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

ui/aura/env.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_ENV_H_
 #define UI_AURA_ENV_H_
 
 #include "base/memory/scoped_ptr.h"
-#include "base/message_loop.h"
+#include "base/message_loop/message_loop.h"
 #include "base/observer_list.h"
 #include "ui/aura/aura_export.h"
 #include "ui/base/events/event_handler.h"
 #include "ui/base/events/event_target.h"
 #include "ui/gfx/point.h"
 
 #if defined(USE_X11)
 #include "ui/aura/device_list_updater_aurax11.h"
 #endif
 
@@ skipping 77 matching lines @@
 #if defined(USE_X11)
   DeviceListUpdaterAuraX11 device_list_updater_aurax11_;
 #endif
 
   DISALLOW_COPY_AND_ASSIGN(Env);
 };
 
 }  // namespace aura
 
 #endif  // UI_AURA_ENV_H_