[ash-md] Corrects a crash when a window is destroyed after leaving overview

ash/common/wm/overview/window_selector_item.h

Index: ash/common/wm/overview/window_selector_item.h
diff --git a/ash/common/wm/overview/window_selector_item.h b/ash/common/wm/overview/window_selector_item.h
index 510690efa1c8c62e7756749a8c4ddd96f334a985..246a8292ca09ef8115be2adb46cfe89c46399537 100644
--- a/ash/common/wm/overview/window_selector_item.h
+++ b/ash/common/wm/overview/window_selector_item.h
@@ -18,6 +18,10 @@
 #include "ui/views/controls/button/label_button.h"
 #include "ui/views/widget/widget.h"
 
+namespace gfx {
+class SlideAnimation;
+}
+
 namespace views {
 class ImageButton;
 }
@@ -201,6 +205,9 @@ class ASH_EXPORT WindowSelectorItem : public views::ButtonListener,
   // Fades out a window caption when exiting overview mode.
   void FadeOut(std::unique_ptr<views::Widget> widget);
 
+  // Allows a test to directly set animation state.
+  gfx::SlideAnimation* GetBackgroundViewAnimation();
+
   static bool hide_header() { return use_mask_ || use_shape_; }
 
   // True if the item is being shown in the overview, false if it's being