Parser: store parameters in a ThreadedList instead of ZoneList.

src/parsing/parser-base.h

Index: src/parsing/parser-base.h
diff --git a/src/parsing/parser-base.h b/src/parsing/parser-base.h
index 3d486b88857fb003ec07c63f76701d8c97afec29..0a9e3deee8369a3b626888a9ab4416764c7c91f6 100644
--- a/src/parsing/parser-base.h
+++ b/src/parsing/parser-base.h
@@ -57,7 +57,7 @@ static inline bool operator&(ParseFunctionFlags bitfield,
   return static_cast<T>(bitfield) & static_cast<T>(mask);
 }
 
-struct FormalParametersBase {
+struct FormalParametersBase : public ZoneObject {
   explicit FormalParametersBase(DeclarationScope* scope) : scope(scope) {}
 
   int num_parameters() const {
@@ -2658,22 +2658,22 @@ ParserBase<Impl>::ParseAssignmentExpression(bool accept_IN, bool* ok) {
 
     scope_snapshot.Reparent(scope);
 
-    FormalParametersT parameters(scope);
+    FormalParametersT* parameters = new (zone()) FormalParametersT(scope);
     if (!classifier()->is_simple_parameter_list()) {
       scope->SetHasNonSimpleParameters();
-      parameters.is_simple = false;
+      parameters->is_simple = false;
     }
 
-    checkpoint.Restore(&parameters.materialized_literals_count);
+    checkpoint.Restore(&parameters->materialized_literals_count);
 
     scope->set_start_position(lhs_beg_pos);
     Scanner::Location duplicate_loc = Scanner::Location::invalid();
-    impl()->DeclareArrowFunctionFormalParameters(&parameters, expression, loc,
+    impl()->DeclareArrowFunctionFormalParameters(parameters, expression, loc,
                                                  &duplicate_loc, CHECK_OK);
     if (duplicate_loc.IsValid()) {
       classifier()->RecordDuplicateFormalParameterError(duplicate_loc);
     }
-    expression = ParseArrowFunctionLiteral(accept_IN, parameters, CHECK_OK);
+    expression = ParseArrowFunctionLiteral(accept_IN, *parameters, CHECK_OK);
     impl()->Discard();
     classifier()->RecordPatternError(arrow_loc,
                                      MessageTemplate::kUnexpectedToken,
@@ -3500,10 +3500,7 @@ void ParserBase<Impl>::ParseFormalParameterList(FormalParametersT* parameters,
     }
   }
 
-  for (int i = 0; i < parameters->arity; ++i) {
-    auto parameter = parameters->at(i);
-    impl()->DeclareFormalParameter(parameters->scope, parameter);
-  }
+  impl()->DeclareFormalParameters(parameters->scope, parameters->params);
 }
 
 template <typename Impl>