Preserve nullability when writing idl with the ildrenderer. Use nullability to call the toNativeWit…

tools/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 720 matching lines @@
     for i, argument in enumerate(arguments):
       type_info = self._TypeInfo(argument.type.id)
       argument_expression_template, type, cls, function = \
           type_info.to_native_info(argument, self._interface.id)
 
       def AllowsNull():
         assert argument.ext_attrs.get('TreatNullAs', 'NullString') == 'NullString'
         if argument.ext_attrs.get('TreatNullAs') == 'NullString':
           return True
 
+        if argument.type.nullable:
+          return True
+
         if isinstance(argument, IDLArgument):
           if IsOptional(argument) and not self._IsArgumentOptionalInWebCore(node, argument):
             return True
           if argument.ext_attrs.get('Default') == 'NullString':
             return True
           if _IsOptionalStringArgumentInInitEventMethod(self._interface, node, argument):
             return True
 
         return False
 
@@ skipping 193 matching lines @@
             '    if (Dart_NativeFunction func = $CLASS_NAME::resolver(name, argumentCount))\n'
             '        return func;\n',
             CLASS_NAME=os.path.splitext(os.path.basename(path))[0])
 
 def _IsOptionalStringArgumentInInitEventMethod(interface, operation, argument):
   return (
       interface.id.endswith('Event') and
       operation.id.startswith('init') and
       argument.ext_attrs.get('Default') == 'Undefined' and
       argument.type.id == 'DOMString')