Switch to null root property tree nodes [spv2]

third_party/WebKit/Source/core/paint/ObjectPaintProperties.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 ObjectPaintProperties_h
 #define ObjectPaintProperties_h
 
 #include "core/CoreExport.h"
 #include "platform/geometry/LayoutPoint.h"
 #include "platform/graphics/paint/ClipPaintPropertyNode.h"
 #include "platform/graphics/paint/EffectPaintPropertyNode.h"
 #include "platform/graphics/paint/GeometryPropertyTreeState.h"
 #include "platform/graphics/paint/PaintChunkProperties.h"
 #include "platform/graphics/paint/ScrollPaintPropertyNode.h"
 #include "platform/graphics/paint/TransformPaintPropertyNode.h"
 #include "wtf/PassRefPtr.h"
 #include "wtf/PtrUtil.h"
 #include "wtf/RefPtr.h"
 #include <memory>
 
 namespace blink {
 
 // This class stores property tree related information associated with a LayoutObject.
 // Currently there are two groups of information:
 // 1. The set of property nodes created locally by this LayoutObject.
-// 2. [Optional] A suite of property nodes (PaintChunkProperties) and paint offset
-//    that can be used to paint the border box of this LayoutObject.
+// 2. LocalBorderBoxProperties which stores the complete set of property tree nodes (including those
+//    created by this object as well as those inherited form other objects) used to start painting
+//    this LayoutObject.
 class CORE_EXPORT ObjectPaintProperties {
     WTF_MAKE_NONCOPYABLE(ObjectPaintProperties);
     USING_FAST_MALLOC(ObjectPaintProperties);
 public:
     struct LocalBorderBoxProperties;
 
     static std::unique_ptr<ObjectPaintProperties> create()
     {
         return wrapUnique(new ObjectPaintProperties());
     }
@@ skipping 111 matching lines @@
     RefPtr<TransformPaintPropertyNode> m_scrollTranslation;
     RefPtr<TransformPaintPropertyNode> m_scrollbarPaintOffset;
     RefPtr<ScrollPaintPropertyNode> m_scroll;
 
     std::unique_ptr<LocalBorderBoxProperties> m_localBorderBoxProperties;
 };
 
 } // namespace blink
 
 #endif // ObjectPaintProperties_h