Replace the now missing ContextAttributes with our previously Firefox-only _TypedContextAttributes

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 353 matching lines @@
       # Section 5.14.3 Setting and getting state
       "@Creates('Null|num|String|bool|JSExtendableArray|"
                 "NativeFloat32List|NativeInt32List|NativeUint32List|"
                 "Framebuffer|Renderbuffer|Texture')",
       "@Returns('Null|num|String|bool|JSExtendableArray|"
                 "NativeFloat32List|NativeInt32List|NativeUint32List|"
                 "Framebuffer|Renderbuffer|Texture')",
     ],
 
     'WebGLRenderingContext.getContextAttributes': [
-      "@Creates('ContextAttributes|=Object')",
+      "@Creates('ContextAttributes|Null')",
     ],
 
     'XMLHttpRequest.response': [
       "@Creates('NativeByteBuffer|Blob|Document|=Object|JSExtendableArray"
                 "|String|num')",
     ],
 }, dart2jsOnly=True)
 
 _blink_experimental_annotations = [
   "@SupportedBrowser(SupportedBrowser.CHROME)",
@@ skipping 470 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()