Hiding in the rest room - a movie query

Does anyone have any idea when the scene where someone hides in a public rest room and overhears or witnesses some important information (Eddie Murphy in Trading Places) or is hiding from someone looking for them (the kid in Witness) was first used in cinema? Google isn't much use in this respect.

Probably dates back to

http://www.citecinema.com/Les-Grands-Films/Les-Annes-1985-A-1929/Les-Vampires.jpg

if not decades prior.