Tests that the private browsing API implementation works as expected

On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".


PASS plugin1.privateBrowsingEnabled is false
PASS plugin1.cachedPrivateBrowsingEnabled is false
PASS plugin1.privateBrowsingEnabled is true
PASS plugin1.cachedPrivateBrowsingEnabled is true
PASS plugin2.privateBrowsingEnabled is true
PASS plugin2.cachedPrivateBrowsingEnabled is true