drivefs: Add chronos to fuse-drivefs group

To read logs and clear caches chronos must have access to drivefs files.

BUG=chromium:829274,b:79395845
TEST=Build image and check 'id chronos'
CQ-DEPEND=CL:1113705

Change-Id: I68339e5660cdcab30a5d34156e76fa30fadd0edb
Reviewed-on: https://chromium-review.googlesource.com/1113174
Commit-Ready: Sergei Datsenko <dats@chromium.org>
Tested-by: Sergei Datsenko <dats@chromium.org>
Reviewed-by: Jorge Lucangeli Obes <jorgelo@chromium.org>
Reviewed-by: Stuart Langley <slangley@chromium.org>
diff --git a/profiles/base/accounts/group/fuse-drivefs b/profiles/base/accounts/group/fuse-drivefs
index 01b986e..921c2e3 100644
--- a/profiles/base/accounts/group/fuse-drivefs
+++ b/profiles/base/accounts/group/fuse-drivefs
@@ -1,3 +1,3 @@
 group:fuse-drivefs
 gid:304
-users:
+users:chronos