[Sync] Make directory types registration explicit in ModelTypeRegistry

components/sync/engine/sync_engine.h

Index: components/sync/engine/sync_engine.h
diff --git a/components/sync/engine/sync_engine.h b/components/sync/engine/sync_engine.h
index af4e53d0b489030cbc8407018440605349b3022b..55cd760c2e62528d888e99c7a239d6b8690dbd17 100644
--- a/components/sync/engine/sync_engine.h
+++ b/components/sync/engine/sync_engine.h
@@ -95,6 +95,11 @@ class SyncEngine : public ModelTypeConfigurer {
   // Updates the engine's SyncCredentials.
   virtual void UpdateCredentials(const SyncCredentials& credentials) = 0;
 
+  // Switches sync engine into configuration mode. In this mode only initial
+  // data for newly enabled types is downloaded from server. No local changes
+  // are committed to server.
+  virtual void StartConfiguration() = 0;
+
   // This starts the sync engine running a Syncer object to communicate with
   // sync servers. Until this is called, no changes will leave or enter this
   // browser from the cloud / sync servers.