Support PostTaskAndReply from a sequenced task.

base/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_TASK_RUNNER_H_
 #define BASE_TASK_RUNNER_H_
 
 #include <stddef.h>
 
 #include "base/base_export.h"
@@ skipping 63 matching lines @@
                                base::TimeDelta delay) = 0;
 
   // Returns true if the current thread is a thread on which a task
   // may be run, and false if no task will be run on the current
   // thread.
   //
   // It is valid for an implementation to always return true, or in
   // general to use 'true' as a default value.
   virtual bool RunsTasksOnCurrentThread() const = 0;
 
-  // Posts |task| on the current TaskRunner.  On completion, |reply|
-  // is posted to the thread that called PostTaskAndReply().  Both
-  // |task| and |reply| are guaranteed to be deleted on the thread
-  // from which PostTaskAndReply() is invoked.  This allows objects
-  // that must be deleted on the originating thread to be bound into
-  // the |task| and |reply| Closures.  In particular, it can be useful
-  // to use WeakPtr<> in the |reply| Closure so that the reply
-  // operation can be canceled. See the following pseudo-code:
+  // Posts |task| on the current TaskRunner.  On completion, |reply| is posted
+  // to the sequence or thread that called PostTaskAndReply(). Can only be
+  // called when SequencedTaskRunnerHandle::IsSet(). Both |task| and |reply| are
+  // guaranteed to be deleted on the sequence or thread from which
+  // PostTaskAndReply() is invoked.  This allows objects that must be deleted on

[robliao, 2016/07/27 17:50:07]

Nit, remove double space.

[fdoray, 2016/07/28 13:40:48]

Done.

+  // the originating thread or sequence to be bound into the |task| and |reply|
+  // Closures. In particular, it can be useful to use WeakPtr<> in the |reply|
+  // Closure so that the reply operation can be canceled. See the following
+  // pseudo-code:
   //
   // class DataBuffer : public RefCountedThreadSafe<DataBuffer> {
   //  public:
   //   // Called to add data into a buffer.
   //   void AddData(void* buf, size_t length);
   //   ...
   // };
   //
   //
   // class DataLoader : public SupportsWeakPtr<DataLoader> {
@@ skipping 40 matching lines @@
   virtual void OnDestruct() const;
 };
 
 struct BASE_EXPORT TaskRunnerTraits {
   static void Destruct(const TaskRunner* task_runner);
 };
 
 }  // namespace base
 
 #endif  // BASE_TASK_RUNNER_H_