Lighthouse doesn't send Accept request header in start_url audit

Hi!

We are using a service worker that serves HTML pages from cache when the request contains the header Accept: text/html.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Accept

We discovered that Lighthouse does not send this header in it’s audit of the start_url causing the test to result in a false negative.

Failures: Service worker does not successfully serve the manifest's start_url.

[patrickhulce]

Yeah 4 is the obvious best, but we haven’t done it mostly because it’s slow to add another pass. #4310 should help with the slowness, so after it lands we might be good to just switch to that 👍

[wardpeet]

@kdzwinel I believe step 4 isn’t as easy as it is because it will need a pass on it’s own to make sure that hte page gets loaded. Doing it in the same pass with other audits will skew the results and can also result in a different final url.