Remove "top_down" flag in the message center code

ui/message_center/views/message_center_view.h

 // 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.
 
 #ifndef UI_MESSAGE_CENTER_VIEWS_MESSAGE_CENTER_VIEW_H_
 #define UI_MESSAGE_CENTER_VIEWS_MESSAGE_CENTER_VIEW_H_
 
 #include <stddef.h>
 
 #include "base/macros.h"
@@ skipping 27 matching lines @@
 class MESSAGE_CENTER_EXPORT MessageCenterView
     : public views::View,
       public MessageCenterObserver,
       public MessageCenterController,
       public MessageListView::Observer,
       public gfx::AnimationDelegate {
  public:
   MessageCenterView(MessageCenter* message_center,
                     MessageCenterTray* tray,
                     int max_height,
-                    bool initially_settings_visible,
-                    bool top_down);
+                    bool initially_settings_visible);
   ~MessageCenterView() override;
 
   void SetNotifications(const NotificationList::Notifications& notifications);
 
   void ClearAllClosableNotifications();
 
   size_t NumMessageViewsForTest() const;
 
   void SetSettingsVisible(bool visible);
   void OnSettingsChanged();
@@ skipping 56 matching lines @@
   // Map notification_id->MessageView*. It contains all MessageViews currently
   // displayed in MessageCenter.
   typedef std::map<std::string, MessageView*> NotificationViewsMap;
   NotificationViewsMap notification_views_;  // Weak.
 
   // Child views.
   views::ScrollView* scroller_;
   std::unique_ptr<MessageListView> message_list_view_;
   NotifierSettingsView* settings_view_;
   MessageCenterButtonBar* button_bar_;
-  bool top_down_;
 
   // Data for transition animation between settings view and message list.
   bool settings_visible_;
 
   // Animation managing transition between message center and settings (and vice
   // versa).
   std::unique_ptr<gfx::MultiAnimation> settings_transition_animation_;
 
   // Helper data to keep track of the transition between settings and
   // message center views.
@@ skipping 13 matching lines @@
   Mode mode_ = Mode::BUTTONS_ONLY;
 
   std::unique_ptr<MessageViewContextMenuController> context_menu_controller_;
 
   DISALLOW_COPY_AND_ASSIGN(MessageCenterView);
 };
 
 }  // namespace message_center
 
 #endif  // UI_MESSAGE_CENTER_VIEWS_MESSAGE_CENTER_VIEW_H_