Bug
1865610: part 7) Add test for internally assigned priority of font-face loaded from `<head>`. r=jfkthame
Tests existing behavior. It differs from Chromium's, which assigns
highest priority instead of high.
The test is added for the fetchpriority feature because loading a
font-face font has overlapping code with linking fonts via `<link
rel=preload as=font>` in `FontPreloader`
(https://searchfox.org/mozilla-central/rev/
d6576544301cacc0e393fbc919c53e4e6b0d46ec/layout/style/FontPreloader.h#25).
I checked that no other tests already test this.
Daniel: see parts 8 and 9 too.
Differential Revision: https://phabricator.services.mozilla.com/
D193550