In order to ensure that execution-time dependencies are met, we need to load `timer.js` before `timer_panel.js` and `stopwatch.js` before `stopwatch_panel.js`. Since `timer.js` and `stopwatch.js` are not interrelated, they may be loaded concurrently (i.e. in the same phase). The same goes for `timer_panel.js` and `stopwatch_panel.js`.