Don't reposition if shutdown is in progress

ash/common/wm/overview/window_selector.h

 // Copyright 2013 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_COMMON_WM_OVERVIEW_WINDOW_SELECTOR_H_
 #define ASH_COMMON_WM_OVERVIEW_WINDOW_SELECTOR_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 55 matching lines @@
 
   // Called when |window| is about to get closed.
   void WindowClosing(WindowSelectorItem* window);
 
   WindowSelectorDelegate* delegate() { return delegate_; }
 
   bool restoring_minimized_windows() const {
     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;
   void OnDisplayRemoved(const display::Display& display) override;
   void OnDisplayMetricsChanged(const display::Display& display,
                                uint32_t metrics) override;
 
   // WmWindowObserver:
   void OnWindowTreeChanged(WmWindow* window,
                            const TreeChangeParams& params) override;
@@ skipping 87 matching lines @@
   size_t num_times_textfield_cleared_;
 
   // Tracks whether minimized windows are currently being restored for overview
   // mode.
   bool restoring_minimized_windows_;
 
   // The distance between the top edge of the screen and the bottom edge of
   // the text filtering textfield.
   int text_filter_bottom_;
 
+  bool is_shut_down_ = false;
+
   DISALLOW_COPY_AND_ASSIGN(WindowSelector);
 };
 
 }  // namespace ash
 
 #endif  // ASH_COMMON_WM_OVERVIEW_WINDOW_SELECTOR_H_