constructor(identifierGenerator, reporter, options, metadata) {
    super(identifierGenerator, reporter, options);
    this.metadata_ = metadata;
  }
Inline's ES6 module imports and outputs to a single ES6 formatted file.
usage: traceur --modules=inline --outputLanguage=es6 --out ./out/some-lib.js -- ./src/root.js

in:
 // a.js
 export function a() {
   return 'A';
 }

 // root.js
 import {a} from './a.js';
 export function b() {
   return a();
 }

 out:
 // some-lib.js
 const $__module__a__js = (function() {
   "use strict";
   function a() {
     return 'A';
   }
   return {get a() {
       return a;
     }};
 })();
 "use strict";
 const {a} = $__module__a__js;
 export function b() {
   return a();
 }