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. Different SingleThreadTaskRunners may be associated

[fdoray, 2017/03/27 20:11:50]

// The Single-Threaded Apartment assigned to the returned SingleThreadTaskRunner
may be shared with other SingleThreadTaskRunners.

[robliao, 2017/03/27 20:28:05]

Changed the note to...
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.

+// with different Single-Threaded Apartments so 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_