ChromeOS: fix OOBE crash.

chrome/browser/chromeos/login/wizard_controller.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/chromeos/login/wizard_controller.h"
 
 #include <signal.h>
 #include <stddef.h>
 #include <stdlib.h>
 #include <sys/types.h>
@@ skipping 401 matching lines @@
   VLOG(1) << "Showing network screen.";
   // Hide the status area initially; it only appears after OOBE first animates
   // in. Keep it visible if the user goes back to the existing network screen.
   SetStatusAreaVisible(HasScreen(kNetworkScreenName));
   SetCurrentScreen(GetScreen(kNetworkScreenName));
 
   MaybeStartListeningForSharkConnection();
 }
 
 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);
   }
   VLOG(1) << "Showing login screen.";
   SetStatusAreaVisible(true);
   host_->StartSignInScreen(context);
   smooth_show_timer_.Stop();
   oobe_ui_ = nullptr;
   login_screen_started_ = true;
@@ skipping 985 matching lines @@
             : policy::EnrollmentConfig::MODE_MANUAL_REENROLLMENT;
   }
 
   EnrollmentScreen* screen = EnrollmentScreen::Get(this);
   screen->SetParameters(effective_config, shark_controller_.get());
   SetStatusAreaVisible(true);
   SetCurrentScreen(screen);
 }
 
 }  // namespace chromeos