If it was anyone but Google I'd suggest their code looked like this:
Had to implement something similar on a booking confirmation page once.
Idiots Users would see their booking details and think "ow, allrighty then!" and navigate away without actually confirming the booking (despite two pretty big buttons to that affect, one at the top and one at the bottom of the page). Add a confirmation dialogue upon leaving the page and invalid booking reports dropped to pretty much zero.
Sure, it's not pretty, but it works.