Tamid posted 
I don't get it. New barrels are chromed. How is that different from chroming der barrels?
Tamid, new barrels are plated on a dedicated line with all the jigs and fixtures ready made up, and with the control gear calibrated and pre-set. The steel will be  a known factor as will the lubricants used in the construction which have to removed chemically. It's essentially a mass production process that can be computer controlled or looked after by a reasonably well trained monkey.
Plating an older gun is going to be a one off requiring a lot of experience and hand skills both in the plating stage and the pre-treatment. Simply getting it into a suitable fixture will be a work of art.  After plating it's almost certain the exterior of the tubes will need to be re-blacked, and someone's going to have to pay the gunsmith for his mechanical work too. All of that obviously has cost implications which is why some of us doubt the cost / benefit ratio. 
You might think of the analogy of buying a couple of bolts from a hardware store as against buying a bit of steel and getting them made up by a craftsman with a lathe. All will be excellent and workmanlike products but one set will cost twenty times t'otherun and be no better.
On a damascus set there are some potential metallurgical problems which may or may not be present, so the best any honest craftsman could say is "Look Guvnor, I'll do the best job I possibly can, but there are no guarantees I can give you." So it can be done, and for the right money I'd be happy to do it on someone else's gun.  

 Nae warrantee though!
This is a link to a pic of the Beretta hard chrome facility. One thing to note is the tubes for semi autos on the left side of the carousel going into the machine are all singletons.  I'm not sure what the procedure is on doubles.There are internal anodes inside the barrel (the rod like arrangement sticking out of the bottom of the jig) made either of lead or more likely platinised titanium. A hand job on a one off has to replicate all that, only on a two tube set.
https://www.flickr.com/photos/guns-for-sale/6147754942/in/photostream/lightbox/Eug