Add Support to Get a COM STA Task Runner from the Task Scheduler API

base/task_scheduler/post_task.h

 // Copyright 2016 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_TASK_SCHEDULER_POST_TASK_H_
 #define BASE_TASK_SCHEDULER_POST_TASK_H_
 
 #include <utility>
 
 #include "base/base_export.h"
 #include "base/bind.h"
 #include "base/callback.h"
 #include "base/location.h"
 #include "base/memory/ref_counted.h"
 #include "base/post_task_and_reply_with_result_internal.h"
 #include "base/sequenced_task_runner.h"
 #include "base/single_thread_task_runner.h"
 #include "base/task_runner.h"
 #include "base/task_scheduler/task_traits.h"
 #include "base/time/time.h"
+#include "build/build_config.h"
 
 namespace base {
 
 // This is the preferred interface to post tasks to the TaskScheduler.
 //
 // To post a simple one-off task with default traits:
 //     PostTask(FROM_HERE, Bind(...));
 //
 // To post a high priority one-off task to respond to a user interaction:
 //     PostTaskWithTraits(
@@ skipping 133 matching lines @@
 //
 // If all you need is to make sure that tasks don't run concurrently (e.g.
 // because they access a data structure which is not thread-safe), use
 // CreateSequencedTaskRunnerWithTraits(). Only use this if you rely on a thread-
 // affine API (it might be safer to assume thread-affinity when dealing with
 // under-documented third-party APIs, e.g. other OS') or share data across tasks
 // using thread-local storage.
 BASE_EXPORT scoped_refptr<SingleThreadTaskRunner>
 CreateSingleThreadTaskRunnerWithTraits(const TaskTraits& traits);
 
+#if defined(OS_WIN)
+// Returns a SingleThreadTaskRunner whose PostTask invocations result in
+// scheduling tasks using |traits| in a COM Single-Threaded Apartment. Tasks run
+// in the same Single-Threaded Apartment in posting order for the returned
+// SingleThreadTaskRunner. There is not necessarily a one-to-one correspondence
+// between SingleThreadTaskRunners and Single-Threaded Apartments. The
+// implementation is free to share apartments or create new apartments as
+// necessary. In either case, care should be taken to make sure COM pointers are
+// not smuggled across apartments.
+BASE_EXPORT scoped_refptr<SingleThreadTaskRunner>
+CreateCOMSTATaskRunnerWithTraits(const TaskTraits& traits);
+#endif  // defined(OS_WIN)
+
 }  // namespace base
 
 #endif  // BASE_TASK_SCHEDULER_POST_TASK_H_