I see this too, if I have autofill enabled, and at least one autofill address entry.
I would guess that Chrome is sending a hash of the <form> (perhaps URL + method?), plus a hash of each of the <input> tags, and Google returns some sort of information about what kind of form it is?
If so, it would mean it's pretty easy for Google to determine which sites you're on from the pattern of hashes sent for each site. e.g. I see this data sent in the clear for pretty much every page on https://www.facebook.com/
I would guess that Chrome is sending a hash of the <form> (perhaps URL + method?), plus a hash of each of the <input> tags, and Google returns some sort of information about what kind of form it is?
If so, it would mean it's pretty easy for Google to determine which sites you're on from the pattern of hashes sent for each site. e.g. I see this data sent in the clear for pretty much every page on https://www.facebook.com/