When we first added ESLint, we added a few directories to the ignore list because it helped ESLint's performance.

I believe at some stage along the way, ESLint improved their indexing performance. Regardless, "including" these directories no longer gives any noticeable performance hit on my machine, so I think we should just include these.

It also will help prevent files sneaking into those directories that should be linted.

Due to these removals, ESLint is now enabled for build/pgo/index.html, so I'm adding a few extra fix ups to make that pass. I've not changed the formatting, since that will hopefully be done with prettier soon.

I'm also pulling the dom lines to the top of the file, since these are the only remaining general exclusions that we're still working on.

I relanded changeset 0d2958471c08 as it was suspected of being the culprit for spidermonkey builds seen here and was mistakenly backed out: https://treeherder.mozilla.org/#/jobs?repo=autoland&resultStatus=testfailed%2Cbusted%2Cexception&selectedJob=249340237&revision=0d2958471c0885b7acdfbeba557b109f1b403da4&searchStr=spidermonkey%2Cdebug

Backout link: https://hg.mozilla.org/integration/autoland/rev/75d012801085b30e79b36ea311755d28ef12b7c8

Reland link: https://hg.mozilla.org/integration/autoland/rev/81b92cef1e230f068da17311b02f0567634907a5

https://hg.mozilla.org/mozilla-central/rev/81b92cef1e23