windowAttentionHandler: Follow app policy for attention notifications

While window attention notifications are created by the shell itself
rather than applications (most likely as a result of focus stealing
prevention), users still commonly link them to the application for
which they are shown. It makes therefore sense to follow the appropriate
policy set by the user rather than showing them unconditionally.

https://bugzilla.gnome.org/show_bug.cgi?id=779974

js/ui/windowAttentionHandler.js

@@ -79,6 +79,15 @@ var Source = new Lang.Class({
         this.signalIDs = [];
     },
 
+    _createPoliy: function() {
+        if (this._app && this._app.get_app_info()) {
+            let id = this._app.get_id().replace(/\.desktop$/,'');
+            return new MessageTray.NotificationApplicationPolicy(id);
+        } else {
+            return new MessageTray.NotificationGenericPolicy();
+        }
+    },
+
     createIcon : function(size) {
         return this._app.create_icon_texture(size);
     },