This is actually how I use Chromium with a proxy right now, but it requires that I launch it from the command line and manually specify the http_proxy (and https_proxy) variables (/usr/bin/env http_proxy="
http://127.0.0.1:8080 https_proxy="
https://127.0.0.1:8080 /usr/bin/chromium). I suppose I could set up some kind of script to launch Chromium (and all other applications) that would check if I'm on my home network and launch all apps with that variable if not, but that seems like a really ugly hack.