devtools: Expose cache status for requests in network monitor.

[mark-buer]

Expose cache status for requests in network monitor.

Testing: Net tests pass. No existing test infrastructure for devtools, adding them seems outside the scope of this PR.
Fixes: #40237

[jdm]

Great work! Did you verify that cached requests appear correctly in the network monitor?

[mark-buer]

Yes, the network requests appear with their correct cache_state in firefox devtools...
except when they don't - but that isn't a problem with this PR per se.

I noticed that cross domain requests show the state as not-from-the-cache when they in fact are from the cache.

I've tracked the issue down to https://github.com/servo/servo/blob/main/components/shared/net/response.rs#L286 which filters the response for cross domain requests. Since the cache_state field isn't exposed to the page or JS (it is used for devtools only) it seems that line (and the one a few lines further down) could be safely removed.

What do you suggest - remove those lines in this PR, in another PR, or something else?

[jschwe]

Net tests pass. No existing test infrastructure for devtools, adding them seems outside the scope of this PR.

There is ./mach test-devtools, so that statement doesn't seem accurate (I'm not familiar with what exactly is tested there though).

[jdm]

Net tests pass. No existing test infrastructure for devtools, adding them seems outside the scope of this PR.

There is ./mach test-devtools, so that statement doesn't seem accurate (I'm not familiar with what exactly is tested there though).

There's no support yet for devtools tests that don't involve the debugger, do that's not something I want to gate this PR on.

[jdm]

What do you suggest - remove those lines in this PR, in another PR, or something else?

Unfortunately this is used in the fetch specification for some steps that we haven't implemented yet (https://fetch.spec.whatwg.org/#ref-for-concept-response-cache-state), so I think we'll need to do this in a separate PR with some more planning first.