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

chromeos/dbus/fake_session_manager_client.cc

Index: chromeos/dbus/fake_session_manager_client.cc
diff --git a/chromeos/dbus/fake_session_manager_client.cc b/chromeos/dbus/fake_session_manager_client.cc
index 27fe2df2bf1ec0eaa04b1b469378b23a65e959e2..ddb6cdec28da580b48b5b841031a103ec6069529 100644
--- a/chromeos/dbus/fake_session_manager_client.cc
+++ b/chromeos/dbus/fake_session_manager_client.cc
@@ -50,11 +50,11 @@ void FakeSessionManagerClient::RestartJob(int pid,
                                           const std::string& command_line) {
 }
 
-void FakeSessionManagerClient::StartSession(const std::string& user_email) {
-  DCHECK_EQ(0UL, user_sessions_.count(user_email));
+void FakeSessionManagerClient::StartSession(const user_manager::UserID& user_id) {
+  DCHECK_EQ(0UL, user_sessions_.count(user_id));
   std::string user_id_hash =
-      CryptohomeClient::GetStubSanitizedUsername(user_email);
-  user_sessions_[user_email] = user_id_hash;
+      CryptohomeClient::GetStubSanitizedUsername(user_id);
+  user_sessions_[user_id] = user_id_hash;
 }
 
 void FakeSessionManagerClient::StopSession() {
@@ -94,15 +94,15 @@ void FakeSessionManagerClient::RetrieveDevicePolicy(
 }
 
 void FakeSessionManagerClient::RetrievePolicyForUser(
-    const std::string& username,
+    const user_manager::UserID& user_id,
     const RetrievePolicyCallback& callback) {
   base::MessageLoop::current()->PostTask(
-      FROM_HERE, base::Bind(callback, user_policies_[username]));
+      FROM_HERE, base::Bind(callback, user_policies_[user_id]));
 }
 
 std::string FakeSessionManagerClient::BlockingRetrievePolicyForUser(
-    const std::string& username) {
-  return user_policies_[username];
+    const user_manager::UserID& user_id) {
+  return user_policies_[user_id];
 }
 
 void FakeSessionManagerClient::RetrieveDeviceLocalAccountPolicy(
@@ -122,10 +122,10 @@ void FakeSessionManagerClient::StoreDevicePolicy(
 }
 
 void FakeSessionManagerClient::StorePolicyForUser(
-    const std::string& username,
+    const user_manager::UserID& user_id,
     const std::string& policy_blob,
     const StorePolicyCallback& callback) {
-  user_policies_[username] = policy_blob;
+  user_policies_[user_id] = policy_blob;
   base::MessageLoop::current()->PostTask(FROM_HERE, base::Bind(callback, true));
 }
 
@@ -138,7 +138,7 @@ void FakeSessionManagerClient::StoreDeviceLocalAccountPolicy(
 }
 
 void FakeSessionManagerClient::SetFlagsForUser(
-    const std::string& username,
+    const user_manager::UserID& user_id,
     const std::vector<std::string>& flags) {
 }
 
@@ -158,15 +158,15 @@ void FakeSessionManagerClient::set_device_policy(
 }
 
 const std::string& FakeSessionManagerClient::user_policy(
-    const std::string& username) const {
-  std::map<std::string, std::string>::const_iterator it =
-      user_policies_.find(username);
+    const user_manager::UserID& user_id) const {
+  std::map<user_manager::UserID, std::string>::const_iterator it =
+      user_policies_.find(user_id);
   return it == user_policies_.end() ? base::EmptyString() : it->second;
 }
 
-void FakeSessionManagerClient::set_user_policy(const std::string& username,
+void FakeSessionManagerClient::set_user_policy(const user_manager::UserID& user_id,
                                                const std::string& policy_blob) {
-  user_policies_[username] = policy_blob;
+  user_policies_[user_id] = policy_blob;
 }
 
 const std::string& FakeSessionManagerClient::device_local_account_policy(