AI 143823: am: CL 143800 am: CL 143748 Fix issue #1743326 (More battery stats)

  Adds stats for:
  - Number of raw user events that have happened in the system.
  - Number of times user activity has been reported, dividied by UID and type of activity.
  - Duration of screen brightness levels in 4 buckets.
  - Per-UID tracking of who has turned on Wifi and how long we can attribute it being on because of them.
  Original author: hackbod
  Merged from: //branches/cupcake/...
  Original author: android-build
  Merged from: //branches/donutburger/...

Automated import of CL 143823