Git introduced a new file storing the topology and some metadata of
the commits in the repo (commitGraph). With this data, git can browse
commit history without parsing the pack, speeding up e.g.
reachability checks.
This change teaches JGit to read commit-graph-format file, following
the upstream format([1]).
JGit can read a commit-graph file from a buffered stream, which means
that we can provide this feature for both FileRepository and
DfsRepository.
[1] https://git-scm.com/docs/commit-graph-format/2.21.0
Bug: 574368
Change-Id: Ib5c0d6678cb242870a0f5841bd413ad3885e95f6
Signed-off-by: kylezhao <kylezhao@tencent.com>
7b0f633b67