Introduce PrefRegistrySyncable, simplifying PrefServiceSyncable.

chrome/browser/sync/profile_sync_components_factory_impl.cc

Index: chrome/browser/sync/profile_sync_components_factory_impl.cc
diff --git a/chrome/browser/sync/profile_sync_components_factory_impl.cc b/chrome/browser/sync/profile_sync_components_factory_impl.cc
index 48207449510ab599c2173ac213821aee9461f5f3..cd3108bc9f0eb34c0ed2964825a0c96bb93104a1 100644
--- a/chrome/browser/sync/profile_sync_components_factory_impl.cc
+++ b/chrome/browser/sync/profile_sync_components_factory_impl.cc
@@ -13,7 +13,7 @@
 #include "chrome/browser/history/history_service.h"
 #include "chrome/browser/history/history_service_factory.h"
 #include "chrome/browser/prefs/pref_model_associator.h"
-#include "chrome/browser/prefs/pref_service.h"
+#include "chrome/browser/prefs/pref_service_syncable.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/search_engines/template_url_service.h"
 #include "chrome/browser/search_engines/template_url_service_factory.h"
@@ -282,7 +282,8 @@ base::WeakPtr<syncer::SyncableService> ProfileSyncComponentsFactoryImpl::
   }
   switch (type) {
     case syncer::PREFERENCES:
-      return profile_->GetPrefs()->GetSyncableService()->AsWeakPtr();
+      return PrefServiceSyncable::FromProfile(

[Mattias Nissler (ping if slow), 2013/02/06 17:53:33]

non-scoring comment: This seems to be the non-test call site  I found that
actually needs a PrefServiceSyncable instead of a PrefService. The answer for
this one could be to split out the syncing stuff.

[Jói, 2013/02/07 14:52:32]

OK.

+          profile_)->GetSyncableService()->AsWeakPtr();
     case syncer::AUTOFILL:
     case syncer::AUTOFILL_PROFILE: {
       if (!web_data_service_.get())