Bindings generation emits (more) correct null checking

Source/bindings/dart/scripts/dart_methods.py

Index: Source/bindings/dart/scripts/dart_methods.py
diff --git a/Source/bindings/dart/scripts/dart_methods.py b/Source/bindings/dart/scripts/dart_methods.py
index 5e3393be34975fb3e5863d71024a36c4bad8c04d..0a59338bc4db6b4893d546b9cfe37e83209bc72c 100644
--- a/Source/bindings/dart/scripts/dart_methods.py
+++ b/Source/bindings/dart/scripts/dart_methods.py
@@ -202,7 +202,7 @@ def generate_argument(interface, method, argument, index):
         'dart_set_return_value_for_main_world': dart_set_return_value(interface.name, method, this_cpp_value, for_main_world=True),
         'dart_set_return_value': dart_set_return_value(interface.name, method, this_cpp_value),
         'arg_index': arg_index,
-        'dart_value_to_local_cpp_value': dart_value_to_local_cpp_value(argument, arg_index, auto_scope),
+        'dart_value_to_local_cpp_value': dart_value_to_local_cpp_value(interface, argument, arg_index, auto_scope),
     }
     return argument_data
 
@@ -286,8 +286,9 @@ def dart_set_return_value(interface_name, method, cpp_value, for_main_world=Fals
                                           auto_scope=auto_scope)
 
 
-def dart_value_to_local_cpp_value(argument, index, auto_scope=True):
+def dart_value_to_local_cpp_value(interface, argument, index, auto_scope=True):
     extended_attributes = argument.extended_attributes
+    interface_extended_attributes = interface.extended_attributes
     idl_type = argument.idl_type
     name = argument.name
     # TODO(terry): Variadic arguments are not handled but treated as one argument.
@@ -306,7 +307,7 @@ def dart_value_to_local_cpp_value(argument, index, auto_scope=True):
                  (argument.default_value and argument.default_value.is_null)
 
     return idl_type.dart_value_to_local_cpp_value(
-        argument.extended_attributes, name, null_check,
+        interface_extended_attributes, extended_attributes, name, null_check,
         index=index, auto_scope=auto_scope)