I wanted to try running some benchmarks on headless chrome. I was hoping it would be as simple as passing "--headless" to telemetry's "--extra-browser-args=". But this failed with:
[0501/194655.855420:ERROR:headless_shell.cc(552)] Malformed proxy server url

Complete log is here: https://chrome-swarming.appspot.com/task?id=35dfd2632145e110&refresh=0&show_raw=1&wide_logs=true

Telemetry passes the --proxy-server flag to Chrome for ts_proxy server, so there is something that Chrome headless does not like here. I was not sure where the bug is so I added both Telemetry and Headless components.