Support Dart optional arguments which are not dispatched, but instead use default values.

client/dom/scripts/systemnative.py

 #!/usr/bin/python
 # Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
 """This module provides shared functionality for the systems to generate
 native binding from the IDL database."""
 
 import emitter
 import os
@@ skipping 660 matching lines @@
         CALLBACK_NAME=callback_name,
         BODY=body)
 
   def _GenerateParameterAdapter(self, emitter, idl_argument, index):
     type_info = GetIDLTypeInfo(idl_argument.type)
     (adapter_type, include_name) = type_info.parameter_adapter_info()
     if include_name:
       self._cpp_impl_includes[include_name] = 1
     flags = ''
     if (idl_argument.ext_attrs.get('Optional') == 'DefaultIsNullString' or
-        ('Optional' in idl_argument.ext_attrs and 'Callback' in idl_argument.ext_attrs)):
+        'RequiredCppParameter' in idl_argument.ext_attrs):
       flags = ', DartUtilities::ConvertNullToDefaultValue'
     emitter.Emit(
         '\n'
         '        const $ADAPTER_TYPE $NAME(Dart_GetNativeArgument(args, $INDEX)$FLAGS);\n'
         '        if (!$NAME.conversionSuccessful()) {\n'
         '            exception = $NAME.exception();\n'
         '            goto fail;\n'
         '        }\n',
         ADAPTER_TYPE=adapter_type,
         NAME=idl_argument.id,
@@ skipping 91 matching lines @@
           '            goto fail;\n'
           '        }\n',
           INVOCATION=invocation_template)
 
     if 'ImplementedBy' in attributes:
       arguments.insert(0, 'receiver')
       self._cpp_impl_includes[attributes['ImplementedBy']] = 1
 
     return emitter.Format(invocation_template,
         FUNCTION_CALL='%s(%s)' % (function_expression, ', '.join(arguments)))