Call ScrollableArea::ShowOverlayScrollbars for explicit scrolls only.

third_party/WebKit/Source/core/frame/FrameView.cpp

Index: third_party/WebKit/Source/core/frame/FrameView.cpp
diff --git a/third_party/WebKit/Source/core/frame/FrameView.cpp b/third_party/WebKit/Source/core/frame/FrameView.cpp
index e41edc420a9a91faa21a6bc6fb62b7d55dd24940..9ff924298d18d1da1576dc6575c0a991110cc341 100644
--- a/third_party/WebKit/Source/core/frame/FrameView.cpp
+++ b/third_party/WebKit/Source/core/frame/FrameView.cpp
@@ -4098,8 +4098,6 @@ void FrameView::UpdateScrollOffset(const ScrollOffset& offset,
   if (scroll_delta.IsZero())
     return;
 
-  ShowOverlayScrollbars();
-
   if (RuntimeEnabledFeatures::rootLayerScrollingEnabled()) {
     // Don't scroll the FrameView!
     ASSERT_NOT_REACHED();
@@ -4144,6 +4142,8 @@ void FrameView::UpdateScrollOffset(const ScrollOffset& offset,
   }
 
   if (IsExplicitScrollType(scroll_type)) {
+    if (scroll_type != kCompositorScroll)
+      ShowOverlayScrollbars();
     ClearFragmentAnchor();
     ClearScrollAnchor();
   }