statementToStateMachine_(statement) {
    let statements;
    if (statement.type === BLOCK)
      statements = statement.statements;
    else
      statements = [statement];
    return this.statementsToStateMachine_(statements);
  }
Converts a statement into a state machine. The statement may not contain a
yield statement directly or indirectly.
@param {ParseTree} statements
@return {StateMachine}