Reland of This CL replaces e-mail with AccountId on user selection screen.

chrome/browser/chromeos/login/screens/chrome_user_selection_screen.h

Index: chrome/browser/chromeos/login/screens/chrome_user_selection_screen.h
diff --git a/chrome/browser/chromeos/login/screens/chrome_user_selection_screen.h b/chrome/browser/chromeos/login/screens/chrome_user_selection_screen.h
index e276911a1136baadd97a1ee5c4691b46335728b8..11ab0d3fa064d4f953b3cbb6af5e67e9843642c1 100644
--- a/chrome/browser/chromeos/login/screens/chrome_user_selection_screen.h
+++ b/chrome/browser/chromeos/login/screens/chrome_user_selection_screen.h
@@ -14,6 +14,8 @@
 #include "base/memory/weak_ptr.h"
 #include "chrome/browser/chromeos/login/screens/user_selection_screen.h"
 #include "chrome/browser/chromeos/policy/device_local_account_policy_service.h"
+
+class AccountId;
 
 namespace chromeos {
 
@@ -45,20 +47,20 @@
 
   // Notify the UI that the display name for a public session has changed,
   // taking the display name from the |User| owned by |UserManager|.
-  void SetPublicSessionDisplayName(const std::string& user_id);
+  void SetPublicSessionDisplayName(const AccountId& account_id);
 
   // Send an updated list of locales for a public session to the UI, consisting
   // of the |recommended_locales| followed by all other available locales.
   void SetPublicSessionLocales(
-      const std::string& user_id,
+      const AccountId& account_id,
       const std::vector<std::string>& recommended_locales);
 
   bool handler_initialized_;
 
   policy::DeviceLocalAccountPolicyService* device_local_account_policy_service_;
 
-  // Map from public session user IDs to their display names set by policy.
-  typedef std::map<std::string, std::string> DisplayNamesMap;
+  // Map from public session account IDs to their display names set by policy.
+  typedef std::map<AccountId, std::string> DisplayNamesMap;
   DisplayNamesMap public_session_display_names_;
 
   base::WeakPtrFactory<ChromeUserSelectionScreen> weak_factory_;