Version: 51
OS: desktop

What steps will reproduce the problem?
(1 )Go to https://9bf5d6a9ae58c0976f64da8a482db42e19365982.googledrive.com/host/0B4ln_TN4AjcNbzd3RDNQYlJRVG8 and save a credential using the form.
(2) Go to https://9bf5d6a9ae58c0976f64da8a482db42e19365982.googledrive.com/host/0B4ln_TN4AjcNbzd3RDNQYlJRVG8
(3) In the console type 
function processResponse(cred) {
window.location = '/';
}
navigator.credentials.get({password: true})
.then(processResponse)
.catch(function (e) { console.log(e); });
(4) The account chooser appears (correct), click the credential.
(5) Go to the page again and repeat. The account chooser appears (wrong, the credential should have became an "auto sign-in" one). Basically, the site will never be able to get a user auto signed-in.

The bug is that the autofill password manager detected successful login and "updated" the credential in the store wrongly.
A solution approved by Vaclav:
Once we return a non-empty credential either via auto-sign-in or the account chooser we should drop all the PasswordFormManager instances for the page. If the returned credential is wrong the Password Manager still should be able to autofill on the fallback form which appears after navigation.