Dejank app switching.

App switching is a little janky, one of the causes seems
like we're doing a call into package manager to see if there
are more applications (to draw the arrow) and that is expensive
(around 10-160ms). Remove this call and maintain a cache and
query that instead.

Bug: 27232284
Change-Id: I9666073944e406b595a3486857f3fe44b2ae2039