But why would you want to do that instead of just using the built-in multiple profiles feature? The only thing I've encountered that required a separate browser instance was using non-default command-line flags for testing something with different proxy options.
Why would I do that when I want to use Chrome only?
I can have both my Github accounts logged in, both of my gmails, etc, and get my favorite interface. I'm glad I don't have to launch Firefox or Safari anymore.
chromium-browser --user-data-dir=~/.profiles/work-mail-profile -app=https://mail.google.com