Revert "GTTF: Remove obsolete sharding_supervisor"

This reverts commit cbb4fe197d5b00b547bf26b3d9c1438181595ad8.

TBR=maruel

BUG=236893

Review URL: https://codereview.chromium.org/65583002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@233706 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 233706