Avoid extra arity and type check on distinguishing argument

Source/bindings/templates/methods.cpp

 {##############################################################################}
 {% macro generate_method(method, world_suffix) %}
 {% filter conditional(method.conditional_string) %}
 static void {{method.name}}{{method.overload_index}}Method{{world_suffix}}(const v8::FunctionCallbackInfo<v8::Value>& info)
 {
     {# Local variables #}
     {% if method.has_exception_state %}
     ExceptionState exceptionState(ExceptionState::ExecutionContext, "{{method.name}}", "{{interface_name}}", info.Holder(), info.GetIsolate());
     {% endif %}
     {% if method.number_of_required_arguments %}
@@ skipping 74 matching lines @@
     {{cpp_method_call(method, argument.v8_set_return_value_for_main_world, argument.cpp_value) | indent}}
     {% else %}
     {{cpp_method_call(method, argument.v8_set_return_value, argument.cpp_value) | indent}}
     {% endif %}
     {% if argument.has_event_listener_argument %}
     {{hidden_dependency_action(method.name) | indent}}
     {% endif %}
     return;
 }
 {% endif %}
-{% if argument.has_type_checking_interface %}
+{% if argument.has_type_checking_interface and argument.index != method.distinguishing_argument_index %}
 {# 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
+   If the argument is the distinguishing argument for an overloaded method,
+   the type is checked as part of overload resolution instead. #}
 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}}
     return;
 }
 {% endif %}
 {% if argument.is_callback_interface %}
 {# FIXME: remove EventListener special case #}
 {% if argument.idl_type == 'EventListener' %}
 {% if method.name == 'removeEventListener' %}
@@ skipping 396 matching lines @@
     {% endfor %}
     {{constructor.cpp_type}} impl = {{cpp_class}}::createForJSConstructor({{constructor.argument_list | join(', ')}});
     {% if is_constructor_raises_exception %}
     if (exceptionState.throwIfNeeded())
         return;
     {% endif %}
 
     {{generate_constructor_wrapper(constructor) | indent}}
 }
 {% endmacro %}