eclass-overlay: Add cups-proxy user and group.

Set up user and group for running the CUPS Proxy Daemon in minijail.

BUG=chromium:945409
TEST=profiles/base/accounts/display-accts.py

Change-Id: I1afd926fd6d3585438e79617031fbde5226b05d8
Reviewed-on: https://chromium-review.googlesource.com/1571285
Commit-Ready: Pi-Hsun Shih <pihsun@chromium.org>
Tested-by: Pi-Hsun Shih <pihsun@chromium.org>
Reviewed-by: Chirantan Ekbote <chirantan@chromium.org>
diff --git a/profiles/base/accounts/group/cups-proxy b/profiles/base/accounts/group/cups-proxy
new file mode 100644
index 0000000..0af4553
--- /dev/null
+++ b/profiles/base/accounts/group/cups-proxy
@@ -0,0 +1,3 @@
+group:cups-proxy
+gid:20136
+users:cups-proxy
diff --git a/profiles/base/accounts/user/cups-proxy b/profiles/base/accounts/user/cups-proxy
new file mode 100644
index 0000000..0afaa88
--- /dev/null
+++ b/profiles/base/accounts/user/cups-proxy
@@ -0,0 +1,6 @@
+user:cups-proxy
+uid:20136
+gid:20136
+gecos:CrOS CUPS proxy daemon
+home:/dev/null
+shell:/bin/false