function getSegment(obj) {
  if (obj && obj[symbols.segment]) {
    return obj[symbols.segment]
  }

  return this.tracer.getSegment()
}
Retrieves the segment associated with the given object, or the current
segment if no object is given.

- `getSegment([obj])`

@memberof Shim.prototype
@param {*} [obj] - The object to retrieve a segment from.
@returns {?TraceSegment} The trace segment associated with the given object or
 the current segment if no object is provided or no segment is associated
 with the object.