This CL replaces user_manager::UserID with AccountId.

ash/system/user/tray_user.cc

Index: ash/system/user/tray_user.cc
diff --git a/ash/system/user/tray_user.cc b/ash/system/user/tray_user.cc
index fd101e7bed26b41d998761ff538456b7b569c6fb..f9546e3ecbc3a46266c85b2a2e340d88549ab5f8 100644
--- a/ash/system/user/tray_user.cc
+++ b/ash/system/user/tray_user.cc
@@ -20,6 +20,7 @@
 #include "ash/system/user/user_view.h"
 #include "base/logging.h"
 #include "base/strings/string16.h"
+#include "components/signin/core/account_id/account_id.h"
 #include "components/user_manager/user_info.h"
 #include "grit/ash_strings.h"
 #include "ui/aura/window.h"
@@ -115,7 +116,8 @@ views::View* TrayUser::CreateDetailedView(user::LoginStatus status) {
   std::string user_id = Shell::GetInstance()
                             ->session_state_delegate()
                             ->GetUserInfo(0)
-                            ->GetUserID();
+                            ->GetUserID()
+                            .GetUserEmail();
   tray::UserAccountsDelegate* delegate =
       Shell::GetInstance()->system_tray_delegate()->GetUserAccountsDelegate(
           user_id);

[stevenjb, 2015/10/22 17:52:36]

Can we actually change GetUserAccountsDelegate to take a const AccountId&
instead? (and change user_id to a const AccountId&)

[Alexander Alekseev, 2015/10/23 09:11:20]

Let's leave this for another CL. This one replaces only interfaces in
UserManager namespace.

Also it is not yet possible to use reference here, because GetUserID() returns a
copy for historic reasons. I'll update this to use reference as soon as UserInfo
would store real ID.

[stevenjb, 2015/10/23 17:17:02]

I suppose that is OK, although it does seem like we would be better off changing
UserInfo to store a copy and return a const& first, otherwise we have a version
that is potentially doing a lot of extra copying.