Remove "changed main thread scrolling reasons" as a reason for scroll nodes.

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

 // 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.
 
 #include "core/paint/PaintPropertyTreeBuilder.h"
 
 #include <memory>
 #include "core/dom/DOMNodeIds.h"
 #include "core/frame/FrameView.h"
 #include "core/frame/LocalFrame.h"
@@ skipping 861 matching lines @@
 
 void PaintPropertyTreeBuilder::UpdateScrollAndScrollTranslation(
     const LayoutObject& object,
     PaintPropertyTreeBuilderContext& context) {
   if (object.NeedsPaintPropertyUpdate() || context.force_subtree_update) {
     bool needs_scroll_properties = false;
     if (object.HasOverflowClip()) {
       auto ancestor_reasons =
           context.current.scroll->GetMainThreadScrollingReasons();
       auto reasons = GetMainThreadScrollingReasons(object, ancestor_reasons);
-      bool scroll_node_needed_for_main_thread_reasons =
-          ancestor_reasons != reasons;
 
       const LayoutBox& box = ToLayoutBox(object);
       auto* scrollable_area = box.GetScrollableArea();
       IntSize scroll_offset = box.ScrolledContentOffset();
-      if (scroll_node_needed_for_main_thread_reasons ||
-          !scroll_offset.IsZero() || scrollable_area->ScrollsOverflow()) {
+      if (!scroll_offset.IsZero() || scrollable_area->ScrollsOverflow()) {
         needs_scroll_properties = true;
         auto& properties =
             object.GetMutableForPainting().EnsurePaintProperties();
 
         IntSize scroll_clip = scrollable_area->VisibleContentRect().Size();
         IntSize scroll_bounds = scrollable_area->ContentsSize();
         bool user_scrollable_horizontal =
             scrollable_area->UserInputScrollable(kHorizontalScrollbar);
         bool user_scrollable_vertical =
             scrollable_area->UserInputScrollable(kVerticalScrollbar);
@@ skipping 257 matching lines @@
   UpdateOverflowClip(object, context);
   UpdatePerspective(object, context);
   UpdateSvgLocalToBorderBoxTransform(object, context);
   UpdateScrollAndScrollTranslation(object, context);
   UpdateOutOfFlowContext(object, context);
 
   context.force_subtree_update |= object.SubtreeNeedsPaintPropertyUpdate();
 }
 
 }  // namespace blink