function assertPasswordLinkingPage(opt_email, opt_idpDisplayName) {
  assertPage_(container, 'firebaseui-id-page-password-linking');
  if (opt_email) {
    assertPageContainsText(opt_email);
  }
  if (opt_idpDisplayName) {
    assertPageContainsText(opt_idpDisplayName);
  }
}
Asserts that password linking page is displayed. If an email is provided, it
checks that the email is populated in the page body.
@param {string=} opt_email Optional email to check.
@param {string=} opt_idpDisplayName Optional idp display name to check.