Bug 1717986 - Fix raster scale update being one frame late r=gfx-reviewers,lsalzman
Bug 1717986 - Fix raster scale update being one frame late r=gfx-reviewers,lsalzman

Updating raster_scale in post_update can mean that it is
updated one frame too late. This can cause reftest failures
in tests that set the scale factor (without an APZ) and then
capture that frame.

Differential Revision: https://phabricator.services.mozilla.com/D118672

[ghsync] From https://hg.mozilla.org/mozilla-central/rev/51f6d331327a74a8496e68aec63b58ac0b5debf9

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