[gnome-maps] utils: Add function to detect if set to prefer dark theme

[Marcus Lundblad <mlundblad src gnome org>]

commit b719aaf0fc9663e1b1445acb930aff1882d5ae73
Author: Marcus Lundblad <ml update uu se>
Date:   Wed Jun 28 22:38:40 2017 +0200

    utils: Add function to detect if set to prefer dark theme
    
    https://bugzilla.gnome.org/show_bug.cgi?id=783602

 src/utils.js |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)
---
diff --git a/src/utils.js b/src/utils.js
index c7fccc3..e738ec6 100644
--- a/src/utils.js
+++ b/src/utils.js
@@ -388,3 +388,9 @@ function normalizeString(string) {
     let normalized = GLib.utf8_normalize(string, -1, GLib.NormalizeMode.ALL);
     return normalized.replace(ACCENTS_REGEX, '');
 }
+
+function isUsingDarkThemeVariant() {
+    let gtkSettings = Gtk.Settings.get_default();
+
+    return gtkSettings.gtk_application_prefer_dark_theme;
+}