ARC Toast: Prevent onClosed event from being called multiple times

ash/system/toast/toast_overlay.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 ASH_SYSTEM_TOAST_TOAST_OVERLAY_H_
 #define ASH_SYSTEM_TOAST_TOAST_OVERLAY_H_
 
 #include "ash/ash_export.h"
 #include "base/memory/scoped_ptr.h"
 #include "ui/compositor/layer_animation_observer.h"
@@ skipping 38 matching lines @@
 
   // gfx::LayerAnimationObserver overrides:
   void OnLayerAnimationEnded(ui::LayerAnimationSequence* sequence) override;
   void OnLayerAnimationAborted(ui::LayerAnimationSequence* sequence) override;
   void OnLayerAnimationScheduled(ui::LayerAnimationSequence* sequence) override;
 
   views::Widget* widget_for_testing();
   void ClickDismissButtonForTesting(const ui::Event& event);
 
   bool is_visible_ = false;
+  bool close_event_fired_ = false;
   Delegate* const delegate_;
   const std::string text_;
   scoped_ptr<views::Widget> overlay_widget_;
   scoped_ptr<ToastOverlayView> overlay_view_;
   gfx::Size widget_size_;
 
   DISALLOW_COPY_AND_ASSIGN(ToastOverlay);
 };
 
 }  // namespace ash
 
 #endif  // ASH_SYSTEM_TOAST_TOAST_OVERLAY_H_