Created attachment 245410 [details] [review]
messageTray: Fix lightbox outside the overview

Commit d0310bd745968 blindly replaced global.overlay_group with
Main.layout.overviewGroup, but unlike the former, the latter is
hidden while the overview is not active, which makes it unsuitable
for the message tray's light box. In fact, with the removal of
global.overlay_group, there is no longer a container which may
be used both inside and outside the overview, so we can either
recreate the lightbox each time we show/hide the overview, or
use different lightboxes altogether; this opts for the latter.

Review of attachment 245410 [details] [review]:

+

::: js/ui/messageTray.js
@@ +1661,3 @@
+        this._lightboxes = [];
+        let lightboxContainers = [global.window_group,
+                                  Main.layoutManager.overviewGroup];

Since only one lightbox can be visible at once, it might be better if  the code only created on lightbox and just moved it around as necessary, but there's something to be said for keeping things straightforward like you have here, too.  Your way seems less likely to go wrong during transitions.

Attachment 245410 [details] pushed as 365cda3 - messageTray: Fix lightbox outside the overview