Fix black wallpaper after repeated crashes

Adds logic to recover from a repeatedly crashing wallpaper. Before,
a wallpaper that crashed twice but not within 10s would not trigger
the recovery logic in WallpaperManagerService, but would also not be
restarted by ActivityManager (because two crashes will effectively
disable a service connection), thus resulting in a black wallpaper.

Change-Id: Ie4f7862dc07a89d13f5e2b56c825a3371ea21114
Fixes: 30250003