Add back a helper pref that holds a system setting.

Change-Id: I7d8978829bde1f1dd15bf59f464557f64aa07beb
(cherry picked from commit 62e81c75ea7fab320264d6f58d2e37d7fa5ddc71)
Use SystemSettingSwitchPreference.

Change-Id: I14fe1c9b1c5ead1ddb20c61ba080bb005f2130d7
(cherry picked from commit 0be93caddd11f7aa12214e00140215eb61d1409f)