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

ash/common/wm/overview/window_selector_item.cc

Index: ash/common/wm/overview/window_selector_item.cc
diff --git a/ash/common/wm/overview/window_selector_item.cc b/ash/common/wm/overview/window_selector_item.cc
index acbdfb1b75402001bc4ef32ae3fb70b80a2f4557..aa0431a9a2c38e9568a4240cab27b295cf4db26b 100644
--- a/ash/common/wm/overview/window_selector_item.cc
+++ b/ash/common/wm/overview/window_selector_item.cc
@@ -33,6 +33,7 @@
 #include "ui/base/resource/resource_bundle.h"
 #include "ui/compositor/layer_animation_sequence.h"
 #include "ui/compositor/scoped_animation_duration_scale_mode.h"
+#include "ui/gfx/animation/slide_animation.h"
 #include "ui/gfx/canvas.h"
 #include "ui/gfx/color_utils.h"
 #include "ui/gfx/geometry/safe_integer_conversions.h"
@@ -197,7 +198,10 @@ class WindowSelectorItem::RoundedContainerView
 
   ~RoundedContainerView() override { StopObservingLayerAnimations(); }
 
-  void OnItemRestored() { item_ = nullptr; }
+  void OnItemRestored() {
+    item_ = nullptr;
+    item_window_ = nullptr;
+  }
 
   // Starts observing layer animations so that actions can be taken when
   // particular animations (opacity) complete. It should only be called once
@@ -216,6 +220,9 @@ class WindowSelectorItem::RoundedContainerView
     layer_ = nullptr;
   }
 
+  // Used by tests to set animation state.
+  gfx::SlideAnimation* animation() { return animation_.get(); }
+
   void set_color(SkColor target_color) { target_color_ = target_color; }
 
   // Starts a color animation using |tween_type|. The animation will change the
@@ -896,4 +903,8 @@ void WindowSelectorItem::FadeOut(std::unique_ptr<views::Widget> widget) {
   widget_ptr->SetOpacity(0.f);
 }
 
+gfx::SlideAnimation* WindowSelectorItem::GetBackgroundViewAnimation() {
+  return background_view_ ? background_view_->animation() : nullptr;
+}
+
 }  // namespace ash