Add an initializer which can compare and re-initialize value

I would like to have a new class which is similar to AtomicSafeInitializer. But we can compare and re-initialize the value.

The use case is to refresh access token (e.g. OAuth) when it expires. Multiple threads tries to refresh the same token at the same time, but there should be only one thread to do it, in addition, only the thread which passes the expired token can trigger the initialization.