Add arc-networkd user

This allows arc-networkd to drop root privileges.

BUG=chromium:670985
TEST=`emerge-veyron_minnie arc-networkd` with updated ebuild

Change-Id: I0b3fb3d1f607ca20ab7270173f341b77f33749e0
Reviewed-on: https://chromium-review.googlesource.com/416272
Commit-Ready: Kevin Cernekee <cernekee@chromium.org>
Tested-by: Kevin Cernekee <cernekee@chromium.org>
Reviewed-by: Kirtika Ruchandani <kirtika@chromium.org>
diff --git a/profiles/base/accounts/group/arc-networkd b/profiles/base/accounts/group/arc-networkd
new file mode 100644
index 0000000..b51bb02
--- /dev/null
+++ b/profiles/base/accounts/group/arc-networkd
@@ -0,0 +1,3 @@
+group:arc-networkd
+gid:284
+users:
diff --git a/profiles/base/accounts/user/arc-networkd b/profiles/base/accounts/user/arc-networkd
new file mode 100644
index 0000000..b4337ee
--- /dev/null
+++ b/profiles/base/accounts/user/arc-networkd
@@ -0,0 +1,6 @@
+user:arc-networkd
+uid:284
+gid:284
+gecos:CrOS ARC network service daemon
+home:/dev/null
+shell:/bin/false