Support PostTaskAndReply from a sequenced task.

base/task_runner.h

Index: base/task_runner.h
diff --git a/base/task_runner.h b/base/task_runner.h
index 9593835eebbdfa51f43e1d236f387f3ee1ac7940..8845b4876773f20eebfbc858c0d4a4cf1033aa90 100644
--- a/base/task_runner.h
+++ b/base/task_runner.h
@@ -81,14 +81,15 @@ class BASE_EXPORT TaskRunner
   // 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: