[Sync] Move ModelType and related classes to 'syncer' namespace

sync/notifier/invalidation_util.h

Index: sync/notifier/invalidation_util.h
diff --git a/sync/notifier/invalidation_util.h b/sync/notifier/invalidation_util.h
index 1ec1235123d0664bd6148b0a7bade5982fe01af4..bf5388f2431274bbad2ab2d045e7674995891484 100644
--- a/sync/notifier/invalidation_util.h
+++ b/sync/notifier/invalidation_util.h
@@ -29,11 +29,11 @@ struct ObjectIdLessThan {
 
 typedef std::set<invalidation::ObjectId, ObjectIdLessThan> ObjectIdSet;
 
-bool RealModelTypeToObjectId(syncable::ModelType model_type,
+bool RealModelTypeToObjectId(syncer::ModelType model_type,
                              invalidation::ObjectId* object_id);
 
 bool ObjectIdToRealModelType(const invalidation::ObjectId& object_id,
-                             syncable::ModelType* model_type);
+                             syncer::ModelType* model_type);
 
 std::string ObjectIdToString(const invalidation::ObjectId& object_id);