Summary:
This introduces a new binary and library that (microwave: it makes warmup
faster..!) that can be used to accelerate cache warmup. The idea is the
microwave binary will run cache warmup and capture things that are loaded
during cache warmup, and commit those to a file.
We can then use that file when starting up a host to get a head start on cache
warmup by injecting all those entries into our local cache before actually
starting cache warmup.
Currently, this only supports filenodes, but that's already a pretty good
improvement. Changesets should be easy to add as well. Blobs might require a
bit more work.
Reviewed By: StanislavGlebik
Differential Revision: D20219905
fbshipit-source-id: 82bb13ca487f82ca53b4a68a90ac5893895a96e9