Remove "top_down" flag in the message center code

ui/message_center/views/message_center_bubble.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 "ui/message_center/views/message_center_bubble.h"
 
 #include "base/macros.h"
 #include "ui/base/l10n/l10n_util.h"
 #include "ui/message_center/message_center_style.h"
 #include "ui/message_center/views/message_center_view.h"
@@ skipping 77 matching lines @@
   init_params.max_height = max_height();
   init_params.can_activate = true;
   return init_params;
 }
 
 void MessageCenterBubble::InitializeContents(
     views::TrayBubbleView* new_bubble_view) {
   set_bubble_view(new_bubble_view);
   bubble_view()->GetWidget()->AddObserver(this);
   message_center_view_ = new MessageCenterView(
-      message_center(), tray(), max_height(), initially_settings_visible_,
-      false); /* MessageCenterBubble should be used only on ChromeOS.
-                 Message center is never shown top down in ChromeOS. */
+      message_center(), tray(), max_height(), initially_settings_visible_);
   bubble_view()->AddChildView(new ContentsView(this, message_center_view_));
   // Resize the content of the bubble view to the given bubble size. This is
   // necessary in case of the bubble border forcing a bigger size then the
   // |new_bubble_view| actually wants. See crbug.com/169390.
   bubble_view()->Layout();
   UpdateBubbleView();
 }
 
 void MessageCenterBubble::OnBubbleViewDestroyed() {
   message_center_view_ = NULL;
@@ skipping 20 matching lines @@
 }
 
 void MessageCenterBubble::OnMouseExitedView() {
 }
 
 size_t MessageCenterBubble::NumMessageViewsForTest() const {
   return message_center_view_->NumMessageViewsForTest();
 }
 
 }  // namespace message_center