webviewNewWindowHandler_(event) {
    var e = /** type {!chrome.NewWindowEvent} */ (event);
    e.preventDefault();
    var removeWebviewTimeout;
    if (e.targetUrl) {
      if (e.targetUrl == 'about:blank') {
        // Add a temporary webview element, looking for redirection URLs
        var aWebview =
            /** @type {Webview} */ (document.createElement('webview'));
        document.body.appendChild(aWebview);

        aWebview.request.onBeforeRequest.addListener(function(event) {
          var response = /** @type {!BlockingResponse} */ ({cancel: false});
          if (event.url == 'about:blank') {
            return response;
          }
          if (event.type !== 'main_frame') {
            return response;
          }
          clearTimeout(removeWebviewTimeout);
          document.body.removeChild(aWebview);
          // Create a new tab in the browser.
          window.open(event.url);
          response.cancel = true;
          return response;
        }, /** @type {!RequestFilter} */ ({urls: ['*://*/*']}), ['blocking']);
        e.window.attach(aWebview);
        removeWebviewTimeout = setTimeout(function() {
          document.body.removeChild(aWebview);
        }, 5000);  // Remove dangling webviews.
      } else {
        window.open(e.targetUrl);
      }
    }
  }
Opens a new window in the browser tab.
@param  {!Event} event The event.
@private