How long any Chrome rim will last before it wears out is not exact science and will depend on many factors of the outside environment. They will not all last the same length of time.
Some main factors can depend on how abrasive your brake pads are and what type of terrain you ride; for instance riding dirt or if you use your brakes a lot, this will wear the chrome faster due to the dirt pulling through the pads more often and working harder on the finish.
Other leading wear issues (this applies more towards the street riding side of things) can be when the rim becomes damaged, This will lead to uneven braking and of course start wearing massively on your rim, this applies to any finish on any rim too.
Finally but not least, dirt and moisture, If you ride in the harsh winter of any country, salt will absolutely eat into the rim, just the same as having dirt on the brake pads or rim will allow scratches and abrasion to completely take the finish off much quicker than if you were to clean the chrome rim(s) every now and then.