code: public static Cache createDefaultCache(Context context) {
      File dir = defaultCacheDir(context);
      return new Cache(dir, calculateDiskCacheSize(dir));
    }
docs: Creates a {@link Cache} that would have otherwise been created by calling
  {@link #OkHttp3Downloader(Context)}. This allows you to build your own {@link OkHttpClient}
  while still getting the default disk cache.