I still don't understand. When I log into gmail, it logs me into all Google services. If I am worried about being tracked, surely my first mistake is logging in in the first place? Or visiting in the first place? After all, even if I click "log out," I'm only trusting Google that they unlinked the browser state from the account. If I trust them to do that, I don't see why I shouldn't trust them to ignore this experiment flag from Chrome, or at least not use it for tracking. If I don't trust them to avoid using the experiment state, I don't really see how you can trust them for anything.

Anyway, if you're not building Chrome from source, then you have to trust that they aren't putting anything bad in it. And if you are building chrome from source, you can observe that they only send this experiment ID to certain domains, and they already know who you are on those domains anyway.