Add some tracking stats to ddlbench

Change-Id: I62d8cdec7dfe126513e616c9966e2a8eb994d95f
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/373880
Reviewed-by: Adlai Holler <adlai@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
1 file changed