Don't reposition if shutdown is in progress

ash/common/wm/overview/window_selector.cc

Index: ash/common/wm/overview/window_selector.cc
diff --git a/ash/common/wm/overview/window_selector.cc b/ash/common/wm/overview/window_selector.cc
index db099179f44f11be6de5ad79f671de3fec268350..2fcb7435b16bf485591a2aa3761f7d3f8ef0a47f 100644
--- a/ash/common/wm/overview/window_selector.cc
+++ b/ash/common/wm/overview/window_selector.cc
@@ -381,6 +381,7 @@ void WindowSelector::Init(const WindowList& windows) {
 // may cause other, unrelated classes, (ie PanelLayoutManager) to make indirect
 // calls to restoring_minimized_windows() on a partially destructed object.
 void WindowSelector::Shutdown() {
+  is_shut_down_ = true;
   // Stop observing screen metrics changes first to avoid auto-positioning
   // windows in response to work area changes from window activation.
   display::Screen::GetScreen()->RemoveObserver(this);