fixup! fixup! fixup! async_hooks: improve resource stack performance

Author: addaleax

src/env.h

@@ -678,6 +678,10 @@ class AsyncHooks : public MemoryRetainer {
   inline AliasedFloat64Array& async_id_fields();
   inline AliasedFloat64Array& async_ids_stack();
   inline v8::Local<v8::Array> js_execution_async_resources();
+  // Returns the native executionAsyncResource value at stack index `index`.
+  // Resources provided on the JS side are not stored on the native stack,
+  // in which case an empty `Local<>` is returned.
+  // The `js_execution_async_resources` array contains the value in that case.
   inline v8::Local<v8::Object> native_execution_async_resource(size_t index);
 
   inline v8::Local<v8::String> provider_string(int idx);