSLengthListInterpolationType(property)
+    { }
+
+private:
+    InterpolationValue maybeConvertValue(const CSSValue& value, const StyleResolverState&, ConversionCheckers&) const final
+    {
+        const CSSValueList& list = toCSSValueList(value);
+        ASSERT(list.length() == 3);
+        return ListInterpolationFunctions::createList(list.length(), [&list](size_t index) {
+            const CSSValue& item = *list.item(index);
+            if (index < 2)
+                return CSSPositionAxisListInterpolationType::convertPositionAxisCSSValue(item);
+            return CSSLengthInterpolationType::maybeConvertCSSValue(item);
+        });
+    }
+};
+
+} // namespace blink
+
+#endif // CSSTransformOriginInterpolationType_h