Have content/ create and destroy its own threads.

chrome/browser/safe_browsing/safe_browsing_service.cc

 // Copyright (c) 2011 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/safe_browsing/safe_browsing_service.h"
 
 #include "base/callback.h"
 #include "base/command_line.h"
 #include "base/lazy_instance.h"
 #include "base/path_service.h"
 #include "base/stl_util.h"
 #include "base/string_util.h"
+#include "base/threading/thread.h"
 #include "base/threading/thread_restrictions.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/metrics/metrics_service.h"
 #include "chrome/browser/prefs/pref_change_registrar.h"
 #include "chrome/browser/prefs/pref_service.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/profiles/profile_manager.h"
 #include "chrome/browser/safe_browsing/client_side_detection_service.h"
 #include "chrome/browser/safe_browsing/download_protection_service.h"
 #include "chrome/browser/safe_browsing/malware_details.h"
@@ skipping 1338 matching lines @@
     Stop();
 
   if (csd_service_.get())
     csd_service_->SetEnabledAndRefreshState(enable);
   if (download_service_.get()) {
     download_service_->SetEnabled(
         enable && CommandLine::ForCurrentProcess()->HasSwitch(
             switches::kEnableImprovedDownloadProtection));
   }
 }