init: Document the locking strategy in class ShutdownState

Let the compiler verify that shutdown_command_lock_ is held when
shutdown_command_ is accessed.

Bug: 266255006
Change-Id: Ibd05137ab65e20f247f35bbb2bb1865e05f51f41
Signed-off-by: Bart Van Assche <bvanassche@google.com>
1 file changed