[Sync] Make directory types registration explicit in ModelTypeRegistry

components/sync/driver/model_association_manager.cc

Index: components/sync/driver/model_association_manager.cc
diff --git a/components/sync/driver/model_association_manager.cc b/components/sync/driver/model_association_manager.cc
index 382c4f1d33bd98d6ec39ccbfa1075a8da02d173d..e8dae8a61c4882122c046eb1770a47a0d35e67ed 100644
--- a/components/sync/driver/model_association_manager.cc
+++ b/components/sync/driver/model_association_manager.cc
@@ -169,6 +169,7 @@ void ModelAssociationManager::LoadEnabledTypes() {
     if (dtc->state() == DataTypeController::NOT_RUNNING) {
       DCHECK(!loaded_types_.Has(dtc->type()));
       DCHECK(!associated_types_.Has(dtc->type()));
+      delegate_->OnSingleDataTypeWillStart(dtc->type());

[maxbogue, 2017/01/18 01:24:11]

Do you need to thread this call through DataTypeManagerImpl? It's just accessing
the DTC and calling BeforeLoadModels on it, and the ModelAssociationManager
could do that right here.

[pavely, 2017/01/18 20:18:07]

All the code that deals with registering types is in DTMI, I didn't want to
pollute MAM with just this one call. And to be honest I think LoadModels doesn't
belong in MAM either.

       dtc->LoadModels(base::Bind(&ModelAssociationManager::ModelLoadCallback,
                                  weak_ptr_factory_.GetWeakPtr()));
     }