Have content/ create and destroy its own threads.

chrome/browser/printing/printer_manager_dialog_linux.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/printing/printer_manager_dialog.h"
 
 #include "base/environment.h"
+#include "base/message_loop.h"
 #include "base/nix/xdg_util.h"
 #include "base/process_util.h"
 #include "content/common/process_watcher.h"
 #include "content/public/browser/browser_thread.h"
 
 using base::Environment;
 using content::BrowserThread;
 
 namespace {
 
@@ skipping 41 matching lines @@
 }  // anonymous namespace
 
 namespace printing {
 
 void PrinterManagerDialog::ShowPrinterManagerDialog() {
   BrowserThread::PostTask(BrowserThread::FILE, FROM_HERE,
       NewRunnableFunction(&DetectAndOpenPrinterConfigDialog));
 }
 
 }  // namespace printing