Re-home the global MessageCenter to support Ash+Win environments.

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/root_window_controller.h"
 #include "ash/shell.h"
 #include "ash/shell_window_ids.h"
 #include "ash/system/status_area_widget.h"
@@ skipping 80 matching lines @@
     : TrayBackgroundView(status_area_widget),
       button_(NULL),
       show_message_center_on_unlock_(false) {
   button_ = new views::ImageButton(this);
   button_->set_triggerable_event_flags(
       ui::EF_LEFT_MOUSE_BUTTON | ui::EF_RIGHT_MOUSE_BUTTON);
   tray_container()->AddChildView(button_);
   SetVisible(false);
   message_center_tray_.reset(new message_center::MessageCenterTray(
       this,
-      Shell::GetInstance()->message_center()));
+      message_center::MessageCenter::Get()));
   OnMessageCenterTrayChanged();
 }
 
 WebNotificationTray::~WebNotificationTray() {
   // Release any child views that might have back pointers before ~View().
   message_center_bubble_.reset();
   popup_bubble_.reset();
   popup_collection_.reset();
   if (quiet_mode_bubble() && quiet_mode_bubble()->GetBubbleWidget())
     quiet_mode_bubble()->GetBubbleWidget()->RemoveObserver(this);
@@ skipping 340 matching lines @@
 
 message_center::MessagePopupBubble*
 WebNotificationTray::GetPopupBubbleForTest() {
   if (!popup_bubble())
     return NULL;
   return static_cast<message_center::MessagePopupBubble*>(
       popup_bubble()->bubble());
 }
 
 }  // namespace ash