GtkTimeline: protect the timeline from unref

The timeline frame function emits several signals, assuming that the
timeline will exist after these signals return.  This assumption can be
invalid if signal handlers unref the timeline.

https://bugzilla.gnome.org/show_bug.cgi?id=668675

gtk/gtktimeline.c

@@ -311,6 +311,9 @@ gtk_timeline_run_frame (GtkTimeline *timeline)
   gdouble delta_progress, progress;
   guint elapsed_time;
 
+  /* the user may unref us during the signals, so save ourselves */
+  g_object_ref (timeline);
+
   priv = timeline->priv;
 
   elapsed_time = (guint) (g_timer_elapsed (priv->timer, NULL) * 1000);
@@ -355,10 +358,13 @@ gtk_timeline_run_frame (GtkTimeline *timeline)
             }
           g_timer_stop (priv->timer);
           g_signal_emit (timeline, signals [FINISHED], 0);
+          g_object_unref (timeline);
           return FALSE;
         }
     }
 
+  g_object_unref (timeline);
+
   return TRUE;
 }