…ack clippy lints. r=Gankro

I don't think it makes much of a difference but clippy is quite vocal about it.

Differential Revision: https://phabricator.services.mozilla.com/D59114

[ghsync] From https://hg.mozilla.org/mozilla-central/rev/d70cc2bb33f62aab04ee8a5ae5a086bcee5ab974