Remove itself from the widget observers in destructor

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 50 matching lines @@
 
 MessageCenterBubble::MessageCenterBubble(MessageCenter* message_center,
                                          MessageCenterTray* tray,
                                          bool first_item_has_no_margin)
     : MessageBubbleBase(message_center, tray),
       message_center_view_(NULL),
       initially_settings_visible_(false),
       first_item_has_no_margin_(first_item_has_no_margin) {}
 
 MessageCenterBubble::~MessageCenterBubble() {
+  // Removs this from the widget observers just in case. MessageCenterBubble
+  // might be destoryed without calling its Widget's Close/CloseNow.
+  if (bubble_view() && bubble_view()->GetWidget())
+    bubble_view()->GetWidget()->RemoveObserver(this);
 }
 
 void MessageCenterBubble::SetSettingsVisible() {
   if (message_center_view_)
     message_center_view_->SetSettingsVisible(true);
   else
     initially_settings_visible_ = true;
 }
 
 views::TrayBubbleView::InitParams MessageCenterBubble::GetInitParams(
@@ skipping 36 matching lines @@
   if (!bubble_view())
     return;  // Could get called after view is closed
   const NotificationList::Notifications& notifications =
       message_center()->GetVisibleNotifications();
   message_center_view_->SetNotifications(notifications);
   bubble_view()->GetWidget()->Show();
   bubble_view()->UpdateBubble();
 }
 
 void MessageCenterBubble::OnWidgetClosing(views::Widget* widget) {
-  bubble_view()->GetWidget()->RemoveObserver(this);
+  if (bubble_view() && bubble_view()->GetWidget())
+    bubble_view()->GetWidget()->RemoveObserver(this);
   if (message_center_view_)
     message_center_view_->SetIsClosing(true);
 }
 
 void MessageCenterBubble::OnMouseEnteredView() {
 }
 
 void MessageCenterBubble::OnMouseExitedView() {
 }
 
 size_t MessageCenterBubble::NumMessageViewsForTest() const {
   return message_center_view_->NumMessageViewsForTest();
 }
 
 }  // namespace message_center