We should use UserID object to identify users instead of username.

chromeos/tpm/tpm_token_info_getter.h

Index: chromeos/tpm/tpm_token_info_getter.h
diff --git a/chromeos/tpm/tpm_token_info_getter.h b/chromeos/tpm/tpm_token_info_getter.h
index f1f39a6e91ba33246b70e8073ca3b15865539f0f..0866526351ee997cc84d5a3cc9ff84ef31a69906 100644
--- a/chromeos/tpm/tpm_token_info_getter.h
+++ b/chromeos/tpm/tpm_token_info_getter.h
@@ -13,6 +13,7 @@
 #include "base/time/time.h"
 #include "chromeos/chromeos_export.h"
 #include "chromeos/dbus/dbus_method_call_status.h"
+#include "components/user_manager/user_id.h"
 
 namespace base {
 class TaskRunner;
@@ -46,7 +47,7 @@ class CHROMEOS_EXPORT TPMTokenInfoGetter {
 
   // Factory method for TPMTokenInfoGetter for a user token.
   static scoped_ptr<TPMTokenInfoGetter> CreateForUserToken(
-      const std::string& user_id,
+      const user_manager::UserID& user_id,
       CryptohomeClient* cryptohome_client,
       const scoped_refptr<base::TaskRunner>& delayed_task_runner);
 
@@ -79,7 +80,7 @@ class CHROMEOS_EXPORT TPMTokenInfoGetter {
 
   TPMTokenInfoGetter(
       Type type,
-      const std::string& user_id,
+      const user_manager::UserID& user_id,
       CryptohomeClient* cryptohome_client,
       const scoped_refptr<base::TaskRunner>& delayed_task_runner);
 
@@ -107,7 +108,7 @@ class CHROMEOS_EXPORT TPMTokenInfoGetter {
   State state_;
 
   // The user id associated with the TPMTokenInfoGetter. Empty for system token.
-  std::string user_id_;
+  user_manager::UserID user_id_;
 
   TPMTokenInfoCallback callback_;