Do not treat callbacks with no handlers as interfaces.

lib/dom/scripts/systemfrog.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
 frog binding from the IDL database."""
 
 import os
 from generator import *
@@ skipping 142 matching lines @@
         ARGUMENTS=constructor_info.ParametersAsArgumentList())
 
   def _ShouldNarrowToImplementationType(self, type_name):
     # TODO(sra): Move into the 'system' and cache the result.
     do_not_narrow = ['DOMStringList', 'DOMStringMap', 'EventListener',
                      'IDBAny', 'IDBKey', 'MediaQueryListListener']
     if type_name in do_not_narrow:
       return False
     if self._system._database.HasInterface(type_name):
       interface = self._system._database.GetInterface(type_name)
-      if RecognizeCallback(interface):
-        # Callbacks are typedef functions so don't have a class.
-        return False
-      return True
+      # Callbacks are typedef functions so don't have a class.
+      return 'Callback' not in interface.ext_attrs
     return False
 
   def _NarrowToImplementationType(self, type_name):
     if self._ShouldNarrowToImplementationType(type_name):
       return self._ImplClassName(self._DartType(type_name))
     return self._DartType(type_name)
 
   def _NarrowInputType(self, type_name):
     return self._NarrowToImplementationType(type_name)
 
@@ skipping 207 matching lines @@
     if native_body:
       native_string = " '''" + native_body + "'''"
 
     self._members_emitter.Emit(
         '\n'
         '  $TYPE $NAME($PARAMS) native$NATIVESTRING;\n',
         TYPE=self._NarrowOutputType(info.type_name),
         NAME=info.name,
         PARAMS=params,
         NATIVESTRING=native_string)