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

ash/test/test_session_state_delegate.cc

Index: ash/test/test_session_state_delegate.cc
diff --git a/ash/test/test_session_state_delegate.cc b/ash/test/test_session_state_delegate.cc
index 482ebea340860772588816f9ba32e84e62efd6ed..bd0bdd37d41f82d795a8e96fd235fd952e5dd0ce 100644
--- a/ash/test/test_session_state_delegate.cc
+++ b/ash/test/test_session_state_delegate.cc
@@ -51,7 +51,7 @@
 
   std::string GetEmail() const override { return display_email_; }
 
-  const AccountId& GetAccountId() const override { return account_id_; }
+  AccountId GetAccountId() const override { return account_id_; }
 
   const gfx::ImageSkia& GetImage() const override { return user_image_; }