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

components/policy/core/common/cloud/component_cloud_policy_store.h

Index: components/policy/core/common/cloud/component_cloud_policy_store.h
diff --git a/components/policy/core/common/cloud/component_cloud_policy_store.h b/components/policy/core/common/cloud/component_cloud_policy_store.h
index 8b9cf8c436ddce73dea89d9c059594804e744982..08bada9d3097a037c62c74f87de35523ff193020 100644
--- a/components/policy/core/common/cloud/component_cloud_policy_store.h
+++ b/components/policy/core/common/cloud/component_cloud_policy_store.h
@@ -15,6 +15,7 @@
 #include "components/policy/core/common/policy_bundle.h"
 #include "components/policy/core/common/policy_namespace.h"
 #include "components/policy/policy_export.h"
+#include "components/user_manager/user_id.h"
 
 namespace enterprise_management {
 class ExternalPolicyData;
@@ -64,10 +65,10 @@ class POLICY_EXPORT ComponentCloudPolicyStore : public base::NonThreadSafe {
   // cached.
   const std::string& GetCachedHash(const PolicyNamespace& ns) const;
 
-  // |username| and |dm_token| are used to validate the cached data, and data
+  // |user_id| and |dm_token| are used to validate the cached data, and data
   // stored later.
   // All ValidatePolicy() requests without credentials fail.
-  void SetCredentials(const std::string& username,
+  void SetCredentials(const user_manager::UserID& user_id,
                       const std::string& dm_token);
 
   // Loads and validates all the currently cached protobufs and policy data.
@@ -131,7 +132,7 @@ class POLICY_EXPORT ComponentCloudPolicyStore : public base::NonThreadSafe {
 
   Delegate* delegate_;
   ResourceCache* cache_;
-  std::string username_;
+  user_manager::UserID user_id_;
   std::string dm_token_;
 
   PolicyBundle policy_bundle_;