Implement Blink-in-JS for DOM methods

Source/bindings/scripts/idl_types.py

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 """IDL type handling.
 
 Classes:
 IdlType
 IdlUnionType
 """
 
@@ skipping 314 matching lines @@
     @property
     def is_sequence(self):
         # We do not support sequences of union types
         return False
 
     @property
     def is_union_type(self):
         return True
 
     @property
+    def may_raise_exception_on_conversion(self):
+        return False
+
+    @property
     def name(self):
         return 'Or'.join(member_type.name for member_type in self.member_types)
 
     def resolve_typedefs(self, typedefs):
         self.member_types = [
             typedefs.get(member_type, member_type)
             for member_type in self.member_types]
         return self