Don't reposition if shutdown is in progress

ash/common/wm/overview/window_selector.h

Index: ash/common/wm/overview/window_selector.h
diff --git a/ash/common/wm/overview/window_selector.h b/ash/common/wm/overview/window_selector.h
index 55311cb619029f39cbc608ecf4914d449ad76d27..f8e473f246129dfd53038bb14f69d59df68a9a63 100644
--- a/ash/common/wm/overview/window_selector.h
+++ b/ash/common/wm/overview/window_selector.h
@@ -73,7 +73,9 @@ class ASH_EXPORT WindowSelector : public display::DisplayObserver,
     return restoring_minimized_windows_;
   }
 
-  int text_filter_bottom() { return text_filter_bottom_; }
+  int text_filter_bottom() const { return text_filter_bottom_; }
+
+  bool is_shut_down() const { return is_shut_down_; }
 
   // display::DisplayObserver:
   void OnDisplayAdded(const display::Display& display) override;
@@ -181,6 +183,8 @@ class ASH_EXPORT WindowSelector : public display::DisplayObserver,
   // the text filtering textfield.
   int text_filter_bottom_;
 
+  bool is_shut_down_ = false;
+
   DISALLOW_COPY_AND_ASSIGN(WindowSelector);
 };