Push owner onto the mounted engine's owner stack for the duration of
fn, so a manual getEngine().boundKeyboard(...) (or any owner-scoped
call) is attributed to that layer/page. The owner is popped in a finally
so a throw inside fn cannot strand it on the stack.
Push
owneronto the mounted engine's owner stack for the duration offn, so a manualgetEngine().boundKeyboard(...)(or any owner-scoped call) is attributed to that layer/page. The owner is popped in afinallyso a throw insidefncannot strand it on the stack.