This is an ad for something related to the product in the product you're using. Banshee has an in-browser affiliate link for the Amazon MP3 store (pointing at GNOME or Canonical, depending on which distro you're using). Skype will gladly advertise Skype credits when you're using its client. Hell, even videogame DLC works this way.
I was expecting some sort of Google Adwords box in the browser or something. Not a small tooltip advertising Chromebook. Please choose a better title: "Google advertises Chromebook in Chrome" or similar.
If you click the close button [X], they won't appear again. It's not a big deal.