components: Move PrefRegistrySyncable into user_prefs namespace.

chrome/browser/ui/alternate_error_tab_observer.h

Index: chrome/browser/ui/alternate_error_tab_observer.h
diff --git a/chrome/browser/ui/alternate_error_tab_observer.h b/chrome/browser/ui/alternate_error_tab_observer.h
index 9ecf45f591508c4b9793fdb6e3da1ac6aee8ea47..475505c497535e23b54fd93a3379340c68cc66cb 100644
--- a/chrome/browser/ui/alternate_error_tab_observer.h
+++ b/chrome/browser/ui/alternate_error_tab_observer.h
@@ -11,9 +11,12 @@
 #include "content/public/browser/web_contents_observer.h"
 #include "content/public/browser/web_contents_user_data.h"
 
-class PrefRegistrySyncable;
 class Profile;
 
+namespace user_prefs {
+class PrefRegistrySyncable;
+}
+
 // Per-tab class to implement alternate error page functionality.
 class AlternateErrorPageTabObserver
     : public content::WebContentsObserver,
@@ -22,7 +25,7 @@ class AlternateErrorPageTabObserver
  public:
   virtual ~AlternateErrorPageTabObserver();
 
-  static void RegisterUserPrefs(PrefRegistrySyncable* registry);
+  static void RegisterUserPrefs(user_prefs::PrefRegistrySyncable* registry);
 
  private:
   explicit AlternateErrorPageTabObserver(content::WebContents* web_contents);