[geary] Add woraround for view source not working under flatpak.

[Michael Gratton <mjog src gnome org>]

commit 919e4b934fd42c854a7ae146a8b1bf881a841e07
Author: Michael James Gratton <mike vee net>
Date:   Fri Sep 29 00:51:50 2017 +1000

    Add woraround for view source not working under flatpak.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=779311
    
    * org.gnome.Geary.json: Grant access to /tmp for now.

 org.gnome.Geary.json |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)
---
diff --git a/org.gnome.Geary.json b/org.gnome.Geary.json
index 5d1eafe..2f809b7 100644
--- a/org.gnome.Geary.json
+++ b/org.gnome.Geary.json
@@ -36,7 +36,10 @@
 
         /* Needed for dconf to work */
         "--filesystem=xdg-run/dconf", "--filesystem=~/.config/dconf:ro",
-        "--talk-name=ca.desrt.dconf", "--env=DCONF_USER_CONFIG_DIR=.config/dconf"
+        "--talk-name=ca.desrt.dconf", "--env=DCONF_USER_CONFIG_DIR=.config/dconf",
+
+        /* Let view source keep on working as-sis for now. Bug 779311. */
+        "--filesystem=/tmp"
     ],
     "build-options" : {
         "cflags": "-O2 -g",