Fix use-after-free in MessageListView.

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 138 matching lines @@
   // message center views.
   views::View* source_view_;
   int source_height_;
   views::View* target_view_;
   int target_height_;
 
   // True when the widget is closing so that further operations should be
   // ignored.
   bool is_closing_;
 
-  bool is_clearing_ = false;
+  bool is_clearing_all_notifications_ = false;
   bool is_locked_ = false;
 
   // Current view mode. During animation, it is the target mode.
   Mode mode_ = Mode::BUTTONS_ONLY;
 
   std::unique_ptr<MessageViewContextMenuController> context_menu_controller_;
 
   views::FocusManager* focus_manager_ = nullptr;
 
   DISALLOW_COPY_AND_ASSIGN(MessageCenterView);
 };
 
 }  // namespace message_center
 
 #endif  // UI_MESSAGE_CENTER_VIEWS_MESSAGE_CENTER_VIEW_H_