well, anti-trust these days is just a buzzword, in a legal sense it is defined in a very strict way, and the cost for companies to anticipate an anti-trust ruling is way higher than just pushing their own interests.
With 66% market share and countless other browsers available, the only question for antitrust when it comes to browsers is if users have equal access to browsers, not whether google supports ad blocking.
I think they will make sure that the ad blocking capability does not explicicly favor google ads.