Jürg Billeter authored Mar 13, 2019 and bst-marge-bot committed Mar 27, 2019

If any blobs required for the action are missing both on the remote
execution CAS server and in the local cache, attempt to fetch these
blobs from the configured artifact servers.

Artifacts are currently still guaranteed to be complete in the local
cache. However, this is in preparation for the planned partial CAS
support.