Incrementally build main thread scrolling reasons [spv2]

third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.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 PaintPropertyTreeBuilder_h
 #define PaintPropertyTreeBuilder_h
 
 #include "platform/geometry/LayoutPoint.h"
 #include "platform/graphics/paint/ClipPaintPropertyNode.h"
 #include "platform/graphics/paint/EffectPaintPropertyNode.h"
@@ skipping 30 matching lines @@
     // The clip node describes the accumulated raster clip for the current
     // subtree.  Note that the computed raster region in canvas space for a clip
     // node is independent from the transform and paint offset above. Also the
     // actual raster region may be affected by layerization and occlusion
     // tracking.
     const ClipPaintPropertyNode* clip = nullptr;
     // The scroll node contains information for scrolling such as the parent
     // scroll space, the extent that can be scrolled, etc. Because scroll nodes
     // reference a scroll offset transform, scroll nodes should be updated if
     // the transform tree changes.
-    ScrollPaintPropertyNode* scroll = nullptr;
+    const ScrollPaintPropertyNode* scroll = nullptr;
   };
 
   ContainingBlockContext current;
 
   // Separate context for out-of-flow positioned and fixed positioned elements
   // are needed because they don't use DOM parent as their containing block.
   // These additional contexts normally pass through untouched, and are only
   // copied from the main context when the current element serves as the
   // containing block of corresponding positioned descendants.  Overflow clips
   // are also inherited by containing block tree instead of DOM tree, thus they
@@ skipping 42 matching lines @@
                                            PaintPropertyTreeBuilderContext&);
   static void updateEffect(const LayoutObject&,
                            PaintPropertyTreeBuilderContext&);
   static void updateCssClip(const LayoutObject&,
                             PaintPropertyTreeBuilderContext&);
   static void updateLocalBorderBoxContext(const LayoutObject&,
                                           PaintPropertyTreeBuilderContext&);
   static void updateScrollbarPaintOffset(
       const LayoutObject&,
       const PaintPropertyTreeBuilderContext&);
-  static void updateMainThreadScrollingReasons(
-      const LayoutObject&,
-      PaintPropertyTreeBuilderContext&);
   static void updateOverflowClip(const LayoutObject&,
                                  PaintPropertyTreeBuilderContext&);
   static void updatePerspective(const LayoutObject&,
                                 PaintPropertyTreeBuilderContext&);
   static void updateSvgLocalToBorderBoxTransform(
       const LayoutObject&,
       PaintPropertyTreeBuilderContext&);
   static void updateScrollAndScrollTranslation(
       const LayoutObject&,
       PaintPropertyTreeBuilderContext&);
   static void updateOutOfFlowContext(const LayoutObject&,
                                      PaintPropertyTreeBuilderContext&);
 };
 
 }  // namespace blink
 
 #endif  // PaintPropertyTreeBuilder_h