Add support for function argument initializers. (#2571)

EcmaScript 2015 14.1.

Note: arrow functions with default arguments are not supported yet.

JerryScript-DCO-1.0-Signed-off-by: Zoltan Herczeg zherczeg.u-szeged@partner.samsung.com

jerry-core/parser/js/js-parser.h

@@ -119,6 +119,9 @@ typedef enum
   PARSER_ERR_INVALID_RETURN,                          /**< return must be inside a function */
   PARSER_ERR_INVALID_RIGHT_SQUARE,                    /**< right square must terminate a block */
   PARSER_ERR_DUPLICATED_LABEL,                        /**< duplicated label */
+#ifndef CONFIG_DISABLE_ES2015_FUNCTION_PARAMETER_INITIALIZER
+  PARSER_ERR_DUPLICATED_ARGUMENT_NAMES,               /**< duplicated argument names */
+#endif /* !CONFIG_DISABLE_ES2015_FUNCTION_PARAMETER_INITIALIZER */
   PARSER_ERR_OBJECT_PROPERTY_REDEFINED,               /**< property of object literal redefined */
   PARSER_ERR_NON_STRICT_ARG_DEFINITION                /**< non-strict argument definition */
 } parser_error_t;