A version of the patch in bug 1895870 caused some WPT tests to time out
because document.fonts.ready never resolves.
This is because I made PresShell::HasPendingReflow look at
mNeedLayoutFlush, and nsIFrame::SchedulePaint() calls
PresShell::ScheduleViewManagerFlush() which sets that bit.
So we end up with mNeedLayoutFlush, but without a flush scheduled, and
the ready promise doesn't resolve until something else schedules a
flush. I fixed the original patch to preserve behavior, but requesting a
repaint shouldn't require a layout flush.
This call was added in bug 598482 part 16:
https://hg.mozilla.org/mozilla-central/rev/71d77495b606fc145bdceabcda29181978bd9405
We only need the layout flush if there are view geometry updates, so
shift the call up to the view manager.
Differential Revision: https://phabricator.services.mozilla.com/D209938
3abe531738