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

components/user_manager/empty_user_info.cc

Index: components/user_manager/empty_user_info.cc
diff --git a/components/user_manager/empty_user_info.cc b/components/user_manager/empty_user_info.cc
index 08d4a19f84512611c8c396ae56b71d5177bb719e..07b4087ba0d9c9652b76ecb98d97e016b64c754d 100644
--- a/components/user_manager/empty_user_info.cc
+++ b/components/user_manager/empty_user_info.cc
@@ -31,7 +31,7 @@ std::string EmptyUserInfo::GetEmail() const {
   return std::string();
 }
 
-AccountId EmptyUserInfo::GetAccountId() const {
+const AccountId& EmptyUserInfo::GetAccountId() const {
   NOTIMPLEMENTED();
   return EmptyAccountId();
 }