I have an old chromed fork (which I will soon be posting on EBay, FWIW), and it is chromed all the way up the tube and threads.

Having said that, one thing to consider is this: just how much will the chrome build up in your threads and on your seating area for the headset bearing races? If the chrome builds up, say, .001", that means a .002" increase in tube/seat diameter, and often a .004" buildup on the threaded pitch diameter. You might have to chase the threads before and after plating.