Method registerElementInWindow_

src/service/extensions-impl.js:388–393

* @param {!Window} win * @param {string} name * @param {typeof ../base-element.BaseElement} implementationClass * @private

(win, name, implementationClass)

   * @private
   */
  registerElementInWindow_(win, name, implementationClass) {
    // Register the element in the window.
    upgradeOrRegisterElement(win, name, implementationClass);
    // Register this extension to resolve its Service Promise.
    registerServiceBuilder(win, name, emptyService);
  }

  /**
   * Add a service to the extension currently being registered. This is a