Use a direct include of the message_loop header in ui/, part 2.

ui/message_center/cocoa/popup_collection_unittest.mm

 // Copyright (c) 2013 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.
 
 #import "ui/message_center/cocoa/popup_collection.h"
 
 #include "base/mac/scoped_nsobject.h"
 #include "base/memory/scoped_ptr.h"
-#include "base/message_loop.h"
+#include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
 #include "base/strings/sys_string_conversions.h"
 #include "base/strings/utf_string_conversions.h"
 #import "ui/base/test/ui_cocoa_test_helper.h"
 #import "ui/message_center/cocoa/notification_controller.h"
 #import "ui/message_center/cocoa/popup_controller.h"
 #include "ui/message_center/message_center.h"
 #include "ui/message_center/message_center_style.h"
 #include "ui/message_center/notification.h"
 
@@ skipping 331 matching lines @@
       string16(),
       std::string(),
       message_center::RichNotificationData(),
       NULL));
   center_->UpdateNotification("1", notification.Pass());
 
   // Release the popup collection before the animation ends. No crash should
   // be expected.
   collection_.reset();
 }