Have content/ create and destroy its own threads.

content/browser/browser_process_io_thread.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 "content/browser/browser_process_io_thread.h"
+
+#include "content/public/browser/browser_thread.h"
+
+namespace content {
+
+BrowserProcessIOThread::BrowserProcessIOThread(IOThreadDelegate* delegate)
+    : BrowserProcessSubThread(BrowserThread::IO),
+      delegate_(delegate) {
+}
+
+BrowserProcessIOThread::~BrowserProcessIOThread() {
+  Stop();
+}
+
+void BrowserProcessIOThread::Init() {
+  BrowserProcessSubThread::Init();
+  if (delegate_)
+    delegate_->Init();
+}
+
+void BrowserProcessIOThread::CleanUp() {
+  BrowserProcessSubThread::CleanUp();
+  if (delegate_)
+    delegate_->CleanUp();
+}
+
+}  // namespace content