[gtk+/wip/alexl/file-chooser-portal] Use the portal when sandboxed

[Matthias Clasen <matthiasc src gnome org>]

commit 32457cded3b5b16af7d07eb6d560ef2148b2150f
Author: Matthias Clasen <mclasen redhat com>
Date:   Mon Jun 13 23:43:12 2016 -0400

    Use the portal when sandboxed
    
    flatpak creates a file called /run/user/1000/flatpak-info that we
    can use to determine whether we are in a sandbox or not.

 gtk/gtkfilechoosernativeportal.c |   14 +++++++++++---
 1 files changed, 11 insertions(+), 3 deletions(-)
---
diff --git a/gtk/gtkfilechoosernativeportal.c b/gtk/gtkfilechoosernativeportal.c
index cd875d3..b8e83fc 100644
--- a/gtk/gtkfilechoosernativeportal.c
+++ b/gtk/gtkfilechoosernativeportal.c
@@ -278,10 +278,18 @@ gtk_file_chooser_native_portal_show (GtkFileChooserNative *self)
   const char *signal_name;
   GDBusSignalCallback signal_callback;
   const char *use_portal;
+  gchar *path;
 
-  use_portal = g_getenv ("GTK_USE_PORTAL");
-  if (!use_portal)
-    use_portal = "";
+  path = g_strdup_printf ("/run/user/%d/flatpak-info", getuid());
+  if (g_file_test (path, G_FILE_TEST_EXISTS))
+    use_portal = "1";
+  else
+    {
+      use_portal = g_getenv ("GTK_USE_PORTAL");
+      if (!use_portal)
+        use_portal = "";
+    }
+  g_free (path);
 
   if (g_str_equal (use_portal, "0"))
     return FALSE;