1754100 - When filtering with "pid:<content process id>", try not to run the sampler thread in the parent process

Status: NEW

(Core :: Gecko Profiler, enhancement, P3)

Description

[Gerald Squelart (he/him) (not at Mozilla since 2022-09-15)]

Thanks to bug 1735397, if the thread-filter string only contains items with "pid:...", the profiler does not even start in other processes (to avoid wasting resources), except in the parent process where it always runs.

This was simpler to implement, and the main cost was coming from having many processes running their profiler, especially with Fission.
Removing that one extra process was a smaller benefit, against the implementation cost of preventing the profiler in the parent process from running.
But it would still be nice to try, if possible.