showInvalidPassword = function(error) {
    firebaseui.auth.ui.element.setValid(component.getPasswordElement(), false);
    firebaseui.auth.ui.element.show(component.getPasswordErrorElement(),
        firebaseui.auth.widget.handler.common.getErrorMessage(error));
  }
Handles the linking flow once the user has entered his password.
@param {firebaseui.auth.AuthUI} app The current Firebase UI instance whose
    configuration is used.
@param {firebaseui.auth.ui.page.PasswordLinking} component The UI component.
@param {string} email The user's email.
@param {!firebase.auth.AuthCredential} pendingCredential The pending
    credential to link to a successfully signed in user.
@private