Bug 1686729 - flip source rect instead of dest. r=mattwoodrow
Bug 1686729 - flip source rect instead of dest. r=mattwoodrow

Differential Revision: https://phabricator.services.mozilla.com/D102513

[ghsync] From https://hg.mozilla.org/mozilla-central/rev/82fdc5a13aa2bb910c026e484c1e0cb75802f0e5

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