Fix race in shutdown of ServiceWorkerVersionBrowserTest.UpdateBypassesCacheAfter24Hours

This test doesn't unregister the service worker unlike others in the same file and
is likely working by accident.  This becomes a problem when we migrate from
MessageLoop to the SequenceManager.

Bug: 863341, 891670
Change-Id: I658ce56f244d1beda44f02e53cceaf0a7ea7b45b
Reviewed-on: https://chromium-review.googlesource.com/c/1356940
Reviewed-by: Matt Falkenhagen <falken@chromium.org>
Reviewed-by: Sami Kyöstilä <skyostil@chromium.org>
Commit-Queue: Alex Clarke <alexclarke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#612669}
1 file changed