Fix debug code in GrDrawingManager

Looks like this code got a little dusty.

Change-Id: Iac0f475abac9d0891e34bba59ddbde3ec63d065a
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/328176
Auto-Submit: Adlai Holler <adlai@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
1 file changed