Css: Don't check fill-opacity in Android 2.3, it's not supported

(cherry-picked from de75b3cc626829c3478a8a6d59dddc948d348b41)
Event: Blacklist the onbeforeunload test in Android 2.3

Similarly to iOS, Android 2.3 has the onbeforeunload property on window
but doesn't support the event. This commit blacklists the test there as well.

(cherry-picked from 6d2ab64df7bdda087e79deaa53db969fa6f2cd92)