base::lambda -> Fn (type alias for std::function).
base::lambda_once -> FnMut (type alias for base::unique_function).
base::lambda_guarded -> crl::guard.
base::lambda_call_type_t -> crl::deduced_call_type.
That way audio files and voice/video messages will play in context
(one after another with ability to go to next or previous in player)
almost always, no matter at what part of message history we are.
John Preston