Test chrome

This does two things:

• Change test:chrome command to work in environments where chrome is not a valid command. This is useful in a lot of Linux environments, where chrome is started by using commands such as chromium, google-chrome, google-chrome-canary etc. I tried simply providing an alias for chrome, but that didn't work, and this seemed simple enough.
• Add a script that runs tests for all browsers (chrome and firefox for the time being), so that it's less tedious for devs to check that nothing's broken.