Enhance DeviceAdminService javadoc and remove TODO.

 * <p>The system searches for it with an intent filter with the

 * {@link DevicePolicyManager#ACTION_DEVICE_ADMIN_SERVICE} action, and tries to keep a bound

 * connection as long as the hosting user is running, so that the device/profile owner is always

 * considered to be in the foreground.

 * considered to be in the foreground.  This is useful to receive implicit broadcasts that

 * can no longer be received by manifest receivers by apps targeting Android version

 * {@link android.os.Build.VERSION_CODES#O}.  Device/profile owners can use a runtime-registered

 * broadcast receiver instead, and have a {@link DeviceAdminService} so that the process is always

 * running.

 *

 * <p>Device/profile owners can use

 * {@link android.content.pm.PackageManager#setComponentEnabledSetting(ComponentName, int, int)}

 * to disable/enable its own service.  For example, when a device/profile owner no longer needs

 * to be in the foreground, it can (and should) disable its service.

 *

 * <p>The service must not be exported.

 * <p>The service must be protected with the permission

 * {@link android.Manifest.permission#BIND_DEVICE_ADMIN}.  Otherwise the system would ignore it.

 *

 * <p>TODO: Describe how the system handles crashes in DO/PO.

 * <p>When the owner process crashes, the service will be re-bound automatically after a

 * back-off.

 *

 * <p>Note the process may still be killed if the system is under heavy memory pressure, in which

 * case the process will be re-started later.

 */

public class DeviceAdminService extends Service {

    private final IDeviceAdminServiceImpl mImpl;