Fix popup crash on ChromeOS.

ash/system/web_notification/web_notification_tray.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 "ash/system/web_notification/web_notification_tray.h"
 
 #include "ash/ash_switches.h"
 #include "ash/root_window_controller.h"
 #include "ash/shelf/shelf_layout_manager.h"
 #include "ash/shelf/shelf_layout_manager_observer.h"
@@ skipping 398 matching lines @@
           internal::kShellWindowId_StatusContainer),
       message_center(),
       message_center_tray_.get(),
       ash::switches::UseAlternateShelfLayout()));
   work_area_observer_->StartObserving(
       popup_collection_.get(), GetWidget()->GetNativeView()->GetRootWindow());
   return true;
 }
 
 void WebNotificationTray::HidePopups() {
+  DCHECK(popup_collection_.get());
+
+  popup_collection_->MarkAllPopupsShown();
   popup_collection_.reset();
   work_area_observer_->StopObserving();
 }
 
 // Private methods.
 
 bool WebNotificationTray::ShouldShowMessageCenter() {
   return status_area_widget()->login_status() != user::LOGGED_IN_LOCKED &&
       !(status_area_widget()->system_tray() &&
         status_area_widget()->system_tray()->HasNotificationBubble());
@@ skipping 183 matching lines @@
 
 message_center::MessageCenterBubble*
 WebNotificationTray::GetMessageCenterBubbleForTest() {
   if (!message_center_bubble())
     return NULL;
   return static_cast<message_center::MessageCenterBubble*>(
       message_center_bubble()->bubble());
 }
 
 }  // namespace ash