This implements an API in `nsIOSKeyStore.idl` and `OSKeyStore.cpp` to encrypt and decrypt bytes with a key that is stored in the OS key store.
There are two OS adapters in this patch.
Libsecret is used on Linux if available.
The NSS key store is used as fallback if no OS specific key store is implemented.
Differential Revision: https://phabricator.services.mozilla.com/D1858
--HG--
extra : rebase_source : 99d7d646968a46a13ffa61885bb246f6d3e443e4