Correct handling of temporaries as parameters.

src/parser.h

Index: src/parser.h
diff --git a/src/parser.h b/src/parser.h
index 87269ed619581862cb4038173286a1c4b0d42b28..c5bee739475532642c2f57a6ce58419052132afc 100644
--- a/src/parser.h
+++ b/src/parser.h
@@ -1318,8 +1318,9 @@ void ParserTraits::DeclareFormalParameter(
   const AstRawString* name = is_simple
                                  ? pattern->AsVariableProxy()->raw_name()
                                  : parser_->ast_value_factory()->empty_string();
+  VariableMode mode = is_simple ? VAR : TEMPORARY;
   Variable* var =
-      parameters->scope->DeclareParameter(name, VAR, is_rest, &is_duplicate);
+      parameters->scope->DeclareParameter(name, mode, is_rest, &is_duplicate);
   parameters->AddParameter(var, is_simple ? nullptr : pattern);
   if (is_duplicate) {
     classifier->RecordDuplicateFormalParameterError(