Have content/ create and destroy its own threads.

chrome/browser/printing/print_dialog_gtk.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/print_dialog_gtk.h"
 
 #include <fcntl.h>
 #include <gtk/gtkpagesetupunixdialog.h>
 #include <gtk/gtkprintjob.h>
 #include <sys/stat.h>
 #include <sys/types.h>
 
 #include <string>
 #include <vector>
 
 #include "base/bind.h"
 #include "base/file_util.h"
 #include "base/file_util_proxy.h"
 #include "base/logging.h"
+#include "base/message_loop_proxy.h"
 #include "base/utf_string_conversions.h"
 #include "chrome/browser/ui/browser_list.h"
 #include "chrome/browser/ui/browser_window.h"
 #include "printing/metafile.h"
 #include "printing/print_job_constants.h"
 #include "printing/print_settings.h"
 #include "printing/print_settings_initializer_gtk.h"
 
 using content::BrowserThread;
 using printing::PageRanges;
@@ skipping 368 matching lines @@
   // Printing finished. Matches AddRef() in PrintDocument();
   Release();
 }
 
 void PrintDialogGtk::InitPrintSettings(const PageRanges& page_ranges,
                                        PrintSettings* settings) {
   printing::PrintSettingsInitializerGtk::InitPrintSettings(
       gtk_settings_, page_setup_, page_ranges, false, settings);
   context_->InitWithSettings(*settings);
 }