Add chronos to lp group

We're going to restrict the cups domain socket (/run/cups/cups.sock) to
user:group root:lp. We want chronos to be able to print, so add it to
lp.

BUG=chromium:633385
TEST=check `id chronos` on newly-built image
CQ-DEPEND=Ia4ddfb93e69c2b6485362fa0c8e96093bebf0666
CQ-DEPEND=*I057946566100d88ee973ac57cb0b3051fed87004

Change-Id: I82b41954334b7855feeae8bbe48a90b324ec9965
Signed-off-by: Brian Norris <briannorris@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/368311
Reviewed-by: Sean Kau <skau@chromium.org>
Reviewed-by: Ricky Zhou <rickyz@chromium.org>
diff --git a/profiles/base/accounts/group/lp b/profiles/base/accounts/group/lp
index 634078b..2b58ac3 100644
--- a/profiles/base/accounts/group/lp
+++ b/profiles/base/accounts/group/lp
@@ -1,3 +1,3 @@
 group:lp
 gid:7
-users:lp,cups
+users:lp,cups,chronos