Revert of base: Remove use of MessageLoopProxy

base/threading/thread.h

Index: base/threading/thread.h
diff --git a/base/threading/thread.h b/base/threading/thread.h
index 49156063929759f62cab534432251947df10dec8..5010f0ec428bdcc69e54a9fdfe723862cacd75aa 100644
--- a/base/threading/thread.h
+++ b/base/threading/thread.h
@@ -11,8 +11,8 @@
 #include "base/callback.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/message_loop/message_loop.h"
+#include "base/message_loop/message_loop_proxy.h"
 #include "base/message_loop/timer_slack.h"
-#include "base/single_thread_task_runner.h"
 #include "base/threading/platform_thread.h"
 
 namespace base {
@@ -156,7 +156,7 @@
   // hold on to this even after the thread is gone; in this situation, attempts
   // to PostTask() will fail.
   scoped_refptr<SingleThreadTaskRunner> task_runner() const {
-    return message_loop_->task_runner();
+    return message_loop_proxy();
   }
 
   // Returns the name of this thread (for display in debugger too).