Turns on a little "DEBUG" banner in debug mode to indicate that the app is in debug mode. This is on by default (in debug mode), to turn it off, set the constructor argument to false. In release mode this has no effect.
To get this banner in your application if you're not using WidgetsApp, include a CheckedModeBanner widget in your app.
This banner is intended to deter people from complaining that your app is slow when it's in debug mode. In debug mode, Flutter enables a large number of expensive diagnostics to aid in development, and so performance in debug mode is not representative of what will happen in release mode.
final bool debugShowCheckedModeBanner;