The cable *should* be OK, and I would worry much more about it pulling on one plug or the other (I think it would do a lot of damage to the car, if it yanked out the plug from the car side).
However, as kort677 noted, I would avoid this as a normal practice as it is going to put un-needed stress on the wires.
Best suggestion would be to move the plug and charger to somewhere between the cars, so it is only going behind the car that is actually charging and would need to unplug anyway.
Second suggestion, make (or buy) a raceway like Wanter noted. you can do it pretty easily if you want with some long pieces of wood (like 2x4) put them far enough apart to put the cable between them, and get some trim for next to them to make getting over them easier, then fasten these to the garage floor so the car cant just push them around.
Some options (
Cable Ramps & Protectors | Discount Ramps)
Alternatively you could look at hanging the wire from the ceiling (there are some pics somewhere on here that show someone doing that).