Many fewer Service Workers detected since October 2021

[rviscomi]

Discovered during #518. According to Chrome Status, the ServiceWorkerControlledPage feature counter dropped steeply after October 2021, going from 1.33% of desktop URLs to 0.51% in December 2021:

Other stats related to service workers have also plummeted. I ran a PWA chapter query that measures the adoption of service worker events and it yielded many fewer pages with service workers (the total field). This metric detects service workers based on the actual resources loaded on the page, unrelated to the feature counter. That both independent approaches are showing similar results strongly suggests that Chrome is actually loading fewer service workers.

I spot checked one page from the dataset that had the feature counter in November, but not in December: https://www.radissonhotels.com/. Testing it today using the public WPT instance shows the SW loading and the HAR does include the feature. Maybe that means the issue resolved itself?

Let's see what the January results look like. Meanwhile I'll ask some Chrome folks about the feature counter.

[rviscomi]

cc @jeffposnick

[rviscomi]

Adoption recovered on its own, closing