Move sequenced_task_runner to base/task

base/sequenced_task_runner_helpers.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_SEQUENCED_TASK_RUNNER_HELPERS_H_
-#define BASE_SEQUENCED_TASK_RUNNER_HELPERS_H_
-
-#include "base/basictypes.h"
-
-// TODO(akalin): Investigate whether it's possible to just have
-// SequencedTaskRunner use these helpers (instead of MessageLoop).
-// Then we can just move these to sequenced_task_runner.h.
-
-namespace tracked_objects {
-class Location;
-}
-
-namespace base {
-
-namespace subtle {
-template <class T, class R> class DeleteHelperInternal;
-template <class T, class R> class ReleaseHelperInternal;
-}
-
-// Template helpers which use function indirection to erase T from the
-// function signature while still remembering it so we can call the
-// correct destructor/release function.
-//
-// We use this trick so we don't need to include bind.h in a header
-// file like sequenced_task_runner.h. We also wrap the helpers in a
-// templated class to make it easier for users of DeleteSoon to
-// declare the helper as a friend.
-template <class T>
-class DeleteHelper {
- private:
-  template <class T2, class R> friend class subtle::DeleteHelperInternal;
-
-  static void DoDelete(const void* object) {
-    delete reinterpret_cast<const T*>(object);
-  }
-
-  DISALLOW_COPY_AND_ASSIGN(DeleteHelper);
-};
-
-template <class T>
-class ReleaseHelper {
- private:
-  template <class T2, class R> friend class subtle::ReleaseHelperInternal;
-
-  static void DoRelease(const void* object) {
-    reinterpret_cast<const T*>(object)->Release();
-  }
-
-  DISALLOW_COPY_AND_ASSIGN(ReleaseHelper);
-};
-
-namespace subtle {
-
-// An internal SequencedTaskRunner-like class helper for DeleteHelper
-// and ReleaseHelper.  We don't want to expose the Do*() functions
-// directly directly since the void* argument makes it possible to
-// pass/ an object of the wrong type to delete.  Instead, we force
-// callers to go through these internal helpers for type
-// safety. SequencedTaskRunner-like classes which expose DeleteSoon or
-// ReleaseSoon methods should friend the appropriate helper and
-// implement a corresponding *Internal method with the following
-// signature:
-//
-// bool(const tracked_objects::Location&,
-//      void(*function)(const void*),
-//      void* object)
-//
-// An implementation of this function should simply create a
-// base::Closure from (function, object) and return the result of
-// posting the task.
-template <class T, class ReturnType>
-class DeleteHelperInternal {
- public:
-  template <class SequencedTaskRunnerType>
-  static ReturnType DeleteViaSequencedTaskRunner(
-      SequencedTaskRunnerType* sequenced_task_runner,
-      const tracked_objects::Location& from_here,
-      const T* object) {
-    return sequenced_task_runner->DeleteSoonInternal(
-        from_here, &DeleteHelper<T>::DoDelete, object);
-  }
-
- private:
-  DISALLOW_COPY_AND_ASSIGN(DeleteHelperInternal);
-};
-
-template <class T, class ReturnType>
-class ReleaseHelperInternal {
- public:
-  template <class SequencedTaskRunnerType>
-  static ReturnType ReleaseViaSequencedTaskRunner(
-      SequencedTaskRunnerType* sequenced_task_runner,
-      const tracked_objects::Location& from_here,
-      const T* object) {
-    return sequenced_task_runner->ReleaseSoonInternal(
-        from_here, &ReleaseHelper<T>::DoRelease, object);
-  }
-
- private:
-  DISALLOW_COPY_AND_ASSIGN(ReleaseHelperInternal);
-};
-
-}  // namespace subtle
-
-}  // namespace base
-
-#endif  // BASE_SEQUENCED_TASK_RUNNER_HELPERS_H_