Unless the extensions include these icons already, we'll have to reach out to all first-party extension owners.

Chary, do we have a process for first-party owners specifically?

Ah, I originally meant this one http://screen/RSMHrq4aUzc , though it'd be nice to have 1st party material design icons where missing.

Also, the screenshot #0 was confusing, Gmail does have icon (This was fake one made by me; sorry for that).

Ohh sorry :) Yeah that's a much more straightforward change!

I don't believe we have an official Gmail extension (https://chrome.google.com/webstore/search/gmail?_category=extensions). If you provide the extension Ids missing high quality icons I can contact the owner to update their extensions if the extension is an official one, i.e. marked as by Google.