Omit '= null' as default value in generated dart:html code.

lib/dom/scripts/generator.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 systems to generate
 Dart APIs from the IDL database."""
 
 import copy
 import re
@@ skipping 407 matching lines @@
   def ParametersAsArgumentList(self):
     """Returns a string of the parameter names suitable for passing the
     parameters as arguments.
     """
     return ', '.join(map(lambda param_info: param_info.name, self.param_infos))
 
   def _FormatParams(self, params, default_value, type_fn):
     def FormatParam(param):
       """Returns a parameter declaration fragment for an ParamInfo."""
       type = type_fn(param)
-      if param.is_optional and default_value:
+      if param.is_optional and default_value and default_value != 'null':
         return '%s%s = %s' % (type, param.name, default_value)
       return '%s%s' % (type, param.name)
 
     required = []
     optional = []
     for param_info in params:
       if param_info.is_optional:
         optional.append(param_info)
       else:
         if optional:
@@ skipping 397 matching lines @@
 
   match = re.match(r'sequence<(\w+)>$', idl_type_name)
   if match:
     return SequenceIDLTypeInfo(idl_type_name, GetIDLTypeInfo(match.group(1)))
 
   match = re.match(r'(\w+)\[\]$', idl_type_name)
   if match:
     return SequenceIDLTypeInfo(idl_type_name, GetIDLTypeInfo(match.group(1)))
 
   return IDLTypeInfo(idl_type_name)