0. Run dart --observe log.dart
1. Visit main isolate's logging page.
2. You should see 'INFO MESSAGE' and 'FINE MESSAGE'.
3. Adjust the level to be 'INFO' and see that 'FINE' messages are hidden.
4. Adjust the level to be 'FINE' and see that all messages are displayed.
5. Adjust the level to be 'SHOUT' and see that no messages are displayed.