Mac: Make ScopedTypeRef require explicit constructors

chrome/browser/ui/cocoa/extensions/chooser_dialog_cocoa.h

 // Copyright 2016 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_COCOA_EXTENSIONS_CHOOSER_DIALOG_COCOA_H_
 #define CHROME_BROWSER_UI_COCOA_EXTENSIONS_CHOOSER_DIALOG_COCOA_H_
 
 #import <Cocoa/Cocoa.h>
 
 #include "base/mac/scoped_nsobject.h"
@@ skipping 27 matching lines @@
   void ShowDialog();
 
   // Call this to close the chooser dialog.
   void Dismissed();
 
   content::WebContents* web_contents() const { return web_contents_; }
 
  private:
   friend class ChooserDialogCocoaControllerTest;
   base::scoped_nsobject<ChooserDialogCocoaController>
-      chooser_dialog_cocoa_controller_ = nullptr;
-  std::unique_ptr<ConstrainedWindowMac> constrained_window_ = nullptr;
+      chooser_dialog_cocoa_controller_;
+  std::unique_ptr<ConstrainedWindowMac> constrained_window_;
   content::WebContents* web_contents_;     // Weak.
   ChooserController* chooser_controller_;  // Weak.
 };
 
 #endif  // CHROME_BROWSER_UI_COCOA_EXTENSIONS_CHOOSER_DIALOG_COCOA_H_