Update stand alone disable-upgrade mixin.

Author: Steven Orvell

lib/mixins/disable-upgrade-mixin.js

@@ -15,6 +15,8 @@ import { dedupingMixin } from '../utils/mixin.js';
 
 const DISABLED_ATTR = 'disable-upgrade';
 
+let observedAttributesGetter;
+
 /**
  * Element class mixin that allows the element to boot up in a non-enabled
  * state when the `disable-upgrade` attribute is present. This mixin is
@@ -51,18 +53,49 @@ export const DisableUpgradeMixin = dedupingMixin((base) => {
    */
   const superClass = ElementMixin(base);
 
+  // Work around for closure bug #126934458. Using `super` in a property
+  // getter does not work so instead we search the Base prototype for an
+  // implementation of observedAttributes so that we can override and call
+  // the `super` getter. Note, this is done one time ever because we assume
+  // that `Base` is always comes from `Polymer.LegacyElementMixn`.
+  if (!observedAttributesGetter) {
+    let ctor = superClass;
+    while (ctor && !observedAttributesGetter) {
+      const desc = Object.getOwnPropertyDescriptor(ctor, 'observedAttributes');
+      if (desc) {
+        observedAttributesGetter = desc.get;
+      }
+      ctor = Object.getPrototypeOf(ctor.prototype).constructor;
+    }
+  }
+
   /**
    * @polymer
    * @mixinClass
    * @implements {Polymer_DisableUpgradeMixin}
    */
   class DisableUpgradeClass extends superClass {
 
-    /**
-     * @suppress {missingProperties} go/missingfnprops
-     */
     static get observedAttributes() {
-      return super.observedAttributes.concat(DISABLED_ATTR);
+      return observedAttributesGetter.call(this).concat(DISABLED_ATTR);
+    }
+
+    // Prevent element from initializing properties when it's upgrade disabled.
+    /** @override */
+    _initializeProperties() {
+      if (!this.hasAttribute(DISABLED_ATTR)) {
+        super._initializeProperties();
+      } else {
+        this.__isUpgradeDisabled = true;
+      }
+    }
+
+    // Prevent element from enabling properties when it's upgrade disabled.
+    /** @override */
+    _enableProperties() {
+      if (!this.__isUpgradeDisabled) {
+        super._enableProperties();
+      }
     }
 
     /**
@@ -75,46 +108,33 @@ export const DisableUpgradeMixin = dedupingMixin((base) => {
      */
     attributeChangedCallback(name, old, value, namespace) {
       if (name == DISABLED_ATTR) {
-        if (!this.__dataEnabled && value == null && this.isConnected) {
-          super.connectedCallback();
+        // When disable-upgrade is removed, intialize properties and
+        // provoke connectedCallback if the element is already connected.
+        if (!this.__dataEnabled && value == null) {
+          super._initializeProperties();
+          this.__isUpgradeDisabled = false;
+          if (this.isConnected) {
+            super.connectedCallback();
+          }
         }
       } else {
         super.attributeChangedCallback(
             name, old, value, /** @type {null|string} */ (namespace));
       }
     }
 
-    /*
-      NOTE: cannot gate on attribute because this is called before
-      attributes are delivered. Therefore, we stub this out and
-      call `super._initializeProperties()` manually.
-    */
-    /** @override */
-    _initializeProperties() {}
-
-    // prevent user code in connected from running
+    // Prevent element from connecting when it's upgrade disabled.
     /** @override */
     connectedCallback() {
-      if (this.__dataEnabled || !this.hasAttribute(DISABLED_ATTR)) {
+      if (!this.__isUpgradeDisabled) {
         super.connectedCallback();
       }
     }
 
-    // prevent element from turning on properties
-    /** @override */
-    _enableProperties() {
-      if (!this.hasAttribute(DISABLED_ATTR)) {
-        if (!this.__dataEnabled) {
-          super._initializeProperties();
-        }
-        super._enableProperties();
-      }
-    }
-
-    // only go if "enabled"
+    // Prevent element from disconnecting when it's upgrade disabled.
     /** @override */
     disconnectedCallback() {
-      if (this.__dataEnabled) {
+      if (!this.__isUpgradeDisabled) {
         super.disconnectedCallback();
       }
     }