Have the drawing manager ref & unref DDLs on playback

Change-Id: I95f6dbfed9bb3ce75ecb260137d11b72e3953d75
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/298820
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Adlai Holler <adlai@google.com>
3 files changed