Don't verify file existence when posting existing commits for review.
Review Request #8881 - Created April 6, 2017 and submitted
We were checking for the existence of each file in a diff for existing
commits in a repository, which is unnecessary. We can trust that those
files exist, since if they didn't, the repository is corrupt and things
will fail anyway.
DiffSet.objects.create_from_data()now accepts a check_existence
parameter, which controls whether to perform file existence checks.
By default this is True, but it's set to False when updating a draft
from a commit.
This speeds things up considerably when posting existing commits for
Tested posting commits for review. Saw that they were posted quickly,
compared to before.
Unit tests pass.