When libwebrtc adds a fieldtrial we automatically ignore it, meaning queries for whether it is enabled return false and queries for whether it is disabled also return false, because we always resort to returning an empty string.

There may be features in libwebrtc that we want to enable through the field trial config. Especially we would want to take a look when new trials are added.

We could assert whenever libwebrtc queries for an unknown key, so we'd catch them on try, and be able to take an informed decision on whether it's a feature we want or not.

This would also give us an overview of all libwebrtc field trial keys, though it may require periodic manual cleanups.