Add additive animation support for CSS properties perspective-origin and object-position

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

Index: third_party/WebKit/Source/core/animation/CSSPositionInterpolationType.h
diff --git a/third_party/WebKit/Source/core/animation/CSSPositionInterpolationType.h b/third_party/WebKit/Source/core/animation/CSSPositionInterpolationType.h
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index 0000000000000000000000000000000000000000..523542e0b575ea3fae5693fa19166742c32261a0
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+++ b/third_party/WebKit/Source/core/animation/CSSPositionInterpolationType.h
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+// 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 CSSPositionInterpolationType_h
+#define CSSPositionInterpolationType_h
+
+#include "core/animation/CSSLengthListInterpolationType.h"
+
+#include "core/animation/CSSPositionAxisListInterpolationType.h"
+#include "core/animation/ListInterpolationFunctions.h"
+#include "core/css/CSSValuePair.h"
+
+namespace blink {
+
+class CSSPositionInterpolationType : public CSSLengthListInterpolationType {
+public:
+    CSSPositionInterpolationType(CSSPropertyID property)
+        : CSSLengthListInterpolationType(property)
+    { }
+
+private:
+    InterpolationValue maybeConvertValue(const CSSValue& value, const StyleResolverState&, ConversionCheckers&) const final
+    {
+        const CSSValuePair& pair = toCSSValuePair(value);
+        return ListInterpolationFunctions::createList(2, [&pair](size_t index) {
+            return CSSPositionAxisListInterpolationType::convertPositionAxisCSSValue(index == 0 ? pair.first() : pair.second());
+        });
+    }
+};
+
+} // namespace blink
+
+#endif // CSSPositionInterpolationType_h