std::chrono methods used by std::condition_variable.
A followup change will add an implemention of
synchronization_internal::Waiter that can use
std:mutex/std::condition_variable to implement the per-thread
semaphore that absl::Mutex waits on. This implementation may at some
point become the default on platforms such as Windows where there
doesn't seem to be an easy way of supporting real absolute timeouts. In
this case we can defer to their standard library to implement correct
support.
PiperOrigin-RevId: 510204786
Change-Id: Icf4d695013fd060abbd53dae23e71ea36f731565
