Switch SupportsUserData uses to use unique_ptr.

extensions/shell/browser/shell_extension_web_contents_observer.h

Index: extensions/shell/browser/shell_extension_web_contents_observer.h
diff --git a/extensions/shell/browser/shell_extension_web_contents_observer.h b/extensions/shell/browser/shell_extension_web_contents_observer.h
index 372b7c2d6ec73b0a0d5b43a1f0126f94ab879fbb..dc458fd375dff60a1b143308f32fc0da8c06e7fb 100644
--- a/extensions/shell/browser/shell_extension_web_contents_observer.h
+++ b/extensions/shell/browser/shell_extension_web_contents_observer.h
@@ -15,12 +15,14 @@ namespace extensions {
 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);
 };