This will enable the new "git-codereview sync-branch" command.
Change-Id: Id2f933f6d13e181817c56d2548172a74b1d0b629
Reviewed-on: https://go-review.googlesource.com/c/go/+/293909
Trust: Katie Hockman <katie@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>
