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

chrome/browser/chromeos/policy/user_cloud_policy_manager_chromeos.cc

Index: chrome/browser/chromeos/policy/user_cloud_policy_manager_chromeos.cc
diff --git a/chrome/browser/chromeos/policy/user_cloud_policy_manager_chromeos.cc b/chrome/browser/chromeos/policy/user_cloud_policy_manager_chromeos.cc
index 91f65eeec8705fe806e14a745212c97437c243f2..785e530284031bc7561d00937cadee395a5596e7 100644
--- a/chrome/browser/chromeos/policy/user_cloud_policy_manager_chromeos.cc
+++ b/chrome/browser/chromeos/policy/user_cloud_policy_manager_chromeos.cc
@@ -55,7 +55,7 @@ const char kUMAInitialFetchOAuth2Error[] =
 const char kUMAInitialFetchOAuth2NetworkError[] =
     "Enterprise.UserPolicyChromeOS.InitialFetch.OAuth2NetworkError";
 
-void OnWildcardCheckCompleted(const std::string& username,
+void OnWildcardCheckCompleted(const user_manager::UserID& user_id,
                               WildcardLoginChecker::Result result) {
   if (result == WildcardLoginChecker::RESULT_BLOCKED) {
     LOG(ERROR) << "Online wildcard login check failed, terminating session.";
@@ -65,7 +65,7 @@ void OnWildcardCheckCompleted(const std::string& username,
     // logged-in session is not possible. Fix this either by delaying the
     // cryptohome deletion operation or by getting rid of the in-session
     // wildcard check.
-    user_manager::UserManager::Get()->RemoveUserFromList(username);
+    user_manager::UserManager::Get()->RemoveUserFromList(user_id);
     chrome::AttemptUserExit();
   }
 }
@@ -89,6 +89,7 @@ UserCloudPolicyManagerChromeOS::UserCloudPolicyManagerChromeOS(
                          io_task_runner),
       store_(store.Pass()),
       external_data_manager_(external_data_manager.Pass()),
+      wildcard_user_id_(std::string(), std::string()),
       component_policy_cache_path_(component_policy_cache_path),
       wait_for_policy_fetch_(wait_for_policy_fetch),
       policy_fetch_timeout_(false, false) {
@@ -146,11 +147,11 @@ void UserCloudPolicyManagerChromeOS::OnAccessTokenAvailable(
     const std::string& access_token) {
   access_token_ = access_token;
 
-  if (!wildcard_username_.empty()) {
+  if (!wildcard_user_id_.empty()) {
     wildcard_login_checker_.reset(new WildcardLoginChecker());
     wildcard_login_checker_->StartWithAccessToken(
         access_token,
-        base::Bind(&OnWildcardCheckCompleted, wildcard_username_));
+        base::Bind(&OnWildcardCheckCompleted, wildcard_user_id_));
   }
 
   if (service() && service()->IsInitializationComplete() &&
@@ -165,9 +166,9 @@ bool UserCloudPolicyManagerChromeOS::IsClientRegistered() const {
 }
 
 void UserCloudPolicyManagerChromeOS::EnableWildcardLoginCheck(
-    const std::string& username) {
+    const user_manager::UserID& user_id) {
   DCHECK(access_token_.empty());
-  wildcard_username_ = username;
+  wildcard_user_id_ = user_id;
 }
 
 void UserCloudPolicyManagerChromeOS::Shutdown() {