Reduce DSLModifiers to a simple struct.

Change-Id: I6bf1c9b5810c514ad9dfadecf1b8eb89fe5f584f
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/697116
Reviewed-by: Brian Osman <brianosman@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
10 files changed