More exactly: Instead of trying to compensate for only the previous sleep over/undershoot, we now try to keep each sampling loop to a schedule based on the very beginning of sampling, by adding the requested interval to the scheduled sampling time.
In addition, the sleep time is always kept to a minimum, to avoid making the system busier by having one loop right after the other -- also, this very-close data may be less useful.
And in presumably very busy times, one sleep and the following sampling work may take much more time than the requested sampling interval, trying to keep to schedule is now futile (it would require trying to effectively multiply the sampling rate, which seems unlikely to succeed, and would impact Firefox even more), in which case we revert to the full sampling interval.
Differential Revision: https://phabricator.services.mozilla.com/D102253
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