Add serially-executing CPU test category to DM

Change-Id: I2fb6334489c7aca8c5b0d1dba6fd606c6a812c73
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/844798
Reviewed-by: Leon Scroggins <scroggo@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
3 files changed