ServiceWorkerVersionBrowserTest* in content_browsertests is flaky.

Findit has detected 3 flake occurrences of tests below within
the past 24 hours:

ServiceWorkerVersionBrowserTest.Activate_NoEventListener
ServiceWorkerVersionBrowserTest.FetchEvent_Response

Please try to find and revert the culprit if the culprit is obvious.
Otherwise please find an appropriate owner.