Change active root window before closing old root windows' children.

BUG=282582

Review URL: https://chromiumcodereview.appspot.com/23494022

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@221497 0039d316-1c4b-4281-b951-d872f2087c98

ash/root_window_controller.cc

@@ -271,12 +271,17 @@ void RootWindowController::Shutdown() {
   wallpaper_controller_.reset();
   animating_wallpaper_controller_.reset();
 
-  CloseChildWindows();
+  // Change the active root window before closing child windows. If any child
+  // being removed triggers a relayout of the shelf it will try to build a
+  // window list adding windows from the active root window's containers which
+  // may have already gone away.
   if (Shell::GetActiveRootWindow() == root_window_) {
     Shell::GetInstance()->set_active_root_window(
         Shell::GetPrimaryRootWindow() == root_window_.get() ?
         NULL : Shell::GetPrimaryRootWindow());
   }
+
+  CloseChildWindows();
   SetRootWindowController(root_window_.get(), NULL);
   screen_dimmer_.reset();
   workspace_controller_.reset();