Make the WebContentsUserData locator key private.

content/public/browser/web_contents_user_data.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 CONTENT_PUBLIC_BROWSER_WEB_CONTENTS_USER_DATA_H_
 #define CONTENT_PUBLIC_BROWSER_WEB_CONTENTS_USER_DATA_H_
 
 #include "base/logging.h"
 #include "base/supports_user_data.h"
 #include "content/public/browser/web_contents.h"
@@ skipping 17 matching lines @@
 // DEFINE_WEB_CONTENTS_USER_DATA_KEY(FooTabHelper)
 //
 template <typename T>
 class WebContentsUserData : public base::SupportsUserData::Data {
  public:
   // Creates an object of type T, and attaches it to the specified WebContents.
   // If an instance is already attached, does nothing.
   static void CreateForWebContents(WebContents* contents) {
     DCHECK(contents);
     if (!FromWebContents(contents))
-      contents->SetUserData(&kLocatorKey, new T(contents));
+      contents->SetUserData(UserDataKey(), new T(contents));
   }
 
   // Retrieves the instance of type T that was attached to the specified
   // WebContents (via CreateForWebContents above) and returns it. If no instance
   // of the type was attached, returns NULL.
   static T* FromWebContents(WebContents* contents) {
     DCHECK(contents);
-    return static_cast<T*>(contents->GetUserData(&kLocatorKey));
+    return static_cast<T*>(contents->GetUserData(UserDataKey()));
   }
   static const T* FromWebContents(const WebContents* contents) {
     DCHECK(contents);
-    return static_cast<const T*>(contents->GetUserData(&kLocatorKey));
+    return static_cast<const T*>(contents->GetUserData(UserDataKey()));
   }
 
+ protected:
+  static inline void* UserDataKey() {
+    return &kLocatorKey;
+  }
+
+ private:
   // The user data key.
   static int kLocatorKey;
 };
 
 // The macro to define the locator key. This key must be defined in the .cc file
 // of the tab helper otherwise different instances for different template types
 // will be collapsed by the Visual Studio linker.
 //
 // The "= 0" is surprising, but is required to effect a definition rather than
 // a declaration. Without it, this would be merely a declaration of a template
 // specialization. (C++98: 14.7.3.15; C++11: 14.7.3.13)
 //
 #define DEFINE_WEB_CONTENTS_USER_DATA_KEY(TYPE) \
 template<>                                      \
 int content::WebContentsUserData<TYPE>::kLocatorKey = 0;
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_WEB_CONTENTS_USER_DATA_H_