anchor elements gatherer slowed down

[paulirish]

#16292 and #16526 recently landed

and I see slowdown in LR starting in july. 95pctl timing of the gatherer went from 1267ms to 9941ms.

I suspect its this loop

https://github.com/GoogleChrome/lighthouse/pull/16292/files#diff-7642dfbc6c215e89a0e480c8d865d4b1522178ac8af9140a92766549c7db09d3R167-R177

it's a lot of DOMDebugger.getEventListeners calls.

[connorjclark]

Do you have a suggestion on how to re-work that commit? Or should we just revert it?