Don't reposition if shutdown is in progress

ash/common/wm/overview/window_grid.cc

 // Copyright 2014 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.
 
 #include "ash/common/wm/overview/window_grid.h"
 
 #include <algorithm>
 #include <functional>
 #include <set>
 #include <utility>
@@ skipping 589 matching lines @@
             ? OverviewAnimationType::OVERVIEW_ANIMATION_LAY_OUT_SELECTOR_ITEMS
             : OverviewAnimationType::OVERVIEW_ANIMATION_NONE);
   }
 
   // If the selection widget is active, reposition it without any animation.
   if (selection_widget_)
     MoveSelectionWidgetToTarget(animate);
 }
 
 void WindowGrid::PositionWindows(bool animate) {
+  if (window_selector_->is_shut_down())
+    return;
+
   if (ash::MaterialDesignController::IsOverviewMaterial()) {
     DCHECK(shield_widget_.get());
     // Keep the background shield widget covering the whole screen.
     WmWindow* widget_window =
         WmLookup::Get()->GetWindowForWidget(shield_widget_.get());
     const gfx::Rect bounds = widget_window->GetParent()->GetBounds();
     widget_window->SetBounds(bounds);
     PositionWindowsMD(animate);
     return;
   }
@@ skipping 396 matching lines @@
         *min_right = left;
       if (*max_right < left)
         *max_right = left;
     }
     *max_bottom = top + height;
   }
   return windows_fit;
 }
 
 }  // namespace ash