Summary:
We have seen that eden will unexpectedly fetch data, we want to know why.
This adds the plumbing to interact with edens current logging to be able to
log when eden fetches data from the server and what caused eden to do this
fetch. Later changes will use the classes created here to log the cause of data
fetches.
Reviewed By: chadaustin
Differential Revision: D22051013
fbshipit-source-id: 27d377d7057e66f3e7a304cd7004f8aa44f8ba62
8d32611a23