[CrendKing]

Bob's browsing history is synced, but to Alice's history

I agree with you that this would upset Alice when she wants to check her personal browsing history. But isn't that the innate consequence of sharing your own computer with other persons? It is the same as Alice lending her MacBook to Bob without logging out herself first. Can't Alice simply log out her Chrome before giving to Bob?

Bob logging in to Gmail on Alice's computer will log out of Alice on Chrome, and log in to Bob

Why should Gmail (or any Google service) be so special? If Bob log in to his Outlook account, shouldn't the same treatment happen (which clearly indicate a persona switch)? It is clear that Google is using its monopoly power between Google services and Chrome to reinforce the bond between "average users" and itself. Imagine if Chrome dwindles at ~10% market share instead. Do you ever think the Chrome team would have done this feature?