Call ScrollableArea::ShowOverlayScrollbars for explicit scrolls only.

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 d1dbb2c358809d9d3ad9edc53de629e98dcb24ab..89ca451fd2736d1b601190de7bccd0cedf59aba3 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
@@ -372,7 +372,6 @@ void PaintLayerScrollableArea::UpdateScrollOffset(
   if (GetScrollOffset() == new_offset)
     return;
 
-  ShowOverlayScrollbars();
   scroll_offset_ = new_offset;
 
   LocalFrame* frame = Box().GetFrame();
@@ -472,6 +471,8 @@ void PaintLayerScrollableArea::UpdateScrollOffset(
   }
 
   if (IsExplicitScrollType(scroll_type)) {
+    if (scroll_type != kCompositorScroll)
+      ShowOverlayScrollbars();
     frame_view->ClearFragmentAnchor();
     if (RuntimeEnabledFeatures::scrollAnchoringEnabled())
       GetScrollAnchor()->Clear();