One of our engineers responded as follows:
Chrome.jsp initiate and add by calling google.principal.initialize and google.principal.add
Saml2post.jsp will complete the process by calling google.principal.complete
All other magic is in “js” file follow the https://www.chromium.org/administrators/advanced-integration-for-saml-sso-on-chrome-devices
He is not so sure about the 2nd answer but his guess is that new OS support this credentials save done out of the box.
Hope this helps!?