Make MessageLoopProxy::current() usable on threads that don't have MessageLoop.

base/thread_main_task_runner.h

+// Copyright (c) 2012 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 BASE_THREAD_MAIN_TASK_RUNNER_H_
+#define BASE_THREAD_MAIN_TASK_RUNNER_H_
+#pragma once
+
+#include "base/base_export.h"
+#include "base/single_thread_task_runner.h"
+
+namespace base {
+
+// ThreadMainTaskRunner is a SingleThreadTaskRunner that is used for
+// the main task runner of a thread. There should never be more than
+// one object implementing this interface per thread. It provides
+// static current() method that returns the instance of this interface
+// that corresponds to the current thread.
+class BASE_EXPORT ThreadMainTaskRunner : public SingleThreadTaskRunner {
+ public:
+  // Gets the ThreadMainTaskRunner for the current thread.
+  static scoped_refptr<ThreadMainTaskRunner> current();
+
+  ThreadMainTaskRunner();
+
+ protected:
+  virtual ~ThreadMainTaskRunner();
+
+  // This method must be called on the thread this object belongs to
+  // before the thread and this object are destroyed.
+  void Detach();
+
+ private:
+  bool detached_;
+};
+
+}  // namespace base
+
+#endif  // BASE_THREAD_MAIN_TASK_RUNNER_H_