Actually, it is possible to chrome plate plastic. What it takes is an intermediate layer of copper that is applied to the plastic first to create a conductive surface that will accept the subsequent layers of nickel and chrome that complete the process. The copper is either sprayed on or done using some kind of immersion process to completely submerge the component and literally encase it in the copper coating. Once that copper layer has dried or set, then, apparently, the item can be treated and dealt with just as if it was metal.
Chroming is actually a term that covers a range of alternatives. Standard chrome is just a layer of nickel and the top coat of chromium, both applied to an otherwise sterile clean surface. The level of cleanliness is vital to get the electrical bond to work properly; any contaminants in or on the metal and the finish might look good and then suddenly start to peel or flake.
"Show Chrome", aka Triple Chrome or Triple Plate, is a process that adds an initial layer or substrate layer of copper to the item being plated. This serves a couple of purposes, The copper is soft and can flow into cracks and crevices that otherwise cannot be buffed or ground out. This useful when working with old or frail components. It also allows for multiple layers of copper to be applied and between each layer, rinsed, and then buffed or polished out to create a totally smooth or flawless surface. After this degree of prep is reached, the component is then thoroughly rinsed and inspected and dried and then it receives its layer of nickel, gets buffed and cleaned again, and then gets chromed. This extensive process is why show chrome displays that deep blue tint in it, the copper, and why it is so hideously expensive, the time and labor needed to do.
There are other variants such as hard or shaft chrome that get used in hydraulic shops when rebuilding the cylinder shafts and rams. Shaft chroming is valuable for the amount of durability and life it can add to to a service item. I had the front fork tubes on my Electro-glide hard chromed almost 40 years ago and they are only just starting to show some wear and tear. Bummer because the hydraulic shop that did the work is no longer in business; long time gone.
And there is a spray on version that uses chemicals to create and simulate a chrome finish; this process was actually discussed and used on an episode of Counting Cars.
You Boob might be useful here as a show and tell source for plating non ferrous materials,