focusStealerListener_(event) {
    // Space, Tab, ENTER, ESC, arrow keys.
    var allowedKeycodes = [
      goog.events.KeyCodes.TAB, goog.events.KeyCodes.SPACE,
      goog.events.KeyCodes.ENTER, goog.events.KeyCodes.ESC,
      goog.events.KeyCodes.LEFT, goog.events.KeyCodes.UP,
      goog.events.KeyCodes.RIGHT, goog.events.KeyCodes.DOWN
    ];

    if (!(goog.array.contains(allowedKeycodes, event.keyCode))) {
      if (event.type == goog.events.EventType.KEYPRESS) {
        this.notifyOfSuppression_();
      }
      goog.dom.getElement('focus-stealer').focus();
      event.preventDefault();
      event.stopPropagation();
      event.stopImmediatePropagation();
    }
  }
Prevents keypresses from reaching the document in the webview by focusing
an invisible element.
@param  {!Event} event
@private