Add foundation for removing AnimatableValues from StyleInterpolation

Source/core/animation/AnimationValue.h

+// Copyright 2015 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 AnimationValue_h
+#define AnimationValue_h
+
+#include "core/animation/InterpolableValue.h"
+#include "core/animation/NonInterpolableValue.h"
+#include "platform/heap/Handle.h"
+
+namespace blink {
+
+class AnimationType;
+
+struct AnimationValue {
+private:
+    DISALLOW_ALLOCATION();
+
+public:
+    const AnimationType* type;
+    OwnPtrWillBeMember<InterpolableValue> interpolableValue;
+    RefPtrWillBeMember<NonInterpolableValue> nonInterpolableValue;
+
+    operator bool() const { return bool(type); }
+
+    AnimationValue()
+        : type(nullptr)
+        , interpolableValue(nullptr)
+        , nonInterpolableValue(nullptr)
+    { }
+
+    AnimationValue(const AnimationType* type, PassOwnPtrWillBeRawPtr<InterpolableValue> interpolableValue, RefPtrWillBeRawPtr<NonInterpolableValue> nonInterpolableValue)
+        : type(type)
+        , interpolableValue(interpolableValue)
+        , nonInterpolableValue(nonInterpolableValue)
+    { }
+
+    void copy(const AnimationValue& other)

[shans, 2015/06/04 00:15:15]

Should this not just be a copy constructor?

[alancutter (OOO until 2018), 2015/06/11 04:15:13]

This is used in "result.copy((fraction < 0.5) ? m_start : m_end)" in
FlipInterpolationPrimitive::interpolate() which would use a copy assignment
rather than a copy constructor. I think copy() is more clear in the caller code
than overloaded operator=.

+    {
+        type = other.type;
+        interpolableValue = other.interpolableValue ? other.interpolableValue->clone() : nullptr;
+        nonInterpolableValue = other.nonInterpolableValue;
+    }
+
+    void clear()
+    {
+        type = nullptr;
+        interpolableValue = nullptr;
+        nonInterpolableValue = nullptr;
+    }
+
+    DEFINE_INLINE_TRACE()
+    {
+        visitor->trace(interpolableValue);
+        visitor->trace(nonInterpolableValue);
+    }
+};
+
+} // namespace blink
+
+#endif // AnimationValue_h