Bug 1754350 - Fix mix-blend mode readbacks on fractional device pixel boundaries r=gfx-reviewers,bradwerth
Bug 1754350 - Fix mix-blend mode readbacks on fractional device pixel boundaries r=gfx-reviewers,bradwerth

Differential Revision: https://phabricator.services.mozilla.com/D138253

[ghsync] From https://hg.mozilla.org/mozilla-central/rev/c60f4861cfa567808d0c80213da0e068f4b6968d

servo/webrender,servo/webrender,servo/webrender,servo/webrender,servo/webrender,servo/webrender