Record non-stacking-context as main thread scrolling reasons

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

Index: third_party/WebKit/Source/core/paint/PaintLayer.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintLayer.cpp b/third_party/WebKit/Source/core/paint/PaintLayer.cpp
index b48cb92fc906ca757a3f832821d809efc31bf978..81cca336987e4571b6f9bc0cc19784e246b8cdd8 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayer.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayer.cpp
@@ -2779,8 +2779,8 @@ bool PaintLayer::CompositesWithOpacity() const {
   return OpacityAncestor() || GetLayoutObject().Style()->HasOpacity();
 }
 
-bool PaintLayer::BackgroundIsKnownToBeOpaqueInRect(
-    const LayoutRect& local_rect) const {
+bool PaintLayer::BackgroundIsKnownToBeOpaqueInRect(const LayoutRect& local_rect,
+                                                   uint32_t* reasons) const {
   if (PaintsWithTransparency(kGlobalPaintNormalPhase))
     return false;
 
@@ -2818,8 +2818,11 @@ bool PaintLayer::BackgroundIsKnownToBeOpaqueInRect(
 
   // We can't consult child layers if we clip, since they might cover
   // parts of the rect that are clipped out.
-  if (GetLayoutObject().HasClipRelatedProperty())
+  if (GetLayoutObject().HasClipRelatedProperty()) {
+    if (reasons && GetLayoutObject().HasOverflowClip())
+      *reasons |= MainThreadScrollingReason::kHasOverflowClipAndLCDText;
     return false;
+  }
 
   // TODO(schenney): This could be improved by unioning the opaque regions of
   // all the children.  That would require a refactoring because currently