libchromeos: Allow overriding signals with built in handlers in Daemon.

Users of chromeos::Daemon may want to override signal handlers for
SIGTERM, SIGINT, and SIGHUP.

BUG=None
TEST=None

Change-Id: I7a087f40e43e0c30b1dd2f6a737d2868797771bd
Reviewed-on: https://chromium-review.googlesource.com/271471
Reviewed-by: Alex Vakulenko <avakulenko@chromium.org>
Reviewed-by: Jorge Lucangeli Obes <jorgelo@chromium.org>
Reviewed-by: Ricky Zhou <rickyz@chromium.org>
Commit-Queue: Ricky Zhou <rickyz@chromium.org>
Tested-by: Ricky Zhou <rickyz@chromium.org>
1 file changed