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

chromeos/login/auth/extended_authenticator.h

Index: chromeos/login/auth/extended_authenticator.h
diff --git a/chromeos/login/auth/extended_authenticator.h b/chromeos/login/auth/extended_authenticator.h
index deaa6c4847a68c51af019b803868ed1e98a56c68..0a0a877802f4416c4e60988e203bffca72f142ea 100644
--- a/chromeos/login/auth/extended_authenticator.h
+++ b/chromeos/login/auth/extended_authenticator.h
@@ -15,6 +15,8 @@
 #include "chromeos/chromeos_export.h"
 #include "chromeos/cryptohome/cryptohome_parameters.h"
 
+class AccountId;
+
 namespace chromeos {
 
 class AuthStatusConsumer;
@@ -68,12 +70,13 @@ class CHROMEOS_EXPORT ExtendedAuthenticator
   virtual void AuthenticateToCheck(const UserContext& context,
                                    const base::Closure& success_callback) = 0;
 
-  // This call will create and mount the home dir for |user_id| with the given
-  // |keys| if the home dir is missing. If the home dir exists already, a mount
-  // attempt will be performed using the first key in |keys| for authentication.
-  // Note that all |keys| should have been transformed from plain text already.
+  // This call will create and mount the home dir for |account_id| with the
+  // given |keys| if the home dir is missing. If the home dir exists already, a
+  // mount attempt will be performed using the first key in |keys| for
+  // authentication.  Note that all |keys| should have been transformed from
+  // plain text already.
   // This method does not alter them.
-  virtual void CreateMount(const std::string& user_id,
+  virtual void CreateMount(const AccountId& account_id,
                            const std::vector<cryptohome::KeyDefinition>& keys,
                            const ResultCallback& success_callback) = 0;