closure fixes

Author: Steven Orvell

lib/mixins/disable-upgrade-mixin.js

@@ -76,6 +76,12 @@ export const DisableUpgradeMixin = dedupingMixin((base) => {
    */
   class DisableUpgradeClass extends superClass {
 
+    constructor() {
+      super();
+      /** @type {boolean|undefined} */
+      this.__isUpgradeDisabled;
+    }
+
     static get observedAttributes() {
       return observedAttributesGetter.call(this).concat(DISABLED_ATTR);
     }

lib/mixins/element-mixin.js

@@ -578,12 +578,12 @@ export const ElementMixin = dedupingMixin(base => {
     }
 
     /**
+     * Determines if a property dfeault can be applied. For example, this
+     * prevents a default from being applied when a property that has no
+     * accessor is overridden by its host before upgrade (e.g. via a binding).
      * @param {string} property Name of the property
      * @returns {boolean} Returns true if the property default can be applied.
      */
-    // A property default can be overridden when a `properties` property with
-    // default but no effects had a property set (e.g. bound) by its host
-    // before upgrade.
     _canApplyPropertyDefault(property) {
       return !this.hasOwnProperty(property);
     }