GS Cache: decompress compressed tar files.

In order to extract files from a compressed tar file (.tgz., .tar.gz,
.tar.bz2, .tar.xz), we need to decompress them first and return the
stream so that caching server can cache it.

BUG=chromium:824580
TEST=Ran unit tests.

Change-Id: I616fec91528297d476bf34269b5d697281544d72
Reviewed-on: https://chromium-review.googlesource.com/1080228
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Tested-by: Congbin Guo <guocb@chromium.org>
Reviewed-by: Aviv Keshet <akeshet@chromium.org>
2 files changed