Add docs for JS self-profiling API

[wbamberg]

Docs for the JS Self-Profiling API.

• I've included a page for samplebufferfull which is mentioned in the spec but not defined, and which doesn't have a BCD entry yet.
• in my experiments I often see samples which only have a timestamp and no stack ID. I believe that these are when the browser is doing some other work that isn't directly executing the program, like GC. Is that right? I should probably say something about this.
• this API is protected using Document Policy which AFAIK is not documented on MDN. I haven't done that as part of this PR but we should. I think there is an issue somewhere to document it but I can't find it in mdn/content.

[github-actions]

Preview URLs (6 pages)

• /en-US/docs/Web/API/JS_Self-Profiling_API/Profile_content_and_format
• /en-US/docs/Web/API/JS_Self-Profiling_API
• /en-US/docs/Web/API/Profiler/Profiler
• /en-US/docs/Web/API/Profiler/samplebufferfull_event
• /en-US/docs/Web/API/Profiler/stop
• /en-US/docs/Web/API/Profiler

External URLs (2)

URL: /en-US/docs/Web/API/Profiler/Profiler
Title: Profiler: Profiler() constructor

• https://wicg.github.io/document-policy/ (1 time) (Note! This may be a new URL 👀)

---

URL: /en-US/docs/Web/API/JS_Self-Profiling_API
Title: JS Self-Profiling API

• https://wicg.github.io/document-policy/ (1 time) (Note! This may be a new URL 👀)

(comment last updated: 2025-01-27 15:34:09)

[captainbrosset]

Looks great to me from a tech writing perspective. Thanks Will.
I'll ping someone from my side to take a look at the technical details too.

[captainbrosset]

It is indeed mentioned briefly in the spec, and is implemented in chromium (it seems).
I think this should be spec'd properly, and then added to BCD.