Have content/ create and destroy its own threads.

chrome/browser/spellchecker/spellcheck_host_impl.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/spellchecker/spellcheck_host_impl.h"
 
 #include <set>
 
 #include "base/bind.h"
 #include "base/file_util.h"
 #include "base/logging.h"
+#include "base/message_loop.h"
 #include "base/path_service.h"
 #include "base/string_split.h"
 #include "base/threading/thread_restrictions.h"
 #include "base/utf_string_conversions.h"
 #include "chrome/browser/prefs/pref_service.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/spellchecker/spellcheck_host_metrics.h"
 #include "chrome/browser/spellchecker/spellcheck_profile_provider.h"
 #include "chrome/browser/spellchecker/spellchecker_platform_engine.h"
 #include "chrome/common/chrome_constants.h"
@@ skipping 454 matching lines @@
 }
 
 void SpellCheckHostImpl::AddWordComplete(const std::string& word) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
 
   for (RenderProcessHost::iterator i(RenderProcessHost::AllHostsIterator());
        !i.IsAtEnd(); i.Advance()) {
     i.GetCurrentValue()->Send(new SpellCheckMsg_WordAdded(word));
   }
 }