Switch WebContentsUserData to be a friended base.

chrome/browser/ui/metro_pin_tab_helper.h

 // Copyright (c) 2012 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_METRO_PIN_TAB_HELPER_H_
 #define CHROME_BROWSER_UI_METRO_PIN_TAB_HELPER_H_
 
 #include "chrome/browser/tab_contents/web_contents_user_data.h"
 #include "content/public/browser/web_contents_observer.h"
 
 // Per-tab class to help manage metro pinning.
 class MetroPinTabHelper : public content::WebContentsObserver,
                           public WebContentsUserData<MetroPinTabHelper> {
  public:
-  explicit MetroPinTabHelper(content::WebContents* tab_contents);
   virtual ~MetroPinTabHelper();
-  static int kUserDataKey;
 
   bool is_pinned() const { return is_pinned_; }
 
   void TogglePinnedToStartScreen();
 
   // content::WebContentsObserver overrides:
   virtual void DidNavigateMainFrame(
       const content::LoadCommittedDetails& details,
       const content::FrameNavigateParams& params) OVERRIDE;
 
  private:
+  explicit MetroPinTabHelper(content::WebContents* tab_contents);
+  static int kUserDataKey;
+  friend class WebContentsUserData<MetroPinTabHelper>;
+
   // Queries the metro driver about the pinned state of the current URL.
   void UpdatePinnedStateForCurrentURL();
 
   // Whether the current URL is pinned to the metro start screen.
   bool is_pinned_;
 
   DISALLOW_COPY_AND_ASSIGN(MetroPinTabHelper);
 };
 
 #endif  // CHROME_BROWSER_UI_METRO_PIN_TAB_HELPER_H_