Refactor to centralize code which decides whether ObjectPaintProperties are needed.

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

 // Copyright 2017 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/RarePaintData.h"
 
 #include "core/paint/ObjectPaintProperties.h"
 #include "core/paint/PaintLayer.h"
 
 namespace blink {
 
 RarePaintData::RarePaintData() {}
 
 RarePaintData::~RarePaintData() {}
 
 void RarePaintData::SetLayer(std::unique_ptr<PaintLayer> layer) {
   layer_ = std::move(layer);
 };
 
 ObjectPaintProperties& RarePaintData::EnsurePaintProperties() {
   if (!paint_properties_)
     paint_properties_ = ObjectPaintProperties::Create();
   return *paint_properties_.get();
 }
 
+void RarePaintData::ClearPaintProperties() {
+  paint_properties_.reset(nullptr);
+}
+
 void RarePaintData::ClearLocalBorderBoxProperties() {
   local_border_box_properties_ = nullptr;
 }
 
 void RarePaintData::SetLocalBorderBoxProperties(PropertyTreeState& state) {
   if (!local_border_box_properties_)
     local_border_box_properties_ = WTF::MakeUnique<PropertyTreeState>(state);
   else
     *local_border_box_properties_ = state;
 }
 
 PropertyTreeState RarePaintData::ContentsProperties() const {
   DCHECK(local_border_box_properties_);
   PropertyTreeState contents(*local_border_box_properties_);
   if (paint_properties_) {
     if (paint_properties_->ScrollTranslation())
       contents.SetTransform(paint_properties_->ScrollTranslation());
     if (paint_properties_->OverflowClip())
       contents.SetClip(paint_properties_->OverflowClip());
     else if (paint_properties_->CssClip())
       contents.SetClip(paint_properties_->CssClip());
   }
 
   // TODO(chrishtr): cssClipFixedPosition needs to be handled somehow.
 
   return contents;
 }
 
 }  // namespace blink