Replace hide-scrollbars flag with a web setting.

ui/native_theme/native_theme_switches.cc

Index: ui/native_theme/native_theme_switches.cc
diff --git a/ui/native_theme/native_theme_switches.cc b/ui/native_theme/native_theme_switches.cc
index 4249fc5b054ac733491b0db4387faa70aa21a00f..873af518985c1dc6226256118424e2a6493dd086 100644
--- a/ui/native_theme/native_theme_switches.cc
+++ b/ui/native_theme/native_theme_switches.cc
@@ -13,10 +13,6 @@ const char kEnableOverlayScrollbar[] = "enable-overlay-scrollbar";
 // Disables overlay scrollbars on Aura or Linux. Does nothing on Mac.
 const char kDisableOverlayScrollbar[] = "disable-overlay-scrollbar";
 
-// Hides scrollbars on Aura, Linux, Android, ChromeOS, MacOS (MacOS
-// support is experimental).
-const char kHideScrollbars[] = "hide-scrollbars";
-
 }  // namespace switches
 
 namespace ui {
@@ -25,10 +21,6 @@ bool IsOverlayScrollbarEnabled() {
   const base::CommandLine& command_line =
       *base::CommandLine::ForCurrentProcess();
 
-  // Hidden scrollbars are realized through never-showing overlay scrollbars.
-  if (ShouldHideScrollbars())
-    return true;
-
   if (command_line.HasSwitch(switches::kDisableOverlayScrollbar))
     return false;
   else if (command_line.HasSwitch(switches::kEnableOverlayScrollbar))
@@ -37,10 +29,4 @@ bool IsOverlayScrollbarEnabled() {
   return false;
 }
 
-bool ShouldHideScrollbars() {
-  const base::CommandLine& command_line =
-      *base::CommandLine::ForCurrentProcess();
-  return command_line.HasSwitch(switches::kHideScrollbars);
-}
-
 }  // namespace ui