It appears we added a dot to some domain names when adding a cookie via WebDriver API, but we don't try to add the dot back when looking for cookies to delete.
Created attachment 337284 [details]
Comment on attachment 337284 [details]
Clearing flags on attachment: 337284
Committed r230367: <https://trac.webkit.org/changeset/230367>
All reviewed patches have been landed. Closing bug.