IDL: make optional arguments (without default) explicit sometimes

Source/bindings/scripts/v8_interface.py

 # Copyright (C) 2013 Google Inc. All rights reserved.
 # coding=utf-8
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 # notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
@@ skipping 851 matching lines @@
     is_constructor_raises_exception = \
         interface.extended_attributes.get('RaisesException') == 'Constructor'
 
     return {
         'arguments': [v8_methods.argument_context(interface, constructor, argument, index)
                       for index, argument in enumerate(constructor.arguments)],
         'arguments_need_try_catch': arguments_need_try_catch,
         'cpp_type': cpp_template_type(
             cpp_ptr_type('RefPtr', 'RawPtr', gc_type(interface)),
             cpp_name(interface)),
-        'cpp_value': v8_methods.cpp_value(
-            interface, constructor, len(constructor.arguments)),
+        'cpp_value': v8_methods.cpp_value(interface, constructor),
         'has_exception_state':
             is_constructor_raises_exception or
             any(argument for argument in constructor.arguments
                 if argument.idl_type.name == 'SerializedScriptValue' or
                    argument.idl_type.may_raise_exception_on_conversion),
         'is_call_with_document':
             # [ConstructorCallWith=Document]
             has_extended_attribute_value(interface,
                 'ConstructorCallWith', 'Document'),
         'is_call_with_execution_context':
@@ skipping 226 matching lines @@
         deleter = next(
             method
             for method in interface.operations
             if ('deleter' in method.specials and
                 len(method.arguments) == 1 and
                 str(method.arguments[0].idl_type) == 'DOMString'))
     except StopIteration:
         return None
 
     return property_deleter(deleter)