At the end of each test, file_chromecommon.js deletes all the cookies, but it
doesn't invalidate the network cache. Some of the files are shared between
tests. When they are loaded from the cache, we don't set the cookies and,
because of this, the tests were reporting a wrong cookie number.
Differential Revision: https://phabricator.services.mozilla.com/D31596
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extra : moz-landing-system : lando