ash: Do not add the tray bubble twice in the message-loop's observer list.

ash/system/tray/system_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/tray/system_tray.h"
 
 #include "ash/shell.h"
 #include "ash/shell/panel_window.h"
 #include "ash/shell_window_ids.h"
 #include "ash/system/audio/tray_volume.h"
@@ skipping 457 matching lines @@
 SystemTrayBubble::SystemTrayBubble(
     ash::SystemTray* tray,
     const std::vector<ash::SystemTrayItem*>& items,
     bool detailed)
     : tray_(tray),
       bubble_view_(NULL),
       bubble_widget_(NULL),
       items_(items),
       detailed_(detailed),
       autoclose_delay_(0) {
-  MessageLoopForUI::current()->AddObserver(this);
 }
 
 SystemTrayBubble::~SystemTrayBubble() {
+  // The bubble may be closing without having been hidden first. So it may still
+  // be in the message-loop's observer list.
   MessageLoopForUI::current()->RemoveObserver(this);
+
   DestroyItemViews();
   // Reset the host pointer in bubble_view_ in case its destruction is deferred.
   if (bubble_view_)
     bubble_view_->reset_host();
   if (bubble_widget_) {
     bubble_widget_->RemoveObserver(this);
     // This triggers the destruction of bubble_view_.
     bubble_widget_->Close();
   }
 }
@@ skipping 10 matching lines @@
     views::View* view = detailed_ ?
         (*it)->CreateDetailedView(login_status) :
         (*it)->CreateDefaultView(login_status);
     if (view)
       bubble_view_->AddChildView(new TrayPopupItemContainer(view));
   }
 
   DCHECK(bubble_widget_ == NULL);
   bubble_widget_ = views::BubbleDelegateView::CreateBubble(bubble_view_);
 
-
   // Must occur after call to CreateBubble()
   bubble_view_->SetAlignment(views::BubbleBorder::ALIGN_EDGE_TO_ANCHOR_EDGE);
   bubble_widget_->non_client_view()->frame_view()->set_background(NULL);
   bubble_view_->SetBubbleBorder(new SystemTrayBubbleBorder(bubble_view_));
 
   bubble_widget_->AddObserver(this);
 
   // Setup animation.
   ash::SetWindowVisibilityAnimationType(
       bubble_widget_->GetNativeWindow(),
@@ skipping 349 matching lines @@
     canvas->DrawFocusRect(container_->bounds());
 }
 
 void SystemTray::UpdateBackground(int alpha) {
   background_->set_alpha(hide_background_animator_.alpha() +
                          hover_background_animator_.alpha());
   SchedulePaint();
 }
 
 }  // namespace ash