text: Title: WARN level missing from the log level selector in log.html
  Body: If you run tests with `--loglevel warn` and tests use `Set Log Level` to change the level to something lower, the log level selector will be shown but the selected option has no value. Clicking the selector allows selecting levels, so this is just a visual UI problem. Running tests with the WARN level is rare, but we could have the level there also otherwise to allow hiding also INFO messages. Implementing this requires only adding `WARN` as one of the possible options in the selector.
  
  The same issue occurs also with the ERROR level. I see even less needs to run tests with the ERROR level than there are needs to use WARN and having WARN is already enough to allow hiding INFO messages. Due to how the log level selector is implemented, this would also require considerably more work. I don't think it's worth the effort.