Have content/ create and destroy its own threads.

content/shell/shell_browser_context.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 "content/shell/shell_browser_context.h"
 
 #include "base/bind.h"
 #include "base/file_util.h"
 #include "base/logging.h"
 #include "base/path_service.h"
+#include "base/threading/thread.h"
 #include "content/browser/appcache/chrome_appcache_service.h"
 #include "content/browser/chrome_blob_storage_context.h"
 #include "content/browser/download/download_id_factory.h"
 #include "content/browser/download/download_manager_impl.h"
 #include "content/browser/download/download_status_updater.h"
 #include "content/browser/file_system/browser_file_system_helper.h"
 #include "content/browser/geolocation/geolocation_permission_context.h"
 #include "content/browser/host_zoom_map.h"
 #include "content/browser/in_process_webkit/webkit_context.h"
 #include "content/browser/speech/speech_input_preferences.h"
@@ skipping 112 matching lines @@
     download_manager_delegate_->SetDownloadManager(download_manager_.get());
     download_manager_->Init(this);
   }
   return download_manager_.get();
 }
 
 net::URLRequestContextGetter* ShellBrowserContext::GetRequestContext()  {
   if (!url_request_getter_) {
     url_request_getter_ = new ShellURLRequestContextGetter(
         GetPath(),
-        shell_main_parts_->io_thread()->message_loop(),
-        shell_main_parts_->file_thread()->message_loop());
+        BrowserThread::UnsafeGetBrowserThread(
+            BrowserThread::IO)->message_loop(),
+        BrowserThread::UnsafeGetBrowserThread(
+            BrowserThread::FILE)->message_loop());
   }
   return url_request_getter_;
 }
 
 net::URLRequestContextGetter*
     ShellBrowserContext::GetRequestContextForRenderProcess(
         int renderer_child_id)  {
   return GetRequestContext();
 }
 
@@ skipping 99 matching lines @@
     base::Bind(
         &ChromeAppCacheService::InitializeOnIOThread,
         appcache_service_.get(),
         IsOffTheRecord()
             ? FilePath() : GetPath().Append(FILE_PATH_LITERAL("AppCache")),
         &GetResourceContext(),
         special_storage_policy));
 }
 
 }  // namespace content