The purpose is to let face unlock always get the camera
successfully. What happened was the camera applications may
have opened the camera in onResume under the lock screen.
This API lets face unlock take the camera from the camera
application. A new permission will be added, so other
applicatoins won't be able to take the camera from the face
unlock.
bug:5584464
Change-Id: Ib3d9dcbc2161815b68db42327dc01148453704c6
a1c41e13b5