Clank has accumulated a lot of bugs where tabs show up as black/white/background color/obsolete content, either briefly during transitions or longer in the tab switcher (either way, clearing up as soon as the tab becomes live and primary).  There are a variety of repro steps, symptoms, root causes and subsystems involved (thumbnail manager, tab model, CC layer structure, readbacks).

Filing this master bug to stay organized as we start to attack this more seriously.  Newly discovered flickers with different repro steps or symptoms should be filed as new bugs blocking this one.