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

chrome/browser/ui/ash/session_state_delegate_chromeos.cc

Index: chrome/browser/ui/ash/session_state_delegate_chromeos.cc
diff --git a/chrome/browser/ui/ash/session_state_delegate_chromeos.cc b/chrome/browser/ui/ash/session_state_delegate_chromeos.cc
index f7dcc0aab8d8d7a21c01b959733bccf8c133ac56..1a518d82266e1882e647e1db8b9a3f4d0239ded0 100644
--- a/chrome/browser/ui/ash/session_state_delegate_chromeos.cc
+++ b/chrome/browser/ui/ash/session_state_delegate_chromeos.cc
@@ -63,7 +63,7 @@ content::BrowserContext* SessionStateDelegateChromeos::GetBrowserContextByIndex(
 content::BrowserContext*
 SessionStateDelegateChromeos::GetBrowserContextForWindow(
     aura::Window* window) {
-  const std::string& user_id =
+  const user_manager::UserID& user_id =
       chrome::MultiUserWindowManager::GetInstance()->GetWindowOwner(window);
   return user_id.empty() ? NULL
                          : multi_user_util::GetProfileFromUserID(user_id);
@@ -72,7 +72,7 @@ SessionStateDelegateChromeos::GetBrowserContextForWindow(
 content::BrowserContext*
 SessionStateDelegateChromeos::GetUserPresentingBrowserContextForWindow(
     aura::Window* window) {
-  const std::string& user_id =
+  const user_manager::UserID& user_id =
       chrome::MultiUserWindowManager::GetInstance()->GetUserPresentingWindow(
           window);
   return user_id.empty() ? NULL
@@ -181,12 +181,12 @@ bool SessionStateDelegateChromeos::ShouldShowAvatar(
 }
 
 void SessionStateDelegateChromeos::SwitchActiveUser(
-    const std::string& user_id) {
+    const user_manager::UserID& user_id) {
   // Disallow switching to an already active user since that might crash.
   // Also check that we got a user id and not an email address.
-  DCHECK_EQ(user_id,
-            gaia::CanonicalizeEmail(gaia::SanitizeEmail(user_id)));
-  if (user_id == user_manager::UserManager::Get()->GetActiveUser()->email())
+  DCHECK_EQ(user_id.GetUserEmail(),
+            gaia::CanonicalizeEmail(gaia::SanitizeEmail(user_id.GetUserEmail())));
+  if (user_id == user_manager::UserManager::Get()->GetActiveUser()->GetUserID())
     return;
   TryToSwitchUser(user_id);
 }
@@ -199,14 +199,14 @@ void SessionStateDelegateChromeos::CycleActiveUser(CycleUser cycle_user) {
   const user_manager::UserList& logged_in_users =
       user_manager::UserManager::Get()->GetLoggedInUsers();
 
-  std::string user_id =
-      user_manager::UserManager::Get()->GetActiveUser()->email();
+  user_manager::UserID user_id =
+      user_manager::UserManager::Get()->GetActiveUser()->GetUserID();
 
   // Get an iterator positioned at the active user.
   user_manager::UserList::const_iterator it;
   for (it = logged_in_users.begin();
        it != logged_in_users.end(); ++it) {
-    if ((*it)->email() == user_id)
+    if ((*it)->GetUserID() == user_id)
       break;
   }
 
@@ -219,14 +219,14 @@ void SessionStateDelegateChromeos::CycleActiveUser(CycleUser cycle_user) {
   switch (cycle_user) {
     case CYCLE_TO_NEXT_USER:
       if (++it == logged_in_users.end())
-        user_id = (*logged_in_users.begin())->email();
+        user_id = (*logged_in_users.begin())->GetUserID();
       else
-        user_id = (*it)->email();
+        user_id = (*it)->GetUserID();
       break;
     case CYCLE_TO_PREVIOUS_USER:
       if (it == logged_in_users.begin())
         it = logged_in_users.end();
-      user_id = (*(--it))->email();
+      user_id = (*(--it))->GetUserID();
       break;
   }
 
@@ -259,14 +259,14 @@ void SessionStateDelegateChromeos::ActiveUserChanged(
     const user_manager::User* active_user) {
   FOR_EACH_OBSERVER(ash::SessionStateObserver,
                     session_state_observer_list_,
-                    ActiveUserChanged(active_user->email()));
+                    ActiveUserChanged(active_user->GetUserID()));
 }
 
 void SessionStateDelegateChromeos::UserAddedToSession(
     const user_manager::User* added_user) {
   FOR_EACH_OBSERVER(ash::SessionStateObserver,
                     session_state_observer_list_,
-                    UserAddedToSession(added_user->email()));
+                    UserAddedToSession(added_user->GetUserID()));
 }
 
 void SessionStateDelegateChromeos::OnUserAddingStarted() {
@@ -292,11 +292,11 @@ void SessionStateDelegateChromeos::NotifySessionStateChanged() {
                     SessionStateChanged(session_state_));
 }
 
-void DoSwitchUser(const std::string& user_id) {
+void DoSwitchUser(const user_manager::UserID& user_id) {
   user_manager::UserManager::Get()->SwitchActiveUser(user_id);
 }
 
 void SessionStateDelegateChromeos::TryToSwitchUser(
-    const std::string& user_id) {
+    const user_manager::UserID& user_id) {
   ash::TrySwitchingActiveUser(base::Bind(&DoSwitchUser, user_id));
 }