Getting a list of triaged bugs for prioritization

[foolip]

Once a directory is fairly well triaged, a natural next step is to look at the resulting list of bugs and see which ones contribute to the most failures, which bugs are actually closed without the test being fixed, etc.

I don't know of any existing code to do this, so I threw together something awful in #589 which did the trick once, I have a spreadsheet of bugs after some manual processing.

Perhaps this would make sense in the "team view" of wpt.fyi that's been brainstormed?

[foolip]

@stephenmcgruer

[foolip]

Around the same time I filed this issue I also wrote a script in https://github.com/web-platform-tests/wpt-metadata/tree/bug-list

cc @KyleJu

[foolip]

That script is now in #1762.