Allow user 'crosvm' to use libvda D-Bus service.

Added a new rule to allow the user 'crosvm' to use libvda D-Bus service
because crosvm is run as 'crosvm' when it's started by vm_concierge.

Bug: b:142864350
Test: Play a video on VM with virtio-vdec
Signed-off-by: Keiichi Watanabe <keiichiw@chromium.org>
Change-Id: I35562356b9a475fc3f72ec7de743cfe636b4a6e9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1883451Reviewed-by: Mattias Nissler <mnissler@chromium.org>
Reviewed-by: Hidehiko Abe <hidehiko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#712483}

chrome/browser/chromeos/dbus/org.chromium.LibvdaService.conf

@@ -13,9 +13,20 @@
   </policy>
 
   <!--
-    libvda (via crosvm, running as root) uses this service to ask Chrome to
-    provide a mojo connection FD.
+    LibvdaService is used by libvda (go/libvda), which is a shared library
+    providing APIs corresponding to mojom::VideoDecodeAccelerator defined in
+    video_decode_accelerator.mojom.
+    libvda uses this service to ask Chrome to provide a mojo connection FD.
+
+    libvda is linked to crosvm and used from its virtio video decoder device.
+    Since crosvm is run as 'crosvm' by vm_concierge or 'root' from the command
+    line, we allow these users.
   -->
+  <policy user="crosvm">
+    <allow send_destination="org.chromium.LibvdaService"
+           send_interface="org.chromium.LibvdaService"/>
+  </policy>
+
   <policy user="root">
     <allow send_destination="org.chromium.LibvdaService"
            send_interface="org.chromium.LibvdaService"/>