Is it antitrust if you leverage your 50% market share in one area to help your monopoly market share in a different area? Because I wouldn't have thought so, and I don't see any way their ad market share helps them push an ad blocker.
The display advertising market share would allow them to weather the storm of an ad blocker, especially if the ad blocker were designed to be friendlier to their ads versus others. Roll it out with aggressive blocking, wait for competitors to die, then relax the rules.
Or they could use the Android entry point. The EU seems to think they have a monopoly there, which would imply a "mobile browser" monopoly.
