new audit: have a valid favicon.ico

[wardpeet]

Provide the steps to reproduce

1. Run LH on https://condescending-haibt-2d0d42.netlify.com/bug.html

What is the current behavior?

URL	Description
/favicon.ico(condescending-haibt-2d0d42.netlify.com)	Failed to load resource: the server responded with a status of 404 ()

What is the expected behavior?

Favicon shouldn't be a violation

Environment Information

• Affected Channels: CLI, Node
• Lighthouse version: 5.6.0
• Chrome version: 80.0.3987.100
• Node.js version: 12.14.1
• Operating System: Windows

Related issues
#10381
#10190

[patrickhulce]

Thanks Ward! :)

In the strictest sense of the audit, I still think this is WAI. It was an error in the console, so we showed it. #6978 points out that this actually disappears when you run headless because it doesnt request the favicon.

Instead of ignoring this one error, I'd be in favor of splitting out the "Failed to load resource" messages into two separate audits, "Network requests failed" and "Page defines a favicon". At least it's clearer what's going wrong without diving into details and it's officially codified as a best practice to provide a favicon :)

[paulirish]

We're on board with a dedicated best-practice has-a-favicon audit (that doesn't 404).

We'll skip a dedicated network-requests-failed audit for now.

[tunetheweb]

We could also check the size of the favicon 404 - great post by @Nooshu here which shows that some favicons are returning a 6MB 404 response!!!

In fact maybe a separate audit should be for any large 404 responses rather than just limiting it to favicons?