components: Move PrefRegistrySyncable into user_prefs namespace.

chrome/browser/media_galleries/media_galleries_preferences.h

Index: chrome/browser/media_galleries/media_galleries_preferences.h
diff --git a/chrome/browser/media_galleries/media_galleries_preferences.h b/chrome/browser/media_galleries/media_galleries_preferences.h
index 2db944d1fc89e03f4a995b009b824cbdfa5e1e95..6ece27dffc047363f4b61e69913ae0baceb0824e 100644
--- a/chrome/browser/media_galleries/media_galleries_preferences.h
+++ b/chrome/browser/media_galleries/media_galleries_preferences.h
@@ -18,7 +18,6 @@
 #include "chrome/browser/profiles/profile_keyed_service.h"
 #include "chrome/browser/storage_monitor/removable_storage_observer.h"
 
-class PrefRegistrySyncable;
 class Profile;
 
 namespace base {
@@ -30,6 +29,10 @@ class Extension;
 class ExtensionPrefs;
 }
 
+namespace user_prefs {
+class PrefRegistrySyncable;
+}
+
 namespace chrome {
 
 typedef uint64 MediaGalleryPrefId;
@@ -190,7 +193,7 @@ class MediaGalleriesPreferences : public ProfileKeyedService,
   // ProfileKeyedService implementation:
   virtual void Shutdown() OVERRIDE;
 
-  static void RegisterUserPrefs(PrefRegistrySyncable* registry);
+  static void RegisterUserPrefs(user_prefs::PrefRegistrySyncable* registry);
 
   // Returns true if the media gallery preferences system has ever been used
   // for this profile. To be exact, it checks if a gallery has ever been added