Remove "tracing" marker type, and migrate to the "category" field.

[gregtatum]

Right now the markers of type "tracing" don't work too nicely with the new marker schema. "type" should be the differentiator on how we display things. However, these markers use a "category" designation instead. This "category" field in the payload should be migrated to the "type" field.

In the marker schema work, I'm working around this by selecting the type OR the category if the type === "tracing".

• Write a front-end upgrader.
• Update the front-end schema usage to not have the above mitigation. TODOs
• Update Gecko - Bug 1662491 Tracing markers Payload serialization

┆Issue is synchronized with this Jira Task

[mstange]

Yeah I'm pretty sure the "category" field was completely ad-hoc. I think these tracing markers can all be identified by their name and the "category" is not worth preserving.

[mstange]

Yeah, those "Paint" category strings are from the very first addition of tracing markers, in bug 918825.

[mstange]

I've proposed an alternative way forward in #5275.