Dan Winship authored Apr 26, 2011 and Jasper St. Pierre committed May 22, 2013

Mutter previously defined display->focus_window as the window that the
server says is focused, but kept display->expected_focus_window to
indicate the window that we have requested to be focused. But it turns
out that "expected_focus_window" was almost always what we wanted.

Make MetaDisplay do a better job of tracking focus-related requests
and events, and change display->focus_window to be our best guess of
the "currently" focused window (ie, the window that will be focused at
the time when the server processes the next request we send it).

https://bugzilla.gnome.org/show_bug.cgi?id=647706