Added operator= on DSLCase

Needed by DSLParser, and should have been defined anyway.

Change-Id: Ieaabe493a8caef80dda30f2ab35068f358901885
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/417677
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
Auto-Submit: Ethan Nicholas <ethannicholas@google.com>
Reviewed-by: John Stiles <johnstiles@google.com>
2 files changed