IDL: Avoid double type-check for variadic interface type arguments

Source/bindings/templates/methods.cpp

Index: Source/bindings/templates/methods.cpp
diff --git a/Source/bindings/templates/methods.cpp b/Source/bindings/templates/methods.cpp
index 004152c91a53a8c350b818f39a4de2caff1cf93a..d1242e4eee3168de2a0b63efbd15664afa8c4eaf 100644
--- a/Source/bindings/templates/methods.cpp
+++ b/Source/bindings/templates/methods.cpp
@@ -121,9 +121,11 @@ if (UNLIKELY(info.Length() <= {{argument.index}})) {
     return;
 }
 {% endif %}
-{% if argument.has_type_checking_interface %}
+{% if argument.has_type_checking_interface and not argument.is_variadic_wrapper_type %}
 {# Type checking for wrapper interface types (if interface not implemented,
-   throw a TypeError), per http://www.w3.org/TR/WebIDL/#es-interface #}
+   throw a TypeError), per http://www.w3.org/TR/WebIDL/#es-interface
+   Note: for variadic arguments, the type checking is done for each matched
+   argument instead; see argument.is_variadic_wrapper_type code-path below. #}
 if (info.Length() > {{argument.index}} && {% if argument.is_nullable %}!isUndefinedOrNull(info[{{argument.index}}]) && {% endif %}!V8{{argument.idl_type}}::hasInstance(info[{{argument.index}}], info.GetIsolate())) {
     {{throw_type_error(method, '"parameter %s is not of type \'%s\'."' %
                                (argument.index + 1, argument.idl_type)) | indent}}