This is maintained just to distinguish whether the digest was negotiated or we
simply fell back to assuming SHA-1 support. No code is sensitive to this flag
and it adds complexity because it is set at a different time, for now, from the
rest of valid_flags.
The flag is new in OpenSSL 1.0.2, so nothing external could be sensitive to it.
Change-Id: I9304e358d56f44d912d78beabf14316d456bf389
Reviewed-on: https://boringssl-review.googlesource.com/2282
Reviewed-by: Adam Langley <agl@google.com>