should provide username suggestions from saved logins in autocomplete instead of form history.
This would probably be easiest to implement like the existing type=password special case in
markAsLoginManagerField) and then teaching the password manager autocomplete search code that the field should be treated as a username field.
- The downside of this approach is that it means that if there are no saved usernames, the user won't get a form history fallback…
The chrome-only API GetAutocompleteInfo exists on <input> to get the parsed values. We can check that the
fieldName returned is "username".