The bottom list flashes because it takes some time to create a
DomainAppPreference, where each perference takes around 6ms to load an
icon. When there are, that say, 30 apps installed, then it will take
around 180ms to be ready, which introduces the flashing issue.
In order to tackle icon loading, this CL applies the icon cache
mechanism to speed up the loading time.
Fixes: 222981986
Test: robotest
Change-Id: Ia8f7cbf5af5ea9f694c352ea40ccca47bedb175c
93f945d516