Bug 1089615 - Add filtered class soonest to avoid black-white flash

I cant think of a meaningful test for this. We could assert the class is there before showing the task manager, but that's not really the point - the outcome we want to assert on is that it doesnt flash black then white. 
I'm concerned that instead of seeing a black screen for a moment we'll now see a white background for a moment in the normal task manager.