[Sync] Make directory types registration explicit in ModelTypeRegistry

components/sync/engine_impl/model_type_registry.h

Index: components/sync/engine_impl/model_type_registry.h
diff --git a/components/sync/engine_impl/model_type_registry.h b/components/sync/engine_impl/model_type_registry.h
index 5229f0d6c9fc80aeed79187d320def1b779afb59..3e25257e86a734439266b5a68c4b7a1536c1014d 100644
--- a/components/sync/engine_impl/model_type_registry.h
+++ b/components/sync/engine_impl/model_type_registry.h
@@ -38,21 +38,17 @@ typedef std::map<ModelType, CommitContributor*> CommitContributorMap;
 class ModelTypeRegistry : public ModelTypeConnector,
                           public SyncEncryptionHandler::Observer {
  public:
-  // Constructs a ModelTypeRegistry that supports directory types.
   ModelTypeRegistry(const std::vector<scoped_refptr<ModelSafeWorker>>& workers,
                     UserShare* user_share,
                     NudgeHandler* nudge_handler,
                     const UssMigrator& uss_migrator);
   ~ModelTypeRegistry() override;
 
-  // Sets the set of enabled types.
-  void SetEnabledDirectoryTypes(const ModelSafeRoutingInfo& routing_info);
-
   // Enables an off-thread type for syncing.  Connects the given proxy
   // and its task_runner to the newly created worker.
   //
   // Expects that the proxy's ModelType is not currently enabled.
-  void ConnectType(
+  void ConnectNonBlockingType(
       ModelType type,
       std::unique_ptr<ActivationContext> activation_context) override;
 
@@ -60,7 +56,15 @@ class ModelTypeRegistry : public ModelTypeConnector,
   //
   // Expects that the type is currently enabled.
   // Deletes the worker associated with the type.
-  void DisconnectType(ModelType type) override;
+  void DisconnectNonBlockingType(ModelType type) override;
+
+  // Creates update handler and commit contributor objects for directory type.
+  // Expects that the type is not yet registered.
+  void RegisterDirectoryType(ModelType type, ModelSafeGroup group) override;
+
+  // Deletes objects related to directory type. Expects that the type is
+  // registered.
+  void UnregisterDirectoryType(ModelType type) override;
 
   // Implementation of SyncEncryptionHandler::Observer.
   void OnPassphraseRequired(
@@ -118,9 +122,9 @@ class ModelTypeRegistry : public ModelTypeConnector,
   }
 
   // Sets of handlers and contributors.
-  std::vector<std::unique_ptr<DirectoryCommitContributor>>
+  std::map<ModelType, std::unique_ptr<DirectoryCommitContributor>>
       directory_commit_contributors_;
-  std::vector<std::unique_ptr<DirectoryUpdateHandler>>
+  std::map<ModelType, std::unique_ptr<DirectoryUpdateHandler>>
       directory_update_handlers_;
 
   std::vector<std::unique_ptr<ModelTypeWorker>> model_type_workers_;
@@ -149,9 +153,6 @@ class ModelTypeRegistry : public ModelTypeConnector,
   // The NudgeHandler.  Not owned.
   NudgeHandler* nudge_handler_;
 
-  // The set of enabled directory types.
-  ModelTypeSet enabled_directory_types_;
-
   // Function to call to migrate data from the directory to USS.
   UssMigrator uss_migrator_;