Convert the overlay scrollbar flag to use FeatureList

ui/native_theme/native_theme_switches.h

Index: ui/native_theme/native_theme_switches.h
diff --git a/ui/native_theme/native_theme_switches.h b/ui/native_theme/native_theme_switches.h
deleted file mode 100644
index 026ee70eca378be31944d0b8c56fd8d6d96583fc..0000000000000000000000000000000000000000
--- a/ui/native_theme/native_theme_switches.h
+++ /dev/null
@@ -1,25 +0,0 @@
-// Copyright 2014 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.
-
-// Defines all the command-line switches used by native theme
-
-#ifndef UI_NATIVE_THEME_NATIVE_THEME_SWITCHES_H_
-#define UI_NATIVE_THEME_NATIVE_THEME_SWITCHES_H_
-
-#include "ui/native_theme/native_theme_export.h"
-
-namespace switches {
-
-NATIVE_THEME_EXPORT extern const char kDisableOverlayScrollbar[];
-NATIVE_THEME_EXPORT extern const char kEnableOverlayScrollbar[];
-
-}  // namespace switches
-
-namespace ui {
-
-NATIVE_THEME_EXPORT bool IsOverlayScrollbarEnabled();
-
-}  // namespace ui
-
-#endif  // UI_NATIVE_THEME_NATIVE_THEME_SWITCHES_H_