Previous to this change the WindowManager was notifying the
BatteryDtatsService about windows that keep the screen on. WM used a
custom WakeLock tag to indicate to PowerManagerService that it had
already notified the BatteryStatsService.
This change eliminates WindowManager notifying the BatteryStatsService
and lets PowerManagerService do the job.
Fixes bug 7030326.
Change-Id: I666dc6ef8f094b8d3d109fea6876be058e057b4f
259328c04c