Fix a ChromeFrame crash which occurs in the background worker thread while dereferencing a NULL a...

chrome_frame/urlmon_url_request.cc

Index: chrome_frame/urlmon_url_request.cc
===================================================================
--- chrome_frame/urlmon_url_request.cc	(revision 107804)
+++ chrome_frame/urlmon_url_request.cc	(working copy)
@@ -1261,6 +1261,8 @@
         NewRunnableMethod(
             this, &UrlmonUrlRequestManager::StopAllRequestsHelper,
             &background_request_map_, &background_resource_map_lock_));
+     background_thread_->Stop();
+     background_thread_.reset();
   }
 }
 
@@ -1374,8 +1376,6 @@
 
 UrlmonUrlRequestManager::~UrlmonUrlRequestManager() {
   StopAll();
-  if (background_worker_thread_enabled_)
-    background_thread_->Stop();
 }
 
 void UrlmonUrlRequestManager::AddPrivacyDataForUrl(