1. Nestle gave Google permission to use the trademark 2. Google is providing advertising for Kit Kat

So I see only two possibilities:

1. Google asked Nestle for permission to use the trademark for no compensation, Nestle agreed, and Google subsequently decided out of the goodness of their heart to advertise the candy bar in a manner that is unprecedented in the history of the company, or

2. Google asked Nestle for permission to use the trademark, and Nestle agreed in exchange for the aforementioned advertising, i.e. a quid pro quo.

I'll leave it to you to decide which is more plausible. But the Google+ thing is a red herring (except insofar as it might provide some insight into why Google decided to give Nestle such a sweetheart deal).

[UPDATE] Just to be clear, I don't think there's anything at all sinister about this deal. In fact, I think the coordinated campaign is rather clever.