constructor(startUrl) {
    super();
    /**
     * Helper proxy attached to the displayed Webview.
     * @type {e2e.ext.utils.WebviewHelperProxy}
     * @private
     */
    this.helperProxy_ = null;
    /**
     * Prompt object.
     * @type {ui.Prompt}
     * @private
     */
    this.prompt_ = null;
    /**
     * Bound focus stealer.
     * @type {function(!Event)}
     * @private
     */
    this.boundFocusStealer_ = goog.bind(this.focusStealerListener_, this);
    /**
     * True iff interaction with the web application in webview is suppressed.
     * @type {!boolean}
     * @private
     */
    this.interactionSuppressed_ = false;
    /**
     * True iff the toggle suppress key is currently down.
     * @type {!boolean}
     * @private
     */
    this.toggleInteractionSuppressKeyDown_ = false;
    /**
     * URL to load in a webview.
     * @type {string}
     * @private
     */
    this.startUrl_ = startUrl;
  }
@param {string} startUrl URL to load in a webview.