Add base::ThreadTaskRunner class.

base/thread_task_runner_handle.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_TASK_RUNNER_HANDLE_H_
+#define BASE_THREAD_TASK_RUNNER_HANDLE_H_
+
+#include "base/base_export.h"
+#include "base/memory/ref_counted.h"
+
+namespace base {
+
+class SingleThreadTaskRunner;
+
+// ThreadTaskRunnerHandle stores a reference to the main task runner
+// for each thread. Not more than one of these objects can be created
+// per thread. After an instance of this object is created the Get()
+// function will return the |task_runner| specified in the
+// constructor.
+class BASE_EXPORT ThreadTaskRunnerHandle {
+ public:
+  // Gets the SingleThreadTaskRunner for the current thread.
+  static scoped_refptr<SingleThreadTaskRunner> Get();
+
+  ThreadTaskRunnerHandle(
+      const scoped_refptr<SingleThreadTaskRunner>& task_runner);
+  ~ThreadTaskRunnerHandle();
+
+ private:
+  scoped_refptr<SingleThreadTaskRunner> task_runner_;
+};
+
+}  // namespace base
+
+#endif  // BASE_THREAD_TASK_RUNNER_HANDLE_H_