code: def track_size(self, ts, sizer):
          
          obj = self.ref()
          self.snapshots.append(
              (ts, sizer.asized(obj, detail=self._resolution_level))
          )
          if obj is not None:
              self.repr = safe_repr(obj, clip=128)
docs: Store timestamp and current size for later evaluation.
          The 'sizer' is a stateful sizing facility that excludes other tracked
          objects.