Move RarePaintData to its own file

third_party/WebKit/Source/core/paint/ObjectPaintProperties.cpp

-// 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.
-
-#include "core/paint/ObjectPaintProperties.h"
-
-namespace blink {
-
-std::unique_ptr<PropertyTreeState> ObjectPaintProperties::contentsProperties(
-    PropertyTreeState* localBorderBoxProperties,
-    ObjectPaintProperties* paintProperties) {
-  if (!localBorderBoxProperties)
-    return nullptr;
-
-  std::unique_ptr<PropertyTreeState> contents =
-      WTF::makeUnique<PropertyTreeState>(*localBorderBoxProperties);
-
-  if (paintProperties) {
-    if (paintProperties->scrollTranslation())
-      contents->setTransform(paintProperties->scrollTranslation());
-    if (paintProperties->overflowClip())
-      contents->setClip(paintProperties->overflowClip());
-    else if (paintProperties->cssClip())
-      contents->setClip(paintProperties->cssClip());
-  }
-
-  // TODO(chrishtr): cssClipFixedPosition needs to be handled somehow.
-
-  return contents;
-}
-
-}  // namespace blink