Add browser test for new user CrOS login flow

chrome/browser/ui/webui/chromeos/login/signin_screen_handler.cc

Index: chrome/browser/ui/webui/chromeos/login/signin_screen_handler.cc
diff --git a/chrome/browser/ui/webui/chromeos/login/signin_screen_handler.cc b/chrome/browser/ui/webui/chromeos/login/signin_screen_handler.cc
index 9ab2c5be9fefa0654898d09ff3a63a6826f138aa..13cff0f1a876d09b43e1061fd137713de4a659fa 100644
--- a/chrome/browser/ui/webui/chromeos/login/signin_screen_handler.cc
+++ b/chrome/browser/ui/webui/chromeos/login/signin_screen_handler.cc
@@ -1110,7 +1110,10 @@ void SigninScreenHandler::LoadAuthExtension(
     params.Set("localizedStrings", localized_strings);
   }
 
-  params.SetString("gaiaOrigin", GaiaUrls::GetInstance()->gaia_origin_url());
+  std::string gaia_origin = GaiaUrls::GetInstance()->gaia_origin_url();
+  if (!gaia_origin_for_test_.empty())
+    gaia_origin = gaia_origin_for_test_;
+  params.SetString("gaiaOrigin", gaia_origin);
   const CommandLine* command_line = CommandLine::ForCurrentProcess();
   if (command_line->HasSwitch(::switches::kGaiaUrlPath)) {
     params.SetString("gaiaUrlPath",