tracing support in webrender

[atbrakhi]

I recently started testing tracing support in WebRender. While I don't see a Servo-specific #[cfg_attr()] in WebRender, I'm not sure if we'll be able to land it upstream as it is very Servo-specific. However, it seems very useful and helps with some measurements on the Servo side.

Anyway, I'm submitting this early work as a draft PR to start a discussion around the best way forward and whether it's worth trying to land upstream or maybe downstream.

I guess I will extend this work once we have a way forward

cc @delan

[mrobinson]

Yeah, I don't think we want to carry these kind of changes downstream as we are shooting for not having any changes on top of upstream at all.

[nical]

Hi,

This is a mirror of WebRender's code. It's fine to open PRs here for discussion but they won't be merged and the actual contribution, when ready, will have to happen in the mozilla-central reprository via phabricator.

The way Firefox integrates its built-in profiler into WebRender is via the ProfilerHooks trait. This avoids having to add a dependency in WebRender itself, and if you can extend and build on top of the same infrastructure it will make it a lot easier to accept the patch.
A big part of the issue is that to accept new crate dependencies in Firefox, a Mozilla employee has to spend quite a bit of time doing a proper audit of all new/updated entries in the dependency tree. From a look at the Cargo.lock changes in this PR, I suspect you are probably going to have a difficult time getting this approach approved.