This would be so great. Unfortunately the Chrome developers didn't like it. I can't find the bug now, but they don't want to add this and also don't allow any user options so that people can configure it :-(

One guy in that bug even wrote he patched that part out, but that's not a solution for me, I don't have time to compile Chronium myself.

Turning off wifi or configuring (in IE!) a fake proxy is the only remedy.