Re: [w3ctag/design-reviews] Incubation: Lightweight and Conditional Tracing for long animation frame timing API (Issue #1224)

guohuideng2024 left a comment (w3ctag/design-reviews#1224)

cc: @noamr

1) "long task" is monitored/reported by `LoAF`. A single long task is sufficient to emit a `LoAF`. Therefore, after this feature is implemented the conditional user timing can analyze long tasks.

2) Our intention is that "conditional user timing" is not only tied to `LoAF`(Long animation frame), but a collection of Performance reporting API. "LoAF" is the very first Performance reporting API that monitors and includes these user timing points. Thus, we use a very general word "conditional".  And we do intend to expand this to other user cases, like "EventTiming" or even `ElementTiming` in the near future.  

3) We use a new name/API like `markConditional` instead of expanding the existing `performance.mark`, based on a number of considerations.

a) They behavior very different from regular `performance.mark/measure`: There is **no overlap** between where regular `mark/measure` can appear and where these conditional user timing can appear; The conditional user points (after the future expansion) operates in parallel in a number of different timelines. Even the implementation of `conditional user timing` has very little overlap of that for `user timing`

b) We want the app developers to be able to deploy more such user timing points, so the user timing points must be lightweight, with minimal performance overhead. Unfortunately, the existing `performance.mark/measure` has a so large collection of functionalities built in, that operations on them cost too much CPU and memory.  Therefore, we explicitly want to exclude these `Option`s in the existing `Performance.mark/measure`. By using a new API/name it's clear that the interface is different.



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