Indicate which authentication flow was used in UserContext

This CL adds a field to UserContext that indicates which authentication
flow was used (online without SAML, online with SAML, offline). This
distinction will be used to implement a policy that forces SAML users to
log in via the online authentication flow periodically.

BUG=332081
TEST=Manual (automated tests coming in follow-up CL that adds the policy)

Review URL: https://codereview.chromium.org/145073003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@246674 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 246674
Rename and deprecate chrome_settings_overrides.bookmarks_ui.hide_bookmark_button key

As discussed in comments on the Remove Bookmark Shortcut extension API proposal:
https://docs.google.com/a/chromium.org/document/d/1C2Mle92O9uGlji5y5gGDM5tNJ_tVE1Vb-2xgsZPNDTk

BUG=335655

Review URL: https://codereview.chromium.org/145173003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@246675 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 246675