Create a new base/message_loop directory and move the message_loop_proxy.

base/message_loop/message_loop_proxy.h

Index: base/message_loop/message_loop_proxy.h
diff --git a/base/message_loop_proxy.h b/base/message_loop/message_loop_proxy.h
similarity index 88%
copy from base/message_loop_proxy.h
copy to base/message_loop/message_loop_proxy.h
index ce949ddf2c30325ce05e4e905ed8288206b7ae78..4ace8026db486f467306fbbcad91a4701c2e571c 100644
--- a/base/message_loop_proxy.h
+++ b/base/message_loop/message_loop_proxy.h
@@ -2,8 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef BASE_MESSAGE_LOOP_PROXY_H_
-#define BASE_MESSAGE_LOOP_PROXY_H_
+#ifndef BASE_MESSAGE_LOOP_MESSAGE_LOOP_PROXY_H_
+#define BASE_MESSAGE_LOOP_MESSAGE_LOOP_PROXY_H_
 
 #include "base/base_export.h"
 #include "base/compiler_specific.h"
@@ -35,4 +35,4 @@ class BASE_EXPORT MessageLoopProxy : public SingleThreadTaskRunner {
 
 }  // namespace base
 
-#endif  // BASE_MESSAGE_LOOP_PROXY_H_
+#endif  // BASE_MESSAGE_LOOP_MESSAGE_LOOP_PROXY_H_