Outside bottom windown trim peeling to expose chrome. What can I do?

Quite common issues as these cars get old and the materials cracks.
 
New ones can be sourced quite easily off a wreck (many times the clips brake though)
 
DB8 has some new ones for sale here: http://www.mr2australia.c./mr2play/tm.aspx?m=22294
 
On my previous MR2 I took them off the car - removed all of the black coating then painted them in satin black.

If you have the time to spend on it here's a process I've used.
 
Mask off the bodywork and glass before you start.  Then clean the trim with some 600grit before giving it a coat of etch primer.  Make sure you have every other surface masked off, this etch primer really etches!  Give the primer coat a quick go with 800grit, then start on the top coats.  IMHO a satin black is the best look, but it is your car.  And as with all spray jobs, take your time and do 3 light coats rather than one heavy one.  Also, feel free to give a light 800 sand between coats.  Once it's done give it a couple of days then in with a good rubbing/waxing compound.
 
Congratulations, you've just made your pride and joy joyful and proud!