function pushTransactionName(pathSegment) {
  const tx = this.tracer.getTransaction()
  if (tx && tx.nameState) {
    tx.nameState.appendPath(pathSegment)
  }
}
Pushes a new path segment onto the transaction naming stack.

- `pushTransactionName(pathSegment)`

Transactions are named for the middlware that sends the response. Some web
frameworks are capable of mounting middlware in complex routing stacks. In
order to maintain the correct name, transactions keep a stack of mount points
for each middlware/router/app/whatever. The instrumentation should push on
the mount path for wrapped things when route resolution enters and pop it
back off when resolution exits the item.

@memberof TransactionShim.prototype
@param {string} pathSegment - The path segment to add to the naming stack.