I found that several other tests could be a lot flaky with NetworkService, because we don't guarantee the ordering between resource loading and channel-associated messages there. The initial SetController could come after the document is created, therefore fairly basic test like external/wpt/service-workers/service-worker/ServiceWorkerGlobalScope/unregister.https.html could be flaky.
Comment 1 by bugdroid1@chromium.org
, Oct 29 2017