Add [TreatReturnedNullStringAs] support for ByteString.

Source/bindings/scripts/v8_types.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 518 matching lines @@
             add_includes_for_type(array_or_sequence_type)
         return 'array'
 
     # Simple types
     base_idl_type = idl_type.base_type
     # Basic types, without additional includes
     if base_idl_type in CPP_INT_TYPES:
         return 'int'
     if base_idl_type in CPP_UNSIGNED_TYPES:
         return 'unsigned'
-    if base_idl_type == 'DOMString':
+    if base_idl_type in ('DOMString', 'ByteString'):
         if 'TreatReturnedNullStringAs' not in extended_attributes:
-            return 'DOMString'
+            return base_idl_type
         treat_returned_null_string_as = extended_attributes['TreatReturnedNullStringAs']
         if treat_returned_null_string_as == 'Null':
             return 'StringOrNull'
         if treat_returned_null_string_as == 'Undefined':
             return 'StringOrUndefined'
         raise 'Unrecognized TreatReturnNullStringAs value: "%s"' % treat_returned_null_string_as
     if idl_type.is_basic_type or base_idl_type == 'ScriptValue':
         return base_idl_type
 
     # Data type with potential additional includes
@@ skipping 114 matching lines @@
 def cpp_value_to_v8_value(idl_type, cpp_value, isolate='info.GetIsolate()', creation_context='info.Holder()', extended_attributes=None):
     """Returns an expression that converts a C++ value to a V8 value."""
     # the isolate parameter is needed for callback interfaces
     idl_type, cpp_value = preprocess_idl_type_and_value(idl_type, cpp_value, extended_attributes)
     this_v8_conversion_type = idl_type.v8_conversion_type(extended_attributes)
     format_string = CPP_VALUE_TO_V8_VALUE[this_v8_conversion_type]
     statement = format_string.format(cpp_value=cpp_value, isolate=isolate, creation_context=creation_context)
     return statement
 
 IdlType.cpp_value_to_v8_value = cpp_value_to_v8_value