This adds a flag to our internal API (i.e. it is not exposed to the user yet), that runs the MergeOp in a dry run. This includes calculating all projects affected by the submission, checking for possible submission problems (ACLs, merge conflicts, etc) Change-Id: I90430a758b52694286e2b22cf9bf3eedeb82876c Signed-off-by: Stefan Beller <sbeller@google.com>