Can you give me an example of an ambiguous case? I can't think of any personally.

Well, the URLs I enter in Chrome for example: is that data belonging to me because I entered it, or is it data about me because they track it?

Or even the connections I have on Google+: is it data belonging to me because I entered it?

You're not really handing over URLs to google saying "here are some urls, please keep them", are you? Bookmarks, yes, and you can easily export them.

> Or even the connections I have on Google+: is it data belonging to me because I entered it?

Yes. Google takeout lets you download your G+ circles, if that helps.