[Sync] Rely on directory to decide which types need to be purged

chrome/browser/sync/glue/sync_backend_host_impl.cc

Index: chrome/browser/sync/glue/sync_backend_host_impl.cc
diff --git a/chrome/browser/sync/glue/sync_backend_host_impl.cc b/chrome/browser/sync/glue/sync_backend_host_impl.cc
index dc0de63237f7dc4872aca1018e7b95145a3bc8db..b8913ea549f2abd4b6bf354c9b9eb8fd73181b98 100644
--- a/chrome/browser/sync/glue/sync_backend_host_impl.cc
+++ b/chrome/browser/sync/glue/sync_backend_host_impl.cc
@@ -339,8 +339,6 @@ void SyncBackendHostImpl::ConfigureDataTypes(
   // backend because configuration requests are never aborted; they are retried
   // until they succeed or the backend is shut down.
 
-  syncer::ModelTypeSet previous_types = registrar_->GetLastConfiguredTypes();
-
   syncer::ModelTypeSet disabled_types =
       GetDataTypesInState(DISABLED, config_state_map);
   syncer::ModelTypeSet fatal_types =
@@ -349,10 +347,8 @@ void SyncBackendHostImpl::ConfigureDataTypes(
       GetDataTypesInState(CRYPTO, config_state_map);
   syncer::ModelTypeSet unready_types =
       GetDataTypesInState(UNREADY, config_state_map);
-  disabled_types.PutAll(fatal_types);
 
-  // TODO(zea): These types won't be fully purged if they are subsequently
-  // disabled by the user. Fix that. See crbug.com/386778
+  disabled_types.PutAll(fatal_types);
   disabled_types.PutAll(crypto_types);
   disabled_types.PutAll(unready_types);
 
@@ -395,7 +391,7 @@ void SyncBackendHostImpl::ConfigureDataTypes(
 
   syncer::ModelTypeSet current_types = registrar_->GetLastConfiguredTypes();
   syncer::ModelTypeSet types_to_purge =
-      syncer::Difference(previous_types, current_types);
+      syncer::Difference(syncer::ModelTypeSet::All(), current_types);
   syncer::ModelTypeSet inactive_types =
       GetDataTypesInState(CONFIGURE_INACTIVE, config_state_map);
   types_to_purge.RemoveAll(inactive_types);