Reduce bandwidth usage when running bfcache check

[mattzeunert]

We've been looking at reducing our bandwidth costs when running Lighthouse recently. If I understand correctly, running Lighthouse currently opens the tested page 1 or 2 times:

1. For the main navigation
2. For the bfcache check, if the page can't be served from the bf cache

Is it possible to block e.g. image requests for the bf cache navigation? And maybe also others like JavaScript? Since the point is just to check if the page can be served from the bfcache. Doing that would also reduce CPU load.

Not sure if there are any reasons to load the page in full. Like bfcache checks for iframes maybe?

I can submit a PR for this if there's interest.

[adamraine]

Not a bad idea, Lighthouse used to test the page with network requests blocked to verify offline behavior I believe. I wonder if we could get away with blocking all network activity. Can maybe disable JS too.