third_party/pkg/protobuf (and possibly others) uses a compressed reference file (.git/packed-refs) rather than the .git/refs/heads/(master|main) file expected by rev_sdk_deps.dart.
modify rev_sdk_deps.dart to use "git show-ref --verify refs/remotes/origin/main" instead.
TEST: I ran the script and it produced the expected commit hashes for both a package that uses a "main" default branch and a "master" default branch.
Change-Id: Ibe2ec2cf368d859ca78d1873f287722eb73e481b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/488262
Reviewed-by: Ryan Macnak <rmacnak@google.com>
Commit-Queue: Brian Quinlan <bquinlan@google.com>
Brian Quinlan
c7e58f832a