1. quit Chrome (Cmd+Q)
2. start it like this from the cmd line `script ~/Desktop/debug.log /Applications/Google\ Chrome.app/Contents/MacOS/Google\ Chrome --enable-logging=stderr --vmodule=*/webrtc/*=3`
3. screen-share something, for example your most embarassing tab

P.S. if you use zsh you need to put quotes around the chrome parameters