Summary:Add a new method to MPMCQueue:
```
template <class Clock, typename... Args>
  bool tryWriteUntil(const std::chrono::time_point<Clock>& when,
                     Args&&... args) noexcept
```
This allows you to write producers which terminate reliably in the absence of consumers.

Returns `true` if `args` was enqueued, `false` otherwise.

`Clock` must be one of the types supported by the underlying call to `folly::detail::Futex::futexWaitUntil`; at time of writing these are `std::chrono::steady_clock` and `std::chrono::system_clock`.

Reviewed By: nbronson

Differential Revision: D2895574

fb-gh-sync-id: bdfabcd043191c149f1271e30ffc28476cc8a36e
shipit-source-id: bdfabcd043191c149f1271e30ffc28476cc8a36e