sync: Introduce ModelTypeRegistry and helpers

sync/engine/process_updates_util.h

Index: sync/engine/process_updates_util.h
diff --git a/sync/engine/process_updates_util.h b/sync/engine/process_updates_util.h
index 6e8bc71b859670ce3012a046584b73a6448abf51..7367ed1337b8588617771c66140ec710a336a2c5 100644
--- a/sync/engine/process_updates_util.h
+++ b/sync/engine/process_updates_util.h
@@ -31,18 +31,7 @@ class Directory;
 
 class Cryptographer;
 
-// TODO(rlarocque): Move these definitions somewhere else?
 typedef std::vector<const sync_pb::SyncEntity*> SyncEntityList;
-typedef std::map<ModelType, SyncEntityList> TypeSyncEntityMap;
-
-// Given a GetUpdates response, iterates over all the returned items and
-// divides them according to their type.  Outputs a map from model types to
-// received SyncEntities.  The output map will have entries (possibly empty)
-// for all types in |requested_types|.
-void PartitionUpdatesByType(
-    const sync_pb::GetUpdatesResponse& updates,
-    ModelTypeSet requested_types,
-    TypeSyncEntityMap* updates_by_type);
 
 // Processes all the updates associated with a single ModelType.
 void ProcessDownloadedUpdates(