chromium/chrome/browser/ash/dbus/org.chromium.ComponentUpdaterService.conf

<!DOCTYPE busconfig PUBLIC "-//freedesktop//DTD D-BUS Bus Configuration 1.0//EN"
  "http://www.freedesktop.org/standards/dbus/1.0/busconfig.dtd">
<!--
  Copyright 2017 The Chromium Authors
  Use of this source code is governed by a BSD-style license that can be
  found in the LICENSE file.
-->
<busconfig>
  <policy user="chronos">
    <allow own="org.chromium.ComponentUpdaterService"/>
  </policy>

  <!-- vm_launcher runs as root -->
  <policy user="root">
    <allow send_destination="org.chromium.ComponentUpdaterService"
           send_interface="org.chromium.ComponentUpdaterService"/>
  </policy>

  <!-- modemfwd runs as modem -->
  <policy user="modem">
    <allow send_destination="org.chromium.ComponentUpdaterService"
           send_interface="org.chromium.ComponentUpdaterService"/>
  </policy>
</busconfig>