They're importing Safari data, so I'd expect them to copy the credentials to a new item to avoid conflicting with Safari managing that data, and creating a new keychain item with permanent access would be the correct response for 'Always Allow', so isn't it possible that's a mistake that they don't correctly respond to the Allow button? I agree storing the credentials outside keychain is not desirable, but again probably that has to do with cross-platform requirements rather than malice on the part of Google.
Have you reported the bug and asked the Chrome team about it?
In contrast to adwords defaulting to automatic payments and auto-bidding, or tracking users across the web universally over all the google services, or pushing people to use G+ everywhere, this wouldn't really benefit Google would it? I'm sure Google do lots of evil things, but I can't see any upside to them in this, and lots of downside.