[trace-events] Tracing Controller should keep list of possible categories

[ofrobots]

Context: https://github.com/nodejs/node/pull/20608/files#r186918294

It would be good for the Tracing Controller to keep a list of categories available for use in the process.

[AndreasMadsen]

I'm not sure how that can be done since we are going to allow users to have their own categories. We could properly maintain a dynamic set object but a static list definitely isn't possible.

[jasnell]

For now at least, the API won't be exposed to end users but this still presents a challenge long term.

We could provide an API via the trace_events module to register categories for that list.

[ofrobots]

I was thinking dynamic list. As a starting point, it can be the list of categories encountered so far in the process, but going forward, we could formalize a register categories concept as @jasnell mentions.

[ofrobots]

BTW, the former works fairly well for Chrome at the moment:

[github-actions]

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