sync: Finish non-blocking type encryption support

sync/internal_api/sync_manager_impl.cc

Index: sync/internal_api/sync_manager_impl.cc
diff --git a/sync/internal_api/sync_manager_impl.cc b/sync/internal_api/sync_manager_impl.cc
index 30bbafd2b4f5c72ac351eb3f595e6fdf1ea5330e..8d2893923d3e7668dfd5e944fbfa1a10a510d019 100644
--- a/sync/internal_api/sync_manager_impl.cc
+++ b/sync/internal_api/sync_manager_impl.cc
@@ -387,6 +387,7 @@ void SyncManagerImpl::Init(InitArgs* args) {
 
   model_type_registry_.reset(
       new ModelTypeRegistry(args->workers, directory(), this));
+  sync_encryption_handler_->AddObserver(model_type_registry_.get());
 
   // Bind the SyncContext WeakPtr to this thread.  This helps us crash earlier
   // if the pointer is misused in debug mode.
@@ -607,6 +608,10 @@ void SyncManagerImpl::ShutdownOnSyncThread(ShutdownReason reason) {
 
   scheduler_.reset();
   session_context_.reset();
+
+  if (model_type_registry_) {
+    sync_encryption_handler_->RemoveObserver(model_type_registry_.get());
+  }
   model_type_registry_.reset();
 
   if (sync_encryption_handler_) {