This directory contains the Prio source from the upstream repo:
https://github.com/mozilla/libprio

Current version: 1.6 [commit 52643cefe6662b4099e16a40a057cb60651ab001]

UPDATING:

Our in-tree copy of Prio does not depend on any generated files from the
upstream build system. Therefore, it should be sufficient to simply overwrite
the in-tree files one the updated ones from upstream to perform updates.

To simplify this, the in-tree copy can be updated by running
  sh update.sh
from within the third_party/libprio directory.

If the collection of source files changes, manual updates to moz.build may be
needed as we don't use the upstream makefiles.