[gnome-terminal] app: Add env var to control headerbar setting

[Christian Persch <chpe src gnome org>]

commit fe21577a5def391d3d535fc4c36320ce48749d11
Author: Christian Persch <chpe src gnome org>
Date:   Mon Dec 10 22:00:33 2018 +0100

    app: Add env var to control headerbar setting
    
    This is useful for debugging.

 src/terminal-app.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)
---
diff --git a/src/terminal-app.c b/src/terminal-app.c
index bb232e09..26fcf93f 100644
--- a/src/terminal-app.c
+++ b/src/terminal-app.c
@@ -705,7 +705,12 @@ terminal_app_init (TerminalApp *app)
    * to override, so we cache them on startup and don't react to changes.
    */
   app->unified_menu = g_settings_get_boolean (app->global_settings, TERMINAL_SETTING_UNIFIED_MENU_KEY);
-  app->use_headerbar = g_settings_get_boolean (app->global_settings, TERMINAL_SETTING_HEADERBAR_KEY);
+
+  const char *env = g_getenv("GNOME_TERMINAL_HEADERBAR");
+  if (env != NULL)
+    app->use_headerbar = g_strcmp0 (env, "1") == 0;
+  else
+    app->use_headerbar = g_settings_get_boolean (app->global_settings, TERMINAL_SETTING_HEADERBAR_KEY);
 
 #if GTK_CHECK_VERSION (3, 19, 0)
   GtkSettings *gtk_settings = gtk_settings_get_default ();