constructor(identifierGenerator, reporter, options) {
    super(identifierGenerator, reporter, options);
    this.shouldAppendThrowCloseState_ = true;
  }
Desugars generator function bodies. Generator function bodies contain
'yield' statements.

At the top level the state machine is translated into this source code:

{
  machine variables
  return $traceurRuntime.createGeneratorInstance(machineFunction);
}