Add "threaded scrolling disabled" main thread scrolling reason [spv2]

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

Index: third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.cpp b/third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.cpp
index 845feea8a627810653cb95f2e49a9ce2f57007a0..98d62c8c2fa164070698f109a86f51b53d277f0e 100644
--- a/third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.cpp
@@ -335,6 +335,9 @@ void PaintPropertyTreeBuilder::updateScrollbarPaintOffset(const LayoutObject& ob
 
 void PaintPropertyTreeBuilder::updateMainThreadScrollingReasons(const LayoutObject& object, PaintPropertyTreeBuilderContext& context)
 {
+    if (context.current.scroll && !object.document().settings()->threadedScrollingEnabled())
+        context.current.scroll->addMainThreadScrollingReasons(MainThreadScrollingReason::kThreadedScrollingDisabled);
+
     if (object.isBackgroundAttachmentFixedObject()) {
         auto* scrollNode = context.current.scroll;
         while (scrollNode && !scrollNode->hasMainThreadScrollingReasons(MainThreadScrollingReason::kHasBackgroundAttachmentFixedObjects)) {