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

chromeos/dbus/session_manager_client.h

Index: chromeos/dbus/session_manager_client.h
diff --git a/chromeos/dbus/session_manager_client.h b/chromeos/dbus/session_manager_client.h
index 254e762d8e988bbe03de793a0268a2fa70424f33..32f1d659780d1c2724d517e8b4b299f0c6b93917 100644
--- a/chromeos/dbus/session_manager_client.h
+++ b/chromeos/dbus/session_manager_client.h
@@ -15,6 +15,10 @@
 #include "chromeos/dbus/dbus_client.h"
 #include "chromeos/dbus/dbus_client_implementation_type.h"
 
+namespace user_manager {
+class UserID;
+}
+
 namespace chromeos {
 
 // SessionManagerClient is used to communicate with the session manager.
@@ -77,7 +81,7 @@ class CHROMEOS_EXPORT SessionManagerClient : public DBusClient {
   virtual void RestartJob(int pid, const std::string& command_line) = 0;
 
   // Starts the session for the user.
-  virtual void StartSession(const std::string& user_email) = 0;
+  virtual void StartSession(const user_manager::UserID& user_id) = 0;
 
   // Stops the current session.
   virtual void StopSession() = 0;
@@ -102,7 +106,7 @@ class CHROMEOS_EXPORT SessionManagerClient : public DBusClient {
 
   // Map that is used to describe the set of active user sessions where |key|
   // is user_id and |value| is user_id_hash.
-  typedef std::map<std::string, std::string> ActiveSessionsMap;
+  typedef std::map<user_manager::UserID, std::string> ActiveSessionsMap;
 
   // The ActiveSessionsCallback is used for the RetrieveActiveSessions()
   // method. It receives |sessions| argument where the keys are user_ids for
@@ -130,10 +134,10 @@ class CHROMEOS_EXPORT SessionManagerClient : public DBusClient {
   virtual void RetrieveDevicePolicy(const RetrievePolicyCallback& callback) = 0;
 
   // Fetches the user policy blob stored by the session manager for the given
-  // |username|. Upon completion of the retrieve attempt, we will call the
+  // |user_id|. Upon completion of the retrieve attempt, we will call the
   // provided callback.
   virtual void RetrievePolicyForUser(
-      const std::string& username,
+      const user_manager::UserID& user_id,
       const RetrievePolicyCallback& callback) = 0;
 
   // Same as RetrievePolicyForUser() but blocks until a reply is received, and
@@ -143,7 +147,7 @@ class CHROMEOS_EXPORT SessionManagerClient : public DBusClient {
   // considered acceptable (e.g. restarting the browser after a crash or after
   // a flag change).
   virtual std::string BlockingRetrievePolicyForUser(
-      const std::string& username) = 0;
+      const user_manager::UserID& user_id) = 0;
 
   // Fetches the policy blob associated with the specified device-local account
   // from session manager.  |callback| is invoked up on completion.
@@ -162,8 +166,8 @@ class CHROMEOS_EXPORT SessionManagerClient : public DBusClient {
                                  const StorePolicyCallback& callback) = 0;
 
   // Attempts to asynchronously store |policy_blob| as user policy for the given
-  // |username|. Upon completion of the store attempt, we will call callback.
-  virtual void StorePolicyForUser(const std::string& username,
+  // |user_id|. Upon completion of the store attempt, we will call callback.
+  virtual void StorePolicyForUser(const user_manager::UserID& user_id,
                                   const std::string& policy_blob,
                                   const StorePolicyCallback& callback) = 0;
 
@@ -176,7 +180,7 @@ class CHROMEOS_EXPORT SessionManagerClient : public DBusClient {
 
   // Sets the flags to be applied next time by the session manager when Chrome
   // is restarted inside an already started session for a particular user.
-  virtual void SetFlagsForUser(const std::string& username,
+  virtual void SetFlagsForUser(const user_manager::UserID& user_id,
                                const std::vector<std::string>& flags) = 0;
 
   typedef base::Callback<void(const std::vector<std::string>& state_keys)>