[Password manager] Recognise squashed login+sign-up forms
Some pages contain a login form and a sign-up form squashed in one <form> element. While that is a bad practice, Chrome should be able to distinguish these forms from change-password forms (the difference being that the former will have at least one non-password text field between the login-part password field and the sign-up part password fields). This distinction enables Chrome to work on the login forms.
BUG=449714
Review URL: https://codereview.chromium.org/
1014683006
Cr-Commit-Position: refs/heads/master@{#321965}