IDL: For DOMString? attribute getters, use null string to represent null

Source/bindings/scripts/v8_attributes.py

 # Copyright (C) 2013 Google Inc. All rights reserved.
 #
 # 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
 # copyright notice, this list of conditions and the following disclaimer
@@ skipping 59 matching lines @@
     has_type_checking_unrestricted = (
         (has_extended_attribute_value(interface, 'TypeChecking', 'Unrestricted') or
          has_extended_attribute_value(attribute, 'TypeChecking', 'Unrestricted')) and
          idl_type.name in ('Float', 'Double'))
 
     if (base_idl_type == 'EventHandler' and
         interface.name in ['Window', 'WorkerGlobalScope'] and
         attribute.name == 'onerror'):
         includes.add('bindings/v8/V8ErrorHandler.h')
 
+    # Nullable type where the corresponding C++ type supports a null value.
+    is_nullable_simple = idl_type.is_nullable and (
+        (idl_type.is_string_type or idl_type.is_wrapper_type) and
+        not idl_type.array_or_sequence_type)
+
     context = {
         'access_control_list': access_control_list(attribute),
         'activity_logging_world_list_for_getter': v8_utilities.activity_logging_world_list(attribute, 'Getter'),  # [ActivityLogging]
         'activity_logging_world_list_for_setter': v8_utilities.activity_logging_world_list(attribute, 'Setter'),  # [ActivityLogging]
         'activity_logging_include_old_value_for_setter': 'LogPreviousValue' in extended_attributes,  # [ActivityLogging]
         'activity_logging_world_check': v8_utilities.activity_logging_world_check(attribute),  # [ActivityLogging]
         'cached_attribute_validation_method': extended_attributes.get('CachedAttribute'),
         'conditional_string': v8_utilities.conditional_string(attribute),
         'constructor_type': idl_type.constructor_type_name
                             if is_constructor_attribute(attribute) else None,
@@ skipping 11 matching lines @@
         'is_check_security_for_node': is_check_security_for_node,
         'is_custom_element_callbacks': is_custom_element_callbacks,
         'is_expose_js_accessors': 'ExposeJSAccessors' in extended_attributes,
         'is_getter_raises_exception':  # [RaisesException]
             'RaisesException' in extended_attributes and
             extended_attributes['RaisesException'] in (None, 'Getter'),
         'is_initialized_by_event_constructor':
             'InitializedByEventConstructor' in extended_attributes,
         'is_keep_alive_for_gc': is_keep_alive_for_gc(interface, attribute),
         'is_nullable': idl_type.is_nullable,
-        'is_nullable_simple': idl_type.is_nullable and idl_type.is_wrapper_type,  # null value maps to C++ null pointer
+        'is_nullable_simple': is_nullable_simple,
         'is_partial_interface_member':
             'PartialInterfaceImplementedAs' in extended_attributes,
         'is_per_world_bindings': 'PerWorldBindings' in extended_attributes,
         'is_read_only': attribute.is_read_only,
         'is_reflect': is_reflect,
         'is_replaceable': 'Replaceable' in attribute.extended_attributes,
         'is_static': attribute.is_static,
         'is_url': 'URL' in extended_attributes,
         'is_unforgeable': 'Unforgeable' in extended_attributes,
         'measure_as': v8_utilities.measure_as(attribute),  # [MeasureAs]
@@ skipping 305 matching lines @@
     lambda self: strip_suffix(self.base_type, 'Constructor'))
 
 
 def is_constructor_attribute(attribute):
     # FIXME: replace this with [ConstructorAttribute] extended attribute
     return attribute.idl_type.base_type.endswith('Constructor')
 
 
 def constructor_getter_context(interface, attribute, context):
     context['needs_constructor_getter_callback'] = context['measure_as'] or context['deprecate_as']