Fix a crash on showing sync setup dialog in guest mode.

chrome/browser/ui/webui/sync_setup_handler.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/ui/webui/sync_setup_handler.h"
 
 #include "base/basictypes.h"
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/command_line.h"
@@ skipping 711 matching lines @@
   ProfileMetrics::LogProfileSyncInfo(ProfileMetrics::SYNC_CUSTOMIZE);
   if (configuration.encrypt_all)
     ProfileMetrics::LogProfileSyncInfo(ProfileMetrics::SYNC_ENCRYPT);
   if (configuration.passphrase_is_gaia && !configuration.passphrase.empty())
     ProfileMetrics::LogProfileSyncInfo(ProfileMetrics::SYNC_PASSPHRASE);
   if (!configuration.sync_everything)
     ProfileMetrics::LogProfileSyncInfo(ProfileMetrics::SYNC_CHOOSE);
 }
 
 void SyncSetupHandler::HandleShowSetupUI(const base::ListValue* args) {
-  ProfileSyncService* service = GetSyncService();
-  DCHECK(service);
+  if (!GetSyncService()) {
+    DLOG(WARNING) << "Cannot display sync UI when sync is disabled";
+    CloseUI();
+    return;
+  }
 
   SigninManagerBase* signin =
       SigninManagerFactory::GetForProfile(GetProfile());
   if (signin->GetAuthenticatedUsername().empty()) {
     // For web-based signin, the signin page is not displayed in an overlay
     // on the settings page. So if we get here, it must be due to the user
     // cancelling signin (by reloading the sync settings page during initial
     // signin) or by directly navigating to settings/syncSetup
     // (http://crbug.com/229836). So just exit and go back to the settings page.
     DLOG(WARNING) << "Cannot display sync setup UI when not signed in";
@@ skipping 175 matching lines @@
 
   LoginUIService* service = GetLoginUIService();
   DCHECK(service);
   service->current_login_ui()->FocusUI();
   return true;
 }
 
 LoginUIService* SyncSetupHandler::GetLoginUIService() const {
   return LoginUIServiceFactory::GetForProfile(GetProfile());
 }