Use a direct include of the message_loop header in ui/, part 1.

ui/aura/root_window_host.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 UI_AURA_ROOT_WINDOW_HOST_H_
 #define UI_AURA_ROOT_WINDOW_HOST_H_
 
 #include <vector>
 
-#include "base/message_loop.h"
+#include "base/message_loop/message_loop.h"
 #include "ui/aura/aura_export.h"
 #include "ui/base/cursor/cursor.h"
 #include "ui/gfx/native_widget_types.h"
 
 class SkCanvas;
 
 namespace gfx {
 class Insets;
 class Point;
 class Rect;
@@ skipping 93 matching lines @@
   // Called when the device scale factor of the root window has chagned.
   virtual void OnDeviceScaleFactorChanged(float device_scale_factor) = 0;
 
   // Stop listening events in preparation for shutdown.
   virtual void PrepareForShutdown() = 0;
 };
 
 }  // namespace aura
 
 #endif  // UI_AURA_ROOT_WINDOW_HOST_H_