Initially this looked simple but our webrtc.org identities made it impossible (see bug 729120) so we're going to have to setup or own Gerrit instance and use that instead. This is tracked in bug 738156. This bug tracks the migration over (changes in https://chromium.googlesource.com/external/webrtc/+/master/codereview.settings).

It's reasonably easy to migrate over by changing that file. During the transition you can set 
git config --local gerrit.host true
to have new CLs go to Gerrit instead of Rietveld (but I assume we also need another property in the file to not default to chromium-review.googlesource.com).

Our instance will most likely be hosted at webrtc-review.googlesource.com.