Both http-auth-private-mode-changed.html and http-auth-private-mode-changed.php must be served over http.

This tests the behavior of http authentication when private browsering is set from on to off. This is for

Test steps:
1. Set Private Browsing on. (Settings -> Privacy & Security -> Private Browsing).
2. Press Start test here.
3. When dialog pops up, enter real credential(username: "aaaa", password: "aaaa") and press Ok button.
4. Set Private Browsing off. (Settings -> Privacy & Security -> Private Browsing).
5. Refresh the page.
6. There should be a dialog for you to input username and password again.
If you can't see the dialog, this test fails.