Added flag gaia-endpoint for testing with different flows

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

Index: chrome/browser/ui/webui/chromeos/login/gaia_screen_handler.cc
diff --git a/chrome/browser/ui/webui/chromeos/login/gaia_screen_handler.cc b/chrome/browser/ui/webui/chromeos/login/gaia_screen_handler.cc
index 3fa96213334c04fd753add6cc344a76858ccae93..f22a6906d10d784ce57073fe6d701762ba9dbdaa 100644
--- a/chrome/browser/ui/webui/chromeos/login/gaia_screen_handler.cc
+++ b/chrome/browser/ui/webui/chromeos/login/gaia_screen_handler.cc
@@ -222,6 +222,10 @@ void GaiaScreenHandler::LoadGaia(const GaiaContext& context) {
           : GaiaUrls::GetInstance()->gaia_url();
   params.SetString("gaiaUrl", gaia_url.spec());
 
+  if (command_line->HasSwitch(switches::kGaiaEndpointChromeOS)) {
+    params.SetString("gaiaEndpoint", command_line->GetSwitchValueASCII(
+                                         switches::kGaiaEndpointChromeOS));
+  }
   if (context.embedded_signin_enabled) {
     params.SetBoolean("useEmbedded", true);
     // We set 'constrained' here to switch troubleshooting page on embedded