record that Gamepad.buttons creates GamepadButtons

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 134 matching lines @@
     ],
 
     'File.lastModifiedDate': [
       "@Creates('Null')", # JS date object.
     ],
 
     'FocusEvent.relatedTarget': [
       "@Creates('Null')",
     ],
 
+    'Gamepad.buttons': [
+        "@Creates('JSExtendableArray|GamepadButton')",
+        "@Returns('JSExtendableArray')",
+    ],
+
     'HTMLCanvasElement.getContext': [
       "@Creates('CanvasRenderingContext2D|RenderingContext')",
       "@Returns('CanvasRenderingContext2D|RenderingContext|Null')",
     ],
 
     'HTMLInputElement.valueAsDate': [
       "@Creates('Null')", # JS date object.
     ],
 
     # Rather than have the result of an IDBRequest as a union over all possible
@@ skipping 722 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()