Provide a default GTlsDatabase implementation
It would be handy if GCR provided a GTlsDatabase implementation that applications could use with GIO's TLS support, so once a cert was pinned via GCR then GTlsConnections using this db impl would automatically pick that up. This would provide a very low-barrier-to-entry means of using GCR for pinning certs.
I'm looking at providing a custom GTlsDatabase for Geary that does just this, and if that works fine, it could provide a basis for this.