Introduce PrefRegistrySyncable, simplifying PrefServiceSyncable.

chrome/browser/net/pref_proxy_config_tracker_impl.h

Index: chrome/browser/net/pref_proxy_config_tracker_impl.h
diff --git a/chrome/browser/net/pref_proxy_config_tracker_impl.h b/chrome/browser/net/pref_proxy_config_tracker_impl.h
index ea546c1d0fe1dcac292154e5e436a1b9a07b1f2c..a449527ce2fb776dac473562f830f063808c4f16 100644
--- a/chrome/browser/net/pref_proxy_config_tracker_impl.h
+++ b/chrome/browser/net/pref_proxy_config_tracker_impl.h
@@ -16,7 +16,7 @@
 
 class PrefService;
 class PrefRegistrySimple;
-class PrefServiceSyncable;
+class PrefRegistrySyncable;
 
 // A net::ProxyConfigService implementation that applies preference proxy
 // settings (pushed from PrefProxyConfigTrackerImpl) as overrides to the proxy
@@ -120,7 +120,7 @@ class PrefProxyConfigTrackerImpl {
   // Registers the proxy preferences. These are actually registered
   // the same way in local state and in user prefs.
   static void RegisterPrefs(PrefRegistrySimple* registry);
-  static void RegisterUserPrefs(PrefServiceSyncable* user_prefs);
+  static void RegisterUserPrefs(PrefRegistrySyncable* registry);
 
  protected:
   // Get the proxy configuration currently defined by preferences.