Steps to reproduce:

1. In unity-greeter, launch Orca
2. Attempt to use flat review
3. Attempt to log in

Expected results: 2 would work and the objects associated with 3 would be presented.

Actual results: 2 seems to fail and nothing is presented during 3.

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It turns out that unity-greeter, which lacks a window manager, stops emitting accessible events when some other window claims and then gives up focus. See:
https://bugs.launchpad.net/unity-greeter/+bug/971926

The above is relevant because Orca's flat review outline is a GtkWindow. So a reasonable workaround would be to just not draw the flat review outline if we don't have a window manager. (Flat review will then work, just no red underline while in unity-greeter.)

We can get the window manager name via GdkX11.X11Screen -- if we tiptoe carefully around https://bugzilla.gnome.org/show_bug.cgi?id=673396.