WIP: Construct SPV2's scroll paint property tree

third_party/WebKit/Source/platform/graphics/paint/PropertyTreeState.h

 // 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 PropertyTreeState_h
 #define PropertyTreeState_h
 
 #include "platform/graphics/paint/ClipPaintPropertyNode.h"
 #include "platform/graphics/paint/EffectPaintPropertyNode.h"
 #include "platform/graphics/paint/TransformPaintPropertyNode.h"
 #include "wtf/HashFunctions.h"
 #include "wtf/HashTraits.h"
 
 namespace blink {
 
 // Represents the combination of transform, clip and effect nodes for a particular coordinate space.
 // See GeometryMapper.
+// Scroll nodes (ScrollPaintPropertyNode) are not needed for mapping geometry and have been left off
+// of this structure.
+// TODO(pdr): Rename this GeometryPropertyTreeState.
 struct PropertyTreeState {
     PropertyTreeState() : PropertyTreeState(nullptr, nullptr, nullptr) {}
 
     PropertyTreeState(
         const TransformPaintPropertyNode* transform,
         const ClipPaintPropertyNode* clip,
         const EffectPaintPropertyNode* effect)
     : transform(transform), clip(clip), effect(effect) {}
 
     RefPtr<const TransformPaintPropertyNode> transform;
@@ skipping 35 matching lines @@
     while (a != b) {
         a = a->parent();
         b = b->parent();
     }
     return a;
 }
 
 } // namespace blink
 
 #endif // PropertyTreeState_h