Comment 2 for bug 1536815

OK, here's a quick workaround for Xmir to get things going:
https://git.launchpad.net/~xmir-team/xorg-server/+git/xmir/commit/?id=18ee4ec59c1ab47c857205d6abbcdc5881ec2f9b

It's a workaround and not a fix because a proper fix will have to occur in Mir itself. Mir's "system compositor" mode needs to be enhanced to not reject surfaces that don't select and fit a physical display. So this will only work with a single monitor. And it will only work after we figure out this USC issue: bug 1548210

Once Mir gets fixed, the workaround in Xmir should be reverted. And theoretically we could then have multi-monitor Xmir inside Mir.