Remove NoNotificationMessageView from empty message center

ui/message_center/views/message_center_view.h

Index: ui/message_center/views/message_center_view.h
diff --git a/ui/message_center/views/message_center_view.h b/ui/message_center/views/message_center_view.h
index 194754f448a7ebfb343f882f70865f1fbb3b213f..940719fa790dacc40c1d75f0a917668910476c2c 100644
--- a/ui/message_center/views/message_center_view.h
+++ b/ui/message_center/views/message_center_view.h
@@ -95,8 +95,12 @@ class MESSAGE_CENTER_EXPORT MessageCenterView : public views::View,
  private:
   friend class MessageCenterViewTest;
 
+  enum class Mode { NOTIFICATIONS, SETTINGS, BUTTONS_ONLY };
+
   void AddNotificationAt(const Notification& notification, int index);
-  void NotificationsChanged();
+  void Update(bool animate);
+  void SetVisibilityMode(Mode mode, bool animate);
+  void UpdateButtonsStatus();
   void SetNotificationViewForTest(MessageView* view);
 
   MessageCenter* message_center_;  // Weak reference.
@@ -110,7 +114,6 @@ class MESSAGE_CENTER_EXPORT MessageCenterView : public views::View,
   // Child views.
   views::ScrollView* scroller_;
   std::unique_ptr<MessageListView> message_list_view_;
-  std::unique_ptr<views::View> empty_list_view_;
   NotifierSettingsView* settings_view_;
   MessageCenterButtonBar* button_bar_;
   bool top_down_;
@@ -133,6 +136,11 @@ class MESSAGE_CENTER_EXPORT MessageCenterView : public views::View,
   // ignored.
   bool is_closing_;
 
+  bool is_clearing_ = false;
+
+  // Current view mode. During animation, it is the target mode.
+  Mode mode_ = Mode::BUTTONS_ONLY;
+
   std::unique_ptr<MessageViewContextMenuController> context_menu_controller_;
 
   DISALLOW_COPY_AND_ASSIGN(MessageCenterView);