Don't use staging GAIA if --gaia-url was explicitly specified in command line

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 ace8995ccdd46eb08ad04b2c383174e6f7b78edb..b5e8a5ca79edfc3290097df3fd479fc379f3b8d7 100644
--- a/chrome/browser/ui/webui/chromeos/login/gaia_screen_handler.cc
+++ b/chrome/browser/ui/webui/chromeos/login/gaia_screen_handler.cc
@@ -246,10 +246,12 @@ void GaiaScreenHandler::LoadGaia(const GaiaContext& context) {
     }
   }
 
-  if (StartupUtils::IsWebviewSigninEnabled()) {
+  if (!command_line->HasSwitch(::switches::kGaiaUrl) &&
+      StartupUtils::IsWebviewSigninEnabled()) {
     // We can't use switch --gaia-url in this case cause we need get
     // auth_code from staging gaia and make all the other auths against prod
     // gaia so user could use all the google services.
+    // TODO(dpolukhin): crbug.com/462204
     const GURL gaia_url = GURL(kStagingGaiaUrl);
     params.SetString("gaiaUrl", gaia_url.spec());
   } else {