Introduce PrefRegistrySyncable, simplifying PrefServiceSyncable.

chrome/browser/media_gallery/media_galleries_preferences.cc

Index: chrome/browser/media_gallery/media_galleries_preferences.cc
diff --git a/chrome/browser/media_gallery/media_galleries_preferences.cc b/chrome/browser/media_gallery/media_galleries_preferences.cc
index 7f21a69f674c694018eed55fa12139070cda22c2..cc55729c89506d834da2755760f3f6b9a25bf421 100644
--- a/chrome/browser/media_gallery/media_galleries_preferences.cc
+++ b/chrome/browser/media_gallery/media_galleries_preferences.cc
@@ -12,6 +12,7 @@
 #include "chrome/browser/extensions/extension_service.h"
 #include "chrome/browser/extensions/extension_system.h"
 #include "chrome/browser/media_gallery/media_file_system_registry.h"
+#include "chrome/browser/prefs/pref_registry_syncable.h"
 #include "chrome/browser/prefs/pref_service.h"
 #include "chrome/browser/prefs/scoped_user_pref_update.h"
 #include "chrome/browser/profiles/profile.h"
@@ -440,12 +441,13 @@ bool MediaGalleriesPreferences::APIHasBeenUsed(Profile* profile) {
 }
 
 // static
-void MediaGalleriesPreferences::RegisterUserPrefs(PrefServiceSyncable* prefs) {
-  prefs->RegisterListPref(prefs::kMediaGalleriesRememberedGalleries,
-                          PrefServiceSyncable::UNSYNCABLE_PREF);
-  prefs->RegisterUint64Pref(prefs::kMediaGalleriesUniqueId,
-                            kInvalidMediaGalleryPrefId + 1,
-                            PrefServiceSyncable::UNSYNCABLE_PREF);
+void MediaGalleriesPreferences::RegisterUserPrefs(
+    PrefRegistrySyncable* registry) {
+  registry->RegisterListPref(prefs::kMediaGalleriesRememberedGalleries,
+                             PrefRegistrySyncable::UNSYNCABLE_PREF);
+  registry->RegisterUint64Pref(prefs::kMediaGalleriesUniqueId,
+                               kInvalidMediaGalleryPrefId + 1,
+                               PrefRegistrySyncable::UNSYNCABLE_PREF);
 }
 
 extensions::ExtensionPrefs*