Annotate __dataEnabled in a way analyzer understands

Author: aomarks

lib/mixins/properties-changed.js

@@ -161,7 +161,7 @@ export const PropertiesChanged = dedupingMixin(
 
     constructor() {
       super();
-      /** @protected {boolean} */
+      /** @type {boolean} */
       this.__dataEnabled = false;
       this.__dataReady = false;
       this.__dataInvalid = false;