Chrome Version       : 71.0.3578.0
URLs (if applicable) : https://www.chegg.com/auth?action=signup&redirect=https%3A%2F%2Fwww.chegg.com%2F

What steps will reproduce the problem?
1. Fill in the username and password
2. Click Student.

What is the expected result?
No DCHECK.

What happens instead of that?
The following DCHECK is hit in PasswordManager::OnLoginSuccessful:
  // If the form is eligible only for saving fallback, it shouldn't go here.
  DCHECK(!submitted_manager->GetPendingCredentials().only_for_fallback_saving);

Notes:
* This only affects the old parser. With chrome://flags/#new-password-form-parsing-for-saving enabled, there is no problem.
* Clicking the Student button hides the password field but seems to keep it in DOM.