get updateComplete() {
        return this._getUpdateComplete();
    }
Returns a Promise that resolves when the element has completed updating.
The Promise value is a boolean that is `true` if the element completed the
update without triggering another update. The Promise result is `false` if
a property was set inside `updated()`. If the Promise is rejected, an
exception was thrown during the update.

To await additional asynchronous work, override the `_getUpdateComplete`
method. For example, it is sometimes useful to await a rendered element
before fulfilling this Promise. To do this, first await
`super._getUpdateComplete()`, then any subsequent state.

@returns {Promise} The Promise returns a boolean that indicates if the
update resolved without triggering another update.