importKeyring_() {
    var importDiv = goog.dom.getElement(constants.ElementId.KEYRING_IMPORT_DIV);
    var fileInput = importDiv.querySelector('input');

    if (fileInput.files.length > 0) {
      this.importCallback_(fileInput.files[0]);
    }
  }
Handles requests from the user to import an existing keyring.
@private