function SourceMapGenerator$2(aArgs) {
  if (!aArgs) {
    aArgs = {};
  }
  this._file = util$2.getArg(aArgs, 'file', null);
  this._sourceRoot = util$2.getArg(aArgs, 'sourceRoot', null);
  this._skipValidation = util$2.getArg(aArgs, 'skipValidation', false);
  this._sources = new ArraySet$1();
  this._names = new ArraySet$1();
  this._mappings = new MappingList();
  this._sourcesContents = null;
}
An instance of the SourceMapGenerator represents a source map which is
being built incrementally. You may pass an object with the following
properties:

  - file: The filename of the generated source.
  - sourceRoot: A root for all relative URLs in this source map.