Incrementally build main thread scrolling reasons [spv2]

third_party/WebKit/Source/core/layout/LayoutObject.h

Index: third_party/WebKit/Source/core/layout/LayoutObject.h
diff --git a/third_party/WebKit/Source/core/layout/LayoutObject.h b/third_party/WebKit/Source/core/layout/LayoutObject.h
index c4bc1dcd7bdf96640eb76f6ad202c34f5e0d966b..d34b4948f6ab3b2b91d2d83d373345d4485ad38d 100644
--- a/third_party/WebKit/Source/core/layout/LayoutObject.h
+++ b/third_party/WebKit/Source/core/layout/LayoutObject.h
@@ -1743,6 +1743,12 @@ class CORE_EXPORT LayoutObject : public ImageResourceObserver,
   void setNeedsPaintPropertyUpdate() {
     m_bitfields.setNeedsPaintPropertyUpdate(true);
   }
+  void setAllAncestorsNeedPaintPropertyUpdate() {
+    if (m_parent && !m_parent->needsPaintPropertyUpdate()) {
+      m_parent->setNeedsPaintPropertyUpdate();
+      m_parent->setAllAncestorsNeedPaintPropertyUpdate();
+    }
+  }
   void clearNeedsPaintPropertyUpdate() {
     DCHECK_EQ(document().lifecycle().state(), DocumentLifecycle::InPrePaint);
     m_bitfields.setNeedsPaintPropertyUpdate(false);