How would the regulator know when you break the rules though?

I may very well be misunderstanding the idea here, but it still seems like it would come down to (for example) Microsoft being required to limit how they send user notifications/recommendations based on Microsoft's own internal analytics for user metrics.

For the Chrome example, the regulator would have to know how Google's proprietary ad targeting algorithm works to confirm that it doesn't target based on user agent or browser manufacturer. I'm not sure how the regulators would really be able to pull that off any better than regulators asking VW software for VW diesel emissions measurements.