function setActiveSegment(segment) {
  const transaction = this.tracer.getTransaction()
  this.tracer.setSegment({ segment, transaction })
  return segment
}
Explicitly sets the active segment to the one passed in. This method
should only be used if there is no function to tie a segment's timing
to.

- `setActiveSegment(segment)`

@memberof Shim.prototype
@param {TraceSegment} segment - The segment to set as the active segment.
@returns {TraceSegment} - The segment set as active on the context.