Implementation of SequencedTaskRunner based on SequencedWorkerPool.

base/threading/sequenced_worker_pool.h

Index: base/threading/sequenced_worker_pool.h
===================================================================
--- base/threading/sequenced_worker_pool.h	(revision 126348)
+++ base/threading/sequenced_worker_pool.h	(working copy)
@@ -26,12 +26,15 @@
 
 template <class T> class DeleteHelper;
 
+class SequencedTaskRunner;
+
 // A worker thread pool that enforces ordering between sets of tasks. It also
 // allows you to specify what should happen to your tasks on shutdown.
 //
 // To enforce ordering, get a unique sequence token from the pool and post all
 // tasks you want to order with the token. All tasks with the same token are
-// guaranteed to execute serially, though not necessarily on the same thread.
+// guaranteed to execute serially (i.e. there is no execution overlap
+// whatsoever), though not necessarily on the same thread.
 //
 // Example:
 //   SequencedWorkerPool::SequenceToken token = pool.GetSequenceToken();
@@ -132,7 +135,7 @@
                       const std::string& thread_name_prefix);
 
   // Returns a unique token that can be used to sequence tasks posted to
-  // PostSequencedWorkerTask(). Valid tokens are alwys nonzero.
+  // PostSequencedWorkerTask(). Valid tokens are always nonzero.
   SequenceToken GetSequenceToken();
 
   // Returns the sequence token associated with the given name. Calling this
@@ -141,6 +144,13 @@
   // will be created.
   SequenceToken GetNamedSequenceToken(const std::string& name);
 
+  // Returns a SequencedTaskRunner wrapper for this SequencedWorkerPool.
+  scoped_refptr<SequencedTaskRunner> GetSequencedTaskRunner();
+  scoped_refptr<SequencedTaskRunner> GetSequencedTaskRunner(
+      SequenceToken token);
+  scoped_refptr<SequencedTaskRunner> GetSequencedTaskRunner(
+      const std::string& token_name);
+
   // Posts the given task for execution in the worker pool. Tasks posted with
   // this function will execute in an unspecified order on a background thread.
   // Returns true if the task was posted. If your tasks have ordering