arc: Fix UpdatePinnedState crash

ui/arc/notification/arc_custom_notification_view.cc

 // Copyright 2016 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/arc/notification/arc_custom_notification_view.h"
 
 #include "base/auto_reset.h"
 #include "components/exo/notification_surface.h"
 #include "components/exo/surface.h"
 #include "third_party/skia/include/core/SkColor.h"
@@ skipping 212 matching lines @@
 
   surface_ = surface;
 
   if (surface_ && surface_->window()) {
     surface_->window()->AddObserver(this);
     surface_->window()->AddPreTargetHandler(event_forwarder_.get());
 
     if (GetWidget())
       AttachSurface();
 
-    UpdatePinnedState();
+    if (item_)

[yoshiki, 2016/09/20 03:43:06]

The patch itself lgtm, but why item is null here?

It means surface is changed after OnItemDestroying, but isn't it weird?

[xiyuan, 2016/09/20 15:58:16]

There is a racing between ArcNotificationService and wayland on notification
close. |item_| is set to null when a notification is removed and mojo call is
made. However, the window closing is async.  Even though we close the window
before we do mojo call in ArcNotificationService. It is still possible that the
notification surface could exist and update via wayland for a short while. Hence
the crash.

+      UpdatePinnedState();
   }
 }
 
 void ArcCustomNotificationView::UpdatePreferredSize() {
   gfx::Size preferred_size =
       surface_ ? surface_->GetSize() : item_ ? item_->snapshot().size()
                                              : gfx::Size();
   if (preferred_size.IsEmpty())
     return;
 
@@ skipping 17 matching lines @@
   if (target_visiblity == floating_close_button_widget_->IsVisible())
     return;
 
   if (target_visiblity)
     floating_close_button_widget_->Show();
   else
     floating_close_button_widget_->Hide();
 }
 
 void ArcCustomNotificationView::UpdatePinnedState() {
+  DCHECK(item_);
+
   if (item_->pinned() && floating_close_button_widget_) {
     floating_close_button_widget_.reset();
   } else if (!item_->pinned() && !floating_close_button_widget_) {
     CreateFloatingCloseButton();
   }
 }
 
 void ArcCustomNotificationView::UpdateSnapshot() {
   // Bail if we have a |surface_| because it controls the sizes and paints UI.
   if (surface_)
@@ skipping 151 matching lines @@
 
 void ArcCustomNotificationView::OnNotificationSurfaceRemoved(
     exo::NotificationSurface* surface) {
   if (surface->notification_id() != notification_key_)
     return;
 
   SetSurface(nullptr);
 }
 
 }  // namespace arc