Convert the overlay scrollbar flag to use FeatureList

ui/native_theme/native_theme_features.h

Index: ui/native_theme/native_theme_features.h
diff --git a/ui/native_theme/native_theme_switches.h b/ui/native_theme/native_theme_features.h
similarity index 61%
rename from ui/native_theme/native_theme_switches.h
rename to ui/native_theme/native_theme_features.h
index 026ee70eca378be31944d0b8c56fd8d6d96583fc..265d7e5ea79105fa954dade2f6226345d4b9522d 100644
--- a/ui/native_theme/native_theme_switches.h
+++ b/ui/native_theme/native_theme_features.h
@@ -4,17 +4,17 @@
 
 // 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_
+#ifndef UI_NATIVE_THEME_NATIVE_THEME_FEATURES_H_
+#define UI_NATIVE_THEME_NATIVE_THEME_FEATURES_H_
 
+#include "base/feature_list.h"
 #include "ui/native_theme/native_theme_export.h"
 
-namespace switches {
+namespace features {
 
-NATIVE_THEME_EXPORT extern const char kDisableOverlayScrollbar[];
-NATIVE_THEME_EXPORT extern const char kEnableOverlayScrollbar[];
+NATIVE_THEME_EXPORT extern const base::Feature kOverlayScrollbar;
 
-}  // namespace switches
+}  // namespace features
 
 namespace ui {