Add missing IWYU message_loop.h includes.

chrome/browser/ui/views/apps/app_info_dialog/app_info_dialog_ash_unittest.cc

 // Copyright 2015 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/test/ash_test_base.h"
 #include "ash/test/ash_test_helper.h"
 #include "ash/test/ash_test_views_delegate.h"
 #include "base/macros.h"
+#include "base/message_loop/message_loop.h"
 #include "chrome/browser/extensions/test_extension_environment.h"
 #include "chrome/browser/ui/views/apps/app_info_dialog/app_info_dialog_views.h"
 #include "chrome/browser/ui/views/apps/app_info_dialog/app_info_footer_panel.h"
 #include "chrome/browser/ui/views/harmony/chrome_layout_provider.h"
 #include "chrome/test/base/testing_profile.h"
 #include "ui/views/controls/button/label_button.h"
 #include "ui/views/widget/widget.h"
 #include "ui/views/window/dialog_delegate.h"
 
 namespace {
@@ skipping 51 matching lines @@
   dialog_footer->SetPinnedToShelf(true);
   EXPECT_FALSE(pin_button->visible());
   EXPECT_TRUE(unpin_button->visible());
   EXPECT_TRUE(unpin_button->HasFocus());
 
   dialog_footer->SetPinnedToShelf(false);
   EXPECT_TRUE(pin_button->visible());
   EXPECT_FALSE(unpin_button->visible());
   EXPECT_TRUE(pin_button->HasFocus());
 }