In the following scenario, we were adding SIGINT handler twice, but
removing it just once:
- Task runner starts testing, creates SigIntWatcher, installs SIGINT
handler.
- Press Ctrl+C, task runner interrupts, disarms SigIntWatcher, SIGINT
handler is not removed due to 1000ms cooldown.
- Task runner starts cleanup, creates SigIntWatcher, installs another
SIGINT handler.
- Cleanup finishes, SigIntWatcher disarms, could remove or not remove
SIGINT handler based on timing (same 1000ms cooldown). In any case, we
have one or two SIGINT handlers still on.
- HTML reporter hangs in onExit, while we still have SIGINT handler up,
so Ctrl+C does not exit.
Regressed in #24265.
ed99ac7395