Add arc-art for ARC.

For security purposes, it is better to run patchoat and dex2oat
outside ARC. User arc-art is created for running ART minijail
container.

BUG=b:65159408
TEST=Build image, check /etc/passwd and /etc/group.
TEST=test_that caroline security_AccountsBaseline
Change-Id: I4488e0ca1743b6434a6d5dee94ab6134d6d34f35
Reviewed-on: https://chromium-review.googlesource.com/646495
Commit-Ready: Xiaoyong Zhou <xzhou@chromium.org>
Tested-by: Xiaoyong Zhou <xzhou@chromium.org>
Reviewed-by: Jorge Lucangeli Obes <jorgelo@chromium.org>
diff --git a/profiles/base/accounts/group/arc-art b/profiles/base/accounts/group/arc-art
new file mode 100644
index 0000000..76817b2
--- /dev/null
+++ b/profiles/base/accounts/group/arc-art
@@ -0,0 +1,3 @@
+group:arc-art
+gid:610
+users:arc-art
diff --git a/profiles/base/accounts/user/arc-art b/profiles/base/accounts/user/arc-art
new file mode 100644
index 0000000..e7851ca
--- /dev/null
+++ b/profiles/base/accounts/user/arc-art
@@ -0,0 +1,7 @@
+user:arc-art
+password:!
+uid:610
+gid:610
+gecos:For ART container in ARC
+home:/dev/null
+shell:/bin/false