Bug 1595767 - Don't use rayon for glyph rasterization unless there is…
6fb9178
… a lot of glyphs to rasterize r=nical Differential Revision: https://phabricator.services.mozilla.com/D57005 [wrupdater] From https://hg.mozilla.org/mozilla-central/rev/29584a35d69ae2c8bb157702be402733fc0ce176
