Bug 1407695 - Clear all cookies from session before running test; r=ato

MozReview-Commit-ID: 9XQiIejBuj4

--HG--
extra : rebase_source : cf7c00674e441e08684d38e34572d0601bdfbb9a

testing/web-platform/tests/webdriver/tests/cookies/get_named_cookie.py

@@ -3,6 +3,7 @@ from tests.support.fixtures import clear_all_cookies
 
 def test_get_named_cookie(session, url):
     session.url = url("/common/blank.html")
+    clear_all_cookies(session)
     session.execute_script("document.cookie = 'foo=bar'")
 
     result = session.transport.send("GET", "session/%s/cookie/foo" % session.session_id)