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

components/user_manager/user_info_impl.h

Index: components/user_manager/user_info_impl.h
diff --git a/components/user_manager/user_info_impl.h b/components/user_manager/user_info_impl.h
index 4922e3694c55e2781a707ca98bf5c4d69e8fb979..d2733ebf5ba889a862a3365317f36231a470b37b 100644
--- a/components/user_manager/user_info_impl.h
+++ b/components/user_manager/user_info_impl.h
@@ -8,6 +8,7 @@
 #include <string>
 
 #include "base/strings/string16.h"
+#include "components/signin/core/account_id/account_id.h"
 #include "components/user_manager/user_info.h"
 #include "components/user_manager/user_manager_export.h"
 #include "ui/gfx/image/image_skia.h"
@@ -24,10 +25,11 @@
   base::string16 GetDisplayName() const override;
   base::string16 GetGivenName() const override;
   std::string GetEmail() const override;
-  AccountId GetAccountId() const override;
+  const AccountId& GetAccountId() const override;
   const gfx::ImageSkia& GetImage() const override;
 
  private:
+  const AccountId account_id_;
   gfx::ImageSkia user_image_;
 
   DISALLOW_COPY_AND_ASSIGN(UserInfoImpl);