React to primary display change instead of removal

chrome/browser/ui/webui/chromeos/login/oobe_display_chooser.h

 // Copyright 2017 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 CHROME_BROWSER_UI_WEBUI_CHROMEOS_LOGIN_OOBE_DISPLAY_CHOOSER_H_
 #define CHROME_BROWSER_UI_WEBUI_CHROMEOS_LOGIN_OOBE_DISPLAY_CHOOSER_H_
 
 #include "base/macros.h"
+#include "base/memory/weak_ptr.h"
 
 namespace chromeos {
 
 // Tries to put the OOBE UI on a connected touch display (if available).
 class OobeDisplayChooser {
  public:
   OobeDisplayChooser();
   ~OobeDisplayChooser();
 
+  // Must be called on the BrowserThread::UI thread.
   void TryToPlaceUiOnTouchDisplay();
 
  private:
   void MoveToTouchDisplay();
 
+  base::WeakPtrFactory<OobeDisplayChooser> weak_ptr_factory_;
+
   DISALLOW_COPY_AND_ASSIGN(OobeDisplayChooser);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_UI_WEBUI_CHROMEOS_LOGIN_OOBE_DISPLAY_CHOOSER_H_