https://mijn.ing.nl/login shows a password form, but Chrome fails to notice it.

The form is hidden in (multiple layers of) shadow DOM. Password manager gathers all password forms in PasswordAutofillAgent::SendPasswordForms via blink::WebDocument::Forms().

This apparently does the same thing as calling document.forms in the enclosing frame, which returns an empty collection on that site, as expected.

If Chrome wants to be able to save and fill forms within shadow DOM, PasswordAutofillAgent would need to get them from Blink via some other API.