I started Firefox, saw the pop-up window and clicked install for Gmail and Google calendar. I get no change in my unity left launcher menu, nor when I tried to type Gmail in the dash.
However when I tried to uninstall the Amazon webapp in the Ubuntu Software Package, it says that I first need to uninstall Gmail and Google calendar. I don't really see why but at least it means that they are somewhere.
When I do
sudo apt-cache search gmail
unity-mail - Mail notifications and count for Unity unity-webapps-gmail - Unity Webapp for GMail