This is the content provider that wallpaper picker will be using to
query for slots, affordances, and selections, and for setting or
unsetting selections.
The CL also includes a contract definition and "client" utility
functions that any customer can use to query and update the content
provider.
Fix: 254857637
Test: end-to-end unit tests included. Manually verified the API by
issuing adb shell content commands and seeing affordances appear and
disappear on the actual lock screen.
Change-Id: Ia47a8ee322028042bb3e118ddb82a92a27eae191
c6c5ae9594