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

chrome/browser/ui/webui/policy_ui.cc

Index: chrome/browser/ui/webui/policy_ui.cc
diff --git a/chrome/browser/ui/webui/policy_ui.cc b/chrome/browser/ui/webui/policy_ui.cc
index 03d43485804641fe4dced0da2ec12c88bcb51905..8ca69211786f5d4e5f44875992bb30818d487578 100644
--- a/chrome/browser/ui/webui/policy_ui.cc
+++ b/chrome/browser/ui/webui/policy_ui.cc
@@ -40,6 +40,7 @@
 #include "components/policy/core/common/schema.h"
 #include "components/policy/core/common/schema_map.h"
 #include "components/policy/core/common/schema_registry.h"
+#include "components/user_manager/user_id.h"
 #include "content/public/browser/web_contents.h"
 #include "content/public/browser/web_ui.h"
 #include "content/public/browser/web_ui_data_source.h"
@@ -331,7 +332,7 @@ class DeviceLocalAccountPolicyStatusProvider
       public policy::DeviceLocalAccountPolicyService::Observer {
  public:
   DeviceLocalAccountPolicyStatusProvider(
-      const std::string& user_id,
+      const user_manager::UserID& user_id,
       policy::DeviceLocalAccountPolicyService* service);
   ~DeviceLocalAccountPolicyStatusProvider() override;
 
@@ -339,11 +340,11 @@ class DeviceLocalAccountPolicyStatusProvider
   void GetStatus(base::DictionaryValue* dict) override;
 
   // policy::DeviceLocalAccountPolicyService::Observer implementation.
-  void OnPolicyUpdated(const std::string& user_id) override;
+  void OnPolicyUpdated(const user_manager::UserID& user_id) override;
   void OnDeviceLocalAccountsChanged() override;
 
  private:
-  const std::string user_id_;
+  const user_manager::UserID user_id_;
   policy::DeviceLocalAccountPolicyService* service_;
 
   DISALLOW_COPY_AND_ASSIGN(DeviceLocalAccountPolicyStatusProvider);
@@ -496,7 +497,7 @@ void DevicePolicyStatusProvider::GetStatus(base::DictionaryValue* dict) {
 }
 
 DeviceLocalAccountPolicyStatusProvider::DeviceLocalAccountPolicyStatusProvider(
-    const std::string& user_id,
+    const user_manager::UserID& user_id,
     policy::DeviceLocalAccountPolicyService* service)
       : user_id_(user_id),
         service_(service) {
@@ -527,7 +528,7 @@ void DeviceLocalAccountPolicyStatusProvider::GetStatus(
 }
 
 void DeviceLocalAccountPolicyStatusProvider::OnPolicyUpdated(
-    const std::string& user_id) {
+    const user_manager::UserID& user_id) {
   if (user_id == user_id_)
     NotifyStatusChange();
 }
@@ -570,7 +571,7 @@ void PolicyUIHandler::RegisterMessages() {
     if (local_account_service) {
       user_status_provider_.reset(
           new DeviceLocalAccountPolicyStatusProvider(
-              user_manager->GetLoggedInUser()->email(), local_account_service));
+              user_manager->GetLoggedInUser()->GetUserID(), local_account_service));
     }
   } else {
     policy::UserCloudPolicyManagerChromeOS* user_cloud_policy_manager =