This code may have worked when written in 2009, but later gjs commit
b5e467d89aea43a8e32a1138d232c8a32e6b0785 removed the priority
parameter from idle_add.
Now, when running a constantly-updating client (es2gears) on an
embedded platform, _updateRegions() does not get called and I see
unresponsive window decorations.
Update the code to use meta_later_add() like other parts of the
shell, which is actually slightly better in this case anyway.
Solves the unresponsiveness problem.
https://bugzilla.gnome.org/show_bug.cgi?id=585500
29485ff24b