ChromeOS cryptohome should be able to use gaia id as user identifier.

chrome/browser/chromeos/login/session/user_session_manager.h

Index: chrome/browser/chromeos/login/session/user_session_manager.h
diff --git a/chrome/browser/chromeos/login/session/user_session_manager.h b/chrome/browser/chromeos/login/session/user_session_manager.h
index e875f2c9ea478f898ac249f86703f889c627d92b..c81a011a8fdd2103ac4cadd8517ccbf915f30673 100644
--- a/chrome/browser/chromeos/login/session/user_session_manager.h
+++ b/chrome/browser/chromeos/login/session/user_session_manager.h
@@ -433,7 +433,9 @@ class UserSessionManager
 
   // User sessions that have to be restored after browser crash.
   // [user_id] > [user_id_hash]
-  SessionManagerClient::ActiveSessionsMap pending_user_sessions_;
+  typedef std::map<AccountId, std::string> PendingUserSessions;

[xiyuan, 2016/02/17 23:14:25]

nit: new preferred the style is 

using PendingUserSessions = std::map<AccountId, std::string>;

See https://chromium-cpp.appspot.com/

[Alexander Alekseev, 2016/02/18 13:45:14]

Done.

+
+  PendingUserSessions pending_user_sessions_;
 
   base::ObserverList<chromeos::UserSessionStateObserver>
       session_state_observer_list_;