Add utility function

src/modules/Switcher.js

@@ -56,7 +56,7 @@ var Switcher = class {
 
 			this.nightlight = new Nightlighter();
 			this.nightlight.enable();
-			this.nightlight.subscribe(this._apply_theme_variant.bind(this));
+			this.nightlight.subscribe(this._on_nightlight_change.bind(this));
 
 			this._apply_theme_variant();
 		}
@@ -96,4 +96,8 @@ var Switcher = class {
 		this._apply_theme_variant();
 	}
 
+	_on_nightlight_change() {
+		this._apply_theme_variant();
+	}
+
 }