Bug 1132566 - Enable test in e10s: browser_privatebrowsing_lastpbcontextexited.js; r=billm

This test appeared to run fine under e10s, so after running 30 times
with "mochitest-browser --e10s --run-until-failure" I've re-enabled it.

--HG--
extra : rebase_source : cfe40b90c62c0973e5636bf0ffc80a166aaeb26e

browser/components/privatebrowsing/test/browser/browser.ini

@@ -32,7 +32,6 @@ skip-if = e10s # Bug 1139953 - Accept cookie dialog shown in private window when
 [browser_privatebrowsing_downloadLastDir_toggle.js]
 [browser_privatebrowsing_geoprompt.js]
 [browser_privatebrowsing_lastpbcontextexited.js]
-skip-if = e10s
 [browser_privatebrowsing_localStorage.js]
 skip-if = e10s
 [browser_privatebrowsing_localStorage_before_after.js]