George Bates shared a screen shot with me on Twitter of a new location extension named "affiliate location extensions" in AdWords. It shows the "relationship type", the country and the available chains you can pick from.
I am not 100% clear on how this works, but it seems like you can define if you are an affiliate and then select the chains Google has available.
Here is a screen shot:
You can see chains such as 7-Eleven, AT&T, Babies R Us, AutoZone and many more popular retail chains.
Again, I am not sure how this works exactly but I suspect we will learn more over time.
Forum discussion at Twitter.
Update: George added more details about this over here.
Update 2: Google announced it 30+ hours later on Google+.
