ChromeOS: fix OOBE crash.

chrome/browser/chromeos/login/wizard_controller.cc

Index: chrome/browser/chromeos/login/wizard_controller.cc
diff --git a/chrome/browser/chromeos/login/wizard_controller.cc b/chrome/browser/chromeos/login/wizard_controller.cc
index 019b4cd21ea1764f610e00203f8cdc83216b8aee..51ea2b3a8d68fc266bda1564958ef8e0ac0c5d15 100644
--- a/chrome/browser/chromeos/login/wizard_controller.cc
+++ b/chrome/browser/chromeos/login/wizard_controller.cc
@@ -419,6 +419,10 @@ void WizardController::ShowNetworkScreen() {
 }
 
 void WizardController::ShowLoginScreen(const LoginScreenContext& context) {
+  // This may be triggered by multiply asynchronous events from the JS side.
+  if (login_screen_started_)
+    return;
+
   if (!time_eula_accepted_.is_null()) {
     base::TimeDelta delta = base::Time::Now() - time_eula_accepted_;
     UMA_HISTOGRAM_MEDIUM_TIMES("OOBE.EULAToSignInTime", delta);