Call ScrollableArea::ShowOverlayScrollbars for explicit scrolls only.

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

 /*
  * Copyright (C) 1998, 1999 Torben Weis <weis@kde.org>
  *                     1999 Lars Knoll <knoll@kde.org>
  *                     1999 Antti Koivisto <koivisto@kde.org>
  *                     2000 Dirk Mueller <mueller@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  *           (C) 2006 Graham Dennis (graham.dennis@gmail.com)
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
@@ skipping 4080 matching lines @@
 
   return scrollbar->TotalSize() - scrollbar->VisibleSize();
 }
 
 void FrameView::UpdateScrollOffset(const ScrollOffset& offset,
                                    ScrollType scroll_type) {
   ScrollOffset scroll_delta = offset - scroll_offset_;
   if (scroll_delta.IsZero())
     return;
 
-  ShowOverlayScrollbars();
-
   if (RuntimeEnabledFeatures::rootLayerScrollingEnabled()) {
     // Don't scroll the FrameView!
     ASSERT_NOT_REACHED();
   }
 
   scroll_offset_ = offset;
 
   if (!ScrollbarsSuppressed())
     pending_scroll_delta_ += scroll_delta;
 
@@ skipping 24 matching lines @@
 
   GetFrame().Loader().SaveScrollState();
   DidChangeScrollOffset();
 
   if (scroll_type == kCompositorScroll && frame_->IsMainFrame()) {
     if (DocumentLoader* document_loader = frame_->Loader().GetDocumentLoader())
       document_loader->GetInitialScrollState().was_scrolled_by_user = true;
   }
 
   if (IsExplicitScrollType(scroll_type)) {
+    if (scroll_type != kCompositorScroll)
+      ShowOverlayScrollbars();
     ClearFragmentAnchor();
     ClearScrollAnchor();
   }
 }
 
 void FrameView::DidChangeScrollOffset() {
   GetFrame().Loader().Client()->DidChangeScrollOffset();
   if (GetFrame().IsMainFrame())
     GetFrame().GetPage()->GetChromeClient().MainFrameScrollOffsetChanged();
 }
@@ skipping 1217 matching lines @@
 void FrameView::SetAnimationHost(
     std::unique_ptr<CompositorAnimationHost> host) {
   animation_host_ = std::move(host);
 }
 
 LayoutUnit FrameView::CaretWidth() const {
   return LayoutUnit(GetChromeClient()->WindowToViewportScalar(1));
 }
 
 }  // namespace blink