Revert of base: Remove use of MessageLoopProxy

base/threading/sequenced_worker_pool.h

Index: base/threading/sequenced_worker_pool.h
diff --git a/base/threading/sequenced_worker_pool.h b/base/threading/sequenced_worker_pool.h
index 2126b0d04d5ce3687458095f9539585345705178..0b6c5f9e392c06f8d9fd3297cd81ae918829bc45 100644
--- a/base/threading/sequenced_worker_pool.h
+++ b/base/threading/sequenced_worker_pool.h
@@ -11,10 +11,8 @@
 #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 {
@@ -23,7 +21,7 @@
 
 namespace base {
 
-class SingleThreadTaskRunner;
+class MessageLoopProxy;
 
 template <class T> class DeleteHelper;
 
@@ -347,7 +345,7 @@
   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_|.