Have content/ create and destroy its own threads.

content/public/browser/io_thread_delegate.h

+// 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.
+
+#ifndef CONTENT_PUBLIC_BROWSER_IO_THREAD_DELEGATE_H_
+#define CONTENT_PUBLIC_BROWSER_IO_THREAD_DELEGATE_H_
+#pragma once
+
+#include "base/basictypes.h"
+
+namespace content {
+
+// Some embedders may want to attach complex state to the IO thread,
+// that is initialized before anything else happens on the thread, and
+// torn down as the last thing that occurs on the thread.
+//
+// This is the interface to the object implementors need to provide
+// via BrowserMainParts::PreMainMessageLoopRun to enable such
+// initialization and teardown.
+class IOThreadDelegate {
+ public:
+  virtual ~IOThreadDelegate() {}
+
+  // Called as the first thing to happen on the IO thread.
+  virtual void Init() = 0;
+
+  // Called as the last thing processed on the IO thread.
+  virtual void CleanUp() = 0;
+};
+
+}  // namespace content
+
+#endif  // CONTENT_PUBLIC_BROWSER_IO_THREAD_DELEGATE_H_