Flesh out ddlbench's startup boiler-plate

Change-Id: I609587db52b442df9565bb56adb83f8808efc0e0
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/376717
Reviewed-by: Adlai Holler <adlai@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
1 file changed