Add test coverage

Hahah sorry @smustgrave I mean the other way around for the tag. Having one for the navigation will make things easier :D

Adding the "Drupal CMS release target" to see if we could hopefully get to it.

I've never written a performance test before, so please, any feedback is welcome. I assumed what was meant by "performance test" was \Drupal\FunctionalJavascriptTests\PerformanceTestBase (see change record → ).

The tests I've added will first get the home page to warm caches. Then delete caches and get the home page again, this time collecting performance data. We then install navigation_top_bar and repeat the process, comparing performance data before and after, expecting that we get the same numbers, eg. navigation_top_bar does not impact performance. If top bar was mistakenly included for anonymous users, as was the case before the parent bug ticket was fixed, we'd see additional cache get/set after navigation_top_bar was enabled.

At least that is what I think I did 😅. My work was inspired by \Drupal\Tests\standard\FunctionalJavascript\StandardPerformanceTest. There wasn't any precedent that I could find in core for comparing before/after performance data like I'm doing here though.

Left some comments/questions on the MR

nice work!

Addressed comments. Ready for review again.

Feedback appears to be addressed.