a lot of plastic parts (from automotive to home appliances to model kits) were mirco-plated (in a vacuum chamber using powdered metal "dust").
It's very thin metal (microns thick) and prone to peeling off the plastic base material over time...I'm sure we ALL have seen that happen!
AFAIK the metal dusts are not usually genuine chromium or nickel (and certainly not real gold) but not sure what they use.
EDIT: I should read the literature before posting! ..."As far as the types of metals, copper plating on plastic is a common industrial practice, especially for applications where electrical conductivity is required. Other metals that are amenable to plating onto plastic include chromium, gold, silver and nickel." and according to shops this is now almost 90% on ABS