The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/242283284b1b8df9b8e3b5dd854728e5589500c4

commit 242283284b1b8df9b8e3b5dd854728e5589500c4
Author: Xiyuan Xia <xiyuan@chromium.org>
Date: Thu Sep 21 19:50:57 2017

cros: SAML flow use auth code to bootstrap user session

If an auth code is issued for SAML flow, use it to perform
the /MergeSession call to bootstrap the user session.

Bug:  767143 
Change-Id: Id42a37c84db468f155edfde557ad789b86ab2c4b
Reviewed-on: https://chromium-review.googlesource.com/677485
Commit-Queue: Xiyuan Xia <xiyuan@chromium.org>
Reviewed-by: Achuith Bhandarkar <achuith@chromium.org>
Cr-Commit-Position: refs/heads/master@{#503539}
[modify] https://crrev.com/242283284b1b8df9b8e3b5dd854728e5589500c4/chrome/browser/chromeos/login/existing_user_controller.cc
[modify] https://crrev.com/242283284b1b8df9b8e3b5dd854728e5589500c4/chrome/browser/chromeos/login/session/user_session_manager.cc