[Notifications] Fix crashes.

ui/arc/notification/arc_custom_notification_view.h

 // 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.
 
 #ifndef UI_ARC_NOTIFICATION_ARC_CUSTOM_NOTIFICATION_VIEW_H_
 #define UI_ARC_NOTIFICATION_ARC_CUSTOM_NOTIFICATION_VIEW_H_
 
 #include <memory>
 #include <string>
 
@@ skipping 52 matching lines @@
     void OnBlur() override;
 
    private:
     ArcCustomNotificationView* const owner_;
 
     DISALLOW_COPY_AND_ASSIGN(ControlButton);
   };
 
   void CreateCloseButton();
   void CreateSettingsButton();
-  void CreateFloatingControlButtons();
+  void MaybeCreateFloatingControlButtons();
   void SetSurface(exo::NotificationSurface* surface);
   void UpdatePreferredSize();
   void UpdateControlButtonsVisibility();
   void UpdatePinnedState();
   void UpdateSnapshot();
   void AttachSurface();
   void ActivateToast();
   void StartControlButtonsColorAnimation();
   bool ShouldUpdateControlButtonsColor() const;
 
@@ skipping 25 matching lines @@
   void OnItemUpdated() override;
 
   // ArcNotificationSurfaceManager::Observer:
   void OnNotificationSurfaceAdded(exo::NotificationSurface* surface) override;
   void OnNotificationSurfaceRemoved(exo::NotificationSurface* surface) override;
 
   // AnimationDelegate
   void AnimationEnded(const gfx::Animation* animation) override;
   void AnimationProgressed(const gfx::Animation* animation) override;
 
+  // If |item_| is null, we may be about to be destroyed. In this case,
+  // we have to be careful about what we do.
   ArcCustomNotificationItem* item_ = nullptr;
   exo::NotificationSurface* surface_ = nullptr;
 
   const std::string notification_key_;
 
   // A pre-target event handler to forward events on the surface to this view.
   // Using a pre-target event handler instead of a target handler on the surface
   // window because it has descendant aura::Window and the events on them need
   // to be handled as well.
   // TODO(xiyuan): Revisit after exo::Surface no longer has an aura::Window.
@@ skipping 17 matching lines @@
   bool in_layout_ = false;
 
   std::unique_ptr<gfx::LinearAnimation> control_button_color_animation_;
 
   DISALLOW_COPY_AND_ASSIGN(ArcCustomNotificationView);
 };
 
 }  // namespace arc
 
 #endif  // UI_ARC_NOTIFICATION_ARC_CUSTOM_NOTIFICATION_VIEW_H_