Fixing dart2js size regression from CustomElement.detail

tools/dom/scripts/dartmetadata.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 to provide Dart metadata for
 DOM APIs.
 """
 
 import copy
@@ skipping 38 matching lines @@
     'CanvasRenderingContext2D.fillStyle': [
       "@Creates('String|CanvasGradient|CanvasPattern')",
       "@Returns('String|CanvasGradient|CanvasPattern')",
     ],
 
     'CanvasRenderingContext2D.strokeStyle': [
       "@Creates('String|CanvasGradient|CanvasPattern')",
       "@Returns('String|CanvasGradient|CanvasPattern')",
     ],
 
-    'CustomEvent.detail': [
+    'CustomEvent._detail': [
       "@Creates('Null')",
     ],
 
     # Normally Window is nevernull, but starting from a <template> element in
     # JavaScript, this will be null:
     #     template.content.ownerDocument.defaultView
     'Document.window': [
       "@Creates('Window|=Object|Null')",
       "@Returns('Window|=Object|Null')",
     ],
@@ skipping 705 matching lines @@
       pass
     else:
       _logger.warn('Unknown support_level - %s:%s' % (interface_id, member_id))
 
     return annotations
 
   def Flush(self):
     json_file = open(self._api_status_path, 'w+')
     json.dump(self._types, json_file, indent=2, separators=(',', ': '), sort_keys=True)
     json_file.close()