Add support for running tests in an unknown browser

[nex3]

There should be a flag for the test runner to support running in browsers that aren't officially supported. If it's passed, the runner should print a URL that loads the host page. It should then wait until N browsers have connected, where N is the number of times the flag was passed, before running the tests.

[zoechi]

Can this be used for tests run in batch mode? This would need some way to read the URL from stdout, parse the output, and pass it as parameter to a command that actually launches the browser.

[nex3]

@zoechi Theoretically yes, but if you have an automated way to launch your browser you should just write a launcher for it—either submit a built-in launcher, or make a plugin with #99.

[zoechi]

right 👍

[nex3]

This hasn't been highly-requested, and on consideration I don't think it's likely to provide a substantial amount of value over what #99 and #391 do.