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

components/policy/core/common/cloud/component_cloud_policy_service.cc

Index: components/policy/core/common/cloud/component_cloud_policy_service.cc
diff --git a/components/policy/core/common/cloud/component_cloud_policy_service.cc b/components/policy/core/common/cloud/component_cloud_policy_service.cc
index ab519594f740e4ca27bcce0ef671feb612018993..081f3fec45f26e18f937b8b5c42bbd68d940871f 100644
--- a/components/policy/core/common/cloud/component_cloud_policy_service.cc
+++ b/components/policy/core/common/cloud/component_cloud_policy_service.cc
@@ -22,6 +22,7 @@
 #include "components/policy/core/common/cloud/resource_cache.h"
 #include "components/policy/core/common/schema.h"
 #include "components/policy/core/common/schema_map.h"
+#include "components/user_manager/user_id.h"
 #include "net/url_request/url_request_context_getter.h"
 #include "policy/proto/device_management_backend.pb.h"
 
@@ -79,8 +80,8 @@ class ComponentCloudPolicyService::Backend
 
   ~Backend() override;
 
-  // |username| and |dm_token| will be  used to validate the cached policies.
-  void SetCredentials(const std::string& username, const std::string& dm_token);
+  // |user_id| and |dm_token| will be  used to validate the cached policies.
+  void SetCredentials(const user_manager::UserID& username, const std::string& dm_token);
 
   // Loads the |store_| and starts downloading updates.
   void Init(scoped_refptr<SchemaMap> schema_map);
@@ -140,13 +141,13 @@ ComponentCloudPolicyService::Backend::Backend(
 ComponentCloudPolicyService::Backend::~Backend() {}
 
 void ComponentCloudPolicyService::Backend::SetCredentials(
-    const std::string& username,
+    const user_manager::UserID& user_id,
     const std::string& dm_token) {
-  if (username.empty() || dm_token.empty()) {
+  if (user_id.empty() || dm_token.empty()) {
     // No sign-in credentials, so drop any cached policy.
     store_.Clear();
   } else {
-    store_.SetCredentials(username, dm_token);
+    store_.SetCredentials(user_id, dm_token);
   }
 }
 
@@ -302,7 +303,8 @@ void ComponentCloudPolicyService::ClearCache() {
   backend_task_runner_->PostTask(FROM_HERE,
                                  base::Bind(&Backend::SetCredentials,
                                             base::Unretained(backend_.get()),
-                                            std::string(), std::string()));
+                                            user_manager::UserID(std::string(), std::string()),
+                                            std::string()));
 }
 
 void ComponentCloudPolicyService::OnSchemaRegistryReady() {
@@ -377,7 +379,7 @@ void ComponentCloudPolicyService::OnStoreLoaded(CloudPolicyStore* store) {
   backend_task_runner_->PostTask(FROM_HERE,
                                  base::Bind(&Backend::SetCredentials,
                                             base::Unretained(backend_.get()),
-                                            username,
+                                            user_manager::UserID(std::string() /* gaia_id */, username),
                                             request_token));
 
   if (!loaded_initial_policy_) {