Record non-stacking-context as main thread scrolling reasons

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

Index: third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp b/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
index ce48c55fb9b17b064537b3b24b6160eee2b6f83b..317ac5b21f03c3f0a0f1e89391310647d1486d68 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
@@ -1852,6 +1852,10 @@ bool PaintLayerScrollableArea::ComputeNeedsCompositedScrolling(
       non_composited_main_thread_scrolling_reasons_ |=
           MainThreadScrollingReason::kBackgroundNotOpaqueInRectAndLCDText;
     }
+    if (!layer->GetLayoutObject().Style()->IsStackingContext()) {
+      non_composited_main_thread_scrolling_reasons_ |=
+          MainThreadScrollingReason::kIsNotStackingContextAndLCDText;
+    }
 
     needs_composited_scrolling = false;
   }