message: Use ObjectIdentitySet for FuncGraph.control_captures
diff: @@ -187,7 +187,7 @@ class FuncGraph(ops.Graph):
  self.inputs = []
  self.outputs = []
  self.control_outputs = []
  - self.control_captures = set()
  + self.control_captures = object_identity.ObjectIdentitySet()
  self.structured_input_signature = None
  self.structured_outputs = None
  self._weak_variables = []
  