message: Fast path `self.x = self.x` (or equivalent).
  Before: 100000 loops, best of 3: 7.21 ?s per loop
  After: loops, best of 3: 556 ns per loop
diff: @@ -74,6 +74,13 @@ class AutoTrackable(base.Trackable):
  def __setattr__(self, name, value):
  """Support self.foo = trackable syntax."""
  + try:
  + if getattr(self, name) is value:
  + # Short circuit for `self.$x = self.$x`.
  + return
  + except AttributeError:
  + pass
  +
  if getattr(self, "_self_setattr_tracking", True):
  value = data_structures.sticky_attribute_assignment(
  trackable=self, value=value, name=name)
  