text: // Helper to access the element, its associated loading promise, and also to
  // resolve the promise.
  class ElementLoadPromise {
    constructor(element_id) {
      this.element_id = element_id;
      this.promise = new Promise(resolve => {
        this.resolve = resolve
      });
    }
    element() {
      return document.getElementById(this.element_id);
    }
  }
  