Introduce PrefRegistrySyncable, simplifying PrefServiceSyncable.

chrome/browser/chromeos/proxy_config_service_impl.cc

Index: chrome/browser/chromeos/proxy_config_service_impl.cc
diff --git a/chrome/browser/chromeos/proxy_config_service_impl.cc b/chrome/browser/chromeos/proxy_config_service_impl.cc
index cb375dd5b9ef826860f69c672cdddfca7f4702c8..528d22d80634e425dc2cfeedfda80e62bb107e41 100644
--- a/chrome/browser/chromeos/proxy_config_service_impl.cc
+++ b/chrome/browser/chromeos/proxy_config_service_impl.cc
@@ -16,6 +16,7 @@
 #include "chrome/browser/chromeos/settings/cros_settings_names.h"
 #include "chrome/browser/policy/proto/chrome_device_policy.pb.h"
 #include "chrome/browser/prefs/pref_registry_simple.h"
+#include "chrome/browser/prefs/pref_registry_syncable.h"
 #include "chrome/browser/prefs/pref_service.h"
 #include "chrome/browser/prefs/proxy_config_dictionary.h"
 #include "chrome/browser/prefs/proxy_prefs.h"
@@ -588,11 +589,10 @@ void ProxyConfigServiceImpl::RegisterPrefs(PrefRegistrySimple* registry) {
 }
 
 // static
-void ProxyConfigServiceImpl::RegisterUserPrefs(
-    PrefServiceSyncable* pref_service) {
-  pref_service->RegisterBooleanPref(prefs::kUseSharedProxies,
-                                    true,
-                                    PrefServiceSyncable::UNSYNCABLE_PREF);
+void ProxyConfigServiceImpl::RegisterUserPrefs(PrefRegistrySyncable* registry) {
+  registry->RegisterBooleanPref(prefs::kUseSharedProxies,
+                                true,
+                                PrefRegistrySyncable::UNSYNCABLE_PREF);
 }
 
 //------------------ ProxyConfigServiceImpl: private methods -------------------