> Hovering over an ad link on Chrome, it shows in bottom bar the link as going to brand.com . How can this be done, it's just an <a href="..."> ? Inspecting or right-click shows the true link to www.googleadservices.com/pagead/aclk...

Google has been doing this since forever (for any search results too)... They update the link target on-click using javascript to be able to track everything you click on.