An API returning a Promise should not throw an exceptions [overload version]

Source/bindings/scripts/v8_interface.py

 # Copyright (C) 2013 Google Inc. All rights reserved.
 # coding=utf-8
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 # notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
@@ skipping 545 matching lines @@
         'deprecate_all_as': common_value(overloads, 'deprecate_as'),  # [DeprecateAs]
         'exposed_test_all': common_value(overloads, 'exposed_test'),  # [Exposed]
         'has_custom_registration_all': common_value(overloads, 'has_custom_registration'),
         'length_tests_methods': length_tests_methods(effective_overloads_by_length),
         # 1. Let maxarg be the length of the longest type list of the
         # entries in S.
         'maxarg': lengths[-1],
         'measure_all_as': common_value(overloads, 'measure_as'),  # [MeasureAs]
         'minarg': lengths[0],
         'per_context_enabled_function_all': common_value(overloads, 'per_context_enabled_function'),  # [PerContextEnabled]
+        'returns_promise_all': promise_overload_count > 0,
         'runtime_enabled_function_all': common_value(overloads, 'runtime_enabled_function'),  # [RuntimeEnabled]
         'valid_arities': lengths
             # Only need to report valid arities if there is a gap in the
             # sequence of possible lengths, otherwise invalid length means
             # "not enough arguments".
             if lengths[-1] - lengths[0] != len(lengths) - 1 else None,
         'visible': has_overload_visible,
         'has_partial_overloads': has_partial_overloads,
     }
 
@@ skipping 645 matching lines @@
         deleter = next(
             method
             for method in interface.operations
             if ('deleter' in method.specials and
                 len(method.arguments) == 1 and
                 str(method.arguments[0].idl_type) == 'DOMString'))
     except StopIteration:
         return None
 
     return property_deleter(deleter)