gs_cache: minor bugs of /extract

Add Content-Length and Content-Type headers.

BUG=chromium:1091501
TEST=Deployed to test devserver(2-6) and ran below command
  $ curl -s -D - -o /dev/null http://chromeos2-devserver6:8888/extract/chromeos-image-archive/veyron_fievel-release/R84-13099.54.0/autotest_packages.tar?file=autotest/packages/dep-telemetry_dep.tar.bz2
  HTTP/1.1 200 OK
  Server: nginx/1.4.6 (Ubuntu)
  Date: Fri, 03 Jul 2020 06:49:40 GMT
  Content-Type: application/octet-stream
  Content-Length: 312259258
  Connection: keep-alive
  Expires: Thu, 31 Dec 2037 23:55:55 GMT
  Cache-Control: max-age=315360000
  Cache-Control: public, max-age=3153600
  X-Cache: MISS

Change-Id: Id198f580f6382d9331189632af060f31a7973616
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/dev-util/+/2280493
Auto-Submit: Congbin Guo <guocb@chromium.org>
Tested-by: Congbin Guo <guocb@chromium.org>
Commit-Queue: Sanika Kulkarni <sanikak@chromium.org>
Reviewed-by: Sanika Kulkarni <sanikak@chromium.org>
1 file changed