Bug 1060118 - Notifications tray cutoff on landscape

Updating notifications tray size when a 'resize' event is received and the tray is already shown
I think rather than adding this validateCachedSizes here, it'd just make sense to leave the original one in ut_show and remove this one. We end up calling validateCachedSizes twice on resize events with this code, and while the second time (probably) won't do anything, this seems a bit unnecessary.