A number of WPT tests leak, as indicated by the leak-threshold and lsan-allowed fields in the ini files. We should fix these leaks and remove the whitelists.

James, when you were initially generating these whitelists, how did you account for intermittents? It seems like some of the leaks might not be present any more, but maybe I just need to retrigger the tests more. I did this try run with the LSan whitelists hackily disabled: https://treeherder.mozilla.org/#/jobs?repo=try&revision=8316377451d2eb7a5fc768521eceaa5badcae1f9

Mostly by doing multiple tryruns and keeping adding to the list until they passed reliably. So yes, there's a difficulty distinguishing between something that was fixed and something that's an infrequent intermittent.