Some service extensions, such as the one that enables the performance
overlay, are enabled.

Tracing is enabled, and tools supporting source-level debugging
(such as DevTools) can connect to the process.

Profile mode for a web app means that:

The build is not minified but tree shaking has been performed.

The app is compiled with the dart2js compiler.

DevTools can’t connect to a Flutter web app running
in profile mode. Use Chrome DevTools to
generate timeline events for a web app.

Your IDE supports this mode. Android Studio, for example,
provides a Run > Profile… menu option.
The command flutter run --profile compiles to profile mode.

Note:
  Use the DevTools suite to profile your app’s performance.

For more information on the build modes, see
Flutter’s build modes.