static fromSourceMap(aSourceMap, aSourceMapURL) {
    return new BasicSourceMapConsumer(aSourceMap.toString())
  }
Create a BasicSourceMapConsumer from a SourceMapGenerator.

@param SourceMapGenerator aSourceMap
       The source map that will be consumed.
@param String aSourceMapURL
       The URL at which the source map can be found (optional)
@returns BasicSourceMapConsumer