dart2js native mixin application should extend 'Interface', not 'Object'

tools/dom/scripts/systemhtml.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 system to generate
 Dart:html APIs from the IDL database."""
 
 import emitter
 import monitored
@@ skipping 509 matching lines @@
 
     implements_str = ''
     if implements:
       implements_str = ' implements ' + ', '.join(set(implements))
 
     mixins = self._backend.Mixins()
     mixins_str = ''
     if mixins:
       mixins_str = ' with ' + ', '.join(mixins)
       if not base_class:
-        base_class = 'Object'
+        base_class = 'Interceptor'
 
     annotations = self._metadata.GetFormattedMetadata(
         self._library_name, self._interface, None, '')
 
     class_modifiers = ''
     if self._renamer.ShouldSuppressInterface(self._interface):
       class_modifiers = 'abstract '
 
     self._implementation_members_emitter = implementation_emitter.Emit(
         self._backend.ImplementationTemplate(),
@@ skipping 626 matching lines @@
     for library_name in libraries:
       self._libraries[library_name] = DartLibrary(
           library_name, template_loader, library_type, output_dir)
 
   def AddFile(self, basename, library_name, path):
     self._libraries[library_name].AddFile(path)
 
   def Emit(self, emitter, auxiliary_dir):
     for lib in self._libraries.values():
       lib.Emit(emitter, auxiliary_dir)