Add missing IWYU message_loop.h includes.

ash/shelf/shelf_layout_manager_unittest.cc

 // 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.
 
 #include "ash/shelf/shelf_layout_manager.h"
 
 #include "ash/accelerators/accelerator_controller.h"
 #include "ash/accelerators/accelerator_table.h"
 #include "ash/focus_cycler.h"
 #include "ash/public/cpp/config.h"
@@ skipping 13 matching lines @@
 #include "ash/test/ash_test_base.h"
 #include "ash/test/test_app_list_view_presenter_impl.h"
 #include "ash/test/test_system_tray_item.h"
 #include "ash/wm/lock_state_controller.h"
 #include "ash/wm/window_state.h"
 #include "ash/wm/window_state_aura.h"
 #include "ash/wm/window_util.h"
 #include "ash/wm_window.h"
 #include "base/command_line.h"
 #include "base/memory/ptr_util.h"
+#include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
 #include "ui/aura/client/aura_constants.h"
 #include "ui/aura/client/window_parenting_client.h"
 #include "ui/aura/window.h"
 #include "ui/aura/window_event_dispatcher.h"
 #include "ui/base/ui_base_switches.h"
 #include "ui/compositor/layer.h"
 #include "ui/compositor/layer_animator.h"
 #include "ui/compositor/scoped_animation_duration_scale_mode.h"
 #include "ui/display/display.h"
@@ skipping 1849 matching lines @@
   // Open keyboard in sticky mode.
   kb_controller->ShowKeyboard(true);
   layout_manager->OnKeyboardBoundsChanging(keyboard_bounds());
 
   // Work area should be changed.
   EXPECT_NE(orig_work_area,
             display::Screen::GetScreen()->GetPrimaryDisplay().work_area());
 }
 
 }  // namespace ash