Add test for switch-case folding.

Change-Id: I3dabd77890a73ea054bb57d466a6ed8273eae3e8
Bug: skia:12811
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/494196
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
4 files changed