Added DSL flags

This adds some basic flags to the DSL initialization which allows us to
toggle things like optimization and validation.

Change-Id: I35b10526af1678c88901eaacd5a2c4a9f5cd21a7
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/406896
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
Reviewed-by: John Stiles <johnstiles@google.com>
5 files changed