Revert of base: Remove use of MessageLoopProxy

base/threading/sequenced_worker_pool.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_THREADING_SEQUENCED_WORKER_POOL_H_
 #define BASE_THREADING_SEQUENCED_WORKER_POOL_H_
 
 #include <cstddef>
 #include <string>
 
 #include "base/base_export.h"
 #include "base/basictypes.h"
 #include "base/callback_forward.h"
-#include "base/location.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
-#include "base/single_thread_task_runner.h"
 #include "base/task_runner.h"
 
 namespace tracked_objects {
 class Location;
 }  // namespace tracked_objects
 
 namespace base {
 
-class SingleThreadTaskRunner;
+class MessageLoopProxy;
 
 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
@@ skipping 303 matching lines @@
 
   void OnDestruct() const override;
 
  private:
   friend class RefCountedThreadSafe<SequencedWorkerPool>;
   friend class DeleteHelper<SequencedWorkerPool>;
 
   class Inner;
   class Worker;
 
-  const scoped_refptr<SingleThreadTaskRunner> constructor_task_runner_;
+  const scoped_refptr<MessageLoopProxy> constructor_message_loop_;
 
   // Avoid pulling in too many headers by putting (almost) everything
   // into |inner_|.
   const scoped_ptr<Inner> inner_;
 
   DISALLOW_COPY_AND_ASSIGN(SequencedWorkerPool);
 };
 
 }  // namespace base
 
 #endif  // BASE_THREADING_SEQUENCED_WORKER_POOL_H_