function extractRequires(filePath) {
  var provideMap = new ProvideMap_();
  var requireMap = new RequireMap_();
  scanFiles([filePath], provideMap, requireMap);
  return requireMap.get(filePath).map(function(ns) {
    return '\'' + ns + '\'';
  }).join(', ');
}
@param {string} filePath
@return {string} requires