Update on "Pass one NDM to backend init"

Take external NDM if it exists, otherwise internal.

Note: by default, xnnpack uses the named_data_map. Constants are not stored with the delegated blob anymore.

Differential Revision: [D73679710](https://our.internmc.facebook.com/intern/diff/D73679710/)

[ghstack-poisoned]

Author: lucylq

extension/flat_tensor/flat_tensor_data_map.cpp

@@ -253,7 +253,8 @@ ET_NODISCARD Result<const char*> FlatTensorDataMap::get_key(
       index,
       num_keys);
 
-  if (flat_tensor_->named_data() != nullptr && index < flat_tensor_->named_data()->size()) {
+  if (flat_tensor_->named_data() != nullptr &&
+      index < flat_tensor_->named_data()->size()) {
     return flat_tensor_->named_data()->Get(index)->key()->c_str();
   } else {
     if (flat_tensor_->named_data() != nullptr) {

runtime/executor/method.cpp

@@ -805,16 +805,16 @@ Error Method::init(
       pte_data_map = pte_data_map_res.get();
     }
 
-    int named_data_map_items =
+    size_t named_data_map_items =
         (named_data_map != nullptr) ? named_data_map->get_num_keys().get() : 0;
-    int pte_map_items =
+    size_t pte_map_items =
         (pte_data_map != nullptr) ? pte_data_map->get_num_keys().get() : 0;
 
     // TODO: implement ndm merge.
     ET_CHECK_OR_RETURN_ERROR(
         (pte_map_items == 0 || named_data_map_items == 0),
         NotImplemented,
-        "NamedDataMap merge not supported. Both pte_data_map and named_data_map are non-empty, don't know what to do.");
+        "NamedDataMap merge not supported; both pte_data_map and named_data_map are non-empty. If you see this error please file an issue at https://github.com/pytorch/executorch/issues");
 
     if (named_data_map_items == 0) {
       named_data_map = pte_data_map;