Enable overlay scrollbars on ChromeOS

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 873af518985c1dc6226256118424e2a6493dd086..98a67ccd9e2f0d4c0fdcfcc821e6a7b9b0f6415d 100644
--- a/ui/native_theme/native_theme_switches.cc
+++ b/ui/native_theme/native_theme_switches.cc
@@ -23,10 +23,12 @@ bool IsOverlayScrollbarEnabled() {
 
   if (command_line.HasSwitch(switches::kDisableOverlayScrollbar))
     return false;
-  else if (command_line.HasSwitch(switches::kEnableOverlayScrollbar))
-    return true;
 
-  return false;
+#if defined(OS_CHROMEOS)
+  return true;
+#else
+  return command_line.HasSwitch(switches::kEnableOverlayScrollbar);
+#endif
 }
 
 }  // namespace ui