Aura Overlay Scrollbars appear when mouse hovers over scroller edge

ui/native_theme/overlay_scrollbar_constants_aura.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_NATIVE_THEME_OVERLAY_SCROLLBAR_CONSTANTS_AURA_H_
 #define UI_NATIVE_THEME_OVERLAY_SCROLLBAR_CONSTANTS_AURA_H_
 
 #include "base/time/time.h"
 #include "ui/gfx/skia_util.h"
 
 namespace ui {
 
 constexpr int kOverlayScrollbarThumbWidthNormal = 6;
 constexpr int kOverlayScrollbarThumbWidthHovered = 10;
 constexpr int kOverlayScrollbarThumbWidthPressed = 10;
 
+// kOverlayScrollbarShowDelay is only for the case where the mouse hovers near
+// the screen edge.
+constexpr base::TimeDelta kOverlayScrollbarShowDelay =
+    base::TimeDelta::FromMilliseconds(1000);
 constexpr base::TimeDelta kOverlayScrollbarFadeOutDelay =
     base::TimeDelta::FromMilliseconds(1000);
 constexpr base::TimeDelta kOverlayScrollbarFadeOutDuration =
     base::TimeDelta::FromMilliseconds(200);
 // TODO(bokan): This is still undetermined. crbug.com/652520.
 constexpr base::TimeDelta kOverlayScrollbarThinningDuration =
     base::TimeDelta::FromMilliseconds(200);
 
-} // namespace ui
+}  // namespace ui
 
-#endif // UI_NATIVE_THEME_OVERLAY_SCROLLBAR_CONSTANTS_AURA_H_
+#endif  // UI_NATIVE_THEME_OVERLAY_SCROLLBAR_CONSTANTS_AURA_H_