Salient parts of http://codereview.chromium.org/8392042/

content/browser/browser_thread_impl.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_BROWSER_BROWSER_THREAD_IMPL_H_
+#define CONTENT_BROWSER_BROWSER_THREAD_IMPL_H_
+#pragma once
+
+#include "content/public/browser/browser_thread.h"
+
+namespace content {
+
+class BrowserThreadImpl : public BrowserThread {
+ public:
+  explicit BrowserThreadImpl(BrowserThread::ID identifier);
+  BrowserThreadImpl(BrowserThread::ID identifier, MessageLoop* message_loop);
+  virtual ~BrowserThreadImpl();
+
+ private:
+  // We implement most functionality on the public set of
+  // BrowserThread functions, but state is stored in the
+  // BrowserThreadImpl to keep the public API cleaner. Therefore make
+  // BrowserThread a friend class.
+  friend class BrowserThread;
+
+  // TODO(brettw) remove this variant when Task->Closure migration is complete.
+  static bool PostTaskHelper(
+      BrowserThread::ID identifier,
+      const tracked_objects::Location& from_here,
+      Task* task,
+      int64 delay_ms,
+      bool nestable);
+  static bool PostTaskHelper(
+      BrowserThread::ID identifier,
+      const tracked_objects::Location& from_here,
+      const base::Closure& task,
+      int64 delay_ms,
+      bool nestable);
+
+  // This lock protects |browser_threads_|.  Do not read or modify that array
+  // without holding this lock.  Do not block while holding this lock.
+  static base::Lock lock_;
+
+  // An array of the BrowserThread objects.  This array is protected by |lock_|.
+  // The threads are not owned by this array.  Typically, the threads are owned
+  // on the UI thread by the g_browser_process object.  BrowserThreads remove
+  // themselves from this array upon destruction.
+  static BrowserThread* browser_threads_[ID_COUNT];
+};
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_BROWSER_THREAD_IMPL_H_