Introduce PrefRegistrySyncable, simplifying PrefServiceSyncable.

chrome/browser/extensions/extension_web_ui.h

Index: chrome/browser/extensions/extension_web_ui.h
diff --git a/chrome/browser/extensions/extension_web_ui.h b/chrome/browser/extensions/extension_web_ui.h
index 46ce3a6dd4ce01b6b7fae4f98d57d056dea82e4d..f1d8f2a6cdcea74b94844f76107102d02bd7e577 100644
--- a/chrome/browser/extensions/extension_web_ui.h
+++ b/chrome/browser/extensions/extension_web_ui.h
@@ -21,7 +21,7 @@ namespace extensions {
 class BookmarkManagerPrivateEventRouter;
 }
 
-class PrefServiceSyncable;
+class PrefRegistrySyncable;
 class Profile;
 
 // This class implements WebUI for extensions and allows extensions to put UI in
@@ -57,7 +57,7 @@ class ExtensionWebUI : public content::WebUIController {
                                           const base::Value* override);
 
   // Called from BrowserPrefs
-  static void RegisterUserPrefs(PrefServiceSyncable* prefs);
+  static void RegisterUserPrefs(PrefRegistrySyncable* registry);
 
   // Get the favicon for the extension by getting an icon from the manifest.
   // Note. |callback| is always run asynchronously.