Switch SupportsUserData uses to use unique_ptr.

extensions/shell/browser/shell_extension_web_contents_observer.h

 // 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.
 
 #ifndef EXTENSIONS_SHELL_BROWSER_SHELL_EXTENSION_WEB_CONTENTS_OBSERVER_H_
 #define EXTENSIONS_SHELL_BROWSER_SHELL_EXTENSION_WEB_CONTENTS_OBSERVER_H_
 
 #include "base/macros.h"
 #include "content/public/browser/web_contents_user_data.h"
 #include "extensions/browser/extension_web_contents_observer.h"
 
 namespace extensions {
 
 // The app_shell version of ExtensionWebContentsObserver.
 class ShellExtensionWebContentsObserver
     : public ExtensionWebContentsObserver,
       public content::WebContentsUserData<ShellExtensionWebContentsObserver> {
+ public:
+  ~ShellExtensionWebContentsObserver() override;
+
  private:
   friend class content::WebContentsUserData<ShellExtensionWebContentsObserver>;
 
   explicit ShellExtensionWebContentsObserver(
       content::WebContents* web_contents);
-  ~ShellExtensionWebContentsObserver() override;
 
   DISALLOW_COPY_AND_ASSIGN(ShellExtensionWebContentsObserver);
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_SHELL_BROWSER_SHELL_EXTENSION_WEB_CONTENTS_OBSERVER_H_