/**
  * We have already handled etag, and will add 'If-Match' & 'Range' value if it works.
  *
  * @see okhttp3.Headers.Builder#add(String, String)
  */
 public BaseDownloadTask addHeader(final String line) {
   checkAndCreateHeader();
   header.add(line);
   return this;
 }
 /**
  * We have already handled etag, and will add 'If-Match' & 'Range' value if it works.
  *
  * @see okhttp3.Headers.Builder#add(String, String)
  */
 public BaseDownloadTask addHeader(final String name, final String value) {
   checkAndCreateHeader();
   header.add(name, value);
   return this;
 }