[es6] implement default/optional parameters (WIP / comments)

src/preparser.h

Index: src/preparser.h
diff --git a/src/preparser.h b/src/preparser.h
index a7c27c1c649153dc250bbadb3b005c5d75bcdc69..76399af44a00f62006b6372e97c1e7247f92c0a6 100644
--- a/src/preparser.h
+++ b/src/preparser.h
@@ -1237,6 +1237,7 @@ class PreParserFactory {
       PreParserIdentifier name, AstValueFactory* ast_value_factory,
       Scope* scope, PreParserStatementList body, int materialized_literal_count,
       int expected_property_count, int handler_count, int parameter_count,
+      PreParserExpressionList default_values,
       FunctionLiteral::ParameterFlag has_duplicate_parameters,
       FunctionLiteral::FunctionType function_type,
       FunctionLiteral::IsFunctionFlag is_function,
@@ -3130,10 +3131,12 @@ ParserBase<Traits>::ParseArrowFunctionLiteral(int start_pos,
     }
   }
 
+  typename Traits::Type::ExpressionList default_values =
+      this->NewExpressionList(0, zone_);
   FunctionLiteralT function_literal = factory()->NewFunctionLiteral(
       this->EmptyIdentifierString(), ast_value_factory(), scope, body,
       materialized_literal_count, expected_property_count, handler_count,
-      num_parameters, FunctionLiteral::kNoDuplicateParameters,
+      num_parameters, default_values, FunctionLiteral::kNoDuplicateParameters,
       FunctionLiteral::ANONYMOUS_EXPRESSION, FunctionLiteral::kIsFunction,
       FunctionLiteral::kNotParenthesized, FunctionKind::kArrowFunction,
       start_pos);